Albian Oceanic Anoxic Event Research Articles

The Early to Late Cretaceous (Albian–Cenomanian) transition in Putumayo, Colombia: a biostratigraphic and carbon isotope stratigraphic correlation for northwestern South America

Despite the rich geological and paleontological record of Colombia, the Putumayo region near Ecuador remains one of the least explored regions in the equatorial Neotropics, mainly due to its thick vegetation, deep rock weathering, soil formation, and ground cover, geographic remoteness, and inaccessibility of well-exposed outcrops. This has resulted in limited comparisons with neighboring basins and thus the generation of more comprehensive biostratigraphic correlations with western and northern South America, as well as other paleobiogeographic regions (e.g., Tethys, Western Interior Seaway). Here, we present 67 occurrences of uppermost Lower Cretaceous to lowermost Upper Cretaceous ammonoids and other macrofossils (e.g., bivalves, decapod crustaceans, osteichthyan fish remains, plant remains), as well as a δ13Corg chemostratigraphic curve derived from 105 samples from the middle Albian of the uppermost Caballos Formation and the upper Albian to lower Cenomanian lower Villeta Formation, collected in situ from a stratigraphic section exposed along the Mocoa–San Francisco Road, Putumayo, Colombia, here called the San Francisco section. The chemostratigraphic, carbon-isotope curve for the region shows a great similarity with the shape of the accepted curve for the late Albian Oceanic Anoxic Event 1d, which is characterized by a worldwide long positive δ13C excursion anomaly. The new biostratigraphic and isotopic data serve as a point of reference to compare the Putumayo Basin with neighboring basins (e.g., Marañon Basin in Perú, Oriente Basin in Ecuador, Upper Magdalena Valley Basin in Colombia), and thus the generation of more comprehensive upper Lower Cretaceous and lower Upper Cretaceous biostratigraphic and chemostratigraphic correlations for northwestern South America.

Carbon cycle during the late Aptian–early Albian OAE 1b: A focus on the Kilian–Paquier levels interval

The Oceanic Anoxic Event (OAE) 1b took place over a protracted time interval during the Aptian/Albian boundary interval, at the dawn of the mid-Cretaceous climatic optimum. OAE 1b is characterized by the occurrence of several sub-events recorded by organic matter-rich levels, which can be traced on regional-to-global scale. Previous studies have highlighted that the climax of the event occurred around the Kilian – Paquier interval, with this latter sub-event being the most extended and pronounced stratigraphic interval. Numerous studies on OAE 1b have however only focused on high-precision investigations of the Kilian and/or Paquier levels, leaving vast uncertainties about the environmental changes and their drivers during the entire OAE 1b, and hence also on the mechanisms leading to the formation of the sub-events themselves. In this study, we have performed a high-resolution multi-proxy analysis of the Briers section, a well-exposed section in the Blue Marls Formation of the SE France Vocontian Basin, continuously covering the Kilian – Paquier interval. Pyrolysis analyses show that most of the organic matter in this section is immature and of continental origin, averaging 1.5% TOC. The Kilian and Paquier levels are characterized by higher TOC values and a substantial increase in the amount of marine organic matter. Comparing TOC values with changes in Al or Ti concentration (proxies for continental weathering) and Hydrogen index (HI values, tracer for the type of organic matter) reveals that the background long-term change in TOC is linked to change in the continental organic matter delivery to the Vocontian Basin tied to changes in continental weathering rates. Sporadic increases in TOC values associated with the Kilian, HN 8, and Paquier levels, are most likely the result of short-lived events of increased marine primary productivity and organic matter preservation superimposed on the background influx of continental organic matter. A high-resolution bulk organic matter carbon isotope record shows that, apart from the Paquier level, all the fluctuations observed in the carbonate carbon isotope ratios are also mirrored in the organic matter record, although with higher amplitudes. This discrepancy in amplitude can be resolved by correcting the bulk organic matter carbon isotope record for fluctuations in the type of organic matter, demonstrating that both oceanic and atmospheric reservoirs were affected by similar carbon isotope fluctuations, which were hence of global extent. The abnormal bulk organic matter carbon isotope record of the Paquier level further confirms the large geographical expansion of unusual organic matter production and/or accumulation during this peculiar event. Overall, this study suggests that Milankovitch-paced (long eccentricity) changes in monsoonal activity and their effect on the accumulation of organic matter in continental wetlands best explains the rhythmic change in the global carbon isotope record across the OAE 1b interval.

