Flooding of a carbonate platform: The Sian Kaʼan Wetlands, Yucatán, Mexico—A model for the formation and evolution of palustrine carbonate factories around the modern Caribbean Sea and in the depositional record

The dynamic inter‐relationships between marine and freshwater carbonate depositional environments are illustrated in the Sian Ka'an Wetlands, a 5 280 km2 complex of groundwater‐fed freshwater marshes, lakes and brackish coastal lagoons in the South‐East Yucatán Peninsula (Mexico). The Yucatán Platform was subaerially emergent and extensively karstified during the last glacial maximum at 18, 000 yr bp. The Late Holocene transgression has caused progressive reflooding of the continental margin, backstepping of the MesoAmerican Reef and encroachment of coastal environments into the platform interior as rising groundwaters flood an interconnected cave and sinkhole system and feed seasonal marshes above. The Sian Ka'an Wetlands form a vast palustrine carbonate factory which is directly juxtaposed and dynamically linked with the marine carbonate factory to seaward. Continuing sea‐level rise has caused synchronous landward migration of marginal marine and freshwater environments as beach barriers were breached and palustrine sloughs flooded to form marginal marine seagrass lagoons. The Rio Hondo Fault conditions fluid inflow while the sub‐environments of the Sian Ka'an Wetlands reflect tectonic controls on microtopography and hydroperiod. Modern analogues for the Sian Ka'an Wetlands include the Florida Everglades, formed during transgression of the Florida Platform, and relict marsh environments preserved on leeward shores of Andros, Abaco and other Bahama islands. A wide range of ancient examples deposited in coastal and continental interior settings similarly reflect seasonal aquifer rise in response to marine transgression and/or onlap of late‐stage basin fill onto a karstified pediment. Freshwater palustrine carbonate factories on carbonate platforms are transient deposystems, controlled by subtle water depth, climate, vegetation and hydrological factors while being critically sensitive to sea‐level changes and tectonics. The preservation potential of palustrine carbonates may be relatively low in coastal settings due to erosion or shallow marine overprinting, while greater further inland where marine flooding is rarer and in tectonically subsident continental interior basins where accommodation space is continuously created.


| INTRODUCTION
Carbonate environments show a range of complex hydrological and ecological changes in response to sea-level and aquifer rise. An understanding of the evolution of coastmarginal carbonate successions over geological time can help to provide important insights into the long-term effects of climate change.
A view commonly cited in the literature is that when carbonate platforms flood following subaerial exposure during a sea-level lowstand, this results in a time lag before the platform reaches water depths sufficient for sedimentation in the marine carbonate factory to resume (Burgess & Pollitt, 2012;Tipper, 1997). However, evidence from the Sian Ka'an Wetlands (SKW) of eastern Mexico and from similar environments around the Caribbean shows that flooding of a carbonate platform results in complex environmental, sedimentological and hydrological transitions reflecting rise of the carbonate aquifer, producing a distinctive freshwater carbonate factory of groundwater-fed coastal marshes. Here the term carbonate factory is used in the sense of Schlager (2003, p. 445) to refer to 'space where the carbonate sediment is produced [while also representing…] the processes that lead to carbonate production'.
Coastal marshes of the Florida Everglades were proposed by Platt and Wright (1992) as an environmental analogue for the deposition of freshwater palustrine carbonates found widely in the stratigraphic record. These sediments show strong evidence of modification by subaerial exposure and pedogenesis, and were interpreted as seasonal discharge wetland deposits by  and Alonso Zarza and Wright (2010).
Nevertheless, many ancient examples and some modern analogues for palustrine carbonate deposition appear to reflect inland settings remote from the coast (Alonso Zarza et al., 2006), and historically facies models for shallow marine and freshwater carbonates have mainly been considered separately. Consequently, the dynamic interrelationships between marine and freshwater carbonate systems and their respective responses to sea-level rise have remained poorly understood. This is surprising given that sea-level change is interpreted as a key driver of facies change in carbonate successions and that orbitally forced significant sea-level fluctuations are thought to have occurred not only during glacial ice-house periods but also as a result of variable aquifer storage within greenhouse Earth intervals (Sames et al., 2020).
The Quaternary emergence, karstification and transgression of Caribbean carbonate platforms is well documented (Beddows, 2004;Purkis et al., 2014) and interpretation of the region's eustatic history underpins an understanding of reef backstepping (Blanchon, 2011;Blanchon & Shaw, 1995) and carbonate diagenesis (Moore et al., 1992;Perry et al., 1989). However, this history has not previously been fully integrated with the evolution of Caribbean palustrine systems and their response to transgression.
This paper introduces and describes a regionally extensive but little-studied freshwater marsh complex in the SKW of the Yucatán Peninsula in South-East Mexico ( Figure 1). The SKW form a vast freshwater carbonate factory located inland of the Caribbean coast yet dynamically linked with the marine carbonate factory offshore (Hernández-Arana et al., 2015;Platt & Wright, 2019) and present a modern analogue for the deposition of many palustrine carbonates which are extensively modified by subaerial exposure and pedogenesis (Freytet & Plaziat, 1982;Kabanov, 2021;Platt & Wright, 1992).
This study commences with a field description of the SKW followed by a comparison with analogue modern palustrine environments in Florida and the Bahamas, with reference also to Bermuda, enabling the construction of integrated regional depositional models which illustrate the dynamic controls of eustasy and tectonics on the evolution of shallow marine and palustrine carbonate environments across the wider Caribbean region. Synthesis of these modern settings provides insights for a review of ancient palustrine carbonate successions which compares and contrasts examples laid down in coastal and continental interior settings and within extensional and compressional basins of Palaeozoic, Mesozoic and Cenozoic age. The work concludes with a discussion of the key factors controlling the sedimentation and preservation of palustrine carbonates in the geological record. Although recording the influence of underlying karstified carbonate pediments and the development of similar hydrological windows in both coastal and inland settings, palustrine further inland where marine flooding is rarer and in tectonically subsident continental interior basins where accommodation space is continuously created.

K E Y W O R D S
coastal drowning, continental basin filling, groundwater dependent ecosystems, karst aquifer displacement, palaeo-hydrology, palustrine carbonate factory, sea-level rise, Yucatán carbonate deposition is likely to be transient in coastal environments, where sea-level changes will commonly result in erosion and overprinting during transgression, while potentially more persistent within continental interior basins where the preservation of thicker palustrine carbonate successions reflects the continuous creation of accommodation space in response to tectonic subsidence.

| MATERIALS AND METHODS
Field observations of sedimentary environments were carried out by boat within the northern SKW and by road in the south and combined with analysis of public domain satellite imagery and coastal aerial photography from the wider SKW and surrounding areas. Results were integrated with published data from the offshore, inshore and onshore areas to evaluate how sea-level changes have influenced the progressive migration of karstic, palustrine and marine environments as the Yucatán Platform has been successively exposed and reflooded as a result of Quaternary sea-level changes which continue today. Previous work has seen limited existing core data gathered from the SKW. Time constraints precluded the collection of new samples from the SKW within the present study and this is a recommendation for further work.

| REGIONAL SETTING
The Yucatán, Florida and Bahamas platforms are longlived and regionally extensive carbonate platforms developed around the Caribbean Sea ( Figure 1), with sedimentary histories of shallow water marine carbonate deposition extending back at least to Cretaceous times (Back & Hanshaw, 1970;Weidie, 1995).
Quaternary sea-level changes have had a profound effect on carbonate platforms across the Caribbean and around the world (see Blanchon & Shaw, 1995). Near Playa del Carmen on the eastern Yucatán coast, the MIS 5e sealevel maximum at ca 125, 000 yr BP led to the deposition of coralliferous shallow marine limestones at elevations up to 6 m above current sea level (Blanchon, 2010). Subsequently a major sea-level minimum around 18, 000 yr BP saw the subaerial exposure of carbonate platforms across the Caribbean. The platforms were extensively karstified during this period, leading to the formation of deep cavities and interconnected cave systems (Beddows, 2004).
Episodic transgression since that time (Gornitz, 2012) has seen sea-level rise by ca 110 m (Figure 2), leading to partial reflooding of the platform interiors as marine waters have encroached progressively onto the platform flanks, while many caves and karstic cavities have also been flooded (Gabriel et al., 2008). Caribbean platform interiors host freshwater marsh areas in the SKW on the eastern margin of the Yucatán Platform in Mexico, across a large area in the Everglades of southern Florida (Gleason & Spackman, 1974;Pederson et al., 2019) and in vestigial areas on the western flank of Andros Island (Maloof & Grotzinger, 2012), Abaco Island (Kovacs et al., 2013) and other islands in the Bahamian archipelago.

| THE YUCATÁN PLATFORM
The Yucatán Platform ( Figure 3) comprises a vast carbonate pediment covering 400, 000 km 2 of South-East Mexico, northern Guatemala and Belize (Perry et al., 2002). This area lies mostly below 150 m of elevation, rising only locally towards 300 m in the central highlands near Calakmul to the east of Escárcega. Geological mapping shows the area to be underlain by a succession of Cretaceous to Cenozoic age carbonates up to 3 km thick (Lopez-Ramos, 1975;Peterson, 1983;Viniegra-O, 1981;Ward et al., 1995).
At the downcurrent ends of cave systems, freshwater emerges from submarine springs (ojos) directly into coastal lagoons, crescent-shaped bays and coastal re-entrants (caletas) and into the sea (Kambesis, 2014;Richards & Richards, 2007;Saint-Loup et al., 2018), as at Cenote Xel-Há and Casa Cenote ( Figures 4B,C). The influx of groundwater run-off is substantial and correlates with a lower salinity lens mapped above marine waters for up to 20 km offshore (Carrillo et al., 2016). The volume of submarine groundwater discharge is estimated as 568 m 3 d −1 m −1 along this section of coast (Null et al., 2014), calculated by Carrillo et al. (2016) as equating to 657 m 3 s −1 along a 100 km length of coastline.
To the south of Tulúm, the coastal marshes of the SKW lie above flooded sinkholes and interconnected extensive cave systems (Meacham et al., 2006;Schiller et al., 2017). Hydrological studies (Gondwe et al., 2010a(Gondwe et al., , 2010b(Gondwe et al., , 2010c(Gondwe et al., , 2010d show that seasonal flooding and emergence in the SKW is controlled by aquifer outflow, reflecting seasonal rainfall in the Yucatán Highlands to the west after a time lag of several months. F I G U R E 4 Hydrology of the Tulúm area. (A) Caves and cenotes north of Tulúm and in the northern Sian Ka'an Wetlands, showing mapped major cave systems (data after Beddows, 2004;Collins et al., 2015;Meacham et al., 2006;Kambesis & Coke, 2016

| SIAN KA'AN WETLANDS
The SKW lie in the south-east of the Yucatán Peninsula, forming a vast, little studied and largely inaccessible area of coastal marshes, swamps, lakes and coastal inlets ( Figure 5) continuing south from Tulúm in South-East Mexico to the Bay of Chetumal, which lies across the Mexico-Belize border (Kramer & Kramer, 2002;Mazzotti et al., 2005). The area is low lying and dominated by lakes and sawgrass marsh in the west and mangrove swamp in the east, with lagoons of progressively increasing salinity and marine influence towards the coast (Fragosa-Servón et al., 2019). The hydrology and water chemistry of the SKW were described by Gondwe et al. (2010aGondwe et al. ( , 2010bGondwe et al. ( , 2010cGondwe et al. ( , 2010d and Lagomasino et al. (2015). The northern sector of the SKW lies in the 5 280 km 2 Sian Ka'an Biosphere Reserve, established in 1986and declared a UNESCO World Heritage Site in 1987(Claudino-Sales, 2019Pirie, 2013).
The wetlands are bounded to the south by the 891 km 2 Uaymil Flora and Fauna Protected Area (https://www.prote ctedp lanet.net/uaymi l-buffe r-zoneflora -and-fauna -prote ction -area) and the 2 773 km 2 Santuario del Manatí extending to the Bahía Chetumal (Morales Vela, 2014;Sánchez-Sánchez et al., 2009). The western edge of the SKW broadly coincides with the Rio Hondo Fault (Gondwe et al., 2010a(Gondwe et al., , 2010b(Gondwe et al., , 2010c(Gondwe et al., , 2010d, a major SSW-NNE lineament (Figure 4) also bounding Laguna Bacalar to the south (Bauer-Gottwein et al., 2011;Gischler et al., 2010;Tobón-Velázquez et al., 2018). The fault has little surface expression further north but appears to focus groundwater flow Perry et al., 2002). The eastern boundary of  the northern SKW is formed by a 40 km long beach ridge  some 200-500 m wide, extending from Tulúm to Boca  Paila and south to Punta Allen (see Figures 4A and 5) with the MesoAmerican Reef close offshore in shallow water to the east.
There are few land entrances ( Figure 5) to the Sian Ka'an Biosphere Reserve (Meacham et al., 2006) and the lack of roads and often challenging ground conditions mean that surface access is difficult. This study describes a west-east transect from Muyil to the coast ( Figure 6). 6 | ENVIRONMENTS

