Fold Belt Research Articles

When did the Dead Sea fault become a transform?

This study re-evaluates the ~20 Myr development of the Dead Sea Fault System (DSFS) and its tectonic definition as a transform plate boundary. The DSFS conveys sinistral displacement between the Arabian-Sinai plates: ~105 km along its ~400 km-long southern segment (Gulf of Aqaba-Eilat to the Hula basin); ~90 km and 4–16 km along the central and northern segments (~190 km long each, across Lebanon, western Syria, and southern Turkey). A review of previous studies, combined with new seismological data analysis, associates the northward displacement decline with obstacles along the DSFS propagation path. During the Miocene, DSFS propagated up to the NW-trending Irbid rift (1st obstacle) and splayed NW towards the Mediterranean and NE along the Late Cretaceous Palmyra fold-thrust belt (2nd obstacle). Its reactivation uplifted the Hermon and the Anti-Lebanon mountain ranges. Northward DSFS propagation into the cold and rigid Aleppo plateau lithosphere (3rd obstacle) was stalled until the early Pliocene (~5 Ma), when volcanism and ongoing regional tectonic forcing enabled the DSFS to shift to the Yammouneh fault and rupture through the Missyaf-Ghab branch farther north (central and northern segments, respectively). During the Pleistocene-recent, connection of the DSFS with the ophiolite belt and East Anatolian Fault System (EAFS) along the Bitlis suture zone (4th obstacle) has not yet been established. Seismological data show a clear separation between the EAFS and the DSFS, while seismicity is scattered across the Aleppo plateau and the central and northern DSFS segments. In contrast, seismicity is localized along the southern DSFS segment. Our findings suggest that, at present, the DSFS has still not made a structural, seismologic, and tectonic connection with the EAFS. Hence, we redefine the DSFS as a pre-transform and suggest its interaction with the EAFS is a world-class example of a fault-fault-fault triple junction in the making.

Detrital zircon provenance record of the northern shelf in the Rakhine Basin, Bay of Bengal

The Cenozoic strata in the Rakhine Basin play a crucial role in hydrocarbon exploration; however, the provenance of these sedimentary rocks remains poorly investigated. In this study, we employed detrital zircon geochronology and geochemistry in the northern Rakhine shelf to investigate the provenance of sedimentary rocks and, combined with the previous studies, to identify their spatial and temporal variations and to elucidate the provenance evolution since the middle Miocene. The geochemical results of the zircons indicate that the primary source rocks of the sedimentary rocks are magmatic and metasedimentary rocks, particularly those of continental arc and post-collision granites. The origin of these rocks can be attributed to the Gangdese arc magmatic belt in the north, as well as the Indo-Burma Ranges in the east. The sedimentary rocks in the northern Rakhine yield zircon U-Pb age peaks primarily at 0-150 Ma, 400-600 Ma, 600-1000 Ma, and 1600-2100 Ma, with minor populations at 150-400 Ma and >2100 Ma. The detrital zircon provenance study shows that the zircons in the Miocene sedimentary rocks were primarily derived from the paleo-Brahmaputra River, with contributions ranging from 68.7% to 77.0%. During the Pliocene, the paleo-Brahmaputra River and the Chittagong-Tripura Fold Belt were the most significant sediment suppliers. Since the early Pleistocene, the northern Rakhine coastal region has played a significant role in their composition. The Brahmaputra River was the predominant contributor to upper Pleistocene rocks, and the Rakhine coastal region’s contribution to the shelf intensified throughout the Pleistocene. In conjunction with regional tectonic evolution, our study underscores the importance of the Indian Plate subduction as a pivotal factor influencing the provenance transitions in the northeastern Bay of Bengal.

Tectonic framework of Iraq. A critical review and discussion

The Iraqi territory forms the northeastern part of the Arabian Plate, which is in collision with the Eurasian Plate. The collision of the plates has formed the Zagros Foreland Basin, which includes the Zagros Fold–Thrust Belt. The belt covers the majority of the northern part of Iraq (Kurdistan Region of Iraq) and parts of the central part of Iraq. South of the belt, the Mesopotamian Foredeep is developed. All these parts of Iraq are considered tectonically unstable. To the west and south of the Mesopotamian Foredeep, the tectonically stable part is developed that has been affected by a lesser amount of deformation as compared to the remaining unstable parts by the exerted forces related to the collision of both plates. All researchers have divided tectonically Iraq into two main tectonic domains; called Stable and Unstable shelves, which are further divided into zones and sub-zones. However, different terms and names were used by different researchers, which has confused readers and workers who have dealt with the tectonics of the Iraqi territory. We have reviewed and discussed all existing divisions by different researchers and have suggested new terminology using the existing maps, reports, scientific published articles, and interpreting satellite images, besides field observations. Moreover, we presented a tectonic map with the suggested new terminology.

