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The present paper reports on the sedimentological and geochemical record of Albian–Turonian neritic carbonates from the eastern subequatorial Pacific domain in Peru. The focus is on one of the most extreme carbon cycle perturbations of the Phanerozoic, the Oceanic Anoxic Event 2 (late Cenomanian–early Turonian). Thanks to the very expanded and well-exposed sections in Peru, the OAE2 interval was sampled at high temporal resolution for both bulk micrite and bulk organic matter carbon isotopes. Despite the scarcity of significant amounts of organic matter or evidence for oxygen deficiency, the δ 13 C curve matches well with global published high-resolution data for coeval successions such as those reported from the English Chalk and the Portland # 1 core. Biostratigraphic data and the detailed sequence stratigraphic interpretation of these sections are combined with the carbon-isotope chemostratigraphy documented here. Applying the characteristic peak and trough chemostratigraphic terminology for OAE2 (A–C), the following main environmental and carbon isotope stratigraphic features are observed from the late Albian to the early middle Turonian in Peru: (i) An Albian to early late Cenomanian heterozoan ramp recording the pre-OAE2 δ 13 C excursions, specifically the Mid-Cenomanian Event. (ii) A late Cenomanian trough of δ 13 C values (B) showing a progressive deepening leading to the short-lived establishment of middle ramp type sedimentation. (iii) A late Cenomanian to early Turonian δ 13 C plateau (C) characterised by benthonic inner ramp sedimentation during a sea-level highstand phase. (iv) A recovery of δ 13 C values at the end of OAE2 associated to a trophic change, increased influx of argillaceous facies and reduced carbonate production. (v) A early to middle Turonian fluctuating δ 13 C curve, linked to a maximum flooding phase in the Mammites nodosoides Zone and carbonate production during the Collignoniceras woollgari Zone. The data shown here are particularly relevant as they come from very expanded neritic sections in the sub-equatorial eastern Pacific. Many of the features recognized share important similarities with Tethyan and Atlantic sections whilst the ramp system as such did not suffer from a carbonate crisis during OAE2 as recorded, for instance, in Mexico and Tibet. [ABSTRACT FROM AUTHOR]

The present paper documents and discusses a new Albian–early Cenomanian carbon isotope (δ 13 C carb and δ 13 C org ) curve from the subequatorial Eastern Pacific in Peru. Chemostratigraphic evidences for the expression of the OAE1b set and for OAE1c and OAE1d are presented. This dataset is relevant inasmuch as previous work is strongly biased towards study sites in North America (Western Interior Basin), in Europe (Tethys) and the Pacific realm. A comparison of the carbon isotope stratigraphy obtained in Peru with published sections from the Central and Western Pacific, the Western Atlantic and Northern and Western Tethys reveals an overall good agreement supporting the global nature of the isotope patterns described here. The δ 13 C from Peru record is constrained by biostratigraphic evidence and 87 Sr/ 86 Sr isotope stratigraphy using well-preserved oyster shells. Furthermore, we document the development of a heterozoan epeiric–neritic mixed carbonate–siliciclastic ramp in the Western Platform of Peru and its corresponding sedimentary facies associations. This dataset was used to elucidate the complex interplay of climatic changes, nutrient supply, and platform drowning, leading to the following conclusions: (i) an upper Aptian–lower Albian major change from siliciclastic-dominated to carbonate sedimentation coincided with the impact of the Kilian Level, (ii) a lower Albian incipient platform drowning linked to the impact of the Paquier Level, (iii) A lower middle Albian major demise of neritic carbonate production that coincides with the Leenhardt Level, followed by middle Albian condensed sedimentation that reports prominent negative values in δ 13 C carb prior to the onset of OAE1c and (iv) finally, renewed carbonate ramp production during the upper Albian–lower Cenomanian. The data shown here represent the foundation for future work documenting the mid-Cretaceous of Peru and its implications for the palaeoceanography of the SE subequatorial Pacific. [ABSTRACT FROM AUTHOR]

