An Early Jurassic (Sinemurian–Toarcian) stratigraphic framework for the occurrence of Organic Matter Preservation Intervals (OMPIs)

Lower Jurassic sedimentary successions in the Atlantic margin basins include several organic-rich intervals, some with source rock potential; time-equivalent units are also identified in onand offshore areas worldwide. Despite decades of research, it is still unclear which mechanisms lead to the deposition of organic-rich sediments during the Early Jurassic. The objectives of this study are to construct a detailed temporal and geographical framework of Sinemurian–Toarcian organic matter preservation intervals (OMPIs; subdivided into local, regional, and superregional) and roughly constrain the relationship of OMPIs with the Lower Jurassic δ13C record. This survey combines an in-depth analysis of literature on the distribution of OM in the Sinemurian–Toarcian with new geochemical studies [total organic carbon (TOC) and organic matter pyrolysis] from selected outcrop sections from Portugal, Spain, and Morocco. Strong local control on OMPIs during most of the Sinemurian is suggested. Regionally widespread organic-rich facies are associated with the most negative δ13C values of the broad Sinemurian–Pliensbachian negative carbon isotopic trend recorded in organic matter (including the Sinemurian–Pliensbachian Boundary Event). Pliensbachian OMPIs are expressed in the areas bordering the proto-Atlantic Ocean and are often linked with positive δ13C excursions and short-lived warm intervals, but OMPIs are also defined for the Late Pliensbachian cool interval. Early Toarcian superregional OMPIs are associated with some of the most pronounced δ13C excursions of the Mesozoic. Toarcian maximum TOC content occurs with the positive δ13C (recovery) trend following the δ13C negative shift typically linked with the Early Toarcian Oceanic Anoxic Event (T-OAE), supporting the notion that peak carbon sequestration/ocean anoxia post-dated the main phase of carbon input into the atmosphere, as also suggested by recent modelling efforts. However, additional superregional OMPIs predate and postdate the TOAE, indicating that conditions favouring preservation of OM (increased productivity and/or enhanced preservation) during the Early Toarcian were not restricted to the T-OAE interval. The compilation of Sinemurian–Toarcian OMPIs presented in this paper demonstrates that organic-rich intervals of regional and superregional expression in the Lower Jurassic sedimentary record are ubiquitous and may even be more numerous than in the Cretaceous. Considering the association of some of the Sinemurian, Pliensbachian, and Toarcian regional and superregional OMPIs with well-defined carbon isotopic excursions, it is here suggested that these hold the same relevance as the secondary OAEs of the Cretaceous, such as the Hauterivian OAE (Faraoni Event), Late Valanginian OAE (Weissert Event), and Late Aptian–Early Albian OAE (OAE 1b clus-

