Conference Agenda

The Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2, ca. 94 Ma) is characterized by a marked positive carbon isotope excursion (CIE), linked to increased organic carbon (OC) burial driven by high productivity and widespread deoxygenation. To date, however, the precise pattern of changes in the burial rate of organic matter has not been well constrained. In this work, we present a compilation of data from 42 globally distributed OAE 2 sites, as well as organic carbon isotope (¹³C_org), total organic carbon (TOC), and trace element concentration data from a new OAE 2 interval in southern Tibet, China. In southern Tibet, the absence of redox-sensitive trace element enrichment through OAE 2 indicates prevailing oxic conditions. Organic carbon (OC) mass accumulation rate (MAR) at this site decreased from the lower part of the CIE to the upper part, in contrast to an approximate doubling of organic carbon MAR in the upper part observed globally. This result, coupled with detailed analysis of the compilation, shows that redox was a key factor controlling organic burial rates during OAE 2, with OC MAR scaling positively with increasing deoxygenation. Leveraging a biogeochemical model to simulate these data suggets that 5-20% of the seafloor became anoxic during OAE 2, and that this deoxygenation was accompanied by 100% to 200% increase in global seawater P concentration. Our findings indicate that during OAE 2, elevated nutrient levels may have resulted from enhanced recycling from sediments under reducing conditions, sustaining intensified primary production and subsequent organic carbon export and burial.

Intensified frequency and scale of wildfires due to global warming has been increasingly recorded in recent years. Studies of wildfire activity during deep time greenhouse climate states are crucial for evaluating their likely impacts on the global environment and ecosystems in the future. Oceanic anoxic event 2 (OAE 2), which was characterized by extremely high global temperature and a reduced equator-pole temperature gradient, could provide insights into our understanding of present-day global change processes. Here we provide data on polycyclic aromatic hydrocarbon (PAH) abundance from the Qiangdong section in the Tethyan Himalaya of southern Tibet to investigate wildfire behavior and its impact on the environment during OAE 2. Our results indicate a significant increase in the frequency of wildfires during the early part of OAE 2, followed by a rapid weakening. The change of PAH composition through OAE 2 in Qiangdong shares a similar trend to that previously found in the Western Interior Seaway, indicating potentially globally elevated wildfire frequency during the early part of OAE 2. We also document a rapid increase in chemical index of alteration values in Qiangdong. These data, coupled with other proxies for weathering intensity through OAE 2, suggest that increased weathering during OAE 2 can be attributed at least in part to the effects of vegetation loss caused by wildfire. As such, we suggest that frequent wildfires during OAE 2 promoted the flux of nutrients to the oceans, thereby stimulating productivity that, in turn, increased the area of oceanic anoxia and organic carbon burial.

Oceanic Anoxic Event 2 (OAE 2) across the Cenomanian/Turonian boundary (93.9 Ma) is characterized by a synchronous positive δ¹³C excursion in both carbonates and organic matter that likely resulted from burial of large amounts of organic carbon in deep-sea and hemipelagic settings. According to several studies, causes for OAE 2 are massive submarine volcanic activity that emitted greenhouse gases and provided biolimiting metals in marine ecosystems, leading to the onset of the Cenomanian-Turonian Thermal Maximum and to the enhancement of ocean fertility. Ocean temperature, sea-surface stratification, nutrient availability, carbonate ion saturation and continental weathering were subject to significant variations during OAE 2 that resulted in fluctuations in diversity, abundance and calcification of marine species.

We analysed the record of the main biocalcifiers of pelagic-hemipelagic settings (planktonic foraminifera and calcareous nannofossils) and of low-latitude carbonate platforms (larger benthic foraminifera and rudist bivalves) by looking at well-dated sections. Using carbon isotope stratigraphy, we performed precise correlation from shallow to deep water and tied the biotic response to the record of geochemical proxies of paleoenvironmental changes. The main extinction event, severely affecting the shallow-water benthic biocalcifiers and to a minor extent the calcareous plankton, occurred within the so-called Plenus Cold Event. High surface seawater temperature and extreme fluctuations over geologically short time intervals were probably the main cause of extinction, with concurrent contributions from decreased seawater carbonate saturation and disruption of ocean stratification. Overall, calcareous plankton fared much better, showing a greater resilience than carbonate-platform biocalcifiers to paleoenvironmental perturbations across the OAE 2.

