Foreland System Research Articles

Cenozoic tectono-sedimentary evolution of the external rif chain (Morocco) derived from mineralogical and geochemical analysis of mudrocks

A model of the Cenozoic tectono-sedimentary evolution of the External Rif Chain (Morocco) is provided by means of the study of the mineralogical and geochemical composition of mudrocks. To date there was a lack of homogeneous data and of a complete and extensive study of the whole External Rif Zone (ERZ). Therefore, this work shows the study of the whole ERZ where the most representative stratigraphic sections have been selected. This work provides important information about the geodynamic evolution and the variations in source-area provenance related to the growing of the Rif orogenic belt. Although there is still much work to be done, this study aims to improve the knowledge of the Cenozoic tectono-sedimentary evolution of the entire western ERZ with a homogeneous method, with a focus on the paleogeographic and paleotectonic evolution, the paleoweathering and the source areas deduced from mineralogical and geochemical data of the Cenozoic mudrocks. The bulk mineralogy is mainly characterized by the presence of calcite, quartz and dolomite plus ankerite. Feldspars have few percentages. The clay minerals are principally represented by mixed-layer illite/smectite (I/S). Illite and kaolinite are in little amount. Femic minerals, mixed-layer chlorite/smectite (C/S) and chlorite are the most abundant. The I/S features suggest a different thermal condition for the three domains. The chemical composition indicates that the mudrocks can be described as mixtures of carbonates with aluminosilicate components. The Al/Ti, Th/Cr, Th/Sc, La/Th and La/Sc ratios, the Cr/V vs. Y/Ni plot, the V-Ni-Th∗10 and La-Th-Sc ternary diagrams indicate a predominantly felsic source with a minor mafic input more evident in the Paleocene-Eocene samples of the External Intrarif and Mesorif. The External Rif Zones changed in the Cenozoic from a passive margin to a complex foreland system with the incoming of the Alpine tectonic phases. In general, the felsic contribution should be linked to the foreland area consisting in the Middle Atlas and Mesetas massifs made of a crystalline domain. This margin probably presented an intermediate narrow oceanic branch in the External Intrarif-Mesorif boundary that surprisingly should start to close during Paleogene times providing the mafic contribution. This Paleogene tectonic activity in these domains is corroborated by the thermal maturity indicating late diagenesis. The chemical weathering indices, such as the CIA (Chemical index of Alteration) and its modifications, show medium-high values and thus suggest generally moderate paleoweathering conditions in agreement with the predominant amount of I/S.

Chronostratigraphy and tectono‐sedimentary history of the Eastern South Pyrenean foreland basin (Ripoll Syncline, North‐East Spain)

AbstractThis paper contributes to an understanding of the tectono‐sedimentary evolution of the South Pyrenean foreland system by reviewing the chronostratigraphic framework of the basin infill in its eastern sector. Six sections are analysed and cross‐correlated to build a 6.5 km thick composite magnetostratigraphy that represents the complete record of the Cadí Nappe in the Ripoll Syncline. New and previous magnetostratigraphic sections are integrated with available biostratigraphy to provide a new age calibration of the sedimentary succession of the Cadí Nappe, encompassing from Palaeocene to Middle Lutetian age. The proposed correlation with the Geomagnetic Polarity Time Scale aims at best reconcile magnetostratigraphic data with the regional biochronology built on the marine Shallow Benthic Zonation (SBZ biozones), the continental mammalian biochronology (MP levels) and the newly collected charophyte data. A subsidence analysis was performed on the calibrated composite succession, resulting in two well‐defined intervals bounded by a hiatus. A Palaeocene to Early Eocene interval with low (11–21 cm/kyr) total subsidence rates, and an Early to Middle Eocene interval, characterised by high (70–75 cm/kyr) total subsidence rates. The detailed trends in both subsidence and sedimentation mark the development and evolution of the foreland depozones, from distal foreland depozones to foredeep and wedge‐top depozones, relative to the emplacement of the Pedraforca Nappe and Cadí Thrust Nappe. The most pronounced sedimentary shift in the Cadí Nappe occurred at 49 Ma, with the rapid drowning of the carbonate platforms and its transition into talus and deep basinal environments. Carbonate platforms collapsed and resedimented on the talus of the elongated trough, newly formed parallel to the orogenic front. This marked the onset of tectonic subsidence triggered by the submarine emplacement of the Lower Pedraforca Nappe. The emersion of the orogenic wedge drove the entry of siliciclastics, lagged by 1 Myr, into the Ripoll Trough. The foredeep filled rapidly (5.5 km thickness in less than 7 Myr) compared to other South Pyrenean regions, favoured by its semi‐enclosed palaeogeography. The emplacement of the Vallfogona Thrust as early as the Middle Lutetian (43 Ma) brought the Cadi Nappe into a wedge‐top setting. However, the Ripoll growth syncline continued acting as a temporary sink for alluvial sedimentation while a foredeep developed further south in the autochthonous Ebro Basin. The flexural response of the Iberian plate to the tectonic thickening of the Axial Zone counterbalanced for a period the local uplift of the Cadi Nappe, providing accommodation space for the top sediments filling the Ripoll Syncline.

