Cenomanian/Turonian mass extinction of macroinvertebrates in the context of Paleoecology; A case study from North Wadi Qena, Eastern Desert, Egypt

Abstract

The paleoenvironment of north Wadi Qena area represents an obvious importance in assessing the effects on the Late Cretaceous biota; such a paleoenvironmental interpretation would include biotic evidence from invertebrate fossils and from geologic or sedimentary features such as paleosols and sequence stratigraphy interpretations. Numerous authors have demonstrated that aspects of modern macrofaunas are highly correlated with environmental variables, suggesting that invertebrate fossils are useful as paleoenvironmental indicators. Major extinction events are cyclic and may be forced by a similar, if not identical, mechanism raised the intriguing possibility that mass extinctions could be readily understood. However, investigations of various Phanerozoic mass extinctions (e.g., Kauffman 1988) have shown that comparisons are not as simple as anticipated. These studies have documented substantial differences between many of the mass extinctions in terms of their biotic, lithologic and geochemical fabrics, despite these differences, the broad pattern of repopulation appears to be comparable between biotic crises, and certain events have a very correlative biotic response from a wide variety of perspectives. This study aims to put constraints on environmental changes that affect the biota based on macroinvertebrates. The mass extinction in macroinvertebrates across the Cenomanian/Turonian transition took place during a peak global greenhouse interval, attributed to maximum sea level rising (the most intense Phanerozoic flooding event). During the C/T interval, the see was probably 255 m higher (Haq et al. 1987) and shelf areas were twice as large as those today. Abrupt environmental changes include the absence of polar ice caps during the peak of a Greenhouse cycle. Atmospheric CO2 at least four times preset levels; global warm, expansion of the oceanic oxygen minimum zone (OAE) to the deep ocean floor and epicontinental sea habitats, initiating trace element advection and chemical stirring of the oceans and oceanic impacts of meteorites and/or comets as part of the Cenomanian impact (Olsson et al., 2001). Herein the boundary represents a great mass extinction event. High global sea level during the Mid and Late Cretaceous are related to fast Atlantic sea-floor spreading (Thurow et al. 1992, p. 269); Although many Egyptian authors studied the C/T transition (e. g. Kora and Hamama 1987; Luger and Groscke 1989; Kassab 1999; Abdelhamid and El-Qot 2001; Galal et al. 2001; El-Hedeny and Nafee 2001; Zakhera 2002a, 2002b, 2003; Abdelhamid and Azab 2003; Khalil and Meshaly 2004; Abdel-Gawad et al. 2004), mass extinction at the C/T transition never been analyzed. The main targets of the present work are to verify environmental, faunal, and architectural changes during phases of growth of the late Cenomanian/Turonian platform north of Wadi Qena, Eastern Desert, Egypt to investigate the interaction with eustatic sea-level, oxygenation, environmental energy and temperature changes and to figure out other possible controlling factors in the mass extinction process. Cenomanian/Turonian mass extinction received extensive investigations backs to the original surveys of Harries (1993, 1999); Harries and Kauffman (1990); Harries and Crispin (1999); Kauffman (1988, 1995); Kauffman and Harries (1996). Detailed investigations of macroinvertebrate fossil groups are needed to highlight the impact of the different faunal groups to detect faunal differences between Cenomanian/Turonian assemblages and to reconstruct in which way these assemblages are influenced by platform flooding and crisis. Some benthic macrofossil groups constitute sensible indicators for environmental changes, such as variations in water depth, oxygen content, nutrient supply or water energy and various studies about these groups as ecological proxies were done. A focus lies on the questions, why many larger benthic fauna disappeared during late Cenomanian times and did not resettle on Turonian Moreover; assemblages of oyster bivalve constitute environmental proxies, do their occurrence and distribution indicate changes of water depth, water temperature and nutrient supply? © 2008 Springer-Verlag Berlin Heidelberg.