Drill Sites

EAlabeled

Drilling Dates


Tugen Hills / Baringo Basin
June 1-15, 2013

West Turkana
June 23-July 8, 2013

Northern Awash
February 22-March 21, 2014

Lake Magadi
June 14-July 4, 2014

Chew Bahir
November 6-28, 2014













Northern Awash, Ethiopia


NorthernAwashDrillSite

The Northern Awash region of Ethiopia has yielded one of the densest accumulations of Pliocene fossil hominins including ~90% of the species Australopithecus afarensis. The region also preserves a rich and highly-resolved record (<105 yr) of late Pliocene mammalian fauna and flora. The drilling target for this site was the lacustrine depocenter of the Hadar Formation ~3.6-2.9 Ma, which is located in the Ledi-Geraru area, ~30 km northeast of the Australopithecus afarensis bearing exposures of Hadar and Dikika. Two sites were drilled (~3 km apart) for a composite stratigraphic interval of approximately 270 m. The top of the core captured the top of the Hadar Formation (<2.93 Ma) whereas the age of the base of the core is still to be determined, but is well below a tephra dated to 3.22 Ma. The lithology of the core is dominated by fine-grained sediments, principally lacustrine deposits, some with periodic subaerial exposure and pedogensis in the upper half, as well as three basalt sequences. Diatom assemblages indicate that lake conditions included deep, well-mixed conditions.

Utilizing a variety of geochronological tie points (40Ar/39Ar dating, tephrostratigraphy, and the Kaena and Mammoth paleomagnetic subchrons), this site will provide the environmental backdrop against which >500 kyr of the evolutionary history of A. afarensis and associated fauna can be interpreted from multiple adjacent paleoanthropological project areas including Hadar, Dikika, Gona, Ledi-Geraru, and Woranso-Mille. This history includes a distinct faunal turnover at ~3.1 Ma indicating a significant ecological change with an increase in, and influx of, more arid-adapted mammalian taxa. This turnover coincides with the onset of high-amplitude climate oscillations and increased aridity in eastern Africa between 3.15 and 2.95 Ma as noted in marine core isotope and dust records. Additionally, this high-resolution lacustrine depocenter has the potential to record the local environmental response to Milankovitch cycles prior to the onset of Northern Hemisphere glaciation and high latitude glacial cycles. The change in the robustness of A. afarensis mandibles after 3.1 Ma may be linked to the taxon becoming more resource-stressed in response to glacial cooling after 3.2 Ma as a result of reduced mean annual rainfall (MAR) and/or extended dry seasons. One hypothesis is that a decrease in MAR and terrestrial temperatures, with corresponding seasonal and vegetation fluctuations, may have resulted in dietary changes in fallback foods for A. afarensis.

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Tugen Hills / Baringo Basin, Kenya


BaringoDrillSite

The Tugen Hills of the central Kenyan Rift Valley comprises the most complete late Neogene section known from the East African rift, with sedimentary strata spanning the last 16 Ma. Within this sequence, the drilling target was a Pliocene portion of the Chemeron Formation (~5.3-1.6 Ma), which contains ~100 fossil vertebrate localities, including three hominin sites, within 3 km of the drill site that can be directly linked to the core. Elsewhere in East Africa at this time period we also observe the diversification of Paranthropus and Homo, the earliest evidence of lithic technology, and the earliest evidence for Oldowan stone toolmaking. The ~228 m borehole from the Tugen Hills, positioned ~20 m from cliff exposures of Chemeron sediments, spans approximately 3.4-2.6 Ma and records fluviolacustrine deposits and floodplain paleosols dominating the lower half of the core, with cyclic deep-lake diatomites and subaerially deposited sediments in the upper half. A high-resolution chronostratigraphic framework for the sequence based on 40Ar/39Ar analyses from multiple tephras from local stratigraphic sections will provide additional age-control and correlations to the core.

