Basement Highs Research Articles

Styles and rates of deformation in the frontal accretionary wedge of the Calabrian Arc (Ionian Sea): controls exerted by the structure of the lower African plate

The Calabrian Arc is a narrow subduction-rollback system resulting from Africa/Eurasia plate convergence. We analysed the structural style of the frontal accretionary wedge through a multi-scale geophysical approach. Pre-stack depth-migrated crustal-scale seismic profiles unravelled the overall geometry of the subduction complex; high-resolution multi-channel seismic and sub-bottom CHIRP profiles, together with morpho-structural maps, integrated deep data and constrained the fine structure of the frontal accretionary wedge, as well as deformation processes along the outer deformation front.We identified four main morpho-structural domains in the western lobe of the frontal wedge: the proto-deformation area at the transition with the abyssal plain; two regions of gentle and tight folding; a hummocky morphology domain with deep depressions and intervening structural highs; a highstanding plateau at the landward limit of the salt-bearing accretionary wedge, where the detachment cuts through deeper levels down to the basement. Variation of structural style and seafloor morphology in these domains are related to a progressively more intense deformation towards the inner wedge, while abrupt changes are linked to inherited structures in the lower African plate. Our data suggest focusing of intense shallow deformation in correspondence of deeply rooted faults and basement highs of the incoming plate.Back-arc extension in the Southern Tyrrhenian Sea has recently ceased, producing a slowdown of slab rollback and plate-boundary re-organization along trans-tensional lithospheric faults segmenting the continental margin. In this complex setting, it is not clear if the accretionary wedge is still growing through frontal accretion. Our data suggest that shortening is still active at the toe of the wedge, and uplift rates along single folds are in the range of 0.25-1.5 mm/yr. An unconformity within the Plio-Quaternary sediments suggests a discontinuity in sedimentation and tectonic processes, i.e. a slowdown of shortening rate or an increase in sedimentation rate, but not a real inactivation of frontal accretion, which still contributes to the migration of the outer deformation front towards the foreland.

Subsurface temperature model of the Hungarian part of the Pannonian Basin

Abstract Hungary is one of the most suitable countries in Europe for geothermal development, as a result of large amounts of Miocene extension and associated thermal attenuation of the lithosphere. For geothermal exploration, it is crucial to have an insight into the subsurface temperature distribution. A new thermal model of Hungary is presented extending from the surface down to the lithosphere-asthenosphere boundary (LAB) based on a new stochastic thermal modeling workflow. The model solves the heat equation in steady-state, assuming conduction as the main heat transfer mechanism. At the top and the base, we adopt a constant surface temperature and basal heat flow condition. For the calibration of the model, temperature measurements were collected from the Geothermal Database of Hungary. The model is built up in a layered structure, where each layer has its own thermal properties. The prior thermal properties and basal condition of the model are updated through the ensemble smoother with multiple data assimilation technique. The prior model shows a misfit with the observed temperatures, which is explained fundamentally by transient thermal effects and non-conductive heat transfer. Other misfits can be attributed to a-priori assumptions on thermal properties, boundary conditions, and uncertainty in the model geometry. The updated models considerably improve the prior model, showing a better fit with measured records. The updated models are capable to reproduce the thermal effect of lithospheric extension and the sedimentary infill of the Pannonian Basin. Results indicate that the hottest areas below 3 km are linked to the basement highs surrounded by deep sub-basins of the Great Hungarian Plain. Our models provide an indication on the potential sites for future EGS in Hungary and can serve as an input for geothermal resource assessment.

