Sandstone Diagenesis as Function of Depositional Environment and Plate Tectonic Setting--Comparison Between Jurassic Sandstones from North Sea Basin and Some Oligocene Sandstones from Coast Ranges of California: ABSTRACT

Abstract

Jurassic sandstones from the North Sea and Oligocene sandstones from the Coast Ranges of California are characterized by very different diagenetic mineral composition, which can be explained by differences in source rocks, sedimentary facies, climate, and ultimately in terms of plate-tectonic setting. The Jurassic sandstones from the North Sea were deposited in a rifted basin and were mostly derived from uplifted Precambrian terrane. A high content of diagenetic kaolinite in these sandstones can be attributed to meteoric water flushing through fluvial and deltaic sediments, causing the breakdown of feldspar and mica and the formation of kaolinite. Montmorillonite and zeolites are rare as authigenic minerals in these sandstones. In California, the rapid subsidence of the b sins in this subduction regime caused marine sandstone facies to predominate. These sandstones contain smaller amounts of kaolinite, probably because they did not experience any strong flushing by meteoric water after deposition. In addition, a drier climate in this region explains why fluvial sandstones such as the Sespe Formation show less evidence of meteoric water diagenesis than the Jurassic North Sea sandstones. Basin subsidence and marine transgression after the deposition of the Sespe Formation also limited the time these sandstones were exposed to meteoric water and thereby the formation of kaolinite. A higher content of mafic clastic minerals and chert, which formed unstable mineral assemblages in the California sandstones, favored extensive growth of diagenetic montmorillonite End_of_Article - Last_Page 1685------------