Sedimentological and hydrochemical spectrum of recent continental sabkha and signs of its capabilities to generate hydrocarbons: a case study in northwest El Fashn area, Western Desert, Egypt

Abstract

The purpose of the present work was to discuss the composition and hydrologic framework of modern continental sabkha in northwest El Fashn area, Western Desert, Egypt, and its possibilities as a source to generate hydrocarbons. The continental sabkha occupies the low topography of a closed basin fringed with sand dunes and Middle Eocene rocks. The site receives the excess of discharged irrigated water, sourced from a well within the limestone rocks (>40-m depth), in addition meteoric water from sand dune aquifers. The capillary rise powered by evaporative pumping mechanism is responsible for continuous feeding of the surface area. Four sedimentological zones are discriminated for sabkha: elevated temporary dry marginal, temporary wet saline mudflat broad, hypersaline pool and permanent saline pan zones. Halite, gypsum, anhydrite, sinjarite, bloedite and bischofite minerals predominate. The non-evaporative minerals are quartz, calcite, plagioclase, hematite and clay minerals. The upward increase in salinity with Na+ and Cl− ions supports the evaporative pumping mechanism that plays a significant role in the upward movement of brines and formation of the evaporative salts under arid conditions. The repeated cycles of salt precipitation reflect the complexity of the diagenetic history in both mineralogy and sedimentary textures. Total organic carbon content confirmed high organic richness. The kerogen content of the organic matter is believed to be derived from algal and biomass, together with microbial content that accumulated under saline to hypersaline and moderately to highly reducing conditions. Thermal maturity of the organic matter is generally low grade hydrocarbons. This result favors the conclusion that the study examples of sabkha are analogs of a possible generation of hydrocarbons.