Tropical northeast Africa in the middle–late Eocene: Paleomagnetism of the marine-mammals sites and basalts in the Fayum province,Egypt |
| |
| Institution: | 1. Department of Geological Sciences, University of Michigan, Ann Arbor, 1100 North University, MI 48109-1005, USA;2. Department of Geology, Fac. Sci., El-Minia University, El-Minia, Egypt;1. Department of Geology, University of Nigeria, Nsukka, Enugu State, Nigeria;2. Geoscan Technical Services, 5/2 Udoka Estate, Awka, Anambra State, Nigeria;1. Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616, USA;2. Department of Population Health and Reproduction, School of Veterinary Medicine University of California, Davis, CA 95616, USA;1. Department of Systems Engineering and Management, Air Force Institute of Technology, 2950 Hobson Way, Wright-Patterson AFB, OH 45433-7765, USA;2. Department of Aeronautics and Astronautics, Air Force Institute of Technology, 2950 Hobson Way, Wright-Patterson AFB, OH 45433-7765, USA;3. Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433-7702, USA;4. Department of Chemistry, Wright State University, 3640 Colonel Glen Highway, Dayton, OH 45435, USA;1. Taxonomy & Systematics Group, Naturalis Biodiversity Center, Postbus 9517, 2300 RA Leiden, the Netherlands;2. c/o Apartment 5, Worsley Point, 251 Worsley Road, Swinton, Manchester M27 0YE, UK;3. Industriestraat 21, 5931 PG Tegelen, the Netherlands;4. Natuurhistorisch Museum Maastricht, de Bosquetplein 6-7, 6211 KJ Maastricht, the Netherlands;1. Dipartimento di Scienze della Terra, Università di Firenze, 50121 Firenze, Italy;2. Department of Biology and Biochemistry, University of Bath, UK;3. CNR – Istituto di Geoscienze e Georisorse, Area della Ricerca di Pisa, 56124 Pisa, Italy;4. Department of Earth Sciences, Mekele University, Mekele, Ethiopia;5. Department of Geology, Khartoum University, Khartoum, Sudan;6. National Museum of Eritrea, Asmara, Eritrea |
| |
| Abstract: | The mid-late Eocene “Valley of Whales” in the Fayum province of Egypt contains hundreds of marine-mammals’ skeletons. Given its paleontological importance, we carried out a paleomagnetic study of the fossil-bearing formations. A sequence of basalts directly overlying the upper Eocene rocks in three distant clusters within a 25 km-long NW–SE graben in the southwestern part of the area was also studied. Thermal demagnetization of three-axis IRM was used to identify and eliminate sites dominated by hematite and/or goethite as potential remanence carriers. Progressive thermal demagnetization of the NRM isolated a characteristic NNE–SSW dual-polarity direction with a shallow inclination that passes both tilt and reversal tests. The mean tilt-corrected direction of the sedimentary formations is D/I = 16°/30° (k = 50, α95 = 3°) yielding a paleomagnetic pole at 70°N/159°E. The anisotropy of magnetic susceptibility (AMS) indicated that the observed inclinations were free from inclination shallowing, as did the nearly identical characteristic remanence of the overlying basalt flows (with a tilt-corrected reversed-polarity direction of D/I = 198°/?28° (k = 38, α95 = 7°) and a pole at 68°N/158°E). The new paleopoles place the Fayum province at a lower paleolatitude (15–17°N) than today (29.5°N), and point to the possible prevalence of tropical climate in northeast Africa during mid-late Eocene times. This tropical position is nearly identical to the paleolatitudes extrapolated from the mean of 36 coeval poles rotated from the other major cratons and from Africa itself. The declinations show a minor easterly deviation from those predicted by extrapolation from other continents. This is interpreted as due to a small clockwise rotation internal to NE Africa, possibly related to Red Sea/Gulf of Suez rifting after the late Eocene. The alternative explanation that the geomagnetic field had a non-zonal non-dipole field contribution is not favored. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
