Karst collapse and gypsum-filled veins in Eocene outcrops, Dammam Dome, Saudi Arabia: Causes and implications

Abstract

• Differential weathering of Dammam Dome through uplift and erosion. • Factors affecting Dammam Dome geomorphology. • Gypsum-filled veins on the Dammam Dome due to karst collapse. • Results from this study can be related with water and hydrocarbon reservoirs. A recent road cut through Dammam Formation outcrop on the Dammam Dome in Dhahran, Saudi Arabia exposed an array of open fractures and gypsum-filled veins. The widespread array of fractures in the road cut was mostly contained within Saila Shale member and consisted of horizontal, vertical, and oblique extensional fractures, most were filled with gypsum. The gypsum veins are of varying thickness with the largest exceeding 2.5 inches. Vertical gypsum veins, similar to those encountered at the road cut, were found in adjacent areas. Thin layer of gypsum (about 1 inch) was also observed in the Rus Formation. The open fractures, in the Saila and Midra Shales members, were devoid of gypsum fill. Most of the open vertical and horizontal fractures were interpreted to be recent with indications of triggered by the excavation work. The open fractures and filled veins cover a stretch of about 250 ft. across the road cut that also exposed what was interpreted as a local karst collapse. Horizontally-layered and continuous rocks overlying the collapse indicated that it was a paleo structure. The causal mechanism for fracture formation and subsequent fill was associated with deformations accompanying post-karst collapse. Here, natural fracturing and fluid transport were not synchronous events. Insights from this interpretation offered an explanation for widespread surface structures with major and subtle morphologies on the Dammam Dome. These insights also highlighted the significance of collapse in the modification of the Dammam Dome over a geological timescale. The unstable nature of gypsum, prevalent in Dammam Formation in the Dammam Dome, has potential implications for integrity of anthropogenic structures such as roads and building foundations.