Miocene evolution of the External Rif Zone (Morocco): Comparison with similar and lateral southern Mediterranean Tethyan margins

The Miocene evolution of the External Rif Zone (NW Africa Plate) was determined through multidisciplinary analysis of fourteen successions. The updated stratigraphic framework shows how Miocene sediments rest on the Cretaceous–Paleogene terrains through unconformity surfaces, whereas it rests with sedimentary continuity in two sectors. After recognition of lithofacies and three unconformities located near the Oligocene–Aquitanian, Aquitanian–Burdigalian and Serravallian–Tortonian boundaries, the Miocene sedimentary record was divided into three stratigraphic intervals representing deep to shallow marine deposits as Aquitanian–Burdigalian, Langhian and Upper Serravallian–Missinian. The two oldest unconformites are restricted to the central sector, while the upper one is generalized and probably related to the nappe tectonics registered in all sectors of the External Rif. Data from analysis of tectofacies, petrology, mineralogy, meaning and implications of unconformities, and subsidence indicate that: (i) mass flow deposits (turbidites, slumps, olistostromes) are common in all successions but more frequent during the Lower Miocene; (ii) petrology of the detrital components of the arenites indicates recycled orogen-derived sediments, with quartz coming from erosion of metamorphic rocks of the Atlas orogen and/or the African craton; (iii) mineralogy of mudstones suggests a complex erosional evolution of local emerged areas derived from a mixture of contributions coming from the erosion of Upper Jurassic to Paleogene suites, and especially from kaolinite-rich Albian–Cenomanian to Paleogene successions with absence of a clear unroofing. The conjunction of all these clues reinforces the idea of a synsedimentary tectonics affecting the margin/basin system during the Miocene. A thickness analysis of the studied sedimentary successions allows proposing the evolution of the orogenic front and main depozones (foredeep, bulges, wedge-top and intramontane sub-basins) integrated in a complex foreland system migrating from north to south with the Atlas-Mesetas area acting as foreland during Miocene. The orogenic front moved from the Internal Intrarif to Mesorif and later to Internal Prerif. The main wedge-top basin also migrated from the Internal Intrarif to External Intrarif. The foredeep migrated from the Mesorif to the Internal Prerif, while the main forebulge was located in the External Prerif and a secondary bulge developed in the External Intrarif. Intramontane basins developed behind the orogenic front in relative extensional conditions moving from the Internal Intrarif to External Intrarif. The reconstructed Miocene evolution was inserted into a 2D paleogeographic-geodynamic evolutionary model using GPlates software, and then compared to those reported in other external margins of the western Tethys (Betic Chain, Tunisian Tell, Sicilian Maghrebids and Apennines), revealing important similarities and local differences.

Strain partitioning in the Patagonian Broken Foreland: influence of structural inheritance of early Andean deformation

In the context of Andean-type oblique convergence, strain partitioning between thrust and strike-slip tectonics is well documented in the arc region. However, the impact of this configuration in the retroarc remains poorly understood, especially in broken foreland systems where basement structures compartmentalize the retroarc into small intermontane sedimentary basins. The spatiotemporal analysis of tectonic evolution and the role of inherited weaknesses in this area are often debated. This study addresses these uncertainties by integrating geometric and kinematic analyses of tectonic structures within the Sañicó Massif in the North Patagonian foreland. Results reveal two deformational episodes. The initial Late Cretaceous to Paleocene episode represents a contractional deformation phase, with NW–SE shortening direction causing the tectonic inversion of pre-Andean rift depocentres. The second episode records a Neogene transpressional regime with both contractional and strike-slip deformation, with east–west to NE–SW shortening direction, which progressed under reactivation of pre-existing structures and generated new faults. This work demonstrates the Neogene propagation of the strike-slip regime towards the retroarc, defining strain partitioning at various scales and highlighting its interaction with pre-existing structures. These results enhance our understanding of the complex tectonic history in oblique subduction settings, providing significant evidence of the structural inheritance in retroarc systems.

STRUCTURAL STYLE AND TIMING OF NW‐SE TRENDING ZAGROS FOLDS IN SW IRAN: INTERACTION WITH NORTH‐SOUTH TRENDING ARABIAN FOLDS AND IMPLICATIONS FOR PETROLEUM GEOLOGY