Oceanic Anoxic Event 2 (OAE2, ~94 Ma) occurred near the Cenomanian-Turonian boundary and marks a major perturbation to global marine environment in the middle Cretaceous. Increased nutrient input into oceans are thought to have stimulated primary productivity and triggered OAE2. Both large igneous province (LIP) - related submarine volcanism and enhanced continental weathering can deliver abundant trace elements including iron in oceans. Because iron is micro-nutrient and its isotopes can fingerprint these processes across OAE2, here we present a high-resolution whole-rock Fe isotope record (δ⁵⁶Fe_T) and Fe_T/Al data of Gongzha section in southern Tibet, an OAE2 reference section in eastern Tethys where redox states and detrital inputs were stable, to investigate the relative roles of enhanced submarine volcanism and continental weathering in triggering OAE2. The iron isotope results show three notable negative shifts at ~94.8 Ma, ~94.5 Ma, and ~94.3 Ma corresponding well to episodes of intensified volcanism as documented by the osmium isotope data indicative of hydrothermally sourced iron inputs. In particular, the most prominent negative δ⁵⁶Fe_T shift by ~0.4‰ occurred at the onset of OAE2 around 94.5 Ma and was followed by a prolonged positive δ⁵⁶Fe_T excursion coeval with the positive δ¹³C shift of OAE2 in the persistent presence of hydrothermally sourced iron. Similar δ⁵⁶Fe_T variation patterns occur in other OAE2 sections worldwide, implying LIP-related submarine volcanism as the driving force for initiating OAE2. Enhanced continental weathering in the middle Cretaceous may have played an increasingly important role in terminating OAE2.

The Coniacian-Santonian is the time of deposition youngest Cretaceous episode of anoxia namely the oceanic anoxic event 3 (OAE3). The OAE3 was confined to the equatorial Atlantic Ocean and adjacent basins rather than being global in scale.

We focused on nannofossil paleoceanography of the late Turonian to early Campanian time interval and applied quantitative analyses to assess the response of calcareous nannoplankton to paleoenvironmental changes across OAE3. The study was conducted on sites from the Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) situated in the Atlantic Ocean and the Indian Ocean.

A detailed, revised, and high-resolution nannofossil biostratigraphy of the selected sites enabled correlations at a supra-regional scale. Quantitative analyses allowed us to characterize paleotemperature and nutrient changes before, during, and after OAE3.

We identified relatively large fluctuations in abundance (“acmes”) of the genera Micula and Marthasterites, across OAE3. The onset of OAE3 coincides with a major increase in abundance (and local dominance) of M. furcatus, suggesting the rapid establishment of new and peculiar paleoceanographic conditions at a widespread to global scale. The most altered paleoceanographic conditions occurred during the core of OAE3 as characterized by the synchronous maximum abundance (climax) of M.staurophora on a global scale. In addition to their value for paleoenvironmental reconstructions, the Micula and Marthasterites “acmes” are useful for the biostratigraphic characterization of the Turonian/Coniacian, Coniacian/Santonian, and Santonian/Campanian boundaries and might be introduced as additional events in future nannofossil zonations for the Late Cretaceous. This research was funded through MUR for ECORD-IODP Italia.

The scarcity of reliable sea surface temperature (SST) records from the eastern Tethys during the Cretaceous is a critical knowledge gap in paleoclimate studies. Cretaceous shallow marine sequences in the Tibetan Himalaya offer exceptional archives for reconstructing Tethyan SSTs. However, conventional paleothermometers – particularly carbonate oxygen isotope systems – suffer substantial diagenetic overprinting associated with Himalayan orogenesis. This study presents oxygen isotope values of bioapatite to estimate the SST during the Albian-early Campanian in the Tibetan Himalaya. Nineteen limestone samples were collected from the Albian-early Campanian in Nirang section and processed to obtain fish remains. In-situ oxygen isotope measurements were conducted using secondary ion mass spectrometry (SIMS), and elemental compositions were analyzed with SEM-EDS and LA-ICP-MS. Results show that fish teeth are composed mainly of bioapatite, with some samples partially replaced by silicon-bearing minerals. Oxygen isotope values (δ¹⁸O) of better preserved fish teeth indicate an average SST ranging from ~21°C to ~32°C (averaging 26.3°C ± 2.4°C). The SST evolution through time reveals a cooler climate during the Albian, with a warming trend through the Cenomanian to early Coniacian, followed by a rapid cooling in the early Campanian. This trend is consistence with previously published TEX₈₆ data compilation, confirming that southeastern Tethyan SST variations predominantly tracked global climatic forcings.