With over 40 years of research on the understanding of the processes leading to Early Jurassic OM enrichment in marine and terrestrial environments, there are still large uncertainties concerning the impact of local versus global factors leading to OM enrichment. Uncertainty arises from the (1) temporal and spatial ambiguity when correlating most Lower Jurassic organic-rich sedimentary successions, (2) limited constraints on the amount, chemical composition, and thermal maturity of OM, and (3) incomplete understanding of environmental and depositional constraints on OM production and preservation at a wide range of geological time intervals. Understanding the link between OM production and preservation/sequestration and climate change is vital to advancing knowledge of processes and feedback mechanisms in the Earth Systems that drive global change at a wide range of time scales and to constrain the relative importance of the many factors (including natural and anthropogenic) contributing to modern-day climate change.
This study focuses on the temporal and spatial occurrence of organic-rich intervals through the Sinemurian-Toarcian interval, comprising most of the Lower Jurassic. The two objectives of this paper are to (1) construct a detailed temporal and geographical framework of Sinemurian-Toarcian organic-rich facies occurrences at a global scale, defined here as organic matter preservation intervals (OMPIs) and (2) approximately constrain the relationship of OMPIs with the Lower Jurassic δ 13 C record. This study combines an in-depth analysis of literature on the distribution and characteristics of OM (quantity of carbon and OM type) in the Sinemurian-Toarcian with new geochemical studies from selected outcrop sections from Portugal, Spain, and Morocco. Silva et al. Earth-Science Reviews xxx (xxxx) 103780 1.1. Production and preservation of organic matter and its impact on the global carbon cycle For convenience, the carbon cycle is usually divided into two cycles, the short-and long-term carbon cycles (Berner, 1999). Carbon in the short-term carbon cycle is rapidly exchanged within the surficial reservoirs, consisting of the oceans, atmosphere, biosphere, and soil, whereas carbon in the long-term cycle is slowly exchanged between the geosphere and the surficial systems (Berner, 1999;Ciais et al., 2013). The short-term carbon cycle is the dominant control on atmospheric pCO 2 over millennia, whereas the long-term carbon cycle controls atmospheric CO 2 and O 2 over millions of years (Berner, 1999(Berner, , 2006. Equilibrium and kinetic fractionation among OM, CO 2 , and HCO 3 − control the carbon isotope ratios of atmospheric CO 2 and oceanic inorganic and organic carbon (e.g. Emerson and Hedges, 2008;Silva et al., 2020a). The main processes that affect the 13 C/ 12 C ratio of the "superficial" carbon reservoirs at geological time intervals are the (1) equilibrium between dissolved inorganic carbon (DIC) and atmospheric CO 2 , (2) fractionation between DIC and carbonate minerals, (3) fixation of CO 2 and production of biomass via photosynthesis, and (4) respiration, remineralisation, preservation, and sedimentary reworking and resuspension of sedimentary OM (Hayes et al., 1999).

Methodology: a stratigraphic framework for Lower Jurassic organic-rich facies
The temporal and spatial occurrence of organic-rich sedimentary successions of Sinemurian-Toarcian age is reviewed by combining published organic geochemical data with new biostratigraphic and geochemical data (total organic carbon, TOC, and organic matter pyrolysis) from Lower Jurassic outcrops from Portugal, Spain, and Morocco (Appendixes 1-4). Some geographic areas are underrepresented in terms of data availability and warrant further studies to better constrain the extent and duration of Early Jurassic organic-rich deposition; a brief review of these locations is presented in Appendix 1 (A1.4. Uncertain data and data underrepresentation). A reference framework for the temporal and spatial occurrence of individual Early Jurassic Organic Matter Preservation Intervals (OMPIs) is presented in Figs. 3 and 4 and Appendixes 2-4.

Organic-rich sedimentary rocks
Organic-rich sedimentary rocks are here defined by present-day TOC values equal or higher than 2%. This cut-off value was chosen because: a) Sedimentary rocks with TOC > 2% appear slightly darker compared to low-TOC rocks, making them more easily recognisable in the field or in hand samples (see also Hunt, 1995) and, therefore, from literature where geochemical data are not available and rocks are only described as organic-rich or black shales (there are, however, other factors that may also result in dark mudstones, for example, mineralogical composition). Black shale is a common classification in the literature and, in its broadest definition, corresponds to a dark coloured, usually laminated mudstone, calcareous mudstone, or marl with TOC ranging from 1 to 30 wt% (e.g. Swanson, 1961;Weissert, 1981). b) This value roughly corresponds to the average TOC of "productive" hydrocarbon source rocks (see discussion in Ronov, 1958;Tissot and Welte, 1984;Jones, 1987;Lewan, 1987;Chinn, 1991;Katz, 1995;Law, 1999;Peters et al., 2005). Silva et al. Earth-Science Reviews xxx (xxxx) 103780 (caption on next page) Silva et al. Earth-Science Reviews xxx (xxxx) 103780 (caption on next page)  Table 1 and Appendix 2 for OMPI identification.