Using a 1D Radially Symmetric Coda Envelope Model for Robust Moment Magnitude (Mw) Estimation in Iraq’s Tectonically Diverse Zones

ABSTRACT Robust estimation of moment magnitude (Mw) can be challenging for Iraq due to the strong lateral heterogeneity across diverse tectonic zones. We aim to improve moment magnitude estimation by investigating the reliability of using a 1D coda envelope model in diverse tectonic zones of different lateral effects and offer a way forward for reliable estimates of Mw for small events that are difficult to waveform model. Iraq comprises two main tectonic zones: (1) the Outer platform, consisting of the northwestern Zagros fold-thrust belt and the Mesopotamian foredeep, and (2) the Inner Arabian platform which is overlain by the Iraqi desert. A simple 1D coda envelope model was used because coda waves have a low sensitivity to the source and path heterogeneity. Three separate coda calibrations were conducted to investigate the robustness of a single 1D calibration to fit the country: Whole-region calibration, Zagros calibration, and Mesopotamia calibration. In the whole-region calibration, we used stations from both the Zagros and Mesopotamia zones. In the two other calibration models, we used only stations that were in those particular zones. Ground-truth reference spectra derived from the coda spectral ratio method were used to constrain high-frequency site terms. There was no drastic difference when comparing the moment magnitudes calculated from the waveform modeling and the three calibration models. The results show that the 1D coda envelope model is a reliable method even for a region with diverse tectonic zones. Hence, we recommend using the whole-region calibration model for moment magnitude estimation that provides more complete path coverage and avoids biases introduced by path correction failures. The proposed calibration is a fundamental step in updating the comprehensive earthquake catalog and probabilistic seismic hazard assessments for Iraq.

Structural style & kinematic analysis of deformation in the northern Dezful Embayment, Zagros Fold-Thrust Belt, SW Iran

A comprehensive understanding of structure and kinematic characteristics of fold and thrust belts provides significant information for hydrocarbon exploration and production. The kinematic evolution and structural style of three subsurface oilfields, Zeloi, Lali and Karun, in the northern part of the Dezful Embayment, a significant petroleum province of the Zagros Fold-Thrust Belt in SW Iran, were investigated using 2D seismic data. Interpretation of the 2D seismic profiles with up to 5 km depth consisting of upper Jurassic to Pleistocene sediments and the balanced cross-sections constructed revealed diverse geometries and kinematics along the oilfields. These results demonstrate that the structural style of the oilfields was controlled by the Gachsaran and Dashtak formations as upper and middle detachment levels, respectively. Tear faults affected the along-strike variations in structural style of the oilfields. Based on the analysis of growth strata, folding evolved as limbs rotated and hinges migrated, beginning in the mid-Miocene. During the later stages of deformation, the initial detachment folds transformed into fault-bend folds.

Structural evolution and exhumation events recorded in the Huingancó Granodiorite, Cordillera del Viento, Southern Central Andes, Argentina

This study seeks to unravel the exhumation history of Permian granodiorites corresponding to the Huingancó volcano-plutonic Complex in the southern sector of the Cordillera del Viento (∼37°S), located within the Chos Malal fold-thrust belt. In this context, mineral chemistry analyses were conducted on the granodiorites using electron microprobe data to infer the P-T conditions of emplacement, resulting in 700–900 °C and pressures ranging between 1 and 2.4 kbar. Employing a geostatic gradient of 3.7 km/kbar, these values give an estimate of emplacement depths between 4 and 9 km. In order to understand their exhumation path, five samples from the Huingancó Granodiorite were taken along the Huaraco creek on the western flank of the Cordillera del Viento anticline to perform apatite fission track (AFT) analysis. This analysis yielded new cooling ages for the study area ranging between 50 and 80 Ma. Furthermore, inverse thermal modeling using the fission track data revealed two significant exhumation events during the Andean cycle: one during the Late Cretaceous-Paleocene and the other in Miocene times, separated by a period of gradual cooling or stability during Eocene-Oligocene times. These important cooling events are associated with the main construction phases of the Cordillera del Viento. Finally, to characterize its deformation evolution, a structural kinematic model is proposed based on a balanced structural section and its reconstruction to its non-deformed pre-Cretaceous state. The resulting model allows us to identify the structures and mechanisms of uplift rising the Cordillera del Viento, and their association with the main exhumation events depicted in the inverse thermal modeling. The main structure of the Cordillera del Viento corresponds to a fault bending fold that involves the basement in the deformation. Subsequently, its insertion as an intracutaneous wedge is related with the development of the thin-skinned structures at the internal sector of the Chos Malal fold and thrust belt.