O arcabouço estrutural da Bacia Sedimentar do Araripe, Província Borborema, baseado em dados aeromagnetométricos

Este trabalho apresenta uma interpretação atualizada da estruturação interna da Bacia Sedimentar do Araripe, localizada ao sul da porção setentrional da Província Borborema, por meio do processamento e da análise de dados aerogeofísicos de magnetometria pertencentes à Companhia de Pesquisa de Recursos Minerais – Serviço Geológico do Brasil. Essa bacia é reconhecida como um conjunto de meio-grábens assimétricos, fragmentados por altos de embasamento e complexos sistemas de falhas e lineamentos E-W a NE-SW, associados ao trend estrutural do Orógeno Borborema, e NW-SE, relacionados a processos extencionais cuja evolução poderia estar associada ao rift-valley na extremidade norte do rift abortado da Bacia do Recôncavo. A partir da imagem geofísica do campo magnético anômalo foram extraídas suas derivadas de primeira ordem nas direções x, y, z, seu gradiente horizontal total, sua amplitude do sinal analítico (ASA) e inclinação do sinal analítico. A deconvolução de Euler foi aplicada ao grid ASA, o que permitiu uma aproximação da posição horizontal e estimativa da profundidade do topo das principais fontes magnéticas. A análise conjunta dos diversos mapas gerados permitiu uma interpretação regional dos domínios e lineamentos magnéticos, os quais foram associados às principais estruturas em subsuperfície que compõem o arcabouço da bacia. Os resultados demonstram que a compartimentação estrutural da Bacia Sedimentar do Araripe é muito mais complexa do que a descrita anteriormente por outros autores. O padrão estrutural da bacia apresenta variação lateral, de W para E, conforme demonstrado pela divisão dos domínios magnéticos, indicando haver variações substanciais na espessura das rochas sedimentares, com áreas mais espessas a E e mais rasas a W.

Applying seismic stratigraphy analysis for assessing upper Oligocene stratigraphic traps in Southeastern Cuu Long Basin

As oil and gas production has been going on over a few decades, conventional plays such as pre-Tertiary fractured basement highs and Cenozoic structural traps become more and more exhausted, and the remaining targets of the same type do not have sufficient reserves for development and production. Exploration activities in Cuu Long basin, therefore, are shifting towards more complicating types of plays which are stratigraphic traps and combination traps. Several researches were conducted in southeastern marginal slope and indicated the possibility of stratigraphic pinch-out traps with insufficient petroleum system and low hydrocarbon potential. In spite of many researches, there are still difficulties in defining the distribution and in evaluating hydrocarbon potential of these traps, so seismic stratigraphy analysis in accompanied with interpretation of seismic attribute and well logs is very necessary to support this problem. Seismic stratigraphic analysis on seismic sections, in agreement with seismic attributes’ and log analysis’ findings, show that the stratigraphic/combination traps in Oligocene C and D were formed during lowstand system tract as sigmoid-oblique clinoforms downlapping onto underlying strata in distributary mouths/delta settings. The integration of seismic attribute analysis and well log interpretation has further defined the fan-shaped distribution of these traps. Thus, using various methods, the stratigraphic traps can be better revealed. Further studies, however, need to be carried out to fully evaluate hydrocarbon potential of these stratigraphic/ combination traps, and minimize risks in exploration drilling.

Basement structure of the United Arab Emirates derived from an analysis of regional gravity and aeromagnetic database

Gravity and aeromagnetic data covering the whole territory of the United Arab Emirates (UAE) have been used to evaluate both shallow and deep geological structures, in particular the depth to basement since it is not imaged by seismic data anywhere within the UAE. Thus, the aim has been to map the basement so that its structure can help to assess its control on the distribution of hydrocarbons within the UAE. Power spectrum analysis reveals gravity and magnetic signatures to have some similarities, in having two main density/susceptibility interfaces widely separated in depth such that regional-residual anomaly separation could effectively be undertaken. The upper density/susceptibility interface occurs at a depth of about 1.0km while the deeper interface varies in depth throughout the UAE. For gravity, this deeper interface is assumed to be due to the combined effect of lateral changes in density structures within the sediments and in depth of basement while for magnetics it is assumed the sediments have negligible susceptibility and the anomalies unrelated to the volcanic/magmatic bodies result from only changes in depth to basement. The power spectrum analysis over the suspect volcanic/magmatic bodies indicates they occur at ~5km depth. The finite tilt-depth and finite local wavenumber methods were used to estimate depth to source and only depths that agree to within 10% of each other were used to generate the depth to basement map. This depth to basement map, to the west of the UAE-Oman Mountains, varies in depth from 5km to in excess of 15km depth and is able to structurally account for the location of the shear structures, seen in the residual magnetic data, and the location of the volcanic/magmatic centres relative to a set of elongate N-S to NE-SW trending basement highs. The majority of oilfields in the UAE are located within these basement highs. Therefore, the hydrocarbon distribution in the UAE basin appears to be controlled by the location of the basement ridges.