The Zagros foldbelt – foreland system in SW Iran is a prolific hydrocarbon province with known reserves of more than 90 billion brl of oil and 800 TCF of natural gas. Establishing the structural style of folding in the Zagros area presents a major challenge due both to the geographical extent of the foldbelt, which is some 1600 km long in total, and the presence of marked lateral variations in fold style related to the complex regional tectonic history. In addition, while numerous high‐quality structural studies of the Zagros have been completed over the last 20 years, they support a variety of different interpretations and are therefore diffcult to synthesize. In this paper, we review the general structural style of the Zagros fold‐and‐thrust belt in SW Iran, and in particular the style of folding in the Lurestan arc, Dezful embayment, Izeh Zone and Fars arc. We summarise relationships between folding in these areas and fracture development, and investigate the timing of folding and the interaction between NW‐SE oriented “Zagros” folds and north‐south oriented “Arabian” folds. Finally, we briefly assess the implications of fold style for petroleum systems in the Zagros area. Although no new data are presented in this paper, a series of unpublished maps are used to illustrate the main results and include: a map showing the extent of the main detachment levels across the Lurestan, Dezful and Fars structural domains; two palaeotectonic maps (for Late Cretaceous – Paleocene and Miocene – Pliocene times, respectively), showing the position of the deformation fronts of the Zagros and the North Oman thrust systems and their potential spatial and temporal relationship with folding; and a set of four maps showing the distribution of reservoir rocks which are grouped by age into the Permian – Triassic Dehram Group, the Late Jurassic – Early Cretaceous Khami Group, the Late Cretaceous Bangestan Group, and the Oligocene – Miocene Asmari Formation. In addition, for the Lurestan, Dezful and Fars structural domains, a series of regional cross‐sections at the same scale are presented and discussed.Most of the data in this review paper were acquired in order to gain an improved understanding of the petroleum systems in the Zagros area; however the data are used here to investigate a range of interacting processes including tectonics, sediment deposition and subsurface fluid flow in the development of the fold‐and‐thrust belt and its associated foreland basins. The resulting synthesis is intended to provice a starting point for future tectonostratigraphic and hydrocarbon‐related studies which will make use of both existing and new multidisciplinary techniques to constrain the results. The knowledge acquired and the techniques used will be of benefit in future challenges including the identification of subsurface reservoirs suitable for the permanent storage of CO2 to mitigate the effects of climate change.

New constraints for the western Paleotethys paleogeography-paleotectonics derived from detrital signatures: Malaguide Carboniferous Culm Cycle (Betic Cordillera, S Spain)

Carboniferous sandstone within the Paleo-Mesomediterranean Domain (Malaguide Subdomain), in southern Spain, represents a key detrital mode within the sedimentary budget of convergent plate boundaries during the Variscan s.s. to Paleotethysian orogenic time span (≈420–300 Ma). This Carboniferous detritus corresponds with Culm lithostratigraphic depositional unit, and it covers an important gap of information (paleogeographic, paleotectonic, source areas) to the area located between the Iberian-French massifs and the African Paleo-Atlas, in the western Paleotethys. Sandstone composition is quartzolithic and records an important high-to-medium-low grade metamorphic content. The source area was a lithic and transitional recycled orogen with a signature of volcanic and ophiolitic detritus (≈330 Ma and/or older). These supplies seem to be derived from a mid-crustal deformed and thrusted pre-late Ordovician to Early Carboniferous terrane, involved in the plate convergence (the southern Europe Iberian-French massifs overriding the north African area) southeatwards of the Variscan s.s. orogenic system, rapidly exhumed and uplifted at mid-Late Carboniferoous time. Consequently, in the overriding hinterland (southern Europe: Iberian-French massifs), metamorphic basement should be already structured during middle Carboniferous when thrusting took place and deposition of Culm facies started in the Malaguide Complex, suggesting Proterozoic-Early Carboniferous (most probably, ≈420 to 330 Ma) metamorphic highlands. The presence of serpentinite-like detritus (≈330 Ma and/or older) seems to indicate a metamorphosed oceanic crust being dismantled at that time. Thus, sources from ophiolitic suture (most probably developed at ≈420–330 Ma) zones are tentatively proposed in other northern Gondwana of southwestern Europe. The occurrence of a synsedimentary volcanic activity (andesitic) should be related to a lost magmatic arc (most probably developed at ≈360–330 Ma), reinforcing the idea of a nearby subduction area. Therefore, the thick terrigenous Culm deposits (≈330–300 Ma) from the Malaguide Subdomain could be deposited in a complex foreland system basin connected northward with carbonate platforms and with a crystalline highland uplifted domain from the southern Europe Iberian-French massifs and southward with the African Paleo-Atlas Domain. The studied mid- to late Carboniferous sandstone petrofacies deeply contributes to paleogeographic reconstructions since block fragmentation and spreading, during the Paleotethysian and Alpine orogenies, rearranged the Paleozoic paleogeography now part of the Cenozoic Perimediterranean Chains. After the correlation with the Carboniferous from other western Paleotethys domains, new paleogeographic-paleotectonic constraints are proposed for the transitional area between the Iberian-French massifs and the African Paleo-Atlas Domain.

Detrital record of sediment influx in the Triassic Chuxiong broken foreland basin in southeastern Tibetan Plateau