| Carbonate pediment and cenotes
The areas to the west of the SKW and to the north and west of Tulúm comprise an extensive, low relief plateau which is heavily forested and largely impenetrable away from the few roads. Near the coast, the plateau surface is formed by Quaternary shallow marine carbonates, studied in detail at Xcaret near Playa del Carmen (see Figure 3) by Blanchon (2010) and interpreted there as dating to the MIS 5e interglacial highstand at ca 125, 000 yr BP (Hearty et al., 2007;Rovere et al., 2016), when sea levels reached a level approximately 5-9 m higher than today.
Remote sensing and surface mapping of the regional pediment reveal the presence of several thousand sinkholes or cenotes ranging from a few metres to >100 m across (Rodríguez-Castillo et al., 2022), locally colonised by mangroves depositing extremely organic carbon-rich sediment (Adame et al., 2021). The cenotes are linked to the vast and serially interconnected cavern systems extending eastwards to the coast north of Tulúm ( Figure 7A) and beneath the SKW (Gerrard, 2015;Meacham et al., 2006;Schiller et al., 2017).
The numerous cenotes connect to the underlying aquifer through sinkholes and collapsed cave systems which were created by karstic dissolution in sea-level lowstands during the Quaternary. Sediment dating from Carwash Cenote (7 km north north-west of Tulúm; Gabriel et al., 2008) indicates that the caves in this area were reflooded by ca 6 800 yr BP. Mangrove colonisation of cenotes is a key factor in the sequestration of soil organic carbon as peats (Adame et al., 2021), while organic matter in contact with the aquifer drives dissolution within the lower reaches of the aquifer, especially where stagnant saline waters are found near the coast (Gulley et al., 2016).

| Laguna Muyil and nearby lakes
Laguna Muyil ( Figure 6) is a freshwater lake lying 500 m to the east of the Mayan archaeological site of the same name. The lake is broadly circular in outline and 1.8 km in diameter while flanked by dense rainforest vegetation to the north-west and by sawgrass marsh to the south-east.
The margins of the lake comprise a shallow shelf, 200 m wide and 1-2 m deep, colonised by reeds, wetland vegetation and charophytes (Figures 7B,C,D) with abundant phytogenic calcium carbonate. The centre of the lake is formed by an approximately circular area of open water ca 1.0-1.2 km across.
Laguna Nopalitos (Figure 6), another similar-sized freshwater lake, lies 2 km to the north north-east. The 800 m diameter Laguna Chumkopó (or Kaan Luum) (see Figure 6) and the similarly sized Lago La Unión are located 6 and 12 km further north north-east along the same bearing, respectively. These lakes show a deeper central area surrounded by 100 m wide shallow shelf margins which are indented by small, circular, deeper features 50-100 m across and ca 60 m deep (Brown et al., 2014). Dating at Laguna Chumkopó indicates that sedimentation in the lake began at around 6 800 yr BP (Brown et al., 2014).
The circular morphology of these various lakes at the north-west margin of the SKW between Muyil and Tulúm suggests that they were formed through the flooding of large sinkholes and collapsed cave entrances. The smaller deep circular features which indent their margins are interpreted as the location of subsidiary sinkholes developed on the shelf of the lakes around the main sinkhole depression in each case.

| Laguna Chunyaxche
This is a larger oval lake 5 km long and 2.5 km wide ( Figure 7E) located 500 m south-east of Laguna Muyil ( Figure 6). The lake has shallow fringing shelves on its north-west and south-east margins, a deeper central area, and features circular depressions 300-500 m across at its south-west and north-east ends. The shelf of the lake is 2-5 m deep, with circular lighter coloured areas 20-50 m across in shallow parts of the lake floor ( Figure 7F).
The larger, elongate outline of Laguna Chunyaxche may reflect collapse of a significant cave system, while the circular depressions at each end of the lake are interpreted as flooded sinkholes connecting underlying cave systems with the surface. The circular lighter coloured areas on the lake floor are interpreted as small sinkholes which have been filled with recent lime mud sediment.

| Sawgrass marsh
The area to the east of Laguna Muyil and around Laguna Chunyaxche ( Figure 6) is formed by wide flat savannas of seasonally flooded, low-lying sawgrass marsh, which form an extensive and wetland landscape showing thick and varied vegetation cover and displaying varying hydroperiods reflecting microtopography ( Figure 7G).
The sawgrass marsh forms a wide, low relief area or palustrine slough (cf Bourgeau-Chavez et al., 2005;Gleason & Spackman, 1974;Monty & Hardie, 1976), which is seasonally flooded as water-level rises in the later part of the wet season. The marsh areas enclose a number of densely forested and elongated small low petenes or 'tree islands' (Stone et al., 2002;Willard et al., 2006), 2-3 m high, 200-800 m long and 100-200 m wide, which are oriented broadly NW-SE, parallel to the marsh margins and the flow direction.

| Channel system
South-east of Laguna Chunyaxche lies a broad, flat area of sawgrass marsh ( Figure 7H) which contains rare tree islands 50-500 m long and up to 50 m across. The marsh is cut by a channel ( Figure 7I) which leads out of the lake and extends for 10 km downstream to the east. This channel provides central drainage for the sawgrass marsh area and may have been artificially enhanced during Mayan times (Witschey, 2005).
The upper reaches of the channel are 1-2 m deep and 3-5 m wide, and its waters have a distinctive pale turquoise hue. The channel floor here comprises indurated or soft white lime mud. The middle reaches of the channel are 5-8 m wide, highly sinuous and show more rapid water flow. Spherical oncoids from 3 to 5 cm across ( Figure 7J) are locally present as basal channel lags developed on the outside of bends, while slower flowing sections are notable for the presence of welldeveloped channel margin point bar features showing rippled or, more rarely, heavily pitted tops ( Figure 7K). The lower reaches of the channels gradually increase in width, reaching 10-50 m or more across as tributaries join downstream ( Figure 7L). Channel floors cease to be visible as water depths increase, but microbial carbonate mud is observed at the margins ( Figure 7M). Large alligators are found in these channels, reflecting more brackish conditions.

| Mangrove swamps
The interchannel areas pass downstream into densely vegetated swamps with surface cover transitioning progressively from sawgrass marsh to red mangrove and then black mangrove (Adame et al., 2013;Parkinson et al., 1994). Downstream, these mangrove swamps form a 2 km wide permanently flooded belt which is dissected by broad channels ( Figure 7N) widening towards Laguna Campechón (see Figure 6).

| Brackish lagoons
Laguna Campechón is an enclosed brackish lagoon in the northern SKW, contrasting with two larger and only partially enclosed lagoons, Bahia de la Ascensión and Bahia del Espíritu Santo in the south (Figure 8).

| Laguna Campechón
This is a 5 km long, 2 km wide, 2-3 m deep and mostly brackish lagoon (Meacham et al., 2006), oriented approximately north-south and wider at its northern end (see Figure 6). The lagoon lies north of a series of partially enclosed coastal lagoons and inlets which are developed parallel to and behind the coastal beach barrier as it extends southwards to the village of Punta Allen (see Figure 5). The lagoon is connected to the Caribbean Sea through a tidal channel at Entrada Boca Paila, 20 km south of Tulúm (Kovacs, 2014).
Zones of rising freshwater, approximately circular in outline and ca 100 m across are observed towards the western shore of the lagoon ( Figure 7O) where they are frequented by manatees. These zones lie above flooded cenotes on the lagoon floor, connecting with the southern sector of the Ox Bel Há cave system (see Figure 4) which continues beneath the SKW (Meacham et al., 2006). 6.6.2 | Bahia de la Ascensión This lagoon forms a 20 × 25 km embayment located seaward of a large palustrine slough area to the west. Water depths of 1 m in the muddy internal embayment of Vigia Grande ( Figure 8C) increase to 2 m in seagrass meadows in the central lagoon and to 6 m at the eastern entrances to the lagoon. Two cenotes lie at the north-western shore of Bahia de la Ascensión (Carnero-Bravo et al., 2016;Medina-Gómez et al., 2014. The eastern lagoon margin is formed by scattered shallow water bars and fragmentary islands which are oriented approximately N-S and colonised by red mangrove (Acosta-Calderón et al., 2016).
Salinity fluctuates markedly through the year, varying from <5‰ in the west to 38‰ in the east where the lagoon connects with the sea (Medina-Gómez et al., 2016). There is increased freshwater inflow from the marsh and karst areas in the west following the rainy seasons, while storms and north-east trade winds periodically drive marine waters into the lagoon from offshore in the east (Carnero-Bravo et al., 2016).

| Bahia del Espíritu Santo
This embayment ( Figure 8C) is ca 15 km × 20 km in size, with water depths of less than 2 m (Acosta-Calderón et al., 2016). The lagoon passes westwards into an extensive palustrine slough (Bezaury Creel et al., 1995). F I G U R E 8 General and regional location maps of the Sian Ka'an Wetlands (A and B) highlighting the Bahia de la Ascensión and Bahia del Espíritu Santo lagoons in the northern sector (C) and Bahia de Chetumal lagoon in the south (D). Seagrass lagoons (S) and MesoAmerican reef (R, dotted pink line) are shown on map B, while maps C and D show detail of reef. Selected lagoonal cenotes are shown as blue circles, towns shown as red circles. Five metres isobath also shown (bathymetry after Carrillo et al., 2009a). A and B: Images: ©2022 Landsat/Copernicus. Data SIO, NOOA, US Navy, NGA, GEBCO. Map data: © 2022 Google Earth.
Manatees are reported to colonise the bay (Niño-Torres et al., 2015). A strong green colour on satellite imagery is interpreted to reflect colonisation by seagrass. There is a partial barrier of linear islands at the eastern margin of the bay, with the MesoAmerican Reef developed offshore beyond these to the east.

| Bahia de Chetumal
In the south of the study area, this more sizeable shallow coastal-estuarine lagoon some 100 km long and up to 20 km wide ( Figure 8D) extends 50 km inland from the coast to reach the city of Chetumal (Espinoza-Ávalos et al., 2009;Yang et al., 2004). This bay is also colonised by manatees (Niño-Torres et al., 2015). Bathymetric maps show the presence in northern areas of the lagoon of flooded cenotes (pozas) up to 42 m deep and 10-100 m across (Carrillo et al., 2009a).
The lagoon is less than 5 m deep in the south, with a deeper area around the cenotes in the north. The floor of the lagoon is predominantly muddy towards the west, passing eastwards into bioclastic facies at the eastern margin of the lagoon with Ambergris Caye and the MesoAmerican Reef beyond (Mazzullo, 2006).
Salinity varies seasonally and geographically from 8‰ in the west during the wet season to a high of 21‰ during the dry season in eastern areas of the lagoon (Carrillo et al., 2009a). The principal input of freshwater is from the Rio Hondo at Chetumal, from which peak wet season inflows of 78-220 m 3 s −1 were reported by Carrillo et al. (2009a). The pozas are stratified and at depth provide access to saline waters of the marine phreatic lens (Carrillo et al., 2009a(Carrillo et al., , 2009b. While Laguna Campechón is a brackish lagoon with only a single connection to the sea at Boca Paila (see Figure 8C), the three larger lagoons are to different extents partially connected to the sea. All four lagoons lie at the downcurrent end of major palustrine sloughs, with red mangrove swamps upstream passing progressively into muddy lagoons and sandy and rocky substrates colonised by seagrass (Acosta-Calderón et al., 2016). Salinity variations in the southern three lagoons record heightened freshwater influx from inlet streams and lagoon floor cenotes (springs) in the west following the wet season and the influence of marine currents and tides entering the lagoons from the east in each case.

