Normal fault growth and early syn‐rift sedimentology and sequence stratigraphy: Thal Fault, Suez Rift, Egypt

Abstract

AbstractThis paper investigates the tectono‐stratigraphic development of a major, segmented rift border fault (Thal Fault) during ca. 6 Myr of initial rifting in the Suez Rift, Egypt. The Thal Fault is interpreted to have evolved by the progressive linkage of at least four fault segments. We focus on two contrasting structural settings in its hangingwall: Gushea, towards the northern tip of the fault, and Musaba Salaama, ca. 20 km along‐strike to the south, towards the centre of the fault. The early syn‐rift stratigraphic succession passes upwards from continental facies, through a condensed marginal marine shell‐rich facies, into fully marine shoreface sandstone and offshore mudstone. Regionally correlatable stratal surfaces within this succession define time‐equivalent stratal units that exhibit considerable along‐strike variability in thickness and facies architecture. During the initial ca. 6 Myr of rifting, the thickest stratigraphy developed towards the centre of the array of fault segments that subsequently hard linked to form the Thal Fault. Thus, a displacement gradient existed between fault segments at the centre and tip of the fault array, suggesting that the fault segments interacted, and a fixed length was established for the fault array, at an early stage in rifting. Towards the centre of the Thal Fault the early syn‐rift succession shows pronounced thickening away from the fault and towards a series of intra‐block antithetic faults that were active for up to ca. 6 Myr. This indicates that a large proportion of fault‐controlled subsidence during the initial ca. 6 Myr of rifting occurred in the hangingwalls of antithetic intra‐block faults, and not the present‐day Thal Fault. The antithetic faults progressively switched off during rifting such that after ca. 6 Myr of rifting, fault‐activity had localised on the Thal Fault enabling it to accrue to the present‐day high level of displacement. Aspects of the development of the Thal Fault appear to be in contrast to many models of fault evolution that predict large‐displacement rift‐climax faults to have always had the greatest displacement during fault population evolution. This study has implications for tectono‐stratigraphic development during early rift basin evolution. In particular, we stress that caution must be taken when relating final rift‐climax fault structure to the early tectono‐stratigraphy, as these may differ considerably.