Evolution Of Depositional Environments Research Articles

The Late Paleozoic Ice Age in western equatorial Pangea: Context for complex interactions among aeolian, alluvial, and shoreface sedimentary environments during the Late Pennsylvanian – early Permian

The evolution of depositional environments in the Late Pennsylvanian-early Permian of the Paradox Basin in Utah, USA, is investigated through detailed sedimentological and high-resolution sequence stratigraphic analyses, in order to define a model of landscape evolution, to discuss the stratigraphic model, and to evaluate the significance of the cyclicity in the paleoclimatic context. Forty high-resolution cycles integrated in 15 minor and two major cycles are observed for the first time throughout the Late Pennsylvanian-early Permian units. A-three steps landscape evolution is recognized. First, the lower Cutler beds, mainly corresponded to a marine environment, with longshore bar, subtidal, tidal, mouth-bar, and with locally fluvial deposits. The upper part of the lower Cutler beds also contains an aeolian dune. Second, the Cedar Mesa Sandstone, corresponded to broad erg deposits which are present across the entire study area, whereas longshore bar, subtidal, mouth-bar, and some fluvial deposits are mainly preserved in the northern part of the studied area. Third, the Organ Rock Formation records decreasing aeolian dune field preservation. To the south, the aeolian environments are interbedded with shoreface deposits, whereas to the north, fluvial deposits with some mouth-bars are more developed. Semi-arid climatic conditions persisted, as indicated by the presence of calcretes. Everywhere in these three steps, root traces within sandstone bars indicate that a soil was once present above the sand dunes. This new model of landscape evolution documents complex interactions between aeolian, fluvial and marine environments within the entire Permian succession of the Paradox Basin. High-resolution stratigraphic analyses allow to discuss the significance of the cyclicity in a scenario that take into consideration sea-level variation in the Late Paleozoic Ice Age paleoclimatic context. This Late Pennsylvanian to early Permian succession reflects both relative sea-level fluctuations and the variability of sediment supply.

Evolution of depositional environment of the Pliensbachian Stage (Lower Jurassic) coal‐bearing series in the Qaidam Basin, NW China

The Qaidam Basin is one of the major coal‐bearing basins in northeastern China with the coal seams mainly preserved in the Lower–Middle Jurassic. The Middle Jurassic sedimentary environment, sequence stratigraphy, paleoclimate, and coal accumulation in the Qaidam Basin have been extensively studied, while the sedimentary characteristics and depositional evolution of the Lower Jurassic coal‐bearing series are less well known. We systematically analysed the facies association, depositional system, basin evolution, and coal accumulation of the Early Jurassic Pliensbachian‐aged coal‐bearing series from the Dameigou section in the northern Qaidam Basin. Five lithological types have been identified, ranging from conglomerates, sandstones, siltstones, and mudstones to combustible organic rocks, which were further subdivided into 12 lithofacies. These lithofacies were grouped into four facies associations, representing the braided fluvial, meandering fluvial, lacustrine, and meandering fluvial‐lacustrine transition deposits, respectively. The Pliensbachian Stage mainly developed as a fluvial‐lacustrine depositional system and an evolution history from braided fluvial to meandering fluvial, then to lacustrine, and finally back to meandering fluvial was reconstructed. We suggest that climate change is the major controlling factor for depositional evolution during the Pliensbachian. The transition of the depositional environment from fluvial to lacustrine in the study area can be attributed to the rapid climatic change induced by volcanism at this interval.

Revisión de la Formación La Veteada en su estratotipo (La Rioja, Argentina): edad, estratigrafía y significado paleoambiental

The La Veteada Formation, in the Sierra de Famatina (west of Argentina), is one of the few records of Early Triassic age in South America verified by isotopic age and palynological assemblages. This unit is composed of sandstones, mudstones, shales, limestones, and marls, with some levels of gypsum, chert, and tuff levels. In its stratotype, the La Veteada Formation rests on Late Permian red beds of the Talampaya Formation and is covered by Neogene breccias and conglomerates belonging to the Del Crestón Formation. The unit is divided into three associations of sedimentary facies. Facies association A (80 m thick) is a red bed succession composed of mudstone and fine-grained sandstone, together with some levels of chert and gypsum. Facies association B (58 m thick) is greenish-gray to yellowish-gray and comprises limestones, marls, shales, and fine- to coarse-grained sandstones. This facies includes stromatolites and several levels of shales and marls where rich palynological assemblages were recovered. Finally, facies association C (24 m thick) is made up of yellowish-gray marls, mudstones, and sandstones. In this section, stromatolites are missing, thin levels of gypsum appear, and evidence of subaerial exposition as mud cracks and raindrop imprints are frequent at the top of the facies. The lithology, sedimentary structures, and vertical stacking of facies suggest that the La Veteada Formation was deposited in a lacustrine environment, which evolved from a shallow ephemeral playa lake system (facies association A) to a perennial lake, in which carbonate production increased compared to clastic sedimentation (facies association B). Regarding the facies association C, the increase in clastic supply, the missing stromatolites, and the presence of gypsum levels suggest a progressive shallowing of the lake and the likely transition to a palustrine environment. The Early Triassic age of the La Veteada Formation is indicated from two different lines of research. Firstly, a zircon U-Pb age of 249.66±0.11 Ma obtained from a tuff level at the middle part of the facies association A. Secondly, the presence of palynological species identified in other Early Triassic units worldwide. The La Veteada Formation records the filling of the embryonic extensional basins formed at the earliest Triassic. Moreover, this unit shows the evolution of depositional environments after the late Permian massive extinction event.

Sedimentary evolution and sea-level fluctuation of a Paleo-Tethyan Permian carbonate-dominated succession from central China

The Paleo-Tethys experienced major geographic, tectonic, climatologic, and environmental changes during the Permian. A newly documented and complete Permian carbonate-dominated succession (>3 km) in the Xikou section, Zhen'an, Shaanxi, central China provides a unique opportunity to record its depositional environment evolution, sea-level fluctuation, and associated paleogeographic and paleoclimatic perturbation of the eastern Paleo-Tethys. Field observation and petrographic analysis document eighteen facies and indicate evolutional facies of a carbonate ramp within the Xikou section. The vertical distribution of those facies in the Xikou section indicates a fluctuated sea-level during the Permian, which reflected the global climatic changes and was associated with eastern Paleo-Tethys evolution. The relatively low sea-level accompanied by high-frequency fluctuations during the Asselian to Artinskian may be related to the expansion of glaciation (P1 and P2), while the followed significant rising at Kungurian may reflect the major deglaciation of the Late Paleozoic Ice Age (LPIA). The abrupt falling of sea-level at the end of the Capitanian was globally synchronous and may be relevant to mid-ocean ridge spreading and superimposed with global cooling (P4), which was in accord with the skeletal grain replacement of the fusulinaceans and dasyclads by small foraminifers and Gymnocodium, and was considered as a major reason for Middle Permian Extinction. The early Wuchiapingian characterized by densely mixed sequences of carbonate and siliciclastic intervals had a highly frequent fluctuating sea-level, which may be influenced by high frequent short-term climatic variations. The sea-level falling after it reached its highest stand during the middle Wuchiapingian, was suggested as a far-field response to the expansion of the Permian glaciation episode P4, or as a result of a regional tectonic transition from extension to compression relevant to the eastern Paleo-Tethys evolution. In addition, the overall rising trend of the sea-level and the thick succession in the Xikou area suggest that the South Qinling belt was primarily under an extensional setting during the Late Carboniferous to Early Triassic, in response to Tethys rifting, which may imply the subduction of Mianlue Ocean was possibly beyond the Permian.

Modeling the Role of Compaction in the Three‐Dimensional Evolution of Depositional Environments

AbstractNatural environments such as coastal wetlands, lowland river floodplains, and deltas are formed by sediment, transported by watercourses and the sea, and deposited over century to millennium timescales. These dynamic environments host vulnerable ecosystems with an essential role for biodiversity conservation, coastal protection and human activities. The body of these landforms consists of unconsolidated sediments with high porosity and compressibility. Consequently, they often experience significant compaction due to their own weight, that is, autocompaction, which creates an important feedback within the geomorphological evolution of the landform. However, this process is generally oversimplified in morphological simulators. We present a novel finite element (FE) simulator that quantifies the impact of natural compaction on landform evolution in a three‐dimensional setting. The model couples a groundwater flow and a compaction module that interact in a time‐evolving domain following landform aggradation. The model input consists of sedimentation varying in time, space and sediment type. A Lagrangian approach underlies the model by means of an adaptive mesh. The number of FEs gradually increases to accommodate newly deposited sediments and each FE changes its shape, that is, becomes compressed, following sediment compaction. We showcase the model capabilities by simulating three long‐term depositional processes at different spatial scales: (a) vertical growth of a tidal marsh, (b) infilling of an oxbow lake, and (c) progradation of a delta lobe. Our simulations show that compaction is the primary process governing the elevation and geomorphological evolution of these landforms. This highlights that autocompaction is an important process that determines the resilience of these low‐lying landforms to climate change.

Reconstruction of the gross depositional environment evolution in the northern Malay Basin, Malaysia-Thailand joint development area (MTJDA)