Organic Matter Preservation Interval (OMPI)
An Organic Matter Preservation Interval (OMPI) corresponds to a constrained time interval (at the Subchron level) characterized by the deposition of organic-rich sediments (organic-rich sedimentary rocks with present day TOC > 2%) at local, regional, or superregional scales (as defined in subsection 2.1). OMPIs are defined irrespective of kerogen type and classification, location, and processes of OM production, accumulation, and diagenesis/maturation. They are classified as local, regional, or superregional (Table 1 a) Local OMPI: Organic-rich sedimentary rocks observed in one section. b) Regional OMPI: Time-equivalent (at Subchronozone scale) organicrich sedimentary rocks observed in two or more sections separated by more than~1000 km (arbitrarily defined) or located in two "non-contiguous" basins. c) Superregional OMPI: Time-equivalent organic-rich sedimentary rocks in two or more non-contiguous paleogeographical domains. Examples of paleogeographical domains are Northern Europe, Tethys, Mediterranean, Central Atlantic, Arctic, Pacific North America, Pacific South America, Asia.
OMPIs are described by first indicating the Age (Subage) where these are defined, followed by Chron, Subchron, and current understanding of the extent of the associated organic-rich facies, e.g. Early Pliensbachian (davoei, maculatum/capricornus) regional OMPI (see Table 1 and Appendix 2 for abbreviations for each OMPI). Uncertainty regarding the spatial representation of an OMPI is noted first by indicating the confirmed and then possible spatial classification, e.g., regional (superregional?). In particular cases, we adopt a historical denomina- Silva et al. Earth-Science Reviews xxx (xxxx) 103780 tion of a recognized feature of the geological record intimately associated with the OMPI, such as the Toarcian Oceanic Anoxic Event [e.g., OMPI T2(OAE)]. The minimum requirement to define an OMPI is a single sample, representative of a continuous bed at outcrop scale, with present day TOC > 2% and a confident stratigraphic age assignment (using, for example, bio-or chemostratigraphy) to a Subchronozone. Organic-rich sedimentary rocks that cannot be confidently assigned to a Subchronozone cannot be used to define an OMPI. However, such loosely dated occurrences may support observations from other betterdated sections, as is the case for the Sinemurian successions of Western North American basins.

OMPIs: temporal and paleogeographical trends
Because δ 13 C records exist for many of the Lower Jurassic sedimentary successions showing organic matter enrichment, below we briefly discuss the stratigraphic occurrence of OMPIs within the context of the Lower Jurassic δ 13 C record (Table 1, Figs. 1-4, and Appendixes 1-4). A detailed discussion on processes leading to Early Jurassic short-and long-term global carbon cycle perturbations is beyond the scope of this study. The Early Sinemurian to Early Pliensbachian interval is marked by multiple shifts of up to around 5‰ in the carbon isotopic composition of organic and inorganic substrates from marine and continental environments (e.g. Jenkyns et al., 2002;van de Schootbrugge et al., 2005a;Suan et al., 2010;Silva et al., 2011;Jenkyns and Weedon, 2013;Duarte et al., 2014;Price et al., 2016;Ruhl et al., 2016;Xu et al., 2017a;Hesselbo et al., 2020;Schöllhorn et al., 2020b;Storm et al., 2020). Organic matter deposition and preservation in the Sinemurian seems to be strongly dependent on local depositional and tectonic conditions (Chadwick, 1986;Stapel et al., 1996;Rasmussen et al., 1998;Alves et al., 2002;Duarte et al., 2010Duarte et al., , 2012Duarte et al., , 2014Poças Ribeiro et al., 2013;Silva et al., 2013), controlling, for example, relative sea-level and organic productivity (Bessereau et al., 1995;Jenkyns and Weedon, 2013;Schöllhorn et al., 2020b). It was suggested that deposition of organicrich facies and black shales in the Sinemurian appears to be restricted to basins and time-intervals marked by extensional faulting and formations of depocenters with a geometry favourable to water mass stratification and organic matter accumulation and preservation (e.g. the Lusitanian and Wessex basins, Fleet et al., 1987).
A strong cyclicity in TOC distribution in the Wessex Basin is observed in the Lower Pliensbachian Jenkyns, 1990, 1999). It was suggested that these cycles resulted from high-frequency climatic variations that controlled the degree of oxygenation at the seafloor (van Buchem et al., 1995). Changes in the clay mineral assemblages in the Cardigan Bay Basin (Deconinck et al., 2019) reinforce the view that high-frequency climatic variations may have played a pivotal role in the OMPIs associated with the broad Late Sinemurian-Pliensbachian negative carbon isotopic excursion (nCIE). It was recently suggested that the stratigraphic occurrence of positive and negative (0.5-2‰ in TOC) CIEs in Sinemurian and Pliensbachian marine sedimentary archives reflect orbital (astronomical) forcing of the global exogenic carbon cycle, with a~405 kyr eccentricity periodicity (Storm et al., 2020).
In the Wessex Basin, the organic-rich sedimentary rocks of the local (superregional?) OMPI S3 are associated with relatively more negative δ 13 C org values (Jenkyns and Weedon, 2013;Schöllhorn et al., 2020b). A similar situation is observed in the Last Creek 2 section from the Cadwallader Terrane (Porter et al., 2014b), where an interval tentatively dated to the top of the leslei (= turneri) Chronozone presents the same relationship between TOC and δ 13 C org . However, a recent study from the Wessex Basin seems to indicate that, when accounting for changes in type and source of OM, a corrected δ 13 C curve (δ 13 C-HI index = measured δ 13 C TOC -(a * HI), a being the slope of the correlation trend between δ 13 C TOC and HI, Schöllhorn et al., 2020b;Suan et al., 2015) shows an association between OMPIs and corrected pCIEs. Further studies are necessary to validate that HI variation truly reflects changes in OM or if, for example, is a reflection of different degradation/diagenetic processes of similar OM Suan et al., 2015;Charbonnier et al., 2020;Storm et al., 2020).