The Triassic Chuxiong basin represents a classic example of a foreland system that is thought to be associated with the closure of eastern branches of the Paleo-Tethys and subsequent Indosinian collision, yet how it was filled remains poorly understood. Here, we use paleocurrent measurements, sandstone petrology, and detrital zircon UPb geochronology to examine the patterns of basin fill. Paleocurrent reconstruction indicates that although some evidence exists for axial transport, the basin was mainly filled transversely with abundant sediment input from the Paleo-Tethyan suture to the west and the Kangdian High to the east. Qualitative determination of sandstone petrology shows that the lithic fragments contained within the Late Triassic strata are not of a uniform mode: volcanic lithics and glass grains are contained within nine Carnian and Rhaetian samples from the western part of the basin, but rarely observed in thirteen samples from the eastern basin. Similarly, detrital zircon UPb geochronology of sandstone samples from five sections reveals marked temporal and spatial changes in their age signatures that can be divided into three distinct types. Type-1 age spectra are represented by a narrow unimodal age probability peak at ca. 250 Ma that correlates with the Indosinian-aged arc sources developed along the Jinsha Jiang-Ailao Shan and Changning-Menglian sutures. Type-2 also shows a major zircon age population, but with a diagnostic peak at ∼780 Ma that corresponds to the Neoproterozoic basement outcropped in Kangdian High. Type-3 is generally characterized by multimodal distribution with major populations of ca. 200–350 Ma, ca. 400–500 Ma, ca. 700–900 Ma, ca. 1750–2000 Ma, and ca. 2350–2600 Ma. Comparing our new data with existing age spectra for the Triassic strata across the western Yangtze and the Indochina blocks demonstrates that the Chuxiong basin was primarily filled by a magmatic arc along the Paleo-Tethyan suture zone during the Carnian, and mostly fed by a reorganized drainage system by incorporating the fold-thrust belt and uplifted foreland basement as source area when the basin expanded eastward through the Norian and Rhaetian as the basin-fill onlaps onto the basement of Kangdian High. The patterns of sediment dispersal of the Triassic Chuxiong basin not only provide a new example of the interplay between orogen and craton sediment input in the peripheral setting but also highlight that the local basement-cored uplifts may dominate the provenance of a broken foreland system during underthrusting.

Decoupling external forcings during the development of Miocene fluvial stratigraphy of the North Patagonian Foreland

AbstractThe Patagonian Andean foreland system includes several intermountain basins filled with a Miocene non‐marine record deposited under syn‐tectonic conditions related to the Andean uplift and a regional climate change triggered by a rain shadow effect. Many of those basins, such as the Collón Cura basin in Neuquén Province, Argentina, present a well‐preserved fluvial record (i.e. the Limay Chico Member of the Caleufú Formation). Sedimentological and palaeomagnetic studies have allowed the interpretation of coeval transverse distributary fan and axial mixed‐load fluvial systems deposited between 10.6 ± 0.2 and 12.8 Ma. The basin infill arrangement shows that, while the axial mixed‐load fluvial system exhibits an aggradational stacking pattern, the transverse distributary fluvial fan system denotes three different orders of stratigraphic patterns: (i) large‐scale progradation of the transverse fluvial fan system over a time scale of 106 year; (ii) intermediate‐scale progradational–retrogradational transverse intra‐basinal fluvial fan episodes over a time scale of 105 year; and (iii) small‐scale transverse lobe progradation over a time scale of 105–104 year. These patterns were interpreted as transverse sediment flux variations triggered by variable external forcings. To decouple those forcings, we estimated the Collón Cura basin equilibrium time at 3–5 × 105 year and compared it with the time scale over which different external forcings varied in the Patagonian Andean and foreland regions during Miocene times. Large‐scale progradation is linked to an increase in sediment flux triggered by a long‐term tectonically driven exhumation forcing associated with the Miocene Patagonian Andean contractional phase. Intermediate‐scale progradational–retrogradational episodes are linked to variations in sediment flux due to a mid‐term tectonic forcing associated with the western fault system activity. The small‐scale fan lobe progradation is related to increases in sediment flux triggered by indistinguishable short‐term autogenic processes and/or high‐frequency tectonic and climatic forcings. This contribution shows the applicability and limitations of the basin equilibrium time concept to decouple external forcings from the geological record, considering their magnitude, nature and time scale, as well as the basin characteristics.

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.

U-Pb Zircon Geochronology of Detrital and Ash Fall Deposits of the Southern Paraná Basin: A Contribution for Provenance, Tectonic Evolution, and the Paleogeography of the SW Gondwana

Zircon U-Pb geochronology was applied to investigate the provenance, depositional ages, and paleogeography of the southwestern Gondwana in detrital and ash fall sediments from Carboniferous to Jurassic succession of the southern Paraná Basin. Four detrital age populations suggest provenance from local and distal sources located to the south, southeast, and southwest: (i) Archean to Paleoproterozoic zircons from the Rio de La Plata Craton, Nico Peres and Taquarembó terranes; (ii) Grenvillian zircons from the basement of the Gondwanides and Namaqua–Natal belts; (iii) Neoproterozoic grains from the Don Feliciano Belt; and (iv) Phanerozoic populations from Paleozoic orogenic belts and related foreland systems in Argentina, as well as eroded units of the Paraná Basin. The paleogeographic reconstruction indicates an evolution in three distinct stages: (1) a gulf open to the Panthalassa Ocean during the Carboniferous; (2) an epicontinental sea with the rise of the Gondwanides Orogeny during the Permian; and (3) continental deposits controlled by an intra-plate graben system during the Triassic. Permian–Triassic volcanogenic zircons provide constrained maximum depositional ages and attested persistent volcanism, related to the Choiyoi magmatism and effects of the climate change episodes. During the Triassic, the extensional graben system recorded the uplift of the basement through regional northwest and northeast fault systems, and the recycling of Permian zircons, modifying source-to-sink relationships.

Controls on sedimentation in a deep‐water foredeep: Central Pindos foreland basin, western Greece

AbstractThis study provides a sedimentological, stratigraphic and palaeocurrent investigation of Upper Eocene to Lower Oligocene deep‐sea fan deposits found in the central part of the Pindos foreland basin in western Greece. According to facies analysis, the examined succession at Amfilochia area has 13 sedimentary facies and 10 facies and sub‐facies associations. Depositional elements include abyssal plain pelagics, outer fan, inner fan, and slope deposits. Outer fan sediments are classified as lobe‐axis, lobe‐off‐axis, lobe‐fringe, and distant lobe‐fringe deposits, while inner fan sediments are classified as channel‐fill, crevasse‐splay, internal and external levee deposits. The stratigraphic study shows an upward shift from abyssal plain pelagics to outer, inner fan, and finally slope deposits, implying submarine fan system progradation and progressive infilling of a deep‐water sediment depocentre. The sediments were deposited in the foredeep of the Pindos foreland system and correspond to the system's underfilled stage, when sedimentation was unable to exceed the accommodation provided by lithospheric flexure. They point to deposition near the onset of the Pindos orogen, after the closure of the Pindos basin because of the collision of the Apulian with the Pelagonian microplate during the Cretaceous‐Palaeogene period. Palaeocurrent data from sole marks show bipolar directions associated with two distinct spreading sub‐marine fan deposits. As a result, the study region was split into Upper (major SE‐direction flow) and Lower (major NW‐direction flow) parts, indicating that axial flows were predominant during sediment deposition. However, as the deposition of the elements continued, the progradation of both systems constrained the space accommodation because of the increased basin sediment supply and forced an increase in the degree of basin confinement that changed the compensational to aggradational stacking pattern. The goals of this research are to develop an updated facies model for these deep‐sea fans as well as a robust correlation framework for the various stratigraphic units in the central Pindos foreland basin. This research also connects the stratigraphic development of deep‐sea fan deposits to the evolutionary phases of the Pindos foreland system, providing fresh insights into the palaeogeographic circumstances in the Pindos foreland basin.

Integrated Geoelectrical and Geological Investigation of a Quaternary Paleo-Depositional Environment in the Haripur Basin, Northern Pakistan: Implications for Groundwater System

The deposition in Haripur basin not only provides a contemporary insight into old fluvial depositional sequences of the Himalayan foreland but also sheds light on the important continental depositions in a monsoon controlled foreland system. The present study emphasizes the evaluation of the paleo-depositional architecture for sustainable groundwater availability by utilizing a total of four field-based geological observations, eleven boreholes, and fifty-nine vertical electrical sounding (VES) datasets. The acquired surface geological data well correlate with resistivity and borehole data. The derived results of the lithostratigraphic cross-sections and spatial distribution maps reveal three-sided closure depositional. These depositional directions indicate thick successions of coarser sediments near the foothills and interbedded mixture of coarser and finer sediments toward the central and southern parts of the basin. The former conditions provide maximum groundwater yielding capacity for sustainable groundwater supply in the north-eastern and north-western parts of the basin. On the contrary, in the central and southern parts of the basin, the groundwater yielding capacities have drastically decreased due to deposition of finer sediments.

Spatial Pattern of Late Quaternary Shortening Rate in the Longmen Shan Foreland, Eastern Margin of the Tibetan Plateau

Abstract As the eastern boundary of the Tibetan Plateau, Longmen Shan possesses a narrow thrust belt with steep topography but lacks matching Cenozoic foreland basin. Multiple kinetic models have been proposed to debate on the dominant mechanism of developing such range–foreland system. Crustal shortening rate is a feasible approach to test different tectonic models and estimate structural patterns. In this study, we focused on the deformation pattern and shortening rate of the complex foreland area of the southern Longmen Shan, which is comprised of the Xiongpo, Sansuchang, and Longquanshan anticlines. By the means of net-based RTK measurement and Quaternary chronology, we measured and dated the six-level terraces of the Qingyi River, which flows southeastward across this region. Excess area method was applied to calculate shortening rate. The results indicate that the Late Quaternary shortening rates of the Xiongpo anticline, Longquanshan anticline, and Sansuchang anticline are 1.01 mm/yr, 0.89 mm/yr, and 0.16 mm/yr, respectively. The total shortening rate of the foreland in southern Longmen Shan is 2.06 mm/yr. Consequently, a mechanical model was presented to show the tectonic pattern: the southern Longmen Shan is an actively expanding edge of the plateau, and the shortening is distributed to the three anticlines dominated by the foreland detachment system. This model supports that crustal shortening is the dominating force in the current orogenesis of the Longmen Shan. In addition, the along-strike variation of the Longmen Shan was further specified from the perspective of crustal shortening distribution. We propose that the southern Longmen Shan and its foreland basin are in a state of compression, while the northern Longmen Shan has both thrust and strike-slip characteristics.

