Foredeep Depozone Research Articles

The Paleogene Carbonate Banks of the Zagros Foreland Basin’s Forebulge, Northern Iraq: Stratigraphic Architectures and Facies Associations

The Paleogene sequence of the Zagros foreland basin of NE Arabiais punctuated by a linear chain of carbonate bank-ramp associations. These carbonate banks had developed over the NW-SE trending basin forebulge. Continued convergence and compressional tectonics of the basin made the forebulge become incipient and shallow enough to commence carbonate sedimentation. The porpose of this work is to investigate the origin, facies and regional stratigraphic relations of these carbonates to the forebulge and other basin depozones. Stratigraphic data of this research are collected from (15), measured outcrop sections distributed over the basin forebulge zone and surroundings. In addition, re-examination and reinterpretation of (30) previously studied surface and subsurface sections are compiled into the study. This done to integrate the regional facies distribution and basin-wide sequence stratigraphic architecture. Stratigraphic investigations include lithostratigraphic logging and correlation, microfacies analysis, and facies modeling. Four major banks were recognized, three of these banks (informally named: Dohuk, Kirkuk, and Sulaimaniyah) were developed over the forebulge zone. The other one (Sinjar bank) of the Sinjar area, is related to basininversion mechanism. The forebulge carbonate banks were developed as the reefal limestone of the Sinjar Formation, and the lagoonal carbonate and shale of the Khurmala Formation. The Sinjar Formation is dominated by coralgal reef and foraminiferal-shoals with facies spectrum forming the basic body of the bank. The ramp setting was developed on both sides of the bank. The bank limestone represents the inner ramp facies, whilea windward ramp is developed as foraminiferal bioclastic limestone fingers into the back-bulge basinal marlstone of the Aaliji Formation. A leeward ramp facies was developed into the foredeep depozone, with bioclastic carbonate intercalations that characterize the upper part of the Kolosh Formation. At a later stage of basin shoaling (Early Eocene), a carbonate back-bank lagoon was developed over the foredeep area. It became gradually, isolated at certain parts of the basin, and finally replaced by the dolostone of the Khurmala Formation.

Neogene to modern foreland basin development in the Sub-Andean zone of southern Bolivia and northern Argentina, 21−23°S

The Sub-Andean retroarc region is a unique example of an active continental-scale retroarc foreland basin system. Heavily targeted for hydrocarbon exploration, the region hosts a large volume of subsurface data coupled to surface studies dedicated to refining its evolution in time and space. This paper presents a regional correlation of stratigraphic markers from seismic reflection and well logs across the Sub-Andean foothills at 23−21°S in southern Bolivia and northern Argentina, which reveals the contrasting along-strike history of Mesozoic to Cenozoic tectonics that preceded the foreland basin setting. Supported by published geochronological data and new zircon U-Pb maximum depositional ages, we describe the depositional transition from pre-Andean to Andean stratigraphy and discrete episodes of foreland basin subsidence and shortening. Based on interpreted stratigraphic breaks, we define the extent and stepwise evolution of this foreland basin, which was characterized by the progressive eastward migration of foreland basin depozones. Based on restored thickness profiles, we present flexural models of basin subsidence for the Sub-Andean foothills region. The modeling of discrete episodes of foreland basin subsidence refines the widely accepted bimodal elastic strength in the foreland basin at 21−23°S, which is weaker in the western ranges (∼20 km effective elastic thickness) and stronger eastward (>40 km). Modeling results also reveal minimum values of subsidence rates (up to 1.2 mm/yr) in the sequential foredeep depozones and suggest that the modeled tectonic load migration—as constrained by the record of syntectonic strata—probably increased over time through the incorporation of Sub-Andean rocks into the orogenic wedge.

Article Review/ The Tectonic Evolution of Erbil Area (Ne Iraq) as a Part of the Northeastern Margin of the Arabian-Nubian Plate Throughout Albian-Early Eocene

