61st Annual Report on Research 2016

The timing of sediment erosion from source regions has a direct implication in the petroleum field in deciphering the timing of major reservoir rock formation in the depositional sink areas. However, the timing of major erosional pulse/s is often associated with uncertainties and controversies. The Blue Nile River network on the Ethiopian Plateau in East African Rift System has incised a 1.6 km deep canyon and supplying ~96% of the Nile sediment load. This sediment load is being deposited to the alluvial fans of Sudan, the Nile Delta and the Nile deep-sea Fan in the Mediterranean. This study is motivated by the necessity of constraining incision history of the Blue Nile that has gained considerable momentum over the past years, where some argues for old and others suggesting a young incision of the plateau. The objective of the proposed study is to initiate this robust research using state-of-the art techniques of integrating apatite (U-Th)/He and 4He/3He thermochronometry. This study will provide crucial data for understanding and constraining incision history of the Ethiopian Plateau as the timing of erosion is critical in understanding temporal probability of reservoir vs. organic-rich source rocks development in the Nile petroleum plays, particularly in the Mediterranean Sea. Moreover, this study holds enormous potential for constraining tectonic models of the northeastern East African Rift, including the formative mechanisms and dynamics of rift faults likely linked to paleotopographic evolution of the Ethiopian Plateau.

Research Effort

This ACS-PRF funding allowed the PI to successfully establish a well-developed research project at the early stage of her academic career in a tenure-track faculty position at a reputed primarily undergraduate institution. As part of this study, the PI developed research collaborations with Dr. Mathijs van Soest at Arizona State University (ASU), and Drs. Giudita Fellin and Sean Willet at ETH, Zurich. Three geology undergraduate students Helen Flynn, Cody Meservy and Christopher William conducted research in this project. Another geology undergraduate student Scott Kaily has started to work on this project as part of her undergraduate research experience. Graduate student Nathaniel Blackburn has successfully completed his MS thesis directly linked to the project supported by Western Kentucky University (WKU) internal seed grants, graduate assistantship and other stipends. Another graduate student, Indu Bhattarai is completing her MS thesis related to this project.

During fall of 2015, summer and spring of 2016, the PI and undergraduate and graduate students accomplished the following project-related tasks:

1) Significant lab work for understanding and implementing the technical aspects of rock sample preparation, thin sections, heavy liquid separation and mineral picking. Undergraduate students Helen Flynn, Cody Meservy and Christopher William were involved in this work. 2) Samples have been sent to ETH Zurich and ASU Group 18 laboratory for mineral picking and thermochronologic dating as part of the PI’s collaborative effort. Several samples were dated using (U-Th)/He thermochronology. Sample dating costs were provided by PI’s ongoing RCAP grants. Graduate student Nathaniel Blackburn conducted this part and completed his MS thesis in spring 2016. 3) Undergraduate student Helen Flynn travelled to Ethiopia in summer 2016 to collect data as part of this project. 4) In summer 2016, graduate student Indu Bhattarai conducted lab work at ASU on sample preparation to be used for dating. 5) The PI and graduate and undergraduate students presented their research findings at multiple national and regional conferences including Geological Society of America (GSA) at Baltimore, Maryland and WKU SRC Conference. Two papers were published in peer-reviewed journal and one is in press. One MS thesis is published. Multiple manuscripts are in preparation for peer-reviewed journals.

Findings during the reporting period:

The project employs apatite (U-Th)/He thermochronology to better understand the timeline and mode of the Blue Nile Canyon incision and the landscape geodynamics of the Ethiopian Plateau. Neoproterozoic basement and Mesozoic sedimentary rock samples were collected in a vertical transect along the Blue Nile Canyon for AHe dating. Euhedral apatite grains that are inclusion and fracture-free were selected for dating. ASI Alfachron and ICP-MS measured the concentrations of radiogenic isotopes uranium (U), thorium (Th), and helium (He) to obtain apatite helium (AHe) dates, providing (U-Th)/He cooling ages ranging from 64 to 460 Ma. These AHe dates are much older than the 30 Ma flood basalt event, thus older than the canyon incision. In this study, a cooling/thermal history is suggested by explaining the data dispersion by the radiation damage effect in the dated apatite grains, which is related to He retention with time. The apatite suite has been subjected to protracted cooling, longer residence time in the He partial retention zone, and partial resetting due to Mesozoic rift-related burial and subsidence from deposition of ~1.2 km thick sedimentary rocks, the extensive emplacement of ~1 km-thick flood basalt at 30 Ma, and differential incision. Radiation Damage Accumulation and Annealing Model thermal models indicate a rapid cooling event, suggesting rapid incision after 10 Ma. Thermal models will be interpreted next to better understand the incision history in this ongoing research.

Securing additional funds:

The PI has submitted two full proposals to NSF programs and obtained a few large amount software grants related to this project including WKU RCAP grants. Graduate and undergraduate students receive several stipends, assistantships and grants to complete MS thesis, present research to conferences, travel to Ethiopia, and for research enhancement. Nathaniel Blackburn obtained VA scholarship to support his MS thesis. Indu Bhattarai was partially awarded $1500 summer stipend from WKU including PRF support to carry out lab works related to sample preparation and dating at ASU. She was also awarded $500 travel scholarship from GSA OTF to present at the annual meeting in Maryland. She also received several travel stipends and graduate assistantship from WKU Geography and Geology Department, Graduate School and Ogden College to support her MS thesis. Undergraduate student Helen Flynn secured WKU FUSE and LTE grants in addition to PRF support as part of this project to travel to Ethiopia, which was made possible because of the PI’s ACS-PRF grant that initiated her undergraduate research.