Widespread wildfires linked to early Albian Ocean Anoxic Event 1b: Evidence from the Fuxin lacustrine basin, NE China

Wildfires are an important source of disturbances in the Earth's system and are of great significance for understanding the interactions between environmental, atmospheric and vegetation changes over deep time. The early Cretaceous was a “high-fire” interval with frequent and widespread wildfires globally, but the timing and global significance of these wildfire events during this time remain uncertain. We undertook a multi-proxy study evaluating kerogen macerals, inertinite reflectance, and polycyclic aromatic hydrocarbons (PAHs) from mudstones to characterize wildfire activity in the Albian coal-forming Fuxin lacustrine Basin, and correlate these with (i) environmental and floral changes on land, and (ii) well-dated marine events including the early Albian Oceanic Anoxic Event 1b (OAE 1b), to consider their environmental and climatic significance. The presence of high inertinite contents demonstrate that multiple, widespread wildfire events occurred during the early Albian, which are correlated stratigraphically to the Kilian, Paquier and Leenhardt sub-events of the early Albian OAE 1b. Inertinite reflectance values ranging from 0.6% to 3.8%Ro show that wildfires in the early Albian were dominated by ground fires, with a smaller proportion of surface fires and almost no crown fires. Atmospheric oxygen concentration (pO2) levels, estimated from inertinite contents, attained ~25% during the early Albian, which exceeded the present atmospheric oxygen level of 21% and was able to support sustained combustion. Climatic conditions and frequent wildfire activity in the early Albian might have acted as an important control on vegetation distribution and diversification, which possibly further promoted the evolution of early angiosperms during the early Cretaceous. Wildfire activity resulted in the burning and destruction of both vegetation and soil structure, enhancing the post-fire erosion associated with intensified continental weathering under warmer and more humid conditions during the early Albian OAE 1b interval. These episodes of high wildfire activity correlate with high nutrients and organic matter levels in lakes and thereby contributed to eutrophication and anoxia in lacustrine and in contemporaneous oceanic systems.

Accumulation of organic-rich sediments associated with Aptian–Albian oceanic anoxic events in central-eastern Mexico

Oceanographic and climate conditions during the early Aptian OAE 1a and the late Aptian–early Albian OAE 1b are reported from an organic-rich succession deposited in the central portion of the Mexican Interior Basin, based on the analysis and integration of geochemical data (δ13Ccarb, total organic and inorganic carbon contents, Rock-Eval parameters and major and trace elements concentrations). The carbon isotope record of the studied section displays trends that correlate with segments C2 to C13. The OAE 1a interval is clearly isotopically defined (segments C3–C6) and includes sediments moderately enriched in organic matter. Although the OAE 1b sub-events are not expressed in the isotope record, the Jacob, Kilian and Paquier events may correspond to distinctive organic-rich levels occurring through C10–C12 segments. Evidence indicates that sediments enriched in organic matter through the section were accumulated under oxygen-depleted and high nutrient conditions. Anoxic-eutrophic conditions induced by a high input of continental-derived nutrients (including biolimiting Fe and P) associated to intense chemical weathering under warm and humid conditions took place during the deposition of the Selli and Paquier levels. Enhanced P recycling and regional upwelling reinforced eutrophic conditions during OAE 1a.

Intensive peatland wildfires during the Aptian–Albian oceanic anoxic event 1b: Evidence from borehole SK-2 in the Songliao Basin, NE China

The Cretaceous has been considered a “high-fire” world accompanied by widespread by-products of combustion in the rock record. The mid-Cretaceous oceanic anoxic event 1b (OAE1b) is marked by one of the major perturbations in the global carbon cycle characterized by deposition of organic-rich sediments in both marine and terrestrial settings. However, our understanding is still limited on changes in wildfire activity during OAE1b period. Here, we carried out a comprehensive analysis, including organic carbon isotope (δ13Corg), total organic carbon (TOC), coal petrology, trace elements, and pyrolytic polycyclic aromatic hydrocarbons (pyroPAHs), of coal seams of the middle Aptian to early Albian Shahezi Formation from borehole SK-2 in Songliao Basin, Northeast China. Two negative δ13Corg excursions in the Shahezi Formation can be corresponded with the 113/Jacob and Kilian sub-events of OAE1b. Moreover, the intensive peatland wildfires have been identified during the sub-event periods of OAE1b based on the co-occurrence of high abundance of charcoal and pyroPAHs at that time. In addition, Sr/Ba, Sr/Cu and Sr/Rb ratios demonstrate that enhanced peatland wildfires were controlled by dryer climate conditions owing to episodic northward migration of arid zones in East Asia related with rising global temperature during the sub-events of OAE1b. The climate-driven extensive wildfire activity in the mid-latitude terrestrial ecosystems can be a contributing factor for OAE1b through the increased flux of nutrients fuelling primary producers in the lake and marine environments and leading to more speculative anoxia to allow the deposition of organic-rich sediments. Our results provide essential understanding of the importance of wildfires in driving mechanism of oceanic anoxic events (OAEs) in Earth's history.

