Cretaceous anoxic–oxic changes in the Moldavids (Carpathians, Romania)
Introduction
The transition from Cretaceous anoxic to oxic environments was observed in many Tethyan areas (Jansa et al., 1979, Arthur & Premoli Silva, 1982, Hu et al., 2005, Jansa & Hu, 2009), including the Carpathians (Švábenická et al., 1997, Bąk, 1998, Michalík et al., 2002, Wang et al., 2005, Melinte-Dobrinescu et al., 2009, Skupien et al., 2009). In the Carpathian mountain belt, the sedimentation of the Upper Cretaceous Oceanic Red Beds (referred as CORB by Hu et al., 2005) follows the Lower Cretaceous black shale deposition. It appears that the development of Cretaceous black shales and CORBs is somehow causally related (Hu et al., 2006). The anoxic–oxic changes may reflect various Earth processes, such as palaeoceanographic shift, tectonic movements, and/or climatic fluctuations that changed the balance between carbon sources and sinks in the world ocean (Wang et al., 2005, Hu et al., 2009).
Colour of sedimentary rocks is an important indicator of environmental conditions in which they have formed. Gray and black shale occurrence is commonly linked to increases in organic matter content, and low oxygen content in bottom waters. In turn, CORB indicate low organic matter content, but well-oxygenated bottom conditions.
Numerous dark-coloured, commonly laminated, organic-rich sediments occur within Mesozoic sequences; they are frequently associated with Upper Jurassic to Lower Cretaceous organic carbon enriched claystones, clayey sandstones and limestones (Wignall, 1994, Pancost et al., 2004). Such beds that are more than 1-cm-thick and contain more than 1% of total organic carbon (TOC) are described as black shales (Pettijohn, 1957, Stow et al., 2001). In general, the term of black shales is used for any dark-colored fine-grained organic carbon rich sediment, in which TOC contents typically range from 1 to 15%. Many black shales are hemipelagites; some, such as black cherts and organic rich limestones, are pelagites; others are fine grained turbidites (Stow et al., 1996). Black shales are also characterized geochemically by high Fe2+ and S2− contents and enrichments in trace elements, such as Ba, Bi, Cr, Ni, Mo, V, Zn (Nijenhuis et al., 1999, Lipinski et al., 2003). The sedimentation of black shales is mostly ascribed to oxygen-poor bottom waters, typically accumulated in deep-ocean basin setting, but they may also occur in shallower sites (Wignall and Newton, 2001).
During the mid-Cretaceous, red oxic sediments, with low content of preserved organic carbon, replaced the deposition of organic-rich black shales in many of the Tethyan areas (Wang et al., 2005). This type of sedimentation is found from low to middle palaeolatitudes up to the end of the Cretaceous (Arthur & Premoli Silva, 1982, Hu et al., 2005, Melinte & Jipa, 2005, Hu et al., 2006). Probably, CORB sedimentation is a response to a palaeoclimatic and/or palaeoceanographic fluctuations, but also is effected by tectonic activity and synorogenic depositional processes (Hu et al., 2005, Wagreich & Krenmayr, 2005, Neuhuber et al., 2007, Melinte-Dobrinescu et al., 2009). The occurrence of CORB may also be linked to changes in bioproductivity, triggered by major palaeoceanographic modifications of the world oceans.
In this paper, we will discuss stratigraphy and examine genetic relationship between Lower Cretaceous organic-rich black shales deposition and overlaying Upper Cretaceous oceanic red beds from the eastern part of the Romanian Carpathian region. We also comment on causes of the Cretaceous anoxic–oxic changes as seen in the Moldavid nappes of the Eastern Carpathians.