| Beach barrier
Three channels on the east of Laguna Campechón lead to the Caribbean Sea through a single 80 m wide break in the beach barrier at Boca Paila (see Figure 7P). The linear beach barrier is 200-500 m wide and extensively vegetated while composed almost entirely of carbonate grains (Kramer & Kramer, 2002).
At Bahia de la Ascensión and Bahia del Espíritu Santo, an increase in marine characteristics eastwards is coincident with the progressive fragmentation of the beach barrier. By contrast, there is no beach barrier present in Bahia de Chetumal where marine influence extends a significant distance inland.
The Yucatán Platform comprises an exclusively carbonate sediment source area, so that terrigenous clastic supply in this area is negligible. Storm action on the MesoAmerican Reef and the carbonate pediment generates a variety of sand-sized carbonate grains which are then reworked by waves and wind.

| MesoAmerican Reef
The area east of the beach barrier comprises a shallow water backreef lagoon colonised by seagrass. Beyond this, the MesoAmerican Reef (see Figure 6) runs broadly N-S to form a discontinuous chain of patch reefs 100 m across, located at a distance from 500 to 800 m offshore and forming part of the extensive reef belt stretching southwards into Belize (Gischler, 2003(Gischler, , 2015Jordán-Dahlgren et al., 1994;Mazzullo, 2006;Purdy & Gischler, 2003).
The MesoAmerican Reef is interpreted as a classic barrier reef which developed from a late Pliocene shallowingupwards ramp into a structurally controlled reef rimmed shelf (Mazzullo, 2006). The morphology of the reef in the Sian Ka'an Biosphere Reserve area is described in detail and mapped by Kramer (2000, 2002) and Smith et al. (2012).

OVERVIEW AND ENVIRONMENTAL MODEL
Overview of the SKW area (Figures 9 and 10) illustrates the juxtapositions of karstic, freshwater palustrine, lagoonal and shallow marine shelf reef environments along the eastern Yucatán coast. Emergence of the karstic aquifer onto the surface in the platform interior feeds a variety of freshwater carbonate marshes and coastal lagoons which pass seaward to the east into barrier islands, carbonate shelf and reefs (Hernández-Arana et al., 2015).
The palustrine settings of the SKW therefore comprise integral elements of the Yucatán carbonate platform depositional system, forming a vast freshwater carbonate factory which has been little studied but is developed directly adjacent to the much better known shallow marine carbonate factory offshore. Figure 9 presents an aerial photography montage from the northern area of the SKW, showing the close juxtaposition of shallow marine and palustrine environments and their relationship with karstic uplands inland. The easily accessed and well-studied shallow marine MesoAmerican Reef and beach areas contrast with the relatively much less accessible and densely vegetated swamp and marsh areas behind the beach, where the palustrine environments of the SKW have received only limited scientific study to date. and the Santuario del Manatí (see Figure 5) to the south. The MesoAmerican Reef runs ca 500 m offshore and parallel with the coast from Bahia Espíritu Santo to Xcalak (see Figure 8). Figure 10B shows its typical groove and spur morphology near Balamku Inn on the Beach, 5 km south of Mahahual. A series of broadly linear and parallel palustrine sloughs inland drain south-westwards into Bahia Chetumal ( Figure 10C), with the westernmost of these linking the northern arm of Bahia Chetumal with Bahia Espíritu Santo. Laguna Bacalar lies 15 km further west along the southward trace of the Rio Hondo Fault.

| Sian Kaan Wetlands environmental model
A simplified environmental model for the SKW is shown in Figure 11. Key factors include the following:

| Hydrology
The annual duration of submergence (hydroperiod) varies across the marsh complex in response to subtle changes in elevation. Sedimentation in the SKW is thought to be largely of microbial origin as in the Everglades (Pederson et al., 2019;Platt & Wright, 1992) where deposits are dominated by carbonate muds containing varying amounts of organic matter and with variable long-term preservation potential depending on the length and frequency of subaerial emergence. Seasonal submersion and emergence cycles are interrupted by hurricane events, which cause storm overwash from the coast when strikes occur around once every decade (McCloskey & Keller, 2009

| Eustasy
Sea level provides a profound control on facies belts. With limited surface relief, the coastal environments are highly sensitive to sea-level rise, which leads to a progressive westward migration of facies belts across the platform as transgression proceeds and marine waters encroach into the platform interior.

| Tectonics
The distribution of the various depositional environments is strongly influenced by the geological structure of the platform ( Figure 12). Fluid paths reflect the NNE-SSW structural grain parallel to the Rio Hondo Fault, with minor surface relief defining the morphology of palustrine sloughs and the margins of coastal lagoons.

TRANSGRESSION OF CARIBBEAN CARBONATE PLATFORMS
Comparison of the SKW with similar wetlands in Florida and Bahamas (see Figure 1) allows construction of a regional flooding model for Caribbean carbonate platforms describing the effect of progressive transgression. While F I G U R E 1 1 Schematic block model for the SKW showing tectonic and sedimentary controls on palustrine carbonate deposition in interior and coastal settings. Progressive transgression leads to breach of the beach barrier and progressive partial flooding of palustrine sloughs to form brackish lagoons and seagrass embayments. Inland, the coastal and interior palustrine basins are intermittently connected at peak transgression. Faults control the distribution of relatively uplifted blocks undergoing continued karstification, as well as the boundaries of palustrine sloughs located in tectonically subsident areas.
the SKW records relatively early flooding, South Florida reflects an intermediate stage of transgression and the Bahama platforms have been more extensively (and locally completely) flooded.

Ka'an Wetlands
The eastern Yucatán coast displays a narrow shelf (see Figures 1 and 3) and encroachment of lagoonal and marginal marine environments onto the platform edge is mainly localised to the area south of Tulúm. Extensive karstification of the carbonate pediment in the late Pleistocene lowstand was followed during Holocene sea-level rise (see Figure 2) by a parallel rise and seasonal outflow of the regional aquifer and the onset of palustrine deposition in low lying areas of the platform interior. Evidence from Cenote Carwash (Gabriel et al., 2008) and Laguna Chunyaxche (Brown et al., 2014) dates the onset of freshwater sedimentation at ca 6 800 yr BP.
These findings are consistent with the flooding of atolls in the southern MesoAmerican reef of Belize between 8 500 yr BP and 6 000 yr BP, with evidence of late Holocene reef backstepping offshore South-East Florida between 8 000 yr BP and 7 400 yr BP (Blanchon, 2011) and more recently offshore Yucatán after 5 500 yr BP (Blanchon et al., 2017). Analysis of the varied coastal morphology of the SKW (Figure 12) further supports an interpretation that sedimentation reflects the parallel progress of flooding in the different environments described, allowing the construction of a five stage model for transgression of the platform ( Figure 12 Cenozoic to Pleistocene carbonates (Ward & Brady, 1979). At Xcaret, near Playa del Carmen some 50 km north-east of Tulúm (see Figure 3), Blanchon (2010) describes Pleistocene coralliferous limestones outcropping at elevations of up to 5.8 m above sea level and recording deposition during the 125 000 yr BP MIS 5e highstand when sea levels were ca 5-9 m higher than today. Coeval freshwater palustrine carbonates were deposited 12 m above sea level on the nearby island of Cozumel (Valera-Fernández et al., 2020).
The densely vegetated carbonate pediment surface of this northern area is now undergoing active karstification. Abundant cenotes of varying size (see Figure 4A) are commonly located along surface lineaments parallel to the Rio Hondo Fault and its northward continuation as the Holbox Fault (Rodríguez-Castillo et al., 2022). The cenotes open into interconnected cave systems beneath (Beddows, 2003;Meacham et al., 2006). Although this sector remains emergent today, sea-level rise has partially breached and transgressed the cave and cenote system at Cenote Xel-Há (Shaw, 2016) to form a 500 m long coastal inlet (see Figure 4), while nearby to the south, waters from inland Cenote Manatí flow directly into the sea within a submerged cenote off the beach at Casa Cenote (see Figures 4 and 7A).

| Stage 2: Palustrine slough
The western margin of the SKW south of Tulúm broadly follows the Rio Hondo Fault. A series of circular freshwater lakes along its length display deep central depressions up to several hundred metres across. The flooding of cenotes and lakes in the fault hangingwall reflects emergence of the aquifer in response to Holocene sea-level rise and seasonal freshwater discharge onto the surface of the platform interior.
Further to the south-east, the northern SKW east of Muyil (see Figure 6) and the southern SKW west of Mahahual (see Figure 10C) comprise extensive sawgrass marshes which include many parallel chains of tree islands. These marshes define palustrine sloughs with variable freshwater surface flow recording seasonal fluctuations in the level of the underlying aquifer. Lateral transitions in vegetation type correspond with areas of differing hydroperiod, and are sharply defined on satellite images as linear trends which are interpreted to reflect underlying structural controls on subtle surface relief ( Figure 12).

| Stage 3: Coastal lagoon
Laguna Campechón at the eastern margin of the northern SKW (see Figures 6 and 8) is a brackish lagoon with freshwater cenotes in its floor fed from an interconnected cave system below (Meacham et al., 2006). Tidal flow into the lagoon takes place through a channel cut through the beach barrier at Entrada Boca Paila ca 20 km to the south of Tulúm (see Figure 6P). This configuration is interpreted as reflecting early transgression of the seaward sectors of a palustrine slough system ( Figure 12).

| Stage 4: Brackish embayment
Bahia del Espíritu Santo and Bahia de la Ascensión, 100 km and 50 km to the south of Tulúm, respectively (see Figure 8), are brackish to marginal marine seagrass lagoons displaying seasonal freshwater aquifer input from upstream palustrine slough areas and from lagoon floor cenotes, while also recording influx of marine waters from the east. In Bahia del Espíritu Santo, a fragmentary beach barrier is formed by Isla Owen and a spit across the southern entrance of the bay, while in Bahia de la Ascensión only the small sandbar of Cayo Culebre remains. In both lagoons, a new beach is now forming on the inland lagoon shore. 8.1.5 | Stage 5: Shallow marine embayment Bahia de Chetumal records a further stage of marine transgression. Mazzullo (2006) dated flooding of the karstified Pleistocene pediment here to ca 6 800 yr BP. The sector north of Chetumal is fed by groundwater inflow from cenotes on the bay floor and from a marsh area to the north. The elongate outline of this northern embayment is consistent with its formation by flooding of a palustrine slough ( Figure 10C), potentially fault-controlled on its north-western margin which runs parallel to Laguna Bacalar as well as to several smaller lakes oriented parallel to it and lying 5-10 km to the south-east. The southern part of the bay comprises a seagrass lagoon connected to the sea south of Ambergris Caye (see Figure 8). 8.1.6 | Sian Kaan Wetlands summary Figure 13 provides a perspective view of the SKW from the north, illustrating the flooding of the platform during transgression. The successive reef backstepping episodes along the eastern Yucatán coast (Blanchon, 2010;Blanchon et al., 2017) and the early encroachment of coastal and shallow marine carbonate environments onto the platform edge ( Figure 12) are accompanied by the progressive westward displacement of freshwater carbonate factories ahead of them in the platform interior. Carnero-Bravo et al. (2016) reviewed the rates of sealevel rise in the Yucatán region, concluding that these decreased from 4.2 mm year −1 in the early Holocene to ca 1.4 mm year −1 from 7 000-4 000 yr BP, before stabilising at 0.4-0.6 mm year −1 . Tidal gauge data from 1947 to 1999 in the northern sector show a current rate of sea-level rise at 3.46 ± 0.03 mm year −1 , while further south nearer to Sian Ka'an, a shorter tide gauge record from 2007 to 2014 shows a recent rate as high as 10.1 ± 0.2 mm year −1 . This suggests that the accretion potential of freshwater carbonates may be limited as further sea-level rise continues to flood the SKW.