Neoproterozoic High-K calc-alkaline granites forming the large Agudos Grandes and Socorro batholiths, SE Brazil: Crystallization conditions and tectonic implications

I-type, high-K calc-alkaline (HKCA) granites are the main components of two large Neoproterozoic batholiths that occur in different tectonic domains in SE Brazil (Agudos Grandes (emplaced in the central Ribeira Fold Belt) and Socorro (emplaced in the Socorro-Guaxupé Nappe). We investigated representative samples from both batholiths using detailed petrography by optical and electronic microscopy and chemical analysis of main minerals (amphibole, biotite and plagioclase) by EPMA aiming to obtain reliable estimates of magmatic temperatures and pressures. Granites from both batholiths show broadly similar whole-rock compositions and crystallized from oxidized magmas at ∼ NNO+1 to +2. However, they were emplaced at different depths (Agudos Grandes: 3–5 kbar; Socorro: 5–6 kbar; Al-in-hornblende geobarometry) and crystallized at slightly, but consistently different temperatures (respectively, lower and greater than 800 °C). The lower temperatures of the Agudos Grandes granites may account for the presence of titanite as a main accessory mineral, in contrast with its absence, or occurrence as thin rims in ilmenite in the Socorro granites. The pressure estimates are consistent with the metamorphic conditions of the country rocks and suggest that magma emplacement was influenced by a combination of density control and evolving tectonic stress regimes, with the dominantly more mafic rocks of Socorro emplaced at greater depths. On the other hand, higher Sr/Y ratios and REE fractionation shown by the Agudos Grandes whole-rocks may result from magma equilibration in a thicker crust (>60 km, as contrasted with ∼50 km for Socorro) at the time of magma generation. However, the possible presence of cumulate components (as suggested, for instance, by high apatite and hornblende saturation temperatures) requires that these contrasts are tested in the future by proxies that are independent of whole-rock composition (e.g., trace-element chemistry of minerals).

The Cenozoic Abanico rift system: Implications of increased southward extension in the southern central Andes, in Chile

The late Eocene-Early Miocene intra-arc Abanico extensional basin represents a major feature in central Chile (∼31°-42°S). Such basin system concentrated the magmatic activity along this Andean region and hosted locally more than 3.000 m of volcanic and volcaniclastic deposits (Abanico Formation) over a southward thinning crust (<35 km thick). South of 34°30′S, major changes occur in and out of the basin realm that modify the rather regular distribution of the geological features observed northwards, namely: 1. Southward termination of the exposures of the Farellones Formation, 2. Increased presence of pre-Abanico volcanic and plutonic exposures in the basin realm, 3. Southward width increase of the basin, 4. Abrupt end in the Maule region of the Cretaceous plutonic swaths exposed in the eastern Coastal Cordillera and westward bend of the swaths of Mesozoic units, 5. Increased presence of primitive volcanic rocks in the west-side of the basin, and 6. Presence, south of 36°S, of the Cura-Mallín Formation on the east-side of the basin. These changes are caused by the oblique orientation of the Abanico basin relative to the Mesozoic structural and paleogeographic trends and are enhanced by the increased southward opening of the basin. This opening would have occurred through a westward scissors-like rotation of the block of continental crust located west of the basin, which corresponds to the present-day Coastal Cordillera south of 34°30′S. The eastern border, which is represented by the El Diablo fault, remained essentially fixed. The westward rotation is supported by the north-northeast orientation of the Mesozoic plutonic and stratified swaths south of 34°30′S. Additionally, the swaths of Mesozoic rocks are obliquely interrupted by the similarly oriented western border of the basin. Previous analogue models designed to understand the opening and closure mechanisms of an extensional basin show that greater extension and subsidence in the basin occur next to the mobile border, which in the Abanico basin was located on its west side. This observation aligns with the increased southward presence of primitive volcanic rocks, like the Colbún Formation, in the region where crustal thinning would have been greater. Analogue models show that the increased southward extension allowed the development of wider depocenters. In the Maule region, an eastern depocenter near the El Diablo fault, hosted the Early to Middle Miocene deposits of the Cura-Mallín Formation. During contraction, deeply rooted reverse faults can involve basement rocks of the basin and bring them up to the surface as observed in the Abanico basin realm in the Tinguiririca and Maule regions. This study also highlights the continuity and importance of the El Diablo fault in the configuration of the basin. It is shown that, notwithstanding the existence of major changes south of 34°30′S, this fault represents a major structural element that remained unchanged along the Andean segment comprised between ∼32° and 36°30′S separating the Cenozoic deposits to the west from Mesozoic deposits to the east. This fault can be traced continuously from, at least, the Aconcagua valley (33°S) to the Maule region (36°30′S), and most probably extends further south. Apart from separating the Cenozoic Abanico basin deposits from the Mesozoic units involved in the east-vergent Andean fold-thrust belt, its trace forms an almost straight line that connects the Palomo, Tinguiririca, Planchón-Peteroa, Descabezados, San Pedro and Rezago volcanic centers and complexes, hot-springs, and hydrothermal alterations.