Abstract: The Early Toarcian is marked by a global perturbation of the carbon cycle and major marine biological changes. These coincide with a general decrease in calcium carbonate production and an increase in organic carbon burial, and culminate in the so-called Toarcian Oceanic Anoxic Event. It is believed that the environmental crisis was triggered by the activity of the Karoo–Ferrar large igneous province. In order to further document the Early Toarcian palaeoenvironmental perturbations, carbon isotope, total organic matter, calcareous nannofossils and phosphorus content of the Amellago section in the High Atlas rift basin of Morocco were investigated. This section is extremely expanded compared to the well-studied European sections. Its position along the northern margin of the Gondwana continent is of critical importance because it enables an assessment of changes of river nutrient input into the western Tethyan realm. The carbon isotope curve shows two negative excursions of equal thickness and amplitude, at the Pliensbachian–Toarcian boundary and at the transition from the Polymorphum to the Levisoni Zone. This confirms the supra-regional nature of these shifts and highlights the possible condensation of the first “boundary” shift in European sections. Phosphorus content is used to trace palaeo-nutrient changes and shows that the two negative carbon isotope shifts are associated with increased nutrient levels, confirming that these episodes are related to enhanced continental weathering, probably due to elevated greenhouse gases in the atmosphere. In the High Atlas Basin, the increase in nutrient levels at the Pliensbachian–Toarcian boundary is moreover likely to be the main factor responsible for the coeval demise of the Saharan carbonate platform. A middle Toarcian event, centered on the boundary between the Bifrons and Gradata Zones, characterized by a positive carbon isotope excursion and nutrient level rise, is documented in the Amellago section. [Copyright &y& Elsevier]

We present the first detailed stable isotope record (δ 13 C, δ 18 O) for the Valanginian (Lower Cretaceous) of the southern Boreal Realm. The observations are based on the geochemical analysis of 286 belemnite rostra from stratigraphically well-dated sections in northwest Germany. A major positive carbon isotope excursion (CIE) of ~ 2‰ in the early late Valanginian documents a perturbation of the carbon cycle. This positive CIE, which is well known as the ‘Weissert Event’ in the Tethys, is also displayed in composite carbon isotope records based on published and own data from three different palaeolatitudes (35°, 39°, 65° North). These findings suggest that the environmental changes indicated by the CIE in the early late Valanginian are synchronous, thereby pointing to a global control. The combined oxygen isotope data sets show long-term fluctuations of up to 7 °C with a cooling in the late Valanginian for both the southern and the arctic part of the Boreal Realm, whilst Tethyan data document only a ca. 1 °C cooling. Based on a reliable bio- and chemostratigraphic correlation between the different realms this study highlights the amplitude of the environmental perturbations in the Valanginian and supports the idea that a combination of regional and global factors caused such shifts. [ABSTRACT FROM AUTHOR]

Abstract: A widely accepted hypothesis proposes that the Early Aptian demise of carbonate platforms in the northern Tethyan realm reflects the impact of environmental changes that eventually led to the deposition of organic-rich basinal sediments during oceanic anoxic event (OAE) 1a. In fact, the temporal correlation of oceanic anoxia and platform drowning has not been rigorously tested and evidence indicating causality is debated. The present paper provides a high-resolution carbon- and strontium-isotope chronostratigraphy combined with detailed sedimentological analysis applied to the Barremian–Aptian Urgonian carbonate platform development at the northern rim of the Tethys (Subalpine Chains, Haute-Savoie, ESE France). A characteristic Barremian–Aptian carbon- and strontium-isotope pattern below the onset of OAE 1a interval permits precise platform-to-basin correlation with the Barremian stratotype locality of Angles (SE France). This chemostratigraphic pattern equally allows for a correlation with well-studied shoal-water and pelagic records of the northern and central Tethys. Strontium-isotope stratigraphy provides a high-resolution numerical age-data set, indicating an earliest Aptian age (<124.5±0.4Ma) of platform demise in the Subalpine Chains. The detailed platform-to-basin correlation obtained in France clearly illustrates that shoal-water carbonate production in the Urgonian platform ceased about 300kyr before the most negative values of the characteristic negative carbon-isotope anomaly, which marks the beginning of OAE 1a black-shale deposition. The stratigraphic results confirm (i) the theory of an Early Aptian northern Tethyan platform drowning episode predating OAE 1a and (ii) document the temporal response of shoal-water carbonate platforms to the environmental perturbations prior to the OAE acme. [Copyright &y& Elsevier]