Piggyback Basin Research Articles

Diapir structure and its constraint on gas hydrate accumulation in the Makran accretionary prism, offshore Pakistan

ABSTRACT The Makran accretionary prism is located at the junction of the Eurasian Plate, Arabian Plate and Indian Plate and is rich in natural gas hydrate (NGH) resources. It consists of a narrow continental shelf, a broad continental slope, and a deformation front. The continental slope can be further divided into the upper slope, middle slope, and lower slope. There are three types of diapir structure in the accretionary prism, namely mud diapir, mud volcano, and gas chimney. (1) The mud diapirs can be grouped into two types, namely the ones with low arching amplitude and weak-medium activity energy and the ones with high arching amplitude and medium-strong activity energy. The mud diapirs increase from offshore areas towards onshore areas in general, while the ones favorable for the formation of NGH are mainly distributed on the middle slope in the central and western parts of the accretionary prism. (2) The mud volcanoes are mainly concentrated along the anticline ridges in the southern part of the lower slope and the deformation front. (3) The gas chimneys can be grouped into three types, which are located in piggyback basins, active anticline ridges, and inactive anticline ridges, respectively. They are mainly distributed on the middle slope in the central and western parts of the accretionary prism and most of them are accompanied with thrust faults. The gas chimneys located at different tectonic locations started to be active at different time and pierced different horizons. The mud diapirs, mud volcanoes, and gas chimneys and thrust faults serve as the main pathways of gas migration, and thus are the important factors that control the formation, accumulation, and distribution of NGH in the Makran accretionary prism. Mud diapir/gas chimney type hydrate develop in the middle slope, mud volcano type hydrate develop in the southern lower slope and the deformation front, and stepped accretionary prism type hydrate develop on the central and northern lower slope. The middle slope, lower slope and deformation front in the central and western parts of the Makran accretionary prism jointly constitute the NGH prospect area.

Detrital zircon U–Pb insights into the timing and provenance of the South Pyrenean Jaca basin

We investigate how sedimentary systems respond to tectonic uplift during the last stages of infilling of a foreland basin. Massive conglomeratic deposits characterize the last stage of basin fill in the Jaca basin, the western portion of the South Pyrenean foreland. We conduct detrital zircon U–Pb geochronology in a 3000 m thick Cenozoic section containing the transition from deltaic to alluvial environments with the aim of reconstructing changes of provenance in this key stage of evolution of the basin. The last conglomeratic deposits of the basin belong to the San Juan de la Peña alluvial fan, which has previously been assigned an early Oligocene age. Our results show the presence of earliest Miocene detrital zircons at the base of the fan. Zircon double-dating reveals identical U–Pb and (U–Th)/He ages, which is indicative of a volcanic origin for these zircons. We therefore conclude that this fan was deposited during early Miocene times. Our data establish a new chronological framework for deformation and sedimentation in the South Pyrenean foreland, with strong implications for the dynamics and palaeogeography governing the last episodes of basin fill. Our results support synchronous sedimentation in the Jaca piggy-back basin and in the autochthonous Ebro basin during the last stages of Pyrenean compression in the Miocene. This work emphasizes the tectonic controls on the configuration of the drainage basin and gives insights into the evolution of the drainage network in internally drained basins. Supplementary material: S1: Extended Zircon U-Pb LA-ICP-MS methodology. S2: Reduced detrital zircon U-Pb dataset for all analysis. S3: All age spectra. S4: zHe data. S5: Sample location for the analyzed samples are available at: https://doi.org/10.6084/m9.figshare.c.4507073

The Pleistocene flora of Bezhan, southeast Albania: early appearance of extant tree species

