--> Miocene basin configuration and tectonic evolution of the Inner Borderland Rift

AAPG Pacific Section and Rocky Mountain Section Joint Meeting

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Miocene basin configuration and tectonic evolution of the Inner Borderland Rift

Abstract

Miocene basins associated with the oblique rifting of the Inner Continental Borderland offshore Southern California are preserved along the flanks of the transpressional Santa Cruz-Catalina Ridge and the southern California coast from the Northern Channel Islands southward into Baja California. Mapping of the basin geometry for middle Miocene and late Miocene basin sedimentary sequences provides evidence regarding the initial configuration of the Inner Borderland Rift. These two time intervals encompass the initial extension and ‘transrotation’ followed by ‘transtensional’ phases of the oblique rifting process. Isopachs and structural contour maps were created using 2-D and 3-D seismic reflection data available from industry, government, and academic sources. Shallow high-resolution 2-D seismic data combined with multibeam bathymetry around the basin margins provide greater accuracy for defining the basin morphology and locations of major faults. Stratigraphic control is provided by wells and boreholes along the continental margin where petroleum exploration has occurred, and by sparse but widespread seafloor sampling over the past 50 years of Borderland research. Segmentation and other distinctive character of the basins around the Inner Borderland Rift margin may be correlated on conjugate flanks to enable more accurate reconstruction of the initial rift configuration. Our working model for oblique rifting in the Borderland resembles the Gulf of California, where right-stepping echelon transform faults link left-stepping extensional basins. This character has been complicated by transrotation and obscured by post-Miocene contraction. Details in the basin configurations may constrain timing and style of important tectonic events including changes in relative plate motion and its effect on basin deformation during the rift evolution.