Everglades and Florida Bay
The Quaternary geology of Florida ( Figure 14) reflects a complex history of eustatic change (Willard & Bernhardt, 2011). Deposition of shallow marine carbonates of the Miami Oolite Formation during a sea-level highstand around 125, 000 yr BP was followed by late Pleistocene sea-level fall and subaerial exposure of much of the Florida Platform before Holocene transgression led to partial reflooding of the pediment.
The pediment was karstified far offshore from the present coastline (Chen et al., 2000;Mallinson et al., 2014), with former sinkholes still active today as submarine springs in Florida Bay (Scott et al., 2004) and off the Florida Keys (Simmons & Love, 1987), where they are emitting groundwater mixed with marine waters. Submarine springs are also developed in the Gulf of Mexico to the west (Saleem, 2007), and in the Atlantic Ocean to the east where Crescent Beach Spring (Swarzenski et al., 2001) lies in 18 m water depth some 4 km off the coast ( Figure 14A). Marine water ingress is occurring further offshore at Red Snapper Sink, which lies 39 km from the coast in 28 m of water and reaches 127 m below the sea floor (Moore, 2010;Spechler & Wilson, 1997).
Karstification is continuing onshore today in northern and central Florida, where regional spring lines are marked by a number of cenote-like sinkholes and cave systems up to 5 km in length (Upchurch et al., 2019a(Upchurch et al., , 2019b, and in southern Florida where sinkholes are abundant on the land surface around Miami. These relatively elevated areas of karstified pediment pass down gradient into the freshwater marsh complex of the Everglades. Although the hydrology of this area has been greatly altered by anthropogenic processes (Ogden, 2005), work by McVoy et al. (2011) has provided a reconstruction of premodification environments ( Figure 14B). The Everglades is underlain by water-filled caves (Florea, 2008;Florea & Yuellig, 2007) which form part of an extensive flooded karst system hosting active southward flow in the regional aquifer from central to South Florida.
Groundwater thus feeds Lake Okeechobee in the northern Everglades and a vast area of seasonally flooded sawgrass marsh to the south (Bernhardt & Willard, 2009), from whence seasonal flow again leads southwards into mangrove swamps and coastal lagoons of the southern Everglades and into Florida Bay, a 250 km wide marginal marine carbonate shelf lying in water depths of 5-10 m (Wanless & Tagett, 1989).
Bounded to the south by the Florida Keys, a 100 km chain of islands at the southern edge of the Florida Platform formed by exhumed coralliferous and ooidal limestones from the 125, 000 yr BP highstand (Lidz, 2006), Florida Bay began to be reflooded in the Holocene transgression at around 6 000-7 000 yr BP. The onset of freshwater sedimentation in the Everglades is also dated from this time (Lidz, 2006; see Figure 2). Continued marine encroachment onto the platform since 4 000 yr BP has led to further to flooding of the Florida Bay coastal lagoon and the northward migration of palustrine environments from the southern coastline towards central Florida (Enos & Perkins, 1979;Jones et al., 2019;Wanless et al., 1994).
Together these areas form a dynamically linked shallow marine and freshwater carbonate depositional system. Sediment cores along a transect in the southern Everglades (Pederson, 2017) record the progressive submergence of the karstified carbonate pediment during transgression, with freshwater seagrass peats and freshwater carbonates overlain unconformably by red mangrove fibrous peats and marginal marine limestones ( Figure 15). Rates of relative sea-level rise in Florida of up to 10 mm year −1 during the early Holocene (Meeder & Parkinson, 2018) declined to 0.35-0.67 mm year −1 in the late Holocene (Jones et al., 2019;Wanless et al., 1994), still significantly higher than late Holocene freshwater carbonate sedimentation rates of 0.2 mm year −1 (Glaser et al., 2012). The outpacing of sedimentation by sea-level rise is consistent with continuing transgression and saline groundwater incursion on the platform (Parkinson & Wdowinski, 2021). Despite their much higher accretion rates, mangrove coasts are expected to be lost to rising sea level over the next 30 years (Saintilan et al., 2020;Sklar et al., 2021).
With extensive marginal marine encroachment onto the platform edge and freshwater wetlands migrating northwards across the platform interior, the Florida Platform now records an intermediate transgression stage.  (Harris et al., 2015;Hine & Neumann, 1977). Andros Island ( Figure 16A) and Abaco Island ( Figure 16B) lie towards the eastern margins of GBB and LBB respectively, with vestigial remnant tidal flat and palustrine zones preserved on their south-western shores (Kovacs et al., 2013;Maloof & Grotzinger, 2012;Monty & Hardie, 1976). Fringing reefs line the north-eastern platform flanks, although these are currently under stress due to the effects of rising sea level (MacIntyre, 2007). The smaller Grand Bahama island and a fringing reef lie on the western margin of LBB.
The surface geology of Andros, Abaco, Eleuthera and other Bahama islands largely comprises Quaternary aeolianite limestones now seeing active karstification (Mylroie et al., , 2020. Multiple sinkholes and blue holes are found on the islands , in marsh and tidal flat areas to the west (van Hengstum et al., 2020) and on eastern and south-western shelves (Whitaker & Smart, 1990, 1997, 2004 where offshore seismic profiles show Holocene deposits lying on karstified relief, with possible channel features observed towards the shelf margin west of Andros Island (Weij et al., 2018). A total of 117 sinkholes were The transgression of the Abaco shelf is dated as commencing at ca 8 790 yr BP, with flooding of the Gulf of Abaco on central GBB occurring at ca 5 900-5 600 yr BP (van Hengstum et al., 2020; see also Figure 2). As sea-levels rose, the flooding of Freshwater River Blue Hole on Abaco saw the successive deposition of peats (8 300-7 600 yr BP), lacustrine carbonate marls (7 600-7 300 yr BP), algal sapropel and lacustrine marl (7 000-2 000 yr BP) and laminated marine carbonate mud (2 300 yr BP to present), recording transitions from freshwater to brackish and finally to shallow marine conditions (van Hengstum et al., 2020), with average sedimentation rates in the Gulf of Abaco estimated at 0.24 mm year −1 (Rasmussen & Neumann, 1988).
Cay Sal Bank (CSB; Figure 16) is another Bahamas platform lying 200 km south of Florida and 60 km west of GBB. Cay Sal Bank saw earlier marine encroachment from 11, 000 yr BP onwards (Purkis et al., 2014) with sealevel rise at an estimated 5.2-11 mm year −1 . By 8 000 yr BP, 50% of the platform surface was submerged and flooding was all but complete by 6 000 yr BP (Purkis et al., 2014). Cay Sal Bank is now fully inundated to water depths of ca 10-20 m. The positions of former islands are marked by submarine outcrop of aeolianite on the north-east platform margin, with degraded reefs located on their flanks. Submerged sinkholes are abundant on the shallower sea floor in the east. Sparse fringing reefs are developed along the eastern platform margin.
Analogous Holocene flooding histories have been described from other Bahama islands including Grand Cayman, where a sedimentary succession commencing 6 000 years ago and comprising freshwater peats and freshwater to lagoonal carbonates passes up into shallow marine carbonates from ca 2 000 yr BP in response to sea-level rise from ca 2 000 yr BP onwards (Booker & Jones, 2020;McKinnon & Jones, 2001), as well as from Bermuda (Gischler & Kuhn, 2018;van Hengstum & Scott, 2012;van Hengstum et al., 2011), where seismic and sediment data illustrate the flooding of coastal cave systems by 7 700 yr BP, associated with the infilling of karst relief by Holocene deposits which pass up from basal peats at 11, 000 yr BP to freshwater, brackish and shallow marine carbonates by 2 500 yr BP, with lagoonal sedimentation rates of ca 0.32 mm year −1 .

| Caribbean summary
A comparison of modern examples across the Caribbean (Figure 17) highlights the dynamic inter-relationships between coastal palustrine and shallow marine carbonate environments, showing how Quaternary palustrine systems have been formed, displaced and destroyed as exposed carbonate platforms were flooded during transgression. Across the region, fringing reefs and beach barriers on eastern windward coasts are backstepping or being abandoned in response to rising sea levels. In parallel, shallow marine and lagoonal environments are now encroaching into the platform interior and flooding coastal lagoons, tidal flats and palustrine environments via the dual processes of marine incursion and aquifer emergence through the underlying karst. Further transgression may subsequently lead to the removal or modification of palustrine sediments as a result of erosion or bioturbation in shallow marine settings following sea-level rise.
The coastal palustrine carbonate environments of the SKW ( Figure 17A) reflect aquifer rise in response to westward marine encroachment onto a subaerially exposed and karstified carbonate platform, accompanied by the landward backstepping of the MesoAmerican Reef offshore. Similarly, the development of coast-marginal palustrine systems in the Florida Everglades ( Figure 17B) reflects rising groundwater associated with continuing transgression and flooding of the karstified Florida Platform. Landward migration of marshland environments is occurring in parallel with the progressive marine flooding of Florida Bay (Jones et al., 2019;Wanless et al., 1994). By contrast, the more extensive and complete flooding of Bahamas platforms ( Figure 17C) preserves only relict palustrine and tidal flat environments on leeward island shores. Freshwater marsh areas and flooded karstic sinkholes (blue holes) are developed along the south-west shorelines of Andros and Abaco (Rasmussen & Neumann, 1988;van Hengstum et al., 2020), and locally on other nearby islands such as Eleuthera (Brady et al., 2013) and Grand Cayman (Liang & Jones, 2015). Barrier Reef of Australia (Webster et al., 2018), where the role of karstification and aquifer control on wetland development in the Great Barrier Reef was briefly discussed by Stieglitz (2005). Table 1 provides a fuller list of modern analogues for palustrine carbonate deposition from locations around the world. These reflect a range of coastal and low-lying areas with limited clastic supply, where seasonally fluctuating water levels result in alternate flooding and emergence of carbonate pediments, leading to the deposition and nearsynchronous subaerial modification of shallow freshwater carbonate facies. 9 | ANCIENT ANALOGUES:

PALUSTRINE CARBONATES
The groundwater-fed coastal carbonate wetlands above provide environmental analogues for the deposition of a range of palustrine carbonates in the rock record which show evidence of pedogenetic modification while sharing an association with palaeokarst and carbonate aquifer discharge. First described in the Palaeogene of South-West France (Freytet & Plaziat, 1982), ancient palustrine carbonates have since been recognised worldwide in ancient successions of Palaeozoic to Quaternary age (see reviews in Alonso Zarza & Wright, 2010;Kabanov, 2021). These deposits show abundant evidence of subaerial exposure and pedogenesis, including desiccation and circumgranular cracking, rhizoliths and rhizolite crusts , fenestrae and irregular karst-like cavities (pseudo-microkarst), peloidal grainstones and black pebbles, as well as rare intercalations of horizons bearing freshwater fauna and flora such as ostracods, gastropods and charophytes.  and Alonso Zarza and Wright (2010) proposed that these carbonates were deposited in seasonal discharge wetlands, within settings described as Groundwater Depositional Environments by Eamus and Froend (2006). Table 2 provides a list of ancient palustrine deposits of different ages from around the world, and the following section describes several examples in more detail. These successions commonly rest on carbonate pediments which have been subaerially exposed as a result of global eustasy and basin-scale tectonics. These controls may act on a longer timescale than the Quaternary glacioeustatic changes which have affected environments in the Caribbean today. Nevertheless, the sedimentary processes and the importance of underlying palaeokarst in establishing groundwater-fed discharge wetlands appear to be essentially the same.
Some of the oldest examples described are from Early-Middle Devonian successions. Palustrine carbonates of this age occur interbedded with continental red beds in Spitzbergen (Blomeier et al., 2003a(Blomeier et al., , 2003b, while thin palustrine limestones are interbedded with rhizocretionbearing palaeosols and coast marginal peritidal carbonates in Canada (Kabanov, 2021).
Palustrine facies of Late Devonian Frasnian age are reported in volcanically active continental basins of Iran (Aharipour et al., 2009), in continental floodplain sediments of the United States (Dunagan & Driese, 1999) and in platform carbonates of Western Canada (MacNeil & Jones, 2006).
A distinctive form of transgressive brackish marsh facies is recorded from a range of successions T A B L E 1 Modern palustrine environments in coastal and continental settings.