ABSTRACT The piggyback basin of Bezhan, southeastern Albania, was formed during the late Neogene and contains Pliocene/Pleistocene deposits. These continental deposits consist of marls, siltstones and clays separated by a thin series of lignite-seams alternating with clays (Bezhan formation). We investigated leaf fossils and dispersed pollen from marls of the upper portion of this formation. Fifty-two plant taxa comprising algae, gymnosperms, and angiosperms were recovered. Of these, at least 19% belong to extant species and less than 16% belong to taxa today extinct in western Eurasia. Tsuga is represented by three pollen taxa with affinities to modern Chinese, Japanese, and North American species. Herbaceous taxa indicative of steppe (Artemisia, Amaranthaceae) occur in low quantities (≤1%) suggesting an interglacial setting. Four vegetation units are recognised: Wet riparian and aquatic vegetation, mesic oak forest, dry sub-Mediterranean woodland, and montane conifer forest. A comparison of the Bezhan flora with well-dated Pliocene and Pleistocene floras of Italy suggests a Calabrian (late early Pleistocene) age for the upper unit. This estimate is based on the abundance of extant taxa, the absence of subtropical taxa, and threshold values of particular taxa (Tsuga, Carya). The findings are in agreement with age estimates for extant tree species from molecular studies.

Structure of the wedge-top and foredeep of the Magallanes-Malvinas basins between 62° W and 67° W (SW Atlantic Ocean)

This work analyzes the geometry and geodynamic development of the offshore sector (between 62° W and 67° W) of the south Magallanes and Malvinas basins wedge-top and foredeep, and associated orogenic wedge. It is based on the interpretation of more than 20,000 km of multichannel seismic profiles, along with bathymetric data. The fold-and-thrust belt front was mapped, and three structural domains were distinguished: western, transitional and eastern. A stepped foredeep characterizes the western domain with flower-structures that affect the basement, and by an intense erosion in the Miocene deposits. Towards the transitional domain, the erosion is less evident, and the wedge-top is more developed. This configuration is associated with the syn-deformational deposition and the generation of thrusts within an acoustically chaotic body in the transitional and eastern domains, deposited by processes of mass removal in the Oligocene. During the Oligocene/Miocene, the area was affected by compression/transpression, which generated an incipient tectonic inversion of the basement extensional faults, with the formation of anticlines associated with piggy-back basins in the wedge-top. The differences observed between the western and eastern domains would be related to the differential movement between the crustal blocks of Tierra del Fuego and Burdwood Bank, respectively, against the South American shelf since the Oligocene.

Geology of the Yeşilyuva and Kocabaş region and its geotectonic significance

Southwestern Turkey experienced a transition from crustal shortening to extension during Late Cenozoic, and evidence of this was recorded in different basin types in the east of Denizli region. The study area comprises a heterogeneous suite of Mesozoic to Recent igneous, metamorphic, and sedimentary rocks. Two main rock groups are distinguished in the area: the basement rocks of pre-Neogene age and the sedimentary cover of Neogene-Quaternary age. In the region, several Late Cenozoic structural basins are filled with terrestrial clastic and volcanic rocks. These basins are different in orientation, geometry, and nature of basin infills. In the studied area, the exposed basal units of the ophiolitic melange correspond to the Lycian Nappe complex. The first sedimentary cover unit, unconformably overlying the nappes, is represented by an E-W-trending basin that is filled with the Oligocene-Lower Miocene shallow marine-terrestrial deposits. The infill of the studied basin consists of the Caykavustu and the Akcay Formations which were deposited during the Late Oligocene and the Early Miocene, respectively. These basins developed as a piggy-back basin along the fault plane on the hanging wall blocks of normal faults. A graben basin (Yesilyuva-Kocabas) started to occur along with NE-SW-trending normal faults which were formed as a result of E-W extensional regime during the Late Miocene. The coarse clastics of the Kizilburun Formation of the Late Miocene age were deposited within an alluvial fan derived from the Elmadag Horst in the east of the basin. Whereas the coarse clastics of the Late Miocene basement were accumulated in front of the hanging fault blocks, the fine-grained clastics of the Saraykoy Formation overlie conformably the Kizilburun Formation. The sequence continues with the lacustrine limestones of the Aktepe Formation. Alkaline magmatics of Early-Late Pliocene cut all successions. E-W-trending fault systems formed with the N-S extensional regime affected the basin, and the recent E-W grabens (Curuksu and Acigol Graben) occurred during the Early Pliocene. The recent morphology of the studied area developed under the control of the Asagidagdere oblique fault zones which are located in the south of the Curuksu Graben.