The Albian-Early Eocene tectonic evolution of the Zagros Foreland Basin of the High Folded Zone in the Iraqi Kurdistan region has been studied based on the recent foreland basin system concept. This study showed that during the cretaceous (Albian – Cenomanian) there was a geodynamic shift from a passive margin to a foreland basin system phase, not to an active margin phase as mentioned in the previous studies. The advance of the continental margin of the Arabian-Nubian Plate (ANP) toward the subduction zone imposed a tectonic load leading to the form of a flexural wave. The consequences of the last tectonic event were reflected by the continuous deposition of the Balambo Formation. in a foredeep depozone. This happened concomitantly with a flexural emergence of the continental shelf further to the west forming a forebulge depozone represented by the deposition of reefal facies of the Qamchuqa Formation. These geodynamic changes are considered here to represent the Megasequence boundary between the Tectonic Megasequence (TMS) of AP8 and AP9. The last sequence of the passive margin was the Qamchuqa Formation Which is called the Pre-Orogenic Carbonate Platform and was separated from the Bekhme Formation by regional unconformity (Megasequence boundary). The latter is represented by the Lower Sequence of the foreland basin system, which is called the Syn-Orogenic Carbonate Platform (SCP). During the Middle Campanian, the Zagros foreland basin started with the underfilled stage, and it was entirely clear by the end of the Cretaceous comprising a broad threefold subdivision of depositional realms that translated into three stratigraphic units known as trinity underfilled units of foreland basin system. The lower carbonate unit, the pelagic and hemipelagic unit, and the upper flysch clastic unit are represented by Bekhme, Shiranish, and Tanjero Formations respectively. All of these units were superimposed during basin depocenter migration and became younger toward the southwest in front of progressing the orogenic wedge toward the Arabian Craton. During the late Maastrichtian to Paleocene – Early Eocene, the Zagros foreland basin underwent a transition from underfill to fill the stage. Deep exhumation of the orogenic wedge and ophiolite assemblage had supplied the clastic sediment of the Kolosh Formation into the basin covering the foredeep and most of the forebulge and backbulge depozones.

Ordovician chitinozoans and review on basin stratigraphy, biostratigraphy and paleobiogeography of northern Argentina along the Proto-Andean margin

Ordovician strata exposed across the Cordillera Oriental and the Sierras Subandinas in northwestern Argentina were part of a large retroarc foreland basin developed along the Proto-Andean margin within the Central Andes in South America. A revised chitinozoan biostratigraphy along and across-strike for the Tremadocian, Floian, Dapingian, Katian and Hirnantian stages, calibrated with other fossil groups in the basin, allow pinpointing the most characteristic events that affected the basin fill testing global versus local controls in accommodation, and suggesting comparisons with other peri-Gondwanan records. According to the chitinozoan data, the glacially-related Ordovician deposits in northwestern Argentina are restricted to the Hirnantian, and unconformably overlie late Katian deposits. In the Caspalá area (Cordillera Oriental), an interval with synsedimentary deformation and reworked chitinozoans correlate with glacially-related deposits in other sites of the eastern part of the basin (Río Capillas and Mecoyita areas). A glacial waning stage is determined by a thin interval of organic‐rich black shales with sparse dropstones at the top of the Zapla Formation, containing Spinachitina oulebsiri associated with Desmochitina gr. minor, which together are typical latest Hirnantian components in other regions of Gondwana. Our study strengthens the foreland systems tract for the Ordovician Central Andean Basin with a volcanically fed interarc and foredeep depozone to the west (Puna region); a lower-accommodation forebulge depozone in the central area (mostly the Cordillera Oriental region); and a backbulge depozone (Sierras Subandinas and Sierras de Santa Bárbara) extending as far as the eastern Paraná Basin (reaching Paraguay and Brazil). Contemporaneous unconformities driven by global sea-level fluctuations were amplified or reduced due to deepening-narrowing or widening-shallowing, allowing contrasted accommodation, respectively associated to loading and relaxation. Ordovician chitinozoans from the Central Andean Basin indicate Northern, Western and peri-Gondwanan affinities, although locally some more cosmopolitan species described in Baltica, Avalonia and South China, are also recorded.

Modern Southern Junggar Foreland Basin System Adjacent to the Northern Tian Shan, Northwestern China

AbstractBuilding-up of the modern Tian Shan range due to the India-Eurasia collision induces the flexural subsidence of the southern Junggar block. The sedimentary infill and subsidence in the southern Junggar foreland basin recorded the growth of the northern Tian Shan. We analyze four seismic profiles, well logging data, and trends in stream morphology in the foreland basin to decipher its architecture, and stratigraphic and subsidence history. The southern Junggar foreland basin system can be divided into the northern Tian Shan wedge-top, Lakes Aiby-Fangcao-Baijiahai foredeep and Luliang forebulge and backbulge depozones. The seismic profiles present the active shortening structures in the wedge top and the northward thinning and onlapping Neogene-Quaternary foreland sequence in the foredeep. The growth strata and unconformities separating the growth and pregrowth strata in the upper part of the foreland sequence are identified in the wedge top depozone. This indicates that the competition between active local folding relief and regional bedrock subsidence determines erosion versus deposition in the wedge top. The logging data of well GQ2 reveal that the present wedge-top depozone evolved from distal lake sedimentation, probably in a foredeep setting, to a braided river in a modern piedmont setting. These lines of sedimentary evidence and the active shortening structures reveal the northward migration process of the southern Junggar foreland basin driven by the northward propagation of the Tian Shan since the Neogene. The north-northeast dipping topography of the northern Tian Shan thrust wedge controls the north-northeastward flowing of all the rivers in the wedge top, and these rivers’ flowing direction changes in the foredeep depozone where the tectonic landform flatten out. Growth of anticlines in the front of the wedge-top depozone may have triggered a northward migration of the meandering channel of the Manas river in its lower reach. The transition between the trends of the stream morphology in the wedge top and foredeep depozones suggests the control of the structures of the foreland basin system on trends in stream morphology.

