Kilometre-scale fault-parallel folds are identified adjacent to normal faults in the Oligo-Miocene Suez Rift, Egypt and are interpreted to have formed in response to fault-propagation folding above upward propagating blind faults. The geometry, scale and distribution of secondary structures within the folds and their cross-cutting relationships with the master faults allow the style and sequence of deformation during fault-propagation folding to be established and suggest that during the initial stages of folding, the proto-footwall underwent extension which was accommodated by layer-parallel slip in encasing mudstone horizons and linked normal faulting and block rotation in carbonate and sandstone units. The proto-hanging wall also contains dominantly extensional normal faults although locally, where the master fault had a convex-into-the-footwall map-view trace, reverse faulting and fracturing occurred. Secondary structures adjacent to the master fault were not all active simultaneously, but initiated and died at different stages during the evolution of the fault-propagation fold. The results of this study confirm many key predictions of numerical and physical analogue models but also highlight several important controls on the evolution of fault propagation folds in extensional settings which existing models cannot capture, such as the influence of the map-view trace of the propagating fault and lateral variations in cover stratigraphy lithology and strength on the style and magnitude of secondary deformation.

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.

The shallow marine, early, syn-rift, Miocene, Nukhul Formation, Suez Rift, Egypt, is highly bioturbated and allows relationships between changes in trace fossils and ichnofabrics within a shallow marine depositional system to be documented and placed in a high resolution sequence stratigraphic framework. Seven ichnofabrics are present in a succession of interfingering, calcareous mudstones and calcarenites forming coarsening-up units of up to 30 m thick, bounded by marine flooding surfaces. The units grade upwards from a basal mudstone package with bed parallel concretions and a Planolites-Chondrites ichnofabric (offshore), through a coarsening-up succession of alternating calcarenites and mudstones with Thalassinoides-mottled sediment (offshore transition), Ophiomorpha irregulaire (lower shoreface), Ophiomorpha nodosa-Thalassinoides (lower middle shoreface), Thalassinoides-Taenidium (middle shoreface) and O. nodosa (upper shoreface) ichnofabrics. Gastrochaenolites (hardground) ichnofabric is separate, as it is not genetically related to the other ichnofabrics. Ichnofabric development is primarily controlled by depositional environment, e.g. bottom water oxygenation, sediment type, food abundance and energy level, which control substrate colonisation, sedimentation rate.Marine flooding surfaces are generally well-cemented and marked by distinctive epifaunal and infaunal colonisation and can be traced out from proximal to distal settings over distances of >5 km. The epifaunal colonisation in proximal settings consists of abundant oysters and corals with the substrate below marine flooding surfaces containing abundant Thalassinoides and Ophiontorpha isp. Abundance and diversity of epifauna and trace fossils and burrow size decreases distally into the basin. In the most distal settings, epifaunal colonisation is absent and only Planolites and Chondrites colonise the basinal mudstone. Marine flooding surfaces in the most distal settings are poorly cemented, but are marked by carbonate concretions 10-15 cm below the surface. (C) 2004 Elsevier B.V. All rights reserved.

Tectono-stratigraphic analysis of the East Tanka fault zone (ETFZ), Suez Rift, indicates that the evolution of normal fault segments was an important control on syn-rift depositional patterns and sequence stratigraphy. Sedimentological and stratigraphic analysis of the Nukhul Formation indicates that it was deposited in a narrow (ca 1-2 km), elongate (co 5 km), fault-bounded, tidally influenced embayment during the low subsidence rift-initiation phase. The Nukhul Formation is composed of transgressive (TST) and highstand (HST) systems tract couplets interpreted as reflecting fault-driven subsidence and the continuous creation of accommodation in the hangingwall to the ETFZ. The overlying Lower Rudeis Formation was deposited during the high subsidence rift-climax phase, and is composed of forced regressive systems tract (FRST) shallow marine sandbodies, and TST to HST offshore mudstones. Activity on the ETFZ led to marked spatial variability in stratal stacking patterns, systems tracts and key stratal surfaces, as footwall uplift, coupled with regressive marine erosion during deposition of FRST sandbodies, led to the removal of intervening TST-HST mudstone-dominated units, and the amalgamation of FRST sandbodies and the stratal surfaces bounding these units in the footwall. This study indicates that the evolution of normal fault segments over relatively short (i.e. < 1 km) length-scales has the potential to enhance or suppress a eustatic sea-level signal, leading to marked spatial variations in stratal stacking patterns, systems tracts and key stratal surfaces. Crucially, these variations in sequence stratigraphic evolution may occur within time-equivalent stratal units, thus caution must be exercised when attempting to correlate syn-rift depositional units based solely on stratal stacking patterns. Furthermore, local, tectonically controlled variations in relative sea level can give rise to syn-rift stacking patterns which are counterintuitive in the context of the structural setting and perceived regional subsidence rates.

