Abd El Aziz L. Abd El Dayem and Bassem S. Nabawy

Tertiary sedimentary rocks, Fayum, Egypt:
Magnetic, fabric and paleomagnetic study
Abd El Aziz L. Abd El Dayem and Bassem S. Nabawy¹

Fac. Sciences, Tanta Univ., and ¹Geologicol and Geophysical Dept., National Research Center, Cairo, Egypt.

The Tertiary sedimentary rocks, north Fayum, consist of Birket Qarun, Qasr EISagha (both of Upper Eocene age) and Gabal Qatrani (Oligocene) Formations. In the present study, the magnetic fabric and the paleomagnetic studies are focused upon both Qasr ElSagha and Gabal Qatrani Fms.

Qasr ElSagha Fm (180 m) represents an oscillation between fossiliferous Oyster and Turritella banks with some fluvial deposits. It can be distinguished into Temple Member (77 m) and Dir Abu-Lifa Member (103 m). Both members deposited in oscillation between fluvial and marine environments proceeded downward by dominant fluvial deposits.

Gabal Qatrani Fm represents dominant fluviatile deposits (334 m). It can be distinguished into lower sequence (167.5 m) and upper sequence (167 m). The lower sequence is mainly gravelly sandstone, red sandstone, green claystone, and variegated sandstones and claystones. The upper sequence consists of two fining upward cycles and a thick paleosole (80 m). These 2 cycles are composed mainly of multicolored sandstone, claystone and dolostone.

Qasr ElSagha and Gabal Qatrani Fms have a weak secondary magnetic fabric (AMS) carried by hematite. This fabric developed after weak NW-SE normal faulting. The primary fabrics in some of the studied sites imply a paleocurrent direction flowing to the SW. This is more or less in accordance with the obtained W trend flowing current introduced by other authors. Paleomagnetically, Qasr ElSagha and Gabal Qatrani rocks have kept a very weak natural remnant magnetization (NRM).

The obtained overall paleopole position of the Eocene time is at Lat. = 60.0^oS and Long. = 225.5^o with A 95^o = 6.7^o, whereas at Lat. = 77.4^oS and Long. = 317.1^o with A 95^o = 6.49^o at the Oligocene time. The obtained data indicate situation of Africa to the south from its present position at the Eocene and Oligocene time revealing a dominant tropical to subtropical climates.

Reliability of paleomagnetic and magnetic fabric data obtained for sedimentary rocks depends mainly upon the microbiologic activities and the three dimensional effect of the dolomitization process.