Accumulation of Organic-Rich Sediments Associated with Aptian–Albian Oceanic Anoxic Events in Central-Eastern Mexico

Accumulation of Organic-Rich Sediments Associated with Aptian–Albian Oceanic Anoxic Events in Central-Eastern Mexico

Terrestrial records of the early Albian Ocean Anoxic Event: Evidence from the Fuxin lacustrine basin, NE China

The early Albian Oceanic Anoxic Event 1b (OAE 1b) is well documented in the Tethys, Pacific and North Atlantic, but few studies have evaluated whether or not terrestrial records of OAE 1b exist. In order to identify terrestrial records of the early Albian OAE 1b and to infer possible driving mechanisms, an integrated multi-proxy study from the late Aptian to Albian in the Fuxin lacustrine basin was conducted, including thick, organic-rich black mudstones, total organic carbon (TOC), organic carbon isotopes (δ13Corg), mercury concentration (Hg) and results from pyrolysis analyses (S2, Tmax and HI). Results show three distinct short-term negative δ13Corg excursions corresponding with relatively high TOC values, which could be counterparts of the Kilian, Paquier and Leenhardt sub-events of the early Albian OAE 1b. Atmospheric CO2 concentration (pCO2) recovered from C3 plant δ13Corg compositions indicates an increasing trend in Unit C during the early Albian, and there are three short-term increases of pCO2 corresponding to the three sub-events of OAE 1b at this time interval. We infer that a trend of increasing pCO2 during the Kilian sub-event in the study area is closely related to volcanism. Continental weathering calculated using chemical weathering indices (CIA, WIP and MIA(O)) show an increasing trend during the OAE 1b interval, likely resulting from warmer and more humid conditions. Mixed sources of terrestrial plants and lacustrine plankton demonstrated by pyrolysis analyses (HI vs. Tmax and S2 vs. TOC), indicate a terrestrial contribution to the organic-rich sediments of the Kilian, Paquier and Leenhardt sub-events of OAE 1b. We suggest that a CO2-forced greenhouse effect during the early Albian might have triggered the relatively warm and humid palaeoclimatic conditions, and intensified chemical weathering that combined to create high nutrient and organic matter levels that were flushed into lakes contributing to eutrophication and anoxia in lacustrine and in contemporaneous oceanic systems.

Biscutum constans coccolith size patterns across the mid Cretaceous in the western Tethys: Paleoecological implications

The morphometric record of the calcareous nannofossil species Biscutum constans from the western Tethys indicates that this species underwent marked size changes across the latest Barremian-Cenomanian interval (~ 28 Myrs). Significant size reduction occurred during the core of the early Aptian Oceanic Anoxic Event (OAE) 1a (~ 120 Ma) and soon after OAE 1a followed by a 9 Myr-long interval characterized by small specimens. Larger coccoliths marked the middle to late Albian and, particularly, the lower part of the nannofossil subzone NC10a was characterized by abundant large specimens. A minor size decrease coincided with the late Albian OAE 1d onset (~ 100 Ma), but very small size was reached again during the latest Cenomanian OAE 2 (~ 94.4 Ma). The sequence of relatively long (millions of years) intervals marked by different average sizes is interpreted to reflect adaptation to changing paleoecological conditions. Temperature and fertility were not directly influencing the size of B. constans. On shorter time scale, abrupt changes in ocean chemistry related to Large Igneous Provinces submarine volcanism played a central role in secretion of small B. constans coccoliths to face ocean acidification during OAE 1a and OAE 2. Contrarily, during the late early Aptian-early Albian time interval, smaller B. constans size was related to cooler temperature which possibly also promoted CO2 sequestration in cooler surface waters forcing B. constans to produce small coccoliths to survive lowered pH. In addition, pulses of subaerial volcanism of the Southern Kerguelen Plateau may have further affected the ocean chemistry. The termination of intense volcanism and warmer temperature in the middle Albian-early Cenomanian coincided with restoration of bigger B. constans specimens.