Paleo–Pacific plate subduction on the eastern Asian margin: Insights from the Jurassic foreland system of the overriding plate

Abstract The subduction of the paleo–Pacific plate beneath the North China block has been well documented in terms of magmatic activity, geophysical investigations, and numerical modeling, but the timing of its onset along the eastern Asian margin and the tectonic processes involved remain poorly understood. We have now reconstructed the structural evolution and sedimentation of the Shihuiyao–Gangzidian–Yuantai region of the southern Liaodong Peninsula, on the overriding plate at the eastern Asian margin, using geologic mapping, borehole data sets, field structural studies, and zircon geochronology. In the Shihuiyao area, based on geologic mapping and drilling, top-to-the-NW thrust faults truncated earlier top-to-the-NE reverse faults and then were subsequently overprinted by normal faults. In the Gangzidian area, geologic mapping and 40 boreholes allowed us to construct eight cross sections revealing the top-to-the-WNW/W thrust faults from the surface to a depth of at least 0.5 km; the sections show that the thrust faults extend to the basement and that subsequent normal faults dip subvertically. In the Yuantai thrust system, the top-to-the-NW thrusts, expressed as four tectonic windows and a duplex on the map scale, were intruded by late porphyry and diabase sills. Integration of the data from the three study areas allowed us to identify one angular unconformity and at least two phases of later deformation (D1 and D2). The pre-D1 unconformity is marked by a foreland basin that was filled with Middle Jurassic clastic rocks that unconformably overlie the Neoproterozoic and Cambrian basement. The D1 deformation is represented by NE-SW–striking thrust faults that displaced Neoproterozoic or Cambrian strata onto the Middle Jurassic strata. The D2 deformation is defined by kilometer-scale, high-angle normal faults with variable dips and strikes. Although three samples from the Middle Jurassic clastic rocks did not yield ideal maximum deposition ages (MDAs; ca. 246 Ma), a porphyry dike and a diabase sill that intruded the Yuantai thrust system and remain undeformed yielded zircon U-Pb ages of ca. 124 and 117 Ma, respectively. Detrital zircon geochronology yielded a MDA of ca. 129 Ma for Cretaceous deposits in graben structures with hanging walls formed by D2 normal faults. Thus, the D1 and D2 deformation events can be constrained to the Late Jurassic and Early Cretaceous, respectively (D1 between ca. 174 and 124 Ma, and D2 after ca. 129 Ma). The provenance of the detritus in the Middle Jurassic Wafangdian Formation suggests that the deposits in the retroarc foreland basin had a source in a thrust sheet of the Paleoproterozoic basement, but the source of deposits in a minigraben (D2) was possibly the nearby Neoproterozoic rocks. Therefore, we reconstructed the retroarc foreland basin and fold-and-thrust belt of the southern Liaodong Peninsula in terms of a subduction margin and constrained a Toarcian–Aptian (ca. 174–124 Ma) age for the onset of paleo–Pacific plate subduction. We interpret the foreland basin system and the subsequent synconvergent extension to have been the result of slab flattening and rollback during episodic subduction of the paleo–Pacific plate.

Combined use of Sm–Nd isotopes and lithogeochemistry in the sedimentary provenance of the southern Ediacaran-Cambrian Bambuí foreland basin system, Brazil

Sedimentary provenance analysis based on lithogeochemistry and isotope data has been extensively applied in the investigation of ancient sedimentary successions. This approach contributes to understand the tectonic setting in which these strata were deposited and to recognize major provenance patterns in time and space. The Ediacaran to Cambrian Bambuí Group is exposed in the São Francisco craton (SE Brazil) and represents the sedimentary record of a foreland basin system developed during the assembly of the West Gondwana. Different lines of evidence indicate that this basin system evolved into a confined setting, due to the overloads imposed on the western and eastern margins of the São Francisco paleoplate by the diachronic Brasília and Araçuaí orogenic systems, respectively. New whole-rock lithogeochemistry and Sm–Nd isotopic data were applied to evaluate the overall sedimentary provenance patterns of the Bambuí strata exposed in the southern portion of the São Francisco craton (i.e., within the Sete Lagoas basement high) and to identify its possible sources. Coupled (La/Yb)n and Th/Sc ratios with 147Sm/144Nd and εNd isotopes allowed the recognition of three contrasting source patterns associated with different 2nd order sequences. The lower sequence comprises carbonate ramp deposits and shows highly heterogeneous and more negative εNd ranging from −10.5 to −4.5, as well as Th/Sc and (La/Yb)n ratios between 0.6 and 0.7 and 0.54 and 0.76, respectively. The provenance patterns point toward intermediate-dominated and isotopically evolved crustal sources, with mean TDM model ages between 1.5 and 2.0 Ga. The overlying 2nd-order sequence is composed of fine-to medium-grained siliciclastics grading upward into platformal oolitic calcarenites and calcilutites. This succession exhibits homogeneous and less negative εNd(t) values between −6.8 and −5.2, with low Th/Sc (0.6–0.8) and (La/Yb)n (0.60–0.84) ratios. The uppermost Bambuí 2nd-order sequence, marked by greenish siltstones and arkoses grading upward into storm-bedded arkoses and lithic sandstones, shows homogeneous εNd(t) ranging from −8.5 to −6.1, slightly more negative than the underlying successions, and relatively higher Th/Sc and (La/Yb)n ratios ranging from 0.7 to 1.3 and 0.85 to 1.28, respectively. The Sm–Nd isotopic signature of the upper deposits indicates felsic-dominated and more isotopically juvenile crustal sources with TDM model ages of 1.5–1.7 Ga, characteristics compatible with Ediacaran arc-related rocks and post-tectonic granites exposed in the Araçuaí orogen. Our data indicate that the Proterozoic cratonic covers, their correlatives in the surrounding orogens, and magmatic rocks from the Araçuaí orogen acted as major sedimentary sources during the first evolutionary stages of the Bambuí basin-cycle in the Sete Lagoas basement high, which behaved as a forebulge depocenter. During the deposition of the overlying sequences, the Araçuaí orogen rocks became increasingly important in sourcing the Ediacaran- Cambrian foreland system in this depocenter. Besides revealing the major provenance patterns through the evolution of an ancient and partially confined foreland basin system, our data also demonstrates that even minor changes in the Sm–Nd system might be useful as reliable elements on the provenance analysis of sedimentary systems elsewhere.