Sedimentary provenance and U-PB detrital zircon in the mesozoic record of the Parecis Basin, Rôndonia and Juruena sub-basin

Sediment provenance analysis is a tool increasingly used in the study of basins. This technique allows identifying the mineralogical and lithological composition of source areas, inferring paleogeography, climate and relief, determining the main sand distribution routes, and estimating the distance and transport time. The Mesozoic volcanic-sedimentary packages of the Parecis Basin mark a significant part of the South American Platform evolution, regarding tectonism, subsidence, sedimentation, basic and alkaline magmatism, uplift and erosion. Also, these packages registers the initial stages of Andean Orogeny subduction. Different authors have established opposite stratigraphic proposals for Parecis Basin regional correlations, and also for its tectonics evolution. Given this context, there are controversies regarding the chronostratigraphic positioning and relationships between the intervals, especially the units called Salto das Nuvens and Utiariti formations. This article presents the faciological framework and facies association, heavy mineral assemblage, ZTR index and sediment sources, and U-Pb detrital zircon ages to both sub-basins. Detrital Zircon data reveal minimum ages of 124 Ma for the Rondônia sub-basin and 245 Ma for the Juruena sub-basin for sedimentary deposition attributed to the base of the Cretaceous units. The detrital age of zircons points to a varied contribution, between elements from different provinces and ages of the Amazon Craton, the Paraguay Fold Belt and records of alkaline magmatism of ages Permo-Triassic and Cretaceous in the different kimberlithic fields of Rondônia and Mato Grosso.

Paleogene stratigraphy in the central area of the Fuegian fold and thrust belt, Austral Basin, Argentina: Implications for the chronology of thrust-belt deformation

We combine extensive field data with calcareous nannofossils and dinocysts analysis and detrital zircon U-Pb ages to identify six Paleocene-Oligocene stratigraphic units in a previously poorly studied area in the external fold and thrust belt of the Fuegian Andes. Detailed petrographic analysis coupled with detrital zircon ages indicate three main provenance peaks, which reflect that 1) the lowermost upper Cretaceous was already exhumed during the Paleocene-early Eocene, 2) the upper Cretaceous rocks were a continuous source at least until the late Eocene, 3) volcanism was coetaneous with the deposition of middle Eocene successions. Three contractional stages known elsewhere in the thrust-belt are identified in the study area in the Danian, the early Eocene-early middle Eocene, and the latest Eocene-early Oligocene. This suggests synchronicity along strike during the evolution of the Fuegian fold and thrust belt.

