Subsidence of the Laguna Salada Basin, northeastern Baja California, Mexico, inferred from Milankovitch climatic changes

Abstract

Laguna Salada in northern Baja California, Mexico, is an active half-graben product of the transtensional tectonics of the Gulf of California. It is sensitive to changes in sediment supply from the Colorado River basin. We present a time series analysis of the upper 980 m of a gamma-ray log from a borehole drilled near the Laguna Salada fault. The power spectrum of the gamma-ray log resembles the spectrum of δ¹⁸O Pleistocene isotopic variations from ice cores and from the deep ocean, known to be strongly controlled by Milankovitch cycles. We correlate δ¹⁸O stages with silty and sandy intervals in the log. Downcore ages for the last 780 ky are constrained within ~10 kyr. We derive a simple time vs. depth calibration relation for the basin over this time interval. Estimated sedimentation rates at the drill site appear to be constant with a value of ~1.6 mm/yr. We propose that this subsidence rate is produced by the Laguna Salada fault.