Three dimensional seismic anatomy of multi-stage mass transport deposits in the Pearl River Mouth Basin, northern South China Sea: Their ages and kinematics

Three superimposed Quaternary mass transport deposits (MTD1, MTD2 and MTD3) in the Pearl River Mouth Basin of the northern South China Sea are identified using high-resolution three dimensional seismic data. This study dissects the three stacked MTDs in detail and interprets their distribution based on antecedent bathymetry and their kinematics from identified structures and sedimentological models. Each MTD is characterized by linear grooves at its base, by chaotic seismic reflections and complex internal structures, such as remnant, rafted and faulted blocks. The linear grooves and internal structures of MTDs indicate that the sediments mainly flowed from the NW to SE in the study area. Moreover, internal structures suggest that MTD2 is a spread and MTD3 is a rotational slump, both terminating upslope at a regional linear escarpment. MTD1 is interpreted as the distal part of a larger MTD. The ages of MTD1, MTD2 and MTD3, based on seismic correlation with ODP Site 1146, are 0.54Ma, 0.79Ma and 1.59Ma respectively. High-amplitude seismic reflections observed below the MTDs are interpreted as coarse-grained turbidites. Headscarp locations are controlled by both the underlying structures (such as basement highs and related faults) and the distribution of weak layers that are probably gas-bearing thin turbidite silt beds. This study provides precise ages of stacked MTDs in the northern South China Sea for the first time and at least locally provides clear evidence for the flow directions and controlling factors of the stacked MTDs. Similar lower slope–rise MTDs, of local origin, may be widespread elsewhere, but would be difficult to distinguish without 3-D seismic data.

U-Pb ages of detrital zircons in Lower Cretaceous non-marine successions of the Gyeongsang Basin, Northeast Asia: Implications for sediment provenance

The Cretaceous Gyeongsang Basin is the largest non-marine Mesozoic sedimentary basin of the Korean Peninsula. The Lower Cretaceous successions of the Gyeongsang Basin are coevally correlated to those of the Cretaceous Gunsan Basin in the Yellow Sea which is located far to the west of the Gyeongsang Basin. This study presents U-Pb ages of detrital zircons to evaluate the sediment provenances of the Gyeongsang Basin. The detrital zircon ages clearly show the different distributions between the northern (Uiseong area) and southern (Jinju area) areas of the Gyeongsang Basin. The detrital zircons of the northern area have an age cluster in the Jurassic or Triassic, whereas the detrital zircons of the southern area show a wide range of ages from early Cretaceous to Neoarchean. In the Gunsan Basin, detrital zircons from a core also yield ages ranging from early Cretaceous to Neoarchean. The age distribution from the Gunsan Basin is similar to those of the southern Gyeongsang Basin, except for the absence of Jurassic detrital zircons. The petrographic modal analysis of sandstones in the Gyeongsang Basin suggests a mixed provenance. This study indicates that possible sediment provenances of the Gyeongsang Basin were shared with those of the Gunsan Basin. We suggest that the sediment provenance of the northern Gyeongsang Basin was adjacent basement highs, whereas sediments to the southern Gyeongsang Basin were probably derived from relatively distant source areas that possibly were located in the vicinity of the Gunsan Basin during the early Cretaceous (ca. 113Ma).