Switzerland, France
Eustatic emergence and flooding of platform interior; tectonic control on subsidence/accommodation space Tresch and Strasser (2010)

Spain, UK, Portugal
Late rift phase of Atlantic and Biscay marginal rifts Platt (1989aPlatt ( , 1989b Iran Syn-rift deposits in intracratonic setting Aharipour et al. (2009) Examples are recorded in the Tournaisian-Visean of western Europe (Muchez & Viaene, 1987;Searl, 1988;Vanstone, 1991;Wright et al., 1997) and the late Visean of Kentucky (Barnett et al., 2013) and the Moscow Basin (Alekseeva et al., 2016;Kabanov et al., 2016). While many of these examples are stratigraphically localised, extensive and long-lived brackish dolomitic coastal wetlands with marshes and lakes, some of which became evaporitic, have been described from Tournaisian greenhouse settings from the Ballagan Formation in South-East Scotland and North-East England (Bennett et al., 2021, and examples therein).
The juxtaposition of these dolomites with terrestrial deposits and shallow marine limestones, their distinctive brackish isotopic signatures and their close association with exposure features, rooted vegetation and the evidence for strongly reducing conditions suggest formation under hydromorphic conditions as rising freshwater aquifers mixed with sea water in coastal marshes.
In some examples, the dolomites cap thin lowstand coastal plain siliciclastics developed on top of a karstic pediment, while in other cases the dolomites are developed directly on karstic substrates (Wright et al., 1997) suggesting that surface runoff into the marshes was derived from a rising aquifer. An example occurs at Chipping Sodbury in South-West England (Wright et al., 1997), where the top of the shallow marine Gully Oolite is marked by a prominent partially karstified horizon. This surface is capped by a 20 cm thick laminar calcrete and incised by up to 3 m of channelised relief which is filled by fine grained dolomicrite displaying vertically elongate microkarst cavities at the top ( Figure 18). Palustrine carbonates of Late Carboniferous age described from the eastern United States by Montañez and F I G U R E 1 8 Ancient analogue: Early Carboniferous of southern England (after Wright et al., 1997). Cecil (2013) are interbedded with distal alluvial deposits and coals. These rocks show non-marine biota and although traceable laterally for >200 km they can not be directly related with marine transgression.

Portugal -Palustrine limestones in coastal lagoons and lakes
The Lusitanian Basin ( Figure 19A) is an Atlantic marginal extensional rift formed during the Triassic and subsequently reactivated in Middle and Late Jurassic times (Ravnås et al., 1997). A thick succession of marine early Jurassic carbonates was deposited on a WNW-dipping carbonate ramp (Azerêdo et al., 2020).
The Lower Bathonian Serra de Aire Formation comprises a series of proximal ramp deposits which show evidence of repeated small-scale sea-level changes. In the Fátima region north-east of Lisbon, the Galinha Quarry succession (Azerêdo et al., 2015) includes an 8 m thick lowstand assemblage of interbedded calcretes, with black clasts, organic-rich seams and lenses of marly clay, carbonates with evaporite traces, microbial laminites and fenestral limestones. These deposits are interpreted as having been deposited on a periodically emergent and wildfire-prone, low relief coastal landscape. Episodic transgression allowed the periodic establishment of marshy environments and the local preservation of organic matter in depressions on the surface before restricted lagoonal conditions were developed and inner ramp deposition resumed.
By contrast, the Mid-Oxfordian Cabaços Formation (Azerêdo et al., 2002a(Azerêdo et al., , 2002b) records deposition during a major transgression which resulted in a transition from freshwater to marine conditions ( Figure 19B,C). The Cabaços Formation comprises a 40-150 m succession of non-marine limestones, marls and lignites, resting on a locally karstified regional disconformity. This surface displays doline-like features 3-5 m deep and 20 m in diameter (Azerêdo et al., 2002b), locally filled with terra F I G U R E 1 9 Ancient analogue: Oxfordian of Portugal (Wright, 1985). Location maps (A), schematic correlation (B) and sedimentological sections (C). Based on data in Azerêdo et al. (2002b) and Wright et al. (2018). The mid Oxfordian Cabaços Formation of west central Portugal represents a transitional terrestrial-to-shallow marine, transgressive unit developed over exposed Middle Jurassic inner-mid ramp carbonates. In more proximal settings (Vale de Ventos) the Middle-Upper Jurassic disconformity displays karstic features and is overlain by terrestrial deposits including palaeosols. The shift to freshwater limestones is interpreted as reflecting a rising karstic aquifer as sea-levels rose, followed by the influx of marine waters. In more distal areas ( rossa-like deposits (Wright & Wilson, 1987) which appear similar to those described from sinkhole fills in the modern Caribbean (Liang & Jones, 2015). A basal section, thickest in the east at Vale de Ventos ( Figure 19C), is composed of up to 14 m of pedogenetic and black-pebble bearing limestones and ferruginous limestones and marls, which are locally associated with thin deltaic sandstones and coral-oyster bioherms interpreted as having been affected by run-off from uplifted basement areas further west (Azerêdo et al., 2002b;Wright, 1985).
The overlying strata contain abundant charophytes and ostracods (Azerêdo & Cabral, 2004), common gastropods, bivalves and fossil wood remains. Marine influence appears to have been reduced in the west of the basin, where the section at Pedrógão ( Figure 19C) shows a diverse and predominantly continental palynomorph assemblage. Wright (1985) interpreted these as shallow freshwater lake and marsh deposits similar to those of Florida and Andros Island. These sediments are overlain by a series of brackish, variable salinity lagoonal and fully marine limestones, which in turn pass upwards into the marine late Oxfordian Montejunto Formation (Azerêdoet al., 2002b;Wright et al., 2018).
The change from terrestrial to freshwater shallow lakes and marshes in the lower Cabaços Formation is interpreted as reflecting the rise of a karstic aquifer in response to the early stages of the Oxfordian transgression, leading to the onset of groundwater discharge from a Middle Jurassic marine limestone pediment which was subaerially exposed to the south and south-east. The transition from terrestrial to marginal marine facies is recorded within a decametre-thick succession which appears to record a subtle balance between subsidence, hydrology and eustasy acting over a prolonged period. This interpretation suggests deposition during an interval when the rates of sea-level rise were relatively low.

Europe-Palustrine limestones in coastal lagoons and interior rift basins
Marginal and non-marine carbonate strata of earliest Cretaceous Berriasian age are well documented across North-West Europe ( Figure 20A), including in southern England, the Swiss Jura Mountains and northern Spain.

| Southern England
The late Jurassic to Berriasian Purbeck Formation of the Wessex Basin ( Figure 20A) rests on a thick succession of Jurassic shallow marine carbonates. Lacustrine and lagoonal carbonates are overlain by evaporites, recording a history of transgression followed by environmental restriction (Gallois et al., 2018;West, 2013). Lateral facies and thickness changes in this succession reflect deposition in half-grabens controlled by east-west extensional faults and linking relay ramps (Gallois, 2013;Gallois et al., 2021).

| Swiss Jura Mountains
Successions of equivalent Berriasian age were correlated in detail across the Swiss Jura Mountains ( Figure 20B through E) by Tresch (2007) and Strasser (2015). These deposits are dominated by marginal marine tidal flat and lagoonal carbonates, with thin freshwater units and stacked karstified horizons present near the base of the succession and in thinner sections near the north-east basin margin. This evolution is consistent with the progressive transgression of a subaerially exposed platform. Lateral facies changes are interpreted as reflecting subtle tectonic controls on subsidence, with greater marine influence in seaward locations in the south-west while karstic infill, palaeosols and tidal flat facies are common in landward sections in the north-east.
These carbonates were originally interpreted as marginal lacustrine and palustrine deposits (Platt, 1989a;Sacristán-Horcajada et al., 2016), although replaced evaporites occur towards the top of the succession (Platt & Pujalte, 1994) where miliolid foraminifera and dasycladacean algae were reported by Mas et al. (2019), recording a short-lived marine incursion from the north-west followed by desiccation and a return to palustrine conditions. Facies evolution and fault controls in the western Cameros Basin are shown in Figure 21. Partial equalisation of the karstified and faulted rift relief by erosion and the deposition of alluvial fan clastics were followed by the onset of freshwater carbonate sedimentation when marine transgression in more seaward connected basins led to aquifer rise through the underlying karst and its clastic cover above. Lateral facies and thickness changes in the Berriasian carbonate succession continued to record differential subsidence within the rift below. Peak transgression in late Berriasian times led to a brief marine incursion in the north-west sector of the basin lying closest to the Bay of Biscay margin.

Europe-Palustrine limestones in coastal and endorheic intramontane basins
A wide variety of ancient palustrine carbonates have been described from foreland settings in southern and North-West Europe where carbonate pediments were uplifted and deformed by Alpine and Pyrenean tectonics, leading to subaerial exposure and deep karstification prior to renewed subsidence and sedimentation. Although the detailed context of these examples is different, the presence of a significant underlying karstic aquifer system was an essential component of the depositional setting in each case.

| Eocene (Southern England)
The Upper Cretaceous Chalk formed a laterally extensive carbonate layer across North-West Europe, in southern England ( Figure 22A) overlain conformably by Palaeocene continental clastics of the Bracklesham and Reading formations (West, 2013). Following the onset of deformation in the early Eocene (Newell & Evans, 2011), the top Chalk surface was subject to differential subaerial erosion and karstification during Cenozoic inversion (Underhill & Paterson, 1998), accompanied by the deposition of transgressive freshwater carbonates of the Headon Hill and Bembridge Limestone formations (King, 2015) which onlap unconformably southwards towards the Isle of Wight monocline ( Figure 22B,C).
Deposition of these freshwater carbonates is consistent with rise onto the basin floor of a regional carbonate aquifer hosted in the karstified Upper Cretaceous Chalk pediment and the overlying Palaeocene clastics. Palustrine carbonate sedimentation in depressions ahead of thrusted anticlines occurred in parallel with a transgression which is recorded in marginal marine deposits of the Solent Group further north (Laurie, 2006).

| Miocene (Switzerland)
The Cenozoic Molasse Basin of Switzerland ( Figure 23A,B) is a foredeep and foreland basin filled with a thick succession of marine and continental clastics deposited north of the collision zone between Italy and Europe and the rising Alps (Homewood et al., 1986;Trümpy, 1980). At the northern feather edge of the Molasse Basin in the Jura Mountains, the marine Jurassic carbonate cover of the European foreland is deformed and at least partly detached on a décollement formed by Triassic evaporites (Laubscher, 1992).
A Cenozoic succession preserved in synclines of the Jura Mountains ( Figure 23B) records intermittent connection with the Rhine Graben to the north (Kälin et al., 2001). Relative uplift saw the subaerial exposure and karstification of the marine Jurassic carbonate pediment from Eocene times onwards, leading to the development of a distinctive unit known as the Sidérolithique or Siderolithikum, comprising mineralised horizons, thin sandstones and gastropod limestones locally filling karst pockets. Previously thought to be of Eocene age, dating by F I G U R E 2 1 Ancient analogue: Kimmeridgian-Berriasian of the western Cameros Basin, Spain (Mas et al., 2019;Platt, 1989aPlatt, , 1990Platt, , 1995. Sedimentological evolution (A-D) with composite sections from the SW and NE basin sectors shown (E). Hofmann et al. (2017) has suggested formation as a terra rossa deposit during a lengthy period of subaerial exposure which at least locally continued into the Miocene at ca 15 Myr BP.
In the Tramelan syncline ( Figure 23C,E), the Sidérolithique is unconformably overlain by onlapping clastics of the Lower Freshwater Molasse and the Upper Marine Molasse (Bertrand, 1990), which pass vertically upwards into freshwater limestones and marls of the Upper Freshwater Molasse (Platt & Matter, 2023). These carbonates are developed in a series of 2-5 m thick shallowing upward cycles, grading upwards from intraclastic limestones through laminated and bioturbated gastropod and charophyte micrites into organic-rich limestones which are interpreted as calcareous peats ( Figure 23F).
A depositional model shows the incipient relief of the early Jura Mountains infilled with marginal marine clastics and re-exposed by sea-level fall. Extensive karstification was followed by renewed transgression, leading to the rise of the regional aquifer onto the carbonate pediment surface and allowing the localised deposition of palustrine carbonates within a series of intermittently linked and restricted palustrine carbonate wetlands and lakes which were developed against the flanks of developing synclinal folds ( Figure 23G).

