A terrestrial reconstruction of Gona, Ethiopia before and during the African Humid Period

The African Humid Period (AHP) resulted in more humid conditions across Northern and Eastern Africa from 15 to 5 thousand years ago (ka). This wetter climate affected flora, fauna and the Homo sapiens living in East Africa. The lack of terrestrial paleoenvironmental reconstructions is a problem in East Africa, especially during the AHP, where most are done utilizing lacustrine or marine proxies. In the case of Gona, Ethiopia, terrestrial proxies are desired due to the rich archaeological and fossil concentrations that occur in the area. Paleosols provide more direct, localized reconstructions that provide context for these finds. This study utilizes paleopedology, geochronology, and geochemistry to reconstruct the environment of Gona during the AHP. We examine paleosols from the Erole and Odele drainages within Gona. The Odele paleosol weathered before the AHP, between the Korina Tuff (\u3c39 \u3eka) and the Kilaitoli Tuff (~25.7 ka). The Erole paleosol is above the Kilaitoli Tuff and immediately above a calibrated 14C age of 12 ka. These paleosols formed in floodplains of tributaries that flowed into the nearby Awash River. Strain calculations show more volumetric collapse at Erole (-39 ± 8 %) than at Odele (-5 ± 4 %). The open-system mass-transfer coefficient, tau, shows average losses of 25 ± 13 % SiO2 and 71 ± 6 % CaO at Erole, which are greater than losses of 8 ± 4 % SiO2 and 7 ± 3 % CaO at Odele. These calculations suggest more weathering and dissolution of minerals during the AHP, as well as more bioturbation. The results of this paleosol comparison are consistent with wetter conditions during the AHP that facilitated the development of grasslands along tributary valleys

Climatic and human influences on Holocene alluvial history and paleoenvironment of the middle Delaware River Valley, USA.

The potential for future prolonged drought episodes in the Northeastern USA is alarming given that a humid climate currently provides water to +50 million people in the northeast, USA. Hydro-climatic projections are hampered by a lack of regionally-based paleoenvironmental reconstructions. The middle Delaware River Valley provides a unique opportunity to expand the Holocene alluvial history and paleoenvironment for the northeast, USA. Thirty-six soil profile descriptions, 332 grain size analyses, and 82 14C ages from trenches and auger borings show that similar alluvial landforms within the river valley have different formation histories and depict a valley that has experienced middle to late Holocene floodplain and terrace reworking. Despite erosion, secular changes in buried soil and sediment properties are closely associated with climate change and land-use. A Holocene time-series was constructed using 149 δ13Csom values from alluvial terrace profiles. There is good agreement between increasing δ13Csom and Panicoideae phytolith concentrations, suggesting that variations in C4 biomass are a contributor to changes in the soil δ13C. A measurement error deconvolution curve over time reveals two isotope stages (II and I), with nine sub-stages exhibiting variations in average δ13Csom (%C4). Stage II, ~10.7-4.3 ka, shows above average δ13Csom (increase %C4) values with evidence of an early Holocene warm/dry interval (sub-stage IIb, 9.8-8.3 ka) that coincides with rapid warming and cool/dry abrupt climate change. Sub-stage IId, 7.0-4.3 ka, is an above average δ13Csom (increase %C4) interval associated with the mid-Holocene warm/dry Hypsithermal. The Stage II-I shift at 4.3 ka documents a transition toward below average δ13Csom (decrease %C4) values, coinciding with decreasing insolation and moisture budget reorganization. Sub-stages Ib and Id (above average %C4) coincide with the first documented occurrence of maize in northeastern USA and population increase during the Late Woodland. These associations suggest that humans influenced δ13Csom during the late Holocene. The influence of land-use is further corroborated by a regionally extensive anthropogenic sedimentation event documented throughout eastern North America, pre-Colonial sediment (PCS) circa: A.D. 1,100–1,600. These data demonstrate that combined prehistoric land-use and climate change impacted eastern North American floodplains several hundred years prior to the onset of European Settlement.Ph.D

Site Formation Processes of the Yaalu Archaeological Site during a Period of Anatomically Modern Human Migration