Sinemurian Liasidium Event. The Early Jurassic Sinemurian Liasidium Event, obtusum chonozone (denotatus Subchronozone)
-oxynotum chronozone (oxynotum Subchronozone) (Riding et al., 2013;Hesselbo et al., 2020) is characterized by the acme of the Liasidium variabile dinoflagellate and high abundances of Classopollis classoides, suggesting an association with high land and sea temperatures (Riding et al., 2013;Hesselbo et al., 2020;Schöllhorn et al., 2020b) (Fig. 4). Masetti et al. (2017) and Franceschi et al. (2019) tentatively correlated the "Arnioceras time Event" nCIE from the southern Alps with the negative shift identified by Riding et al. (2013). So far, this carbon isotopic disturbance appears not to be stratigraphically associated with widespread deposition of OM. How- Silva et al. Earth-Science Reviews xxx (xxxx) 103780 ever, a poorly age constrained organic-rich interval (currently not defined as an OMPI due to uncertain age assignment) in the Lusitanian Basin (Portugal) may be contemporaneous with the Sinemurian Liasidium Event (Appendixes 2 and 3).
Earth system processes leading to the long ranging Sinemurian-Pliensbachian nCIE and climatic and environmental changes are largely unknown but are speculated to relate to either the opening of the Hispanic Corridor or a late phase of enhanced global continental (silicate) weathering induced by the Central Atlantic Margin Province volcanism (see discussion in Korte and Hesselbo, 2011;Porter et al., 2013;Gómez et al., 2016b;Price et al., 2016;Ruhl et al., 2016;Danisch et al., 2019;Franceschi et al., 2019;Schöllhorn et al., 2020b, Schöllhorn et al., 2020aStorm et al., 2020). Considering the extremely limited stratigraphic data outside the northern western Tethys realm (see A1.4), significant accumulation of OM (high TOC) during the Sinemurian-Pliensbachian nCIE appears to be most expressive in the Wessex and Lusitanian basins; the exception is the regional (superregional?) OMPI S-P where sedimentary OM enrichment was more widespread (Fig. 3). The regional (superregional?) OMPI S-P is associated with the most negative δ 13 C values of the broad Sinemurian-Pliensbachian nCIE [including the Sinemurian-Pliensbachian boundary event (S-PBE) cf. Korte and Hesselbo, 2011], and coincides with the final stages of the Late Sinemurian warming event and transition to subsequent cooling (Korte and Hesselbo, 2011;Gómez et al., 2016b). The Trento platform (Italy) is marked by platform sedimentary deposits with relatively elevated TOC, but below 2%, which are interpreted to be associated with the S-PBE, suggesting relative OM enrichment even in shallow areas at this time (Franceschi et al., 2014(Franceschi et al., , 2019.
Despite the recognized gaps in data coverage, organic-rich facies associated with the Late Pliensbachian pCIE are (apparently) concentrated mainly along the areas bordering the proto-Atlantic Ocean and possibly the Boral Sea (Fig. 3). During the Late Pliensbachian, organic productivity and preservation were enhanced during major transgres-sive episodes (Hallam, 1981;de Oliveira et al., 2006;Duarte et al., 2010;Silva et al., 2011Silva et al., , 2012. Rosales et al. (2006) suggested a link between second-order relative sea-level changes in the Basque-Cantabrian Basin and variations in seawater geochemistry during the Early Jurassic, noting a coincidence between transgressions and increasing δ 13 C, TOC and Hydrogen Index (and viceversa for regressions). It was also suggested that the Late Pliensbachian black shales were associated with warm temperatures (hyperthermals?) within the relatively cooler Late Pliensbachian Schöllhorn et al., 2020b).

