November 3, 2024 Nancy Chabot

From a report submitted to the Endowment Committee by: Marian Selorm Sapah, University of Ghana

This work was supported by a Meteoritical Society Research Grant. Visit the Grants webpage for more information about the program and see these previous news stories for information about other funded Meteoritical Society Endowment Grant efforts.

Looking for impact shock features in quartz grains from the Victoria Island Structure. A potential buried impact crater.

Project Title: EBSD Analyses of Quartz Grains from Drill Cuttings from the Victoria Island Structure, a Potential Buried Impact Crater, San Joaquin County, California

Brief Summary: A 3-D seismic survey and well logs analysis carried out in the southwestern Sacramento basin, San Joaquin County, California, have revealed a subsurface, circular, ~5.5-km-diameter anomaly that is thought to represent an complex impact crater. This structure presently known as the Victoria Island structure is buried 1,490–1,600 m below sea level under shale sediments and is thought to be between 37 and 49 million years old. A preliminary optical microscopic study was carried out by colleagues at Stanford University on quartz grains separated from drill cuttings (1200-1650m) from the Victoria Island structure, to examine the frequency of Planar Deformation Features (PDFs). Out of a total of 151 quartz grains studies, 18 showed PDFs indicating shock.

This study performed Electron Backscatter Diffraction (EBSD) analysis of quartz grains from the same drill cuttings to further investigate impact shock features in these samples. All analyses were carried out using a Thermoscientific Apreo field emission SEM equipped with Aztec software at the Department of Earth & Planetary Sciences, University of California, Santa Cruz, in collaboration with Prof. Myriam Telus. The results from the EBDS analyses are currently being processed, while further sample preparation, optical microscopic analysis and EBSD analysis are being carried out.