Three-dimensional characterisation of sedimentary heterogeneity and its impact on subsurface flow behaviour through the braided-to-meandering fluvial deposits of the Castissent Formation (late Ypresian, Tremp-Graus Basin, Spain)

Abstract Fluvial deposits of the Castissent Formation (late Ypresian) form part of the Eocene infill of the Tremp-Graus piggyback basin. The Castissent Formation has been subdivided into three complexes (A, B, and C). This project focuses on the proximal fluvial-sandstones of Complex A in the Mas de Faro outcrop (NE Iberian Peninsula). There, three amalgamated channel belts are exposed in a 15–24 m thick succession that passes upwards from sandy braided-river deposits (A1-A2) to coarse-grained meandering-river deposits (A3). Sedimentary heterogeneities within these deposits are characterised and their impact on oil recovery in a reservoir analogue are estimated using field descriptions, virtual outcrop interpretation, a 3D geocellular facies model and fluid-flow simulations. Petrophysical values of different facies types were derived from well data through analogous fluvial deposits of the Eiriksson Formation, in the Norwegian North Sea. Facies analysis show a waning succession of gravel channel lags, unit-bar and dune deposits in A1; a basal mud-clast channel lag, unit-bars and dune deposits in A2, and a coarse-grained point-bar succession in A3. Flow simulation shows: a) fingering of the waterfront related to the gravel channel lag and unit-bars of A1 and A2, and the gravel bars, scour-and-fill deposits and dunes of A3, which act as thief zones hindering efficient sweeping of the intervals immediately above; b) segregation of the injected fluids towards the base of the channel belts due to the fining-upwards successions; and c) vertical compartmentalization due to a relatively impermeable barrier at mud-clast channel lag beds. Permeability contrasts trapped 35% of the original oil in place after 0.5–0.6 pore volumes were injected.

Landscape evolution and deduction of surface deformation in the Soan Dun, NW Himalaya, India

The consequence of strain accumulation along various Himalayan thrusts is manifested in shaping the topography and present day lanscape features of the Himalaya. Consequently, the strain accomodation is attributed to the occurrence of various devastating earthquakes in the Himalayan domain including 1905 Kangra earthquake (Mw 7.8) which occurred along the Kangra valley fault. In the present study, we analyzed and estimatedsss fault related parameters, gradient-length anomaly (GLA) analysis together with Interferometric Synthetic Aperture Radar (In-SAR) measurements to understand the landscape evolution and deformation pattern within the Soan dun (piggy back basin) in the northwest Himalayan front. We combined the results of geodetic, geological, geomorphology and InSAR to constrain the uplift and subsidence between Himalayan Frontal Thrust (HFT) and Main Boundary Thrust (MBT) zones. The estimated results of fault parameters reveal that the horizontal shortening of northwest Himalaya is higher than the vertical uplift. The computed values of GLA magnitude analysis for the uplifted region vary from −9.21 to −0.77, whereas these range from 5.48 to 26.60 for the subsided region. The depicted range of vertical deformation observed from the InSAR measurements ranges from −3.13 to +3.14 mm/y, where the positive and negative value of phases are correlated with the ground uplift and subsidence. The rate of deformation observed from Persistent Scatterer Interferometry (PSI) phase velocity and GLA magnitude is positively supported by the chronologically constrained uplift rates as 3.4 ± 0.3 mm/y. The geomorphic evidences such as folded, tilted and truncated alluvial fan surfaces, offsetting of channels, fault scarps and displaced sedimentary sequences indicate active nature of the Soan dun. The study would be eventually useful for seismic hazard assessment and future infrastructure development in the seismotectonically active regions like Soan dun of NW Himalayan front.

