- Email: [email protected]
U-Th burial dating of ostrich eggshell: A new geochronometer for African archaeological sites
198
Abstracts / Quaternary International 404 (2016) 174e213
East-west orientated valleys with extremely ephemeral modern channel flow are a significant landscape feature of northwest Namibia. Today these valleys are important sources of aeolian dust, as each year plumes during Berg wind events fertilise Atlantic waters off the Skeleton Coast. Here we provide an OSL chronology for silts from the Huab valley, demonstrating a temporally complex Holocene sequence of valley-wide infilling (with early phases associated with the African humid period?) and subsequent late Holocene entrenchment during confined channel flows. Age data affirm fluvial histories from the Hoanib system (Eitel et al 2006), but additionally provide an association with modern aeolian dynamics and dust-sourcing that points to the vital role of wet e accumulation as sourcing the aeolian systems of today's hyper-arid regime. Keywords: Holocene, valley fills, luminescence dating, aeolian dust References: Eitel, B., Kadereit, A., Blumel, W.-D., Huser, K., Lomax, J., Hilgers, A., 2006. Environmental changes at the eastern Namib Desert margin before and after the Last Glacial Maximum: new evidence from fluvial deposits in the upper Hoanib River catchment, northwestern Namibia. Palaeogeography, Palaeoclimatology, Palaeoecology 234, 201e222.
8. DATING AND CORRELATION OF AFRICAN ARCHIVES OF ENVIRONMENTAL CHANGE AND ARCHAEOLOGY SPATIAL AND TEMPORAL VARIATION IN NORTH AFRICAN PALAEOENVIRONMENTAL AND ARCHAEOLOGICAL RECORDS DURING MARINE ISOTOPE STAGE 4 L. Farr*, S. Jones. The McDonald Institute for Archaeological Research, University of Cambridge, UK. E-mail address: [email protected].
Marine Isotope Stage 4 (MIS4) covers the timeframe of c.74e59 ka and is generally regarded as a period of sudden and rapid climatic deterioration in North Africa. MIS4 is argued to coincide with regional decreases in population size and density in North Africa, possibly concomitant with retraction into refugia in certain locales. Sitting awkwardly against this picture is recent mtDNA evidence from living human populations which suggests that, approximately c.60 ka, Homo sapiens groups exited Africa in a successful migration that resulted in colonisation of Asia, Australia and Europe. These dispersals of Homo sapiens are usually attributed to humid climatic phases in MIS5 and MIS3, when hydrological networks are argued to have been reactivated in response to pluvial events, resulting in the wetting of normally arid regions such as the Sahara. This paper reviews palaeoenvironmental and archaeological data from marine and terrestrial archives in the North African region, which are dated to the MIS4 timeframe. We evaluate spatial and temporal variation in the datasets in relation to global climate records and investigate their reliability to inform us of millennial and sub-millennial environmental change, and demographic processes in North Africa. In particular, we look at the chronometric dating of palaeoenvironmental and archaeological datasets and investigate issues regarding chronological precision, spatial resolution and geoarchaeological context. We present geoarchaeological and lithic data from part of the Haua Fteah cave sequence (Libya) which has associated MIS4 dates, and discuss how these findings fit into a wider picture of regional environment change and human population dynamics. Keywords: MIS4, North Africa, dating, environment, geoarchaeology
* Corresponding author.
DEVELOPING A HOLOCENE TEPHROSTRATIGRAPHY OF ETHIOPIA C. Martin-Jones 1,*, C.S. Lane 2, H.F. Lamb 1, N.J.G. Pearce 1, V.C. Smith 3. Department of Geography and Earth Sciences, Aberystwyth University, UK; 2 Department of Geography, University of Manchester, UK; 3 RLAHA, University of Oxford, UK. 1
E-mail address: [email protected].
