Epicontinental Seaways Research Articles

Taxonomic review, palaeoecological, and palaeobiogeographical significances of Campanian Tethyan oysters from the North Eastern Desert, Egypt

The Late Cretaceous was a time of high eustatic sea level that enabled extensive epicontinental seaways and carbonate platforms across the Tethyan Realm, providing favorable habitats for oyster communities to flourish. This study focuses on the Campanian Tethyan oysters from the North Eastern Desert of Egypt regarding taxonomy, palaeoecology, and palaeobiogeography. Three oyster species, Nicaisolopha nicaisei (Coquand, 1862), Pycnodonte (Phygraea) vesicularis (Lamarck, 1806), and Ambigostrea bretoni (Thomas and Peron, 1891), were identified from the Campanian succession in two studied sections. The sampled specimens of the genus Nicaisolopha have undergone a systematic palaeontological revision. As a result, N. tissoti (Thomas and Peron, 1891) is considered herein a junior synonym of N. nicaisei (Coquand, 1862). Palaeobiogeographically, the likely primary migration pattern of the studied oysters suggests an east–west trend along the Southern Tethys margin. All identified oysters in this study exhibit a Tethyan affinity and are primarily abundant in two main provinces: the Southern Tethys and the Western Tethys. The macrofaunal contents are categorized into two fossil associations: the Nicaisolopha nicaisei association of the middle-late Campanian age and the Pycnodonte vesicularis association of the late Campanian age. These macrofaunal associations indicate a deepening trend during the middle-late Campanian age, suggesting a transition from shallow inner neritic to middle neritic environments. Additionally, it is observed that Pycnodonteinae tend to grow larger under eutrophic conditions, low-energy environments, and nutrient-rich waters with high carbonate contents.

The Eurasian epicontinental sea was an important carbon sink during the Palaeocene-Eocene thermal maximum

The Palaeocene-Eocene Thermal Maximum (ca. 56 million years ago) offers a primary analogue for future global warming and carbon cycle recovery. Yet, where and how massive carbon emissions were mitigated during this climate warming event remains largely unknown. Here we show that organic carbon burial in the vast epicontinental seaways that extended over Eurasia provided a major carbon sink during the Palaeocene-Eocene Thermal Maximum. We coupled new and existing stratigraphic analyses to a detailed paleogeographic framework and using spatiotemporal interpolation calculated ca. 720–1300 Gt organic carbon excess burial, focused in the eastern parts of the Eurasian epicontinental seaways. A much larger amount (2160–3900 Gt C, and when accounting for the increase in inundated shelf area 7400–10300 Gt C) could have been sequestered in similar environments globally. With the disappearance of most epicontinental seas since the Oligocene-Miocene, an effective negative carbon cycle feedback also disappeared making the modern carbon cycle critically dependent on the slower silicate weathering feedback.

A tropically hot mid-Cretaceous North American Western Interior Seaway

AbstractThe mid-Cretaceous thermal maximum (KTM) during Cenomanian to Santonian times from ca. 100 to 83 Ma is considered among Earth's warmest sustained intervals of the Phanerozoic. The time interval is also characterized by major paleoceanographic changes in the form of an oceanic anoxic event and the flooding of epicontinental seaways, such as the Western Interior Seaway in North America. We report carbonate clumped isotope (Δ47) paleotemperatures (TΔ47) of the KTM measured from Cenomanian oyster fossils of the Western Interior Seaway. Following screening of specimens for carbonate diagenesis and exclusion of geographic zones with evidence consistent with solid-state Δ47 reordering, a mean TΔ47 of 28–34 °C (95% confidence interval for the standard error of mean) for primary oyster calcite quantifies extreme mid-latitude warmth in North America. When combined with existing Campanian and Maastrichtian marine TΔ47 records, the new data constrain Late Cretaceous temperature trends underlying the evolution of North American faunal and stratigraphic records. These TΔ47 data from the peak KTM highlight the potential of this proxy to quantitatively resolve the upper thermal limits of Phanerozoic greenhouse climates.

