Calcite cementation along the Refugio/Carneros fault, Coastal California: a link between deformation, fluid movement and fluid-rock interaction at a basin margin

Calcite cement occurs at two localities 24 km apart at the ends of the steep-dipping, east-west trending Refugio/Carneros fault, Santa Barbara area, California coast. These occurrences offer clear evidence for interrelated faulting and fluid movement. The Refugio fault juxtaposes Oligocene Vaqueros sandstone, with about 100 m of apparent normal offset, against overlying Miocene Rincon shale. At the western end of the fault, calcite, up to 1.5 m thick with individual crystals 20 cm across, fills the fault zone and extends via small fractures into the adjacent sandstone. Physical and geochemical evidence from the calcite demonstrates repeated episodes of deformation and fluid movement. The carbon isotopic values of this fault-related calcite (delta(13)C(PDB) -40 to -45 parts per thousand) indicate the carbon was generated from oxidation of methane. Estimated crystallization temperatures are around 100 degrees C, although the outcrop is calculated to have been submerged at least a few 100 m subsea depth. (C) 2000 Elsevier Science B.V. All rights reserved.