Different stacking patterns along an active fold-and-thrust belt—Acerenza Bay, Southern Apennines (Italy)

Traditional sequence stratigraphic models provide limited understanding of internal complexity and variability when applied to mixed siliciclastic-carbonate strata accumulated in tectonically active settings. Coeval Lower Pleistocene (Gelasian) shallow-marine, mixed siliciclastic-carbonate depositional wedges accumulated within an active piggy-back basin along the southern Italy fold-and thrust-belt are characterized by similar internal architecture of sequences but different stacking patterns. In particular, four coastal wedges (up to 30 m thick each), just a few kilometers (~2 km) apart from each other, show aggradational versus progradational stacking patterns related to their location within a deforming piggy-back basin. In all the studied sections, mixed siliciclastic-carbonate strata form isolated sedimentary wedges organized into three vertically stacked transgressive–regressive sequences bounded by sharp flooding surfaces. Aggradational versus progradational internal architecture results from (1) local syndepositional compressive and/or extensional tectonics controlling differential uplift and subsidence, and (2) sediment supply characterized by a combination of intrabasinal and extrabasinal siliclicastics and carbonates. Aggradation occurs in areas showing a balance between both accommodation and sediment supply, and siliciclastic and carbonate fractions. Progradation is typical of supply-dominated areas located close to the active anticline, and dominated by the carbonate fraction. The present work documents the local variability of stratal stacking patterns and sediment supply (siliciclatic-carbonate ratio). We highlight the limitations of using sequence architectures and systems tracts for base-level changes and basin reconstructions in tectonically active settings. It is of great importance not only to correctly interpret the stacking pattern, but also to increase our understanding of the type of sediment (siliciclastic versus carbonate) and sedimentation rate, sedimentation loci, and subsurface prediction.

The influence of intrabasinal tectonics in the stratigraphic evolution of piggyback basin fills: Towards a model from the Tremp-Graus-Ainsa Basin (South-Pyrenean Zone, Spain)

Piggyback basins often display asymmetric sedimentary successions influenced by both regional and local syn-depositional tectonic structures. There are few examples where a complete exhumed piggyback basin fill can be analyzed, from proximal, close to source areas, to the distal deep-water sinks. The study of these basins is a key to extract the stratigraphic signal of intrabasinal tectonics, which often competes and can even overprint other controlling factors such as eustasy, climate, or autogenic processes. The purpose of this paper is to propose a more detailed model of the evolution of piggyback basin fills, which recognizes the influence of intrabasinal tectonic activity, specific to the piggyback context and the resulting stratigraphic architecture. We investigate the Tremp-Graus-Ainsa piggyback basin, located in the southern Pyrenees, during early Eocene, which was influenced by the development of the Montsec frontal thrust. Twenty four stratigraphic sections, totaling 14 km of logged thickness, are analyzed, covering 60 km of the basin. The stratigraphic surfaces have been correlated in order to define large-scale stratigraphic units and a new sequence stratigraphic framework. The influence of local tectonics in the basin record is identified by abrupt lateral sediment thickness variations, abrupt changes of depositional environments, local erosion surfaces, and changes in dominant sedimentary process regimes and paleocurrent directions through space and time. As a result, we propose a new tectono-stratigraphic model for the development of the Tremp-Graus-Ainsa Basin. Specifically, we identify (1) an underfilled stage with initial high flexural subsidence and a frontal subaqueous blind anticline thrust propagation that controls a dominantly carbonate environment, followed by a progressive increase in siliciclastic sediment supply, and (2) an overfilled stage with an increase in frontal thrust propagation causing new emergent sediment sources. This second stage evolves from an active emerged blind anticline thrust to a migrating thrust that moved along lateral ramps, and which caused the decoupling of the Tremp-Graus uplifted wedge-top sub-basin from the Ainsa subsiding foredeep domain. Finally, we provide a new model intrinsic to the piggyback basin development with four main stages, controlled by changes in intrabasinal tectonic activity, flexural subsidence and orogeny axial zone evolution, which ultimately modulate sediment supply and creation and distribution of accommodation space.

