Sedimentary architecture of the ediacaran mixed carbonate-siliciclastic system, NW arabian plate: Regionally extensive marine incursion or syntectonic fault-controlled basin?

Ediacaran sedimentary successions worldwide are commonly characterized by mixed siliciclastic-carbonate deposits exhibiting contemporaneous deposition. In NW parts of the Arabian plate, a similar style of sedimentation is observed within a series of isolated basins along the NW-trending Najd Fault System. Two contrasting depositional models have been proposed to explain the formation of Km-thick Ediacaran sedimentary sequences in the region, from regionally extensive marine platform to fault-controlled basins with syntectonic deposition. To date, this question remains unanswered and the controlling factors governing the mode of formation, the evolution and the sedimentary architecture for these Ediacaran sequences remain enigmatic. In this study, we explore this mixed siliciclastic and carbonate sedimentation by conducting detailed sedimentology and stratigraphic analysis of the Ediacaran Dhaiqa basin, a transtensional basin formed along the Najd Fault system of western Saudi Arabia. Eight sedimentary facies are identified, ranging from polymict conglomerate to microbial carbonate which most likely represent accumulation in continental (alluvial to lacustrine) to marginal marine settings. In addition to sedimentological evidences for syn-sedimentary tectonic activity, we observed four 3rd-order fining- and deepening-upwards sequences, which may suggest multi-stage, fault-controlled sedimentation related to local tectonic activity in the Dhaiqa basin. Variations in sequence arrangement and thickness further indicate discrete fluctuations in the development of local accommodation space in the basin. These findings highlight how the style of sedimentation in the Ediacaran basins of the Arabian-Nubian Shield may be primarily controlled by local fault-related accommodation, which might differ from many Ediacaran successions that record relative and eustatic base level changes, but is similar to the basins formed in the regions influenced by tectonism. Such information provides a better framework to compare Ediacaran rocks across multiple isolated basins spread across the northwestern regions of the Arabian-Nubian Shield, and may provide base for the future correlations of these sequences with mixed siliciclastic carbonate successions in similar syn-tectonic basins worldwide.