JCSET | Watershed Studies Institute Research Symposium

Title

Reconstructing the dynamic Middle to Late Pleistocene hominin environments of Gona, Ethiopia: A fossil soil-based study

Academic Level at Time of Presentation

Graduate

Major

Earth and Environmental Sciences

List all Project Mentors & Advisor(s)

Gary Stinchcomb, PhD

Presentation Format

Oral Presentation

Abstract/Description

What drove dispersals of Homo sapiens out of Africa? Reconstructing the Critical Zones (CZs) with which our early ancestors interacted over time is an essential step toward addressing this question. The well-preserved fossil soils, or paleosols found in the sedimentary record at Gona, Ethiopia, contain a geochemical archive of our past environments, alongside one of the most comprehensive East African records of hominin-related archaeology and a well-constrained chronostratigraphic history.

Ten paleosol profiles near hominin fossil and artifact sites that range in age from 380 to 11 ka were analyzed to reconstruct the paleo-CZs of Gona. These ten fine-grained paleosols weathered mixed alluvium and had vertic features. δ13C values (-2.40 to -7.77 +/- 0.16 ‰) derived from pedogenic soil carbonate are consistent with previous studies that show that paleo-Vertisols with this range of isotopic values at Gona likely developed within an open floodplain, dominated by riparian grassland. The constant landscape position provides this study with a control, allowing us to track changes in climate, organisms, and duration of soil formation over time. Characterization of these paleosols revealed two distinct paleosol types (i.e., pedotypes): Alsa (“Moon” in the Afar language) and Ayro (“Sun” in Afar). Alsa paleosols were darker colored with mean soil organic carbon (SOC) of 0.92 wt. %; whereas, Ayro paleosols were lighter and had lower mean SOC of 0.14 wt. %. Mass-balance geochemistry of total soil P, an essential plant nutrient, shows an average of >100 % gain in the darker Alsa paleosols compared to the lighter Ayro paleosols. Total Ca loss was greater in the Alsa (-66 %) than Ayro (-42 %), whereas total Mg loss was minimal in the Alsa (0 %), and Ayro showed Mg gain (27 %). Consistent with Ca loss, mean inorganic carbon of the <2 mm fraction is lower in Alsa (0.22 wt. %) than Ayro (0.63 wt. %).

Overall, these data infer that the Alsa paleosol was more productive, experiencing more biogeochemical cycling of plant nutrients. Additionally, paleo-rainfall estimates and age-modeling suggest that the Alsa paleosols weathered under wetter climates during known pluvials. This record of Middle to Late Pleistocene floodplain CZs at Gona provides evidence of climate-influenced changes on land occupied by early humans.

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Watershed Studies Institute Symposium

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Reconstructing the dynamic Middle to Late Pleistocene hominin environments of Gona, Ethiopia: A fossil soil-based study

What drove dispersals of Homo sapiens out of Africa? Reconstructing the Critical Zones (CZs) with which our early ancestors interacted over time is an essential step toward addressing this question. The well-preserved fossil soils, or paleosols found in the sedimentary record at Gona, Ethiopia, contain a geochemical archive of our past environments, alongside one of the most comprehensive East African records of hominin-related archaeology and a well-constrained chronostratigraphic history.

Ten paleosol profiles near hominin fossil and artifact sites that range in age from 380 to 11 ka were analyzed to reconstruct the paleo-CZs of Gona. These ten fine-grained paleosols weathered mixed alluvium and had vertic features. δ13C values (-2.40 to -7.77 +/- 0.16 ‰) derived from pedogenic soil carbonate are consistent with previous studies that show that paleo-Vertisols with this range of isotopic values at Gona likely developed within an open floodplain, dominated by riparian grassland. The constant landscape position provides this study with a control, allowing us to track changes in climate, organisms, and duration of soil formation over time. Characterization of these paleosols revealed two distinct paleosol types (i.e., pedotypes): Alsa (“Moon” in the Afar language) and Ayro (“Sun” in Afar). Alsa paleosols were darker colored with mean soil organic carbon (SOC) of 0.92 wt. %; whereas, Ayro paleosols were lighter and had lower mean SOC of 0.14 wt. %. Mass-balance geochemistry of total soil P, an essential plant nutrient, shows an average of >100 % gain in the darker Alsa paleosols compared to the lighter Ayro paleosols. Total Ca loss was greater in the Alsa (-66 %) than Ayro (-42 %), whereas total Mg loss was minimal in the Alsa (0 %), and Ayro showed Mg gain (27 %). Consistent with Ca loss, mean inorganic carbon of the <2 mm fraction is lower in Alsa>(0.22 wt. %) than Ayro (0.63 wt. %).

Overall, these data infer that the Alsa paleosol was more productive, experiencing more biogeochemical cycling of plant nutrients. Additionally, paleo-rainfall estimates and age-modeling suggest that the Alsa paleosols weathered under wetter climates during known pluvials. This record of Middle to Late Pleistocene floodplain CZs at Gona provides evidence of climate-influenced changes on land occupied by early humans.