Foraminifera dissolution phases in the upper cretaceous succession of Jebel Duwi, Egypt

Abstract

The present work examines the function of differential dissolution in planktic and benthic foraminifera and introduces the major factors that affect dissolution in early Mid-Maastrichtian Event MME and Late Maastrichtian Event LME paleoenvironmental reconstructions. Two observations on foraminifera dissolution in the Dakhla Formation, where planktic foraminifera are more susceptible to dissolution than benthic foraminifera in the Hamama Member of the Jebel Duwi section, Eastern Desert (Egypt). They are characterized by a decline in the planktic/benthic (P/B) ratio and a rise in the agglutinated percentage. The results of those observations are used for revealing foraminiferal dissolution in these two zones (Racemiguembelina fructicosa CF4a and Pseudoguembelina palpebra CF2). During these two zones, there were excessive relative abundances of agglutinated foraminifera, indicating that these two intervals witnessed severe carbonate dissolution. The high total organic carbon (TOC) and low pH due to the presence of a lot of organic matter in the black shale’s of the Dakhla Formation of the upper Maastrichtian age is the explanation for the observed dissolution that has nothing to do with oceanographic or volcanic processes. The presence of pyrite within the black shale interval suggests low oxygen conditions and the potential for meteoric water to react with the pyrite and form sulfuric acid. This acid could dissolve any carbonate material well after the original deposition.