Spinatum nCIE: OMPI P11
The spinatum Chronozone is generally regarded as a cool interval (Hinnov and Park, 1999;Price, 1999;Dera et al., 2009b;Dera et al., 2009a;Suan et al., 2010;Korte and Hesselbo, 2011;Gómez et al., 2016b;Ruebsam et al., 2019;Deconinck et al., 2020;Storm et al., 2020). It has been suggested that geological storage of OM associated with the Late Pliensbachian pCIE resulted in decreased atmospheric CO 2 , triggering and/or amplifying cooling in the spinatum Chron (e.g. Suan et al., 2010;Silva et al., 2011;Storm et al., 2020). It was also speculated that a potentially early onset of North Sea doming may have caused the development of regressive facies in the Late Pliensbachian of the North Sea region, which may have promoted the regional shift from a warm to a cooler climate mode (Korte et al., 2015) (Fig. 2). More recently, De Lena et al. (2019) suggested the degassing of volcanic S-species (SO 2 ) was an unlikely driving mechanism of the cool and dry climate of the late Pliensbachian.

P-Toa nCIE: OMPI P-Toa
A smaller-scale (~2-3‰ in TOC) nCIE is observed at the base of the Toarcian polymorphum Chronozone, the Pliensbachian-Toarcian event (P-Toa Event), coincidental with the superregional OMPI P-Toa (Hesselbo et al., 2007;Littler et al., 2010). It was suggested that the P-Toa event resulted from a carbon cycle perturbation analogous to the one marking the T-OAE (Littler et al., 2010), and it is stratigraphically associated with an extinction phase in marine benthos at the base of the Toarcian (e.g. Little and Benton, 1995;Littler et al., 2010;Caruthers et al., 2013) and significant continental weathering and volcanic activity (Percival et al., 2015(Percival et al., , 2016.
The superregional OMPIs T2(OAE), T3(OAE), and T4(OAE) are associated with widespread deposition of organic-rich facies with high TOC, including black shales. Maximum TOC contents are frequently observed in the superregional OMPI T4(OAE), associated with the positive δ 13 C trend of the T-OAE nCIE (the positive carbon isotopic trend of the T-OAE nCIE is here defined as the interval between minimum δ 13 C and maximum δ 13 C that marks the end of the T-OAE interval) (Fig. 4). The superregional OMPI T4(OAE) is observed even in areas not characterized by significant Lower Toarcian organic-rich deposition, such as the Lusitanian Basin (de Oliveira et al., 2006;Hesselbo et al., 2007;Rodrigues et al., 2016Rodrigues et al., , 2020a. Carbon sequestration during the T-OAE seems to be broadly associated with a peak in 187 Os/ 188 Os (Cohen et al., 2004;Percival et al., 2016;Them et al., 2017;van Acken et al., 2019) and a minimum in δ 18 O (Suan et al., 2008;Dera et al., 2011;Krencker et al., 2014;Ullmann et al., 2014Ullmann et al., , 2020Korte et al., 2015), suggesting that maximum organic carbon sequestration during the T-OAE was concomitant with sustained high temperatures and enhancement of the hydrological cycling and increased weathering rates (Jenkyns, 2010;Xu et al., 2017b;Fantasia et al., 2019a;Rodrigues et al., 2020b;Ullmann et al., 2020). The here demonstrated offset between the T-OAE δ 13 C negative trend and the maximum sedimentary TOC values combined with the widespread nature of the superregional OMPI T4(OAE) agree with recent modelling efforts indicating a lag between peak greenhouse gas input and peak anoxia/carbon sequestration .
