Garzón Massif basement tectonics: Structural control on evolution of petroleum systems in upper Magdalena and Putumayo basins,Colombia

The Garzón Massif, is an active Laramide style basement uplift flanked by the Upper Magdalena Valley (UMV) and the Putumayo Basin. In this paper we use new gravity, magnetic, well and seismic data for the first geophysical interpretation of the Garzón Massif. The Garzón/Algeciras fault has been previously interpreted as a right-lateral strike-slip fault. The new seismic, well, and gravity data demonstrates that the Garzón fault is also a low-angle (12–17°) Andean age fault thrusting PreCambrian basement 10–17 km northwestward over Miocene sediments of the UMV in a prospective footwall anticline.The new geophysical data as well as previous field mapping were used to produce the first gravity and magnetic maps and retrodeformable structural cross section of the northern Garzón Massif. The new model distinguishes for the first time distinct episodes of “thin-skinned” and “thick-skinned” deformation in the Garzón Massif. The model indicates approximately 43 km of Early to Middle Miocene shortening by “thin-skinned” imbricate thrusting contemporaneous with the uplift of the nearby southern Central Cordillera (∼9–16 Ma) and the main hydrocarbon expulsion event for the UMV and Putumayo Basin. This was followed by at least 22 km of Late Miocene (3–6 Ma) “thick-skinned” Andean shortening and 7 km of uplift on the symmetrical Garzón thrust and a SE-verging basement thrust fault zone. The Andean uplift interrupted and exposed the hydrocarbon migration pathways to the Putumayo Basin.3-D volume fracture analysis was used for the first time in this paper together with the first seismic and well data published for the Topoyaco and Miraflor structures to test closure models for the Topoyaco foothills. Intense fracturing is observed in the Topoyaco basement monocline from the near-surface to depths of over 3.5 km. The high level of fracturing permitted freshwater flushing and oil biodegradation and hydrocarbon escape. In contrast, the Miraflor-1 well, located just southwest of the Topoyaco block, tested light gravity oil and is sealed from groundwater flushing and biodegradation by a backthrust.     

Cenozoic folding in the Cumuruxatiba basin,Brazil: An approach to the deformation trigger by the Abrolhos magmatism

The Cumuruxatiba basin is located in the central portion of the eastern Brazilian margin surrounded by Cenozoic magmatic highs that belong to the Abrolhos Magmatic Complex. This basin was formed by rifting, in the Neocomian followed by thermal subsidence during late Cretaceous like other basins along the Eastern Brazilian margin. In the Cenozoic, the Abrolhos magmatism took place as sills and dykes intruded the sedimentary section, primarily during the Paleogene. In that time, there was a strong NS contractional deformation in the basin represented by folds related to reverse faults coeval with Abrolhos magmatism activity. The structural restorations of regional 2D seismic sections revealed that most of the contractional deformation was concentrated at the beginning of the Cenozoic with maximum peak at the Eocene (up to 33% of total shortening and rate of 6 km/Ma). The Post-Eocene period was marked by a decrease in the strain rate that continues to the present day (around 4 km/Ma to less than 1). 3D structural modelling exhibited a major, well-developed E–W to NE–SW fold belt that accommodated most of the contractional Cenozoic deformation between Royal Charlotte and Sulphur Minerva magmatic highs. Volcanic eruptions and magmatic flows from the Abrolhos complex resulted in differential overburden on edge of the basin, acting as a trigger for halokinesis and the subsequent formation of fault-related folds. In general, such structures were developed close to adjacent magmatic highs, commonly exhibiting vergence towards the centre of the basin. Some magmatic features formed coeval with Cenozoic syn-deformation sediments clearly indicate that Abrolhos magmatism activity and contractional deformation development were associated. The study of the thickness variation of the syn-deformation section in relation to fault-related folds on deformation maps and maximum strain diagrams revealed that most folds were activated and re-activated several times during the Cenozoic without a systematic kinematic pattern. This lack of systematic deformation might be related to the variation of the magmatic pulse activity of adjacent magmatic highs resulting in a complex interference pattern of Cenozoic folds. These structural interpretations of the timing of fault-related folds that are potential Cenozoic traps in the Cumuruxatiba basin play a fundamental role in petroleum systems and exploration of low-risk hydrocarbon prospects.     

The role of basement tectonic reactivation on the structural evolution of Campos Basin,offshore Brazil: Evidence from 3D seismic analysis and section restoration

The structural analysis of regional 3D seismic data shows evidence of long-term tectonic inheritance in Campos Basin, offshore Brazil. Main Lower Cretaceous rift structures controlled themselves by strike-slip deformation belts related to Proterozoic orogenic events, have been episodically reactivated during the divergent margin phase of Campos Basin, from the Albian to the Miocene. Balanced cross-sections of major salt structures indicate that such tectonic reactivations have been controlling thin-skinned salt tectonics, triggering pulses of gravitational gliding above the Aptian salt detachment. Additionally, major basin features like the Neogene progradation front and the salt tectonic domains are constrained by the main Proterozoic orogenic trends of the Ribeira Belt (NE–SW) and the Vitória-Colatina Belt (NNW–SSE). As the basement involved structures observed in Campos Basin can be attributed to general geodynamic processes, it is suggested that basement tectonic reactivation can be as relevant as isostatic adjustment and detached thin-skinned tectonics on the structural evolution of divergent margin settings.     