Characterization of organic-rich mineral debris revealed by rapid glacier retreat, Indren Glacier, European Alps

In the summer of 2003 and 2004, characterized by a rapid glacier retreat, a stony surface covered by well-structured organic-rich mineral debris was observed very close to the Indren glacier terminus (Monte Rosa Massif, NW Italy, 3100 m ASL), on an area covered by the glacier tongue till the year before. The origin and type of this organic-rich material were investigated, in order to detect their characteristics, potential sources and fate within the foreland system. The deposits were dated using Carbon-14 and analyzed for the chemical characteristics of the organic component, the elemental composition of the mineral fraction and presence of microbial markers. The material, granular and dark in color, had a total organic carbon (TOC) content ranging between 17.4 ± 0.39 and 28.1 ± 0.63 g kg−1 dry weight (dw), significantly higher than the surrounding glacial till (~ 1.4 g kg−1 dw), although only 0.33% of it was in water soluble form. Microbial carbon (C) and nitrogen (N) accounted for 10.6% and 3.13% of TOC and total N, respectively. Dissolved nitrogen (N), mainly present as ammonium, represented 2.40% of the total N. The low aromatic component and large presence of nitrogen (N)-derived compounds suggested that most of the organic carbon (OC) in these organic-rich mineral deposits was derived from microbial cells, although the high average radiocarbon age of about 2900 years may also point to the contribution of aeolian depositions of anthropogenic or natural origin. Elemental composition and the crustal enrichment factor of trace elements in the mineral fraction of the aggregates corroborated the hypothesis that most part of the accumulated material derived from ice meltwater. Some indicators of the colonization of these deposits by microbial communities were also reported, from the abundance of DNA and phylogenetic markers, to the presence of bacterial taxa commonly able to thrive in similar habitats. All these elements suggested that such kind of deposits may have a potential role as energy and nutrient sources in recently deglaciated areas, highlighting the necessity to better understand the processes underlying their formation and their evolution.

U-Pb ZIRCON DATING OF MIDDLE EOCENE CLASTIC ROCKS FROM THE GERCUS MOLASSE, NE IRAQ: NEW CONSTRAINTS ON THEIR PROVENANCE, AND TECTONIC EVOLUTION

The provenance of Middle Eocene clastic rock from the Gercus Molasse, NE Iraq was determined by detrital zircon (DZ) U-Pb geochronology. The Gercus Molasse in the Iraqi segment of the north-eastern Zagros Thrust Zone provides an ideal example of foreland system evolution with respect to the transition from passive margin to the accretionary complex terrene-flexural foreland basins. The DZ U-Pb age spectra from the Gercus Molasse suggest that the foreland sediments either influx from multiple provenances or are the result of recycling from the accretionary complex terrane. During pre-accretion, however, the radiolarite basin (Qulqula Radiolarite, 221 Ma) located along Arabian passive margin likely acted as an intermediate sediment repository for most or all of the DZ. Representative DZ U-Pb measurements revealed that the Gercus clastic rocks fall into several separable age population ranges of 92-102 (Albian-Cenomanian), 221 (Upper Triassic), 395-511 (Cambrian), 570- 645 (Neoproterozoic), 1111 (Mesoproterozoic), and lesser numbers of Paleoproterozoic (1622-1991 Ma) ages. The source of Proterozoic detrital Zircons is enigmatic; the age peaks at 1.1, 1.5, 1.6, and 1.9 Ga (Proterozoic) does not correspond to any known outcrops of Precambrian rocks in Iraq, and it may be useful to continue to search for such basement. The detrital zircons with age populations at 0.63–0.86 Ga probably originated from the Arabian-Nubian Shield. The age peak at 0.55 Ga correlates with Cadomian Magmatism reported from north Gondwana. The age peaks at ~0.4 Ga is interpreted to represent Gondwana rifting and the opening of Paleotethys. The youngest ages populations at 93 Ma indicate that fraction of DZ were transported directly from the contemporaneously active magmatic arc (Zagros Ophiolite segments). The paleogeography and tectonic evolution of the Neogene Zagros foreland basin were reconstructed and divided into two tectonic stages. The early stage is defined by the Campanian accreted terranes (i.e. orogenic wedge) form loads sufficient to produce flexural basin with a deepest part is situated next to the tip of the loads. This flexural basin is filled by the flysch clastics of the Maastrichtian– Early Eocene (i.e. referred to by the Tanjero-Kolosh flysch sequence). The late stage is marked by a synchronized modification of the clastics fill of the basin and changes in dip directions to compensate for the reduction of the load by both erosion and extension and the basin, therefore, was sealed by a shallowing upwards depositional sequence ending with the terrestrial Gercus Formation.