Albian (Lower Cretaceous) carbon isotope chemozones, Texas Comanche Shelf and Mexican Chihuahua Trough: Implications for OAEs

Organic-carbon-rich black shale beds that are associated with positive carbon isotope excursions and yield pelagic fossils are evidence of short-term changes in ocean water mass and are important chronostratigraphic correlation tools. Five recognized Cretaceous Oceanic Anoxic Events (OAEs) are well documented in many basins on the Texas Comanche Shelf and the northern Mexico Chihuahua Trough: lower Aptian OAE 1a, Aptian-Albian OAE 1b, upper Albian OAE 1c, uppermost Albian OAE 1d, and Cenomanian-Turonian OAE 2. Two of these chemozones have previously been documented in Mexico and Texas, OAE 1b by a positive δ13C excursion of 2‰ and OAE 1d with a positive δ13C excursion of 1.6–1.9‰. Here we document for the first time OAE 1c in gray marine shale of the Boracho Formation in West Texas by a positive δ13C excursion of 1‰; the Boracho records the late Albian flooding of the Western Interior. On the interior shelf in shallow water carbonates the absence of carbon isotopic excursions suggests that dysaerobic waters did not affect the upper part of the water column. Review of biotic assemblages of each Gulf of Mexico Albian OAE suggests that water depths ranged from at least 300 m to just below storm wave base at about 15–30 m. These Albian OAEs were identified in the Mediterranean area and in the deep Atlantic Ocean and are recognized on the North American cratonic blocks, which supports the hypothesis that ocean/climate conditions favoring low-oxygen water masses were widespread although deposition was in local basins.

Geochemical and mineralogical records of late Albian oceanic anoxic event 1d (OAE-1d) in the La Grita Member (southwestern Venezuela): Implications for weathering and provenance

In this paper, stratigraphic distributions of major, trace and rare earth element (REE) concentrations as well as the bulk and clay mineralogy of organic-rich calcareous rocks of the La Grita Member (Capacho Formation) in southwestern Venezuela were studied to constrain sedimentary depositional conditions during the late Albian-early Cenomanian oceanic anoxic event 1-d (OAE-1d; 103 to 99.5 Ma). The statistically significant correlations observed between total REEs and Al, total organic carbon (TOC) and phyllosilicates suggest that REEs mainly occur in clay minerals and organic matter. Ce anomalies are mainly controlled by detrital input and cannot be used as redox proxies in this stratigraphic sequence. Detrital proxies, notably phyllosilicate/(K-feldspar + plagioclase), K-feldspar/(K-feldspar + plagioclase), and kaolinite/illite, suggest that greenhouse warming established during the OAE-1d intensified the hydrologic cycle and consequently increased continental chemical weathering rates. The Zr/Sc ratio and Al2O3–TiO2–Zr ternary diagram suggest detrital input dominated by recycling of older sedimentary rocks, while the La–Th-Sc ternary relationship indicates that most sediment samples were deposited between a passive margin and a continental island arc setting. Sedimentary discrimination diagrams (including La–Th-Sc and Co/Th vs. La/Sc), combined with chondrite-normalized REE patterns, suggest that siliciclastic sediments of the La Grita Member were mainly supplied by metasedimentary and intracratonic rocks of the Guayana Craton, notably the Roraima Formation, suggesting that this area was the main source for siliciclastic sediments during the Cretaceous. The Santander Massif and Merida and El Baúl Arches likely acted as secondary provenance areas, confirming previous work using U–Pb detrital zircon geochronology.

Paleoenvironmental changes during the late Albian oceanic anoxic event 1d: An example from the Capacho Formation, southwestern Venezuela