| Miocene (Spain)
The Ebro and Duero basins of northern Spain ( Figure 24A) were formed in the Eocene (Vacherat et al., 2018;Valero et al., 2014), when continental collision of Iberia with Europe led to the uplift and inversion of Mesozoic basins. The Ebro Basin formed to the south of the Pyrenees and folds at the southern margin of the inverted Basco-Cantabrian Basin, to the north of the Iberian Ranges and east of the Catalan Coastal Ranges. Similarly, the Duero Basin formed a depocentre south of the Cantabrian Mountains and north of the Central System, while bounded by the inverted Cameros Basin and Iberian Ranges to the north-east.
From Eocene until late Miocene times, the Ebro and Duero basins were endorheic with no marine connection. Fluvial outflow from the Ebro Basin did not begin until breach of the Catalan Coastal Ranges at 7.5-12 Myr BP (García-Castellanos & Larrasoaña, 2015;Regard et al., 2021), while outflow from the Duero Basin was likely established significantly later (Antón et al., 2019). The landlocked condition of both basins saw continental deposition across a vast interconnected intramontane depression reaching across the Iberian Peninsula from west to east. Abundant clastic supply in response to active F I G U R E 2 2 Ancient analogue: Eocene, Isle of Wight, southern England (Armenteros & Edwards, 2012). Location maps (A); stratigraphic correlation between Bembridge (1), Brading (2) and Whitecliff Bay (3); sedimentological section at Whitecliff Bay (C); stratal geometries at Headon Hill (D); depositional model (E). thrusting and unroofing of Palaeozoic and basement rocks saw alluvial fan deposition at the margins of both basins ( Figure 24A), grading basinwards into sheetflood and distal alluvial clastics and lacustrine deposits (Larena et al., 2020).
In the frontal External Sierras of the Pyrenees at the northern Ebro Basin margin, thrusting saw uplift of Upper Cretaceous marine carbonates in a series of folds onlapped by syntectonic conglomerates (Nichols, 1987(Nichols, , 2005 while in distal basin areas the deposition of lacustrine and palustrine carbonates over a 20 Myr period reflected aquifer outflow from Jurassic carbonates in the Iberian Chains to the south (Cabrera & Saez, 1987;Sánchez-Navarro et al., 1999;Vacherat et al., 2018;Valero et al., 2014).
While earlier Eocene carbonates show some marine influence and are intercalated with coals (Cabrera & Saez, 1987), the Miocene examples are interbedded with evaporites, consistent with deposition in a drier climate as Pyrenean deformation led to isolation from the sea.
The Duero Basin contains a thick Cenozoic continental succession recording infill of compressional relief by Eocene syntectonic and Miocene post-tectonic deposits. At the inverted south-western margin of the Cameros Basin ( Figure 24B), Eocene and Miocene strata onlap a pediment of Upper Cretaceous shallow marine carbonates deformed into a series of emergent and blind thrust anticlines (Platt, 1990). The Miocene succession comprises a series of fining upward sequences from alluvial clastics into calcretes and palustrine limestones ( Figure 24C,D), interpreted as reflecting successive cycles of groundwater rise (Armenteros & Huerta, 2006;Huerta & Amenteros, 2005). The Miocene Lower and Upper Páramo limestones are separated by an intra-Vallesian discontinuity (Krijgsman et al., 1996), with the upper unit representing the youngest deposits in the Duero Basin before the establishment of external drainage (Struth et al., 2021).
In both basins, palustrine deposits were deposited during tectonically quiescent periods when sedimentary gradients had been equalised and a rise in base level allowed discharge of the aquifer onto the basin floor. The Miocene strata of the Duero Basin record the final stage of basin fill, with onlap onto karstified Upper Cretaceous carbonates before overspill beyond the basin boundaries and the onset of erosion ( Figure 24E).

| Miocene (S Australia)-Palustrine limestones as relict karst fills
The Miocene Nullarbor Limestone of southern Australia ( Figure 25A) was deposited on a vast sub-tropical carbonate platform which opened seawards to the south F I G U R E 2 3 Ancient analogue: Miocene, Swiss Jura Mountains (Bertrand, 1990;Platt & Matter, 2023). Location map of Europe (A), Switzerland (B) and the Tramelan syncline (C) showing locations of the A1 and A2 boreholes, stratigraphy (D) and logged section (E). Sedimentological model (F) and depositional block diagram (G). while periodically emergent in its landward northern sector O'Connell et al., 2012). An environmental reconstruction of the area shows a shallow coastal embayment, allowing comparison with Bahia de la Ascensión in the Yucatán ( Figure 25B), which shows broadly similar morphology although developed on a much smaller geographical scale.
Environments represented in the Nullarbor Limestone include a karstified platform interior with extensive cave development and relict fills of palustrine limestone, beach barrier, seagrass embayments, shallow shelf and fringing reefs, as shown in a unified depositional model in Figure 25C. Miller et al. (2012) described rare occurrences of palustrine facies in isolated palaeokarst pockets, interpreting these as recording the temporary establishment of palustrine conditions in the platform interior at times of maximum transgression. The morphology of the karstic F I G U R E 2 4 Duero and Ebro basins (Upper Miocene). (A) Location map; (B) Tectonic setting and palaeogeographical sketch illustrating endorheic setting (after Vera et al., 2004;Valero et al., 2014). Modern basin drainage exit points shown. (C) Geological map of the SE Duero Basin (Huerta & Amenteros, 2005). (D and E) Stratigraphy, schematic section and typical small scale sequence (after Armenteros & Huerta, 2006). (F) Tectonic sketch (modified after Platt, 1989b;Platt & Wright, 1991).
depressions appears similar to sinkholes, cenotes and cave fills in the modern Caribbean, with the extremely localised occurrence of palustrine facies consistent with a limited preservation potential within palaeokarst depressions in coastal areas.
The exceptional tectonic stability of the vast Nullarbor Platform and the lack of more recent flooding events nevertheless allows the Miocene karst surface and fills to be clearly identified. In less stable platform settings, palustrine infills within karstified marine carbonates may be much more challenging to recognise.

| Groundwater dependent carbonate factories
Study of modern Caribbean wetland environments and ancient coastal palustrine deposits helps to illustrate the evolution of freshwater carbonate factories, while providing insights into their ancient depositional record and the roles of sea-level change and tectonics. Aquifer rise can occur as a hydrological response to sea-level change in coastal settings or on regional carbonate pediments in response to basin filling inland.
Hydrological studies of the east Yucatán aquifer (Gondwe et al., 2010a(Gondwe et al., , 2010b(Gondwe et al., , 2010c(Gondwe et al., , 2010d(Gondwe et al., , 2012 and regional cave exploration (Meacham et al., 2006) show how enhanced fluid flow today follows tectonically defined pathways enhanced by karstification of the platform during Holocene subaerial exposure, with active groundwater discharge now emerging onto the surface at regional spring lines located along major faults.
In vast tracts of low-lying landscape in the SKW, as in freshwater environments across Florida and the Bahamas, low clastic supply and the emergence of carbonate-saturated groundwaters onto the surface of the platform interior provide the conditions for freshwater periphyton, microbial mats and charophyte algae to trigger extensive carbonate precipitation, leading to the formation of extensive palustrine carbonate factories. These wetlands can be described as 'Groundwater Dependent Carbonate Factories' (GDCFs), with this nomenclature echoing the GDEs (Groundwater Dependent Ecosystems) described by Eamus and Froend (2006) and Kløve et al. (2011aKløve et al. ( , 2011b, which were defined as 'ecosystems for which current composition, structure and function are reliant on a supply of groundwater'.

| Early research and historic problems
In their pioneering study of groundwater-fed ('algal marsh') environments in the Everglades and on Andros Island, Monty and Hardie (1976) appreciated the role of rising meteoric groundwaters and climate in coastal settings, as well as the importance of preservational factors in freshwater carbonate sedimentation. They noted freshwater algal marsh deposits accumulating directly in karst depressions in the Pleistocene bedrock as groundwaters rose, forming a homogenous layer which seemed to be progressively destroyed by the landward migrating tidal flats. They suggested that such carbonates might be found in four settings: 1. At the base, or ahead, of a transgressive sequence, when the sea slowly invades a flat and low-lying platform, producing inland a progressive and gentle rise of the freshwater lens. 2. At the top of a regressive calcareous sequence where the marsh progrades over retreating shores and former intertidal flat sediments. 3. At a smaller scale, in rhythmic, cyclothemic deposits, at the top of shallowing-upward cycles. 4. Over palaeokarsts, during low sea-level stands.
However, several authors (MacNeil & Jones, 2006;Wright, 1985) note that while subaerial exposure surfaces are common in the geological record, associated groundwater-fed freshwater carbonates have been identified much more rarely, potentially reflecting depositional, preservational or recognition aspects: (i) Climate may be insufficiently humid. (ii) Carbonate catchment area may not be sufficient for active groundwater recharge to develop. (iii) Greenhouse intervals may result in sea-level changes of low magnitude or rate, not providing sufficient hydraulic head for active groundwater flow or time for these carbonates to form. (iv) Preservation may be incomplete due to erosion or homogenisation with overlying lagoonal marine sediments via bioturbation and root action in cases where transgression continues. (v) Recognition may be an issue, with limited awareness explaining the relative paucity of records, particularly in regressive settings where a complex mix of facies is likely to develop.

| Climate
There is scope for confusion concerning the control of climate on ancient palustrine carbonate deposition, since ancient deposits appear to show evidence both of subaqueous carbonate deposition and of subaerial exposure, potentially providing contradictory indicators for synchronous humid and arid conditions. Some authors had interpreted intense pedogenetic modification, desiccation and intercalated evaporites in ancient palustrine carbonate successions as indicating deposition under periodically arid climate conditions (Platt, 1989a), drawing comparison with evaporitic coasts of the Persian Gulf (Purser, 1973) which have annual rainfall of 50-150 mm and seasonally high salinities reflecting a restricted marine connection. However, the presence in other examples of coals (Cabrera & Saez, 1987) was linked to a more humid climate. Proposing the Florida Everglades as an analogue for palustrine carbonate systems, Platt and Wright (1992) presented hydroperiod as a key control acting across a spectrum of environments, with some areas being nearly permanently immersed and others flooded for only a few days each year, inferring that pedogenetic modification occurred during repeated seasonal emergence within palustrine systems which were highly sensitive to the effects of microtopography on hydrology.
Subsequently  suggested that alternating subaerial exposure and flooding events were likely to reflect seasonal groundwater fluctuations rather than the direct effect of local rainfall alone. The extent of flooding in the 5 280 km 2 SKW was mapped by  using space-based synthetic aperture radar (SAR) and SAR interferogram (inSAR) techniques as varying seasonally from 1 067 to 2 588 km 2 during the period from July 2006 to March 2008, while gauge measurements of water-level changes showed seasonal variations in water level of up to 28 cm in amplitude. The largest fluctuations occurred at the downstream coastal outlets of the SKW, with seasonal maxima observed between October and December following the wet season.
The modern Caribbean examples described are developed in humid tropical to subtropical climates, with rainfall varying from 1 100 mm in Tulúm to 1 700 mm in Miami. Rainfall is strongly seasonal, while markedly higher on Atlantic coasts than in leeward or inland settings. As described above, salinity variations in the internal areas of seagrass lagoons such as Bahia del Espíritu Santo and Bahia de Chetumal primarily reflect seasonal changes in aquifer flow relative to marine influx and evaporation, rather than rainfall in the lagoon area itself. Sedimentation across these downstream areas of the coastal carbonate factory is strongly dependent on seasonal discharge of bicarbonate-rich groundwaters from the aquifer. 10.2.2 | Carbonate catchment area Although palustrine dolomites are described from the early Carboniferous ice-house ramp cyclothems of the eastern USA, they are conspicuously absent from flattopped platforms of the same age (Barnett et al., 2013;Wright et al., 1997), suggesting that drainage from extensive areas of subaerially exposed carbonate pediment may be required for these systems to develop. In modern carbonate settings with mixed catchment area geology, such as the Queensland coast to the west of the Great Barrier Reef in Australia (Webster et al., 2018), higher clastic supply may also limit the potential for freshwater carbonate factories to form.