Coarse-grained meandering distributive fluvial system of the basal Cedar Mountain Formation, U.S.A.

ABSTRACT The analysis of downstream changes in ancient fluvial systems can better inform depositional models for foreland-basin systems. Herein we analyze the basal deposits of the Early Cretaceous Cedar Mountain Formation of Utah to better understand the variety of fluvial deposits present and to develop a depositional model for the Sevier foreland basin. We also evaluate the long-held interpretation of a braided origin for these deposits and document numerous examples of point-bar deposition in highly sinuous meandering rivers by analysis of large (20 to 60 km2) plan-view exposures. These plan-view exposures allow comparisons between planform and cross-sectional geometries. The study utilizes outcrop data, virtual outcrop models, and satellite imagery to develop a facies model and analyze the architecture of channel bodies in the Buckhorn Conglomerate and Poison Strip Sandstone of the Cedar Mountain Formation. We document downstream (west to east) decreases in lateral channel migration, sinuosity, channel amalgamation, grain size, and percent of fluvial channel facies (conglomerate and sandstone). Fluvial channel deposits occur arranged into larger stratal bodies: multistory–multilateral channel bodies that are dominantly composed of clast-supported conglomerate in the west to a mix of multistory, multilateral, and isolated channel bodies composed of matrix-supported conglomerate in the east. The median width of highly sinuous point bars is similar across the field area (344 m to 477 m), but the inclusion of narrower (median = 174 m), low-sinuosity bar elements in the east indicates an overall reduction in lateral channel migration and sinuosity downstream. Net-to-gross values range from 100% in much of the western outcrops to as low as 38% in the east. Paleocurrent analysis reveals a transverse (west to east) paleoflow for the study interval that merges with axial (south–north) paleoflow near the Utah–Colorado state line. We estimate 104 m3/s-scale discharge and 106 kilometer-scale drainage area for axial rivers based on paleohydraulic analysis which represents a significant part of the Early Cretaceous continental-scale drainage. The observed downstream trends in lateral channel migration, sinuosity, channel amalgamation, grain size, and net-to-gross for the basal Cedar Mountain Formation are consistent with expected trends for sinuous single-thread distributive fluvial systems and are similar to observed trends in the Jurassic Morrison Formation. Medial (Buckhorn Conglomerate) to distal (Poison Strip Sandstone) zones are preserved and span the forebulge to backbulge depozones of a foreland-basin system. Postulated deposits of the proximal distributive fluvial system have been removed during erosion of the foredeep depozone. The easternmost Poison Strip Sandstone and coeval Burro Canyon Formation represent deposits of an axial system at which western-sourced distributive fluvial systems end. Distributive fluvial systems dominate modern foreland basins, and this study suggests that they may constitute a significant proportion of ancient successions.

Effects of contemporaneous orogenesis on sedimentation in the Late Cretaceous Western Interior Basin, northern Utah and southwestern Wyoming

AbstractThree drivers of subsidence are recognized in the Western Interior Basin: Mesozoic–early Cenozoic flexure adjacent to the thin‐skinned, eastward propagating Sevier Orogeny, Late Cretaceous–Eocene flexure associated with thick‐skinned Laramide Uplifts and Late Cretaceous dynamic subsidence. This study combines outcrop lithofacies, palaeocurrent measurements, detrital zircon geochronology, biostratigraphy, stratigraphic correlations and isopach maps of Coniacian–Maastrichtian (89–66 Ma) units to identify these subsidence mechanisms impact on basin geometry and stratigraphic architecture in the northern Utah to southwestern Wyoming segment of the North American Cordillera. Detrital zircon maximum depositional ages and biostratigraphy support that the Maastrichtian Hams Fork Conglomerate was deposited above the Moxa unconformity in the wedgetop and foredeep depozones. The Moxa unconformity underlies the progradational Ericson Formation in the distal foredeep. The Hams Fork, however, is younger than the Ericson Formation, and instead equivalent to upper Almond Formation. Therefore, the hiatus associated with the Moxa unconformity continued for several million years longer in the fold belt and proximal basin than in the distal foredeep, with Ericson Formation‐equivalent strata onlapping the Moxa unconformity towards the west. Regional thickness patterns record and constrain the timing of the transition from Sevier to Laramide‐style tectonic regimes. From 88 to 83 Ma (upper Baxter Formation) a westward‐thickening stratigraphic wedge characterized the foredeep developed by lithospheric flexure by thrust‐belt loading. Nevertheless, the presence of >500 m of subsidence >200 km from the thrust front suggests a long‐wavelength subsidence mechanism consistent with dynamic subsidence. By 83 Ma (Blair Formation) the long‐wavelength depocentre shifted away from the thrust belt, with no evidence of a Sevier foredeep. This depocentre continued migrating eastward during the early‐mid Campanian (ca. 81–77 Ma). The late Campanian–Maastrichtian (ca. 74–66 Ma) is marked by narrow sedimentary wedges adjacent to the Wind River, Granite and Uinta Mountain uplifts and attributed to flexural loading by Laramide deformation.