PALAEOGRAPHIC EVOLUTION OF PINDOS BASIN DURING PALEOGENE USING CALCAREOUS NANNOFOSSILS

A different basin evolution is suggested between the northern and southern parts of the Pindos basin, based on biostratigraphic dating results. Characteristic nannofossils showed that flysch sedimentation in the whole basin started in the Paleocene and generally finished during the Eocene, with the exception of the Konitsa and Milia areas where sedimentation lasted until Early Oligocene. Although, basin depth increased southwards, Kastaniotikos and Sperchios faults affected the geometry of Pindos basin, creating ridges and troughs within the basin. Due to this segmentation of the basin, the continuity of the sedimentation in the northern part of the study area until Oligocene is suggested. Calcareous nannofossils recovered from this northern part indicate a Paleocene NP5 to early Cligocene (NP20-21) age. On the other hand, in the southern part, sedimentation of flysch was lasted until middle Eocene. According this model, sedimentation in the southern part, stopped during the middle Eocene, was followed by subaerial exposure and the migration of clastic sedimentation to the western part of Pindos zones (Pindos foreland basin of Ionian zone). At this time, in the northern part, a small-restricted basin was continuously active as a piggyback basin from upper Eocene to lower Oligocene and shallow deposits (slope and submarine canyon deposits, delta fan deposits) accumulated.

Neogene-Quaternary evolution of the offshore sector of the Southern Apennines accretionary wedge, Gulf of Taranto, Italy

Southern Apennines represent a collisional orogenic belt whose compressional regime is commonly assumed to have ceased during Middle Quaternary. On the other hand, to the south the Calabria Arc is still characterized by subduction and the principal aim of the present research is to shed some light on the space and time transition from the ceased collision to the active subduction. Accordingly, we investigated the offshore sector of the Southern Apennines accretionary wedge, corresponding to the Taranto Gulf. To gain insights into the offshore accretionary wedge, we reconstructed a 3D geological and tectonic model by interpreting a grid of 40 seismic reflection lines (1100 km, 80 intersections), within an area of ca. 104 km2, calibrated with 17 wells. The geometric and chronological constraints allow documenting a systematic Messinian-Quaternary thrust migration from internal towards external sectors of the wedge. The migrating deformational process was essentially associated with a leading-imbricate thrust system with a general NE-younging direction, where we could recognize and distinguish some major advancing phases characterized by alternating fast thrust propagation events and strain accumulation periods within the wedge. This process is well emphasized by the jump of the foredeep and piggy-back basins. The NE-wards wedge migration was also associated with a lithospheric-scale flexural folding that generated a set of normal faults striking parallel to the coeval thrusts, likely reactivating optimally oriented structures inherited from Mesozoic events. Finally, a persisting thrust activity up to the latest Quaternary and possibly up to Present in correspondence of the externalmost sector of the accretionary wedge has been documented and explained in terms of strain partitioning in the frame of a recent oblique convergence. The results of this research have possible implications for the seismic hazard assessment of the broader region which is possibly greater than previously assumed.

From conventional outcrop datasets and digital outcrop models to flow simulation in the Pont de Montanyana point-bar deposits (Ypresian, Southern Pyrenees)

Abstract The Pont de Montanyana outcrop exposes strata of the lower Eocene Montllobat Formation deposited in alluvial plains and in meandering river systems of the Tremp-Graus piggyback basin (Southern Pyrenees, Spain). This article focuses on the characterisation of the outcrop using conventional descriptions (photomosaics, correlated stratigraphic logs and palaeocurrent data) together with 3D interpretations of digital outcrop models. The architectural elements identified include lateral-accretion deposits, channel fills (meandering, chute and distal alluvial-fan types), overbank sheets (wings and crevasse splay deposits) and floodplain fines. The channelised deposits were collectively classified, using the width (W) and thickness (T) ratio, as ribbons (W/T ≤ 15) to narrow sheets (W/T ≤ 100). Variations in sandstone/mudstone ratio (between 20% and more than 90% of sandstone) and in the internal architecture of the meandering channel fills suggest deposition in the abandoned channel at different times of the cut-off process and at different locations in relation to the position of the active channel. A high-resolution 3D facies model of the upper stratigraphic interval was constructed, containing point-bar deposits and an associated channel fill. The model was subsequently populated with petrophysical data representative of point-bar reservoirs. Flow simulations based on a water-injection development strategy were carried out. The flow behaviour and the distribution of the bypassed oil are determined by the high degree of internal heterogeneity in the meandering channelised deposits. This heterogeneity is produced by the facies variability, the inclined bedding of the lateral-accretion deposits, the lithology of the channel fill, the downstream fining along the bend and by the change in the orientation of the lateral-accretion surfaces due to expansion and rotation of the point bar. The moveable oil was effectively drained from the sandstone-dominated channel-fill body. However, more than 27% of the moveable oil remained trapped in the uppermost part of the lateral-accretion deposits.

