BIOSTRATIGRAPHY AND ENVIRONMENTAL RECONSTRUCTION OF THE AKASHAT FORMATION (PALEOCENE PHOSPHATIC SEQUENCE), WESTERN DESERT, IRAQ

  • Sahira A. Karim Retired expert (Micropaleontology), Iraq Geological Survey, GEOSURV, Baghdad, Iraq
  • Kifah N. Al-Kubaysi Retired Senior Chief Geologists (Micropaleontology), Iraq Geological Survey, GEOSURV, Baghdad, Iraq
Keywords: Paleocene, Danian, Phosphorite, Akashat Formation, Western Desert, Iraq

Abstract

The exposure of the Paleocene sequence (Akashat Formation) in the Rutbah area is distributed in a relatively thin N – S strip extending from north of the Ga'ara depression down to the Iraqi – Saudi Arabian international border, and it is roughly 40 – 50 m thick, truncated east of the Ga'ara depression. The Paleocene sequence, in its exposures north and west of Rutbah area, is phosphatic. The biostratigraphy and depositional environment of the surface exposure of the sequence and that of borehole sections to the west of the exposure areas is studied in some detail in this work. The Paleocene sequence is conformably overlain by the Eocene sequence throughout the exposed and subsurface sections (except in the eastern side of the Ga'ara depression). The underlying sequence belongs to the Late Cretaceous with a hiatus of variable durations. South of Rutbah – Amman highway the break is relatively shorter than that in the Akashat area, especially along the western and northern rims of the Ga'ara depression. In boreholes to the west, the Paleocene sequence increases in thickness, the break with the underlying Late Cretaceous sequence may be negligible or missing. The following planktonic zones are recorded from subsurface and surface sections:

1- Marozovella valasconsis Zone, Late Paleocene (Thanatain)

2- Marozovella angulata Zone, Middle Paleocene (Selandian)

3- Globoconusa daubgergensis Zone, Early Paleocene (Danian)

Published
2020-11-16
Section
Articles