Carnian (Triassic) aridization on the Levant margin: evidence from the M1 member, Mohilla Formation, Makhtesh Ramon, south Israel

Abstract

The Carnian Pluvial Event was followed by extreme aridity around the Mediterranean region, but the relationship between these climatic modes and the evaporite deposits of the north Arabian margin has not been established. The Mohilla Formation in Israel was deposited on the rifted Levant margin of the Neotethyan seaway during the Carnian (Late Triassic). The lowermost member, M1 (carbonate, shale, minor evaporite), records sea-level and climate change of the transition from open-marine deposits to the thick evaporite of the overlying M2 member. Field, petrographic and cathodoluminescence investigation of the M1 member exposed at Makhtesh Ramon, southern Israel, enabled tracking of changing paleoenvironments. The M1 member can be subdivided into six sea-level controlled sedimentary cycles, each terminating in subaerial exposure. Open-marine, lagoonal, and supratidal belts are represented, but environments become increasingly restricted upwards. Three of the exposure horizons are marked by well-developed early diagenetic features, including dissolution porosity and meteoric cements. These changing facies belts and the superposed diagenetic modes formed under an oscillating climate regime of three relatively humid episodes dominated by deposition of carbonate, alternating with evaporitic sediments indicating aridity. Deposition of the M1 member can be correlated with the transition in the western Tethys from the Carnian pluvial episode to aridity. This transition in the Levant region is characterized by an oscillatory climate that culminated in a thick evaporite unit from the extreme arid phase. The oscillations may be attributed to shifting global climate belts, overprinted by monsoonal strengthening and weakening, in the equatorial belt.