Paleoecology and paleogeography of Eocene ostracod faunas from the Nile Valley between Minia and Maghagha, Upper Egypt

Abstract

Sixty-four ostracod species and morphs in 130 samples from five sections along the Nile Valley between Minia and Maghagha cities could define the paleoenvironmental conditions that prevailed during the Eocene in the study area. Cluster analysis based on the Jaccard coefficient of similarity (the paired group average method) led to the distinction of three biofacies of ostracod assemblages, each of them with its particular paleoenvironment. The Minia biofacies represents the early Eocene, and is characterized by deposition in an inner to outer shelf environment. The Maghagha biofacies is middle Eocene and represents a restricted shallow water environment, possibly with more or less reduced salinity. At the base of the sequence, these restricted conditions were accompanied by reduced, dissolved oxygen conditions. At the top, calm water conditions prevailed. The Qarara biofacies is also middle Eocene in age and was deposited in turbulent water conditions, gradually shallowing over time. On the other hand, the Samalut Formation, which was barren of microfossils, can be attributed, according to its lithological composition, to a particular type of facies representing a shallow marine environment. The ostracod species of the study area provide evidence of distinct migration of ostracods during the Paleogene along the southern shores of the Tethys. © Springer-Verlag Berlin Heidelberg 2005.