Structural
Analysis of Sandstone Dykes: Implications for Remobilisation of Deepwater Sand
Reservoirs
William, Vetel1, Cartwright
Joe1, Mario Vigorito2 (1) Cardiff University, Cardiff,
United Kingdom (2) Aberdeen University, Aberdeen, United Kingdom
We present a structural analysis of
sandstone dyke swarms developed with a series of injectite systems in California and France. The sandstone dykes
range in aperture from a few centimetres to several meters. These dykes were
intruded into mudstones, silty mudstone, and/or diatomaceous mudstones host
rocks after burial by several hundred meters. The dykes exhibit many of the
classical geometrical relationships seen in igneous dyke systems, including
branching, segmentation and/or tip fingering. Our analysis focuses on dyke
orientation. We find two end-members: (1) dyke swarms with strongly bimodal
strike distributions (e.g. medial-upper portion of the Panoche Hills injection
complex, San Joaquin Basin, California) and (2) randomly
oriented dyke swarms (e.g. Sisteron, Provence, France). We interpret the
bimodal end member to be representative of remobilisation and intrusion during
a phase of active tectonism, in which horizontal stresses were strongly aligned
in the prevailing tectonic stress regime. We interpret the randomly oriented
end member to have formed in a passive tectonic setting, in which horizontal
stress was isotropic. These preliminary models for the occurrence of sandstone
dyke swarms are the first step in an attempt to develop predictive models to allow
sandstone intrusions to be built into reservoir models. They also have
considerable implications for reconstruction of in situ stress regimes in
petroliferous basins.