From marine bands to hybrid flows: Sedimentology of a Mississippian black shale

AbstractOrganic‐rich mudstones have long been of interest as conventional and unconventional source rocks and are an important organic carbon sink. Yet the processes that deposited organic‐rich muds in epicontinental seaways are poorly understood, partly because few modern analogues exist. This study investigates the processes that transported and deposited sediment and organic matter through part of the Bowland Shale Formation, from the Mississippian Rheic–Tethys seaway. Field to micron‐scale sedimentological analysis reveals a heterogeneous succession of carbonate‐rich, siliceous, and siliciclastic, argillaceous muds. Deposition of these facies at basinal and slope locations was moderated by progradation of the nearby Pendle delta system, fourth‐order eustatic sea‐level fluctuation and localized block and basin tectonism. Marine transgressions deposited bioclastic ‘marine band’ (hemi)pelagic packages. These include abundant euhaline macrofaunal tests, and phosphatic concretions of organic matter and radiolarian tests interpreted as faecal pellets sourced from a productive water column. Lens‐rich (lenticular) mudstones, hybrid, debrite and turbidite beds successively overlie marine band packages and suggest reducing basin accommodation promoted sediment deposition via laminar and hybrid flows sourced from the basin margins. Mud lenses in lenticular mudstones lack organic linings and bioclasts and are equant in early‐cemented lenses and in plan‐view, and are largest and most abundant in mudstones overlying marine band packages. Thus, lenses likely represent partially consolidated mud clasts that were scoured and transported in bedload from the shelf or proximal slope, as a ‘shelf to basin’ conveyor, during periods of reduced basin accommodation. Candidate in situ microbial mats in strongly lenticular mudstones, and as rip‐up fragments in the down‐dip hybrid beds, suggest that these were potentially key biostabilizers of mud. Deltaic mud export was fast, despite the intrabasinal complexity, likely an order of magnitude higher than similar successions deposited in North America. Epicontinental basins remotely linked to delta systems were therefore capable of rapidly accumulating both sediment and organic matter.

Local to global controls on the deposition of organic-rich muds across the Late Jurassic Laurasian Seaway

Muds deposited in large-scale epicontinental seaways provide deep insights into palaeoclimates, biogeochemical cycles, sedimentation processes and organic carbon burial during exceptionally warm periods throughout the Phanerozoic. Temporal changes can be monitored at single locations but the key, larger scale oceanographical and related biogeochemical processes are likely to be more clearly revealed by comparisons between individual sub-basins within seaways. Here, we compare inorganic geochemical records from the Jurassic (upper Pectinatites wheatleyensis to lower Pectinatites pectinatus ammonite zones) of the Swanworth Quarry 1 Core from the Wessex Basin (Dorset, UK) to time-equivalent records from the Ebberston 87 Core in the Cleveland Basin (Yorkshire, UK), 400 km apart. Our synthesis shows that while the Dorset sediments were deposited in an energetically more dynamic setting than the Yorkshire sediments, the overarching climatic and oceanographical processes responsible for variations in organic carbon enrichment and sedimentation were similar. Intervals of coeval organic carbon-rich sedimentation occurred in both basins, and a particulate shuttle was intermittently active in both basins. Consistent with recent climate simulations, we conclude that tropical climate conditions, associated with enhanced nutrient supply, were key drivers of sedimentation between the Jurassic Wessex and Cleveland Basins. Supplementary material: Geochemical data discussed in the manuscript is available at: https://doi.org/10.6084/m9.figshare.c.4531532

Paleogeography and paleoenvironments of the Late Devonian Kellwasser event: A review of its sedimentological and geochemical expression

The Late Devonian (383-359 Ma) was a time of prolonged climate instability with catastrophic perturbation of global marine ecosystems at the Frasnian-Famennian (F-F) and the Devonian-Carboniferous (D-C) boundaries. The causes and mechanisms of anoxia and extinction at the F-F interval are not clearly delineated, and alternative explanations for virtually every aspect of this interval are still intensely debated. In many (but not all) locations, the F-F interval is characterized by two dark, organic-rich lithologies: the Lower and Upper Kellwasser beds (as originally described in Germany) that represent a stepwise ocean anoxia and extinction sequence. The Upper and Lower Kellwasser anoxia event beds are often collectively termed the Kellwasser Event, and the termination of this sequence is within the Upper Kellwasser Event at the F-F boundary. Current knowledge is limited by significant sampling bias, as most previous studies sampled epicontinental seaways or passive continental shelves, primarily from localities across Europe and North America. Together these formed a single equatorial continent with a rising mountain chain during the Late Devonian. Our understanding of the Kellwasser Event is thus based on data and observations from a restricted set of paleoenvironments that may not represent the complete range of Late Devonian environments and oceanic conditions. In the last decade, new methodologies and research in additional paleoenvironments around the world confirm that the Kellwasser Event was global in scope, but also that its expression varies with both paleoenvironment and paleogeography. Studying the many differing geochemical and lithological expressions of the Kellwasser Event using a) a wide variety of paleoenvironments, b) a multiproxy approach, and c) placement of results into the broader context of Late Devonian marine biodiversity patterns is vital for understanding the true scope of ocean anoxia, and determining the causes of the marine biodiversity crisis at the F-F boundary.