Several OMPIs are observed after the T-OAE ( Fig. 4 and Appendixes 2 and 3). The superregional OMPIs T5 and T6 and the regional OMPI T7 are associated with the decreasing limb of the broad Early Toarcian δ 13 C positive excursion initiated at the base of the tenuicostatum Chronozone (Fig. 4). Oxygen stressed conditions and carbon sequestration were prevalent from the mid-semicelatum Subchron (tenuicostatum Chron) to the upper bifrons Chron in several locations, as recorded in the German sections (Röhl et al., 2001), Cleveland Basin (Thibault et al., 2018), and Slyne Basin . Post-OAE black shales in the Paris Basin were likely concomitant with third-order sea-level changes (Hermoso et al., 2013;sensu de Graciansky et al., 1998).

Comparison with the Cretaceous OAEs
OAEs were initially defined as brief time intervals during which significant portions of the global oceans were extensively deoxygenated (Schlanger and Jenkyns, 1976;Jenkyns, 1980Jenkyns, , 2010Arthur et al., 1990;Leckie et al., 2002). Although a comprehensive model to explain all OAEs is not yet fully constrained, the consensus is that these events are associated with a sudden influx of greenhouse gasses into the atmosphere and global warming, leading to an acceleration of the hydrological cycle, increased continental weathering, enhanced nutrient delivery to the oceans, intensified oceanic upwelling, and increased productivity in marine and continental environments (Schlanger and Jenkyns, 1976;Weissert, 1989;Arthur et al., 1990;Hesselbo et al., 2000a;Leckie et al., 2002;Bodin et al., 2010;Jenkyns, 2010;Trabucho-Alexandre et al., 2011;Herrle et al., 2015;Montero-Serrano et al., 2015;Xu et al., 2017b;Fantasia et al., 2018;Silva et al., 2020b).
OAEs are characterized by negative or positive CIEs, interpreted to reflect the sudden influx of isotopically light CO 2 into the atmosphere (either from, for example, volcanism, metamorphic degassing, or destabilization of gas hydrates) or burial of vast amounts of organic carbon, respectively (Jenkyns, 2010). However, local basinal responses often override global forcing on the occurrence, onset, and termination of organic-rich deposition associated with OAEs (e.g. Trabucho-Alexandre et al., 2011;Fantasia et al., 2019a;Rodrigues et al., 2019Rodrigues et al., , 2020a and CIEs (reflecting global carbon cycle change) in combination with evidence for regional to superregional bottom-water deoxygenation have become the accepted characteristic features of an OAE, rather than widespread organic-rich deposition alone (Jenkyns, 2010).
The compilation of Sinemurian-Toarcian OMPIs presented in this paper demonstrates that regional and superregional sedimentary sequestration of OM during the Early Jurassic was more common than previously thought (Fig. 5). Because of the association of OMPIs with well-constrained CIEs (Figs. 3 and 4 and Appendices 3 and 4), we propose that the regional (superregional?) OMPI S-P and the superregional OMPI P11 and OMPI P-Toa should now be considered as secondary OAEs, similarly to the secondary Cretaceous OAEs.
The Early Toarcian superregional OMPIs T1, T5, T6, and the regional (superregional?) OMPI T7 occur in association with the Lower Toarcian pCIE, and their spatial spread supports some degree of equivalency to the secondary Cretaceous OAEs. These OMPIs demonstrate that the establishment of (global?) environmental and depositional conditions leading to widespread preservation of OM in the Late Pliensbachian-Early Toarcian was not exclusively associated with the T-OAE.

