Synsedimentary deformation structures and their implications for stylolitization during deeper burial

Abstract

Synsedimentary faults related to a delta front collapse in the Cretaceous Helvetiafjellet Formation at Spitsbergen, Arctic Norway, are described. Listric faults cutting through channel sandstones do not display discrete slip-planes but consist of sandstone-dominated fault zones. The fault zones are 5–40 cm wide, contain fault parallel laminae, are enriched in clay minerals and micas along their margins, and are clearly distinguished from the adjacent sandstone beds in the mesoscopic scale. Fault movement probably occurred in two stages. The first stage involved hydroplastic deformation of the channel sands caused by rapid fluid escape along the developing faults. The second stage, which is inferred from folding of the fault zone laminae, took place after the sediments comprising the fault zones had achieved cohesion. Slickensides along the fault zone margins could have developed at this time, but may also have been generated during later uplift. Maximum depth of burial for the sediments was approximately 3500 m prior to early Tertiary uplift and erosion. Nucleation and development of stylolites, which are observed at high angles to bedding and parallel with laminations within the fault zones, could have formed at this depth during normal burial stress and without major horizontal compression. The stress component acting perpendicular to the steeply dipping clay- and mica-rich fault zone laminae, together with a temperature of approximately 120°C is sufficiently large to cause stylolitization.