The Paleocene-Eocene thermal maximum (PETM) initiated a global biotic event with major evolutionary impacts. Since a series of minor δ13C and δ18O excursions, indicative of hyperthermals, now appears to characterize early Eocene climate, it remains to be investigated how the biosphere responded to these warming events. We studied the Esna Formation at Dababiya (Nile Basin, Egypt), in order to identify Eocene thermal maximum 2 (ETM-2) and to evaluate the foraminiferal and ostracode patterns. The studied interval generally consists of gray-brown marls and shales and is interrupted by a sequence of deviating lithologies, representing an early Eocene Egyptian environmental perturbation that can be linked to ETM-2. The ETM-2 interval consists of brownish shales (bed 1) to marls (bed 2) at the base that grade into a foraminifera-rich chalky limestone (bed 3) at the top. This conspicuous white limestone bed forms the base of the Abu Had Member. A distinct negative δ13C excursion of approximately 1.6‰ is recorded encom- passing this interval and a second negative δ13C shift of 1‰ occurs 5 m higher. These two isotope events are situated respectively in the basal and lower part of the calcareous nannoplankton zone NP11 and appear to correlate with the H1 and H2(?) excursions observed in the deep-sea records. The lower δ13C excursion is associated with benthic foraminiferal and ostracode changes and settlement of impoverished anomalous foraminiferal (planktic and benthic) assemblages, indicating a transient environmental anomaly, disrupting the entire marine ecosystem during ETM-2. Our observations indicate some similarities between the sedimentary and biotic expressions of ETM-2 and the PETM at Dababiya, pointing to similar processes operating in the Egyptian Basin during these global warming events.
Located in
Library
/
RBINS Staff Publications
This study is concerned with the Late Holocene floodplain history of the Karkheh River in Lower Khuzestan, and in particular with the role of human action upon its channel shifts. The research was conducted in a multidisciplinary way, in which resources and approaches from different research fields were combined: (1) geomorphological mapping based on the interpretation of Landsat and CORONA satellite imagery, (2) analyses of geological sequences, including the identification of sedimentary facies and radiocarbon dating of organic material, (3) an archaeological field survey of ancient settlements, and (4) consultation of historical documents, mainly Arabic texts from the 9th–14th century and European travel literature from the 16th-early 20th century. Three main channel belts of the Karkheh were identified (labelled Kh1, Kh2 and Kh3), corresponding to successive stages in the evolution of the floodplain. Two river shifts are documented in the datasets, both taking place within the last 2000 years. The first avulsion regards a shift from channel belt Kh1, once a tributary of the Karun, to the straight river bed of Kh2, taking place at least after 1240–1310 cal BP/710–640 AD. The second avulsion, from Kh2 to Kh3, is clearly documented in historical sources and happened in a single night event in the year 1837/113 cal BP. Reactivation of the Kh2 river bed and its irrigation canals can be attributed to the recent construction of an artificial canal bypassing the second avulsion point. Both river shifts were strongly influenced by human interference, whereby an artificial irrigation canal took over the entire river flow from the main channel belt. Most likely, a combination of human-induced factors, such as weakening of the river levees, high sedimentation rates and disadvantageous channel gradients, led to a situation prone to avulsion.
Located in
Library
/
RBINS Staff Publications