Limitations and future challenges
The methodology presented here for resolving OMPIs applies to any geological interval, is simple and straightforward, and provides a framework for exploratory research on large scale sedimentary organic matter sequestration and its impacts on the global carbon cycle. However, mechanistic understanding of sedimentary OM sequestration at . The Sinemurian-Pliensbachian record was created using the time scale and δ 13 C from the reference Mochras core, Cardigan Bay Basin, UK (Storm et al., 2020). The Toarcian and Cretaceous time scale (Ogg et al., 2016) and δ 13 C record (Herrle et al., 2004;Reichelt, 2005;Föllmi et al., 2006;Jarvis et al., 2006;Hesselbo et al., 2007;Voigt et al., 2012;Martinez et al., 2015;Xu et al., 2018) were generated using TSCreator software (PUBLIC7.4_windows10_latest_06September2019). Cretaceous OAEs are from Arthur et al. (1990) Silva et al. Earth-Science Reviews xxx (xxxx) 103780 basinal, intrabasinal, and global scales is often hampered by the lack of spatial data coverage, temporal data uncertainty, and sampling/data resolution for many of the intervals studied (see A1.4). In addition, understanding of sedimentation rates and their impact on true rates of organic carbon accumulation, or carbon burial fluxes, is often limited or non-existent; this is particularly important when using a fixed cut-off value of 2% present-day TOC to define an OMPI or possible sourcerocks. For example, sedimentary successions with low TOC/high sedimentation rate may represent the same organic matter accumulation per time unit as high TOC/low sedimentation rate depositional environments. Furthermore, the intrabasinal spatial extent of an OMPI is often unconstrained, even when using the most advanced imaging/modelling tools (e.g. Bruneau et al., 2017). A detailed assessment of sedimentation rates and the translation of present-day TOC values into organic matter accumulation/sequestration rates (or fluxes) for individual OMPIs at the outcrop and basin-scale are however outside the scope of this study. Thermal maturation may also lead to an underestimation of the original OM accumulation rate, and possibly even the spatial extent of OMPIs, especially if original TOC approximated 2% in now highly mature successions. The magnitude of this effect depends mainly on the level of maturity and the relative proportions of generative and nongenerative organic carbon compounds, with type I and type II kerogens having a higher proportion of generative organic carbon which therefore are prone to have depressed original TOC values (Jarvie, 2012). Type III and type IV kerogens are less affected by thermal maturation, and its suppressing effect on TOC, as hydrocarbons generation was limited. Therefore, the loss of carbon via maturation and expulsion may thus have resulted in an underestimation of organic carbon burial throughout geological history and during Early Jurassic OMPIs when using uncorrected present-day TOC values as a proxy.
Although the present work presents a framework for the stratigraphic distribution of OMPIs across the~20 Myr of the Sinemurian-Toarcian time interval, we emphasize that without a detailed assessment of (1) inter-and intrabasinal bio-and chronostratigraphic correlations, (2) duration and stratigraphic completeness, (3) TOC stratigraphic and basinal variability, and (4) thermal maturation and diagenesis, the study of OMPIs as defined here will generally underestimate the spatial and temporal patterns in geological organic carbon storage and, therefore, result in inaccurate estimates on OM burial and as a sink of atmospheric CO 2 . Future research should aim to disentangle (1) the noted complexities in estimating original TOC and organic carbon accumulation rates, (2) temporal and spatial variability in environmental or Earth system feedback mechanisms driving sedimentary carbon sequestration, and (3) their combined impact on the global carbon cycle. Further work is expected to define additional Early Jurassic OM-PIs and to improve current understanding of the spatial and temporal distribution of individual OMPIs.