Quantifying the missing sink for global organic carbon burial during a Cretaceous oceanic anoxic event

The Cretaceous experienced numerous global and local climatic perturbations to the ocean–atmosphere system, especially during periods of known widespread organic-carbon burial termed oceanic anoxic events (OAEs). The Cenomanian–Turonian boundary event (∼93.9 Ma), or OAE-2, is the best documented and widespread organic carbon (OC) burial event in Earth history—with more than 170 sections published. Despite the substantial number of locations, the majority is found within the proto-Atlantic Ocean, Tethys Ocean and epicontinental seaways. It has been hypothesized that the pervasive burial of OC during OAE-2 caused the observed positive carbon isotope excursion (2 to 7‰, average ∼3‰). The isotope excursion can help constrain the global burial of OC, even for unstudied portions of the global ocean. This approach can solve for ‘missing’ OC sinks by comparing model estimates with the known distribution of OAE-2 sediments and their OC contents. Specifically, mapping the known spatial extent of OC burial in terms of mass accumulation rates (MARs), and comparing those results with the prediction using a forward box model to derive the amount of OC burial to reproduce the globally observed positive carbon isotope excursion. The available OC data from outcrop and drill core, with reasonable extrapolation to analogous settings without data, quantifies ∼13% of the total seafloor, mostly from marginal marine and epicontinental/epeiric settings. However, this extrapolation for OC burial, plus using most appropriate MARs to unknown portions of the seafloor, fail to account for the amount of OC burial predicted for a 3‰ positive carbon isotope excursion. This discrepancy remains even when considering additional sinks of organic carbon burial such as coal, lacustrine environments, authigenic carbonate, and the loss of OC associated with hydrocarbon reservoirs. This outcome points to a large reservoir of OC that is not currently constrained, such as highly productive margins and/or equatorial regions, or a small but significant increase deep ocean OC burial. Another possibility is that the carbon fluxes are less than those used in the model which would require less OC burial to explain a ∼3‰ carbon isotope excursion.

First evidence of the Jurassic thalattosuchian (both teleosaurid and metriorhynchid) crocodylomorphs from Slovakia (Western Carpathians)

We report here finds of thalattosuchians from Western Carpathians. The material consists of two isolated teeth from two different localities of the Pieniny Klippen Belt. The material represents the first evidence of the occurrence of both clades Teleosauridae and Metriorhynchidae in Slovakia. The first, a small tooth comes from the locality Beňatina and is dated early Middle Jurassic (Aalenian). Identification of the specimen shows it belongs to a longirostrine teleosaurid, possibly to Steneosaurus. Teleosaurids were largely restricted to lagoonal/near-shore environments. Their limbs allow them to support and walk on land. Regarding that fact, the presence of this taxon in Beňatina might be an indication of terrestrial land in the nearby area and shows a location of epicontinental seaways. A second larger tooth was found in the Upper Jurassic (Tithonian) sediments of the locality Kyjov, and is tentatively allocated in the genus Plesiosuchus. The members of Plesiosuchina are known in England, France, Portugal and Sicily. Our findings indicate a much wider spatial distribution of this clade in Europe and it fits well with the previous interpretation of sediments of the locality Kyjov as deep-water pelagic deposits.

Stratigraphic evolution of the Neoproterozoic Callison Lake Formation: Linking the break-up of Rodinia to the Islay carbon isotope excursion

The ∼780 to 540 Ma Windermere Supergroup of western North America records the protracted development of the western Laurentian passive margin and provides insights into the nature, timing, and kinematics of Rodinia9s fragmentation. Here we present a refined tectono- and chemo-stratigraphic model for circa 780 to 720 Ma sedimentation in NW Canada through a study of the Callison Lake Formation (formalized herein) of the Mount Harper Group, spectacularly exposed in the Coal Creek and Hart River inliers of the Ogilvie Mountains of Yukon, Canada. Twenty-one stratigraphic sections are integrated with geological mapping, facies analysis, carbon and oxygen isotope chemostratigraphy, and Re-Os geochronology to provide a depositional reconstruction for the Callison Lake Formation. Mixed siliciclastic, carbonate, and evaporite sediments accumulated in marginal marine embayments formed in discrete hangingwall depocenters of a prominent Windermere extensional fault zone. Deposition of the Windermere Supergroup in NW Canada post dates the eruption of the circa 780 Ma Gunbarrel Large Igneous Province by ∼30 million years, is locally associated with compressional or transpressional tectonism, and predates the successful rift-drift transition by ∼200 million years. In order to accommodate evidence for coeval extensional and compressional tectonism, abrupt facies change, and Neoproterozoic fault geometries, we propose that NW Laurentia experienced strike-slip deformation during the ∼740 to 660 Ma early fragmentation of the supercontinent Rodinia. Sequence stratigraphic data from the Callison Lake Formation and other basal Windermere successions in the northern Canadian Cordillera delineate three distinct depositional sequences, or transgressive-regressive (T-R) cycles, that are coeval with similar stratigraphic packages in the ∼780 to 720 Ma Chuar-Uinta Mountain-Pahrump basins of the western United States. The global circa 735 Ma Islay carbon isotope excursion is consistently present in carbonate strata of the third T-R cycle and is interpreted to represent a primary perturbation to the global carbon cycle, possibly driven by the uplift and weathering of extensive shallow epicontinental seaways and evaporite basins.

A new model for the Kellwasser Anoxia Events (Late Devonian): Shallow water anoxia in an open oceanic setting in the Central Asian Orogenic Belt

The Frasnian–Famennian mass extinction event devastated tropical marine ecosystems and ranks in the top six in taxonomic and ecological severity. The close stratigraphic association between the extinction and the Kellwasser Anoxia Events support a link between oceanographic anoxia and extinction. The Upper and Lower Kellwasser horizons have been identified in epicontinental and basinal settings in Laurussia, Gondwana, Siberia, and South China. The Hongguleleng Formation (Late Devonian) in northwestern Xinjiang, China, contains both the Frasnian–Famennian boundary and the rebound from the Frasnian–Famennian extinction event in a highly fossiliferous shallow marine setting associated with a Devonian oceanic island arc complex (part of the Central Asian Orogenic Belt, or CAOB). Here we show that the Hongguleleng Formation also records the Upper Kellwasser Anoxia Event through analysis of multiple geochemical proxies. In contrast to previous studies asserting that the Kellwasser Events were restricted to epicontinental seaways and basins, our results indicate that it occurred not only along the shallow continental margins of the closing Rheic Ocean, but also in shallow water in the open oceanic part of Paleotethys. Previous explanations for the Kellwasser Events from epicontinental margins and basins call for the migration of deep anoxic bottom water into shallow water environments as a kill mechanism for shallow marine ecosystems or attribute it to sea level rise and subsequent stagnation. There is no evidence that the Devonian oceans completely overturned during the Kellwasser Events; similarly, many transgressive events in the Devonian are not associated with black shales. We therefore suggest an alternative mechanism for the Kellwasser Events based on new evidence from the CAOB, where anoxia is driven by episodic eutrophication of surface waters.

Black shale deposition during Toarcian super-greenhouse driven by sea level

Abstract. One of the most elusive aspects of the Toarcian oceanic anoxic event (T-OAE) is the paradox between carbon isotopes that indicate intense global primary productivity and organic carbon burial at a global scale, and the delayed expression of anoxia in Europe. During the earliest Toarcian, no black shales were deposited in the European epicontinental seaways, and most organic carbon enrichment of the sediments postdated the end of the overarching positive trend in the carbon isotopes that characterises the T-OAE. In the present study, we have attempted to establish a sequence stratigraphic framework for Early Toarcian deposits recovered from a core drilled in the Paris Basin using a combination of mineralogical (quartz and clay relative abundance) and geochemical (Si, Zr, Ti and Al) measurements. Combined with the evolution in redox sensitive elements (Fe, V and Mo), the data suggest that expression of anoxia was hampered in European epicontinental seas during most of the T-OAE (defined by the positive carbon isotope trend) due to insufficient water depth that prevented stratification of the water column. Only the first stratigraphic occurrence of black shales in Europe corresponds to the "global" event. This interval is characterised by >10% Total Organic Carbon (TOC) content that contains relatively low concentration of molybdenum compared to subsequent black shale horizons. Additionally, this first black shale occurrence is coeval with the record of the major negative Carbon Isotope Excursion (CIE), likely corresponding to a period of transient greenhouse intensification likely due to massive injection of carbon into the atmosphere–ocean system. As a response to enhanced weathering and riverine run-off, increased fresh water supply to the basin may have promoted the development of full anoxic conditions through haline stratification of the water column. In contrast, post T-OAE black shales during the serpentinum and bifrons Zones were restricted to epicontinental seas (higher Mo to TOC ratios) during a period of relative high sea level, and carbon isotopes returning to pre-T-OAE values. Comparing palaeoredox proxies with the inferred sequence stratigraphy for Sancerre suggests that episodes of short-term organic carbon enrichment were primarily driven by third-order sea level changes. These black shales exhibit remarkably well-expressed higher-frequency cyclicities in the oxygen availability in the water column whose nature has still to be determined through cyclostratigraphic analysis.