A ~957 Ma Metamorphism in the Mesoarchaean Hindoli Group Supracrustal Rocks from the Jahazpur Shear Zone, East Rajasthan (India): Constraints from Sm-Nd Dating and Phase Equilibria Modeling

ABSTRACT A petrological-chronological investigation of the Hindoli Group of rocks within the Jahazpur Shear Zone in the eastern segment of the Aravalli Delhi Fold Belt (ADFB), NW India, has been conducted. We infer two stages of deformation (D1 and D2) and metamorphism (M1 and M2) for the garnet - muscovite - biotiteschists interleaved with meta dolomite, Banded Iron Formation (BIF) amphibolite, and foliated granite. The D2 deformation corresponds to the northeast-trending Jahazpur shear zone on a regional scale. Garnet porphyroblasts, syntectonic with the D2 deformation, are chemically zoned with spessartine-rich cores. Geothermobarometry and pseudosection analyses yield peak P-T conditions of ~7.5 kbar, 580°C, followed by decompression and cooling along a clockwise P-T path. The Sm-Nd isotope analysis of the whole rock yields a date of ~3.0 Ga from an amphibolite. This data is interpreted as the age of formation of the litho-units of the Hindoli Group. Sm-Nd analyses of garnet grains yield an age of ~957 Ma. This date corresponds with the age of nucleation of the Jahazpur shear zone. A good correlation is established between the Neoproterozoic crustal segments of the Jiangnan Fold Belt of the South China Craton and that of the ADFB during the formation of the Rodinia Supercontinent.

Geochemical Characterization and Constraints on Provenance, Tectonic setting and Paleoweathering of the Miocene Bhuban Sandstone Exposed in Sakhan Anticline, Tripura Fold Belt, Surma Basin, India

ABSTRACT The petrography of sandstone, major oxides, trace and REE compositions of the Bhuban formation, exposed in the Sakhan Anticline of Tripura Frontal Fold Belt have been studied to determine the source rock, depositional tectonic setup and paleoweathering conditions. The average modal composition of the Bhuban Sandstone (Q89.27F4.40L6.33) classified them as quartz arenite and sub litharenite types. The modal composition data (Q-F-L) indicates a craton interior and recycled source for these sediments and deposited in an active continental basin margin as suggested by the bivariate plot of SiO2 vs. K2O/Na2O. The binary discrimination plot of Hf vs. La/Th suggests acidic and older sedimentary component as source for the studied sandstone. The ternary plot of V-Ni-Th×10 pointed towards felsic igneous provenance. Trace and rare earth elemental ratios, chondrite-normalize REE plot suggests the source of the Bhuban sediments are derived from felsic terrain. The CIA values (66.48-75.41), A-CN-K plot (A=Al2O3, CN=CaO+ Na2O, K=K2O) and distinct depletion of Na2O, CaO, U, Sr and Ba suggests moderate degree of chemical weathering of the source rocks which may indicate humid climatic conditions in the source area.

The Sierra Madre Oriental Orocline: Paleomagnetism of the Nazas Province in NE Mexico

AbstractCurved mountain belts are spectacular natural features that contain crucial 3D information about the tectonic evolution of orogenic systems in the absence of other kinematic markers. The Mesozoic units exposed in the Mexican Fold and Thrust Belt in northeastern Mexico show a striking curvature, whose kinematic history has not been studied. The existing tectonic models of the region simply assumed the shape of the tectonic units as an inherent feature to the orogen. We investigated the kinematic history of this curvature through paleomagnetism and rock magnetism analyses, coupled with an exhaustive review of available published literature. The studied data sets indicate a protracted history of (re)magnetizations that occurred during the Late Jurassic‐Paleocene times at least during the Late Jurassic, Cretaceous and early Eocene. More significantly, they show significant counterclockwise rotations in the northern flank of the curvature and moderate clockwise vertical axis rotations along its southern flank. This data set suggests that the Sierra Madre Oriental was a linear belt that experienced oroclinal bending or buckling during the Cretaceous to early Eocene period (120–50 Ma).

Spatial and temporal variation of Syrian Arc structures in the onshore and offshore Eastern Mediterranean region

Syrian Arc structures form a belt of folds and faults oriented northeast to southwest and north-northeast to south-southwest extending from the Western Desert of Egypt (and farther westward to Tunisia) via northern Sinai to Levant eastward. Detailed studies of surface and subsurface areas in onshore Egypt as well as the offshore Eastern Mediterranean show evidence for continued deformation since the Santonian with local mild start during the Turonian. Santonian deformation was the strongest, whereas the later continued deformation was less. Previous studies of Syrian Arc structures proposed discrete phases of deformation, but the present study shows evidence that deformation was continuous since the Santonian. The lack of a continuous rock record, erosion of the crestal areas of some folds, nondeposition of younger sediments, and the scattered nature of younger rocks at the exposed Syrian Arc folds led some investigators to propose a short period(s) of Syrian Arc deformation. The relatively well-preserved subsurface stratigraphic record of Syrian Arc structures in some onshore and offshore areas led to the conclusion that the Syrian Arc folding continued to present time. However, the intensity of deformation and the associated structural relief have varied through time and space with its climax during Santonian time. We consider the Late Cretaceous–Cenozoic Syrian Arc structures to be the manifestation of the closure history of the Neo-Tethys Ocean and its successor, the Mediterranean Sea.

The September 6, 2021 MW 5.4 Tofalaria earthquake at a weakly active segment of the Main Sayan fault (Eastern Siberia)

We study in detail the Mw 5.4 September 6, 2021 Tofalaria earthquake occurred in a mountain area of the Eastern Sayan which is characterized by a low level of seismic activity. An interest in the seismic event is caused, on the one hand, by poor knowledge about stress-strain field of the crust in the considered region, and, on the other hand, by its relation to the NW segment of the ancient Main Sayan fault – a structural boundary between the Sayan-Baikal fold belt and the tectonically stable Siberian platform. Seismic moment tensors and hypocentral depths of the mainshock and its largest aftershock (Mw 4.6) are inverted from intermediate-period surface wave amplitude spectra calculated at the stations located at teleseismic distances. Integral source parameters of the mainshock, characterizing its spatio-temporal development, are also estimated and the fault plane is determined. Epicenters of 31 aftershocks with M ≥ 1.8, occurred up to the end of 2021, are constrained from body waves recorded at regional seismic stations. The obtained results show that the Tofalaria earthquake occurred under the influence of the SW-NE compression, which is observed in Western Mongolia. Focal mechanism of the largest aftershock and the NE elongation of the aftershock epicentral field (22 km) indicate stress redistribution after the mainshock in a local crustal volume, bordered by small-scale faults.

Base-metal exploration by using remote sensing, geological, geophysical, and geochemical datasets with clues from ancient mining: A comprehensive review on Aravalli-Delhi Fold Belt, Rajasthan, India

Base metal deposits are present in different continents with evidences of their mining activities during ancient times as mentioned in the historical literature. Aravalli – Delhi Fold Belt (ADFB) in Rajasthan, India is having numerous base metal prospects where ancient mining signages are recorded. Modern-day mining has commenced taking clues from these evidences. Present-day techniques such as remote sensing, geological mapping, geophysical survey, geochemical survey, and exploration/drilling are utilized for the identification of surficial ancient mining features and identification of the mineralized zones. These techniques utilize their unique criteria to get an idea of the mineral association. The integration of all the unique characteristics of modern techniques with the help of weighted overlay analysis, fuzzy logic, multi-criteria overlay analysis, etc. helps to identify the mineral potential zones from the ancient working sites. Their integrated results provide the surficial as well as sub-surficial information of the region that gives a better revelation about the region and helps in decision-making towards the mineralization status of the region. World-over surficial ancient features have been recorded in exploratory sites for base metals, and the case histories where integrated techniques were used for mineral exploration are discussed. Zawar – Dungarpur belt also has the potential for base metals therefore, the boolean approach, weighted overlay, and multi-criteria overlay analysis were performed using remote sensing, structural, and geochemical datasets. The integrated results showed that the head zone and southern broader part near Keekawat have the potential for base metals.

Heterolytic tide-dominated sedimentary facies and depositional environment: An Example from the Boka Bil formation, Sitapahar anticline, Bangladesh

The Baraichari Shale Formation, which is equivalent to the Boka Bil Formation, is well exposed within the Neogene sequence of the Sitapahar Anticline in the Chittagong-Tripura Fold Belt, Bengal Basin, Bangladesh. Regardless of its importance in hydrocarbon accumulation, a comprehensive facies analysis is essential to understand and explain the heterogeneity within different depositional architectural elements. The purpose of this work is to delineate the lithofacies characteristics, depositional environment heterogeneities and propose a generic depositional model for the Middle to Late Miocene shallow marine sediments of the formation. The sedimentary facies were investigated at three outcrops along the Kaptai–Chandraghona road cut sections of the Sitapahar anticline. The formation is composed of dark to bluish-gray shale, silty shale, yellowish brown siltstone, and gray to yellowish brown fine-to medium-grained sandstone. Eight distinct sedimentary facies have been identified and were categorized into three facies associations: subtidal or estuarine, mixed flats with tidal creeks, and tidal mud flats. The subtidal facies, predominant in the middle member, consists of fine to medium-grained ripple cross-stratified sandstone-siltstone, herringbone cross-stratified sandstone, and trough cross-stratified sandstone, indicating sub-tidal channel deposition. Mixed flats with tidal creeks exhibit heterolithic facies, suggesting energy level changes in intertidal to sub-tidal zones influenced by tidal currents. Tidal mud flats are predominantly laminated shale/mudstone and lenticular laminated sandstone-siltstone, reflecting deposition during tide transitions in the intertidal zone. Fining upward cycles within the formation indicate progressive progradation or changes in inner tidal flats conditions during regressive periods. These depositional settings serve as analogs for equivalent subsurface reservoirs and contribute to the construction of reservoir models with greater accuracy.