The upper portion of the core is directly correlatable to the outcrop sequence between 2.69-2.58 Ma, consisting of a distinctive series of lacustrine/diatomite units documenting abrupt and repeated cycles of major freshwater lake systems alternating with terrigenous sediments. The lacustrine phases have been linked directly to insolation forcing by precession at 23 kyr pacing, at the maximum of an eccentricity cycle. The specific link between the timing of the five paleolakes and insolation maximum for the June/July 30°N insolation curve, indicate that precipitation patterns in the region were controlled by the orbital forcing of the African summer monsoon and that climatic processes outweighed tectonic influences on hydrologic patterns at <105 yr timescales during the early Pleistocene in the Baringo Basin. Critically, this sequence spans the period prior to Northern Hemisphere glaciation, the onset of glaciation, and the intensification of glaciation. This provides us with a unique opportunity to explore not only how the terrestrial community responded across a major global climate transition, but also how shifting insolation patterns and/or glacial cycles influenced environmental changes in the Rift Valley via pervasive, short term climatic fluctuations.

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West Turkana, Kenya


WestTurkanaDrillSite

The Turkana Basin of northern Kenya and southern Ethiopia contains one of the richest long-term records of Plio-Pleistocene faunal evolution. The cored interval targeted the early Pleistocene lacustrine strata of the Kaitio and Natoo Members of the Nachukui Formation. The core spans ~1.9-1.4 Ma and documents a well-known lacustrine interval in the basin (the Lorenyang Lake) that existed during a phase of overall increasing African continental aridity punctuated by major lake-level fluctuations, which appear to reflect insolation-forced climate cycles. The ~216 m borehole from the Kaitio locality was positioned adjacent to exposed outcrops of equivalent age, which are the subject of a parallel study. The lower three-quarters consist of massive to laminated lacustrine clays with intervals of episodic exposure and pedogenesis whereas the upper quarter of the core reflects more terrestrial deposition. Overall the succession represents a regressive lacustrine sequence from deep lake, to fluctuating lake margin, to delta plain.

Using the top of the Olduvai paleomagnetic subchron as well as several tephrostratigraphic tie points, the Kaitio core can be directly associated with the rich Pleistocene paleontological and archaeological record of the Turkana Basin. The hominins in this time frame include significant specimens, including some of the earliest and most complete fossils of early Homo (H. habilis/rudolfensis) and H. ergaster, and the archaeological inventory includes both the Oldowan tradition as well as the earliest Acheulean material. The critical interval covered by the Kaitio core also includes the period when hominins first displayed fully terrestrial adaptations similar to modern humans as well as when they expanded their range outside of Africa, an expansion of East African grassland habitats, and an episode of major faunal turnover in the region. The West Turkana datasets will allow us to test several key hypotheses relating major events in hominin and other faunal evolution shortly after 2 Ma to environmental change. In particular, we can explore if and how Turkana Basin environments, especially the Lorenyang Lake, responded to a peak in high-latitude climate sensitivity, increased precessional forcing and African humid phases, and/or an intensification in the development of Walker circulation in the Pacific Ocean starting around 1.8 Ma. Additionally, we can also test whether potentially non-climatic forcings, such as volcano-tectonic events, may have led to hydrologic or topographic changes in the basin that altered basinal habitats.

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Lake Magadi, Kenya


MagadiDrillSite

The HSPDP and its sister project, the Olorgesailie Drilling Project (ODP), targeted two adjacent Pleistocene-modern depocenters in the southern Kenya rift to provide regional equatorial paleoclimate records over the past ~1 Ma, encompassing the history of the major Middle-Late Pleistocene climate transitions. Extensive outcrops of the Olorgesailie Formation (0.5-1.2 Ma) and post-Olorgesailie Formation sediments (~12-350 ka) in the southern Kenya Rift provide a rich and well-calibrated record of archaeological sites, faunas, and changing paleoenvironments. This includes a record of the major transition from the persistent Acheulean technology, which is characterized by large cutting tools from nearby rock sources, to a novel system of behavior, the early Middle Stone Age (MSA), characterized by diverse tool kits and greater dependence on distant rock sources for stone tools. The southern Kenyan cores will also provide a record of local paleoclimatic conditions and water availability during an important turnover in the large mammal fauna ~600-362 ka, documented at nearby Lainyamok (15 km from the Magadi drill site), when the dominant mid-Pleistocene, large-bodied grazers of the Kenya Rift became extinct and were replaced by mammals typical of the modern East African ecosystem.