Gona, Ethiopia’s sedimentary record spans six million years, containing hominin specimens from Ardipithecus ramidus to Homo sapiens. This record also contains paleosols, or fossilized soil horizons, that provide terrestrial paleoenvironmental reconstructions for archaeological and paleoanthropological sites. A terrestrial-based climate record for East Africa is largely incomplete, as most reconstructions are performed using lacustrine or marine proxies, which fail to deliver a specific, localized reconstruction for hominins, terrestrial mammals. Geologic mapping, sampling, and lab analysis performed using paleosols and other sedimentary deposits from Gona show fluctuation in climate, as wet and dry periods are evident throughout. Recent research suggests that changing climates help to drive and facilitate human evolution and migration, but little is known about Anatomically Modern Human (AMH) migration due to spatially and temporally incomplete records. Ongoing stratigraphic work at Gona shows a high-resolution, intact record of environmental change. A newly discovered site at Yaalu yields a Homo sapiens cranium as well as other fossils and artifacts dating to 85-70 thousand years ago (ka). This corresponds with evidence of AMH migration out of Africa, with Homo activity appearing in the Levant during this time. No geoarchaeological work has been done at Yaalu. A detailed analysis of the site formation processes will tell the story of the climate and environmental conditions of Yaalu before, during, and after the occupation using sediments gathered from a “megatrench” in 2020. Evidence of the Toba supereruption in present day Indonesia, which occurred ~75 ka, may also be present in sediments. The impact of this event on East African populations is relatively unknown, and an isotopic analysis will be performed using sediments collected from this megatrench. These geoarchaeological analyses give a context that is crucial to the understanding of human cultural activities and migration patterns in East Africa at a time period with few archaeological and environmental records

Searching for evidence of a global catastrophe in the East African Rift Basin: Did the Toba supereruption alter paleoflora at Gona, Ethiopia?

Approximately 75,500 (+/- 900) years ago, the largest supereruption of the Late Pleistocene occurred in Sumatra, Indonesia. This explosion introduced ~1015 grams of fine ash into the atmosphere, produced ~3000 km3 of magma, and pyroclastic flows carpeted a ~105 km2 radius around the epicenter of the eruption. All flora and fauna within a 350 km radius were annihilated, and the enormous amount of ash that was aerosolized into the atmosphere is thought to have increased the Earth’s average albedo, which is speculated to be a possible catalyst for a period of global cooling. The advent of the Toba supereruption coincides with a period of Anatomically Modern Human (AMH) migration out-of-Africa. While recent studies show that the effects from the “environmental catastrophe” observed in Sumatra likely did not significantly alter the environments of East Africa during this time, there are only two comprehensive studies of cryptotephra (microscopic ash) layers from the Toba volcano in the East African Rift System, only one of which focuses on the variability in vegetation pre- and post-eruption. Additionally, both of those studies are focused on localities in Lake Malawi, records of which are sourced from lacustrine cores. As AMH are terrestrial-based mammals, and only passively interact with lacustrine environments, the question then arises, How did the vegetation in terrestrial areas with AMH activity change pre- and post-Toba supereruption? The answer to this question may lie in the sediments and soils of Gona, Ethiopia, a significant paleoanthropological project area that contains an abundance of Early and Middle-to-Late Pleistocene archaeological and hominin fossil sites, fluvial sediments and soils, and a well-constrained chronostratigraphic record. Yaalu (11° 3\u27 51.55 N, 40° 25\u27 23.12 E), a paleoanthropological site in Gona, has strata that have been dated to 85-70ka. During the 2020 field season, an undergraduate assistant and I will scout the area for an outcrop or series of outcroppings that encompass the full strata. Once a suitable site is located, a step-trench will be dug down-section to reveal the underlying strata. Individual soil horizons will be characterized, and oriented samples that encompass the full scope of the trench will be extracted. Sediment and soil samples will then be examined for evidence of cryptotephra, and phytoliths, silicic imprints of cellular structures from flora, will be extracted and characterized. Phytoliths will be point-counted, and percent relative abundance calculations will be derived from total phytolith count, alongside the starting dry weight. Namely, the tree cover and aridity indexes will be utilized, to see the change in low elevation semi-deciduous forests, and the expansion or contraction of riparian grass communities in the area. This study will allow us to see examine the variability of flora (or lack thereof) at Gona during a critical period of early human development. If phytolith assemblages significantly change, or if the overall concentration of phytoliths decreases at Yaalu post-Toba, then one could infer that the Toba supereruption was a catalyst for, at the very least, minimal change within Gona’s ecosystem