The late Albian–early Cenomanian oceanic anoxic event 1d (OAE-1d; ~103 to 99.5 Ma) represents a global interval of enhanced organic carbon burial due to widespread oxygen deficiency in the water column and/or increased primary productivity. The biostratigraphy and geochemistry of organic-rich sediments in the La Grita Member (Capacho Formation) in southwestern Venezuela were studied to document the paleoenvironmental conditions that governed the deposition of this succession during OAE-1d. Carbon-isotope (δ13Ccarb and δ13CCorg) chemostratigraphy and biostratigraphic constraints show that the La Grita Member spans the late Aptian period (Rotalipora appenninica Zone), and that OAE-1d is well recorded in this succession. A prominent increase in total organic carbon (TOC) values (up to 10%) is clearly recorded through the onset of OAE-1d, coinciding with a prominent change in overall redox-sensitive proxies suggesting that the La Grita Member sediments accumulated under anoxic (and possibly euxinic) bottom-water conditions in a partially restricted basin. The detrital proxies suggest that the greenhouse climate prevailing during OAE-1d induced significant acceleration of the hydrologic cycle and an increase in continental chemical weathering rates. Overall, the carbon and oxygen isotope records, TOC contents, as well as the detrital proxies show cyclic variation during the late Albian stage. These variations support the hypothesis that orbital forcing likely also modulated the equatorial monsoonal activity during the OAE-1d.

The Albian oceanic anoxic events record in central and northern Tunisia: Geochemical data and paleotectonic controls

The Albian organic-rich successions of the lower part of the Fahdene Formation (Albian to Cenomanian, Tunisia) were studied using sedimentology (analysis of carbonate contents and observation of thin sections), bulk organic geochemistry (Rock-Eval pyrolysis), and molecular biomarker distributions. The selected outcrops cover different structural domains from western central Tunisia (Jebel Hamra) to the Diapir zone or the Tunisian Trough (Koudiat Berkouchia, Jebel Ghazouan and Ain Asker from the southwest to the northeast, respectively). Total Organic Carbon values between 0.17 and 3.43% evidenced the record of the Albian oceanic anoxic events OAE1b and OAE1c in this southern Tethys margin. Rock-Eval data and molecular biomarkers (n-alkanes, steranes and terpanes) revealed thermally mature organic matter (OM) consisting of a mixed Type II/III OM (marine planktonic and continental origins). The abundant tricyclic terpanes, C30 17α(H) Diahopanes, and the regular decrease of homohopanes (C31 to C35) in the terpane series, were also indicative of a high contribution of bacterial OM that had been developed under stagnant dysoxic/anoxic environments.

High-resolution carbonate isotopic study of the Mural Formation (Cerro Pimas section), Sonora, México: Implications for early Albian oceanic anoxic events

The 420-m thick stratigraphic section of the Mural Formation that is exposed in the Cerro Pimas area of northern Sonora, Mexico, is composed of limestone lithofacies ranging from bioclastic wackestone to boundstone, whose biota is characterized by low diversity. Prominent age-diagnostic fossils are benthic foraminifera and long-ranging calcareous algae that indicate the Aptian/Albian boundary is close to the base of the Los Coyotes Member. The carbonates of this formation have negative to positive δ13C values (−4.63 to +2.6‰) and highly depleted δ18O values that range from −12.74 to −8.34‰. The absence of correlation between δ13C and δ18O values supports a primary marine origin for the δ13C values of these limestones.The carbon-isotopic curve of the Cerro Pimas stratigraphic section has well-defined δ13C segments (C8 – C15) that compare with published curves of similar age. In the lower part of the early Albian Los Coyotes Member, the presence of OAE 1b is indicated by an increase followed by a decrease in δ13C values, suggesting correlation with the Kilian Event. The middle part of the Los Coyotes Member has a significant negative carbon-isotope excursion correlated with the globally recognizable early Albian Paquier event. Moreover, another significant negative carbon-isotope shift is observed in the upper part of the Los Coyotes Member, which can be correlated with the Leenhardt Event. The occurrence of the Kilian, Paquier and Leenhardt Events (OAE 1b cluster) in the Cerro Pimas stratigraphy confirms the global nature of these early Albian disturbances of the carbon cycle.

Multistratigraphic records of the Lower Cretaceous (Valanginian–Cenomanian) Puez key area in N. Italy

