Thermal Alteration of Organic Matter in the Contact of a Rift-Related Basaltic Dyke: An Example from the Black Limestone, Wadi Matulla, West Central Sinai, Egypt

Abstract

In the Wadi Matulla area, central Sinai, Egypt, an asymmetric baked zone having an average width of 103 m was formed on both sides of a sub-aerial rift-related Oligocene basaltic dyke cross-cutting organic matter-bearing chalky limestone of the Upper Cretaceous Sudr Formation. Advection was the significant heat transfer mechanism. Very narrow metamorphic and metasomatic zones are developed in the country rock at the immediate contact with the dyke. The change in the thermal maturation of organic matter is reflected in the differences in values of the total organic carbon (TOC) within the baked zone. Such differences account for the color variation of the snow-white limestone from shades of brown, in the mature to barren samples, to black, in the totally carbonized overmature metamorphic ones. This study presents for the first time the thermal effect of mafic dykes on some exposed organic matter-bearing rocks in the Gulf of Suez (GOS) region, and turns attention to the local maturation of source rocks in contact with rift-related intrusives at a relatively greater burial depth in the rift basin.