--> --> Abstract: Geometry of Sandstone Dykes and Sills as Indicator of Processes of Emplacement, by William Vetel, Joe Cartwright, Mario Vigorito, Andrew Hurst, and Olivier Stanzione; #90082 (2008)

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Geometry of Sandstone Dykes and Sills as Indicator of Processes of Emplacement

William Vetel1, Joe Cartwright1, Mario Vigorito2, Andrew Hurst2, and Olivier Stanzione2
1Earth, Cardiff University 3D lab, Cardiff, United Kingdom
2Earth, Aberdeen University, Aberdeen, United Kingdom

The well-exposed Panoche Giant Sand Injection Complex (PGIC), California, constitutes an excellent analogue for subsurface hydrocarbon reservoirs which have been modified by sand remobilization. The PGIC, Late Paleocene in age, is one of the world’s finest outcrop examples of an injection network. Sand intrudes 1200 m of stratigraphy of the western part of the Great Valley forearc basin and is exposed over more than 300 km2. The PGIC represents upwards infilling of natural hydraulic fractures above overpressured Cretaceous channels (Panoche Formation). Over 1000 orientation measurements of dykes and sills have been made. The dykes are almost randomly oriented, suggesting an almost isotropic state of horizontal compressive stress during intrusion. Dykes are systematically segmented in a pattern consistent with radial propagation and tip fingering classically observed for other Mode 1 fractures. Using a novel set of kinematic indicators, we observe a non-systematic sense of opening for the intrusions, which we interpret as the result of complex near-range mechanical interactions. Extensive cross-cutting relationships between dykes and sills implies a diachronous timing and a fluid pressure in the source units in excess of lithostatic. Finally we document a suite of minor structures within the host section allow the strain of the forcefully intruded sand to be accommodated. These can provide useful analogues for reservoir scale intrusions in petroleum provinces.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery