Synsedimentary Tectonics Research Articles

Linking source and sink: The timing of deposition of Paleogene syntectonic strata in Central Asia

Abstract Determining the age of siliciclastic continental sequences in the absence of comprehensive biostratigraphy or radiometric dating of geological markers (e.g., volcanic layers) is inherently challenging. This issue is well exemplified in the current debate on the age of Cenozoic terrestrial strata in Central Asia, where competing age models constrained by non-unique paleomagnetic correlations are interpreted to reflect the growth of the Tibetan Plateau and its impact on Central Asian climate change. Here we present a new approach to evaluate competing age models by comparing the onset of rapid basement exhumation constrained by low-temperature thermochronology in the sediment source region with the initiation of growth strata in the adjacent sedimentary sink. We first validate this method in regions with well-constrained age models and subsequently apply this approach to the Tarim and Qaidam Basins in the northern Tibetan Plateau. The results of this analysis show that syntectonic sedimentation had already initiated during the Paleocene–Eocene and was followed by intensified Oligocene–Miocene mountain building along the northern margin of the plateau. Based on this refined Paleogene tectonic history, we further arrive at a temporal correlation between Paleogene tectonism in Northern Tibet and the retreat of the Proto-Paratethys Sea, a major water body that extended across Eurasia and was closely associated with climatic and biodiversity changes. We thus highlight the previously underestimated role tectonics in Northern Tibet had in the evolution and demise of the Proto-Paratethys Sea during the Paleogene.

Cdem: A macOS program for discrete element modeling of tectonic structures

Abstract cdem is a macOS document-based application for two-dimensional discrete element modeling of tectonic structures and their associated deformation. Documents encapsulate simulations that can be run and explored simultaneously. A document contains three main views: (1) Set-up view, to define the assembly size, element properties, anisotropy, boundary conditions (type of faulting), overburden stress, erosion, and syn-tectonic sedimentation; (2) Summary view, which displays the details of the model after initialization; and (3) Results view, which displays the geometry of the model while it is running or after the run and allows exploring the model’s evolution in terms of geometry, displacement, strain, or stress. We illustrate the use of the program for assembly calibration and the modeling of contractional and extensional structures without and with syn-tectonic sedimentation. In all these cases, cdem produces realistic incremental and finite deformation. cdem is less powerful than its precursor cdem2D, but it can import and visualize cdem2D results, making the combined use of these two programs a robust suite for mechanically modeling tectonic structures.

Middle Jurassic syn-sedimentary tectonics and palaeoenvironmental evolution in the eastern part of the Alborz Mountains (N Iran)

The facies variations in the Middle Jurassic deposits of northern Iran (northeastern Neotethys) were studied in two stratigraphic sections (Tapal and Kalariz) in the eastern part of the Alborz Basin to reconstruct the palaeoenvironmental evolution in this region. Six different palaeoenvironments were recognized based on alternation of sedimentary facies in the four formations of the studied sections (upper part of the Fillzamin, Dansirit, Dalichai and lower part of the Lar formations). The upper Fillzamin Formation (lower Bajocian) records a gradual shallowing-upward sequence from seaward to landward margin of a prodelta environment in the study area. This shallowing trend terminated with the Mid-Cimmerian tectonic event and unconformity, which is characterized by a thin limonite layer at the base of the Dansirit Formation in the Tapal section. The Dansirit Formation (lower upper Bajocian) represents heterolithic marginal marine, sand and gravel bars and terrestrial environments. The subsequent deposits of the Dalichai Formation (upper Bajocian–Callovian) represent a deepening sequence, which is associated with the appearance of pelagic strata and ammonitico rosso facies in the upper part of the formation. The ammonitico rosso facies, which is related to the development of pelagic swells in the rift basin, gives direct evidence of an extension phase and presence of a swell/trough system in the region. The rifting and subsidence are attributed to the opening of the South Caspian Basin (north of the Alborz region). The lack of correlation between the sea-level changes recorded by the upper Bajocian strata of the sections and the long-term eustatic sea-level changes suggest tectonic influence on the facies variations and sea-level fluctuations in the Alborz region. From the upper Bajocian upwards, a deepening trend in the studied sections can be correlated with the global sea-level changes, while tectonic (rifting and subsidence) overprinted the eustatic sea-level rise.

Structural styles at the junction between the Eastern Atlas Fold and Thrust Belt and the northern Sahel-Gulf of Hammamet foreland basin (Tunisia)

The Tunisian Eastern Atlas Fold and Thrust Belt is characterized by NE-SW fold-thrust structures derived from intracontinental basin inversion during the convergence between Africa and Eurasia. In this paper, we study the transition from this folding-thrusting domain to its foreland basins by discussing a regional structural transect based on field investigations, well data correlations and, seismic lines interpretation. Well correlations highlight significant thickness and facies variations particularly affecting the Cretaceous units, deposited during the Tethyan rifting. Successive compressional events during the Eocene and the upper Miocene-Quaternary have controlled the inversion process, thus shaping the overall present-day structure. Along the Atlas, we observed several large anticlines controlled by deep NE-SW thrusts that root down into a regional-scale major décollement that corresponds to Triassic evaporites. In the field, contractional structures such as fault propagation folds and pop-ups are identified. Unlike the Atlas Fold and Thrust Belt, the Sahel Mesozoic and Paleogene series are buried under thick Neogene to Quaternary syntectonic deposits with sediments supplied from the erosion of the uplifted Atlas structures, recording a high subsidence rate. The Sahel foreland is characterized by buried fold and thrust structures, which define an outer deformation front. Besides contraction, the Sahel Foreland basin is also affected by extension related to the Strait of Sicily rift. Seismic profile interpretation highlights the presence of a large scale rollover developed over a listric fault controlled by a deeper extensional system affecting the Paleozoic series.

LA SUCCESSIONE OLIGOCENICA TRA OVADA E CASSINELLE (ALESSANDRIA) EVOLUZIONE PALEOGEOGRAFICA ED IMPLICAZIONI STRUTTURALI

Facies succession of the Oligocene terrigenous sequences from a seccar of Piedmont Tertiary Basin (between Ovada and Cassinelle, Alessandria) are here described and their significance discussed. The palaeogeographic evolution of the area results to be controlled by a synsedimentary tectonics. In the Early Oligocene, a generalised vertical mobility affected the region which, as a conse­quence, was splitted in some blocks with a differential tectonic behaviour by tensive lineaments; that is testified by a widesprcad continental facies characteristic of a high energy environment (lower pare of "Formazione di Molare"). Successively, ali the area subsided, and the sea transgressed over it (upper part of "Formazione di Molare"). During the Late Oligocene subsidence acted differentially along synse­dimentary faults and the deeper portions are individuated; which became location of relatively deep marine deposition ("Marne di Rigoroso"). The intense tectonic activity was responsible for the deposition of large conglomeratic and arenaceous bodies interbedded within the hemipelagic sequences (in the areas with precocious and intense drowning).

Towards an improved discrimination and correlation of Permian-Lower Triassic sediments in Central Europe: A chemostratigraphic approach

The stratigraphic classification and correlation of Permian-Lower Triassic clastic beds in the Central European Basin System traditionally rely on geophysical, bio-, and lithostratigraphic methods. However, in basin margin areas, the accuracy of these tools is diminished due to the heterogeneous distribution of stratigraphic markers, lack of index fossils, and greater climatic and tectonic disturbance. To overcome these limitations, this study introduces a more versatile, multifaceted and chemostratigraphy-based approach. By integrating results from bulk X-ray fluorescence analysis, sandstone petrography, Raman heavy mineral analysis, lithofacies characterisation and borehole gamma-ray logs, we produce robust multi-stratigraphic schemes for selected sequences in the Franconian Basin (SE Central European Basin System). Hierarchical chemostratigraphic zones, comprising five chemozones and sixteen subzones, were designed using key elemental ratios (Ga/Rb, Rb/K, Na/K, Ca/Mg, Cr/Ti, Th/Ti, Nb/Th, Ti/Nb, P/Ti, Zr/P, Zr/Y), whose changes through time reflect modifications in the mineralogical composition of sedimentary rocks. To ensure precise interpretations of geochemical data, we established links between mineralogical and chemical components through statistical processing and direct comparison with mineralogical assemblages. Our results demonstrate that chemostratigraphic boundaries can identify major changes in palaeo-depositional environments and sediment sources induced by eustatic, tectonic and climatic disturbances. For example, changes in the P/Ti and Zr/P ratios across the CP3-CT1 document the increased abundance in apatite-rich granitic detritus, resulting from the exposure of new source lithologies in the catchment area due to Early Triassic synsedimentary tectonism. Since these perturbations had a regional impact on sedimentation, their geochemical fingerprints are correlated across the basin, regardless of lithofacies variability or distance between sections. Moreover, integrating characteristic geochemical signals into multi-stratigraphic schemes enables more precise placement of stratigraphic boundaries, identification of locally deposited/preserved stratigraphic markers, and overall refinement of outdated classification schemes. The chemostratigraphic approach introduced in this study offers a solution to the limitations of conventional stratigraphic tools, allowing robust characterisations and correlations of Permian-Triassic sequences in the marginal regions of the Central European Basin System. In addition, the multi-analytical workflow for processing geochemical data, refining stratigraphic schemes and attributing geochemical anomalies to environmental perturbations represents a further step towards more precise applications of chemostratigraphy to the depositional record.

Early-middle Miocene Inversion of the Abu Jir Fault in the Western Iraq: a Possible Consequence of the Arabian Plate Northward Movement

The Abu Jir fault zone in western Iraq that marks the western limit of the Zagros foreland basin merges with the Anah graben in the north. The northern segment of the Abu Jir fault zone and the western Anah graben are inverted structures. In this study, we investigated the timing and mechanism of the northern Abu Jir fault zone inversion in comparison with other inverted structures like Tel Hajar and Sinjar, which are located in the north and closer to Arabia–Eurasia collision zone. In the study area the Abu Jir fault zone is characterized by a local-scale northwestern-trending asymmetric fold, associated with inverted normal faults, positive flower structures, right–lateral strike-slip faults, and seismically induced early middle Miocene slump structures. Based on the structural synthesis of the surface geology and age constraints from syntectonic deposits at the northern Abu Jir fault area, the Abu Jir fault inversion and its western block northward movement were inferred to be resulted from forces that originated from the south to the north, unlike the northern younger inverted structures. This early middle Miocene age of the Abu Jir fault inversion is comparable to the arrival time of the Afar plume hot mantle material flow from the south to the north in western Arabia. Therefore, we argue that the Abu-Jir fault inversion is more likely to be due to dragging of the Arabian plate by mantle flow from the south to the north rather than shortening propagation from the north to the south.

Cretaceous tectonostratigraphy of ‘the Great Coverham section’ and adjacent areas, northeastern Waiau Toa/Clarence valley, New Zealand

ABSTRACT Late Early–Late Cretaceous strata preserved at the northeastern end of the Waiau Toa/Clarence valley, northeastern South Island, New Zealand, have been central to ongoing debates concerning the end of Mesozoic subduction on the Zealandian margin of Gondwana and the initiation of extension. New geological mapping within this area at Coverham, Kekerengu and Wharekiri, has resolved complex relationships between Cretaceous stratigraphic units and faults. Results indicate that, within the interval 110–100 Ma, Champagne and lower Split Rock formations record syn-tectonic deposition by marine mass-transport processes within confined sub-basins with steep seafloor gradients. Upper Split Rock Formation and overlying Nidd Formation record progressive burial of seafloor topography between c. 100–86 Ma. Although uncertainties remain, three or four faults appear to have been low-angle structures with normal displacements that were active within the interval c. 105–89 Ma; one of these faults experienced brief reversal of offset between c. 91 and 87 Ma. The new data are most consistent with a model of subduction shutdown between c. 105–100 Ma, following impact of the Hikurangi Plateau large igneous province at the subduction margin. Widespread uplift along the margin between 97 and 95 Ma may reflect subsequent rebound of the subducted plate.

Paleogene evolution of the External Rif Zone (Morocco) and comparison with other western Tethyan margins

The Paleogene evolution of the NW margin of the African Plate (Western External Rif Zone) was studied by means of multidisciplinary analyses of twenty-one stratigraphic logs, including tectofacies recognition, petro-mineralogical results, and thicknesses analysis. Four stratigraphic intervals were recognized separated by three unconformities coarsely aligned with the Cretaceous–Paleogene, Eocene–Oligocene and Oligocene–Miocene boundaries, respectively. Tectofacies appear from the late Ypresian being more frequents from the Oligocene as the tectonic activity increases. The petrology of detrital suites indicates recycled orogen-derived sediments, with quartz supplied from metamorphic rocks of the Atlas orogen and/or the African craton. On the basis of Mesozoic clay mineral assemblages reported in the literature, the clay mineralogy of mudstones suggests upper Jurassic to upper Cretaceous terrains from the Internal Intrarif as the main source area of the Paleocene–Eocene successions, with sediment provenance reversion during the Oligocene and additional contribution of Paleocene to lower Eocene suites. The different displacement capability of the identified aluminic-magnesic clay mineralogy enabled to deduce the relative proximity of the source area. These findings point out a complex sedimentary evolution characterized by a mixture of different lithotypes dating back to upper Jurassic. X-ray parameters helped to identify evidences of synsedimentary tectonics overprinting the inherited mineralogy during some periods with weak burial diagenesis at most. During the Paleogene a foreland basin is formed mainly in the Mesorif and Prerif sub-domains. This foredeep was represented by two ‘sub-geosynclines’ separated by a relative bulge located in the External Mesorif. The Internal Intrarif could represent the relative orogenic front, advancing on the External Intrarif. The Eocene forebulge was located in the Ridges Domain, while the Gharb Basin was the backbulge of the system. During the Oligocene the depocentral area migrated southward and a homogeneization of thicknesses took also place in the whole margin. In this new configuration, the foredeep would be located in the External Mesorif (previously a relative bulge) while the Ridges Domain and the Gharb Basin continued to act as the system forebulge and backbulge, respectively. A comparison with the Paleogene evolution of other western Tethys external margins (Betic Chain, Tunisian Tell, Sicilian Maghrebids, and Apennines) has revealed more similarities than differences. The effects of the Eo-Alpine tectonics are recognized everywhere even if they decrease both from N to S, and from W to E in the different considered margins. The evolution of the compared margins shows a common pre-foredeed (Paleocene-Eocene) and beginning of foredeep (Oligocene) stages in the foreland basins.

Syntectonic sediment loading and fold-thrust belt structural architecture: An example from the central Appalachians (USA)

AbstractFluid inclusion microthermometry of synkinematic veins is used to estimate the maximum syntectonic load that was deposited on the wedge top in the central Appalachians (northeastern United States) during the Alleghanian orogeny. The restored loads indicate two major depocenters during the Alleghanian orogeny: one above Broadtop synclinorium, with as much as 7 km of Pennsylvanian–Permian load probably sourced by the erosion of rocks uplifted by the growing Blue Ridge massif and emplacement of the North Mountain thrust sheet; the other above the Anthracite belt, with as much as 16 km of syntectonic load likely sourced by the erosion of rocks uplifted by the growing Reading Prong massif. The loads were generally <3 km in the intervening Juniata culmination. In areas of high load, the structural architecture of the basin is that of widely spaced thrusts (~17–22 km) with large leadingedge anticlines in the Cambrian–Ordovician lithotectonic unit, while in areas of low load, thrusts are more closely spaced (~15 km) and deformed into an imbricate stack. The relationship between observed syntectonic loads, thrust spacing, and structural style reflect modeled relationships.

The Gondwanide deformation along the southwestern border of the Río de la Plata Craton: Geochemical and geochronological constraints on ductile shear zones from the Ventania System basement, Argentina

This work deals with the study of Gondwanide ductile shear zones developed in Neoproterozoic–middle Cambrian basement rocks of the Ventania System and possibly related to the reactivation of the Sierra de la Ventana Shear Zone. This reactivation was caused by the northeastward migration of the Gondwanide deformation from the North Patagonian Massif. The crustal shortening related to the Gondwanide Orogeny gave rise to thrusting of the Ventania System basement over Paleoproterozoic rocks of the Río de la Plata Craton. This work focuses on the study of muscovite ± quartz phyllonites of the Ventania System basement and quartz ± muscovite veins crosscutting basement and Paleozoic cover rocks of the system. Structural and magnetic surveys were performed in order to characterize the Gondwanide structures of the basement, while petrographic, X-ray diffraction, geochemical, and geochronological studies were carried out in order to investigate the nature, P-T conditions, element mobility, and age of these shear zone-related rocks. In the Sauce Chico Inlier, mylonitized basement rocks crop out along the western edge of the system, near the basement–Paleozoic cover interface, where the main structures are top-to-NNE reverse ductile shear zones with related phyllonites. Ductile shearing under greenschist-grade conditions (125–340 MPa and 300–400 °C) promoted major and trace element mobility. Phyllonites are the result of extreme hydrolysis of feldspars from the acidic igneous rocks of the basement, producing muscovite and releasing aqueous SiO2 later redeposited as quartz veins. These phyllonites developed in connection with reactivated contacts between basement units and also the basement–Paleozoic cover interface. New Rb–Sr quartz-muscovite and Ar/Ar muscovite ages for phyllonites and a quartz vein indicate a protracted tectono-metamorphic history mainly restricted to the Cisuralian (ca. 287 Ma), comprising regional folding and metamorphism, shear zone activity, vein-type mineralization, and syntectonic deposition of the Tunas Formation. Subsequent reactivations during the Lopingian (ca. 256 Ma) and probably in Late Triassic times (ca. 227 Ma) resulted from localized shearing along mylonitic belts.

Sedimentary evolution of the late Cretaceous - Eocene deep carbonates series of the foreland Magrebian chain. The Tellian domain of northern Tunisia

This paper aims to give an overview of the Upper Cretaceous – Eocene in the Tellian domain of the Magrebian chain in Tunisia. The sedimentological studies of the carbonates of this time interval, in the Fernana - Ain Draham area, offer a better knowledge of the Tellian foreland. Stratigraphic analysis of ten sections located in the structural units (Autochthonous, Para-autochthonous, and the allochthonous, Ediss Unit, Ain Draham - Adissa Unit and Kasseb unit) brings new results. The facies analysis of the nappes zone reinforces the definition of the allochthonous units that have undergone planar displacements during late Tertiary phases. The depositional setting evolutions during the Late Cretaceous - Eocene period testify to an area in the process of deformation. Since the late Cretaceous (Maastrichtian), the abundance of older dismantling rocks in the allochthonous units is interpreted as a synchronous shortening of the basin. The clastic deposits attributed to mélanges chaotic deposits forming events layers testify two tectonic stages of the early foreland basin formation with details: the upper Cretaceous (Gansseri Biozone) and the early Eocene (Lutetian). The studied deposits outcropping in the Tellian domain (part of the Maghrebian chain) invoke the earliest stage of synchronous compressive syn-sedimentary tectonics of the subduction of Europe over the African plate southern branch, as observed in the Mediterranean rim.

Sedimentary characteristics and geophysical architecture of the Cretaceous Bambalo claystone formation (Mayo Oulo-Lere Basin, North Cameroon)

• Depth and spatial development of Bambalo sedimentary sequences during the Cretaceous. • The Bambalo Formation described in terms of lithostratigraphy, VES and ERT. • Fluvio-lacustrine deposits including claystone, siltstone and limestone. • Sequences dominated by retrogradational sequences in a lacustrine environment. The Mayo-Oulo-Lere Basin, with an overall surface area of 122 km 2 is located in northern Cameroon between the western extension of the Doba Basin and the eastern edge of the Benue Trough. This study maps the depth and spatial development of Bambalo sedimentary sequences in the Mayo Oulo-Lere Basin that were deposited during the Cretaceous. The depositional sequences present an exposure of crocodile fossils and plants evidenced by superficial alteration. The Bambalo Formation is described in terms of lithostratigraphy, vertical electrical sounding (VES) and electrical resistivity tomography (ERT) to provide a better understanding of stratigraphic evolution and setting conditions during sedimentation. Sedimentary deposits in the Mayo Oulo-Lere Basin are mainly fluvio-lacustrine deposits consisting of alternating claystone, siltstone and limestone. The lithostratigraphic log of Bambalo for the subsurface geology up to 25 m presents three main depositional sequences named S1, S2 and S3. S1 presents ripples marks and desiccation cracks that are directly observed on the surface outcrop. The separation between S1-S2 and S2-S3 is marked by unconformity surfaces. The sedimentary sequences are dominated by retrogradational depositional trends that describe short sequences of fining-upwards successions. The ERT image results obtained from geophysical analysis using Res2Dinv display local features associated with folding in the aforementioned sedimentary thickness of approximately 30 m. Additionally, the VES analyses using ipi2win software show that the upper 78 m part of the Bambalo formations is composed of four layers (L1, L2, L3 and L4) distinct by resistivity. L4 Layer correlated with the top of lithostratigraphic log S3, while L3 is a semiresistive set of 78 Ω·m layering S1 and S2 lithostratigraphy sequences. Layer L2 corresponds to a conductive set with resistivity of approximately 27 Ω·m above the lower layer L1, a resistive sequence with resistivity greater than 1000 Ω·m. The combination between the major rifting faults (N70°, N110° and N130°E), syntectonic sedimentation and Barremian-Aptian age attributed to sediments of Bambalo demonstrate clearly that the sediments were deposited during or few time after the rifting phases. The sediments are resulting from a rapid filling of the basin characterised with retrogradational sequences that are controlled by the evolution between accommodation space created after each tectonic phase and the base water level rise within the basin. The rapid elevation of water and sedimentation might be one of the reasons of the massive death of crocodilians. The results of this study demonstrate that the combination of ERT and lithostratigraphic analysis is a powerful tool for a better understanding of the Bambalo sedimentary process and basin evolution. The lateral and vertical evolution of the layers being proven, a future deep excavation will certainly make it possible to bring to light new types of fossils from these deposits and in the neighbouring basins.

Triassic Nappe in the Central Part of the Southern Central Asian Orogenic Belt (Ejinaq, NW China): Evidence from Structural Analysis and Geothermochronology

AbstractThe thrust nappe played an important role in the Mesozoic tectonic evolution of the middle part of the Central Asian Orogenic Belt (CAOB). However, the timing, structural style and kinematic processes of the thrust nappe remain controversial, particularly the detail of the thrust nappe in the Guaizihu region (110 km east of Ejinaq). In this study, we investigate new field mapping, seismic sections, geochronology and low‐temperature thermochronometric dating to provide constraints on the history of this thrust nappe in the Chaheilingashun area (northwestern Guaizihu region). The field mapping, seismic sections and structural analysis reveal that the autochthonous system had developed a series of strong fold structures in the upper Permian strata. The allochthonous system mainly contains Devonian monzogranite (U‐Pb age, ranges from 386.7 to 389.0 Ma) and Meso–Neoproterozoic schists (the maximum depositional age, ∼880 Ma), which were thrust upon the upper Permian strata during Middle to Late Triassic. Based on similar rocks, geochronological dating and the Yagan thrust, we suggest that the postulated root zone of this allochthon might have originated from the Huhetaoergai area (40–60 km northwest of the study area). The geochronological results reveal that the lower age limit of this thrust nappe is constrained by the Lower–Middle Triassic syntectonic sediments (tuffaceous sandstone, ∼247 Ma), which is the sedimentary response of the fold structure., The timing of the termination of this thrust nappe is defined by the cooling age (40Ar/39Ar data, 217–211 Ma) of the Devonian monzogranite and Meso–Neoproterozoic schists. Thus, we consider this thrust event in the study area to potentially have occurred in the period from 247 Ma to 211 Ma, which may represent the tectonic response to the closure of the Paleo‐Asian Ocean.

Sedimentology and New Paleogeographic Data of the Lower Eocene Chouabine Formation in the Gafsa Basin (Tunisia), Southern Tethyan Margin

Abstract Facies and paleo-environment reconstruction applied to the lower Eocene Chouabine deposits occurring in the Gafsa area in Tunisia provided important information on sediment cyclicity and paleogeographic conditions. From west to east, four sections were surveyed: Tamerza (25 m), Oued Thelja (48 m), Jebel Ong (25 m), and Jebel Chamsi (45 m). Furthermore, the facies stacking pattern allowed for the reconstruction of depositional environments in relation to sea level changes. The Chouabine Formation is formed by the succession of three sequences composed of marls, phosphorites, and carbonates. There are five main facies organized into two transgressive cycles. The gradual transition of facies from intertidal to circatidal environments unraveled the sedimentation on a homoclinal ramp, episodically swept by upwelling currents. The Chouabine Formation is made of deepening–upwards cycles. Each cycle ranges from 2 to 5 m in thickness. The proximal-distal transition of depositional environments was gradually increasing from intertidal to offshore environments. Lateral variation of thickness and facies is generated by the reactivation of inherited NW-SE extensive and/or transtensive faults, acting since the late Cretaceous during the intermediate closing phase of the Neotethys. Synsedimentary tectonics has created trap structures favouring confinement conditions in the center of the basin, permitting the accumulation and preservation of large thicknesses of phosphate deposits. Based on new litho- and biostratigraphic data, this study presents for the first time a clear and detailed regional stratigraphic correlation and paleogeographic maps.