Conclusions
The recognition of several Early Jurassic organic matter preservation intervals (OMPIs) of regional and superregional extent gives new insight into the role that OM sequestration played in Earth System process and provides support to current theoretical models for carbon cycle perturbations in the Early Jurassic (e.g., the T-OAE). From this study, we conclude that: 1. Sinemurian regional OMPIs were mainly restricted to a small number of European basins. A relatively more widespread OMPI was associated with the most negative δ 13 C interval of the longterm Sinemurian-Pliensbachian δ 13 C excursion. The stratigraphic and causal relationship between OMPIs and CIEs (as representative of global carbon cycle perturbations) is not always straightforward.
2. Pliensbachian regional (superregional?) OMPIs occur mostly in the basins bordering the proto-Atlantic Ocean, often associated with positive δ 13 C excursions and short-lived warming intervals (hyperthermals?). As suggested previously, it is apparent that significant OM sequestration predates [regional (superregional?) OMPIs 7, 8, and 9] and coincides with the onset of the Late Pliensbachian cool episode and the spinatum nCIE (superregional OMPI 11). 3. As extensively discussed in the existing literature, Early Toarcian OMPIs are widespread. The Early Toarcian superregional OMPIs T2 (OAE), T3(OAE) and T4(OAE) are associated with the most pronounced δ 13 C negative carbon isotopic excursion in the Mesozoic. Maximum TOC contents [superregional OMPI T4(OAE)] occur in association with the positive δ 13 C trend of the Early Toarcian Oceanic Anoxic Event (T-OAE), indicating, and as suggested by recent modelling efforts, that peak OM sequestration and anoxia post-dated the main event of carbon injection into the atmosphere. However, several superregional OMPIs pre-and postdated the TOAE interval. These OMPIs demonstrate that the establishment of (global?) environmental and depositional changes led to widespread preservation of OM in the Late Pliensbachian and Early Toarcian and thus not exclusively during the main Early Toarcian OAE. 4. This study demonstrates that organic-rich intervals of regional and superregional expression in the Early Jurassic are more common than previously thought. It is contended that considering the association of the regional (superregional?) OMPI S-P (raricostatum, raricostatoides-jamesoni, polymorphus) and the superregional OMPI P11 (spinatum, hawskerense) and OMPI P-Toa with wellcharacterized CIEs, these should now be considered secondary OAEs, similarly to the secondary Cretaceous OAEs. The superregional Early Toarcian OMPIs T1 (tenuicostatum, paltum-tenuicostatum), T5 (falciferum, elegans-falciferum), T6 (bifrons, commune), and the regional (superregional?) OMPI T7 (bifrons, fibulatum) occur in association with the broad lower Toarcian pCIE.

Declaration of Competing Interest
None.

Acknowledgements
This research was supported by the Source Rock and Geochemistry of the Central Atlantic Margins consortium (Dalhousie University, Basin and Reservoir Lab, PI-Grant Wach). Ricardo L. Silva was also supported by iCRAG (project: Temporal and spatial variability in Lower Jurassic hydrocarbon source rock quality in Irish off-shore marine basins, PI-Dr Micha Ruhl). Luis V. Duarte was partially supported by the strategic project UID/MAR/04292/2019 granted to the Marine and Environmental Sciences Centre (MARE). Stephen Hesselbo acknowledges funding from NERC (NE/N018508/1). We gratefully acknowledge the Editor Shuhab Khan, and Stephane Bodin and three other anonymous referees for their insightful comments that greatly benefited and improved the manuscript. This study is a contribution to the UNESCO-IUGS projects IGCP 655 Toarcian Oceanic Anoxic Event: Impact on marine carbon cycle and ecosystems and IGCP 739 The Mesozoic-Paleogene hyperthermal events.

Appendix A. Supplementary data
Supplementary data to this article can be found online at https:// doi.org/10.1016/j.earscirev.2021.103780.