Forebulge migration in the foreland basin system of the central‐southern Apennine fold‐thrust belt (Italy): New high‐resolution Sr‐isotope dating constraints

AbstractThe Apennines are a retreating collisional belt where the foreland basin system, across large domains, is floored by a subaerial forebulge unconformity developed due to forebulge uplift and erosion. This unconformity is overlain by a diachronous sequence of three lithostratigraphic units made of (a) shallow‐water carbonates, (b) hemipelagic marls and shales and (c) siliciclastic turbidites. Typically, the latter two have been interpreted regionally as the onset of syn‐orogenic deposition in the foredeep depozone, whereas little attention has been given to the underlying unit. Accordingly, the rate of migration of the central‐southern Apennine fold‐thrust belt‐foreland basin system has been constrained, so far, exclusively considering the age of the hemipelagites and turbidites, which largely post‐date the onset of foredeep depozone. In this work, we provide new high‐resolution ages obtained by strontium isotope stratigraphy applied to calcitic bivalve shells sampled at the base of the first syn‐orogenic deposits overlying the Eocene‐Cretaceous pre‐orogenic substratum. Integration of our results with published data indicates progressive rejuvenation of the strata sealing the forebulge unconformity towards the outer portions of the fold‐thrust belt. In particular, the age of the forebulge unconformity linearly scales with the pre‐orogenic position of the analysed sites, pointing to an overall constant migration velocity of the forebulge wave in the last 25 Myr.

Tidal estuarine deposits of the transgressive Naturita Formation (Dakota Sandstone): San Rafael Swell, Utah, U.S.A.

ABSTRACTThin tidal estuarine deposits of the Naturita Formation (0–23 m) of the San Rafael Swell record the initial flooding of the Cretaceous Western Interior Seaway, Utah, and capture the transition from inland fluvial systems to fully marine conditions over a time period of 5 My or less. A tide-dominated estuarine environment is favored due to the combined presence of mud and/or carbonaceous drapes on ripples and dunes, bidirectional flow indicators, sigmoidal cross-stratification, herring-bone cross-stratification, and bimodal paleocurrent measurements. Facies associations are arranged in a predictable manner. Locally at the base of the Naturita Formation, tidally influenced fluvial channel deposits are present. These are overlain by tidal bars, including subtidal bars and intertidal point bars. Overlying the tidal bars are sand-flat and mud-flat deposits as well as bedded coal and carbonaceous mudstone that represents a supratidal setting in the estuary. The Formation can be capped by a thin transgressive lag composed of shell debris, and/or pebbles, that marks the final transition into the fully marine Tununk Shale Member of the overlying Mancos Shale.Lateral relationships between estuaries and adjacent paleohighs shed light on the influence of foreland-basin tectonics on the location and preservation of tide-dominated estuaries. Estuarine and shoreface deposits are absent along the eastern flank of the San Rafael Swell and eastward for more than 80 km. This zone of nondeposition or erosion is coincident with the location of the forebulge in the developing foreland basin, implying that growth of the forebulge prohibited the development of, or enhanced the later erosion of, estuarine deposits. Conversely, enhanced accommodation in the transition into the foredeep depozone allow the preservation of tide-dominated estuarine deposits along the western flank of the San Rafael Swell. Additionally, the possibility of a pre-Laramide tectonic history for the San Rafael Swell is indicated by a distinct lack of Naturita Formation deposits in an area that is coincident with the modern-day axis of the anticline.Overall, the Naturita records the initial flooding of the Western Interior Seaway in the San Rafael Swell region and provides an excellent case study of the deposits that are laid down in a transgressive system that passes from coastal-plain to offshore deposits.