Középső-triász dolomitok képződésének története és töréses deformációja a Szegedi-medence területén

A Pannon-medence aljzatának egyik részmedencéje a Szegedi-medence, mely szénhidrogén-földtani szempontból hazánk egyik kiemelt fontosságú területe. A prekainozoos aljzat legelterjedtebb mezozoos képződményei a középső-triász dolomitok, melyek fontos szerepet töltenek be a terület szénhidrogén-rendszerének felépítésében. Jelen tanulmány célja, hogy az évtizedek óta nem vizsgált képződmények képződéséről és deformációtörténetéről új, korszerű leírást nyújtson. Értelmezésünket általános petrográfiai leírásra, fluoreszcens és katódlumineszcens vizsgálati módszerekre, valamint a területről szóló szakirodalomra alapozzuk.A vizsgált anisusi képződmények változatos partszegélyi, sekélytengeri környezetben ülepedtek le. Ezek a leülepedést követő süllyedés következtében, a sekély és közepes betemetődés után, a kora-krétára juthattak a mély betemetődési diagenezis zónájába. Ezen zónákban a képződmények feltehetően többfázisú, részben szövetmegőrző, részben szövet -romboló dolomitosodási folyamatokon mentek keresztül. A petrográfiai alapon elkülönített dolomit típusok közülközepes vagy mély betemetődési környezetet jeleznek a porfirotópos és cukorszövetű dolomitok, valamint a póruskitöltő nyeregdolomit, de ezek szerepe alárendelt a korábbi dolomitosodási folyamatokhoz viszonyítva. A középső-miocént megelőzően a kőzeteket többször is töréses deformáció érte, melynek hatására breccsa, ezt követően pedig üreg- és repedéskitöltő nyeregdolomit képződött. A nyeregdolomit kristályai több esetben kőolajtartalmú fluidumzárványokat csapdáztak. A dolomittestek felszínközeli helyzetét középső-miocén, abráziósparti kör -nyezetben leülepedett fedőkőzetek jelzik, továbbá dedolomitosodás is kapcsolódhat ehhez a szakaszhoz. A Pannon-medence kialakulásával párhuzamos süllyedés és eltemetődés hatására a képződmények ismét nagy mélységbe kerültek, mely során újabb töréses deformáció és cementáció folyt. A legfiatalabb repedéskitöltő ásványegyüttest fluoreszcens tulajdonságú dolomit, valamint pirit és szilárd bitumen alkotja.A vizsgált dolomitok többfázisú diagenezis- és deformációtörténetéhez többfázisú szénhidrogén-migrációs események kapcsolhatóak, melyek pontosabb megismerése és elhelyezése a medence fejlődéstörténetében kulcsfontosságú. Az erősen átalakult nyeregdolomit tartalmú minták további vizsgálata rezervoárgeológiai szempontból a jövőben szintén fontos feladat.

Subsurface biodegradation of crude oil in a fractured basement reservoir, Shropshire, UK

Subsurface biodegradation of crude oil in current oil reservoirs is well established, but there are few examples of ancient subsurface degradation. Biomarker compositions of viscous and solid oil residues (‘bitumen’) in fractured Precambrian and other basement rocks below the Carboniferous cover in Shropshire, UK, show that they are variably biodegraded. High levels of 25-norhopanes imply that degradation occurred in the subsurface. Lower levels of 25-norhopanes occur in active seepages. Liquid oil trapped in fluid inclusions in mineral veins in the fractured basement confirms that the oil was emplaced fresh before subsurface degradation. A Triassic age for the veins implies a 200 myr history of hydrocarbon migration in the basement rocks. The data record microbial biodegradation of hydrocarbons in a fractured basement reservoir, and add to evidence in modern basement aquifers for microbial activity in deep fracture systems. Buried basement highs may be especially favourable to colonization, through channelling fluid flow to shallow depths and relatively low temperatures, and are therefore an important habitat within the deep biosphere.

