Rapid Faunal Change Across the Cenomanian/Turonian Cretaceous Boundary in Egypt

Stratigraphic significance of rapid faunal change across the Cenomanian–Turonian boundary in the Eastern Desert, Egypt

Author:

Nagm

Abstract:

A significant and rapid faunal change across the Cenomanian–Turonian boundary in the Eastern Desert of Egypt has been recognized by reconstructing the stratigraphic ranges of macroinvertebrates within the upper Cenomanian–lower Turonian Galala and Abu Qada formations. The faunal change initiated with a considerable loss of taxa during the late Cenomanian at the top of the Neolobites vibrayeanus ammonite zone, coinciding with sequence boundary SB Ce 5, ∼400 ka before the Cenomanian–Turonian boundary (93.9 Ma). Only 10% of the taxa that existed during the late Cenomanian have been recorded from lower Turonian strata. The changes in the macroinvertebrate faunas continued across the Cenomanian–Turonian boundary and new faunal associations evolved after the earliest Turonian Vascoceras proprium ammonite zone of (∼200 ka after the Cenomanian–Turonian boundary). Therefore, the crisis that caused this faunal change around the Cenomanian–Turonian boundary over approximately 600 ka. The timing of the macrofaunal change recognized in the study area completely overlaps with the well-known Oceanic Anoxic Event (OAE) 2 and most probably it is one of the effects of the major environmental perturbations (critical warming, high atmospheric CO2 concentration, and ocean water acidification) associated with this event. In addition, the sequence-stratigraphic analysis shows strong correlation exists between pattern of first and last occurrences of macroinvertebrate faunas and sea-level changes. Therefore, the oceanographic changes (rapid sea-level rise) may have also contributed to the Cenomanian–Turonian faunal change in the study area.