Lithostratigraphy, foraminiferal biostratigraphy and geological history of the Upper Cretaceous in West Jordan
The stratigraphy of the Upper Cretaceous (Cenomanian - Lower Maastrichtian) rocks in West Jordan is described based on four measured sections: Ajlun/Jerash (north); Wadi Mujib (central); Wadi Mussa and Ras en-Naqb (south). Over 285 samples collected from these sections were processed for microfossils; 214 samples were thin sectioned for microfacies analysis. Despite significant lithofacies changes southward, eight formations and six members have been recognised and correlated across the region. The thickest marine strata are located in the northern and central areas; thicknesses decrease and the sand content gradually increases towards the south. Microfossil, principally foraminiferal, biostratigraphy has been used for detailed stratigraphic correlation. Over 420 species constituting 170 genera are documented, many for the first time from the area. Microfossil species identified include 80 planktonic and 331 benthic foraminifera (104 calcareous and 227 agglutinated), and 10 radiolaria. Taxonomic analyses of all foraminiferal and radiolarian species are presented, including remarks on each species and its geographic and stratigraphic distribution. Most species are illustrated by Scanning Electron Microscope (SEM) photographs. Microfossil range charts are presented for each measured section, based on detailed analysis of each microfossil sample, and local assemblage zones are described. Six regional foraminiferal assemblage zones are proposed: Conorboides umiatensis / Haplophragmoides spp. Zone (lower to mid-Cenomanian); Heterohelix calabarflanki / Whiteinella inornata Zone (upper Cenomanian); Gavelinella stephensoni / Whiteinella archaeocretacea Zone (Turonian); Archaeoglobigerina blowi / Concavatotruncana concavata Zone (upper Coniacian - Santonian); Rugotruncana subcircumnodifer Zone (upper Campanian); Globotruncanella havanensis Zone (lower Maastrichtian), based largely on evidence from Wadi Mujib, which is proposed as a reference section for the area. Palaeoenvironmental studies, including microfacies analyses and the quantitative evaluation of foraminiferal assemblages (planktonic and benthic), provide evidence of four major marine sedimentary sequences: (1) early - mid Cenomanian; (2) late Cenomanian - middle Turonian; (3) late Coniacian - late Santonian; (4) early Campanian to early Maastrichtian, each separated by hiatuses caused either by global falls in sea level and/or local tectonic activity.