Ethiopia experiences a highly variable climatic regime, subject to the seasonal migration of the Inter-Tropical Convergence Zone (ITCZ) and monsoon variability. These climatic changes are recorded in Holocene lake sediments throughout the Ethiopian Rift Valley. Synchronizing widespread regional palaeoclimate archives requires accurate and precise chronological control. Explosive volcanic eruptions generate large volumes of volcanic ash (tephra) which may be transported over continental scales and deposited in sedimentary sequences rapidly. A tephra layer represents a time-parallel marker which can be used to link sedimentary archives. Tephra from the same eruption is traced between different sites on the basis of its unique geochemical ‘fingerprint’. Ultra-distal ‘non-visible’ cryptotephra layers are increasingly used to extend the geographical range over which palaeoenvironmental archives can be correlated. Many caldera forming eruptions occurred from East African Rift volcanoes during the early Holocene to late Pleistocene. The tephras deposited provide chronological control on Pleistocene Ethiopian palaeoanthropological sites. However, Holocene tephra deposits remain largely un-documented in Ethiopia. Lacustrine cores were collected from Ethiopian Rift lakes (Ashenge, Hayk, Dendi, Hora, Tilo, Awassa and Chamo) covering 50 cm thick tephras in Lakes Tilo and Awassa during ~ 700 e 9,800 cal yr BP. These tephras have a similar major element composition to those in Lake Hora sediments (250 km NE of Lake Tilo). Distal rhyolitic tephra, possibly originating from the Afar, were deposited in Lakes Ashenge and Hayk between ~ 5,400 e 14,500 cal yr BP. Further work is now required in order to test potential correlations between these lacustrine archives. The resulting tephrostratigraphy will provide a dossier of regional Holocene volcanism and allow temporal and spatial climatic changes in this region to be investigated. Keywords: tephrochronology, geochemistry
correlation,
palaeoclimate,
Ethiopia,
U-TH BURIAL DATING OF OSTRICH EGGSHELL: A NEW GEOCHRONOMETER FOR AFRICAN ARCHAEOLOGICAL SITES W. Sharp 1,*, N.D. Fylstra 1, C.A. Tryon 2, J.T. Faith 3, D.J. Peppe 4. 1 Berkeley Geochronology Center, USA; 2 Harvard University, USA; 3 University of Queensland, Australia; 4 Baylor University, USA. E-mail address: [email protected].
Obtaining precise and accurate dates can be challenging at African archaeological sites, especially those that lie beyond the range of radiocarbon dating. We report herein a promising new approach to U-series dating of ostrich eggshell (OES) fragments and beads that occur widely in African archaeological contexts. U-Th dating has about ten times the range of radiocarbon dating ~500 ka rather than 50 ka) and ancient OES are generally geochemically suitable for the U-Th technique. U in OES is acquired after burial but the burial age may be estimated from measured apparent ages if U uptake takes place by diffusion. Using OES from three Pleistocene-eHolocene east African sites, we have: (1) measured U concentration profiles of OES normal to their exterior surface (by laser ablation ICP-MS), (2) determined apparent U-Th ages on outer and inner layers of eggshells (by solution ICP-MS), and (3) calculated U-Th burial ages using a simple model for diffusive uptake of uranium. We have assessed our method by comparing the U-Th burial ages with radiocarbon dates for OES calcite from the same shells and find good
Abstracts / Quaternary International 404 (2016) 174e213
agreement in 9 out of 11 cases. Moreover, two corrupt U-Th dates reveal themselves via anomalous patterns of apparent ages, providing reliability criteria innate to the U-Th data. The oldest OES we have tried yielded apparently reliable U-Th burial ages of ~140 ka, indicating that this approach may be applicable throughout the Late Pleistocene. Keywords: U-Th dating, ostrich eggshell, late Pleistocene, geochronology, Middle Stone Age
199
overlying sediments. Having optimised measurement conditions and data analysis techniques to circumvent these problems, the Howiesons Poort layers yield ages consistent with the 64.8e59.5 ka chronology published by Jacobs et al. (2008). The implications of these findings for the ongoing debate concerning the age and duration of the Howiesons Poort technorin et al., logical complex (e.g. Jacobs et al., 2008, Tribolo et al., 2013, Gue 2013) will be discussed. Keywords: chronology, OSL, MSA, Howiesons Poort
DATING THE DESERT: A DECADE IN THE DARK WITH KALAHARI QUARTZ S. Burrough*, R.M. Bailey, D.S.G. Thomas. School of Geography and Environment, University of Oxford, UK. E-mail address: [email protected].
