Abstract Sedimentologic and hydrocarbon systems modeling of continental rift systems often incorporate deposition of organic-rich source rocks in deep, long-lived lacustrine settings as a central premise. A corollary of these models is that the lakes in which organic material can be produced and preserved form during the main phase of synrift extension and associated subsidence; i.e. , during the middle of the rifting history. The deep-lake model has been very successful as an exploration tool but does not describe the relationships observed in all hydrocarbon producing continental rifts. In the Mesozoic basins of the Western Desert of Egypt, the most important and regionally extensive source rock occurs at the base of the synrift fill. These Middle Jurassic Khatatba Formation strata were deposited in broad fluvial flood plains with overbank swamps and small lakes transitional to estuarine or lagoonal environments. Total organic carbon content generally varies from ~1–3% in the shale intervals. The crude oils derived from these shales have variable wax content and a wide range of API gravities. Thin to locally thick coal seams are also commonly present and contribute mostly gas. Production tests of over 8000 barrels per day have been recorded from reservoirs sourced by these Khatatba oils. The deeper stratigraphic position and different lithologic facies of the Western Desert source rocks results in different exploration strategies than those applied to the lacustrine model. The Jurassic source rocks: (1) were deposited over very broad areas and not just along main basin depocenters; (2) were capable of sourcing oils to high-quality prerift Paleozoic reservoirs due to simple proximity of source and reservoir; and (3) are thermally mature in some areas where the Early Cretaceous main subsidence phase strata are not. The fluvial-estuarine source rock model offers an additional exploration strategy in continental rift systems.

Abstract The East Ras Budran Concession is located in the eastern rift shoulder of the Gulf of Suez. Syn- and pre-rift rocks are exposed in the north and east of the concession, and the Markha alluvial plain covers the SW. The Markha plain occupies the hanging wall of a large extensional fault which preserves most of the pre-rift stratigraphic sequence and >3500 m of syn-rift strata. Vertical wells drilled in 1999 indicated the presence of a >200 m oil column in low-porosity naturally fractured limestone beds of the Eocene Darat and Thebes formations. Outcrop, borehole image and core data define NW, WNW, N, NE, and ENE steeply dipping fracture sets. Borehole breakouts and drilling-induced fractures show that the minimum horizontal stress is aligned NNE to NE, so the NW and WNW fractures should be open in the subsurface. Using this structural picture, a near-horizontal well of 300 m length was drilled into the Darat in a NE direction. During testing, the well flowed at a rate of 1900 barrels of oil per day with no water. Future development of the field includes drilling similarly oriented wells with longer horizontal sections.

Abstract The Red Sea—Gulf of Aden rift System provides a superb example of the formation of passive continental margins. Three phases are well represented: (1) continental rifting (Gulf of Suez); (2) rift-to-drift transition (northern Red Sea); and (3) sea-floor spreading (Gulf of Aden and southern Red Sea). Recently published radiometric and biostratigraphic ages, outcrop studies, and reflection seismic profiles more tightly constrain the evolution of this rift system. The principal driving force for separation of Arabia from Africa was slab-pull beneath the approaching Urumieh-Dokhtar volcanic arc on the north side of Neotethys. However, the rifting trigger was impingement of the Afar plume beneath northeast Africa at ~31 Ma. Rifting followed quickly thereafter, initiating in the Gulf of Aden, perhaps in the area between Socotra Island and southern Oman. Extension occurred in the central Gulf of Aden by ~29 Ma. Shortly thereafter, at ~27 Ma, rifting jumped to Eritrea, east of the Danakil region. Rifting then spread from Eritrea to Egypt at ~24 Ma, accompanied by a major dike-emplacement event that covered more than 2,000 km in possibly less than 1 Ma. At ~14 Ma, the Levant transform boundary formed, largely isolating the Gulf of Suez from later extension. Constriction of the Suez-Mediterranean and Red Sea-Aden marine connections resulted in widespread evaporite deposition at this time. Sea-floor spreading began in the eastern Gulf of Aden at ~19 Ma, the western Gulf of Aden at ~10 Ma, and in the south-central Red Sea at ~5 Ma. Propagation of the oceanic ridge has taken much longer than the propagation of its continental rift predecessor. Therefore, the rift-to-drift transition is diachronous and is not marked by a specific “breakup” unconformity. The Red Sea sub-basins are each structurally asymmetric during the syn-rift phase and this is seen in the geometries obtained when its present paired conjugate margins are palinspastically restored. During the Late Miocene and Pliocene, regional-scale, intrasalt detachment faulting, salt flowage, and mass-movement of the post-Miocene salt section toward the basin axis masked the deeper fault block geometry of most of the Red Sea basin. This young halokinesis has enormous consequences for hydrocarbon exploration.

