OLIGOCENE CHARACTERISTICS OF AFRO-ARABIAN HABITATS: NEW EVIDENCE FROM PALEOSOLS OF THE SHUMAYSI FORMATION, WESTERN SAUDI ARABIA

Recent investigation of terrestrial sediments from the upper part of the Shumaysi Formation, exposed along the Red Sea coast at Harrat Al Ujayfa, western Saudi Arabia, led to the discovery of new vertebrate fossil localities. These localities have yielded a terrestrial mammalian fauna which includes hyraxes, embrithopods, proboscideans, artiodactyls, and primates. Primate Saadanius hijazensis is of particular interest because it is an advanced stem catarrhine that shares a tubular ectotympanic with crown catarrhines, and therefore is likely close to the common ancestry of Old World monkeys, apes, and humans. Despite the significant body of research on the stratigraphy of Afro-Arabian Paleogene sites, little work has been done to characterize the environmental contexts of the Arabian subcontinent during the Oligocene. New work has been undertaken in the magnetostratigraphy, paleopedology, geochemistry, and phytolith biostratigraphy of the Harrat Al Ujayfa (the type locality of Saadanius hijazensis), where the Shumaysi Formation exposes a 73-meter section of fluvially deposited siltstones and sandstones with significant evidence of pedogenesis. High-resolution magnetostratigraphic sampling through the formation indicates that the section was deposited during the latest early or early late Oligocene (latest Rupelian to early Chattian, roughly 30-25 Ma). Field identification of paleosols indicate a suite that includes primarily Alfisols and Ultisols, most of which exhibit significant redoximorphic features and Bt horizons. Together these indicate a floodplain paleoenvironment with significant soil development, consistent with humid, forested conditions. Trends from carbon isotope stratigraphy showing lighter δ¹³C values, whole rock geochemical results indicating moderate mean annual temperatures and higher precipitation, and phytolith assemblage compositions that record primarily forest habitats all indicate environmental continuity and the extension of these habitats across Afro-Arabia during this time period. The upper Shumaysi Formation accommodated the widespread expansion of ecosystems that dominated a large landmass during a time when Africa and Arabia were contiguous, with forest habitats similar to those recorded in the earliest Oligocene in Egypt and Oman.