Fault-bounded Margin Research Articles

A tale of two Arabian Cenozoic ooids: Factors controlling the differential growth of ooids across the Arabian Plate

Ooids are a critical yet enigmatic carbonate grains in the geological record. Previous studies have focused their efforts on studying the mode of ooid formation throughout the Phanerozoic via experimental, numerical simulations, and field studies. To date, however, there is little discussion around factors governing the texture, mineralogy, structure, size, and geometry of Cenozoic ooids, particularly in Saudi Arabia. The present article aims to provide insights on key factors controlling the differential growth of Cenozoic ooids in Saudi Arabia by comparing two contrasting carbonate environments and tectonic settings. Here, we studied the Holocene (0.4–2 kya) ooids developed in the tidally dominated carbonate ramp of the Arabian Gulf under a passive margin setting and the Miocene (15–21 mya) ooids from the Red Sea that were developed in a tectonically active, wave-dominated fault-bounded carbonate platform. The Holocene ooids were characterized by aragonitic, heavily micritized and small (max:550 μm) ooids with bioclast-dominated nuclei. In contrast, the Miocene ooids were replaced by dolomite, larger in size (max:820 μm) and significantly less micritized with variable nuclei compositions, such as rock fragments and bioclasts. The variation in the intensity of bioerosion and micritization suggest the Miocene ooids experienced lesser resting stage time than the Holocene ooids developed under the tide regime due to active wave actions. In addition, the Miocene ooids were developed in a fault-bounded margin allowing a higher carbonate saturation state to concentrate in that zone while the Holocene ooids were developed under a widespread distribution of carbonate saturation state in a vast carbonate ramp setting. These findings indicate that original platform geometry and depositional system (tide-vs wave-dominated) are substantial in dictating the duration of ooid resting stage and distribution of carbonate saturation state across the platforms. All these combined, allows the Miocene ooids to grow larger and reaching its equilibrium size faster. This study highlights the importance of coupling platform architecture and other key environmental parameters (wave actions, sediment supply, and tectonic activities) in understanding the formation of Cenozoic ooids.

Transformation of sediment delivery and dispersal patterns controlled by relay-ramp evolution along the boundary fault of a lacustrine rift: The Eocene Shahejie formation, Dongying Sag, Bohai Bay Basin, NE China

The boundary fault of the Dongying Sag is divided into isolated and scattered segments and small-scale relay zones, which are important geomorphic features controlling sedimentation in the early stage of rift evolution. Previous studies have shown changes in facies in deposits of thousands of meters in thickness on fault-bounded margins, where deep-water fan systems are vertically stacked with delta deposits in the same way as in many basins around the world. However, changes in sedimentation processes and sedimentary systems and their relationship with the evolution of the main boundary fault remain a matter of debate. We focus on the transition from shallow-water to deep-water systems and their responses to relay-ramp evolution in the Yanjia Subsag of the Eocene Dongying Sag in the Bohai Basin. A relatively simple assemblage of local structures provides an ideal opportunity to investigate the impact of relay-ramp evolution on the early synrift deposits. An integrated dataset of 3D seismic volumes, cores and wireline logs is used to analyze the evolution of the Chennan Fault, to delineate thirteen lithofacies, and to recognize two depositional styles (including fan deltas and nearshore subaqueous fans) and their distribution during different stages of the relay-zone evolution. In the early stage of rifting, the depositional style changes, from the development of axial and transverse systems in the early to middle period to the development of transverse systems in the late period; this is mainly controlled by the evolution of the relay ramp. The change is accompanied by a rapid decrease in the rate of sediment supply, architectural changes in transport conduit from the relay ramp to a canyon, and local geomorphic changes that control transport routes, sediment delivery, and depositional locations. Floods ultimately become dominant transport mechanism with a new system, such that hyperpycnal flows form, leading to another transformation of the sedimentary systems from a fan-delta system to a nearshore subaqueous fan system. On the basis of these transformations in sedimentary systems we are able to propose new recommendations for reservoir exploration in continental rift basins, which include exploration potential, source reservoir cap assemblage, and spatiotemporal evolution of plays.