Radiogenic isotope composition of Carboniferous seawater from North American epicontinental seas

Abundant marine sedimentary deposits accumulated in the epeiric seas of North America during the Carboniferous Period (359–299Ma) when the Earth's climate shifted from a global “greenhouse” to “icehouse”. Geochemical records extracted from these deposits are often assumed to reflect global ocean processes and are increasingly being used to infer relationships between tectonism, carbon cycling and climate change. We analyzed radiogenic isotopes (Sr, Nd) in biogenic apatite along a North American transect to constrain the degree of coupling between the epicontinental seas and the open ocean. In many samples the primary Sr signal is altered, however the original Nd isotopic composition of the biogenic apatite seems to be preserved. The εNd(t) values range from −8.6 to −4.5 in the US midcontinent basins and from −11.4 to −5.7 at Arrow Canyon (Nevada, USA), indicating the development of an east–west geochemical gradient throughout the Pennsylvanian. This apparent decoupling of the epicontinental seas from the open ocean was established by the latest Mississippian. Thus, circulation of waters between epicontinental seaways of western US and the basins to the east and south was periodically restricted. Shifts toward unradiogenic Nd at Arrow Canyon seem to correspond with glacio-eustatic changes across the mid-Carboniferous boundary. These εNd(t) variations may have been caused by changes in weathering rates/sources, marine circulation or a combination of both.

Spatial variability of watermass conditions within the European Epicontinental Seaway during the Early Jurassic (Pliensbachian–Toarcian)

AbstractIn order to constrain spatial variability in watermass conditions within the European Epicontinental Seaway prior to, during and after the Toarcian Oceanic Anoxic Event, carbon (δ13Cbel, δ13Ccarb) and oxygen (δ18Obel, δ18Ocarb) isotope records were obtained from three sections in the Grands Causses Basin (southern France). These data were then compared with similar records along a north–south transect across the European Epicontinental Seaway. As the conclusions reached here strongly depend on the reliability of belemnite calcites as archives of palaeoceanographic changes, an attempt was made to improve the understanding of isotope signals recorded in belemnite calcite. Intra‐rostral carbon and oxygen‐isotope data from six belemnite specimens belonging to the genusPassaloteuthiswere collected. Intra‐rostral carbon‐isotopes are influenced by vital effects, whereas oxygen‐isotopes reflect relative changes in temperature and salinity. Palaeotemperatures calculated from δ18Obel‐isotope records from the Grands Causses Basin confirm relatively low temperatures throughout the Late Pliensbachian. Similar cool water conditions have previously been shown in Germany, England, Spain and Portugal. A temperature increase of up to 6 °C is observed across the Pliensbachian–Toarcian boundary. A pronounced negative shift of at least −3‰ (Vienna‐Pee Dee Belemnite) is recorded in bulk carbonate carbon during the lowerHarpoceras serpentinumzone, typical of the Toarcian Oceanic Anoxic Event. Before and after the Toarcian Oceanic Anoxic Event, a good correlation between δ13Ccarband δ13Cbelexists, indicating well‐ventilated bottom‐waters and normal marine conditions. Instead, data for the Toarcian Oceanic Anoxic Event indicate the development of a strong north–south gradient in salinity stratification and surface‐water productivity for the Western Tethyan realm. This study thus lends further support to a pronounced regional overprint on carbon and oxygen‐isotope records in epicontinental seaways.