Section snippets
Geological setting
The Eastern Carpathians represent a segment (over 600 km long) of the Carpathian tectonic chain. Inwards (westwards), this mountainous chain is bordered by the Transylvanian Basin and the easternmost part of the Pannonian Basin, while outwards (eastwards), it is bordered by the Moldavian and Scythian Platforms (at the E) and by the Moesian Platform (towards SE and S). The Eastern Carpathians are mainly composed of Jurassic–Miocene sedimentary rocks, deposited in several basins, folded and
Materials and methods
We have studied several sections located in the Inner and Outer Moldavids, displaying a continuous transition from organic-rich black shales to CORB. However, we have selected to present herein only three of the most representative sections, located at the southern and central parts of the Eastern Carpathians, in the Audia and the Tarcău nappes. The most complete investigated section is placed in the Audia Nappe, being located in the Carpathian Bend region (Bota River, tributary of the Buzău
Organic-rich black shales
In the southernmost investigated section, located in the Audia Nappe (A in Fig. 1), the Audia Formation, 190 m in thickness, displays all three members of the black shale strata (Fig. 2, Fig. 3), which are from the base to the top:
- (i)
The Lower Member, 80 m in thickness, that contains at its lower part mainly laminated black shales. The upper part is composed of decimetre-thick rhythmically alternating lithic and sublithic sandstones, siltstones and dark grey shales. The organic rich black shales
Black shales
The laminated organic-rich black shales are the main lithological component of the Upper Valanginian–Upper Albian Audia Formation. They also occur, within the Albian–Cenomanian boundary interval, as cm levels interbedded in the CORB units of the Moldavids. These shales are composed of phyllosilicates, quartz and subordinately siliceous bioclasts (radiolarian and sponge spicules); they also include carbonate bioclasts with foraminifera, bivalve and echinids (Grigorescu, 1971; Papiu &
Conclusions
In the Eastern Carpathians, black shales intercalated with carbonates (marls and micrites) firstly appeared in the Valanginian, with the latter rocks progressively diminishing up to the Aptian. During the Late Valanginian–Late Barremian interval, carbonate hemipelagites and pelagites, with rare siliceous rocks, accumulated in the Moldavids. These sediments of an abyssal plain are interbedded with thin distal siliciclastic and bioclastic turbidites. Taking into account the presence of the green
Acknowledgments
We thank to Dan Jipa (National Institute of Marine Geology and Geo-ecology, GEOECOMAR Bucharest) for the fruitful discussion and comments on an earlier version of this paper. The authors are also indebted to Titus Brustur and Stefan-Andrei Szobotka (National Institute of Marine Geology and Geo-ecology, Bucharest), for the assistance during field trips in the Eastern Carpathians. This paper is a contribution to the IGCP Project 555 ‘Rapid Environmental/Climate Change in the Cretaceous Greenhouse
References (76)
Sedimentological, geochemical and microfaunal responses to environmental changes around the Cenomanian–Turonian boundary in the Outer Carpathian Basin; a record from the Subsilesian Nappe, Poland
Palaeogeography, Palaeoclimatology, Palaeoecology
(2006)Deep-water facies succession around the Cenomanian/Turonian boundary in the Outer Carpathian basin: sedimentary, biotic and chemical records in the Silesian Nappe, Poland
Palaeogeography, Palaeoclimatology, Palaeoecology
(2007)- et al.
Latest Jurassic to Earliest Cretaceous Paleoenvironmental Changes in the Southern Carpathians (Romania): regional record of the Late Valanginian Nutrification Event
Cretaceous Research
(2008) - et al.
Calcareous nannofossil zonation of the Jurassic–Cretaceous boundary interval and correlation with the geomagnetic polarity timescale
Marine Micropaleontology
(1989) - et al.
Mesozoic plate tectonic reconstruction of the Carpathian region
Palaeogeography, Palaeoclimatology, Palaeoecology
(2004) - et al.
Upper Cretaceous Oceanic Red Beds (CORB) in the Tethys: occurrence, lithofacies, age and correlation
Cretaceous Research
(2005) - et al.
Mid-Cretaceous oceanic red beds in the Umbria-Marche Basin, central Italy: constraints on paleoceanography and paleoclimate
Palaeogeography, Palaeoclimatology, Palaeoecology
(2006) - et al.
Biostratigraphy of the Upper Cretaceous of Romania
Cretaceous Research
(1994) - et al.
Trace metal signatures of Jurassic/Cretaceous black shales from the Norwegian Shelf and the Barents Sea
Palaeogeography, Palaeoclimatology, Palaeoecology
(2003) - et al.
