Morpho-sedimentary characteristics and generated primary sedimentary structures on the modern microtidal sandy coast of eastern Nile Delta, Egypt

Abstract

Abstract Spatial distribution and implication of primary sedimentary structures are combined with morpho-sedimentary features to suggest a sedimentologic–neoichnological model for the low microtidal sandy coast of eastern Nile Delta. Ten linear transects normal to the shoreline were investigated across four to five parallel geomorphic landforms. Intertidal sub-environment is characterized by abundant marine-affinity surface sedimentary structures (such as beach cusps, swash marks, air holes/volcanoes, foam impressions, raindrop imprints, rill marks and tool marks) in addition to the parallel lamination and oscillation ripples. Lower supratidal sub-environment is characterized by parallel lamination, current and wind ripples. Nebkas and wind ripples dominate the nebka/inter-nebka landforms, whereas microbial-induced sedimentary structures which including cyanobacterial mats, efflorescent salt crusts, polygonal cracks and tepee structures prevail in salinas and sabkhatized landform. Marine life-trace assemblage in the intertidal zone, belonging to infaunal and epifaunal bivalves and gastropods, resembles the poor expressions of shallow-marine Skolithos ichnofacies. Predation holes in bivalves and clavate borings in drifted tree trunks are analogous to Oichnus simplex and Teredolites isp., respectively. Transitional marine life-trace assemblage of abundant ghost crab burrows and trackways represents a modern example of seaward suites of the paleoichnological backshore Psilonichnus ichnofacies. Terrestrial life-trace assemblage of beetles, ants, vertebrate tracks and rhizoliths show similarity to the landward expression of Psilonichnus ichnofacies. Despite low to moderate preservation potentiality of modern microtidal sedimentary structures, the preserved structures are invaluable in revealing depositional processes and paleoenvironments of ancient coastal systems.