The use of logarithmic fitting in interpreting gravity data, Tokar Delta, Sudan

Abstract

Abstract Gravity data are incorporated with surface geology, seismic and borehole data to study the subsurface geology of Tokar Delta, Sudan. Gravity data obtained by Agip Mineraria, Chevron and Technoexport were compiled by Robertson Research International to produce the Bouguer anomaly map of the area. Five profiles are constructed across this map in an approximately ENE direction perpendicular to the Red Sea main structural trend. Two of the conventional analytical methods are attempted to separate the residual anomaly: least-square and polynomial fitting with different orders, but neither of them was found to be convenient, as they give positive residual anomalies in areas of known considerable thickness of sediments. Logarithmic fitting gives the best result over the other two methods. In three of the five profiles the residual anomaly obtained by the logarithmic fitting coincides typically with the geological constraints of the profile. The residual anomaly for the other two profiles is obtained by calculating the gravity effect of a presumed body controlled by the geological constraints of the profile. Five models are constructed for these profiles from which a depth to Basement map is constructed. Geological sections are drawn along three of these profiles. Borehole data of Digna-1, Durwara-2, and Marafit-1 are incorporated in the construction of these sections. Tokar Delta is a part of a NW-SE trending fault-controlled sedimentary basin. The basin is of an average width of 180 km and maximum thickness of 7. 5 km. The sediments are generally deposited in horst and graben structures.