10 Myr evolution of sedimentation rates in a deep marine to non‐marine foreland basin system: Tectonic and sedimentary controls (Eocene, Tremp–Jaca Basin, Southern Pyrenees, NE Spain)

AbstractThe propagation of the deformation front in foreland systems is typically accompanied by the incorporation of parts of the basin into wedge‐top piggy‐back basins, this process is likely producing considerable changes to sedimentation rates (SR). Here we investigate the spatial‐temporal evolution of SR for the Tremp–Jaca Basin in the Southern Pyrenees during its evolution from a wedge‐top, foreredeep, forebulge configuration to a wedge‐top stage. SR were controlled by a series of tectonic structures that influenced subsidence distribution and modified the sediment dispersal patterns. We compare the decompacted SR calculated from 12 magnetostratigraphic sections located throughout the Tremp–Jaca Basin represent the full range of depositional environment and times. While the derived long‐term SR range between 9.0 and 84.5 cm/kyr, compiled data at the scale of magnetozones (0.1–2.5 Myr) yield SR that range from 3.0 to 170 cm/kyr. From this analysis, three main types of depocenter are recognized: a regional depocenter in the foredeep depozone; depocenters related to both regional subsidence and salt tectonics in the wedge‐top depozone; and a depocenter related to clastic shelf building showing transgressive and regressive trends with graded and non‐graded episodes. From the evolution of SR we distinguish two stages. The Lutetian Stage (from 49.1–41.2 Ma) portrays a compartmentalized basin characterized by variable SR in dominantly underfilled accommodation areas. The markedly different advance of the deformation front between the Central and Western Pyrenees resulted in a complex distribution of the foreland depozones during this stage. The Bartonian–Priabonian Stage (41.2–36.9 Ma) represents the integration of the whole basin into the wedge‐top, showing a generalized reduction of SR in a mostly overfilled relatively uniform basin. The stacking of basement units in the hinterland during the whole period produced unusually high SR in the wedge‐top depozone.

EFFECT OF TECTONIC SETTING ON DISTRIBUTION OF PELAGIC SEDIMENT UNIT (SHIRANISH FORMATION) IN ZAGROS FORELAND BASIN, IRAQI SEGMENT

Shiranish Formation represents the uppermost Cretaceous pelagic sediment unit of the Iraqi segment within the western Zagros fold and the thrust belt. The occurrence of the formation governed by the northern edge of the Neabo-Arabian plate`s tectonic activity and the distribution has now been interpreted according to the modern tectonic concept of the foreland basin system. Field data and Isopach map have shown that two main basins existed on both sides of the Forebulge (Qamchuqa Formation). Currently, the first one has extended north west-southeast within the foredeep depozone, while the second one, which represents the Backbulge Depozone. The influence of the tectonic rise of the Forebulge Depozone leads to a non-existing pelagic sediments unit of the Shiranish Formation in the area restricted from northwest Amadiya town (the south limb of Mateen Anticline) towards southeast areas (Gara Anticline), thereafter to Aqra areas. Thus, the absence of the formation in the Shikhan area (e.g.) refers to inhomogeneity on the backbulge basin causing exposed or submerged areas during the age of upper Cretaceous.

Provenance analysis of Cretaceous peripheral foreland basin in central Tibet: Implications to precise timing on the initial Lhasa-Qiangtang collision

Mesozoic strata along northern margin of the Lhasa terrane near Dingqing, Tibet provide a semi-continuous record of the Bangong-Nujiang Ocean closure and the subsequent Lhasa-Qiangtang collision. In this study, we present results of sandstone petrographic, detrital zircon UPb, and Cr-spinel geochemical data to determine the provenance of the Mesozoic strata (from the Triassic Quehala Group and the Mid-Jurassic to Lower Cretaceous Xihu, Lagongtang, and Duoni Formations, which are young from ~220 Ma to ~100 Ma) in this region, thereby allowing for interpretation of their tectonic setting. The similar 1200–900 age cluster from the lower Xihu Formation to that of the Triassic Quehala Group and the distinct age peaks at ~200 Ma and ~146 Ma from the upper Xihu Formation suggest a Lhasa terrane provenance to the south. Distinctive age clusters of 300–210 Ma and ~1800 Ma and Cr-spinel composition analysis of the Lagongtang Formation indicate a provenance shift from the Lhasa terrane to the Qiangtang terrane and the Bangong-Nujiang suture zone to the north. The Lagongtang Formation was deposited in a bathyal-abyssal to shallow-slope environment from north to south, that we interpret as the foredeep depozone and distal foredeep of a peripheral foreland basin system that developed due to flexural subsidence related to the Lhasa-Qiangtang collision and terrane accretion. The age of the Lhasa-Qiangtang collision is constrained by a ~140 Ma tuffite UPb age at the base of the foreland basin strata. An angular unconformity between the Xihu and Lagongtang Formation, which we interpret as the result of the Lhasa-Qiangtang collision. Our results indicate that the Lhasa-Qiangtang collision initiated around ~140 Ma in the Dingqing region, simultaneously with previous determinations 1200 km to the west near Gaize area. Therefore, we prefer quasi-simultaneous onset of collision along-strike to zippering collision models wherein the east collision age is older than the west.