The Baiyun and Liwan Sags: Two supradetachment basins on the passive continental margin of the northern South China Sea

Detachment faults have been reported on the northern and southern margins of the South China Sea (SCS) but have not been recognized in the Paleocene-Eocene Baiyun and Liwan Sags of the Pearl River Mouth Basin (PRMB). This is despite the well-known, very thin crust beneath the two sags. In this study, we use 2D and 3D seismic data to interpret the sequence stratigraphy, as well as identify faults and other important structural features in the Baiyun and Liwan Sags. We show that high-amplitude seismic reflectors, corresponding to detachment faults in the two sags, occur in multistep ramp-flat geometries associated with important structures including: (1) alternating sub-sags and sub-uplifts developing on the hanging walls, (2) secondary faults, (3) dome structures, and (4) extensional allochthons. The detachment faults dip landward and seaward in the Baiyun and Liwan Sags, respectively, indicating paired detachment systems. Hence, integrated with thin crust and subsidence centers offset at great distances from the fault-bounded margins, the Baiyun and Liwan Sags are demonstrated to be supradetachment basins seated on the distal domain of the northern SCS's passive continental margin. The well-correlated sequence stratigraphic framework in all sub-sags shows that the detachment faults fit the standard detachment model in which faults are continuously active. Furthermore, two detachment basins are inferred to have developed over hot ductile crust resulting from plate subduction in the Mesozoic. Since the upper crust stretches far less than the middle/lower crust, the fault-controlled extension is proposed to have had a smaller contribution to the thinned crust than a ductile extension did within the middle/lower crust in the study area. The recognition of detachment faults and supradetachment basins is a significant contribution towards understanding the formation of the northern passive continental margin of the SCS.

Neotectonics and seismicity of Erzurum pull-apart basin, East Turkey

The study area is the Erzurum pull-apart basin located in the East Anatolian Tectonic Block (EATB), which is under the control of a strike-slip neotectonic regime since the beginning of Quaternary. The Quaternary Erzurum pull-apart basin is an about 1-30 km wide, 90 km long and actively growing strike-slip depression. It is bounded by the Erzurum-Dumlu sinistral strike-slip fault zone to the east-southeast, by the Askale sinistral strike-slip fault zone to the north-northwest, and by the Baskoy-Kandilli reverse fault zone and the N-S-trending Ilica oblique-slip normal fault set to the west. The Erzurum pull-apart basin was evolved by the deformation and subdivision of an E-W-trending older intermontane basin. The new basin has a 0.5 km thick, flat-lying (undeformed) and uconsolidated fill, which overlies, with an angular unconformitry, the deformed (folded and faulted) basement rocks of pre-Quaternary age. Basin fill consists of coarser-grained marginal facies (fault terrace, fan, fan-apron and superimposed fan deposits) and finer-grained depocentral facies represented by flood plain to organic material-rich marsh deposits. All gradations are seen among these lithofacies.The seismicity of the Erzurum pull-apart basin is quite high. The magnitude of the peak earthquake to be sourced from the active faults (e.g., the Erzurum fault) is about Mw = 7.0. This was proved by both the historical and recent earthquakes. Numerous settlements in the size of a large city (e.g., Erzurum), county, town and small villages with a total population of over 766,000 are located in and along the active fault-bounded margins of the Erzurum pull-apart basin. They are under the threat of destructive earthquakes to be sourced from the margin-boundary faults. Therefore, based on both the active fault parameters and the water-saturated basin fill, a large-scale earthquake hazard map has to be prepared. This map has to be used in both the earthquake hazard to risk analyses and the redesign of city planning and all type of constructions in Erzurum and other settlements in this region.

Lacustrine sedimentation in the diapir-controlled Miocene Bicorb Basin, eastern Spain

The Miocene Bicorb Basin is a small elongated basin developed by normal faulting of a thick Jurassic–Cretaceous carbonate succession and subsequent diapirism of Upper Triassic mudstones and evaporites. The basin fill comprises a sequence over 650 m thick formed by two units. The lower, alluvial unit consists of a complex alternation of conglomerates, sandstones, mudstones, and minor lacustrine limestones. The upper unit comprises marginal alluvial and lacustrine deposits in which seven lacustrine facies associations have been distinguished. The inner lacustrine deposits comprise mudstones and carbonates with minor evaporitic deposits. At the northeast and southwest basin edges, alluvial inputs led to the development of delta and fan-delta environments where sandstone and conglomerate deposits dominate. The latter stages of the lake evolution are represented by an expansive thick limestone sequence which close to the NW fault-bounded margin pass laterally to breccias. The hierarchical arrangement of the upper unit shows five different orders of sequences. The first-order sequence defines a major vertical trend of lake expansion whereas three second-order sequences are linked to major flooding-expansion episodes. All these sequences are related to the tectonic evolution of the diapir. Metre-scale, third- and fourth-order sequences and fifth-order sequences, which consist of finely laminated rhythmite deposits probably record climatically forced processes. The diapir–graben system evolution and the climatic variations have exerted major controls on the sequential arrangement and evolution of the lacustrine system. Both factors have also strongly influenced the changes in the gastropod assemblages.