Extensional fault evolution within the Exmouth Sub-basin,North West Shelf,Australia

Structural analysis of the Indian Merge 3D seismic survey identified three populations of normal faults within the Exmouth Sub-basin of the North West Shelf volcanic margin of Australia. They comprise (1) latest-Triassic to Middle Jurassic N-NNE-trending normal faults (Fault Population I); (2) Late Jurassic to Early Cretaceous NE-trending normal faults (Fault Population II); and (3) latest-Triassic to Early Cretaceous N-NNE faults (Fault Population III). Quantitative evaluation of >100 faults demonstrates that fault displacement occurred during two time periods (210–163 and 145–138 Ma) separated by ∼20 Myr of tectonic quiescence. Latest Jurassic to Early Cretaceous (145–138 Ma) evolution comprises magmatic addition and contemporaneous domal uplift ∼70 km wide characterised by ≥ 900 m of denudation. The areally restricted subcircular uplift centred on the southern edge of the extended continental promontory of the southern Exmouth Sub-basin supports latest Jurassic mantle plume upwelling that initiated progradation of the Barrow Delta. This polyphase and bimodal structural evolution impacts current hydrocarbon exploration rationale by defining the nature of latest Jurassic to Early Cretaceous fault nucleation and reactivation within the southern Exmouth Sub-basin.     

Salt diapirs in the Dead Sea basin and their relationship to Quaternary extensional tectonics

Regional extension of a brittle overburden and underlying salt causes differential loading that is thought to initiate the rise of reactive diapirs below and through regions of thin overburden. We present a modern example of a large salt diapir in the Dead Sea pull-apart basin, the Lisan diapir, which we believe was formed during the Quaternary due to basin transtension and subsidence. Using newly released seismic data that are correlated to several deep wells, we determine the size of the diapir to be 13×10 km, its maximum depth 7.2 km, and its roof 125 m below the surface. From seismic stratigraphy, we infer that the diapir started rising during the early to middle Pleistocene as this section of the basin underwent rapid subsidence and significant extension of the overburden. During the middle to late Pleistocene, the diapir pierced through the extensionally thinned overburden, as indicated by rim synclines, which attest to rapid salt withdrawal from the surrounding regions. Slight positive topography above the diapir and shallow folded horizons indicate that it is still rising intermittently. The smaller Sedom diapir, exposed along the western bounding fault of the basin is presently rising and forms a 200 m-high ridge. Its initiation is explained by localized E–W extension due monoclinal draping over the edge of a rapidly subsiding basin during the early to middle Pleistocene, and its continued rise by lateral squeezing due to continued rotation of the Amazyahu diagonal fault.     

Deep crustal structure of the conjugate margins of the SW South China Sea from wide-angle refraction seismic data

The South China Sea is the largest marginal basin of SE Asia, yet its mechanism of formation is still debated. A 1000-km long wide-angle refraction seismic profile was recently acquired along the conjugate margins of the SW sub-basin of the South China Sea, over the longest extended continental crust. A joint reflection and refraction seismic travel time inversion is performed to derive a 2-D velocity model of the crustal structure and upper mantle. Based on this new tomographic model, northern and southern margins are genetically linked since they share common structural characteristics. Most of the continental crust deforms in a brittle manner. Two scales of deformation are imaged and correlate well with seismic reflection observations. Small-scale normal faults (grabens, horsts and rotated faults blocks) are often associated with a tilt of the velocity isocontours affecting the upper crust. The mid-crust shows high lateral velocity variation defining low velocity bodies bounded by large-scale normal faults recognized in seismic reflection profiles. Major sedimentary basins are located above low velocity bodies interpreted as hanging-wall blocks. Along the northern margin, spacing between these velocity bodies decreases from 90 to 45 km as the total crust thins toward the Continent–Ocean Transition. The Continent–Ocean Transitions are narrow and slightly asymmetric – 60 km on the northern side and no more than 30 km on the southern side – indicating little space for significant hyper-stretched crust. Although we have no direct indication for mantle exhumation, shallow high velocities are observed at the Continent–Ocean Transition. The Moho interface remains rather flat over the extended domain, and remains undisturbed by the large-scale normal faults. The main décollement is thus within the ductile lower crust.     

