SEDIMENTOLOGY AND STRATIGRAPHY OF EARLY MIOCENE HOMINOID-BEARING STRATA AT MORUOROT, WEST TURKANA, KENYA

The Lothidok Formation of West Turkana, Kenya, preserves fossiliferous strata of the Early and Middle Miocene. Prior work established a stratigraphic framework for the Lothidok Formation, yet detailed paleoenvironmental analyses have yet to be carried out. This study focuses on outcrops associated with the Moruorot fossil localities, which span three stratigraphic members: the Moruorot, Kalodirr, and Naserte Members. We characterized sedimentary deposits in terms of facies associations, and ongoing laboratory analyses will include geochemical and petrographic analyses. The Moruorot Member contains alluvial fan and fluvial channel deposits interspersed with red sandstone to mudstone floodplain paleosols. Only the upper portion of the Moruorot Member contains volcanic ash and lahar deposits, the latter of which tend to plug fluvial channels and/or drape attached floodplain fines. The transition to the Kalodirr Member is gradual and marked by a substantial increase in reworked tuffs and lahars. These tuffs commonly contain ripple lamination, dewatering structures, raindrop impressions, and trackways, suggesting fluvial reworking shortly after deposition. The transition to the Naserte Member is gradual and defined by an increase in pumice clasts in fluvial deposits, airfall tuffs, and sand-dominated fluvial channels. Stable landscapes (represented by paleosols) are rare throughout the stratigraphy, though the few paleosols present in the Moruorot Member suggest humid and seasonal paleoclimate conditions. Fossils primarily occur in lower energy fluvial sandstones capping paleosols in the Moruorot Member, though large, broken bone fragments are found in conglomerates. Relatively few fossils occur in the Kalodirr Member at the Moruorot localities, in contrast to the highly fossiliferous Kalodirr fossil localities roughly 15 km to the northwest. Overall, the stratigraphic trends observed at Moruorot suggest that sedimentary changes were largely triggered by variations in volcanic activity and source, and no clear evidence for changing climate or biome are evident from the archives we observed.