Mineralisation controls for the diverse Cape manganese occurrences, South Africa

Abstract The Cape Fold Belt, comprising folded sedimentary sequences from predominantly the Palaeozoic Cape Supergroup, hosts a multitude of manganese occurrences and mineral deposits, many of which were subject to historical mining activity. Although size, grade and quality issues negate their modern-day exploitation for the steel-making process, the mechanisms by which Mn has enriched at these sites holds scientific value for our understanding of low-temperature Mn (bio-)geochemical cycling. Deposits located within the Cape Fold Belt comprise structure-hosted Mn deposits and a little described class of Mn mound deposits associated with chalybeate thermal springs (temperature = 41 to 48°C). Although the relationships between the two remain tenuous, detailed study of both classes provides insight into the conditions that favour Mn accumulation in the near-surface and sub-aerial environments. Comparisons between the physicochemistry of manganiferous- and non-manganiferous thermal springs suggest that manganese solubility is favoured by warm, acidic and slightly reducing fluids with elevated salinity. Transport, and associated fluid focusing typically within highly permeable sandstone units, serves to locate Mn mineralisation in near-surface structurally-complex trap sites that provide both accommodation space and conditions that are sufficiently oxidising. Where manganiferous spring waters spill out at surface, oxidation is caused by contact with atmospheric O2 to form Mn mound deposits, and ambient Mn-oxidising microbiota (e.g., genus Ramlibacter, and members of Burkholderiales, Rhodocyclaceae, and Oxalobacteraceae) are likely to play a role in enhancing the kinetics of this process. Relative to the structure-hosted deposits, these Mn mound deposits are typically lower grade (higher iron content) and relatively friable (high porosity and fine grain sizes). Supergene and diagenetic processes can lead to localised upgrade of the Mn mound material, although typically not to ore grade.

Biostratigraphy of the Late Oligocene-Early Miocene Anah and Bajwan Formations at Selected Sections of Northern Iraq

The Late Oligocene-Early Miocene including Anah and Bajwan formations have been studied in selected areas of Sulamaniyah (Aj-Dagh and Basara sections) and Kirkuk governorate within Bai Hassan Oilfield (BH-3 and BH-4), which is located within the Western Zagros Fold Thrust Belt, Northern, and Northeastern Iraq. The palaeontological investigations mainly depended on benthonic foraminifera of the studied sections of Aj-Dagh and Basara, as well as the studied wells of Bai Hassan OilField (BH-3, and BH-4) of Anah and Bajwan formations, twenty-four species belonging to fourteen genera recognized of benthonic foraminifera, with five index fossils determining the age of the formations as Late Oligocene-Early Miocene, which have been recognized through this study, especially benthonic foraminiferal, indicating four zones as Praerhapydionina delicata range zone, Austrotrillina howchini-Peneroplis evolutus zone, Concurrent range, and Miogypsinoides complanate-Lepidocyclina (Nephrolepidina) sp. Concurrent zone.

Mountain building process of the Taiwan orogeny.

The Taiwan orogeny, an example of arc-continental collision, exhibits complex geological structures and rapid exhumation. Many models have tried and failed to fully capture the dynamics of these processes. We developed a comprehensive thermomechanical model that considers the transition from brittle to ductile behavior with depth, lithology-dependent erosion and observed decollement and backstop geometries. This model successfully reproduces the intricate structures observed within the Taiwan orogeny, aligns with structural complexities, metamorphic temperature profiles, thermochronological records, strain distributions, and the rates of exhumation and cooling and elucidates the roles of ductile deformation and ramp structures in forming the Hsuehshan Range and the Western fold and thrust belt. The insights from this model offer potential applicability to other orogenic wedges worldwide.