Structural characteristics of central depression belt in deep-water area of the Qiongdongnan Basin and the hydrocarbon discovery of Songnan low bulge

The Qiongdongnan Basin has the first proprietary high-yield gas field in deep-water areas of China and makes the significant breakthroughs in oil and gas exploration. The central depression belt of deep-water area in the Qiongdongnan Basin is constituted by five sags, i.e. Ledong Sag, Lingshui Sag, Songnan Sag, Baodao Sag and Changchang Sag. It is a Cenozoic extensional basin with the basement of pre-Paleogene as a whole. The structural research in central depression belt of deep-water area in the Qiongdongnan Basin has the important meaning in solving the basic geological problems, and improving the exploration of oil and gas of this basin. The seismic interpretation and structural analysis in this article was operated with the 3D seismic of about 1.5×10~4 km~2 and the 2D seismic of about 1×10~4 km. Eighteen sampling points were selected to calculate the fault activity rates of the No.2 Fault. The deposition rate was calculated by the ratio of residual formation thickness to deposition time scale. The paleo-geomorphic restoration was obtained by residual thickness method and impression method. The faults in the central depression belt of deep-water area of this basin were mainly developed during Paleogene, and chiefly trend in NE–SW, E–W and NW–SE directions. The architectures of these sags change regularly from east to west: the asymmetric grabens are developed in the Ledong Sag, western Lingshui Sag, eastern Baodao Sag, and western Changchang Sag; half-grabens are developed in the Songnan Sag, eastern Lingshui Sag, and eastern Changchang Sag. The tectonic evolution history in deep-water area of this basin can be divided into three stages,i.e. faulted-depression stage, thermal subsidence stage, and neotectonic stage. The Ledong-Lingshui sags, near the Red River Fault, developed large-scale sedimentary and subsidence by the uplift of Qinghai-Tibet Plateau during neotectonic stage. The Baodao-Changchang sags, near the northwest oceanic sub-basin, developed the large-scale magmatic activities and the transition of stress direction by the expansion of the South China Sea. The east sag belt and west sag belt of the deep-water area in the Qiongdongnan Basin, separated by the ancient Songnan bulge, present prominent differences in deposition filling, diaper genesis, and sag connectivity. The west sag belt has the advantages in high maturity, well-developed fluid diapirs and channel sand bodies, thus it has superior conditions for oil and gas migration and accumulation. The east sag belt is qualified by the abundant resources of oil and gas. The Paleogene of Songnan low bulge, located between the west sag belt and the east sag belt, is the exploration potential. The YL 8 area, located in the southwestern high part of the Songnan low bulge, is a favorable target for the future gas exploration. The Well 8-1-1 was drilled in August 2018 and obtained potential business discovery, and the Well YL8-3-1 was drilled in July 2019 and obtained the business discovery.     

Coupled stratigraphic and fault seal modelling used to describe trap integrity in the frontier Bight Basin,Australia

Top seals and faults represent key risks to trap integrity and therefore preservation of hydrocarbons in the frontier Ceduna Sub-basin, offshore Southern Australia. Due to a paucity of well data in the basin, to provide constraint to the stratigraphic distribution of the prospective Cretaceous deltaic and marine sequences, stratigraphic forward modelling was utilised to create facies, grain size and V_shale volumes. These modelled V_shale volumes were subsequently used to investigate the structural control(s) on potential hydrocarbon leakage and migration within key stratigraphic sequences in the sub-basin.A set of coarse (20 km horizontal resolution), large scale (1100 × 600 km) stratigraphic forward models simulated the deposition of Late Jurassic to Tertiary stratigraphic sequences in the sub-basin with an initial 1 Ma interval. Smaller (80 × 60 km), finer scale (0.5 km horizontal resolution, 200 ka interval), models focussing on the Tiger and Hammerhead Supersequences over the Trim 3D seismic survey were used to investigate fault seal and top seal frameworks, using shale gouge ratio and silt and shale thicknesses from V_shale volume. Four stratigraphic forward models were produced to match a range of estimates of V_shale derived from the Gnarlyknots-1A well, the only well penetrating the central Ceduna Sub-basin. These stratigraphies were in turn integrated into a geological model interpreted from the Trim 3D seismic survey creating a geocellular model to test potential migration and trapping scenarios for potential hydrocarbons generated in the sub-basin.Fault and top seal models from the most likely scenario suggest (i) restricted potential for structural trapping near the base of the Tiger Supersequence, (ii) the possible presence of a regional migration pathway associated with sandy shoreface deposits at the transition between the Tiger and Hammerhead Supersequences, and (iii) the association of intraformational top seals and increasing fault seal potential in the deltaic sediments of the Hammerhead Supersequence feasibly resulting in a series of stacked structural traps.     

