Depositional environments of the Kurnub group (Early Cretaceous) in northern Jordan

Abstract

Seven facies associations comprise the Early Cretaceous Kurnub Group (KG) in northern Jordan. They are assigned to the following five depositional environments: proximal to distal alluvial braidplain; tidal flat; tidal marsh-coastal swamp; inner shelf; and meandering river. According to the evolution of these depositional facies associations, the KG can be split into three regressive-transgressive depositional sequences. This development of the depositional environment of the KG through the Early Cretaceous Epoch is portrayed as a six-block depositional model. The depositional history of the KG began with the first regression, when a conglomerate and sandstone facies association of a proximal to distal alluvial braidplain system was deposited above a regional angular unconformity, truncating Triassic and Jurassic strata. Afterwards, the Tethys Seaway inundated northern Jordan, giving rise to the first transgressive sequence, consisting of a tidal flat-mixed carbonate-siliciclastic and coastal swamp-carbonaceous shalelignite facies association. Due to the second regression of the sea, a medial to distal unconfined braided river system resumed in northern Jordan. The second transgression of the Tethys covered most of the region during the middle interval of the KG, and deposited a mixed carbonate-siliciclastic sequence with interbedded inner shelf carbonates, subtidal oolitic ironstones and tidal marsh-coastal swamp black shales and lignites. During the next interval of the KG, the Tethys regressed from the area and was replaced by a moderate sinuosity meandering river system that deposited the third regressive fluvial sequence. The third transgression of the sea developed a marginal to shallow marine depositional system, which affected northernmost Jordan, giving rise to a mixed carbonate-siliciclastic tidal flat and an inner shelf carbonate sequence. The climate in Jordan during the Early Cretaceous Epoch was generally humid and temperate.