Ohio University faculty will make an impact with 23 presentations at the Geological Society of America’s 125th Anniversary Annual Meeting & Exposition Oct. 27–30 in Denver.
Pat O’Connor, Nancy Stevens, Eric Roberts, Joe Sertich, Eric Gorscak of the Department of Biomedical Sciences, present on UNCOVERING THE CRETACEOUS TERRESTRIAL VERTEBRATE RECORD OF SUB-SAHARAN AFRICA: NEW INFORMATION FROM THE MIDDLE CRETACEOUS GALULA FORMATION, RUKWA RIFT BASIN (EAST AFRICAN RIFT SYSTEM), SOUTHWESTERN TANZANIA
The Cretaceous terrestrial vertebrate record from the Southern Hemisphere has improved dramatically over the past 20 years. Nonetheless, large gaps remain with regard to major regions of Gondwana. Principal among the latter is Afro-Arabia, the large, central portion of the former supercontinent. Whereas the northern half of this landmass preserves both marine and continental sequences of Cretaceous age and yields a respectable fossil record, the southern half of the continent does not. During this time most of southern Africa existed as a stable platform with the development of minimal accommodation space, resulting in few significant continental deposits and any associated fossils. Hence, any new information from this fossil-depauperate region will have immediate impact for evaluating paleobiogeographic models, not to mention providing a basis for characterizing how large-scale landform dynamics (e.g., rifting, uplift) and any climatic sequelae have influenced biotic evolution during the Cretaceous. Annual expeditions since 2002 to the Rukwa Rift Basin in southwestern Tanzania have resulted in the recovery of a novel and diverse Cretaceous terrestrial vertebrate fauna from the middle Cretaceous Galula Fm. These expeditions have revealed extensive outcrops with vertebrate fossils along a series of drainages excising through rift flank sequences. Fossils recovered to date represent of all major vertebrate clades, including fishes, crocodyliforms, dinosaurs, and the most complete mammal yet recovered from Continental Africa. Notable among them are 4 taxa each of saurischian dinosaurs and notosuchian crocodyliforms, both of which represent ideal groups for integrating into current models aimed at understanding large-scale biogeographic patterns. Specifically, the presence of both notosuchian crocodyliforms and titanosaurian sauropods that are most closely related to geographically proximate clademates from the Dinosaur Beds of Malawi suggests a regional endemism signal during the middle Cretaceous. Ongoing work will further constrain a number of novel tectono-sedimentary relationships in the region and characterize the developing faunas, floras, and paleoenvironments for integration into biogeographic and climatic models related to the Cretaceous of Gondwana.
Nancy Stevens, Pat O’Connor, Eric Roberts also present CONTINENTAL VERTEBRATES FROM THE LATE OLIGOCENE NSUNGWE FORMATION (SOUTHWESTERN TANZANIA) AND FAUNAL DYNAMICS IN SUB-SAHARAN AFRICA DURING THE PALEOGENE-NEOGENE TRANSITION.
Field and laboratory studies of Red Sandstone Group strata in the Rukwa Rift of southwestern Tanzania document a complex basin history with at least three time-distinct tectonic and depositional events, represented by alluvial fans transitioning into fluvial and lacustrine depositional environments during the Cenozoic. Localities in the late Oligocene Songwe Member of the Nsungwe Formation predominantly preserve microfauna including rodents, macroscelideans, hyracoids, and small strepsirrhine and anthropoid primates, together with crocodylians, lepidosaurians, anurans, and a variety of invertebrates. These facies are dated at ~25 MYA using both radiometric dating of intercalated tuffs and detrital zircon geochronology. The Nsungwe 2B locality has revealed an increasingly diverse array of specimens including fossils commonly found in other localities such as micromammals, fishes, invertebrates and anurans, in addition to many larger specimens including two new catarrhine primate taxa. Nsungwe Formation discoveries offer a glimpse at the evolutionary history of late Oligocene terrestrial and freshwater habitats in eastern Africa, providing data on the complex tectono-sedimentary history of the Rukwa Rift Basin. Continued exploration offers a new window into the Paleogene-Neogene transition on continental Africa, with expanded opportunities for recognizing paleobiological diversity by sampling different habitat types within the region.
Hannah Hilbert-Wolf, Eric Roberts, Cassy Mtelela, Pat O’Connor, & Nancy Stevens present CONSTRAINING THE TIMING OF CENOZOIC RIFTING AND BASIN DEVELOPMENT IN THE RUKWA RIFT BASIN OF THE EAST AFRICAN RIFT SYSTEM VIA DETRITAL ZIRCON GEOCHRONOLOGY.
Preliminary zircon analyses (U/Pb ages via LA-ICPMS; n=~1,000) from a suite of samples spanning the spatial and temporal extent of the Lake Beds megasequence, the youngest sedimentary package in the Rukwa Rift Basin of the western branch of the East African Rift System in Tanzania, reveal a maximum depositional age of ~7 Ma. Our new data suggests the initiation of a late Cenozoic rifting event, further constraining the timing of rifting and basin development in the western branch. These results complement recent work that confirms active volcanism and topographic uplift in the Rukwa Rift Basin ~25 Ma, signaling the contemporaneous development of the western and eastern rift branches. The nature of sedimentary fill in a rift basin depends on climate, provenance, and subsidence rates. Since extensional events in the East African Rift System are marked by sedimentation and magmatism, the age and provenance of both detrital and tuffaceous zircons from the Rukwa Rift Basin strata provide reliable insight into the timing of rift development and erosion linked to uplift and landscape change in the western branch. Our suggested timing for basin development (~7 Ma) is consistent with demonstrated rifting in Uganda and Malawi, as well as with the initiation of volcanism in the Rungwe Volcanic Province, and the estimated development of Lake Tanganyika to the north.
The late Cenozoic rifting and sediment deposition gleaned from our analyses of rift fill strata provides important temporal context for the rich faunal record described from the East African Rift. The Rukwa Rift Basin is an important setting for the evolution of unique flora and fauna. Recovered fossils, including the oldest known members of both the ape and Old World monkey clades, suggest that climate and landscape change linked with tectonic activity may have been critical to the evolution of Africa’s unique biota. Decoding the provenance of the sediments that entomb this rich fossil record is a key to illuminating the tectonic and environmental backdrop of early hominoid evolution and later, larger-scale faunal shifts in East Africa. This work contributes to understanding the tectonic history of the East African Rift by using detrital and tuff-derived zircons to constrain Paleogene to Neogene rifting events and sediment deposition in the Rukwa Rift Basin.
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