Structural controls on the formation of BSR over a diapiric anticline from a dense MCS survey offshore southwestern Taiwan

A dense seismic reflection survey with up to 250-m line-spacing has been conducted in a 15 × 15 km wide area offshore southwestern Taiwan where Bottom Simulating Reflector is highly concentrated and geochemical signals for the presence of gas hydrate are strong. A complex interplay between north–south trending thrust faults and northwest–southeast oblique ramps exists in this region, leading to the formation of 3 plunging anticlines arranged in a relay pattern. Landward in the slope basin, a north–south trending diapiric fold, accompanied by bright reflections and numerous diffractions on the seismic profiles, extends across the entire survey area. This fold is bounded to the west by a minor east-verging back-thrust and assumes a symmetric shape, except at the northern and southern edges of this area, where it actively overrides the anticlines along a west-verging thrust, forming a duplex structure. A clear BSR is observed along 67% of the acquired profiles. The BSR is almost continuous in the slope basin but poorly imaged near the crest of the anticlines. Local geothermal gradient values estimated from BSR sub-bottom depths are low along the western limb and crest of the anticlines ranging from 40 to 50 °C/km, increase toward 50–60 °C/km in the slope basin and 55–65 °C/km along the diapiric fold, and reach maximum values of 70 °C/km at the southern tip of the Good Weather Ridge. Furthermore, the local dips of BSR and sedimentary strata that crosscut the BSR at intersections of any 2 seismic profiles have been computed. The stratigraphic dips indicated a dominant east–west shortening in the study area, but strata near the crest of the plunging anticlines generally strike to southwest almost perpendicular to the direction of plate convergence. The intensity of the estimated bedding-guided fluid and gas flux into the hydrate stability zone is weaker than 2 in the slope basin and the south-central half of the diapiric fold, increases to 7 in the northern half of the diapiric fold and plunging anticlines, and reaches a maximum of 16 at the western frontal thrust system. Rapid sedimentation, active tectonics and fluid migration paths with significant dissolved gas content impact on the mechanism for BSR formation and gas hydrate accumulation. As we begin to integrate the results from these studies, we are able to outline the regional variations, and discuss the importance of structural controls in the mechanisms leading to the gas hydrate emplacements.     

Sedimentary characteristics and seismic geomorphology of gravity-flow channels in a rift basin: Oligocene Shahejie Formation,Qinan Slope,Huanghua Depression of Bohai Bay Basin,China

Deep-water gravity-flow sandstones are important hydrocarbon exploration and production targets in the Bohai Bay Basin, a Paleogene intra-continental rift basin in eastern China. In this paper, the seismic-sedimentology techniques are used to characterize, in plan view, the temporal and spatial evolution of a gravity-flow-channel complex of the Paleogene Shahejie Formation (Es) on the Qinan faulted-monoslope (Qinan Slope), Bohai Bay Basin. The results show that two or three gravity-flow channels, 9–12 km long and 0.5–2 km wide, were successively developed in later Es (Es1z–Es1s). The channels initially experienced westward migration and then shifted eastward. The corresponding wireline logs of the channel-fill sequences mainly present blocky-shaped or bell-like configurations, whereas their seismic profile features are characterized by strong amplitude reflections, such as U-shaped, plate-like, spindle-shaped and lenticular configurations.The syndepositional activity of three normal faults, i.e., the Nandagang Fault to the northwest, the Zhangbei Fault to the northeast and the Zhaobei Fault to the east led to gradient changes of the Qinan Slope, which have controlled the plan morphology (width, curvature, and bifurcation) of the gravity-flow channels. In the medium-late period of Es1z, triggered by intensive faulting on the three faults, the gradient of the Qinan Slope was steepened abruptly, resulting in an increase of flow velocity and erosion amplitude to underlying deposits. As a result, channels exhibiting narrow and straight configurations in plan view were formed. During the stage of early Es1z and Es1s, tectonic activity intensity was relatively low and the gradient of the Qinan Slope was gentle, so channels with great width and curvature were bifurcated and merged downstream.Comparison of the faulting amplitude of the three syndepositional faults suggests that the Nandagang and Zhaobei faults were inversely strengthened in the Es1z and Es1s. The Nandagang Fault to the west was found to be more active than the Zhaobei Fault to the east in the Es1z stage. This condition was reversed in Es1s. For that reason, the channels migrated to the west in the Es1z stage and then went back to the east during Es1s.Core analysis shows that the channel fills are mainly composed of sandy-debrites, slumps and turbidites. Among them, sandy debrites dominate deposition in terms of reservoir volume and hydrocarbon potential. These units primarily consist of sandstones and gravel-bearing sandstones, with bed thicknesses ranging from 10 to 40 m, an average porosity of 11% and a permeability of 25 mD. Being mostly encased in organic-rich dark mudstones, these sandy debrites are significant hydrocarbon exploration targets.The results of this study are not only useful to the hydrocarbon exploration and development planning for the Qinan Slope, but also helpful when considering other faulted-depressions in the Bohai Bay Basin and other intra-continent rifted basins around the world, particularly in terms of gravity-flow hydrocarbon exploration and research.     

