From field study to numerical modeling of hydrothermal dolomitization in Early Cretaceous platform carbonates (Cantabrian mountains, northern Spain)

The investigated hydrothermal dolomites, which are exposed in the Aptian-Albian platform carbonates in the Cantabrian mountains are spatially associated with faults and fractures, which are believed to have provided pathways for the fluids responsible for the dolomitization. The orientation of the major fractures, along which most of the observed dolomites are found trends SW-NE. Fluid inclusion analyses show homogenization temperatures varying from 120 to 200 °C and estimated salinities ranges between 10 and 24 eq. wt. % NaCl. There are various possible sources of dolomitizing fluids, which include buried Triassic evaporitic strata, Keuper salt diapirs in the surrounding areas, Lower Cretaceous transitional marine shales and sandstones in the nearby Bilbao Trough, as well as fluids that interacted with Mg bearing igneous rocks (e.g. gabbro, basalt). The present contribution discusses the construction, and subsequent testing, of a 3D geostatistical model covering a surface area of 5×2 km and a depth of 2 km. This model is based on interpretation of aerial photographs, geological and topographic maps, as well as field observations. All data were initially entered into an Arcview-GIS environment, whereby the interpreted fractures were traced and organized into three groups according to the scale of viewing. The resulting fracture orientations were comparedwith field observations. Dolomite outcrops, which exhibit a distinctive beige color compared to