Formation and Forward Propagation of the Indosinian Foreland Fold‐Thrust Belt and Nanpanjiang Foreland Basin in SW China

AbstractOrogenic growth, characterized by formation and forward propagation of fold‐thrust belts and foreland basins, is predicted by wedge models of thrust systems. The growth of the Nanpanjiang fold‐thrust belt and foreland basin system of the Indosinian orogenic belt in the southwestern South China remains poorly understood. The development of the Indosinian foreland system remains underappreciated due to few constraints on structural styles, kinematics and ages. Surface cross sections, seismic profiles and detrital zircon data are presented to address the structural styles and evolution of the Indosinian foreland system. The results reveal that the fold‐thrust belt is characterized by fault‐related folds with deeper duplexes and shallower imbricates, which yield a NNE‐SSW regional shortening magnitude of ∼36%. Our new constraints indicate that the Nanpanjiang region experienced multi‐staged thrusting during the Indosinian orogeny (D1). The D11affected the southernmost southern fold‐thrust belt, producing thick‐skinned thrusts involving Neoproterozoic basement and initiating the Nanpanjiang foreland basin. During the D12, NNE‐verging thick‐skinned thrusting continued and was followed by thin‐skinned thrusting in the northern fold‐thrust belt. Locally preserved foreland basin deposits at the northernmost Nanpanjiang Basin define D13. The progressive D14co‐axially deformed the residual basin into a wide and gentle syncline. Thus, the progressive D11to D14deformation sequence of NNE‐verging in‐sequence thrusting and foreland basin migration describe the kinematic and dynamic relationship between fold‐thrust belt and foreland basin during the Indosinian tectonic event. Indosinian D1structures were subsequently refolded by the Yanshanian tectonic event (D2), forming N‐ to NE‐striking cleavage and arcuation of D1fold axes.

Stratigraphic and paleogeographic development of a deep-marine foredeep: Central Pindos foreland basin, western Greece

This research presents a sedimentological, stratigraphic and paleocurrent analysis of the Upper Eocene to Lower Oligocene submarine fan deposits that occur in the central part of Pindos foreland basin, western Greece. Facies analysis suggests that the studied succession includes thirteen sedimentary facies and ten facies and sub-facies associations. The environments of deposition comprise abyssal plain, outer fan and inner fan deposits. Outer fan sediments are subdivided into lobe-axis, lobe off-axis, lobe-fringe and distal lobe-fringe deposits whereas, inner fan deposits include channel-fill, crevasse-splay, internal and external levee deposits. The stratigraphic analysis documents an upward transition from abyssal plain to outer and eventually to inner fan deposits suggesting progradation of the submarine fan system and progressive infilling of a deep-water sediment depocenter. The sediments were accumulated in the foredeep province of the Pindos foreland system and correspond to the underfilled stage of the system. They suggest deposition close to the onset of Pindos orogen, when sedimentation was unable to exceed the accommodation space created by lithospheric flexure. Paleocurrent data from sole marks reveal a NE-SW direction, suggesting that axial flows were dominant during the sediment deposition. The objectives of this study are to provide an updated facies model for these submarine fans and offer a robust correlation framework for the different stratigraphic units in the central Pindos foreland basin. Further, this study links for the first time the stratigraphic evolution of the deep-sea fan deposits with the evolutionary stages of the Pindos foreland system and provides new insights into the paleogeographic conditions in the Pindos foreland basin.

Late Carboniferous differential subsidence in the Campine Basin as part of the Variscan foreland system

During the Westphalian C (middle Pennsylvanian), the southeastern Campine Basin was part of the foreland of the Variscan Orogen. Deposition was dominated by rhythmic successions of coal-mudstone-sandstone sequences. Correlations between marker horizons within these sequences indicate a consistent thinning of the intercalated units towards the northwest. On seismic data, this thinning is expressed by subtly northwestwards converging intra-Westphalian C seismic reflectors. Since sedimentation kept up with subsidence, the northwestern thinning reflects a decrease in subsidence in the same direction. We interpret this asymmetric, flexural subsidence as the result of flexural downwarping of the underlying continental crust due to an increase in tectonic load generated by the Variscan Orogen that approached from the southeast. The southeastern Campine Basin was thereby situated in a Variscan foreland system, more specifically along the forebulge flank of a foredeep. The crest of the Variscan forebulge was located further northwest in the Campine Basin. The different Westphalian C units in the study area show varying percentages (between 32 and 50%) of thickness decreases in the direction of the forebulge. Our model fits with existing thickness and burial data from the surrounding areas in the Variscan foreland, and is compatible with the published forebulge migration model in the Ruhr Coal Basin.