The Neuquén group: The reconstruction of a Late Cretaceous foreland basin in the southern Central Andes (35–37°S)

In the southern Central Andes of Argentina, between 34° and 41°S, the Neuquén Group records Upper Cretaceous nonmarine deposits that provide direct evidence of synorogenic sedimentation associated with the development of an early foreland basin. The configuration of this basin and its relation to the Malargüe fold and thrust belt are analyzed in this article using sedimentological analyses, U-Pb dating of detrital zircons and seismic and surface structural data. The remnant wedge-top depozone preserved in the Argentinian Andean slope exposes sedimentological information that indicates that braided fluvial systems, which may have formed part of broader fluvial fans, transported and deposited the sediments from an extensive relief area located in the present western Andean slope to the Chilean Coastal Range zones. The eastern border of this depositional system was defined by a basement uplift, interpreted either as a forebulge or an incipient broken foreland system, from where gravel-sandy braided river systems fed the foredeep depozone transporting and depositing sediments from the exposed cratonic area in the east. Consequently, an initial underfilled foreland basin was configured. The evolution of this early basin and the areas of sediment supply were controlled by the eastern expansion of the Malargüe fold and thrust belt, through the development of thick-skinned anticlines, which progressively fragmented the wedge-top zone. The evidence collected suggests that the Late Cretaceous uplift was a major tectonic event that exposed the entire Mesozoic column of the Neuquén basin up to the Permian-Triassic basement, which implies more than 2,500 m of denudation at that time. U-Pb determinations yielded a maximum depositional age of ca. 91 ± 2 Ma (Late Turonian), which suggests either non-deposition or cannibalization of a sedimentary interval of ca. 10 My at 36°S, when compared to the age of the basal sections of the Neuquén Group at other latitudes.

Provenance evolution of the Paleoproterozoic metasedimentary cover sequences in northern Fennoscandia: Age distribution, geochemistry, and zircon morphology

The metasedimentary basin-fill successions of the Central Lapland belt, Peräpohja belt, and Kuusamo belt form an important part of the northern Fennoscandia Shield. They each record ca. 600 Ma (2.5–1.9 Ga) of sedimentation history and tectonic evolution, providing important information about past depositional conditions and tectonic settings. Detrital zircon geochronology shows that Archean age populations between 3.00 and 2.70 Ga have provenances from the surrounding basement complexes of granitoid/TTG rocks, whereas the Paleoproterozoic age populations (≤2.25–1.86 Ga) can be linked to the surrounding granitoids in northern Finland and Sweden. Zircon morphology studies indicate that basin sedimentation and/or provenance area(s) were likely influenced by eolian processes ca. 2.3–2.1 (or possible earlier). Major and trace element geochemistry indicates minor to moderate weathering trends, closely resembling Archean-Proterozoic sandstones and shales. Provenance signatures of tectonic settings vary from rift to arc and collisional. We propose five basin evolution stages for the Central Lapland belt, Peräpohja belt, and Kuusamo belt: a rifting stage from 2.5 to 2.1 Ga including (i) initial rifting/early syn-rift, (ii) syn-rift, and (iii) syn-rift to early post-rift; (iv) a passive margin (post-rift) stage from 2.1 to 1.94–1.92 Ga; and (v) a foreland basin system 1.94–1.92 to 1.88 Ga. The rifting stage includes bimodal subaerial to subaqueous volcanism with continental to marine sedimentation, and the initial accumulation of carbonate and evaporate successions, indicating later local tectonic stability and restricted hydrological circulation. The early development of an epeiric sea setting was followed by a passive margin stage and the development of aulacogens, controlled by cyclic sea-level fluctuations superimposed on long-term thermal subsidence. This stage was characterized by the accumulation of hemipelagic deposits together with gravity-driven sandstone deposits and associated subaqueous volcanism. The foreland basin system comprises an initial compressional stage with the development of forebulge and foredeep depozones and magmatic arc collision. This was followed by the main compressional stage, where basin inversion resulted in a foreland fold-thrust belt. The foreland basin system includes syn- and post-orogenic deposystems and a transition from underfilled marine sedimentation to overfilled non-marine deposits.