What is an ‘elasmobranch’? The impact of palaeontology in understanding elasmobranch phylogeny and evolution

The Subclass Elasmobranchii is widely considered nowadays to be the sister group of the Subclass Holocephali, although chimaeroid fishes were originally classified as elasmobranchs along with modern sharks and rays. While this modern systematic treatment provides an accurate reflection of the phylogenetic relationships among extant taxa, the classification of many extinct non-holocephalan shark-like chondrichthyans as elasmobranchs is challenged. A revised, apomorphy-based definition of elasmobranchs is presented in which they are considered the equivalent of neoselachians, i.e. a monophyletic group of modern sharks and rays which not only excludes all stem and crown holocephalans, but also many Palaeozoic shark-like chondrichthyans and even close extinct relatives of neoselachians such as hybodonts. The fossil record of elasmobranchs (i.e. neoselachians) is reviewed, focusing not only on their earliest records but also on their subsequent distribution patterns through time. The value and limitations of the fossil record in answering questions about elasmobranch phylogeny are discussed. Extinction is seen as a major factor in shaping early elasmobranch history, especially during the Triassic. Extinctions may also have helped shape modern lamniform diversity, despite uncertainties surrounding the phylogenetic affinities of supposedly extinct clades such as cretoxyrhinids, anacoracids and odontids. Apart from these examples, and the supposed Cretaceous extinction of 'sclerorhynchids', elasmobranch evolution since the Jurassic has mostly involved increased diversification (especially during the Cretaceous). The biogeographical distribution of early elasmobranchs may be obscured by sampling bias, but the earliest records of numerous groups are located within the Tethyan realm. The break-up of Gondwana, and particularly the opening of the South Atlantic Ocean (together with the development of epicontinental seaways across Brazil and Africa during the Cretaceous), provided repeated opportunities for dispersal from both eastern (European) and western (Caribbean) Tethys into newly formed ocean basins.

The Jurassic–Cretaceous transition of the Fårarp-1 core, southern Sweden: Sedimentological and phytological indications of climate change

The 116 m deep Fårarp-1 core drilled in the Vomb Trough in southernmost Sweden is dated by integrated terrestrial and marine palynostratigraphy. The lower part of the succession (ca 84 m) encompasses uppermost Jurassic to lowermost Cretaceous (uppermost Tithonian to Valanginian) strata. An unconformity separates the Valanginian strata from an overlying ca 1 m thick interval of upper Albian to Cenomanian Arnager Greensand Formation. The uppermost part of the core is a repetitive succession of lowermost Cretaceous sediments. During the Jurassic–Cretaceous (J/K) transition NW Europe was located in mid latitudes, and comprised an archipelago of large and small islands separated by deeper grabens and epicontinental seaways that connected the Boreal Sea to the north with the warmer Tethys Ocean to the south. Boundary strata in England, France, the Netherlands and Germany are characterised by relatively prominent climatic change from arid/semi arid to subhumid/humid conditions. Southernmost Sweden was located on the margin of a large landmass comprising most of the Fennoscandian Shield bordering a large epicontinental sea to the west. By combining sedimentology, clay mineralogy and palynofacies the Tithonian to Valanginian cored succession of the Fårarp-1 core provides complementary information on how marginal deposits from the eastern part of the epicontinental sea reflect the climatological and environmental changes observed in other parts of NW Europe. The Fårarp-1 core shows that during the Tithonian to earliest Berriasian deposition took place in a terrestrial but near-marine depositional setting, in coastal lakes or lagoons with little marine influence. A dry climatic regime favoured stagnant water conditions with common algal blooms of primarily Botryococcus and zygnemataceae. Palynofacies and sedimentology indicate limited transport of freshwater and material to the basin. The stagnant depositional environment was terminated by a marine flooding in the early Berriasian. During the remaining Berriasian and the early Valanginian conditions shifted between near marine and marine settings in a dynamic coastal environment, similar to contemporaneous assemblages reported from the Danish Island of Bornholm. A shift in clay mineralogy, from a dominance of 10 Å minerals to increasing amounts of mixed layer and kaolinite indicates a change to more humid conditions in the latest Tithonian. Cheirolepidacean pollen ( Classopollis) are present but never common in the cored succession, and a similar conspicuous decrease of these pollen, as previously reported from England, Germany and France, is not evident in the Fårarp-1 core. Instead a subsequent shift in both palynofacies and palynoflora, marked by an increase in abundance of heavy terrigenous material, i.e. wood and coal particles, upland pollen grains and reworked palynomorphs is also observed in the uppermost Tithonian–lowermost Berriasian interval. At the same level spores and pollen classified as warmer/drier elements decrease in abundance. This is interpreted as representing a shift to more humid climatic conditions with increased runoff from the hinterland. Thus, the combined sedimentological and palynological data from the Fårarp-1 core suggest that climatic conditions in the area changed from more seasonally dry (semi-arid) to more humid (semi-humid) across the J/K boundary (latest Tithonian to earliest Berriasian) and hence earlier than the mid-Berriasian climatic shift recorded from e.g. England and the Netherlands.

As sucessões carbonáticas neoproterozóicas do Cráton do São Francisco e os depósitos de fosfato: correlações e fosfogênese

The neoproterozoic carbonate successions of the Sao Francisco craton are formed by thick carbonate and siliciclastic strata accumulated in epicontinental seaways, andon passive margins. At least two transgressive-regressive sea level cycles have been recognized during the evolution of the carbonate mega-sequences. These successions, represented by the Vazante, Bambui, and Una Groups, lie above basal glacio-marine diamictites of probable Sturtian age, and an upper glacio-marine diamictite, was observed in upper units of the Vazante Group. The broad similarities of lithofacies, as well as the presence of phosphate and sulfide (Zn,Pb) deposits restricted to narrow stratigraphic intervals, suggest that the Vazante, Bambui and Una Groups may be correlative. The Sr isotope data from well preserved carbonates and carbonate fluorapatite from each of these successions , ranging from 0.70763 to 0.70794, support the general correlation and are indicative of seawater composition around 650 Ma, although the lower 87 Sr/ 86 Sr values of 0.70614 at the Vazante carbonates may suggest that this unit is older than the Bambui and Una carbonate rocks. Carbon isotope data of carbonate fluorapatite reveal sharp negative excursions between -3.47 and -12.25‰ VPDB in the cratonic area , and between -1.3 and -9.61‰ VPDB in the carbonate fluorapatite hosted by the passive margin Vazante carbonates, suggesting that primary P concentration was accumulated in strong anoxic environments in both geotectonic settings. Carbonate hosting the phosphate deposits in these units are moderately enriched in 13 C , ranging from positive a 13 C values of +2.0 and +9.6‰ VPDB in the different sections. Primary phosphate accumulations occur above glaciogenic successions. We suggest that these concentrations may be due to high organic productivity after glacial events.

Chemostratigraphic correlation of Neoproterozoic successions in South America

The Neoproterozoic successions of South America largely accumulated during extensional events associated with the breakup of Rodinia. These units are preserved as thick carbonate and siliciclastic strata in epicontinental seaways and shallow marine environments on passive cratonal margins, which have been intensely deformed in mobile belts surrounding the craton. Volcaniclastic and siliciclastic materials are associated with some of the marginal fold belts. Three mega-sequences are represented in the cratonal area: glaciogenic, carbonate and molasse . At least two transgressive-regressive sea level cycles occurred during the evolution of the carbonate mega-sequence, which lies above iron-cemented glacio-marine diamictite of probable Sturtian age. We report high resolution carbon, oxygen, strontium and sulfur isotope trends from analyses of well-preserved sample sets and use principally strontium and carbon isotopes from the best preserved samples in concert with lithostratigraphic and biostratigraphic observations to provide detailed correlations of the South American Neoproterozoic successions. Lead–zinc deposits, some of which with important metal reserves seem to be restricted to the Sturtian carbonate succession and associated with a sequence boundary at the end of the first transgressive–regressive cycle. Phosphate deposits are found in both Sturtian and Varangerian/Marinoan carbonate successions, above glaciogenic sequences.