The sand mantled interior of southern Africa preserves in its landscape an intriguing and important record of past environmental change. The highly aerobic and oxidative sediment conditions of the Kalahari basin are however not favourable to organic preservation: understanding the nature and timescale of environmental change using conventional (and unconventional) proxies has therefore proved challenging. Luminescence dating has, for 20 years, provided an alternative, landscape dynamics perspective, directly dating the deposition of sedimentary quartz in the shorelines of huge, now-dry, lacustrine systems and enabling us to place a timeframe on to past periods of activity of dunefields that today remain stable and inactive. More than 700 OSL dates later, however, a number of issues arise that challenge the ability to develop a clear record of Late Quaternary landscape dynamics in the Kalahari. The lack of coherence from optically dated geoproxy records emerging from the Kalahari basin has been variously attributed to evolving techniques and the existence of poor quality data; sampling frequency, termites, tectonics and an incomplete understanding of the relationship between landscape activity and climatic conditions. Using new data from the Northern Kalahari, this paper outlines the limits of luminescence dating in the southern African interior and reports current progress on developing a reliable and robust optical chronology for Kalahari basin landforms and, importantly, a clear understanding of what exactly that chronology can and can't tell us about environmental change. Keywords: Kalahari, landscape dynamics, OSL, dunes
SINGLE-GRAIN OSL DATING OF THE HOWIESONS POORT LAYERS AT KLIPDRIFT SHELTER, SOUTHERN CAPE, SOUTH AFRICA S. Armitage 1, *, C.S. Henshilwood 2, 3, K.L. van Niekerk 2. 1 Royal Holloway University of London, UK; 2 Institute for Archaeology, History, Culture and Religious Studies, University of Bergen, Norway; 3 Evolutionary Studies Institute, University of the Witwatersrand, South Africa. E-mail address: [email protected].
Klipdrift Shelter in the De Hoop Nature Reserve, southern Cape, South Africa is part of a cave complex containing Later Stone Age and Middle Stone Age deposits. Excavations at Klipdrift Shelter yielded a lithic component consistent with the Howiesons Poort technological complex. The preliminary results from Klipdrift Shelter provide new insights into the Howiesons Poort and contribute further to ongoing knowledge about the complex behaviours of early Homo sapiens in southern Africa. However, the significance of the Klipdrift Shelter finds are dependent upon the temporal relationships between this and other Middle Stone Age sites in southern Africa. Single-grain OSL dating was applied to a suite of eight samples, spanning the Howiesons Poort layers at Klipdrift Shelter. Initial analysis indicated indicate inter-sample variability in the optimal preheating regime, a phenomenon also observed at Diepkloof Rock Shelter (Tribolo et al., 2013). In addition, some samples yielded complex equivalent dose distributions, consistent with either incomplete resetting of the OSL signal prior to burial, or the post-depositional incorporation of younger grains from
* Corresponding author.
References: Tribolo, Chantal, et al. (2013) “OSL and TL dating of the Middle Stone Age sequence at Diepkloof Rock Shelter (South Africa): a clarification.” Journal of Archaeological Science 40(9): 3401e3411. Jacobs, Z., Roberts, R.G., Galbraith, R.F., Deacon, H.J., Grun, R., Mackay, A., Mitchell, P., Vogelsang, R., Wadley, L., 2008. Ages for the Middle Stone Age of Southern Africa: Implications for Human Behavior and Dispersal, Science 322, 733e735. rin, G., Murray, A.S., Jain, M., Thomsen, K.J., Mercier, N., 2013. How Gue confident are we in the chronology of the transition between Howieson's Poort and Still Bay. Journal of Human Evolution 64, 314e317.
THE OLORGESAILIE DRILLING PROJECT (ODP): UNDERSTANDING THE LAST 1 MA OF PALAEOCLIMATE AND HUMAN EVOLUTION IN EAST AFRICA A. Deino*, R. Potts, R. Dommain, A.K. Behrensmeyer. Olorgesailie Drilling Project (ODP) Research Group, Kenya. E-mail address: [email protected].