Facies and tectono-stratigraphic models for the tidally influenced Miocene Nukhul Formation are presented, based on outcrop data from Hammam Faraun fault block, Suez Rift, Egypt. Deposits of the Nukhul Formation are attributed to two linked depositional settings, offshore to shoreface and estuary settings, and were deposited during initial stages of rifting in hanging-wall depocenters of early-formed propagating fault segments. The offshore to shoreface deposits consist of variably bioturbated mudstones that pass gradationally upward to bioturbated bioclastic sandstones. The more landward estuary deposits can be separated into a tripartite division of estuary mouth, estuary funnel with bayhead delta, and upper estuary channel deposits. Estuarine processes generated a complex intercalation of lithologies, with both gradational and sharp facies transitions. In the estuary deposits, tidal ravinement surfaces are typically characterized by mudstones of the estuary-funnel association below, passing abruptly up to erosionally based estuary mouth sandstones. Maximum flooding surfaces are expressed by an abrupt erosional contact separating estuary-mouth sandstones below and estuary-funnel mudstones above.Stratigraphic development was strongly influenced by the evolving early-rift structure. Depocenters were narrow (2-5 km wide) and elongate (< 10 km long) parallel to the strike of normal-fault segments. The shoreface shoal prevented wave energy in the estuary and increased the relative influence of tidal currents. The elongate, fault-controlled geometry of the depocenters confined the bayhead delta and further enhanced tidal influence. Stratal geometry reflects deformation associated with low-relief growth folds and surface-breaking faults that, together, formed part of an evolving fault array. This basin configuration and associated Nukhul stratigraphy is markedly different to tectono-stratigraphic models for crustal-scale tilted fault blocks that are applicable from late stages of rifting.

Fault segment linkage, migration of the locus of fault activity, and displacement localisation were important processes controlling the late Oligocene–Recent evolution of the normal fault population of the Hammam Faraun fault block, Suez rift. Initial fault activity was distributed across the fault block on fault segments that had attained their final length within 1–2My of rifting. These initial segments then either grew by increasing displacement and linked to form longer segmented fault zones or died, during a rift initiation phase that lasted 6–8My. Following this rift initiation phase, displacement became localised onto >25-km-long border fault zones bounding the fault block and many of the early high-displacement intra-block fault zones died. Following displacement localisation onto the major faults bounding the fault block, the locus of maximum displacement continued to migrate, with post-Middle Miocene displacement focused on the western margin of the fault block. This migration of fault activity between major crustal-scale normal faults can be viewed in terms of strain localisation at the rift scale. The results from this study question conventional fault growth models based on final displacement distributions, and highlight the sequential nature of faulting on major normal faults bounding domino-style tilted fault blocks.

This 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.

ABSTRACT This paper investigates syn‐rift stratigraphic architecture and facies relationships along a 7 km long strike section towards the tip of a major, basin‐bounding normal fault segment (Thal Fault) in the Suez Rift, Egypt. In this location, the fault is composed of two precursor fault strands, Gushea and Abu Ideimat, linked by a jog or transfer fault. We document a Miocene syn‐rift succession, deposited more than c. 5.5 Myr after rift initiation, that is composed of a range of carbonate‐clastic facies associated with coarse‐grained deltaic, shoreface and offshore depositional systems. Key regionally correlatable stratal surfaces within this succession define time equivalent stratal units that exhibit variability in thickness and architecture, related to the interplay of both regional and local controls, in particular, the evolution of two, small‐scale (<6 km long) precursor fault strands (Gushea and Abu Ideimat). Integration of structural and stratigraphic data indicates that the boundary (relay ramp) between these two fault strands was a relative high during much of the rift event, with hard‐linkage and considerable displacement accumulation not occurring until at least c. 7.5 Myr after rift initiation. This is because: (i) the preserved stratigraphy is thinner in the hanging wall of the strand boundary; (ii) a eustatic sea‐level fall with an amplitude of 100 m generated more than 25 m of incision at the strand boundary, a region that has a final fault displacement of c. 600 m; and (iii) the fault strand boundary persisted as a footwall low and transport pathway for coarse‐grained deltas entering the basin. This study indicates that variability in stratal thickness and stratigraphic architecture towards the tip of the Thal Fault was related to the linkage history of two small‐scale ( c. 6 km long) precursor fault segments. We suggest that similar, small‐scale stratal variability may occur repeatedly along the entire length of major basin‐bounding fault segments due to the process of fault growth by the linkage of smaller scale precursor strands.