Ophiolites and global geochemical cycles: implications for the isotopic evolution of seawater

Abstract Isotopic profiles through ophiolite complexes provide the necessary link between the study of global geochemical cycles and plate tectonics. The hydrothermal circulation that occurs beneath the sea floor is the primary mechanism for exchange between the mantle of the Earth and the hydrosphere. The subduction of the hydrothermally altered crust and overlying sediments is the primary mechanism for crustal recycling. Oxygen and strontium isotopes of seawater track the competition between continental weathering and mid-ocean ridge hydrothermal exchange to control the composition of the oceans. Information derived from ophiolite studies on the elemental fluxes and the depth of seawater penetration into the oceanic crust provides constraints on the important rate constants associated with these competing processes. The same tectonic rates that account for the Sr isotope evolution of seawater indicate that the oxygen isotopic composition of the ocean is constrained to vary within narrow limits (per mil level). Isotopic analysis of dredge samples and ophiolite complexes demonstrates that seawater-ocean crust interactions result in a oxygen isotopic zonation of the oceanic crust with masses (concentration times volume) centred on the initial isotopic composition of the crust. This requires that the oxygen isotopic composition of the ocean resides at near steady-state conditions over Earth history. The inferences from ophiolite complexes contrast strongly with the results of measurements on carbonates from epicontinental seaways, particularly for the Palaeozoic. Ophiolites and greenstone belts track exchange processes between the ocean and the igneous crust whereas most carbonate measurements track the surface ocean on continental shelves. For oxygen isotopes, the mass of epicontinental seaways and the rates of meteoric water input suggest a resolution to the controversy that accounts for both data sets.

Biogeography of Grimmia teretinervis (Bryopsida, Grimmiaceae) in North America

Grimmia teretinervis is thought to occur sporadically across the North American continent. New site records from Alberta, the Yukon Territory, and Alaska are linked to the margin of the Cretaceous epicontinental seaway. Geological maps from other areas of the continent reveal that G. teretinervis is associated with deposits from other ancient epicontinental seaways. All areas have experienced either faulting or fluvial erosion that have exposed massive sections of calcareous sediments that are suitable microhabitats for G. teretinervis.

Multivariate hierarchical analyses of Miocene mollusk assemblages of Europe: Paleogeographic, paleoecological, and biostratigraphic implications

Mollusk-dominated fossil assemblages from the marine Miocene bioprovinces of Europe (the Boreal province and the Paratethys) were analyzed by using bulk samples collected hierarchically across several spatiotemporal scales. The study explores quantitative patterns recorded by benthic mollusk assemblages (including implications for paleogeographic, biostratigraphic, and paleoenvironmental patterns), and the relationship between spatiotemporal scale of analysis and levels of variability in paleontological data. A total of 8455 specimens from 23 samples were collected from siliciclastic sediments (clay and sand) at 12 localities from France, Belgium, the Netherlands, Germany, Poland, Austria, and Hungary. With the exception of one sample of Serravallian age from the southeastern North Atlantic, all samples came from Burdigalian and Langhian deposits of the Paratethys and the Boreal province. All specimens were identified to species level (297 species total), classified in terms of ecology, and analyzed by using multivariate and computer-intensive methods. The analyses focused on (1) bivalve/gastropod ratios, (2) diversity levels, (3) multivariate taxonomic and ecological patterns, and (4) multivariate Euclidean distances between samples compared at five different scales (within sites, within localities, within facies, among facies, among provinces). The bivalve/gastropod ratio is a highly volatile parameter; thus, its informative value is highly limited. The estimates of alpha diversity (sample species richness) standardized by rarefaction indicate that fossil assemblages of the Boreal province display higher diversity levels than those of the Paratethys. This result is consistent with the general tendency of isolated epicontinental basins to display impoverished fauna and may be due to geographic barriers limiting larval dispersal and to environmental instabilities inherent to marginal environments of epicontinental seaways. Rarefactions of pooled data indicate that, for both provinces, the taxonomic turnover among sites (beta diversity) accounts for 30%–40% of species diversity. Multivariate analyses indicate that biogeographic variation between the provinces is the most important factor controlling differences among samples, whereas facies type and stratigraphic position of samples play a secondary role. The strong biogeographic signature is consistent with recent paleogeographic reconstructions that suggest a lack of a direct marine connection between the two provinces at that time. The relatively poorer discrimination of mollusk assemblages across facies and biostratigraphic stages reflects the overriding role of the middle Miocene biogeography in controlling the composition of mollusk assemblages. The hierarchical multivariate analysis shows that with the increase in the scale of observation (within sites, within localities, within facies, among facies, among provinces), the average multivariate distance between samples increases continuously—new heterogeneities that add notable amounts of new variation exist at each scale of observation. The highest increase is observed for the “among provinces” comparison level, again indicating the major role of geographic sources of variation in the data. The hierarchical approach provides a rigorous way to quantify the effects of scale-dependent sources of variability on paleontological patterns.