Lithostratigraphy of the Late Miocene to Early Pleistocene, hominid-bearing Galili Formation, Southern Afar Depression, Ethiopia

The Horn of Africa is yields famous Miocene to Pleistocene fossil sites including hominid remains. The fossiliferous sediments were deposited in fluvio-deltaic to lacustrine environments. The basin development is mainly controlled by the tectonic development of the Afar Depression. The Galili research area represents a new fossil site in the southern Afar Depression, Ethiopia. The exposed sediments and volcanics have been organized in the 230 m thick Galili Formation that consists in ascending stratigraphic order of the Lasdanan, Dhidinley, Godiray, Lower and Upper Shabeley Laag, Dhagax and Caashacado Members. The individual members are defined by volcanic layers like basalts, ignimbrites and tuffs. Feldspars separated from several volcanic layers have been dated using 40Ar/39Ar. The Lasdanan Member (>5.37 - 4.43 Ma) comprises thick basalt flows with intervening fluvial and lacustrine deposits. The Dhidinley Member (4.43 - 3.94 Ma) is characterized by thick lacustrine mudstones erosively overlain by fluviodeltaic sandy sediments capped by a widespread grey ignimbrite. The Godiray Member (<3.94) represents a short fluvial interval with adjacent floodplain mudstones and calcretes topped by a whitish lapilli tuff. The Shabeley Laag Member (<3.94 - >3.87 Ma) has been subdivided into a lower and upper member. The lower Shabeley Laag Member starts with shallow lacustrine mudstones that are followed by bluish-grey fluvio-deltaic sandstones. A pillow basalt flow defines the upper boundary of the lower Shabeley Laag Member. The upper Shabeley Laag Member shows a similar development and is capped by thick basalt flows with intervening paleosol horizons. The stacked basalt flows are either overlain by the deposits of the Dhagax (> 2.335 Ma) or the Caashacado Member (< 2.335 Ma). Both members consist of shallow lacustrine mudstones, fluvial sandy deposits, tuffs and ignimbrite layers. The eruption of the thick basalt flows on top of the Shabeley Laag Member is considered as reason for the recorded pause in sedimentation. Abundant mammal fossils have been recovered from fluvio-deltaic sands and lacustrine-floodplain mudstones of the Lasdanan, Dhidinley and Shabeley Laag Members including several hominid fossils. The most prominent hominid fossil site within the Dhidinley Member yielded a well preserved hominid femur. The deposits of the Galili Formation are partly time-equivalent with the sediments of the Adu-Asa, Sagantole, Hadar and Busidima Formations exposed at Middle Awash, Gona, Hadar and Woranso-Mille.