The Olorgesailie Drilling Project (ODP) is an effort to directly link the outcrop geology of the famous and well-studied palaeoanthropological site of Olorgesailie, southern Kenya Rift, with a penecontemporaneous core removed from a nearby accumulation basin. The project is an international, multi-disciplinary consortium of geoscientists led by Dr. Rick Potts of the Smithsonian Institution. Olorgesailie has been investigated for many years, with a detailed outcrop record that covers the last 1.2 Ma, but parts of the section are missing due to erosion, non-deposition, and channelized deposition in the past ~500 ka. The Koora Plain, ~10e20 km south of Olorgesailie, was targeted for drilling for its potential to record a more continuous palaeoenvironmental record contemporaneous with deposition of latter half of the Olorgesailie sequence. In October, 2012, two cores reaching depths of 166 and 110 m, spaced ~1.5 km apart, were recovered from the Koora Plain. These cores have been characterized lithologically and sampled for a wide variety of palaeoenvironmental indicators (pollen, phytoliths, fungal spores, diatoms, ostracodes, isotope chemistry, plant biomarkers, charcoal, clay chemistry) as well as geochronological and geological studies (40Ar/39Ar dating, tephra geochemistry, palaeomagnetism, petrology). Microscopic analysis of 242 smear slide samples extracted from the longer core revealed a complex depositional sequence of deep lake phases rich in diatoms, volcanic ash layers, pure diatomites, shallow near shore phases, sandy fluvial deposits, pedogenically modified zones, and interspersed carbonate layers. Variable charcoal frequency indicates several periods of higher fire activity. Approximately 140 samples of tephra and trachytic basement lavas were sampled from the two cores. Initial 40Ar/39Ar dating results indicate, in the longest core, that the sequence extends from ~70 ka at the top, to ~1.07 Ma at basement lava floor underlying the sedimentary sequence. Age constraints derived from the more than 20 ArAr dates obtained so far will help construct a reliable age model for the cores. Keywords: Kenya, 40Ar/39Ar dating, Olorgesailie, Koora Plain, Pleistocene
HOLOCENE ECOSYSTEM, SOCIAL AND LANDSCAPE DYNAMICS IN EAST AFRICA E. Githumbi*, C.C. Mustaphi, R. Marchant. York Institute for Tropical Ecosystems (KITE), Environment Department, University of York, UK. E-mail address: [email protected].
Abstracts / Quaternary International 404 (2016) 174e213
East-west orientated valleys with extremely ephemeral modern channel flow are a significant landscape feature of northwest Namibia. Today these valleys are important sources of aeolian dust, as each year plumes during Berg wind events fertilise Atlantic waters off the Skeleton Coast. Here we provide an OSL chronology for silts from the Huab valley, demonstrating a temporally complex Holocene sequence of valley-wide infilling (with early phases associated with the African humid period?) and subsequent late Holocene entrenchment during confined channel flows. Age data affirm fluvial histories from the Hoanib system (Eitel et al 2006), but additionally provide an association with modern aeolian dynamics and dust-sourcing that points to the vital role of wet e accumulation as sourcing the aeolian systems of today's hyper-arid regime. Keywords: Holocene, valley fills, luminescence dating, aeolian dust References: Eitel, B., Kadereit, A., Blumel, W.-D., Huser, K., Lomax, J., Hilgers, A., 2006. Environmental changes at the eastern Namib Desert margin before and after the Last Glacial Maximum: new evidence from fluvial deposits in the upper Hoanib River catchment, northwestern Namibia. Palaeogeography, Palaeoclimatology, Palaeoecology 234, 201e222.
8. DATING AND CORRELATION OF AFRICAN ARCHIVES OF ENVIRONMENTAL CHANGE AND ARCHAEOLOGY SPATIAL AND TEMPORAL VARIATION IN NORTH AFRICAN PALAEOENVIRONMENTAL AND ARCHAEOLOGICAL RECORDS DURING MARINE ISOTOPE STAGE 4 L. Farr*, S. Jones. The McDonald Institute for Archaeological Research, University of Cambridge, UK. E-mail address: [email protected].
