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Abstract

Hubbard, S. M., B. W. Romans, and S. A. Graham, 2007, An outcrop example of large-scale conglomeratic intrusions sourced from deep-water channel deposits, Cerro Toro Formation, Magallanes basin, southern Chile, in A. Hurst and J. Cartwright, eds., Sand injectites: Implications for hydrocarbon exploration and production: AAPG Memoir 87, p. 199-207.

DOI:10.1306/1209863M873265

Copyright copy2007 by The American Association of Petroleum Geologists.

An Outcrop Example of Large-scale Conglomeratic Intrusions Sourced from Deep-water Channel Deposits, Cerro Toro Formation, Magallanes Basin, Southern Chile

Stephen M. Hubbard,1 Brian W. Romans,2 Stephan A. Graham3

1Department of Geological and Environmental Sciences, Stanford University, Stanford, California, U.S.A.
2Department of Geological and Environmental Sciences, Stanford University, Stanford, California, U.S.A.
3Department of Geological and Environmental Sciences, Stanford University, Stanford, California, U.S.A.

ACKNOWLEDGMENTS

We thank affiliate members of the Stanford Project on Deep-water Depositional Systems, including Anadarko, BP, ChevronTexaco, Emerald Trail LLC, Eni-Agip, ExxonMobil, Marathon, Nexen, Occidental, Petrobras, Rohoumll-Aufsuchungs A.G., and Unocal for financial support of our research. Reviews by John Cosgrove, Adrian Hartley, and Andrew Hurst have improved the clarity of the manuscript and are greatly appreciated.

ABSTRACT

Large-scale vertical to subvertical clastic intrusions (as much as 67 m [219 ft] wide and gt100 m [gt330 ft] high) are present in Cretaceous strata (Cerro Toro Formation) of the Ultima Esperanza district, southern Chile. The injectites emanate from the margins of submarine-channel deposits that accumulated at water depths of 1000–2000 m (3300–6600 ft) in the Magallanes foreland basin. The remobilized sediment is very coarse, consisting of sandy matrix conglomerate, muddy matrix conglomerate, and poorly sorted sandstone. The injectite bodies sometimes bifurcate upward and are circular in plan view and, thus, are geometrically analogous in many respects to numerous injection features mapped seismically in the North Sea Basin.

The remobilization of coarse sediment was likely induced after the burial of the parent deposit to at least a few hundred meters. The controlling factors on injection are difficult to discern; however, it is probable that the highly energetic process involved gas charging of the source body and, potentially, a seismic event trigger associated with the uplift of the Patagonian Andes.

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