Evidence of Late Pleistocene and Holocene paleo-Critical Zones at Gona, Ethiopia

The African Humid Period (AHP), spanning a period of approximately 12-5 ka, resulted in Northern and Eastern Africa being wetter than today and had notable impacts on flora, fauna, and humans. Much of the work pertaining to the AHP across Eastern Africa utilizes lacustrine and marine proxies rather than fluvial. Gona, located in the Afar region of Ethiopia, is known for its extensive archaeological and fossil records in fluvial deposits. However, the paleoenvironments of the AHP at Gona have not been investigated. This study uses stratigraphy, geochronology, and paleopedology to reconstruct the Late Pleistocene and AHP paleoenvironments, i.e., paleo-Critical Zones. We examine two paleosols, the Odele and Erole paleosols, located in the Asbole study region of Gona. The Odele paleosol is between the Korina Tuff (\u3c39 ka) and the Kilaitoli Tuff (~25.7 ka) and weathered during late-stage MIS-3 and MIS-2. The Erole paleosol, a relict soil that weathered during the AHP, is ~15 m above the Kilaitoli Tuff and immediately above a calibrated 14C age of 12 ka. Both paleosols formed along paleo-tributaries of the ancestral Awash River, as only matrix-supported gravels are found. The Erole paleosol displays consistently darker Munsell values than the Odele paleosol. Average strain calculations using paleosol geochemistry show a volumetric collapse on the order of 34 ± 4% in the Erole paleosol and little to no dilation/collapse in the Odele paleosol, 0 ± 2%. Calculations of open-system mass transport of elements through the profiles (Tau) show an 18 ± 7% loss of SiO2 and a 69 ± 5% loss of CaO in the Erole paleosol, which are greater than the 2 ± 1% loss of SiO2 and 1 ± 3% loss of CaO in the Odele paleosol. These strain and tau results suggest more intense weathering and elemental loss in the Erole paleosol. These results are consistent with recent paleoclimate reconstructions, and we infer that the collapse and elemental loss in the Erole paleosol are due to a period of increased rainfall during the AHP than the preceding MIS-3 and MIS-2 tim

Paleopedology associated with the rise and dispersal of Anatomically Modern Humans at Gona, Ethiopia

Geologists and paleoanthropologists continue to debate the onset, development, and rate of change of out-of-Africa dispersals by Anatomically Modern Humans (AMH). Climatic and environmental variability is often inferred to be the catalysts of these migrations, yet the precise context of these dispersals, including climate effects on local flora and fauna, remains unclear. This study addresses this uncertainty by examining a series of eleven fossilized soils (paleosols) that range in age from the Middle Pleistocene (~570 ka) to present at Gona, Ethiopia, a significant paleoanthropological area that has abundant archaeological and AMH fossil sites. Paleosols provide an ideal archive for reconstructing the localized changes in paleoenvironment and paleoclimate associated with Gona’s archaeological and fossil sites, as they are a reservoir of biogeochemical dynamics related to the surrounding environment. Initial morphological observations from the paleosols of the Yaalu (~80 ka) and Erole (12 ka) fossil sites show the presence of soil carbonate and shrink-swell features indicative of seasonal climate. Bulk geochemical data supports these observations, with the Yaalu paleosols yielding average mean annual precipitation (MAP) and temperature (MAT) values of 723 mm/yr (± 108) and 14.0°C (± 4.4), with Erole paleosols yielding average MAP and MAT values of 832 mm/yr (± 108) and 13.3°C (± 4.4), respectively. These data will continue to be expanded upon and will encompass eight archaeological and fossil localities in eleven different sites. Although these results are preliminary, this growing dataset will compliment more regional-scale paleoenvironmental and paleoclimate records when interpreting the forcings and responses of Out-of-Africa migrations

Reconstruction of Late Pleistocene Paleoenvironments Using Bulk Geochemistry of Paleosols from the Lake Victoria Region