Marine Isotope Stage 4 (MIS4) covers the timeframe of c.74e59 ka and is generally regarded as a period of sudden and rapid climatic deterioration in North Africa. MIS4 is argued to coincide with regional decreases in population size and density in North Africa, possibly concomitant with retraction into refugia in certain locales. Sitting awkwardly against this picture is recent mtDNA evidence from living human populations which suggests that, approximately c.60 ka, Homo sapiens groups exited Africa in a successful migration that resulted in colonisation of Asia, Australia and Europe. These dispersals of Homo sapiens are usually attributed to humid climatic phases in MIS5 and MIS3, when hydrological networks are argued to have been reactivated in response to pluvial events, resulting in the wetting of normally arid regions such as the Sahara. This paper reviews palaeoenvironmental and archaeological data from marine and terrestrial archives in the North African region, which are dated to the MIS4 timeframe. We evaluate spatial and temporal variation in the datasets in relation to global climate records and investigate their reliability to inform us of millennial and sub-millennial environmental change, and demographic processes in North Africa. In particular, we look at the chronometric dating of palaeoenvironmental and archaeological datasets and investigate issues regarding chronological precision, spatial resolution and geoarchaeological context. We present geoarchaeological and lithic data from part of the Haua Fteah cave sequence (Libya) which has associated MIS4 dates, and discuss how these findings fit into a wider picture of regional environment change and human population dynamics. Keywords: MIS4, North Africa, dating, environment, geoarchaeology
* Corresponding author.
DEVELOPING A HOLOCENE TEPHROSTRATIGRAPHY OF ETHIOPIA C. Martin-Jones 1,*, C.S. Lane 2, H.F. Lamb 1, N.J.G. Pearce 1, V.C. Smith 3. Department of Geography and Earth Sciences, Aberystwyth University, UK; 2 Department of Geography, University of Manchester, UK; 3 RLAHA, University of Oxford, UK. 1
E-mail address: [email protected].
Ethiopia experiences a highly variable climatic regime, subject to the seasonal migration of the Inter-Tropical Convergence Zone (ITCZ) and monsoon variability. These climatic changes are recorded in Holocene lake sediments throughout the Ethiopian Rift Valley. Synchronizing widespread regional palaeoclimate archives requires accurate and precise chronological control. Explosive volcanic eruptions generate large volumes of volcanic ash (tephra) which may be transported over continental scales and deposited in sedimentary sequences rapidly. A tephra layer represents a time-parallel marker which can be used to link sedimentary archives. Tephra from the same eruption is traced between different sites on the basis of its unique geochemical ‘fingerprint’. Ultra-distal ‘non-visible’ cryptotephra layers are increasingly used to extend the geographical range over which palaeoenvironmental archives can be correlated. Many caldera forming eruptions occurred from East African Rift volcanoes during the early Holocene to late Pleistocene. The tephras deposited provide chronological control on Pleistocene Ethiopian palaeoanthropological sites. However, Holocene tephra deposits remain largely un-documented in Ethiopia. Lacustrine cores were collected from Ethiopian Rift lakes (Ashenge, Hayk, Dendi, Hora, Tilo, Awassa and Chamo) covering 50 cm thick tephras in Lakes Tilo and Awassa during ~ 700 e 9,800 cal yr BP. These tephras have a similar major element composition to those in Lake Hora sediments (250 km NE of Lake Tilo). Distal rhyolitic tephra, possibly originating from the Afar, were deposited in Lakes Ashenge and Hayk between ~ 5,400 e 14,500 cal yr BP. Further work is now required in order to test potential correlations between these lacustrine archives. The resulting tephrostratigraphy will provide a dossier of regional Holocene volcanism and allow temporal and spatial climatic changes in this region to be investigated. Keywords: tephrochronology, geochemistry
correlation,
palaeoclimate,
Ethiopia,
U-TH BURIAL DATING OF OSTRICH EGGSHELL: A NEW GEOCHRONOMETER FOR AFRICAN ARCHAEOLOGICAL SITES W. Sharp 1,*, N.D. Fylstra 1, C.A. Tryon 2, J.T. Faith 3, D.J. Peppe 4. 1 Berkeley Geochronology Center, USA; 2 Harvard University, USA; 3 University of Queensland, Australia; 4 Baylor University, USA. E-mail address: [email protected].