Obduction of lower Paleozoic North American continental margin rocks during the Taconic orogeny led to the formation of extensive northern Appalachian mélange terranes. These include the mélanges associated with the Hamburg klippe in Pennsylvania, the classic Taconic mélanges of eastern New York, the foreland mélanges of Quebec, and the Companion and related mélanges of western Newfoundland. These mélanges are generally unmetamorphosed, although they do contain rare blocks of low- and medium-grade metamorphic rock. They are typified by an assemblage of flyschlike graywacke, siltstone, and argillite blocks within a phacoidally cleaved, fine-grained matrix. The dominant meso-scale deformation mechanisms are progressive shear fracturing and block rotation, accommodated at the grain scale by microshearing, grain-boundary sliding, extension fracturing and limited diffusive mass transfer. These processes occurred within a deformational environment that is inferred to have undergone both high strain rates and high degrees of noncoaxiality. Measured strain states are generally of the form S 1 >> S 2 > 1 > S 3 , with S 1 trending parallel to the regionally deduced transport direction in areas that have escaped post-mélange formation deformations. The minimum deformation represented by phacoidal fabrics appears to involve about 100 percent layer-parallel extension and shear strains ( γ max ) greater than approximately three. Some extension parallel to regional strike (S 2 >1) is noted in most mélange samples. This is accommodated at least in part by zones with prolate ellipsoid strain states in which strike-parallel shortening occurs, and probably also by larger scale structures such as lateral ramps. Tectonic dewatering may have accompanied the formation of some of the mélange units within this regional association. However, this can be shown to have been a noncritical factor in the general mélange deformational history, as both poorly consolidated and well-indurated (completely dewatered) flysch sequences were transformed into mélange at different points and at different times within the orogen, producing very similar end products. Fabric relationships within the Taconic orogen of eastern New York demonstrate that significant westward transport occurred after the development of the regional slaty cleavage, whereas in western Newfoundland the regional slaty cleavage postdates emplacement of the allochthonous terranes in roughly their present positions. Comparison of mélange fabrics from the northern Appalachians and those of other orogenic belts suggests that a simple, consistent structural classification of rock types can be defined that differentiates among undeformed units, deformed but undisrupted units, olistostromes, and mélanges on the basis solely of foliation development and degree of stratal disruption. These are both readily recognizable field characteristics that are nongenetic yet process-oriented. In this classification, a mélange then becomes simply blocks within a phacoidally cleaved matrix.

Location Bald Mountain is located in the southeast corner of the Fort Miller 7½-minute Quadrangle, Washington County, eastern New York. Access is gained via New York 40 north from Greenwich, New York (Fig. 1). A paved secondary road (Bald Mountain Road) leads past the quarries on the west side of the mountain, and the quarry faces can be reached by walking along an overgrowngravel track (entered near the intersection of Bald Mountainand Lick Springs roads). The quarries are abandoned, butadjacent landowners should be notified of your intentions. Schaghticoke Gorge is located south of Bald Mountain in the Schaghticoke 7½-minute Quadrangle at Schaghticoke, New York. Access is also from New York 40 at Chestnut Street on thesouth side of the village. A dirt road is followed from the villagestreet to the lower gorge of the Hoosick River (Fig. 1). The mainexposures here lie in the river bottom, and are therefore best seenin the late summer and fall. The river bottom is public domain, but cars should not be driven over the old concrete bridge at theriver (see Fig. 4), as this is owned by the power company.

The Taconic melanges of eastern New York developed through the progressive deformation of a synorogenic flysch sequence deposited within a N-S elongate foreland basin. This basin formed in front of the Taconic Allochthon as it was emplaced onto the North American continental shelf during the medial Ordovician Taconic Orogeny. The flysch was derived from, and was subsequently overridden by the allochthon, resulting in the formation of belts of tectonic melange. An east to west decrease in deformation intensity allows interpretation of the structural history of the melange and study of the flysch-melange transition. The formation of the melange involved: isoclinal folding, boudinage and disruption of graywacke-shale sequences due to ductility contrasts; sub-aqueous slumping and deposition of olistoliths which were subsequently tectonized and incorporated into the melange; and imbrication of the overthrust and underthrust sedimentary sections into the melange. The characteristic microstructure of the melange is a phacoidal conjugate-shear cleavage, which is intimately associated with high strains and bedding disruption. Rootless isoclines within the melange have apparently been rotated into an east-west shear direction, consistent with fault, fold, and cleavage orientations within the flysch. The melange zones are best modeled as zones of high shear strain developed during the emplacement of the Taconic Allochthon. Total displacement across these melange zones is estimated to be in excess of 60 kilometers.