Re-sedimented deposits in the rift section of the Campos Basin

An integrated petrologic-sedimentologic-stratigraphic-seismic study of the Lagoa Feia Group, rift section of the Campos Basin, has shown that rift sedimentation was dominantly intrabasinal (carbonate and stevensitic deposits), with siliciclastic deposits restricted to the proximity of graben border faults. The bivalve bioclastic rudstones (“coquinas”) that constitute the rift reservoirs show commonly limited abrasion of the bioclasts, and were deposited both on basement highs and lows throughout the rift section. Although in situ deposits of stevensite ooids and peloids occur dominantly at the base of the succession, these particles are ubiquitous to the entire rift section, mixed in variable proportion with siliciclastic and carbonate sediments. The environmental conditions required for the formation of stevensite and the growth of bivalves are mutually exclusive, as stevensite forms only at pH greater than 10, while bivalves cannot tolerate pH greater than 9. The common mixture of well-rounded basaltic rock fragments with angular, granitic-gneissic rock fragments and feldspars in the sandstones and conglomerates indicates recycling of epiclastic deposits from the early rift section, combined with first-cycle contribution from the plutonic basement. The studied cores show no evidence of subaerial exposure, and there is a lack of bioturbation, suggesting harsh environmental conditions. The rift deposits are dominantly massive or faintly-laminated, with diffuse facies boundaries. Structures indicative of unidirectional or oscillatory flow are subordinate. Integration of seismic, sedimentologic and petrographic evidence indicates that the Campos Basin rift section is formed mostly by re-sedimented gravitational deposits. The onset of the rift sedimentation occurred in synformal depressions, where bivalve banks or stevensite ooids were formed in shallow lacustrine environments under variable alkalinity conditions. With the development of half-grabens and concentration of the tectonic activity along the border faults, recurrent tectonic events promoted the mixing and gravitational re-deposition of stevensitic, clastic and bioclastic sediments in deeper, fault-bounded troughs. Large-scale units, hundreds of meters thick, were generated by major tectonic events, whereas compositional variations in the scale of meters were possibly a product of lake-level climatic fluctuations. Thus, due to syn-rift and mainly to post-rift erosion (the Neo-Aptian unconformity), the preserved rift section of the Lagoa Feia Group comprises mostly sediments deposited in the central troughs of the half-graben structures. Marginal sediments were extensively eroded and re-sedimented as gravity-driven mixed deposits. This new model, constructed form the integration of seismic, stratigraphic, sedimentologic and petrologic data, diverges substantially from the presently accepted model for the sedimentation of the rift section, opening new possibilities for the exploration of Campos Basin, as well as of similar settings, as in the adjacent Santos Basin.

Late Miocene sedimentary record of the Danube/Kisalföld Basin: interregional correlation of depositional systems, stratigraphy and structural evolution

AbstractThe Danube / Kisalföld Basin is the north-western sub-basin of the Pannonian Basin System. The lithostratigraphic subdivision of the several-km-thick Upper Miocene to Pliocene sedimentary succession related to Lake Pannon has been developed independently in Slovakia and Hungary. A study of the sedimentary formations across the entire basin led us to claim that these formations are identical or similar between the two basin parts to such an extent that their correlation is indeed a matter of nomenclature only. Nemčiňany corresponds to the Kálla Formation, representing locally derived coarse clastics along the basin margins (11- 9.5 Ma). The deep lacustrine sediments are collectively designated the Ivanka Formation in Slovakia, while in Hungary they are subdivided into Szák (fine-grained transgressive deposits above basement highs, 10.5 - 8.9 Ma), Endrőd (deep lacustrine marls, 11.6 -10 Ma), Szolnok (turbidites, 10.5 - 9.2 Ma) and Algyő Formations (fine-grained slope deposits, 10 - 9 Ma). The Beladice Formation represents shallow lacustrine deltaic deposits, fully corresponding to Újfalu (10.5 - 8.7 Ma). The overlying fluvial deposits are the Volkovce and Zagyva Formations (10 - 6 Ma). The synoptic description and characterization of these sediments offer a basin-wide insight into the development of the basin during the Late Miocene. The turbidite systems, the slope, the overlying deltaic and fluvial systems are all genetically related and are coeval at any time slice after the regression of Lake Pannon initiated about 10 Ma ago. All these formations get younger towards the S, SE as the progradation of the shelf-slope went on. The basin got filled up to lake level by 8.7 Ma, since then fluvial deposition dominated.

