SYNRIFT CONTINENTAL TO MARINE DEPOSITIONAL SEQUENCES, TERTIARY, GULF-OF-ADEN, YEMEN

Tertiary synrift deposits along the northern margin of the Gulf of Ade n, Republic of Yemen, provide new information on the controls on depos ition and stratigraphic relationships during the transition from conti nental to marine rift sedimentation, Intracontinental rifting in the r egion commenced in the Oligocene, developing into a marine extensional margin in the Miocene, The outcropping part of a small subbasin at Wa di Hiru, west of Mukalla, contains carbonate platform, alluvial-fan, f an-delta, and raised-beach deposits that record the development of the rift margin, The spatial relationships between carbonate and elastic units, their location adjacent to rift-border faults, and timing of se a-level changes indicate that tectonics was the overriding control on relative sea-level changes. Accommodation space created by fault movem ent and the morphology of older sediment bodies dictated the three-dim ensional architecture of carbonate platforms and elastic fans, Fault m ovements are documented by changes in clast provenance in fanglomerate s. Rift-parallel and rift-perpendicular faults formed a trap-door conf iguration that controlled long-lived pathways of terrigenous elastic s upply throughout rifting, Five local depositional sequences, bounded b y erosion surfaces, are recognized, Sequences have a distinct tectonic signature in the form of sequence boundaries overlain by thick fanglo merates followed by transgressive and highstand carbonates, Two of the se sequences were dated using Sr-87/Sr-86 isotope dating, The relative sea-level curve derived from this study bears little relationship to published ''eustatic'' curves.