We present a stratigraphic investigation of a Hauterivian to Cenomanian hemipelagic succession from Col Puez, in the Dolomites (Southern Alps, northern Italy). A composite section of seven segments was studied with bio-, magneto-, and chemostratigraphy, which enabled detailed and robust age calibration of the Puez succession. It also revealed the paleoceanographic history and helped identify the important global climatic events of that period. The age of the Lower Cretaceous Puez Formation in the Dolomites is refined as late Hauterivian to early Cenomanian. Ammonoids provide a detailed biostratigraphic subdivision that forms the basis for analyses of the faunal distribution and the paleoenvironmental evolution of basins and plateaus across the Tethys. The succession consists of facies similar to those of coeval units in the Tethys, apart from the late Barremian to late Aptian interval, which is marked by a major hiatus followed by a few-meters-thick redbed of late Aptian age. The Lower Cretaceous was characterized by a weak (~1‰) positive δ13C trend, punctuated by a positive shift in the late Hauterivian corresponding to the Faraoni Level. Oxygen isotope values show a decreasing trend from the Hauterivian to the Albian/Cenomanian, which mirrors a long-term increasing trend in paleotemperatures from ~15–18°C to ~25–30°C. This is in agreement with global paleotemperature reconstructions for this period representing the onset of mid-Cretaceous super-greenhouse conditions. Nonetheless, no black shale occurs at the intervals equivalent to Aptian–Albian oceanic anoxic events (OAE), suggesting unique paleoceanographic conditions (enhanced current activity on a submarine height) on the Trento Plateau area during the mid-Cretaceous.

Carbon isotope records of the early Albian oceanic anoxic event (OAE) 1b from eastern Tethys (southern Tibet, China)

The early Albian Oceanic Anoxic Event (OAE), i.e., OAE1b, is well documented in western Tethys and in the primary North Atlantic Ocean, but has not yet been reported from eastern Tethys. In this paper, we present bulk carbon isotope data of hemipelagites to examine if it was recorded in eastern Tethys. Samples were taken from the upper Chuangdepu Member (nannofossil zone CC8) of the lower Gyabula (former Shadui) Formation at the Bangbu section, Qonggyai, southern Tibet of China. The δ13C values mainly range from −0.6‰ to 1.8‰ with a maximum of 1.87‰ and a minimum of −0.69‰. Three stages of carbon isotope evolution were distinguished with three boundaries. By the constraint of the stratigraphic sequence and nannofossil biostratigraphic zone CC8, the rapid δ13C change and correlation with western Tethys and Atlantic Ocean together suggest that these three boundaries of the carbon isotope evolution probably correspond to three subevents of the early Albian OAE1b, and the subevent levels of upper Kilian, Paquier, and Leenhardt are recorded in eastern Tethys (southern Tibet). The fact that the amount of δ13C shift is less by ∼1.5–2.0‰ in eastern Tethys than in western Tethys and Atlantic Ocean is interpreted as a result of possible cool sea surface (∼14–16 °C) of the southeastern Tethys (northern Indian passive margin of Greater India), which was probably located in a medium–high latitude during the Albian, leading to low primary productivity. The recognition of OAE-1b from Tethys Himalaya can improve our understanding of the Tethys and global paleoclimatic and paleoceanographic changes during the mid-Cretaceous.

High-resolution chemostratigraphy of the late Aptian–early Albian oceanic anoxic event (OAE 1b) from the Poggio le Guaine section (Umbria–Marche Basin, central Italy)

Abstract An integrated study of multiple geochemical proxies (δ13Ccarb, δ13Corg, TOC, HI, CaCO3, trace elements/Al ratios) of the late Aptian–early Albian oceanic anoxic event (OAE) 1b has been performed on the pelagic sedimentary sequence of Poggio le Guaine (Umbria–Marche Basin, central Italy). A comparison of the newly collected stable isotope carbon curve with the records from the Vocontian Basin (SE France), DSDP Site 545 and Hole 1049C provided a reliable and precise identification of the four main prominent black shale levels (113/Jacob, Kilian, Urbino/Paquier and Leenhardt) that characterize the OAE 1b. The studied record shows an increase in the marine organic carbon accumulation rate, in particular in the 113/Jacob and Urbino/Paquier levels. In the other black shales, TOC values are Notably, the Kilian and Urbino/Paquier levels from the PLG section are characterized by the absence of correlative shifts in δ13Ccarb and δ13Corg. The increase in the δ13Corg values in these levels is explained by an increase in the relative contribution of 13C enriched marine planktonic archaeal biomass, while the concomitant negative excursions recorded in the δ13Ccarb could reflect a major contribution of isotopically light terrestrial carbonate ions from increased continental runoff during documented more humid conditions.