Variations in Isochore Thickness of the Ecca Sediments in the Eastern Cape Province of South Africa, as Deduced from Gravity Models

AbstractGravity modelling was carried out along five profiles that traverse the Eastern Cape Province of South Africa in order to determine the depositional surface and isochore thickness of the Ecca sediments. Gravity models of the subsurface rock density reveal that the Ecca Group has a maximum vertical thickness of about 3215 ± 160 m. The maximum depositional surface (elevation) above sea level for the Ecca sediments is about 500 m, whilst the depth below sea level reaches about 10000 m. Correlation of the isochore thickness maps with the depositional surfaces shows that the sediments in the basement highs were subsided, deformed, eroded and deposited in the basement lows. The basement highs served as the source area(s) for the sediments in the basement lows, thus basement highs are characterized with thin sediment cover whilst the lows have thick sediment cover.

Fault zone characteristics and basin complexity in the southern Salton Trough, California

Abstract Ongoing oblique slip at the Pacific–North America plate boundary in the Salton Trough produced the Imperial Valley (California, USA), a seismically active area with deformation distributed across a complex network of exposed and buried faults. To better understand the shallow crustal structure in this region and the connectivity of faults and seismicity lineaments, we used data primarily from the Salton Seismic Imaging Project to construct a three-dimensional P-wave velocity model down to 8 km depth and a velocity profile to 15 km depth, both at 1 km grid spacing. A VP = 5.65–5.85 km/s layer of possibly metamorphosed sediments within, and crystalline basement outside, the valley is locally as thick as 5 km, but is thickest and deepest in fault zones and near seismicity lineaments, suggesting a causative relationship between the low velocities and faulting. Both seismicity lineaments and surface faults control the structural architecture of the western part of the larger wedge-shaped basin, where two deep subbasins are located. We estimate basement depths, and show that high velocities at shallow depths and possible basement highs characterize the geothermal areas.

The Carrancas Formation, Bambuí Group: A record of pre-Marinoan sedimentation on the southern São Francisco craton, Brazil

The Carrancas Formation outcrops in east-central Brazil on the southern margin of the São Francisco craton where it comprises the base of the late Neoproterozoic Bambuí Group. It is overlain by the basal Ediacaran cap carbonate Sete Lagoas Formation and was for a long time considered to be glacially influenced and correlative with the glaciogenic Jequitaí Formation. New stratigraphic, isotopic and geochronologic data imply that the Carrancas Formation was instead formed by the shedding of debris from basement highs uplifted during an episode of minor continental rifting. Reddish dolostones in the upper Carrancas Formation have δ13C values ranging from +7.1 to +9.6‰, which is a unique C isotopic composition for the lowermost Bambuí Group but similar to values found in the Tijucuçu sequence, a pre-glacial unit in the Araçuaí fold belt on the eastern margin of the São Francisco craton. The stratigraphic position below basal Ediacaran cap carbonates and the highly positive δ13C values together indicate a Cryogenian interglacial age for the Carrancas Formation, with the high δ13C values representing the so-called Keele peak, which precedes the pre-Marinoan Trezona negative δ13C excursion in other well characterized Cryogenian sequences. Hence, The Carrancas Formation pre-dates de Marinoan Jequitaí Formation and represents an interval of Cryogenian stratigraphy not previously known to occur on the southern margin of São Francicso craton. Documentation of Cryogenian interglacial strata on the São Francisco craton reinforces recent revisions to the age of Bambuí Group strata and has implications for the development of the Bambuí basin.