Cretaceous strata at the west edge of the Canadian Rocky Mountains—A piggyback basin remnant of the Western Canada foreland basin

Cretaceous strata at the west edge of the Canadian Rocky Mountains—A piggyback basin remnant of the Western Canada foreland basin

Comment on: Coexistent pre-existing extensional and subsequent compressional tectonic deformation in the Kashmir basin, NW Himalaya by Akhtar et al., 2017 (article in press)

Kashmir basin is a piggyback basin that has developed at the last stage of the ongoing collision between India and Eurasia, and it is ~4 Ma old and contains 1300 m thick blanket of Plio-Pleistocene to Holocene deposits. These unconsolidated sediments are locally known as Karewas, which are deformed and displaced by a number of normal faults. These young normal faults are previously linked to the tectonic collision, however, here we question such consensus on the tectonic origin of the faults by demonstrating that the widely reported field evidence for active normal faulting in Kashmir is actually non-tectonic because the faults have formed by gravitational tectonics. This was achieved by reevaluation of all of the major studies that have reported the field data on active normal faulting in the region. We supplement our results with the structural, geological, geodetic and earthquakes centroid moment tensor data, which clearly consolidate our interpretations and demonstrate that active normal faults in Kashmir basin are not tectonically formed, and instead the lithological contrast between the Upper and Lower Karewas have created suitable conditions for structural failure. So, the faults are active, and would be expected to remain so as long as the vertical load favors the slip on the faults but these faults will not produce major earthquakes as are expected on the major Himalayan fault systems, and therefore the seismic hazard associated with such faults is minimum, which needs to be quantified and implemented in the future earthquake scenario maps.

The San Marcos mélange, Cordillera Septentrional of the Dominican Republic. Nature, origin and age

Understanding the nature, origin, and age of a mélange is crucial to deciphering the evolution of certain orogenic belts. Located in the Cordillera Septentrional of the Dominican Republic, the San Marcos Mélange is characterized by a blocks-in-matrix internal structure. Apparently arranged chaotically, the blocks have centimeter to kilometer sizes, include exotic ophiolitic, volcaniclastic, and intrabasinal sedimentary lithologies, and are of Cretaceous to Miocene in age, all immersed in a scaly and variably sheared argillaceous matrix. In less-deformed coherent sections, the Mélange consists of alternating sandstones, siltstones, and clays, indicative of a distal turbiditic depositional environment. Syn-sedimentary deformation is pervasive and produces systems of conjugated extensional shear fractures, veins filled with calcite, cataclastic bands, and boudinage and pinch-and-swell, symmetrical and asymmetrical structures. They are consistent with a layer parallel extension, produced in a low-energy slope setting, and indicate a low-ductility contrast between few or no lithified lithologies. Paleostress analysis of fractures and veins establishes a NE-SW trend of sub-horizontal extension, suggesting an orientation of the basin along a WNW-ESE to NW-SE axis (current coordinates). The biochronological data of nannofossils present in the matrix gives a sedimentary age for the Mélange from, at least, the top of the lower Miocene to the base of the upper Miocene. The San Marcos Mélange has therefore an essentially gravitational origin. Its deformation was temporally syn-sedimentary and was produced by processes of gravitational sliding, probably triggered by both instability processes within the basin and tectonic (earthquake shaking) mechanisms. Blocks and megablocks of ophiolitic rocks derived from the underlying Puerto Plata complex and of well-lithified, volcaniclastic and sedimentary rocks of the Imbert Fm, represent "exotic" blocks caused by the gravitational collapse of the high topographically margins of the depositional basin, slide down, and emplaced into the unconsolidated slope and basin turbiditic deposits, at least in the lower and middle Miocene. The existence of a large-scale, syn-sedimentary shearing surface directed to-the-ONO at the basal contact suggests that the whole Mélange was displaced once or several times in that direction, contributing to the chaotic nature of the unit. The San Marcos Mélange is not a subduction-zone mélange, but was caused by the submarine landslide of turbiditic sediments in a syn-collisional, piggy-back basin, transported on top of a supra-subduction zone ophiolite of the Caribbean plate.

