T40 Creative Contributions in Volcanology and Petrology: In Honor of Katharine V. Cashman, Recipient of the 2023 Distinguished Geological Career Award from the Mineralogy, Geochemistry, Petrology and Volcanology Division (Posters)

Sunday, 15 October 2023
8:00 AM - 5:30 PM
Hall B

GEOCHEMICAL ANALYSIS OF TUFFS AT THE ARDIPITHECUS RAMIDUS SITE AT ARAMIS, ETHIOPIA

Paper number: T40-9
Program: Technical Sessions
Time: 8:00 AM – 5:30 PM

Authors

  • William C. Kilgore Presenting Author
    Western Kentucky University, BOWLING GREEN, KY
  • M. Royhan Gani
    Western Kentucky UniversityEarth, Environ, & Atmospheric Sciences, Bowling Green, KY
  • Nahid Gani
    Western Kentucky University, Bowling Green, KY

Abstract

Three tuff layers were sampled from the Lower Aramis Member at Aramis, Ethiopia, where the in-situ skeleton of Ardipithecus ramidus (4.4 Ma old) was excavated. These tephra layers that bracketed the basal hominin fossil are intercalated with floodplain mudstones and sandstones. From older to younger, these tuffs include the 1+ m thick Gaala Tuff Complex (GATC), an unnamed tuff that is 20 cm thick, and the 10 cm thick Daam Aatu Basaltic Tuff (DABT). According to previous publications, the GATC and DABT have statistically indistinguishable 40Ar/39Ar dates of 4.4 Ma.

This on-going study uses electron microprobe, SEM microscopy, Raman microscopy, and thin-section petrography to investigate geochemical signatures of these tuff layers. Results of the electron microprobe analysis are compiled to make a number of bivariate plots like iron (III) oxide against aluminum oxide, calcium oxide, and titanium oxide. SiO2, Na2O and K2O contents are also assessed, particularly to characterize the unnamed tuff. These analyses suggest that the unnamed tuff is predominantly trachytic in character. Three tuff layers are largely indistinguishable from each other in the bivariate plots (Fe2O3 vs Al2O3, Fe2O3 vs CaO, and Fe2O3 vs TiO2). Whereas TiO2 vs Cl plot is found effective in distinguishing these tephra layers. Geochemical fingerprints of these tuffs can be useful in correlating these event beds with tephra layers in other hominin fossil sites in East Africa.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-393566

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