Emplacement mechanics of sandstone intrusions: insights from the Panoche Giant Injection Complex, California

Abstract

The Panoche Giant Injection Complex (PGIC; California) constitutes the most complete sandstone intrusion network yet described, and is an excellent analogue for subsurface hydrocarbon reservoirs modified by sand remobilisation. Sandstone dykes and sills were intruded during the Late Palaeocene into slope mudstones of the Great Valley forearc basin, and are exposed for more than 300 km2. The PGIC consists of dykes and sills and represents upwards infilling of natural hydraulic fractures sourced from highly overpressured Cretaceous sand bodies. Over 1300 orientation measurements show that dykes are almost randomly oriented with only a slight orientation bias trending NE–SW, N–S or NW–SE, suggesting either a horizontally isotropic state of stress during intrusion or modification of stress by newly‐formed fractures that override the remote stress. Dykes are segmented in a pattern consistent with radial propagation with fingering towards tips similar to that observed for other mixed mode fractures. Kinematic indicators reveal there was no systematic sense of opening for the intrusions. This is interpreted as the result of short‐range mechanical interactions. Cross‐cutting relationships between injections imply a diachronous timing and a fluid pressure in the source units that was in excess of the lithostatic load. Finally we document a suite of minor structures within the host section that allowed the strain of the forcefully intruded sand to be accommodated.

Structure and tectonic setting of the SE Sardinia mafic dyke swarm. Insights for the stress state during magma emplacement in the upper crust

“…It has been applied in several studies of dyke emplacement (e.g. Baer and Beyth, 1990;Riley et al, 2005;Vétel and Cartwright, 2010;Martínez-Poza et al, 2014).…”

Sand injectites network as a marker of the palaeo–stress field, the structural framework and the distance to the sand source: Example in the Vocontian Basin, SE France

“…For decades, numerous networks of sand injectites in sedimentary basins worldwide have either been interpreted from seismic data (Timbrell, 1993;MacLeod et al, 1999;Lonergan et al, 2000;Molyneux et al, 2002;Huuse and Mickelson, 2004;Huuse et al, , 2007De Boer et al, 2007;Jackson, 2007Jackson, , 2011Szarawarska et al, 2010) or directly observed in the field (Truswell, 1972;Hiscott, 1979;Surlyk et NoeeNygaard, 2001;Fri es and Parize, 2003;Hubbard et al, 2007;V etel and Cartwright, 2009;Kane, 2010). Because the emplacement of clastic sills and dykes depends on many parameters such as the nature of fluids, the host rock properties, the nature of sand from the source, the depth of the sand source, and the process of injection, each sand injectite network is considered as unique in terms of its dimensions, the geometry of the network, and the distribution, density and orientation of injected sands.…”

Mechanisms of biogenic gas migration revealed by seep carbonate paragenesis, Panoche Hills, California

“…); their length ranges from a few meters to 150 m (500 ft). They are characterized by abundant en echelon segmentation ( Figure 6A), a characteristic described as common in the area by Vétel and Cartwright (2010). …”

“…We propose the following hypotheses for the mechanisms of expulsion and migration of methane (Figures 14, 15). Vétel and Cartwright (2010) described the mechanism of depressurization of an injectite network after its emplacement as follows: from an initial pressure above the minimum stress (s min ), the critical value necessary for maintaining an open fracture, pressure rapidly decreases by pervasive fluid infiltration into the pore space of the host sediment or by connection to another permeable sand body or to the surface. In outcrops A and B, the tips of the dykes reached a depth very close to the sea floor and may even have erupted locally as sand volcanoes (Vigorito et al, 2008).…”

“…The Panoche giant injection complex developed from the sandy turbidites of the Upper Cretaceous Panoche Formation through the overlying Maastrichtian to Danian low porosity Moreno Formation along a vertical section of 1200 m (0.75 mi) and over at least 300 km 2 (115 mi 2 ). The Panoche giant injection complex has been extensively studied by many authors (Vigorito et al, 2008;Vétel and Cartwright, 2010;Vigorito and Hurst, 2010;Scott et al, 2013). Schwartz et al (2003) and Minisini and Schwartz (2007) described seep carbonates at the top of the Moreno Formation.…”