Comment on “Miocene to Quaternary tectonostratigraphic evolution of the middle section of the Burdur-Fethiye Shear Zone, south-western Turkey: Implications for the wide inter-plate shear zones. Tectonophysics 690, 336–354”

• An attempt to stratigraphy and tectonosedimentary evolution for Çameli Basin has restored. • A constant deposition from early Miocene onward is proposed without actual age data. • It conflicts and deviates from the well-articulated stratigraphy and geodynamic. • We highlight complete marine and terrestrial fossil data for the Çameli Basin area. • An early-mid Miocene piggy-back basin is superimposed by Vallesian-Villanyian graben.

Four major unknown active faults identified, using satellite data, in India and Pakistan portions of NW Himalaya

New mapping through geomorphic analysis of tectonic landforms using a variety of freely available satellite data, including shuttle radar topography and Google Maps, has revealed four major curvilinear ~NW–SE trending faults in NW Himalaya regions of India and Pakistan. From north-west to south-east, these are named as Mawer, Tunda, Gulmarg, and Mughal Road fault zones. Some of these faults show evidence of oblique faulting where thrusting is accompanied by a small component of sinistral strike–slip faulting, and this possibly increases towards south-east. The active nature of deformation on these faults is demonstrated by occurrence of triangular facets, fault rupture scarps, topographic breaks, displaced ridges, shutter ridges, deflected drainages, plus uplift and back tilting of Holocene sedimentary deposits. This is further supported by the fact that these fault traces truncate the previously mapped active structures such as Kashmir basin/Balapore fault and main boundary thrust. The abrupt termination of most of these faults in north-west indicates a strong structural control. These faults are active, and their dimensions and geometrical configurations indicate their potential to host major earthquakes that could be similar or greater than what we witnessed during Kashmir earthquake of 2005. Further, active deformation is also mapped within Udhampur Piggyback basin, which lies within the Riasi fault system in Jammu and Kashmir, NW Himalaya. The emergent thrusting further suggests splay faulting from one of the branches of the Riasi fault system (Mandili-Kishanpur thrust). The structural configuration of the basin indicates a possible structural control on the formation and deformation of the basin. The geomorphic expression of active faulting is manifested in the overall morphology of the oval-shaped basin (similar to Kashmir basin in NW Himalaya). The shape is structurally controlled by faults as the whole of the basin is riding on Riasi fault system. Within the valley, the active faults are only visible on the ~SE portion. This has divided the basin into two distinctive geomorphic divisions: SE and NW domains. These domains are delineated by a structural break that could be ~NE–SW trending fault zone because the mapped faults do not continue beyond this topographic break in the basin. And since the SE tectonic domain is faulted, the streams are deeply incising into the bedrock forming deep canyons. The tributaries are short because their lengths are trimmed by the faults. Thus, the tributaries on the hanging wall have permanently lost their headwater source and are orphaned. Such geomorphic features are not visible in the NW domains, which have not been faulted, and thus, the streams are following the natural slope. All the streams feed the basin merge into a major stream (Tawi River) that cuts through the anticlinal ridge of Suruin–Mastgarh anticline. This river roughly follows the interpreted ~NE–SW trending topographic break, which could mean that it follows a fault. Such an interpretation is backed by the evidence that the anticlinal ridge is only broken at this portion of the ridge.