An integrated tectono-stratigraphic analysis of the East Tanka fault zone, Suez rift, indicates fault growth by linkage of initially isolated fault segments that is consistent with fault growth models based on displacement-length (D-L) scaling laws. During the initial 2.4 Ma of rifting, the East Tanka fault zone was composed of two en-echelon fault segments c. 1-1.5 km long, separated by a hanging-wall intrabasin high that controlled the geometry of depocentres filled with continental deposits, Alluvial fan conglomerates were fed through the region between the two fault segments, and form a discrete coarse-grained body, preserved in the immediate hanging wall of the fault zone. Subsequent stratigraphic patterns indicate that the two faults hard-linked to form a single fault zone c. 3.5 km long. Hard linkage of the segments resulted in migration of the zone of maximum displacement and subsidence into the zone of linkage. Uplift due to the migration of activity caused modification of drainage in the footwall of the fault zone that terminated the growth of the alluvial fan. This study demonstrates the need to integrate structural and stratigraphic data when attempting to reconstruct the temporal and spatial evolution of normal fault zones. Additionally, the fault dynamics illustrated have implications for tectono-stratigraphic models of rift basins, and syn-rift stratigraphic evolution.

This study focuses on Miocene sedimentation and stratigraphic evolution in a major transfer zone at the northern tip of the Thal Fault segment, Gulf of Suez. The succession generally shoals upwards from offshore mudstone containing pro‐delta turbidites, into conglomeratic delta foresets and topsets, with sandstone‐dominated shoreface facies coexisting laterally. Despite this upward shoaling, key stratal surfaces marking abrupt changes in relative sea‐level allow the succession to be divided into four stratal units. The stacking pattern of the stratal units suggests an initial relative sea‐level rise that generated a major marine flooding surface. A relative sea‐level fall followed, resulting in widespread exposure and incision. During the ensuing relative sea‐level rise a lowstand coarse‐grained delta and coeval shoreface succession prograded several kilometres basinward. The stratigraphic development of the transfer zone delta is in marked contrast to that of aggradationally stacked deltas that occur near the centre of the Baba‐Sidri fault segment, further south. At the transfer zone, low rates of subsidence and accommodation development coupled with a high sediment supply derived from a large fault tip drainage catchment have produced a strongly progradational delta subject to marked changes in relative sea‐level. In the fault centre location, however, higher rates of accommodation development coupled with lower rates of sediment supply from footwall catchments have produced aggradationally stacked deltas. The results from this study have implications for sequence stratigraphic models and hydrocarbon exploration within extensional basins.

Field data from the Oligocene-Miocene Gulf of Suez rift demonstrate that coeval growth faults, folds, and transfer zones exerted a major control on synrift stratigraphic sequence development. Growth folds in the Suez rift are related to steeply dipping normal faults that propagated upward, resulting in broad, upward-widening monoclines in overlying strata, Folding during fault propagation was accommodated by layer-parallel slip and detachment along mudstone horizons as well as by normal and rare reverse secondary faults that propagated away from the master fault. The eventual propagation of the master fault through to the surface left the steep limb of the monocline and most of the secondary faults in the hanging wall.This evolving structural style exerted a marked control on the geometry and stacking patterns of coeval synrift sediments. Synrift sediments display onlap and intraformational unconformities toward the growth monoclines and buried faults, whereas they diverge into broadly synclinal expanded sections away from the growth monocline. Continued movement across buried faults resulted in the progressive rotation of the monoclinal limb and associated synrift sediments, each successively younger sequence dipping basinward at a shallower angle than the previous one. The resulting synrift geometries differ significantly from stratal geometries normally anticipated adjacent to normal faults. Along-strike variations in facies stacking patterns are also commonly associated with decreasing displacement across faults and associated folds toward low-relief transfer zones. Data from other rift basins indicate that fault-propagation folds are not unique to the Gulf of Suez.