PALEOBATHYMETRIC EVOLUTION OF THE EARLY LATE MIOCENE DEPOSITS OF THE PRE-APULIAN ZONE, LEVKAS ISLAND, IONIAN SEA

The Manassi section in Levkas Island belongs to the Pre-Apulian (Paxos) zone, the most external domain of the Hellenic realm. Its Early Tortonian sediments contain a rich foraminiferal fauna dominated, in numbers of individuals, by planktic species. Its benthic foraminiferal assemblage is characterized by a high number of taxa, with low numbers of individuals. Their study provides a basis for interpreting the paleobathymetry of the basin.The Manassi section represents deposition in upper to lower bathyal depths, during a period of intense tectonic activity. Downslope transport of fauna by turbidity currents partly overprints the signal of paleobathymetrically-diagnostic foraminifera distribution. The recognition of allochthonous taxa is used, together with %P, to identify turbidite beds intercalated with in-situ marly sediments. The micropaleontological and paleobathymetrical analyses of the studied sediments indicate that these correspond to distal atypical flysch deposited in the foredeep depozone of the most external domain (Pre-Apulian zone) of the Hellenide foreland basin.

New insights on sedimentology, sequence stratigraphy and palaeogeographic reconstruction of the Tortonian-Early Messinian Kechabta series in Kechabta Foreland Basin (Northern Tunisia)

The Kechabta Basin is part of the Tunisian Foreland Basin in front of the Numidian and Tellian nappes. During the Tortonian, this basin records a strong subsidence rate due to flexural process, in front of the nappes. Contrary to previous interpretations, a sedimentological investigation of the thick Tortonian-Early Messinian Kechabta Formation (over 1300 m) reveals that this siliciclastic series corresponds to a complex deltaic shorelines deposit dominated by waves and influenced by tides. This formation is mainly made of a large number of high frequency, mudstone to sandy prograding parasequences representing repeated progradational phases of the coastal wedge. Facies successions within many of the parasequences show normal regressive trends. These parasequences present offshore grey-brown mudstone, followed by transition offshore sandy storm beds alternating with mudstone, then by shoreface sandstones bearing hummocky-cross stratification and wave ripples, then by foreshore facies or tidal flat facies. However, many other parasequences reveal forced regressions during the progradational phases. This evidences that the progradational phases were driven by small, stepped, relative sea-level falls due to a tectonic activity related to the compressive Atlassic phase.This new paleoenvironmental interpretation suggests new elements for the palaeogeographic reconstruction of Northern Tunisia foredeep depozone during the Tortonian-Early Messinian. The base of the Kechabta Formation record the sedimentary response to regional marine transgression of the Mediterranean Sea from the East. This basin was an elongated shallow marine gulf parallel to the thrust front. The fluvio-deltaic systems of the paleo-Medjerda Rivers provided the bulk of the Kechabta siliciclastic sedimentary flux and extensive prograding delta are formed.

The South American retroarc foreland system: The development of the Bauru Basin in the back-bulge province

The aim of this research is to understand the tectonic setting of the Bauru Basin. This basin in central-eastern South America has been classified as intracratonic, but the basin-fill geometry, the involved subsidence mechanisms and the age of the deposits are poorly understood. In this work, the ranges of the fossil taxa are analyzed and ages are proposed for the lithostratigraphic units. Isopach maps were used to reconstruct the stratigraphic intervals of the basin fill. The stratigraphy of the Bauru Basin is compared with that of the adjacent basins, and the data are integrated with the available information on South American geodynamics. The fossil record indicates that sediment accumulated from the Cenomanian to early Paleocene, beginning after the Mochica Phase of the Andean orogeny. The basin-fill geometry demonstrates migration of the depocenter through time, which occurred simultaneously with migration of the Andean Basin and immediately after the orogenic events of the Peruvian Phase. We propose that the Bauru Basin is a component of a retroarc foreland system developed during the early stages of the Andean evolution and that it was developed in the back-bulge province of this system. The Andean Basin constitutes the foredeep depozone of this foreland system (including the Potosí, Oriente, Acre and Marañon basins). In addition, the Upper Cretaceous of the Parecis and Solimões basins were likely also developed in the back-bulge province. The thickness of the Bauru accumulation indicates that other mechanisms might have overlapped the flexural subsidence in this back-bulge province.

Evolution of the passive margin of the peripheral foreland basin: an example from the Lower Miocene Carpathian Foredeep (Czech Republic)