Detachment fold vs. ramp anticline: a gravity survey in the southern Pyrenean front (External Sierras)

The Santo Domingo Anticline (External Sierras, Southern Pyrenees), which separates the Jaca piggyback basin from the Ebro foreland basin, is a key structure of the Pyrenees. Its geometry has been interpreted both as a detachment fold and as a hangingwall anticline associated with an underlying thrust. In this paper, we present the results from a gravity survey and 2.5D gravity modelling carried out around the Santo Domingo Anticline. Density measurements indicate a sharp density contrast between the Triassic evaporites‐mudstones in the core of the anticline and the sedimentary sequence (limestones and sandstones) at its limbs. Gravity anomalies together with 2.5D gravity models allow to discern the along‐strike structural changes. From east to west, we document a change from the ramp‐associated fold to the detachment anticline. The capabilities and limitations of the gravimetric method for the determination of fold geometry are also discussed. Copyright © 2017 John Wiley & Sons, Ltd.

Is pull-apart basin tectonic model feasible for the formation of Kashmir basin, NW Himalaya

Kashmir Basin in NW Himalaya is considered a Neogene-Quatermary piggyback basin that was formed as result of the continent-continent collision of Indian and Eurasian plates. This model however is recently challenged by a pull-apart basin model, which argues that a major dextral strike-slip fault that runs through the Kashmir basin is responsible for its formation. And here it is demonstrated that this tectonic model is structurally unrealistic, and poses problems with geomorphology, geology, and tectonic setting of Kashmir basin. The major flaw of the model remains its orientation, and geometry, because a major dextral fault, which form a pull-apart basin, cannot cut through the center of a basin. It is therefore shown that the recently suggested pull-apart model is structurally impossible, and thus the Central Kashmir Fault (CKF), a proposed major dextral fault of Alam et al. (2015), could not exist.

Mélange versus forearc contributions to sedimentation and uplift, during rapid denudation of a young Banda forearc-continent collisional belt

New sedimentary geochemistry and petrographic analyses provide the most extensive sedimentary documentation yet of the rapid denudation of the young Timor orogen. The data from three basins including two widely-separated, well-dated sections of the Synorogenic Megasequence of Timor-Leste, and a re-dated DSDP 262, constrain the source and timing of detrital sediment flux during forearc-continent collision along the Timor sector of the Banda Arc. The exhumed synorogenic piggy-back basins formed above a mélange unit that developed at the expense of a weak stratigraphic horizon in the Mesozoic stratigraphy, and was exhumed to the sea floor in latest Messinian time. Following an interval of deep marine chalky marl sedimentation, an increasingly muddy sediment flux indicates that the island of Timor became emergent and shed sediment by 4.5Ma. Comparison of exhumed sections with similar patterns in the DSDP262 chemistry suggests that the sediment source was probably located some 50–60km distant from the basin, which is consistent with the Aileu region of Timor-Leste that shows an appropriate exhumation history. All sedimentation between 4.5 and 3.2Ma was probably derived from a low-relief, rapidly eroding, and mudstone-dominated landscape with geochemical affinities to the Triassic-mudstone-derived synorogenic mélange. The mélange unit overlies and surrounds the Banda Terrane, and was presumably structurally emplaced by propagation of a decollement through the Triassic rocks during the collision. After 3.2Ma, sedimentation was dominated by hard rock lithologies of the Banda Terrane, consisting of forearc cover and basement, the latter including elements of metamafic rocks and metapelites. This phase of sedimentation was accompanied by rapid uplift, which may have been partly driven by a transient imbalance between rock uplift and denudation as resistant lithologies emerged from below mélange-like mudstone. Previous work has suggested that the timing of collision in Timor-Leste and West Timor was substantially different. Our reevaluation of DSDP 262 facies migration history in the context of the re-dating presented here, favours a relatively synchronous onset of uplift in both halves of the island, but with different partitioning of strain between the foreland and hinterland in each half of the island.