Tectonostratigraphic evolution of the northern Porcupine Basin,Irish Atlantic margin,during the Late Jurassic–Early Cretaceous,implication for a regional compressional event

The conventional interpretation of the Jurassic–Lower Cretaceous succession in the Porcupine Basin suggests an extensional setting with progressive deepening of the basin. However, well data show a prominent gap of several million years between the Upper Jurassic and Lower Cretaceous. A data base of 15 key wells and approximately 5,000 km of seismic reflection data were examined in the northern Porcupine Basin, in order to understand the nature, controls and mechanisms of this unconformity. Seven seismic markers, constrained by well data, are mapped. It is shown that during the Late Jurassic (possibly the Oxfordian–Kimmeridgian), the basin experienced extension and synrift deposition. During the latest Jurassic–earliest Cretaceous (possibly the Tithonian–early Berriasian), a series of north-trending structural highs and lows developed and extensive areas in the northern Porcupine Basin experienced folding, uplift and erosion. Evidence from the study suggests that compression, uplift and erosion played an important role in the shaping of the depositional and structural architecture of the basin and caused formation of the regional Base Cretaceous Unconformity in the northern basin. It is suggested that the deformation in the northern Porcupine Basin during the latest Jurassic–earliest Cretaceous may be related to the initial closure of the Alpine Tethys during the late Tithonian. This tectonic event may also have resulted in compressional deformation and formation of the Base Cretaceous Unconformity elsewhere in Western Europe.     

Superposed deformation straddling the continental-oceanic transition in deep-water Angola

The Angolan margin is the type area for raft tectonics. New seismic data reveal the contractional buffer for this thin-skinned extension. A 200-km-long composite section from the Lower Congo Basin and Kwanza Basin illustrates a complex history of superposed deformation caused by: (1) progradation of the margin; and (2) episodic Tertiary epeirogenic uplift. Late Cretaceous tectonics was driven by a gentle slope created by thermal subsidence; extensional rafting took place updip, contractional thrusting and buckling downdip; some distal folds were possibly unroofed to form massive salt walls. Oligocene deformation was triggered by gentle kinking of the Atlantic Hinge Zone as the shelf and coastal plain rose by 2 or 3 km; relative uplift stripped Paleogene cover off the shelf, provided space for Miocene progradation, and steepened the continental slope, triggering more extension and buckling. In the Neogene, a subsalt half graben was inverted or reactivated, creating keystone faults that may have controlled the Congo Canyon; a thrust duplex of seaward-displaced salt jacked up the former abyssal plain, creating a plateau of salt 3–4 km thick on the present lower slope. The Angola Escarpment may be the toe of the Angola thrust nappe, in which a largely Cretaceous roof of gently buckled strata, was transported seawards above the thickened salt by up to 20 km.     

Regional structure and tectonic history of the obliquely colliding Columbus foreland basin, offshore Trinidad and Venezuela

Cenozoic eastward migration of the Caribbean plate relative to the South American plate is recorded by an 1100-km-long Venezuela-Trinidad foreland basin which is oldest in western Venezuela (65-55 Ma), of intermediate age in eastern Venezuela (34-20 Ma) and youngest beneath the shelf and slope area of eastern offshore Trinidad (submarine Columbus basin, 15.0 Ma-Recent). In this study of the regional structure, fault families, and chronology of faulting and tectonic events affecting the hydrocarbon-rich Columbus foreland basin of eastern offshore Trinidad, we have integrated approximately 775 km of deep-penetration 2D seismic lines acquired by the 2004 Broadband Ocean-Land Investigations of Venezuela and the Antilles arc Region (BOLIVAR) survey, 325 km of vintage GULFREX seismic data collected by Gulf Oil Company in 1974, and published industry well data that can be tied to some of the seismic reflection lines. Top Cretaceous depth structure maps in the Columbus basin made from integration of all available seismic and well data define for the first time the elongate subsurface geometry of the 11-15 km thick and highly asymmetrical middle Miocene-Recent depocenter of the Columbus basin. The main depocenter located 150-200 km east of Trinidad and now the object of deepwater hydrocarbon exploration is completely filled by shelf and deepwater sediments derived mainly from the Orinoco delta. The submarine Darien ridge exhibits moderate (20-140 m) seafloor relief, forms the steep (12°-24°), northern structural boundary of the Columbus basin, and is known from industry wells to be composed of 0.5-4.5 km thick, folded and thrust-imbricated, hydrocarbon-bearing section of Cretaceous and early Tertiary limestones and clastic rocks. The eastern and southern boundaries of the basin are formed by the gently (1.7°-4.5°), northward-dipping Cretaceous-Paleogene passive margin of South America that is in turn underlain by Precambrian rocks of the Guyana shield.Interpretation of seismic sections tied to wells reveals the following fault chronology: (1) middle Miocene thrusting along the Darien ridge related to highly oblique convergence between the Caribbean plate and the passive margin of northern South America; continuing thrusting and transpression in an oblique foreland basin setting through the early Pleistocene; (2) early Pliocene-recent low-angle normal faults along the top of the Cretaceous passive margin; these faults were triggered by oversteepening related to formation of the downdip, structurally and bathymetrically deeper, and more seaward Columbus basin; large transfer faults with dominantly strike-slip displacements connect gravity-driven normal faults that cluster near the modern shelf-slope break and trend in the downslope direction; to the south no normal faults are present because the top Cretaceous horizon has not been oversteepened as it is adjacent to the foreland basin; (3) early Pliocene-Recent strike-slip faults parallel the trend of the Darien ridge and accommodate present-day plate motions.     

