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Giant clastic intrusions primed by silica diagenesis

¹ Centre for Research into Earth Energy Systems, Department of Earth Sciences, Science Labs, University of Durham, Durham DH1 3LE, UK
² Department of Geology and Petroleum Geology, University of Aberdeen, Aberdeen AB24 3UE, UK
³ BP, Chertsey Road, Sunbury on Thames, Middlesex TW16 7LN, UK
⁴ 3DLab, School of Earth, Ocean and Planetary Sciences, Main Building, Park Place, Cardiff University, Cardiff CF10 3YE, UK
⁵ School of Earth, Ocean and Planetary Sciences, Main Building, Park Place, Cardiff University, Cardiff CF10 3YE, UK

Postdepositional sediment mobilization is a common phenomenon that occurs over large areas of sedimentary basins, usually within mudstone-rich successions; however, defining the exact mechanism that initiates this process has proved elusive. Here we describe a number of large-scale clastic intrusions (injectites), 50 to >300 m in height, hosted within fine-grained biosiliceous upper Eocene to Pliocene strata in four sedimentary basins. Within these basins diagenetic conversion of opal A into opal CT (cristobalite and tridymite) causes a marked reduction in sediment porosity and the liberation of bound water, often at relatively shallow burial (<0.5 km). We propose that this occurs over geologically short time periods over large expanses of sedimentary basins, causing rapid pore fluid expulsion and overpressure buildup within interbedded sands. The liberated fluids primed these sands, rendering them susceptible to remobilization. This mechanism should have broad applicability.

Key Words: injectites • pore fluid • opal A • opal CT • overpressure

This article has been cited by other articles:

				R. J. Davies, N. R. Goulty, and D. Meadows Fluid flow due to the advance of basin-scale silica reaction zones Geological Society of America Bulletin, January 1, 2008; 120(1-2): 195 - 206. [Abstract] [Full Text] [PDF]

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