Three-dimensional density structures of Taiwan and tectonic implications based on the analysis of gravity data

Taiwan is located in a collision and subduction area and has a complex tectonic history. To better understand the complicated structure beneath Taiwan, gravity studies, in addition to seismic and geological studies, provide useful geophysical information for studying shallow depths. Previous gravity studies of Taiwan in the last 30years focused on local regionalized explanations and 2-D profile modeling. This study is the first to complete a 3-D gravity inversion of Taiwan, and it provides a more comprehensive and large-scale tectonic analysis.Following 3-D gravity inversion using the least squares method, we sliced horizontal and vertical profiles from the 3-D density model to visualize tectonic changes. The low Bouguer anomaly was caused by thick sediment and crust layers. The high-density layers are located in special tectonic areas such as the Peikang and Kuanying basement highs. The deepest Moho depth beneath the middle of the Central Range is 45–50km. The high gradient changes of the eastern section of the Moho relief are shown by the complex mechanism of plate collision. The geometry of plate subduction is apparent in northeastern Taiwan, and the oceanic crust is observable under eastern Taiwan, showing arc-collision boundaries.Our 3-D density model, when combined with updated gravity data and seismic tomography, offers better resolution for deep structures than the previous 2-D forward results and serves as a physical property reference to better understand the tectonic structure beneath Taiwan.

Tracing the Initiation of the Tribeč Mountain Exhumation by Laser-Probe 40Ar/39Ar Dating of Seismogenic Pseudotachylytes (Western Carpathians, Slovakia)

AbstractThe seismogenic pseudotachylytes from the Tribec Mountains (Western Carpathians, Slovakia) were dated by means of the laser microprobe 40Ar/39Ar method. The Tribec Mountain crystalline basement was buried to 5–7.5-km depths, where it experienced approximately >110°C and <210°C thermal conditions. The dated pseudotachylytes have spot ages between 58 ± 1 and 46 ± 1 Ma with a weighted mean age of 49.7 ± 1.3 Ma, indicating that seismic activity caused their origin, the propagation of subvertical basement marginal faults, and/or the inception of basement unroofing processes in the southern part of the Central Carpathian Paleogene Basin. The extensional tectonics were responsible for the exhumation of basement highs and the opening of the intramontane depressions on the northwest margin of the Pannonian Basin.

Rangal Supermodel 2015

More than 6,000 boreholes were compiled to develop a consistent regional scale stratigraphic framework for the Permian Rangal, Baralaba and Bandana coal measures (CMs) within the Bowen Basin. Coal beds and tuff horizons were used as stratigraphic markers, supported by chemostratigraphy and age dating. Results corroborate the general subdivisions of these different coal measures relative to basin location, but increase resolution on migrating depocentres in response to foreland loading and subsidence on coal thickness and splitting patterns. In the north, the Rangal CMs comprise two main seams, correlated as Leichhardt and Vermont. The Yarrabee Tuff is consistently present and splits the Vermont seam. The main Leichhardt seam exhibits relatively simple offset stacking relationships with the underlying Vermont and overlying Phillips seams. In the southwest, the Bandana CMs comprise two to three significant seams—the Aries-Castor, Pollux (Leichhardt equivalent) and Orion—along with the Pisces containing the Yarrabee Tuff. Seams exhibit complex Z splitting and vertical interburden stacking. Locally super-thick seams (crabs) form from convergence of thinner split seams in areas of relative stability over basement highs. In the Taroom Trough, the Baralaba CMs show the greatest response to loading, as seams thin and split along the eastern margin. The variability in the splitting patterns, coupled with the coal measures total thickness, corroborate the extension of the final basin depocentre northward, which was not preserved.

