ABSTRACT
The Paleogene record of Afro-Arabia is represented by few fossil localities, most of which are coastal. Here we report sedimentological and paleontological data from continental Oligocene strata in northwestern Ethiopia. These have produced abundant plant fossils and unique assemblages of vertebrates, thus filling a gap in what is known of Paleogene interior Afro-Arabia. The study area is approximately 60 km west of Gondar, Chilga Woreda; covers about 100 km2; and represents as few as 1 Myr based on radiometric dates and paleomagnetic chronostratigraphy. The sedimentary strata are 150 m thick, and dominated by kaolinitic and smectitic mudstones and airfall tuff deposits. Five main paleosol types are interpreted as representing Protosols (gleyed or ferric), Histosols, Gleysols, Vertisols, and Argillisols. Varied, poor drainage conditions produced lateral variation in paleosols, and stratigraphic variation probably resulted from lateral changes in drainage conditions through time. Vertebrate fossils occur in sediments associated with ferric Protosols and occur with fruits, seeds, and leaf impressions. Plant fossils also occur as in situ forests on interfluves, leaf and flower compressions associated with in situ carbonized trees in overbank deposits (Gleyed Protosols), and compressions of leaves, twigs and seeds in tuffs. Plant fossil assemblages document diverse forests, from 20-35 m tall, of locally heterogeneous composition, and representing families occurring commonly (legumes) or uncommonly (palms) in forests today. Sedimentological and paleobotanical data are consistent with a nearly flat landscape where a meandering river and ample rainfall supported lush vegetation. Over time, the region was subject to intermittent ashfalls. A unique fauna of archaic mammalian endemics, such as arsinoitheres and primitive hyracoids, lived here with the earliest deinotheres.
Bonnie Jacobs. Environmental Science Program, Southern Methodist University, P.O. Box 750395, Dallas, Texas 75275-0395, USA.
Neil Tabor. Department of Geological Sciences, Southern Methodist University, P.O. Box 750395, Dallas, Texas 75275-0395, USA.
Mulugeta Feseha. Institute of Development Research, Department of Geology and Geophysics, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia.
Aaron Pan. Department of Geological Sciences, Southern Methodist University, P.O. Box 750395, Dallas, Texas 75275-0395, USA.
John Kappelman. Department of Anthropology, University of Texas at Austin, 1 University Station C 3200, Austin, Texas 78712, USA.
Tab Rasmussen. Department of Anthropology, Washington University, Campus Box 1114, St. Louis, Missouri 63130-4899, USA.
William Sanders. Museum of Paleontology, University of Michigan, 1109 Geddes Avenue, Ann Arbor, Michigan 48109, USA.
Michael Wiemann. Center for Wood Anatomy Research, USDA Forest Service, Forest Products Laboratory,
One Gifford Pinchot Drive, Madison, Wisconsin 53726-2398, USA.
Jeff Crabaugh. Oklahoma State University, T. Boone Pickens School of Geology, 105 Noble Research Center, Stillwater, Oklahoma 74078-3031, USA.
Juan Leandro Garcia Massini. Department of Geological Sciences, Southern Methodist University, P.O. Box 750395, Dallas, Texas 75275-0395, USA.
KEY WORDS: Ethiopia; paleosols; paleobotany; vertebrate paleontology, Paleogene, Oligocene
PE Article Number: 8.1.25A
Copyright: Paleontological Society May 2005.
Submission: 8 January 2005. Acceptance: 6 March 2005