Obtaining precise and accurate dates can be challenging at African archaeological sites, especially those that lie beyond the range of radiocarbon dating. We report herein a promising new approach to U-series dating of ostrich eggshell (OES) fragments and beads that occur widely in African archaeological contexts. U-Th dating has about ten times the range of radiocarbon dating ~500 ka rather than 50 ka) and ancient OES are generally geochemically suitable for the U-Th technique. U in OES is acquired after burial but the burial age may be estimated from measured apparent ages if U uptake takes place by diffusion. Using OES from three Pleistocene-eHolocene east African sites, we have: (1) measured U concentration profiles of OES normal to their exterior surface (by laser ablation ICP-MS), (2) determined apparent U-Th ages on outer and inner layers of eggshells (by solution ICP-MS), and (3) calculated U-Th burial ages using a simple model for diffusive uptake of uranium. We have assessed our method by comparing the U-Th burial ages with radiocarbon dates for OES calcite from the same shells and find good
Abstracts / Quaternary International 404 (2016) 174e213
agreement in 9 out of 11 cases. Moreover, two corrupt U-Th dates reveal themselves via anomalous patterns of apparent ages, providing reliability criteria innate to the U-Th data. The oldest OES we have tried yielded apparently reliable U-Th burial ages of ~140 ka, indicating that this approach may be applicable throughout the Late Pleistocene. Keywords: U-Th dating, ostrich eggshell, late Pleistocene, geochronology, Middle Stone Age
199
overlying sediments. Having optimised measurement conditions and data analysis techniques to circumvent these problems, the Howiesons Poort layers yield ages consistent with the 64.8e59.5 ka chronology published by Jacobs et al. (2008). The implications of these findings for the ongoing debate concerning the age and duration of the Howiesons Poort technorin et al., logical complex (e.g. Jacobs et al., 2008, Tribolo et al., 2013, Gue 2013) will be discussed. Keywords: chronology, OSL, MSA, Howiesons Poort
DATING THE DESERT: A DECADE IN THE DARK WITH KALAHARI QUARTZ S. Burrough*, R.M. Bailey, D.S.G. Thomas. School of Geography and Environment, University of Oxford, UK. E-mail address: [email protected].
The sand mantled interior of southern Africa preserves in its landscape an intriguing and important record of past environmental change. The highly aerobic and oxidative sediment conditions of the Kalahari basin are however not favourable to organic preservation: understanding the nature and timescale of environmental change using conventional (and unconventional) proxies has therefore proved challenging. Luminescence dating has, for 20 years, provided an alternative, landscape dynamics perspective, directly dating the deposition of sedimentary quartz in the shorelines of huge, now-dry, lacustrine systems and enabling us to place a timeframe on to past periods of activity of dunefields that today remain stable and inactive. More than 700 OSL dates later, however, a number of issues arise that challenge the ability to develop a clear record of Late Quaternary landscape dynamics in the Kalahari. The lack of coherence from optically dated geoproxy records emerging from the Kalahari basin has been variously attributed to evolving techniques and the existence of poor quality data; sampling frequency, termites, tectonics and an incomplete understanding of the relationship between landscape activity and climatic conditions. Using new data from the Northern Kalahari, this paper outlines the limits of luminescence dating in the southern African interior and reports current progress on developing a reliable and robust optical chronology for Kalahari basin landforms and, importantly, a clear understanding of what exactly that chronology can and can't tell us about environmental change. Keywords: Kalahari, landscape dynamics, OSL, dunes
SINGLE-GRAIN OSL DATING OF THE HOWIESONS POORT LAYERS AT KLIPDRIFT SHELTER, SOUTHERN CAPE, SOUTH AFRICA S. Armitage 1, *, C.S. Henshilwood 2, 3, K.L. van Niekerk 2. 1 Royal Holloway University of London, UK; 2 Institute for Archaeology, History, Culture and Religious Studies, University of Bergen, Norway; 3 Evolutionary Studies Institute, University of the Witwatersrand, South Africa. E-mail address: [email protected].