The depositional environments and tectonic development of a Mesozoic intra-arc basin, Atacama Region, Chile

AbstractA thick succession of continental redbeds was deposited in a 50 km wide intra-arc basin on the Andean active continental margin in the Atacama region of northern Chile during early Cretaceous times. Upper Jurassic to early Cretaceous marine limestones were buried by the seaward progradation of a succession of coastal dunes, saline lakes and sandflats. Aeolian dune fields migrating towards the east across these coastal plains became stabilized by the growth of vegetation. Interdune alluvial areas between the sand dunes and dune fields developed into extensive alluvial braid plains which were in turn superimposed by alluvial fans. These fans were inundated by a regionally extensive saline lake produced by tectonic or volcanic damming of the sedimentary basin. This lake dried up leaving a large area of playa-lake mudflats. The climate was warm and semi-arid with a low and seasonal rainfall. Parts of the area supported a substantial vegetation of woody plants, together with a vertebrate fauna of dinosaurs, pterosaurs and crocodiles. The continental redbeds were derived from a volcanic source and were deposited on continental crust in a deep but narrow, north-south elongated, fault-bounded graben. This extensional basin formed in an intra-arc setting within an active andesitic volcanic chain. Upwards-coarsening sedimentary successions were the product of uplift of the fault-bounded margins of the basin.

Fan-Delta and Interdeltaic Shoreline Sediments of Middle Devonian Granite Wash and Keg River Clastics, Red Earth Field, North Alberta Basin, Canada: ABSTRACT

A detailed sedimentological investigation of over 4000 ft of core and 500 well logs of the Middle Devonian granite wash and Keg River clastics in the Red Earth field, North Alberta basin, Canada, has led to the recognition of a granite wash subaerial fan-delta system that is laterally continuous with a Keg River subaqueous delta component along an eastern shoreline of the ancestral Peace River arch. The subaerial fan delta includes alluvial fan facies, sheet wash and mud flows, and playa lakes. The subaqueous delta component includes lower shoreface, upper shoreface, beach-foreshore, eolian sand dunes, lagoon, washover sands, tidal channels and flats, and supratidal carbonates and anhydrites. Within this system, six mappable units are defined. A conceptual depositional model for the sequence depicts four main events. (1) Erosion of Peach River arch uplifted fault blocks, which produced coarse-grained fan-delta sediments in an adjacent fault-bounded margin. Subsequent fluvial reworking resulted in the deposition of thick, lenticular, wedge-shaped alluvial fans of granite wash. (2) Progradation of alluvial fans seaward into the Keg River Sea. (3) Transgression by Middle Devonian seas from the east, which reworked alluvial fans and led to deposition of discontinuous linear sand bodies represented by the Keg River regressivemore » shoreline sediments. (4) Restriction of the sea by the Presqu'ile barrier reef to the north, which deposited evaporites of the Muskeg Formation over the whole sequence. Modern analog to this fan-delta system is the coastal fans of the Gulf of Aqaba, Red Sea. Red Earth field contains over 27 million bbl of recoverable oil, related to a combination structural-stratigraphic trap.« less