Structural evolution of the Kopeh Dagh fold-and-thrust belt (NE Iran) and interactions with the South Caspian Sea Basin and Amu Darya Basin

We present a detailed stratigraphic and structural study of the Kopeh Dagh fold-and-thrust belt in NE Iran, which is an investigation of the complex polyphased tectonic history of this belt and its links with the adjacent South Caspian Sea and Amu Darya basins. Based on numerous field surveys, a large amount of 2D and 3D seismic data, borehole data and more than 150 new biostratigaphic datings, a new detailed biostratigraphic chart and 4 main regional cross-sections illustrate the importance of lateral facies variations and structural inheritance in the present-day structure of the belt.After the Cimmerian orogeny corresponding to the closure of the Paleotethys Ocean in Late Triassic/Early Jurassic times, a Middle Jurassic post-collisional rifting event was associated with the deposition of one of the main source rocks of the Kopeh Dagh and the Amu Darya Basin (Kashafrud Formation). Following this rifting event, over 7 km of sediments were accumulated until the Tertiary above a regional post-Triassic unconformity. The occurrence of local uplifts during the Late Cretaceous-Early Paleocene is interpreted as a consequence of regional-scale modification of plate-slab coupling in the Neotethys subduction zone. The main inversion of the Kopeh Dagh occurred at Late Eocene times, when the far-field deformation developed in Eurasia as a consequence of the locking of the Neo-Tethys subduction. This folding phase is sealed in the western part of the belt by a major Eocene-Oligocene unconformity at the base of the thick sedimentary series belonging to the South Caspian Sea Basin. The bulk of sedimentary infill in the South Caspian Sea Basin is Oligocene and younger, and it is probably related to syn-compressional downward flexure of the resistant basement basin at the onset of the Alpine phase. In the eastern part of the Kopeh Dagh, this deformation is characterized by Middle Jurassic graben inversion with evidence of forced folding, short-cuts and as well by larger scale basement uplifts. In contrast, the northwestern part of the belt shows thrust faults involving basement and fault-propagation folds within the sedimentary sequence. The Kopeh Dagh presents tectonic structures that are parallel to the Paleotethys suture zone, which emphasizes the importance of the structural inheritance and inversion processes during the structural evolution of the belt. Finally, a change from a mostly dip-slip to a mostly strike-slip tectonics occurred during the Pliocene within the Kopeh Dagh as a consequence of a major tectonic reorganization in North-East Iran.     

Structural controls on Quaternary deepwater sedimentation, mud diapirism, and hydrocarbon distribution within the actively evolving Columbus foreland basin, eastern offshore Trinidad

Eastward migration of the Caribbean plate relative to the South American plate has caused lithospheric loading along the northern margin of South America, which is recorded by an 1100-km-long foreland basin which is oldest in the west (Maracaibo basin, 65-55 Ma) and youngest in the east (Columbus basin, eastern offshore Trinidad, 15-0 Ma). The Orinoco River has been the primary source of sediment for the basin since early Miocene. We have integrated approximately 775 km of deep-penetration 2D seismic lines acquired in the area of eastern offshore Trinidad as part of the 2004 “Broadband Ocean-Land Investigations of Venezuela and the Antilles arc Region” (BOLIVAR) project, 8000 km² of shallow industry 3D seismic data, and published industry well data from offshore eastern Trinidad. Active mud diapirism in the Columbus basin is widespread and is related to overthrusting and tectono-sedimentary loading of upper Miocene-lower Pliocene age mud. Analysis of the shallow 3D seismic data reveals the presence of extensive gravity-flow depositional elements on the Columbus basin slope and the deepwater area. These stacked gravity-flow deposits are characterized by mass-transport deposits at the base, turbidite frontal-splay deposits, leveed-channel deposits, and capped by fine-grained condensed-section deposits. Exploration targets in the deepwater area are located towards the center of the Columbus basin, where northeast-trending fault-propagation folds are important Plio-Pleistocene trap-forming elements. Deep basin wells drilled in recent years have proven that turbidites were transported into the deepwater Columbus basin during the Plio-Pleistocene. Analysis of these well results suggests that a deeper oil charge is present within the deepwater Columbus basin area. The primary uncertainty for this variable hydrocarbon system is whether fault or diapiric pathways connect or divert the petroleum charge at depth with shallower reservoir rocks.     