A new perspective on sequence stratigraphy of syn-orogenic basins: insights from the Tertiary Piedmont Basin (Italy) and implications for play concepts and reservoir heterogeneity

Abstract The Tertiary Piedmont Basin was reshaped as the Apennines progressively overrode the Alpine retroforeland. Nine basin-wide unconformities were followed by abrupt accommodation turnarounds or high-accommodation/high sediment supply intervals. Unusual stratigraphic discontinuities require a different perspective to reconcile allostratigraphy and sequence stratigraphy, highlighting a wider range of tectonically driven discontinuities (subaerial/subaqueous/regressive/transgressive), diachronism of accommodation and sediment–fairway turnarounds, unusual routing to deepwater, and relationships between fourth- and fifth-order sequences. This approach allows innovative play concepts and prediction of reservoir heterogeneity. Steep gradients and high sediment fluxes favour the development of coarse-grained deltas dominated by hyperpycnal processes and large-scale instability/sediment failures, often expressed by retrogressive slump scars, owing to over-steepening generated by drowning unconformities related to orogenic collapse or basin inversion. During increasing-accommodation intervals, subaqueous erosion leaves remnants of drowned deltas forming stratigraphic traps sealed by prodelta-slope muds. The sediments removed feed turbidites, generated during transgressive intervals and deposited at the toe of oversteepened slopes. These may eventually back-fill the slump scar system and show a fining-upward stacking-pattern owing to the re-establishment of the equilibrium profile. Another play concept relies on the combination of onlapping non-marine to marginal marine deposits against fault-bounded basement highs, sealed by marine muds deposited during the subsequent drowning.

Tectonic styles and crustal shortening of the Central Andes “Pampean” flat-slab segment in northern Chile (27–29°S)

The Andean orogenic belt, located in the Central Andes “Pampean flat-slab” segment in northern Chile (27–29°S), is composed of two major tectonic regions: the Coastal Cordillera and the Frontal Cordillera. To understand their internal tectonic styles, history of growth and the shortening absorbed by the upper crustal structure of this segment, we combined regional geological mapping data, new ages obtained from radiometric U–Pb dating, and a semibalanced and restored cross-section 225.18km in length. The results as shown in the previous Mesozoic extensional fault systems, established in northern Chile by the Gondwana breakup, have played a fundamental role in the orogenic buildup. The central structure is characterized by an asymmetric basin (Upper Cretaceous–Paleocene) confined by a doubly vergent fault system composed of inverted faults related to the edges of the Mesozoic Chañarcillo and Lautaro Basins. The U–Pb geochronological data obtained from synorogenic volcano-sedimentary deposits and the angular unconformities recorded between the Cenozoic geological units have revealed that the compressive deformation in this segment started at around ~80Ma by tectonic inversion in the eastern Coastal Cordillera and western Frontal Cordillera, however, the presence of Paleocene and Miocene synorogenic successions at the footwall of the basement reverse faults of the Frontal Cordillera suggests a migration of Andean deformation from the west to the east during the Paleocene–Miocene by propagation of ramps involving inherited basement highs. The pre-compression restoration makes it possible to estimate 40.94km of minimum shortening, concentrated by inversion anticlines and fault-controlled basement highs across the Frontal Cordillera.

Contemporary stress orientations in the Faroe–Shetland region

The Faroe–Shetland region of the NE Atlantic continental margin contains a number of complexly structured Mesozoic–Palaeogene-age rift basins, but in comparison with the contiguous British Isles and North Sea Basin, the state of crustal stress in the Faroe–Shetland region is poorly understood. The orientation of maximum horizontal compressional stress (σ Hmax ) across most of NW Europe is roughly NW–SE, which is considered to be controlled by forces acting at the plate boundaries. We have determined 16 B–D quality σ Hmax orientations based on borehole breakouts interpreted in petroleum wells, and define three distinct stress provinces within the Faroe–Shetland region. Stress orientations in the NE are roughly NW–SE, consistent with the regional pattern of stresses in NW Europe and local neotectonic structural trends. However, contemporary stress orientations in the central and SW of the Faroe–Shetland region exhibit short-wavelength (distances &lt;10–50 km) variation, with NE–SW, north–south and east–west orientations that are parallel or subparallel to underlying structural trends. This variation is interpreted in terms of stress deflections towards weak faults that downthrow the Mesozoic–Cenozoic sedimentary successions against basement highs. These local-scale sources are superimposed on a background roughly WNW–ESE σ Hmax orientation that is controlled by both plate boundary forces and regional-scale sources of stresses.