Foraminiferal Biostratigraphy and Depositional Environment of the Early Cretaceous Drilled Succession in Durban Basin, East Coast, South Africa

>Magister Scientiae - MScDurban Basin located on the eastern coast of South Africa has been a focus of interest for Petroleum Exploration for the last few decades. Only four exploratory wells have been drilled in this offshore basin without success. During the initial stage of its creation, the basin suffered major tectonic disturbance as evident from the presence extensional faults followed by intense igneous activities. This was followed by marine sedimentation in the late Mesozoic (late Jurassic-early Cretaceous). An attempt has been made in this work to understand the distribution of the rock in space and time for the early Cretaceous sediments considered most prospective for hydrocarbon exploration in Southern Africa. Temporal distribution of planktonic foraminifera helps in identification of the three early Cretaceous (Barremian to Albian) stages within the drilled intervals. Foraminiferal biostratigraphic studies integrated with sedimentology, log motif analysis and seismic data analysis helps to predict paleodepth and depositional environment during early Cretaceous in this research. The integrated analysis reveals that during the Barremian-early Aptian stages graben filled sediments were deposited in a marine shelf in the northern part of the studied area (site Jc-D1) whereas, in the central and southern part finer clastics were deposited in middle slope (site Jc-B1 and Jc-C1). The thick claystone section and presence of minor limestone lenses and their benthic foraminifera assemblage in late Aptian-Albian stage in the northern area indicates possibility of submarine fan. Overlying succession dated between late Aptian to Albian and early part of Cenomanian interval in the three studied exploratory wells shows serrated log signatures. The dominant claystone lithology with intermittent siltstone/sandstone units and the benthic foraminifera indicates fluctuating distal marine slope environment with periodic shallowness in the entire area

Modeling Continental Weathering Across the End-Permian Mass Extinction

The Earth experienced the loss of 80-90% of marine species and 70% of land species during the end-Permian mass extinction event (EPME) that occurred about 252 million years ago. The Siberian Traps (ST) volcanism is thought to have triggered the EPME through the release of large amount of carbon dioxide (CO2) into the atmosphere. Despite decades of research on the EPME, the exact impact of the ST volcanism on the EPME and the detailed patterns of the subsequent recovery of life are still hotly debated. Silicate weathering and organic carbon burial are thought to be responsible for sequestering CO2 from the atmosphere, but the relative roles of these processes remain unclear in driving the Earth’s system recovery from the CO2 emissions and global warming. We hypothesize that during the EPME and subsequent recovery, increased silicate weathering rate is not sufficient to lower the atmospheric CO2 levels and temperature remains high after the EPME. To test this hypothesis, we use lithium isotopes (delta7Li) as a proxy for changes in silicate weathering across the EPME. Fifty delta7Li data were obtained on shales from the Finnmark and Trøndelag Platforms in Norway that span the Permian-Triassic boundary (PTB). The results follow similar trend as those in the carbonate rich Meishan Section in South China published previously. The delta7Li data show an initial increase from 19‰ to 24‰ just before the PTB, followed by a decrease from 24‰ to 18‰ following the PTB. A dynamic lithium cycle box model suggests that the decreased delta7Li values suggest that weathering rates may have increased by 3 to 4 times during the PTB as a result of the elevated CO2 concentrations and temperature. However, continued outgassing from the ST may have exceeded the rate of carbon sequestration facilitated by silicate weathering, leading to long-term warming