SUBTROPICAL PALEOGEOGRAPHY OF MARINE-MAMMAL SITES IN THE LATE EOCENE IN EGYPT: A PALEOMAGNETIC STUDY IN THE FAYUM PROVINCE

Vertebrate paleontologists have long appreciated the merits of the Fayum Province in Egypt because of its diverse Late Eocene and earliest Oligocene mammalian and other vertebrate fossils. Our paleomagnetic study was designed to determine the paleotectonic position of Africa around Late Eocene time and to shed light on the paleoclimate that allowed such a diverse marine and terrestrial biota to prosper. We sampled Middle-Late Eocene and earliest Oligocene sedimentary rocks throughout Fayum province [18 000 km2] and overlying basalts in a 25km-long NW-SE graben, SW of Fayum.

Acquisition of three-axis Isothermal Remanent Magnetization followed by progressive thermal demagnetization allowed us to avoid sites dominated by hematite and/or goethite, which are likely to be secondary in origin. Thermal demagnetization of the magnetite-dominated sites isolated a characteristic dual-polarity NNE-SSW shallow stable component in the range of 350-450 degrees C in most samples. Site-means are better grouped after correction for the slight tilts. The overall mean direction was D/I=27/22 (k=20, alpha-95=4.8 degrees), yielding a Late Eocene paleomagnetic pole at 59N/150E. In addition, the basalt flows were entirely reversed but their directions were nearly identical to those of the sediments. Their mean characteristic D/I is 201/-28 (k=35, alpha-95=6.6 degrees) yielding a pole at 66N/154E.

These poles correlate well with coeval NE African poles, but show a systematic difference from poles rotated from other continents into African coordinates, as compiled by Besse and Courtillot (2002, JGR vol. 101, B11). Explanations for this discrepancy could be found in structural, global tectonic, or geomagnetic field features that are, at this time, poorly understood.

Paleotectonically, the obtained paleopoles place NE Africa far south of its present-day position; Fayum is now located at 29.5N, but was positioned at paleolatitudes of 11-15N in Late Eocene time. Moreover, the African Plate was oriented about 25 degrees anticlockwise with respect to present-day north. Therefore, during the Late Eocene, northeast Africa seems to have been dominated by subtropical climates. Given the anticlockwise azimuthal orientation of Africa, the Western Tethys (Mediterranean) was, apparently, relatively wider than its eastern part