Structural significance of an evaporite formation with lateral stratigraphic heterogeneities (Southeastern Pyrenean Basin,NE Spain)

We run a series of analogue models to study the effect of stratigraphic heterogeneities of an evaporite formation on thin-skinned deformation of the Southeastern Pyrenean Basin (SPB; NE Spain). This basin is characterized by the existence of evaporites, deposited during the Early-Middle Eocene with lateral variations in thickness and lithological composition. These evaporites are distributed in three lithostratigraphic units, known as Serrat Evaporites, Vallfogona and Beuda Gypsum formations and acted as décollement levels, during compressional deformation in the Lutetian. In addition to analogue modeling, we have used field data, detailed geological mapping and key cross-sections supported by seismic and well data to build a new structural interpretation for the SPB. In this interpretation, it is recognized that the basal and upper parts of the Serrat Evaporites acted as the main décollement levels of the so-called Cadí thrust sheet and Serrat unit. A balanced restoration of the basin indicates that thrust faults nucleated at the stratigraphic transition of the Serrat Evaporites (zone with lateral variations of thickness and lithological composition), characterized by a wedge of anhydrite and shale. The analogue models were setup based on information extracted from cross-sections, built in two sectors with different lithology and stratigraphy of the evaporites, and the restored section of the SPB. In these models, deformation preferentially concentrated in areas where thickness change, defined by wedges of the ductile materials, was inbuilt. Based on the structural interpretation and model results, a kinematic evolution of the SPB is proposed. The kinematic model is characterized by the generation of out-of-sequence structures developed due to lateral stratigraphic variations of the Serrat Evaporites. The present work shows a good example of the role of stratigraphic heterogeneities of an evaporite formation which acts as décollement level on structural deformation in a fold-thrust belt. The results of this work have implications for hydrocarbon exploration and are relevant for studying structural geometry and mechanics in shortened evaporite basins.     

The Monagas Fold-Thrust Belt of Eastern Venezuela. Part I: Structural and thermal modeling

The Eastern Venezuelan Basin (EVB) contains one of the largest hydrocarbon accumulations in the world. Main petroleum targets are buried structures of the Monagas Fold-Thrust Belt (MFTB) which forms the northeastern edge of the EVB. The objective of this study is to integrate the seismic and well data that has been acquired over the last 10 years across the MFTB and EVB, to create an updated structural model. Three regional cross sections 60-75 km long are presented across an area of 4000 km².Five structural domains are described: Amarilis, Furrial, Jusepín, Cotoperí and Pirital. They are characterized by thrusts and high-angle reverse faults. Structural style changes along strike are related to variations in depth of detachment levels and to the strike-slip component of the deformation. We have estimated a shortening between 43 and 59 km that increases eastward over a distance of 40 km.The evolution of the MFTB is divided in four episodes based on stratigraphic, structural and thermal maturity evidences: (1) Oligocene-early Miocene initial movement of Pirital thrust. (2) Early Miocene simultaneous movement on Pirital, Furrial and Cotoperí thrusts. (3) Middle Miocene increases in velocity and change in geometry of Pirital thrust, during an out of sequence period of thrusting. (4) Late Miocene to Holocene minor thrust activity. This evolution is consistent with the oblique convergence between the Caribbean and South American plates and the convergence between North and South America that affected Eastern Venezuela during the Cenozoic.By analyzing the along-strike variations in structural style, new exploratory opportunities have been identified. Under the Orocual and Santa Bárbara fields two untested duplex structures are proposed; they were developed during the middle Miocene. Other prospective hydrocarbon traps are associated to oblique transpressive faults that create anticline structures.     

Cold seeps at the salt front in the Lower Congo Basin II: The impact of spatial and temporal evolution of salt-tectonics on hydrocarbon seepage

This study investigates the distribution and evolution of seafloor seepage in the vicinity of the salt front, i.e., the seaward boundary of salt-induced deformation in the Lower Congo Basin (LCB). Seafloor topography, backscatter data and TV-sled observations indicate active fluid seepage from the seafloor directly at the salt front, whereas suspected seepage sites appear to be inactive at a distance of >10 km landward of the deformation front. High resolution multichannel seismic data give detailed information on the structural development of the area and its influence on the activity of individual seeps during the geologic evolution of the salt front region. The unimpeded migration of gas from fan deposits along sedimentary strata towards the base of the gas hydrate stability zone within topographic ridges associated with relatively young salt-tectonic deformation facilitates seafloor seepage at the salt front. Bright and flat spots within sedimentary successions suggest geological trapping of gas on the flanks of mature salt structures in the eastern part of the study area. Onlap structures associated with fan deposits which were formed after the onset of salt-tectonic deformation represent potential traps for gas, which may hinder gas migration towards seafloor seeps. Faults related to the thrusting of salt bodies seawards also disrupt along-strata gas migration pathways. Additionally, the development of an effective gas hydrate seal after the cessation of active salt-induced uplift and the near-surface location of salt bodies may hamper or prohibit seafloor seepage in areas of advanced salt-tectonic deformation. This process of seaward shifting active seafloor seepage may propagate as seaward migrating deformation affects Congo Fan deposits on the abyssal plain. These observations of the influence of the geologic evolution of the salt front area on seafloor seepage allows for a characterization of the large variety of hydrocarbon seepage activity throughout this compressional tectonic setting.     

