Jackson School of Geosciences

This talk will highlight research that aims to investigate dune formation and dune shape in big and small rivers and in shallow laboratory flows. This investigation allows the comparison and validation of the key processes controlling the formation of low-angle dunes. I then identify and discuss the conditions when one process may dominate in creating complex dune shapes. This talk highlights the balance between bedform superimposition and sediment suspension as controls on the formation of low-angle dunes. This information is vital to improving our approach to managing contemporary rivers under modern stressors and revealing the deposits of ancient rivers.

Abstract: With recent advances in the large-scale deployment of distributed acoustic sensing (DAS) approaches utilizing telecommunication infrastructure, the asymmetry between the per-channel cost of high-resolution passive seismic recording and corresponding active source deployments continues to increase. This has motivated renewed interest in both large-scale ambient noise studies as well as improved utilization of shallow natural seismicity for imaging applications. In this study, we highlight three approaches for using DAS, ambient noise, and shallow earthquakes to constrain larger scale S-wave velocity and reflectivity structure utilizing data acquired as part of the Imperial Valley Dark Fiber Project (IVDFP). The project targets structures near the Brawley Geothermal Field relevant to understanding the seismic signatures of hidden geothermal systems; to date, almost 19 months of continuous DAS data has been acquired on a 27 km (7000+ channel) dark fiber array stretching from Calipatria to Imperial, CA. In our first example, we show on-going work seeking to combine the high spatial density of DAS and anthropogenic ambient noise imaging to constrain zones of hydrothermal alteration directly beneath the Brawley field. In the second example, we attempt to utilize the abundant natural seismicity in the Brawley Seismic Zone (BMZ) recorded by DAS, and local earthquake tomography to improve constraints on S-wave structure over a larger region. In the third example, we image large lateral reflectivity features near the field using coherently scattered S-waves and 3D migration, an approach not possible using the classical sparse seismic arrays. These results are compared to existing datasets and interpreted to be related to deep hydrothermal alteration and fault-related structures at the southern termination of the Brawley Seismic Zone (BSZ).
Further information in: Ajo‐Franklin, J., Rodríguez Tribaldos, V., Nayak, A., Cheng, F., Mellors, R., Chi, B., Wood, T., Robertson, M., Rotermund, C., Matzel, E. and Templeton, D.C., 2022. The Imperial Valley Dark Fiber Project: toward seismic studies using DAS and telecom infrastructure for geothermal applications. Seismological Society of America, 93(5), pp.2906-2919.

In my work, we are developing multi-mineral isotopic and petrographic methods to understand the role of temperature, fluid chemistry, and diagenesis on two isotopic systems—oxygen isotopes and clumped isotopes—that reefs and other carbonates record as they grow. We are developing local records and present details of those alongside a new high-resolution record of bulk carbonate oxygen isotopes for the last billion years of Earth’s history.

My results suggest one solution to the previous ambiguity surrounding seawater oxygen isotope composition through time. Based on our results to date, and other distinctive features of our high resolution oxygen isotope record, we hypothesize that temperature, and not just atmospheric oxygen levels, was a key factor for understanding emergence, diversification and subsequent trajectory of complex life.