A Valanginian (Early Cretaceous) ‘boreal nannoplankton excursion’ in sections from Romania
Marine Micropaleontology
(2001)
Turonian Oceanic Red Beds in the Eastern Alps: Concepts for palaeoceanographic changes in the Mediterranean Tethys
Palaeogeography, Palaeoclimatology, Palaeoecology
Organic matter and trace element rich sapropels and black shales: a geochemical comparison
Earth and Planetary Science Letters
Depositional processes of black shales in deep water
Marine and Petroleum Geology
Upper Cretaceous oceanic red beds (CORB) in the Northern Calcareous Alps (Nierental Formation, Austria): slope topography and clastic input as primary controlling factors
Cretaceous Research
Biostratigraphy of the lower red shale interval in the Rhenodanubian Flysch Zone of Austria
Cretaceous Research
Upper Cretaceous oceanic red beds in southern Tibet: a major change from anoxic to oxic, deep-sea environments
Cretaceous Research
Black shales on the basin margin: a model based on examples from the Upper Jurassic, of the Boulonnais, northern France
Sedimentary Geology
Nouvelles donées biostratigraphiques (palynologiques et micropaléontologiques) concernant les schistes noirs et les argiles barriolées des Carpates Orientales
Dări de Seamă ale Institutului de Geologie şi Geofizică
Development of widespread organic carbon-rich strata in the Mediterranean Tethys
Planktonic foraminiferal biostratigraphy, Upper Cretaceous red pelagic deposits, Pieniny Klippen Belt, Carpathians
Studia Geologica Polonica
The Black Shale Formation of the East Carpathians, lithostratigraphy and oil potential
Anuarul Institutului de Geologie şi Geofizică.
Sulphate reduction, organic matter decomposition and pyrite formation
Philosophical Transactions of the Royal Society, Mathematical, Physical and Engineering Sciences
Sedimentology of some Flysch deposits: a graphic approach to facies interpretation
Sur le Crétacé de la zone du flysch interne entre les rivières de Teleajen et Trotuş et les implications sur la structure des Carpates Orientales
Stratigraphy based on microfauna in the Western Polish Carpathians
Biuletyn Instytutu Geologicznego
Late Carboniferous–Neogene geodynamic evolution and palaeogeography of the circum-Carpathian region and adjacent areas
Annales. Societatis Geologorum Poloniae
Geodynamic evolution and palaeogeography of the Polish Carpathians and adjacent areas during Neo-Cimmerian and preceding events (latest Triassic–earliest Cretaceous)
Flişul carpatic. Petrografie şi consideraţii economice
Constituenţii clastici grosieri ai depozitelor cretacice din unitatea şisturilor negre: semnificaţie sedimentologică
Studii şi cercetări geologice, geofizice şi geografice, Seria geologie
Origin of Cretaceous oceanic red beds from the Vispi Quarry section, central Italy: visible reflectance and inorganic geochemistry
Microbiostratigraphie, associations et zones des foraminifères du Crétacé du Flysch externe des Carpates Orientales (Roumanie)
Cretaceous pelagic black shales and red beds in western Tethys: origins, paleoclimate, and paleoceanographic implications
Cited by (22)
Structure and petroleum systems of the Eastern Carpathians, Romania
2023, Marine and Petroleum GeologyCretaceous sedimentation in the outer Eastern Carpathians: Implications for the facies model reconstruction of the Moldavide Basin
2017, Sedimentary GeologyCitation Excerpt :The paleosetting is mainly anoxic in the Moldavide nappes and subordinately dysoxic, as grey shales with cm-scale turbidites are rarely encountered, typical for basin plain and mud-rich slope apron systems. Anoxic sedimentation in the Outer Moldavide nappes, such as at Tarcău and Vrancea (Figs. 10A, B, 11, 12), started in the Hauterivian (Melinte-Dobrinescu and Roban, 2011), as in some parts of the Inner Moldavides, e.g., Audia Nappe, where the black shales had accumulated since the Hauterivian (Alexandrescu, 1966, 1971; Ion, 1975; Melinte-Dobrinescu et al., 2009). We assume that the deep basin of the Moldavides was mostly fed by fluvial systems from the Eastern Carpathian Foreland, reworked on the shelf (Fig. 10A, B).
The Kapanboğazı formation: A key unit for understanding Late Cretaceous evolution of the Pontides, N Turkey
2016, Palaeogeography, Palaeoclimatology, PalaeoecologyPaleoceanographic changes during the Albian-Cenomanian in the Tethys and North Atlantic and the onset of the Cretaceous chalk
2015, Global and Planetary Change