The flexural margin,the foredeep,and the orogenic margin of a northern Cordilleran foreland basin: Cretaceous tectonostratigraphy and detrital zircon provenance,northwestern Canada

Reconstructions of the Albian to Campanian foreland basin adjacent to the northern Canadian Cordillera are based on outcrop and well log correlations, seismic interpretation, and reconnaissance-level detrital zircon analysis. The succession is subdivided into two tectonostratigraphic units. First is an Albian tectonostratigraphic unit that was deposited on the flexural margin of a foreland basin. At the base is a shallow marine sandstone interval that was deposited during transgressive reworking of sediment from cratonic sources east of the basin that resulted in a dominant 2000–1800 Ma detrital zircon age fraction. Subsequent deposition in a west-facing muddy ramp setting was followed by east-to-west shoreface progradation into the basin.Near the Albian–Cenomanian boundary, regional uplift and exhumation resulted in an angular unconformity at the base of the Cenomanian–Campanian tectonostratigraphic unit. Renewed subsidence in the Cenomanian resulted in deposition of organic-rich, radioactive, black mudstone of the Slater River Formation in a foredeep setting. Cenomanian–Turonian time saw west-to-east progradation of a shoreface-shelf system from the orogenic margin of the foreland basin over the foredeep deposits. Detrital zircon age peaks of approximately 1300 Ma, 1000 Ma, and 400 Ma from a Turonian sample are consistent with recycling of Mississippian and older strata from the Cordillera west of the study area, and show that the orogen-attached depositional system delivered sediment from the orogen to the foreland basin. A near syndepositional detrital zircon age of ca. 93 Ma overlaps with known granitoid ages from the Cordillera. After the shelf system prograded across the study area, subsequent pulses of subsidence and uplift resulted in dramatic thickness variations across an older structural belt, the Keele Tectonic Zone, from the Turonian to the Campanian.The succession of depositional systems in the study area from flexural margin to foredeep to orogenic margin is attributed to coupled foreland propagation of the front of the Cordilleran orogen and the foreland basin. Propagation of crustal thickening and deformation toward the foreland is a typical feature of orogens and so the distal to proximal evolution of the foreland basin should also be considered as typical.     

Geophysical investigations of crust-scale structural model of the Qiongdongnan Basin, Northern South China Sea

Rifting of the Qiongdongnan Basin was initiated in the Cenozoic above a pre-Cenozoic basement, which was overprinted by extensional tectonics and soon after the basin became part of the rifted passive continental margin of the South China Sea. We have integrated available grids of sedimentary horizons, wells, seismic reflection data, and the observed gravity field into the first crust-scale structural model of the Qiongdongnan Basin. Many characteristics of this model reflect the tectonostratigraphic history of the basin. The structure and isopach maps of the basin allow us to reconstruct the history of the basin comprising: (a) The sediments of central depression are about 10 km thicker than on the northern and southern sides; (b) The sediments in the western part of the basin are about 6 km thicker than that in the eastern part; (c) a dominant structural trend of gradually shifting depocentres from the Paleogene sequence (45–23.3 Ma) to the Neogene to Quaternary sequence (23.3 Ma–present) towards the west or southwest. The present-day configuration of the basin reveals that the Cenozoic sediments are thinner towards the east. By integrating several reflection seismic profiles, interval velocity and performing gravity modeling, we model the sub-sedimentary basement of the Qiongdongnan Basin. There are about 2–4 km thick high-velocity bodies horizontal extended for a about 40–70 km in the lower crust (v > 7.0 km/s) and most probably these are underplated to the lower stretched continental crust during the final rifting and early spreading phase. The crystalline continental crust spans from the weakly stretched domains (about 25 km thick) near the continental shelf to the extremely thinned domains (<2.8 km) in the central depression, representing the continental margin rifting process in the Qiongdongnan Basin. Our crust-scale structural model shows that the thinnest crystalline crust (<3 km) is found in the Changchang Sag located in the east of the basin, and the relatively thinner crystalline crust (<3.5 km) is in the Ledong Lingshui Sag in the west of the basin. The distribution of crustal extension factor β show that β in central depression is higher (>7.0), while that on northern and southern sides is lower (<3.0). This model can illuminate future numerical simulations, including the reconstruction of the evolutionary processes from the rifted basin to the passive margin and the evolution of the thermal field of the basin.