Klipdrift Shelter in the De Hoop Nature Reserve, southern Cape, South Africa is part of a cave complex containing Later Stone Age and Middle Stone Age deposits. Excavations at Klipdrift Shelter yielded a lithic component consistent with the Howiesons Poort technological complex. The preliminary results from Klipdrift Shelter provide new insights into the Howiesons Poort and contribute further to ongoing knowledge about the complex behaviours of early Homo sapiens in southern Africa. However, the significance of the Klipdrift Shelter finds are dependent upon the temporal relationships between this and other Middle Stone Age sites in southern Africa. Single-grain OSL dating was applied to a suite of eight samples, spanning the Howiesons Poort layers at Klipdrift Shelter. Initial analysis indicated indicate inter-sample variability in the optimal preheating regime, a phenomenon also observed at Diepkloof Rock Shelter (Tribolo et al., 2013). In addition, some samples yielded complex equivalent dose distributions, consistent with either incomplete resetting of the OSL signal prior to burial, or the post-depositional incorporation of younger grains from
* Corresponding author.
References: Tribolo, Chantal, et al. (2013) “OSL and TL dating of the Middle Stone Age sequence at Diepkloof Rock Shelter (South Africa): a clarification.” Journal of Archaeological Science 40(9): 3401e3411. Jacobs, Z., Roberts, R.G., Galbraith, R.F., Deacon, H.J., Grun, R., Mackay, A., Mitchell, P., Vogelsang, R., Wadley, L., 2008. Ages for the Middle Stone Age of Southern Africa: Implications for Human Behavior and Dispersal, Science 322, 733e735. rin, G., Murray, A.S., Jain, M., Thomsen, K.J., Mercier, N., 2013. How Gue confident are we in the chronology of the transition between Howieson's Poort and Still Bay. Journal of Human Evolution 64, 314e317.
THE OLORGESAILIE DRILLING PROJECT (ODP): UNDERSTANDING THE LAST 1 MA OF PALAEOCLIMATE AND HUMAN EVOLUTION IN EAST AFRICA A. Deino*, R. Potts, R. Dommain, A.K. Behrensmeyer. Olorgesailie Drilling Project (ODP) Research Group, Kenya. E-mail address: [email protected].
The Olorgesailie Drilling Project (ODP) is an effort to directly link the outcrop geology of the famous and well-studied palaeoanthropological site of Olorgesailie, southern Kenya Rift, with a penecontemporaneous core removed from a nearby accumulation basin. The project is an international, multi-disciplinary consortium of geoscientists led by Dr. Rick Potts of the Smithsonian Institution. Olorgesailie has been investigated for many years, with a detailed outcrop record that covers the last 1.2 Ma, but parts of the section are missing due to erosion, non-deposition, and channelized deposition in the past ~500 ka. The Koora Plain, ~10e20 km south of Olorgesailie, was targeted for drilling for its potential to record a more continuous palaeoenvironmental record contemporaneous with deposition of latter half of the Olorgesailie sequence. In October, 2012, two cores reaching depths of 166 and 110 m, spaced ~1.5 km apart, were recovered from the Koora Plain. These cores have been characterized lithologically and sampled for a wide variety of palaeoenvironmental indicators (pollen, phytoliths, fungal spores, diatoms, ostracodes, isotope chemistry, plant biomarkers, charcoal, clay chemistry) as well as geochronological and geological studies (40Ar/39Ar dating, tephra geochemistry, palaeomagnetism, petrology). Microscopic analysis of 242 smear slide samples extracted from the longer core revealed a complex depositional sequence of deep lake phases rich in diatoms, volcanic ash layers, pure diatomites, shallow near shore phases, sandy fluvial deposits, pedogenically modified zones, and interspersed carbonate layers. Variable charcoal frequency indicates several periods of higher fire activity. Approximately 140 samples of tephra and trachytic basement lavas were sampled from the two cores. Initial 40Ar/39Ar dating results indicate, in the longest core, that the sequence extends from ~70 ka at the top, to ~1.07 Ma at basement lava floor underlying the sedimentary sequence. Age constraints derived from the more than 20 ArAr dates obtained so far will help construct a reliable age model for the cores. Keywords: Kenya, 40Ar/39Ar dating, Olorgesailie, Koora Plain, Pleistocene
HOLOCENE ECOSYSTEM, SOCIAL AND LANDSCAPE DYNAMICS IN EAST AFRICA E. Githumbi*, C.C. Mustaphi, R. Marchant. York Institute for Tropical Ecosystems (KITE), Environment Department, University of York, UK. E-mail address: [email protected].