A revised tectonostratigraphic model for the Ajlun and Belqa Groups (Upper Cretaceous-Eocene) in Jordan has been developed by integrating extensive outcrop and subsurface stratigraphic data. This updated model allows for precise dating of the Hamza Graben’s initiation and evolution as Santonian to early Campanian in age. This timing aligns the Hamza Graben with the major tectonic reorganisation that occurred around the Arabian Plate at that time.

The Ajlun (Cenomanian – Early Coniacian) and Belqa (Late Coniacian – Eocene) Groups of Jordan contain a remarkable succession of sedimentary lithofacies, including shallow water limestone, chalk, sandstone, chert, phosphorite, and organic-rich marls, deposited along the passive southern margin of the Neo-Tethys Ocean. In western Jordan, these groups outcrop in deep wadis along the Aqaba-Dead Sea Transform, providing detailed study opportunities. By applying sequence stratigraphic methods along with new nannofossil age dating, carbon and oxygen isotope stratigraphy, and strontium isotope stratigraphy, the stratigraphic interpretation of these successions has been refined. Despite significant variations in lithology and sedimentation patterns, the formations identified at outcrop can be reliably correlated with subsurface well logs and seismic data. This enhanced stratigraphic framework has enabled the creation of isopach maps at both group and formation scales.

In southern Jordan, the Ajlun and Belqa Groups exhibit a progressive thickening and deepening trend to the north, suggesting a relatively stable tectonic setting along the southern Tethyan margin. A similar northward thickening trend is observed in northeastern Jordan for the Ajlun Group, indicating the continuity of this stable area. However, this pattern change dramatically in the Late Coniacian to Early Campanian period (lower part of the Belqa Group) when the northwest-trending Hamza Graben in central Jordan formed, creating significant accommodation space, approximately 1800 meters across a half-graben width of 35 km. This half-graben extends southeast to the Wadi Sirhan Graben in northeastern Saudi Arabia and northwest to the Syrian Arc. Thickness trends and growth-strata visible in seismic imagery reveal that the primary extension phase of the graben occurred during the Lower Campanian (Amman Silicified Limestone Formation), characterized by 1300 meters of chert-rich dolomites and limestones. The overlying phosphate-rich Upper Campanian sequence (Al Hissa Phosphorite Formation) is uniformly thick across Jordan, signaling a return to a more stable tectonic regime. The subsequent organic-rich sequence (Muwaqqar Chalk-Marl Formation) shows a slight thickening trend across the Hamza Graben, indicating renewed subsidence.

The enhanced age dating of the Hamza Graben’s evolution has placed its orientation and timing within the broader context of the transition from passive to active margins along the eastern and southern edges of the Arabian Plate. This synthesis offers new insights into the local intra-plate dynamics during this significant tectonic event and highlights the contemporary formation of petroleum plays in these graben structures.