An astronomical time scale of early Pliocene from the Mediterranean Sea, Egypt

Abstract

Pliocene diachronism and mismatches between planktic foraminifera and nannofossil bioevents are clearly observed in the Mediterranean Sea. Hence, astronomical tuning combined with calcareous nannofossils and plankton foraminiferal biozones constitutes one of the important tools for regional correlation between different paleolatitudes. Consecutive and high-resolution well logs from the Sapphire-Dd borehole in the Mediterranean contributed a vital role in exploring the astronomically forced sedimentation in Pliocene strata. A detailed cyclostratigraphic analysis is applied to the natural gamma-ray spectrum logging data that is used as a paleoenvironmental and paleoclimatic proxy to construct a floating astronomical time scale (ATS) for the first time in Egypt. The results show that the hierarchy of sedimentary cycles with a ratio of ~20 : 5 : 2 : 1 in the Kafr EI Sheikh Formation can be interpreted as Milankovitch cycles of eccentricity, obliquity, and precession cycles, respectively. The ATS is established by tuning the Gamma Ray log to the target curves of the insolation of the La2004 solution based on the biozones time framework of the Sapphire-Dd core, which indicates the highest occurrence (HO) of calcareous nannofossils Sphenolithus verensis at 4.03 Ma, the HO of Triquetrorhabdulus rugosus at 5.24 Ma, the highest common occurrence at 4.093 Ma; and the lowest common occurrence of planktic foraminifera Globorotalia margaritae at 5.1 Ma, respectively. The new time scale yields more reliable age constraints on the evolution of paleoclimate and paleoenvironment in southeastern Mediterranean area since the Pliocene.