Fan-deltas and braid deltas: Varieties of coarse-grained deltas

Two types of coarse-grained deltas are recognized: fan-deltas and braid deltas. Fan-deltas are gravel-rich deltas formed where an alluvial fan is deposited directly into a standing body of water from an adjacent highland. They occupy a space between the highland (usually a fault-bounded margin) and the standing body of water. In contrast, braid deltas (here introduced) are gravel-rich deltas that form where a braided fluvial system progrades into a standing body of water. Braid deltas have no necessary relationship with alluvial fans, as exemplified by fluvioglacial braid deltas. Braid deltas have previously been classified as fan-deltas even though the geomorphic and sedimentologic settings of the two systems can be vastly different. Braid deltas are a common present-day geomorphic feature and are abundant in the geological record. Fan-deltas and braid deltas can be distinguished in the rock record by distinctive subaerial components of these depositional systems; the shoreline and subaqueous components of both are similar. Fan-delta sequences have a subaerial component that is an alluvial-fan facies comprising interbedded sheetflood, debris-flow, and braided-channel deposits. Fan-deltas produce small (a few tens of square kilometres), wedge-shaped bodies of sediment, commonly displaying high variability in paleocurrent patterns and abrupt changes in facies. The deposits are generally very coarse grained (with large out-sized clasts), very poorly sorted, matrix-rich, polymictic, heterolithic, partially cemented by penecontemporaneous carbonate, and have low porosity and permeability. Braid-deltas, in contrast, have a subaerial component consisting entirely of braided-river or braidplain facies. Their deposits display better sorting, roundness, and clast orientation than do fan-delta sediments; they lack a muddy matrix; they display size grading and bar migration; they commonly have a sheet geometry with high lateral continuity (tens to hundreds of square kilometres); and they exhibit moderate to high porosity and permeability. Valuable paleogeographic and tectonic information concerning the proximity of highlands and major fault zones may be misinterpreted or lost if these two coarse-grained deltaic systems are not differentiated.

Sedimentation in Pull-Apart Basins: Active Examples in Eastern Turkey

The Erzincan, Susehri, Niksar, and Lake Hazar basins are actively evolving pull-apart basins in eastern Turkey. Their structural, drainage, and depositional systems generally support a pull-apart basin sedimentation model based on ancient pull-apart basin deposits. This model involves marginal coarse-grained sedimentation adjacent to master faults, axial fine-grained sedimentation away from master faults, and high sedimentation rates. However, studies of the Turkish pull-apart basins suggest the following refinements in the model. (1) Detailed sedimentary facies patterns and the dominant facies of a pull-apart basin vary according to basin shape, climate, drainage character, and volcanic activity. Depositional environments near fault-bounded margins include alluvial fan, fan delta, and alluvial apron. Depositional environments in central areas away from fault-bounded margins include active braid plain, inactive braid plain, meander plain, salt playa, marsh, lacustrine, mouth-bar delta, and volcanic. (2) If internally drained, a pull-apart basin is likely to contain axial and transverse drainages. If externally drained, the drainage pattern varies and may exit the basin axially or transversely. (3) Pull-apart basin shapes are not necessarily rhomboidal. Comparison of data from the Turkish pull-aparts with other modern and ancient pull-apart basins suggests that sediment thickness (y) is related to length of a pull-apart basin parallel to master fault overlap (x) by the equation y = .08x + .26. This relationship predicts sediment thickness in the Erzincan, Susehri, Niksar, and Lake Hazar pull-apart basins is 2.9, 2.1, 1.5, and 0.68 km, respectively.

Emplacement and deformation of the archean Saganaga batholith, vermilion district, northeastern Minnesota

The Saganaga “quartz eye” tonalite forms a crescent-shaped batholith which was intruded 2.7 b.y. ago, rapidly unroofed, and subsequently deformed. It contains four major petrologic phases and displays intrusive relations along the eastern and southern borders and fault-bounded margins on the west and north. Penetrative structures are developed to varying degrees throughout the body with lineation commonly aligned in the plane of foliation. Ductile zones of cataclasis occur locally within the pluton. Cumulate, homogeneous strain was analyzed using deformed quartz phenocrysts in samples from throughout the batholith by measuring particle dimensions and angular relationships of particle axes to principal planes. Strain parameters were calculated using the shape factor grid method although other methods were tested. Strain varies both in pattern and magnitude throughout the body. Flattening predominates near the northern, western and southern boundaries and is well developed ( E s = 0.3–3.7). Lineations generally plunge eastward from 10–20° along the western margin to 60° on the east and are moderately developed ( E s = 0.6–1.5). A zone in the interior of the pluton contains north-trending shallow lineations which are weakly developed ( E s = 0.2–0.3). The neutral zone does not coincide precisely with the change in attitude of penetrative structures. The overall strain pattern of the body indicates that it was emplaced as a crescent-shaped synform along the interface between older gneiss and greenstone units. Field evidence indicates that the body was at least partly molten during emplacement. The magnitude, pattern and geometry of strain suggest that either the body was restricted by boundary conditions during emplacement or that it was deformed after emplacement and erosion. Diapirism of the pluton after erosion appears most compatible with the strains observed as well as the regional pattern of deformation. Late-stage faulting displays right-lateral displacement along the northern and western margins of the batholith and development of cataclastic zones within the batholith postdate the penetrative deformation. Faulting and cataclasis occurred prior to 1.7 b.y. and two periods of faulting are evident.