| Greenhouse and icehouse intervals
Rates and amplitudes of relative sea-level change are typically lower in greenhouse intervals of geological time than in icehouse periods (Sames et al., 2020). The more modest aquifer fluctuations resulting may limit the karstification depths and vertical extents of caves and blue holes that are formed, although subaerial exposure and subsequent aquifer recharge may endure over longer periods. Greenhouse intervals are also thought to have seen slower rates of relative sea-level rise at ca 0.1 mm year −1 (Miller et al., 2005), potentially allowing freshwater carbonate sedimentation to keep pace with transgression for significant time spans.
The late Palaeozoic contains relatively few examples of palustrine carbonates (Kabanov, 2021) and the distinctive palustrine dolomites of the early Carboniferous are associated with both greenhouse and ice-house intervals (Barnett et al., 2013).
Candidate palustrine carbonates recorded from greenhouse peritidal cyclothems where the presence of underlying karstic aquifers is unclear include a range of Barremian-Aptian examples described from across southern Europe by Martin-Chivelet and Gimenez (1992), Raspini (1998Raspini ( , 2001 and Császár (1989). The Berriasian of the Swiss Jura shows fewer karst features than its Spanish equivalents and could also be included in this category.
By contrast, deep and extensive karstic aquifers with a powerful hydraulic head will result from the high amplitude fluctuations in relative sea level typical of icehouse intervals such as the current late Cenozoic glaciation which has seen Caribbean and global carbonate platforms subject to repeated emergence, intense karstification and reflooding on a 10, 000+ year timescale. Although not every cycle has resulted in flooding of the platform interiors (Eberli, 2013), the 125, 000 yr BP peak event appears to have seen palustrine carbonate deposition both in Florida (Hickey et al., 2010) andin Mexico (Salgado-Garrido et al., 2022;Valera-Fernández et al., 2020).

| Preservation
If the current rate of freshwater carbonate accretion in Florida of 0.2 mm year −1 (Glaser et al., 2012) is typical of the past, then the scarcity of palustrine carbonates in ancient ice-house intervals may not be surprising, since icehouse transgression rates of up to 5-12 mm year −1 (Smoak et al., 2013;Wanless et al., 1994) may tend to cause rapid drowning of freshwater systems almost as soon as they are formed. The relatively lower rates of sea-level rise recorded from the late Holocene of Florida (see above) are still significantly higher than Everglades sediment accretion rates. Although freshwater carbonate muds are accumulating in the area today, they may be unlikely to form thick deposits; a prediction supported by the thin units recorded from older Pleistocene sections by Galli (1991) and Hickey et al. (2010). This suggests that although palustrine carbonate successions can be deposited during periods of glacio-eustatically driven sea-level oscillation, the relatively rapid sea-level rises of ice-house intervals may lead to incomplete preservation, since swift landward shoreline migration will see freshwater carbonates deposited only for short intervals before continued flooding risks erosion and mixing with younger deposits via bioturbation and root action.

| Recognition
Furthermore, while the late Pleistocene records of Florida and of Yucatán demonstrate that thin freshwater carbonates can survive marine transgressions and also the effects of later subaerial exposure, freshwater units truncated by subaerial lowstands may be prone to strong overprinting by soil processes, making their identification difficult.
Recognition of thin carbonate wetland intervals intercalated amongst complex cyclical alternations of shallow marine carbonate facies will similarly be challenging and likely dependent on finding clear alternative evidence of freshwater input. If indicators such as charophyte gyrogonites, and especially encrusted stems, are not present, carbonate muds displaying a range of exposure and pedogenic features may simply be interpreted as palaeosols. Palustrine carbonate strata may therefore be present within shallow marine and peritidal successions more commonly than currently recognised while potentially being relatively easily overlooked.

| Sequence stratigraphic context
In each of the modern and ancient coastal examples described previously, palustrine carbonates occur above major sequence boundaries. Evidence for subaerial exposure during sedimentation has been interpreted by some authors as indicating deposition during lowstands. This view might initially seem to be strengthened by the occurrence of palustrine facies within palaeokarst cavities or draping karstified relief, as in the Miocene of South Australia (Miller, 2012), the Lower Cretaceous of Croatia (Dini et al., 1998) and the late Visean of the Moscow Basin (Alekseeva et al., 2016;Kabanov et al., 2016). However, the present-day context of Caribbean freshwater carbonate factories suggests deposition later within eustatic cycles, when transgression causes groundwater levels to rise through the karst of caves, cenotes and sinkholes.
The palustrine carbonates associated with caps to greenhouse cyclothems discussed above might potentially record deposition during regression as postulated by Monty and Hardie (1976). However, in cases where a shallowing upwards trend results purely from sediment aggradation and progradation with no fall in sea level involved (a forced regression) then the development of any vadose zone is likely to be limited, without significant karstic porosity development or hydraulic head. In cases where shallowing upward trends reflect a physical fall in sea level, the meteoric discharge zone will migrate seawards as marine groundwaters are displaced (Werner & Simmons, 2009) so that shallow marine carbonates will be capped by freshwater carbonates. Nevertheless, their relatively low preservation potential in this scenario may leave no identifiable record of palustrine conditions.
In regressive settings, shoreline advances may proceed by jumps, where the formation of beach ridges results in shallow lagoons being abruptly isolated from the sea while still affected by marine groundwaters. These scenarios will likely result in successions showing a complex mix of freshwater, marine and saline influences, potentially similar to those documented by Azerêdo et al. (2015) from the Middle Jurassic of Portugal or from modern coastal strandplains of the Coorong in South Australia (Murray-Wallace, 2018). MacNeil and Jones (2006) provided stratigraphic models for palustrine carbonates in carbonate platform settings, distinguishing between freshwater 'disconnected' marshes, located landward of the supratidal zone and equivalent to the 'interior marshes' of Monty and Hardie (1976), and marginal marine supratidal marshes. Evidence from modern Caribbean carbonate platforms shows that meteoric water outflow occurs in both settings due to seasonal discharge of a rising carbonate aquifer, and that interior marshes progressively change in character as they are encroached by marine waters during continued transgression.
MacNeil and Jones (2006) proposed that the top of supratidal palustrine deposits recorded maximum regression, subsequently followed by the deposition of transgressive sediments if sea-level rose, or denuded if relative sea-level fell. This interpretation placed palustrine carbonates as the final deposits of a regression, truncated by an erosional ravinement surface or overlain directly by marine strata resting on a sequence boundary above.
However, the first evidence of transgression in the platform interior is commonly provided not by the ravinement surface itself but by the underlying transgressive deposits, beneath which the lowstand sediments can be preserved (Riding & Wright, 1981;Wright et al., 1997; see Figure 18). Evidence from the Caribbean records the development of modern freshwater carbonate factories fed by a carbonate aquifer rising in response to transgression. This perspective sees palustrine deposits more typically resting upon and not beneath sequence boundaries, which mark an appreciable time gap during which an epikarstic surface or pedogenetic calcrete formed during subaerial exposure. While a correlative conformity may occur where marine lowstand deposits accumulate downdip, in the platform interior palustrine deposits are typically developed above a disconformity, although still potentially showing pedogenically modified caps (Galli, 1991;Hickey et al., 2010).

| Accommodation space
The acute sensitivity of coastal carbonate systems to subtle changes in elevation means that even relatively modest tectonic movements provide a powerful mechanism capable of causing karstification during uplift and relative aquifer rise during subsidence. Regional aquifer flow will reflect the pattern of faults and fractures, and the distribution of platform interior environments and facies is likely to be highly sensitive to microtopography and subtle differential subsidence reflecting the internal structure of the platform and relief on the pediment surface (see . Footwall crests may form the sites of preferential reef development offshore and are likely to be subject to longer karstification onshore. Where tectonically subsident areas intersect the coast, as in the Bahia de Chetumal (see Figure 10), these may form a focus for significant erosional incision of pediment topography during low sea level stands (Mazzullo, 2006). Possible channel features have also been observed on the karstified Pleistocene surface towards the shelf margin west of Andros Island (Weij et al., 2018). Topographic depressions can potentially provide initial entry points and pathways for marine incursions to reach far inland into coastal lagoons and palustrine sloughs during subsequent transgression. The continuous creation of accommodation space is also likely to favour the preservation of thick palustrine successions in tectonically controlled depressions extending inland. More rapid burial may also favour the preservation of organic-rich horizons and coals as occurs in ancient examples from the Eocene of the Ebro Basin (Cabrera & Saez, 1987) and the Miocene of the Jura Mountains (Platt & Matter, 2023).
A Pleistocene example potentially recording significant tectonic movements comes from coastal Tanzania, where Reuter et al. (2009Reuter et al. ( , 2010) described a succession of palustrine carbonates 10 m thick. This succession was deposited during a geologically short window from 44, 000 to 33, 000 yr BP when sea levels were 60-90 m lower than today. Although interpreted by the authors as recording deposition during a regression, the occurrence today of palustrine and near coeval marginal marine deposits at elevations of 21 m above sea level demonstrates that rapid vertical tectonic movements were likely a prime factor controlling the subsidence and subsequent uplift of the basin floor in this case.

| Schematic stratigraphic model
Integration of ancient and modern examples allows the construction of a schematic stratigraphic model for palustrine carbonate facies and successions developed in coastal settings (Figure 26).
The model shows the flooding of a carbonate platform margin as intermittently reaching into linked interior basins, where localisation of fluid flow at major faults and rise of the regional aquifer onto the pediment surface allows freshwater marsh conditions to develop far inland in areas which experience marine incursion events only rarely at times of maximum transgression. Freshwater facies accumulate preferentially in tectonically subsident depocentres, while being more commonly overprinted near the platform margin as transgression continues.
In actively subsiding basins inland from the coast, and dependent on the subcrop geology, erosion and proximity to unroofed highland areas may deliver clastic supply from uplifted basin margins. While coarse grained incised valley fill clastics will typically be thickest in the hangingwall of basin-bounding faults ( Figure 26A), eroding carbonate pediment footwalls are likely to be strongly karstified. Once initial basin floor relief has been infilled, sedimentation in inland basin areas will typically comprise onlapping successions of fine grained distal alluvial clastics interbedded with freshwater marsh carbonates which are extensively altered by desiccation and pedogenetic modification. If present, intercalations of open lacustrine and lagoonal carbonates may correlate with brief marine incursions at maximum transgression.
Nearer to the coast, marine and freshwater facies record repeated transgressive and regressive events ( Figure 26B) with lagoonal and freshwater interbeds potentially proving difficult to distinguish owing to their similar fabrics and faunas and heavy later overprinting following emergence or further transgression. Sedimentation in coastal areas ( Figure 26C) is likely to be dominated by marginal marine carbonate facies with only thin intercalated freshwater units preserved. Basal relict calcrete drapes on subaerial exposure surfaces and palustrine fills of solution cavities may again prove challenging to recognise, especially in cases where significant karstic relief is present.

