Rift-initiation development of normal fault blocks: insights from the Hammam Faraun fault block, Suez Rift, Egypt

摘要

An integrated structural and stratigraphic study of the Hammam Faraun fault block, Suez Rift, Egypt, provides insights into the rift-initiation tectonostratigraphic evolution of the crustal-scale normal fault blocks. The shallow marine to offshore Tayiba Formation (Lower Oligocene) represents the youngest preserved pre-rift unit, and key stratal surface development indicates that relative sea-level variations exerted a marked control on its stratigraphic evolution. A major sea-level fall, which may have been a regional (i.e. eustatic) event, occurred during the mid-Oligocene and was synchronous with the onset of rifting. A major erosional unconformity (the base synrift unconformity) formed in response to the sea-level fall and defines a series of NNE–SSW- to NE–SW-trending palaeovalleys up to 40 m deep by 500 m wide, which are infilled by continental deposits and volcanic rocks of the Abu Zenima Formation (Upper Oligocene–Lower Miocene). During the rift initiation, palaeovalleys controlled depositional patterns and the evolving fault-controlled topography was insufficient to modify drainage patterns. Through time, however, surface-breaking faults began to exert a marked control on deposition. This study indicates the complexity that can occur during the rift-initiation phase caused by extrabasinal factors such as eustatic sea-level variations and antecedent drainage.