| Popis: |
A recent road cut through a Dammam Formation outcrop on the Dammam Dome in Dhahran, Saudi Arabia, exposed an array of open fractures and gypsum-filled veins. The discontinuities were mostly contained within the Saila Shale member and consisted of horizontal, vertical, and inclined extensional fractures, most of which were filled with gypsum. The veins were 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. A thin layer of gypsum (about 1 inch) was also observed in the Upper Rus Formation. The open vertical and horizontal fractures, in the Saila and Midra Shale members, were devoid of gypsum fill, and were interpreted to be recent with indications of being triggered by the excavation work. The open fractures and filled veins covered 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. |