The impact of changing environments on the evolution and dispersal of Homo sapiens is highly debated, but few data are available from equatorial Africa. Lake Victoria is the largest freshwater lake in the tropics and is currently a biogeographic barrier between the eastern and western branches of the East African Rift. The lake has previously desiccated at ~17 ka and again at ~15 ka, but little is known from this region prior to the Last Glacial Maximum. The Pleistocene terrestrial deposits on the northeast coast of Lake Victoria (94–36 ka) are ideal for paleoenvironmental reconstructions where volcaniclastic deposits (tuffs), fluvial deposits, tufa, and paleosols are exposed, which can be used to reconstruct Critical Zones (CZ) of the past (paleo-CZs). The paleo-CZ is a holistic concept that reconstructs the entire landscape using geologic records of the atmosphere, hydrosphere, lithosphere, biosphere, and pedosphere (the focus of this study). New paleosol-based mean annual precipitation (MAP) proxies from Karungu, Rusinga Island, and Mfangano Island indicate an average MAP of 750 ± 108 mm year−1 (CALMAG), 800 ± 182 mm year−1 (CIA-K), and 1,010 ± 228 mm year−1 (PPM1.0) with no statistical difference throughout the 11 m thick sequence. This corresponds to between 54 and 72% of modern precipitation. Tephras bracketing these paleosols have been correlated across seven sites, and sample a regional paleo-CZ across a ~55 km transect along the eastern shoreline of the modern lake. Given the sensitivity of Lake Victoria to precipitation, it is likely that the lake was significantly smaller than modern between 94 and 36 ka. This would have removed a major barrier for the movement of fauna (including early modern humans) and provided a dispersal corridor across the equator and between the rifts. It is also consistent with the associated fossil faunal assemblage indicative of semi-arid grasslands. During the Late Pleistocene, the combined geologic and paleontological evidence suggests a seasonally dry, open grassland environment for the Lake Victoria region that is significantly drier than today, which may have facilitated human and faunal dispersals across equatorial East Africa

The persistence of salt-affected paleosols at Gona, Ethiopia: A sedimentary archive of Middle to Late Pleistocene soil salinity within a corridor of early human migration

The origin of Homo sapiens and their subsequent dispersal out of Africa during the Mid-to-Late Pleistocene are hallmark events in the evolution of humans and are recorded as snapshots within terrestrial sedimentary deposits in East Africa. This study uses paleosols to reconstruct paleoenvironments of those events at Gona, Ethiopia - an area with one of the most continuous records of East African Paleolithic and Neolithic archaeology. A preliminary survey of Gona paleosols from the past 250,000 years shows a wide range of paleosol types that resemble modern-day Entisols, Inceptisols and Vertisols. Approximate paleosol ages were estimated using nearby OSL, 14 C, U-series, 40 Ar/ 39 Ar and volcanic glass chemistry. The pH and EC of these paleosols were measured as they are weakly compacted and show few signs of diagenesis. Mean pH values are slightly alkaline (7.8 ±0.63) and mean EC values (9.8 ±7.9) are saline, suggesting salt-affected soil development. The high standard deviation of EC results from low-EC sodic soils found in some units. These pH and EC findings are consistent with bulk geochemical-based pedotransfer functions on paleo-Vertisols, which indicate the presence of saline and sodic conditions. Much like modern-day tributary and trunk-channel floodplains, these paleosols likely hosted halophytes like Tamarix, Vachellia and salt-tolerant grasses, flora which are commonly found at present-day Gona. Notably, some late Pleistocene salt-affected paleosols that coincide with Marine Isotope Stage 5 and the African Humid Period show signs of prolonged soil saturation and nearby standing water. High evapotranspiration due to Gona’s semi-arid climate likely resulted in low infiltration and subsurface drainage of water, insufficient to transport salt out of the system, resulting in abundant saline soil formation at the site. The high salinity of Mid-to-Late Pleistocene Gona paleosols, likely due to source material, climate, and drainage, limits the use of many bulk geochemical proxies that were developed using mostly normal, non-saline soils. Despite this, the results of this study shed light on the climate and environment of our ancestors at the pedon scale