Deformation structural style of the rioni foreland fold-and-thrust belt, western greater caucasus: Insight from the balanced cross-section

The Rioni foreland fold-and-thrust belt is part of the Greater Caucasus pro-wedge and is one of the most important examples of the collision-driven far-field deformation of the Arabia-Eurasia convergence zone. Here we show the deformation structural style of the Rioni foreland fold-and-thrust belt based on seismic reflection profiles and regional balanced cross-section. The main style of deformation within the Rioni foreland fold-and-thrust belt is represented by a set of fault-propagation folds, duplexes, and triangle zone. The regional balanced cross-section shows that fault-propagation folds above the upper detachment level can develop by piggyback and break-back thrust sequences. Formation of fault-bend fold duplex structures above the lower detachment is related to piggyback thrust sequences. A balanced section restoration of compressional structures across the Rioni foreland fold-and-thrust belt provides a minimum estimate of shortening of −40%, equivalent −42.78 km. The synclines within the Rioni foreland fold-and-thrust belt are filled by the Middle Miocene-Pleistocene shallow marine and continental syn-tectonic sediments, forming a series of typical thrust-top basins. Fault-propagation folds and duplex structures formed the main structure of the thrust-top basin. The evolution of the thrust-top basins was mainly controlled by the kinematics of thrust sequences. Using end-member modes of thrust sequences, the thrust-top basins are divided into: 1) Type I-piggyback basin, 2) Type II-break-back basin, and 3) Type III—formation of thrust-top basin characterized by bi-vergent geometry and related to combined, piggyback and piggyback back thrust sequences.

Microbiostratigraphy, microfacies analysis and lateral basin evolution of Lower Cretaceous deposits in the south of Kerman region, SE Iran

Detailed microbiostratigraphy and basin evolution of the Lower Cretaceous deposits in the Rayen area, south of Kerman Region, SE Iran are investigated for the first time in two sections. The section no. 1 is 324.6m in thickness and comprises five lithostratigraphic units. The section no. 2 is 218 m in thickness and includes three lithostratigraphic units. The identified fauna and flora include 41 benthic foraminifera and 11 calcareous algae species. The identified assemblage indicates that the marine strata in both sections were deposited during the Barremian to Albian. The microfacies analyses carried out on 22 carbonate and 2 clastic microfacies indicate that the deposits in the section no. 1 were deposited on a homoclinal carbonate ramp, whereas in the section no. 2 they were deposited on a rimmed carbonate shelf. Generally, the Cretaceous deposit in the two studied sections represent different sedimentary models and fossil content indicating different basin evolution histories. The paleogeographic setting of the studied area on the south eastern margin of the Central-East Iranian Microcontinent and the active tectonic history during the Mesozoic suggest that the syndepositional tectonism influenced the basement’s morphology and resulted in changes in the fossil diversity and sedimentary nature of adjacent sedimentary basins.

Cenozoic multi-phase intracontinental deformation of the Tianshan Range (NW China): Constraints from detrital zircon provenance and syn-tectonic sedimentation of the Kuqa Depression

Influenced by the far-field effect of the India–Eurasia collision during the Cenozoic, both the Tianshan Range and Kuqa Depression underwent multi-phases of intracontinental tectonic activation. The extremely thick Cenozoic sediments in the Kuqa Depression recorded the basin-mountain coupling process of the South Tianshan and Kuqa Depression. In this study, detailed structural investigations, stratigraphic analysis, and detrital zircon U–Pb dating of the Cenozoic sediments were conducted in the Kuqa Depression to reconstruct the Cenozoic uplift history of the South Tianshan Range. U–Pb ages of detrital zircon from sandstones show four age peaks that correspond to four significant provenance changes in the Kuqa Depression. These four periods of changes occurred at the Cretaceous–Early Cenozoic, Late Eocene–Oligocene, Early Miocene–Middle Miocene, and Early Pliocene–Early Pleistocene. These changes in provenance reflect variations in tectonic activation and paleogeographic settings in the Kuqa Depression–Tianshan Range. Combined with the syn-tectonic growth strata and previously published magnetostratigraphy and low-temperature thermochronology data, we therefore argue that significant Cenozoic deformation and uplift of the Tianshan Range was initiated at the Early Eocene (50–46 Ma), strengthening in the Late Eocene(∼36 Ma), becoming more evident and extending to the entire Tianshan and Basin–Range boundary during the Middle Miocene (13–10 Ma), and culminating and extending to the southern Kuqa Depression since the Early Pliocene (∼6.5 Ma), thus suggesting the continuous convergence of the on-going India–Eurasia collision in the Cenozoic.