| Continental palustrine carbonates
From their classic first description by Freytet and Plaziat (1982) in South-West France and in numerous subsequent examples reviewed by Platt and Wright (1992), Freytet and Verrecchia (2002) and Alonso Zarza and Wright (2010), many ancient palustrine carbonate successions have been described from rift and foreland basins which were apparently located considerable distances inland at the time of deposition. How can these ancient continental examples be reconciled with modern palustrine environmental analogues from coastal settings such as the Caribbean?
A partial answer is that some palustrine deposits occurring in some apparently 'inland' basins may still have been strongly influenced by sea-level change via intermittent connection with the sea. Thus, for example, while palustrine carbonates in the Berriasian of the Cameros Basin of Spain were previously interpreted as marginal lacustrine deposits (Platt, 1989a), with facies evolution related to climate-controlled lake expansion and retreat during alternating wetter and drier periods, more recent work by Mas et al. (2019) has indicated a marine connection at the north-west limits of the basin during the later stages of deposition. Palustrine sedimentation prior to this and in more landward areas of the basin may also have been influenced by a rise in aquifer level in response to sealevel rise, noting that coastal encroachment may have progressed landward through a series of linked basins before providing a brief connection with the sea at the time of maximum Berriasian transgression.
While a comparable seaward transition from palustrine to shallow marine deposits can also be demonstrated in the Eocene of the Isle of Wight in southern England and the Miocene of South Australia as described above, the Miocene successions of the Ebro and Duero basins appear to have been laid down at considerable altitude above sea level and in exclusively inland settings where no coastal influence can easily be invoked (Anton et al., 2018;Vazquez-Urbez et al., 2013). Similarly, the modern groundwater-fed palustrine wetlands of the Tablas de Daimiel along the Guadiana River of south-central Spain (Alonso Zarza & Wright, 2010;Alonso Zarza et al., 2006;Bravo-Martin et al., 2019) have developed at an elevation from 634 to 605 m above sea level and with no connection to the sea. Nevertheless, the fabrics, facies and spatial relationship with underlying carbonate pediments are sufficiently similar to coastal palustrine carbonates that a parallel role can be inferred for aquifer rise in controlling the development of palustrine environments in these settings.
What controls might facilitate aquifer rise and the deposition of seasonal freshwater carbonates in isolated continental basins? It is suggested here that such a situation can occur where a carbonate pediment is onlapped, especially during periods of wetter climate or when drainage gradient is reduced in response to eustasy, tectonics or basin infilling. In such conditions, the emergence of groundwaters at a rising spring line can lead to a progressive expansion and landward migration of carbonate wetland areas over a previously karstified pediment in a manner which broadly mimics the landward migration of environments during transgression at the coast.

| Extensional and compressional settings
An example of a palustrine carbonate succession in an extensional setting is provided by the succession described above from the Berriasian of northern Spain. While coastally deposited equivalents in the Swiss Jura show only rare karst and sparse preservation of thin, metre-scale freshwater beds, palustrine carbonates in the Cameros and Basco-Cantabrian basins are up to 100-500 m thick, reflecting the consistent creation of accommodation space allowing the preservation of a thick succession.
By contrast, the Cenozoic of southern Europe includes numerous examples of continental palustrine carbonates laid down within the distal sectors of foreland and intramontane basins, generally where alluvial clastic supply was lower and regionally extensive Upper Cretaceous and marine Jurassic carbonate pediments were subaerially exposed and karstified while being passively onlapped at deformed basin margins. Examples include the Narbonnais and flanks of the Montagne Noire north of the Pyrenees (Fretytet & Plaziat, 1982) and the Aix Basin in Provence (Cojan, 1993(Cojan, , 1999, both in southern France, and various Cenozoic basins of Spain (Alonso Zarza, 2003;Cabrera & Saez, 1987;Calvo et al., 1993). The Eocene of southern England described above (Armenteros & Edwards, 2012) was also formed in a foreland setting, with coastal facies passing inland into palustrine carbonates onlapping a deforming fold. Similarly, the Miocene palustrine carbonates described above from the Duero and Ebro basins were also laid down in compressional settings surrounded by basement massifs and the Mesozoic marine carbonate cover of actively deforming fold belts, leading to the hydrographic isolation of endorheic basins (Vázquez-Urbez et al., 2013) where palustrine deposition must have relied on the rise of an inland carbonate aquifer as at Tablas de Daimiel.
The association of palustrine carbonates in tectonically active continental basins with major unconformities might initially suggest that they are syntectonic deposits. However, ancient examples show that palustrine sedimentation commonly follows equalisation of tectonic relief by subaerial erosion and the deposition of lowstand incised valley fills. In continental basins, palustrine carbonates will commonly form as early post-rift or post-orogenic deposits, recording periods of differential subsidence with reduced sedimentary gradient (see Afify et al., 2022) and laid down in tectonic settings which recall the overfilled lake basins described by Bohacs et al. (2000), although with much reduced clastic supply.
Progressive aquifer rise through a karstified pediment and its initial permeable clastic cover may then see palustrine carbonates resting on fining upwards clastic successions in basin centres while onlapping and overstepping onto the carbonate pediment at intrabasin highs and basin margins. In basins affected by multiple tectonic cycles, palustrine carbonate successions may then develop repeatedly, although they may be especially common during late basin fill.
Faulting is also likely to control the sedimentary architecture of palustrine successions in tectonically active basins, as in the SKW defining the extent of the system as well as the internal distribution of karstic corridors, palustrine sloughs and seagrass lagoons.

| Palustrine carbonates within integrated carbonate facies models
While studies of marine carbonates in the stratigraphic record have emphasised sequence stratigraphic analysis in relation to relative sea-level change (Sarg, 1988), the study of non-marine carbonate successions has historically concentrated on deciphering the effects of climate change and tectonics. Although the study of modern carbonate sedimentology has drawn heavily on the Caribbean geology of the Yucatán, Florida and the Bahamas, classical carbonate facies models have tended to overlook or to treat separately the distinctive and areally vast freshwater carbonate factories that are dynamically linked with shallow marine settings. This omission likely reflects the fact that like the SKW, many modern palustrine carbonate environments are challenging to access despite lying in plain sight directly behind the beach. Coastal palustrine carbonates can now be included within integrated carbonate facies models linking the seaward platform margin with the landward platform interior, marsh and karstified pediments ( Figure 27).
Finally, comparison of modern freshwater carbonate environments from the Caribbean with ancient palustrine carbonates allows the construction of facies models for freshwater carbonate sedimentation in continental interior basins within extensional and compressional settings ( Figure 28). Here palustrine carbonate deposition typically takes place towards the end of a tectonic cycle, following the equalisation of fault or thrust relief through erosion acting at footwall highs and emergent thrust culminations and the deposition of syntectonic lowstand clastics in hangingwall and foreland lows. Together these processes cause a progressive reduction in clastic supply and sedimentary gradient. Where late-stage sedimentary fills onlap onto extensively karstified terrain in areas where clastic supply is low, aquifer rise may then allow the formation of inland freshwater carbonate factories within the bounds of a hydrologically isolated basin.

| CONCLUSIONS
Palustrine carbonates represent a distinctive type of freshwater carbonate factory associated with seasonal wetlands and carbonate aquifers. They have been recognised on modern and ancient exposed carbonate platforms and in continental interior basins. It is clear from a review of present-day Caribbean coastal settings that as a consequence of rising sea level, complex hydrological and ecological changes take place which lead to the development of extensive GDCFs. The SKW of the Yucatán (South-East Mexico) provide an example which can be compared with similar environments in Florida and the Bahamas, illustrating how these modern palustrine wetlands form integral elements of dynamically linked coastal systems, where freshwater wetland carbonate factories are interconnected and directly juxtaposed with shallow marine carbonate environments to seaward while displaying parallel histories which are conditioned by regionally extensive late Pleistocene karstification and subsequent Holocene sea-level rise.
As transgression of an exposed carbonate platform commences, seasonal discharge from the aquifer onto the pediment surface sees the formation of palustrine environments in subsident areas below the spring line, with facies distributions acting as sensitive indicators of aquifer evolution and of tectonic subsidence. Freshwater environments pass seaward into brackish and marginal marine lagoons, beach barriers, reefs and offshore settings. Progressive transgression sees increasing marine incursion into the platform interior occurring in parallel with the landward backstepping of reefs offshore. Continued sea-level rise can result in the local breach of beach barriers and the establishment of distinctive seagrass lagoons filling former palustrine sloughs, eventually leading to shallow marine flooding of the outer palustrine zone as seen along parts of the Yucatán coast and in Florida Bay today. A series of evolutionary stages can be recognised within a transgressive cycle, associated with the formation and landward migration of groundwater-fed wetlands before their eventual destruction when shallow marine conditions are finally established across the entirety of a fully flooded platform.
The formation and preservation of coastal groundwaterfed carbonates is sensitive to a range of subtle controls reflecting climate, pediment geology, rates of sea-level change and tectonic subsidence. The record of the transient palustrine factory in carbonate platform successions may be incomplete or even absent as continued transgression results in erosion or mixing with younger marine sediments by bioturbation: the volumetric proportion of palustrine carbonates being very low in such settings in comparison with the marine carbonates with which they are interbedded. In some cases, the preservation of palustrine deposits may be limited to palimpsest karst depressions.
Ancient palustrine carbonate deposits developed in platform successions are similarly associated with extensive palaeokarst systems formed during subaerial exposure of regional carbonate pediments while reflecting aquifer discharge during subsequent sea-level rise. These GDCFs are primarily a feature of transgressive phases rather than of sea-level lowstands.
It is instructive to compare and contrast these coastal palustrine carbonates with those from more continental settings. The latter are more likely to be preserved where transgression reaches further inland into tectonically subsident inner platform areas, where marine flooding occurs much more rarely and accommodation space is being continuously created. In these settings, volumetric proportions are typically reversed, with the greater part of these successions composed of freshwater and pedogenetically modified non-marine carbonates reflecting seasonal groundwater flooding and subaerial emergence, with only thin marine carbonate intercalations recording deposition at maximum transgression. Thicker palustrine carbonate successions may also develop in continental interior extensional or intramontane basins where late-stage fill and onlap onto karstified carbonate subcrop limits clastic supply and sees the development of a similar hydrological window where the carbonate aquifer emerges seasonally onto the surface.
Subaerial exposure and karstification events in continental basins are likely to reflect climate and tectonic controls similarly acting over geologically longer timescales, However, karstic discharge and aquifer rise remain key controlling factors on the development of groundwaterfed carbonate wetlands and on the evolution of palustrine environments in both coastal and continental interior settings. Although modern palustrine environments and ancient palustrine deposits show a strong association with karstified discontinuities and erosional unconformities, sequence stratigraphy and basin analysis suggest that aquifer rise is less likely to occur during maximum lowstand or peak tectonic subsidence than later when transgression or basin infilling allows seasonal flooding via karstic discharge onto the surface.
Despite the current extent of groundwater dependent freshwater carbonate factories in the Caribbean region, their significance has been underrepresented in classical shallow marine carbonate facies models. By contrast, the common occurrence of palustrine carbonates in tectonically active continental basins apparently far from the coast, within thick clastic successions and with few marine indicators, has seen these deposits studied by different researchers and considered within separate facies models. Comparative study of modern Caribbean palustrine environments and ancient palustrine carbonates now allows the construction of integrated facies models for marine and freshwater carbonate factories.

ACKNO WLE DGE MENTS
The authors' interests, over many years, in groundwaterdependent carbonate wetlands were inspired by the highly original and seminal publication on continental carbonates by Freytet and Plaziat (1982). Our special thanks go to Rebecca St Johnston for introducing us to the Yucatán Peninsula, to Alessandro Agostini and Edison E&P UK Ltd for supporting the project, and to Chelsea Pederson and two anonymous reviewers for their helpful comments on the manuscript. Guides from Amigos de Sian Ka'an provided transport in the Biosphere Reserve. Satellite images are from Google Maps and Google Earth and their partners as shown. Aerial imagery in Figure 9 is reproduced with the kind permission of locog ringo.com with retrieval details as indicated.

FUNDING INFORMATION
Edison E&P UK Limited.

CONFLICT OF INTEREST
The authors declare no conflict of interest.

DATA AVAILABILITY STATEMENT
The authors confirm that the data supporting the findings of this study are available within the article and its supporting references; additional data are available from the corresponding author upon request.