Evolving fluvial—transitional—marine deposition through the Cambrian sequence of Jordan

The Cambrian sequence in Jordan crops out in a belt-like pattern extending over more than 300 km from the Arabian-Nubian Shield source rock in the south, located on a stable shelf platform, to the invading southern (Baltic) side of the Tethys seaway. The analysis of the lithofacies association, ichnofossil content, together with the architecture of fluvial and paralic sandstone bodies reveals the development of the depositional environments of the Cambrian deposits of Jordan. The depositional environment evolved from proximal alluvial fans into major sand flats of braided rivers or directly into distal braidplains dominated by 3-D megaripples. In the following depositional phase, various marine environments prevailed including platform carbonates, clastic-, carbonate- and mixed-tidal fiats and supratidal sabkhas, and less common lagoons. All these marine, or marine-influenced environments changed back into distal braidplains or sand fiats of braided streams. The latter persisted through the remaining period of the Cambrian. The study has revealed that shales containing Cruziana interbedded within the fluviatile sandstone sequence are time markers that can be used for correlation, and could be deposited in a braidplain, if the detrital influx was very low. It is the latter that enabled the Cruziana-producing trilobites to migrate from the sea through river mouths to reach distal braidplains and lagoons.