The interplay between deformation and deposition in a Pleistocene push moraine: New insight from structural interpretation and area-depth-strain analysis of the growth strata

There are many examples suggesting that push moraine formation requires building up of the proglacial wedge and then post-depositional folding and/or faulting. Only a few studies have been carried out on syntectonic deposition and erosion within proglacial sediment wedges; however, the resulting growth strata were determined based on the high variability in thickness and occurrence of erosional unconformities across the deformed sequence. This study shows how structural interpretation and the area-depth-strain (ADS) balancing method of the growth strata can be applied to better understand the interplay between deformation and deposition within an evolving push moraine primarily composed of a folded sequence of a glaciofluvial fan. This approach, together with analysis of the onlap/overlap relationships, allowed us to determine the relative rate between deposition and deformation. Moreover it provides an insight into the topography of the push moraine that may be inherited not only from the geometry of deformation structures but also from depositional processes controlling the spatial distribution and thickness variation of the growth strata. This study also gives an opportunity to reconstruct the ranges of probable parameters to quantitatively describe the heavily eroded push moraine in terms of the primary topography, height and relative time frame within which it formed. In addition, the probable thermo-hydro-mechanical properties of the deformed strata are interpreted in terms of drained/undrained conditions of volume strain evidenced by structural data and possibilities of lateral flow from beneath synclines into anticlines indicated by ADS-based balancing.

Structure and Alpine tectonic evolution of a salt canopy in the western Betic Cordillera (Spain)

Surface geology, well data, and seismic profiles confirm the occurrence of an extensive salt canopy in the western Betic Cordillera. Upper Triassic (Keuper) evaporites were emplaced allochthonously in the South-Iberian paleomargin of the Tethys during Upper Cretaceous–Paleogene time. The canopy was later deformed during the Neogene (Miocene–Pliocene) Alpine compression, overthrusting the South-Iberian Mesozoic platform and cover and the Guadalquivir foreland basin. The orogenic advance of the canopy originated a frontal open toe and an accretionary wedge (the Guadalquivir Accretionary Wedge). This wedge, which is a shaly mélange (with blocks of Triassic evaporites) deformed by foreland-directed thrusts with associated piggyback basins and syn-sedimentary listric faults. The structure of the western Betic Cordillera is described through several regional cross sections. The subsalt level involved a Jurassic–Lower Cretaceous thick section, deformed with inverted half-grabens through foreland-directed salt-detached thrusts (northwest vergence). Contraction affects previous salt structures, like Triassic half-grabens, primary minibasins, salt rollers, and a possible large salt pillow. The subsalt deformation shows a thin-skinned subsalt folded belt detached from the Paleozoic section of the Iberian Massif. The salt canopy shows pervasive basal shearing, internal evaporite flow and folding, and brittle thrusting along possible evaporite stringers and preexisting sutures. The suprasalt series consists of secondary and tertiary minibasins and carapaces or rafts. Secondary minibasins are isolated basins infilled with a deepening Upper Cretaceous–Lower Miocene marine sequence. Rotated carapaces or rafts with a condensed Jurassic–Lower Cretaceous sequence, stacked minibasins and welds are the main features of this part of the Betics. The latest stages of the Alpine contraction are accompanied by syn-tectonic (Tortonian–early Pliocene) sedimentation in slightly deformed gentle, marine–to–continental depocenters (referred to here as tertiary minibasins). This salt canopy is comparable in origin to other allochthonous shale sheets, like in the Gulf of Mexico, although as it was later deformed by Alpine compression, it complements observations in other salt-involved orogens like the western Alps, Sivas Basin or the Salina del Istmo Basin, Mexico.