A number of recent papers have stressed the importance of lateral and vertical fault propagation on sediment geometries in active rift settings. However, the majority of these studies have been based on outcrop data. This contribution addresses the evolution of a single, major normal fault and its interaction with adjacent active faults using high‐resolution 3D seismic data from the Smørbukk and Smørbukk South hydrocarbon fields, Halten Terrace, Mid‐Norway. The major fault dividing the two fields, the Trestakk–Smørbukk fault, evolves from a southern segment with a well‐defined set of rift wedges in its hangingwall to a northern segment where the fault tip is buried and a fault‐tip fold is developed. Isochore maps of three Jurassic intervals illustrate a south to north evolution where, initially, Early Jurassic fault activity is limited to the southern part of the study area. Middle to Upper Jurassic intervals display a northwards migration in activity and linkage with two other major faults in the study area. This northwards migration had a profound effect on sediment geometries and depocentres in an area where previously only Late Jurassic rift activity has been recognized.

Field data from onshore exposures of the Oligo‐Miocene Gulf of Suez Rift in the Sinai document the passive rotation of early formed mesoscale synthetic and antithetic faults and associated half‐graben due to long‐lived activity on large displacement (2–5 km) block‐bounding faults. Early formed small‐displacement (<350 m) mesoscale antithetic faults and half‐graben within regional‐scale fault blocks underwent progressive steepening due to footwall uplift, rotational faulting and footwall flexing on large‐displacement, block‐bounding faults. In contrast, mesoscale synthetic faults were progressively rotated to shallower angles. Analysis of palaeohorizontal surfaces within synrift sediments deposited in half‐graben adjacent to the mesoscale faults indicate passive rotations of up to 25° about horizontal axes since deposition. Passive burial and in‐filling of early formed mesoscale faults and half‐graben by synrift sediments is consistent with extension being transferred from numerous mesoscale faults to few block‐bounding macroscale faults as extension preceded. Furthermore, this transfer of extension appears to be associated with a marked change in basin configuration, synrift sediment dispersal patterns and facies development. Identification of early formed, passively rotated normal faults and half‐graben is important for correctly reconstructing the early stages of basin palaeogeography and sediment dispersal, and for addressing models of rift basin evolution.

Although fault growth is an important control on drainage development in modern rifts, such links are difficult to establish in ancient basins. To understand how the growth and interaction of normal fault segments controls stratigraphic patterns, we investigate the response of a coarse‐grained delta system to evolution of a fault array in a Miocene half‐graben basin, Suez rift. The early Miocene Alaqa delta complex comprises a vertically stacked set of footwall‐sourced Gilbert deltas located in the immediate hangingwall of the rift border fault, adjacent to a major intrabasinal relay zone. Sedimentological and stratigraphic studies, in combination with structural analysis of the basin‐bounding fault system, permit reconstruction of the architecture, dispersal patterns and evolution of proximal Gilbert delta systems in relation to the growth and interaction of normal fault segments. Structural geometries demonstrate that fault‐related folds developed along the basin margin above upward and laterally propagating normal faults during the early stages of extension. Palaeocurrent data indicate that the delta complex formed a point‐sourced depositional system developed at the intersection of two normal fault segments. Gilbert deltas prograded transverse into the basin and laterally parallel to faults. Development of the transverse delta complex is proposed to be a function of its location adjacent to an evolving zone of fault overlap, together with focusing of dispersal between adjacent fault segments growing towards each other. Growth strata onlap and converge onto the monoclinal fold limbs indicating that these structures formed evolving structural topography. During fold growth, Gilbert deltas prograded across the deforming fold surface, became progressively rotated and incorporated into fold limbs. Spatial variability of facies architecture is linked to along‐strike variation in the style of fault/fold growth, and in particular variation in rates of crestal uplift and fold limb rotation. Our results clearly show that the growth and linkage of fault segments during fault array evolution has a fundamental control on patterns of sediment dispersal in rift basins.

C. Ash, N. A. Saunders, N. Kachwalla, T. G. Harrison, A. G. Taylor, I. R. Sharp and A. Bailey, Anal. Proc., 1988, 25, 127 DOI: 10.1039/AP9882500127