[First Hit]

AAPG Annual Convention and Exhibition

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Faulting of an Alternating Sandstones and Shales Turbidite Sequence: Previous HitFaultNext Hit Mechanism and Architecture and Their Roles in Previous HitFaultNext Hit Seal

Abstract

Characterization of the faulting mechanism and Previous HitfaultNext Hit architecture of a 5 km-long, N40°E-striking Previous HitfaultNext Hit zone in a thick turbidite sequence of sandstones and shales exposed along the flank of an anticline in the Simi Hills, southern California, provides new insights into the interplay between the Previous HitfaultNext Hit and the groundwater. Numerous monitoring boreholes across and along the Previous HitfaultNext Hit within the sequence consistently dipping 20° to 30° to NW define the 3D distribution of the groundwater table in the area. Except for a small lateral step along the Previous HitfaultNext Hit, hydraulic head measurements consistently show differences of 10s of meters from one side to another side of the Previous HitfaultNext Hit. The Previous HitfaultNext Hit is made up of at least three segments named here as northern, central and southern segments. Key information about the faulting mechanism has been collected at two sites. The first one is an outcrop of the central segment and the second one is a 194 m-long borehole, which intersects the northern segment at near its bottom. At the first site the Previous HitfaultNext Hit zone juxtaposes sandstones against shales and consists of a 13 meter-wide Previous HitfaultNext Hit rock including a highly deformed sliver of sandstone. The central core is 8 m-wide and contains mostly shale characterized by diffuse deformation with a complex texture. At the southeastern edge of the Previous HitfaultNext Hit exposure, a shale unit parallel the Previous HitfaultNext Hit zone and dipping 50° NW towards the Previous HitfaultNext Hit zone provides the key evidence that the shale unit was incorporated into the Previous HitfaultNext Hit zone in a manner consistent with shale smearing mechanism. At the second site, based on an optical televiewer image supplemented by rock cores, a juxtaposition plane (dipping 75° SE) between a highly fractured sandstone and a intensely deformed shale Previous HitfaultNext Hit rock has been interpreted as the southeastern boundary of the Previous HitfaultNext Hit zone. The shale Previous HitfaultNext Hit rock is noticeably folded and brecciated with locally complex cataclastic texture. The observations and interpretations presented above suggest that the drop of hydraulic head detected across the Previous HitfaultNext Hit segments is primarily due to the low-permeability shaly Previous HitfaultNext Hit rock incorporated into the Previous HitfaultNext Hit zone by the shale smearing process. Interestingly, at around the lateral step between the northern and the central Previous HitfaultNext Hit segments, where the Previous HitfaultNext Hit offset is expected to diminish (no hard link, no significant shaly Previous HitfaultNext Hit rock and possible sandstone-to-sandstone juxtaposition), the groundwater levels measured on either sides of the Previous HitfaultTop zone are more-or-less equal.