Abstract While Olduvai Gorge, Tanzania, is most famous for its impressive and formative record of early human technology, Pleistocene fauna and hominin fossils, its geological record is equally important. At Olduvai, palaeoanthropologically significant sites are often preserved in primary context (not redeposited), and they can be contextualized within the palaeoenvironments in which the hominins lived. This has provided an exceptional opportunity to assess not only hominin evolutionary changes over time, but also to understand their adaptive behaviour including toolmaking, foraging and sociality. Abundant volcanic material from the nearby Ngorongoro Volcanic Highlands, interspersed within and between archaeology-bearing deposits, made Olduvai a target for some of the earliest applications of radiometric dating using the K/Ar system. Ultimately, the 40 Ar/ 39 Ar dating system has produced ages with exceptional precision. Early radiometric dating at Olduvai helped establish the antiquity of the hominin lineage, and early palaeomagnetic studies (and the ‘Olduvai event,’ the longest normal subchron within the reversed Matuyama Chron) were critical in establishing the importance of Olduvai in the field of geochronology. More recently, high-resolution palaeoclimate studies of the palaeolake that once occupied the Olduvai Basin have helped to reconstruct the palaeoenvironments encountered by hominin species. Over a century of geological research has secured Olduvai's status as an important site for geoheritage.

Abstract This study provides a comprehensive examination of the Oligocene–Miocene Ethiopian Flood Basalt Province (EFBP) within the Blue Nile (Abay) Basin (BNB), Ethiopia. Extensive logging through 29 new sections has enabled an updated stratigraphic account of the BNB to be elucidated and reveals the significance of intravolcanic sedimentary systems within the EFBP. Five sub- and intra-volcanic surfaces were modelled using spot heights to generate isopach maps that were used to constrain the thickness variations within the stratigraphy. Additionally, lineaments, Strahler stream segments and volcanic cones were mapped out from digital elevation models (SRTM DEM) and satellite data (ASTER and LANDSAT 8 imagery). These data were used in conjunction with the isopach maps to better understand the basinal controls on the distribution of intravolcanic sedimentary systems within the BNB. The study reveals how NNE and ESE/SE structural trends have influenced the distribution of volcanoes within the basin, which has in turn disrupted the distribution and lithofacies architecture of the volcanic sequences. The presence of intrabasinal ridges parallel to the major structural trends are also revealed, which formed relatively short-lived drainage divides. The implications of these intrabasinal highs on the composition and the reservoir potential of intravolcanic sedimentary successions are discussed.

Abstract The upper Awash runs across a volcano-sedimentary succession dated from the Early to Middle Pleistocene and located on the western margin of the northern portion of the Main Ethiopian Rift. The succession lies above Late Miocene to Pliocene lava flows, domes and large volume ignimbrites. The succession formed within a fluvial system that developed within transversal rift faults. The stratigraphy consists of primary volcanic deposits interbedded with reworked sediments emplaced in a low-energy floodplain developed in a subsiding area. The lower part of the volcaniclastic sequence is dominated by a 1.2 Ma old, low aspect ratio, pyroclastic density current deposit (Kella ignimbrite). This eruption was followed by an eruptive stasis and reorganization of the drainage system. Tephra deposition in the floodplain climaxed again between 0.9 and 0.7 Ma and was associated with extensive tephra reworking. Sedimentation rates significantly decreased after 0.6 myr ago, probably owing to declining volcanic activity. Dynamic interaction between tectonics and volcanic activity created a complex sedimentary environment preserving numerous artefacts (lithic tools), animal and hominin remains. Stratigraphic correlation is based on the interpretation of the basin evolution and has relevance for the reconstruction of the palaeoenvironment and the interpretation of the palaeontological and archaeological data.