Abstract The Karpatian deposits of the central part of the Carpathian Foredeep in Moravia, which are deeply buried under the Outer Western Carpathians, provide a unique opportunity to reconstruct the former evolutionary stages of this peripheral foreland basin and its paleogeography. A succession of three depositional units characterized by a distinct depositional environment, provenance, and partly also foreland basin depozone, have been identified. The first depositional unit represents a proximal forebulge depozone and consists of lagoon-estuary and barred coastline deposits. The source from the “local” crystalline basement played here an important role. The second depositional unit consists of coastline to shallow marine deposits and is interpreted as a forebulge depozone. Tidalites recognized within this unit represent the only described tide-generated deposits of the Neogene infill of the Carpathian Foredeep basin in Moravia. The source from the basin passive margin (the Bohemian Massif) has been proved. The third depositional unit is formed by offshore deposits and represents a foredeep depozone. The provenance from both passive and active basin margin (Silesian Unit of the Western Carpathian Flysch Zone) has been proved. Thus, both a stepwise migration of the foredeep basin axis and shift of basin depozones outwards/cratonwards were documented, together with forebulge retreat. The shift of the foreland basin depozones more than 50 km cratonward can be assumed. The renewed thrusting along the basin’s active margin finally completely changed the basin shape and paleogeography. The upper part of the infill was deformed outside the prograding thrust front of flysch nappes and the flysch rocks together with a strip of Miocene sediments were superposed onto the inner part of the basin. The width and bathymetric gradient of the entire basin was changed/reduced and the deposition continued toward the platform. The basin evolution and changes in its geometry are interpreted as a consequence of the phases of the thrust-sheet stacking and sediment loading in combination with sea-level change.

Early–Middle Jurassic evolution of the northern Yangtze foreland basin: a record of uplift following Triassic continent–continent collision to form the Qinling–Dabieshan orogenic belt

The northern Yangtze foreland basin system was formed during the Mesozoic continental collision between the North and South China plates along the Mianlue suture. In response to the later phase of intra-continental thrust deformation, an extensive E–W-trending molasse basin with river, deltaic, and lake deposits was produced in front of the southern Qinling–Dabieshan foreland fold-and-thrust belt during the Early–Middle Jurassic (201–163 Ma). The basin originated during the Early Jurassic (201–174 Ma) and substantially subsided during the Middle Jurassic (174–163 Ma). A gravelly alluvial fan depositional system developed in the lower part of the Baitianba Formation (Lower Jurassic) and progressively evolved into a meandering river fluvial plain and lake systems to the south. The alluvial fan conglomerates responded to the initial uplift of the southern Qinling–Dabieshan foreland fold-and-thrust belt after the oblique collision between the Yangtze and North China plates during the Late Triassic. The Qianfoya Formation (lower Middle Jurassic) mainly developed from shore-shallow lacustrine depositional systems. The Shaximiao Formation (upper Middle Jurassic) predominantly consists of thick-bedded braided river delta successions that serve as the main body of the basin-filling sequences. The upward-coarsening succession of the Shaximiao Formation was controlled by intense thrusting in the southern Qinling–Dabieshan fold-and-thrust belt. Palaeogeographic reconstructions indicated an extensive E–W foredeep depozone along the fold-and-thrust belt during the Middle Jurassic (174–163 Ma) that was nearly 150 km wide. The depozone extended westward to the Longmenshan and further east to the northern middle Yangtze plate. The northern Yangtze foreland basin was almost completely buried or modified by the subsequent differential thrusting of Dabashan and its eastern regions (Late Jurassic to Cenozoic).

Stratigraphic and provenance evolution of the Southern Apennines foreland basin system during the Middle Miocene to Pliocene (Irpinia-Sannio successions, Italy)

The paper deals with original stratigraphic, petrographic and structural data concerning the evolution of the southern Apennines chain (Italy). The main Langhian to Pliocene deposits cropping out in the northern sector of the southern Apennines foreland basin system (Sannio-Irpinia area) have been studied and correlated in order to document the effects of tectonic changes on the evolution of sandstone detrital modes and stratigraphic architecture. The studied sandstone units can be grouped in five key intervals: a) Numidian Flysch, mostly formed by Langhian mature quartzarenitic deposits and conformable Serravallian post-Numidian successions, formed by arkosic and calciclastic arenaceous-pelitic beds (foreland depozones); b) Langhian to Tortonian San Giorgio Fm., mostly composed of quartzofeldspatic sandstones (foredeep depozone); c) Tortonian to Early Messinian, quartz-feldspatic and partly sedimentary-carbonatoclastic petrofacies, thrust-top successions (Vallone Ponticello, Villanova del Battista and San Bartolomeo fms.); d) Late Messinian quartzolithic to quartzofeldspatic sandstones (Torrente Fiumarella, Anzano Molasse and Tufo-Altavilla unit), which can be referred to infilled thrust-top basins; e) unconformity-bounded Pliocene quartzofeldspatic sandstone strata (wedge-top depozones), characterized by synsedimentary tectonic activity.Detrital modes of the Serravallian through Middle Pliocene sandstones of the southern Apennines foreland basin system testify clear provenance relations from the accreted terranes forming the southern Apennine thrust-belt. The studied clastics show almost the same blended (quartz-feldspatic) composition; this condition could be related to the tectonic transport over thrust ramp of source rocks, as suggested by the tectonic evolutionary model. This study, dealing with sedimentary provenance analysis and tectonostratigraphic evolution, provides an example of the close relations between clastic compositions and foreland basin system development in southern Apennines.