Occurrence of Upper Jurassic–Lower Cretaceous black organic-rich pelitic sediments as targets for unconventional hydrocarbon exploration in the Outer Carpathians and adjacent part of the Alps

Our work on the dark pelitic sediments of the Polish Carpathians and eastern Alps shows that these Jurassic through Lower Cretaceous sediments owe their organic content to a combination of global processes, such as climatic changes and changes to the carbonate compensation depth (CCD), and local controls, such as basin morphology, input of terrestrial organic material, and local volcanic activity. These sediments developed in basins both floored by oceanic crust as well as within the continental crust (North European platform). Our data show that these anoxic or poorly oxygenated deposits (average total organic carbon [TOC] value is around 2.5 wt. %) were laid down in the individual basins at different times, from the Late Jurassic to the Barremian and almost continuously up to the early Cenomanian, a period of 30 to 50 m.y., and their thickness reached hundreds of meters. This long time span made it impossible to distinguish precisely the known Aptian and Albian oceanic anoxic events (OAE). Our data show that sedimentation of dark organic-rich deposits was not only controlled by global events such as climatic and CCD changes, but also by local ones as a result of differences in their basin morphology and development, input of land-plant detritus, and local volcanic activity. As an example of the anoxic succession, a detailed description of the black sediments of the proto-Silesian basin is presented. Some of these anoxic shales were buried to a depth of a few thousand meters during the folding and overthrusting movements. We propose that these shales could represent a unique shale-oil and shale-gas resource in an intensely structured basin.

Cretaceous black shale: a window into microbial life adaptation

Terra Nova, 23, 362–368, 2011AbstractAs bacteria are usually incompletely preserved in the geological record, their recognition can only be based on their degradation‐resistant cell walls. However, the latter provide no indication about conditions occurring before the death of the bacteria. In this article, we attempt to demonstrate the syngenecity of bacteria found in the Albian oceanic anoxic event (OAE1b) from the Urbino level and highlight their physiology from their possible intracellular components. Dark storage inclusions have been identified as inorganic polyphosphate, in addition to carotenoids which have been encountered in the cell. Before death, stress and deprivation resulted in drastic changes in physiology generating properties such as regulatory functions of polyphosphates and the ability of carotenoids to rigidify membranes. Therefore, this starvation strategy induced a more resistant state possibly enhancing the preservation of these bacteria. These results demonstrate the potential for exploring indications of past microbial life in other black shales.

Albian oceanic anoxic events in northern Tunisia: Biostratigraphic and geochemical insights

Albian pelagic successions of the Nebeur area in northwestern Tunisia consist of radiolarian-bearing and organic-rich black shale beds, which represent the lower part of the Fahdene Formation. The carbonate content of the organic-rich beds ranges between 40 and 48%. Total organic carbon (TOC) analyses via Rock Eval pyrolysis yielded values ranging between 0.7 and 2.8% and a mixed marine/terrestrial origin. T max values vary between 424 and 450 °C, indicative of submature to mature organic matter. High resolution planktic foraminiferal and radiolarian biostratigraphy suggest that the black shales beds span the mid- to late Albian, confined to the middle part of the Ticinella primula zone, upper Biticinella breggiensis zone and lower appeninica + buxtorfi zone. Episodes of organic-rich deposition in the “Tunisian Trough” are interpreted as being the sedimentary record of the global oceanic anoxic events OAE1b, c, and d respectively. Age-diagnostic radiolarian assemblages recovered from late Albian organic-rich black shales lie within the UA13–UA14 boundary biochronozones. The abundance of radiolarian and calcispheres (i.e. pithonella) within the black shales suggests high productivity periods and eutrophic conditions probably triggered by upwelling currents.

Diversity and biotic changes of Archaeodictyomitrid Radiolaria from the Aptian/Albian transition (OAE1b) of southern Albania

Moderately well-preserved Archaeodictyomitrid radiolarian assemblages extracted from the Aptian/Albian transition interval (zones NC7 and NC8 of calcareous nannofossils) of the Sopoti section in southern Albania provide new data for the Radiolarian record during the lower Albian Oceanic Anoxic Event (OAE1b), which was previously unexplored in Tethyan sediments. Two new species (Archaeodictyomitra ioniana n.sp. and Mita amphora n.sp.) are described and the age range of a number of Archaeodictyomitrid species is specifi ed. The introduction of Mita amphora and M. gracilis at the base of the Albian refl ects a biotic change that is highlighted by a longer/larger overall test size, wide intercostal pores and the development of robust costae throughout the test. These morphological changes are tentatively regarded as the biotic response of Archaeodictyomitrid radiolarian communities within the Ionian Zone to the palaeoceanographic changes that took place during the Aptian/Albian boundary interval.