Less than 20 km from the Koora Graben site, the HSPDP targeted Lake Magadi, a regional sump for water and sediments in the axis of the southern Kenya Rift. Modern Lake Magadi is a saline pan, a successor to a series of paleolakes that have likely occupied the basin for about one million years. Two different sites were cored by the HSPDP at Lake Magadi, ~3 km apart and <20 km from the ODP site. Similar to the ODP site, cores reached the bedrock trachyte at a maximum depth of ~194 m. The age-model of these cores, to be constructed via radiocarbon, Uranium-series (of evaporites), 40Ar/39Ar dating techniques, are still in process. Most of the cores are composed of laminated or massive lacustrine muds interbedded with varying proportions of chert. This variation in lithology complicated coring efforts and resulted in core recovery of only ~60%. The upper 30-40 m of the cores are trona and trona-bearing mud. In sharp contrast to modern conditions, diatom and mineral assemblages indicate freshwater phases early in Lake Magadi’s history.

Despite their proximity, the Koora and Magadi basins have been hydrologically distinct for most of their history, but under nearly identical regional climatic conditions. As such, their parallel records can be used to address local and regional responses to larger-scale climate change, e.g., differentiating climatically controlled environmental changes from tectonic- or groundwater-controlled changes.

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Chew Bahir, Ethiopia


ChewBahirDrillSite

The Chew Bahir basin in southern Ethiopia is located ~100 km east of the earliest documented Homo sapiens fossils (Omo I and II) in the adjacent Lower Omo Valley that date to ~195 ka. Additionally, the southwest Ethiopian highlands are hypothesized to have been a refugium during hyper-arid intervals of the Late Pleistocene, where a bottleneck population of anatomically modern hunter-gatherers could have developed the social, technological and linguistic skills necessary to survive and eventually spread across Africa and onward to Asia, Australia and Europe. Subsequent economic innovations, technology transfer, and subsistence intensification in the SW Ethiopian highlands and Turkana basin led to the emergence of distinct food production systems in the Horn (intensive highland agriculture) and eastern Africa (pastoralism). Although the Chew Bahir cores are not from the same sedimentary basin as the Omo I and II fossils, attempts to link the chronology of the two sequences via geochronology and tephrostratigraphy are underway. Additionally, the Chew Bahir cores will still provide a regional-scale environmental context for the first appearance and subsequent evolution of H. sapiens in the adjacent lower Omo valley and SW Ethiopian highlands over the last 200,000 years.

The modern surface of the Chew Bahir basin is a playa saline mudflat, but seismic survey of the basin for petroleum exploration by Tullow Oil Company confirmed the presence of more than 3 km of sediment fill beneath. Chew Bahir lies at the transition between the Main Ethiopian and Kenyan Rifts, and between the distinct Ethiopian and Kenyan highlands. The basin also lies in the transition between tropical equatorial and summer monsoonal climates, and between Atlantic and Indian monsoon systems. Pilot study short cores from Chew Bahir up to ~20 m depth reaching back to ~60 ka have already been collected and analyzed. Results indicate fluctuations in moisture availability on decadal to centennial and millennial timescales, and to the precessional cycle. In close cooperation with European-based scientific projects, ICDP-HSPDP collected a 40 m core in March 2014 from the central part of the Chew Bahir basin, while two parallel cores with a maximum depth of ~280 m were drilled closer to its southwestern border in November 2014. Material from these long cores consist predominantly of silty and sandy clays, with occasional coarser silt and sand beds, particularly in the upper 100 m. Shell-rich horizons also occur throughout the core. Based on sedimentation rates from the Chew Bahir short cores, the longer cores are estimated to extend deep into the Middle Pleistocene.

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