This paper provides new insight on the complex interactions between regional tectonic evolution, differential subsidence across the basin, and variation in sediment supply based on a reconstruction of the gross depositional environment in the northern part of Malay Basin. In addition, the variation in sedimentary facies, established from an integrated analysis based on seismic interpretation, well-log analysis, and core evaluation, are used to establish the gross depositional environment for key surfaces within the Oligocene to Miocene succession.The basin fill comprises Oligocene syn-rift and Miocene post-rift successions. The syn-rift successions are Syn-Rift Unconformity (SRU)-Base of Syn-Rift (BSR), and Base Chattian Unconformity (BCU)-Syn-Rift Unconformity (SRU) sequences. Whereas, the post-rift successions represent by Intra-Aquitanian MFS (IAM)-Base Chattian Unconformity (BCU), Intra-Burdigalian MFS (IBM)-Intra-Aquitanian MFS (IAM), Miocene Transgressive-Regressive (MTR)-Intra-Burdigalian MFS (IBM), Intra-Serravalian MFS (ISM)-Miocene Transgressive-Regressive (MTR), and Intra-Tortonian (ITM)-Intra-Serravalian MFS (ISM) sequences.The Oligocene-early Miocene syn-rift succession in the study area is characterized by aggradational stacking patterns, with an indication of retrogradation in individual sand packages for SRU-BSR, and BCU-SRU intervals, whereas an overall aggradational stacking pattern can be observed within the IAM-BCU sequence. The depositional environment of the syn-rift succession is mainly deltaic, fluvial, alluvial fan, shallow and deep lacustrine at the basin center.The early-middle Miocene post-rift succession is characterized by mostly aggradational and fining upwards stacking within the IBM-IAM sequence. This gradually changed to a retrogradational pattern in the MTR-ISM sequence. Depositional environments for this succession consist of an alternation between fluvio-marine and sub-tidal to marine sedimentation. Depositional environments for the overlying late Miocene Intra-Tortonian to Intra-Serravalian (ITM-ISM) was estuarine or tidally-influenced environments comprising fluvial channel, tidal or distributary channel, tidal sand flat, and tidal flat deposition. This interval mainly consists of coarsening upward units that gradually changed to a stacked higher-order fining upwards package. The deeper stratigraphic units are generally more continental (non-marine) in character, but fluvio-tidally influenced marine environments became more dominant in the shallower sequences.

Nitrogen burial characteristics of Quaternary sediments and its controls on high ammonium groundwater in the Central Yangtze River Basin

As the strata sedimentary process proceeds, considerable amounts of nitrogen (N) is buried in sediments, which controls the sources and fate of N in the “groundwater-sediment” system. However, there is little concern regarding N burial characteristics in continuous sediment profiles from surface layer to deep aquifer thus far. In this study, lithology, grain size, geochronology, exchangeable N contents and geochemical proxies of sediments were analyzed to reveal the controlling mechanisms of N burial characteristics in Quaternary sediments and to interpret the enrichment of N in groundwater of central Yangtze River Basin. The results demonstrated a similar distribution trend for buried N in two sedimentary cores, which were high in the surface layer and decreased to stable in the deep aquifer. Excessive exchangeable N (EX-N) contents in sediments were mainly attributed to geologic origin. The N burial characteristics were controlled by the evolution of depositional environment: sedimentary facies determined the concentrations of total organic nitrogen (TON), further affecting the mineralization capacity of sediments; while paleoclimate regulated the intensity of the N transformation processes, ultimately influencing the actual concentrations of EX-N in sediments. In addition, due to the fast accumulation of alluvial deposits after Last Glacial Maximum and rapid development of Jianghan Lake Groups during Holocene, abundant organic matter (with high TON contents) was buried in sediments, which were still able to produce more ammonium or nitrate, and further posing continuous threats to groundwater quality. This study provided a new interpretation for the formation of high-ammonium aquifer in terms of depositional evolution.

Evolution of syn‐ to early post‐rift facies in rift basins: insights from the Cretaceous–Paleocene of the Great South Basin, New Zealand

AbstractEvolution of rift basin fill and geometry depend on the complex interactions between fault growth, sediment supply, base level changes and pre‐existing basement fabric. This study integrates multiple datasets in the Great South Basin (GSB), southeast New Zealand, and provides key insights into the evolution of depositional environments in rift basins, including the interplay between normal faulting, sediment supply and sediment dispersal patterns. It also examines the control of pre‐existing basement fabric on rift geometry and sediment distribution in the syn‐ and post rift successions. The syn‐rift is up to ~5.5 km thick in the GSB, and is underlain by several different basement terranes. Three syn‐rift stages are recognised; c.105–101, 101–90 and 90–83 Ma. During the initial syn‐rift, isolated northeast‐trending graben developed, with resultant alluvial fan/fan delta, fluvial, coastal and lacustrine sediment fill. The balance between sediment supply and accommodation space exerted considerable control on facies, especially the presence of lacustrine facies. During the later stages of syn‐rift, marine transgression occurred and connectivity between the graben developed, with shelfal, shoreface and marginal‐marine facies deposited. With marine transgression across the hinterland, sediment supply was significantly reduced in the northeast of the basin, leading to underfilling of graben, and preservation of rift topography for up to ~20 Myr after the cessation of faulting. In the west, where sediment supply was higher, rift topography was quickly filled. The NW‐trending basement terrane boundaries controlled accommodation space development during the initial stages of graben formation. Later in the syn‐ and post rift stages, these terrane boundaries formed long‐lived sediment input points into the basin, and controlled the position of repeated large deltaic depositional units.

Evolution of Depositional Environments in Response to the Holocene Sea-Level Change in the Lower Delta Plain of Nakdong River Delta, Korea

The Nakdong River delta, located in southeastern Korea, preserves thick and wide sediments, which are suitable for the high-resolution study of the evolution of depositional environments in the lower delta plain area. This study traces the Holocene evolution of the Nakdong River delta using deep drill core (ND-3; 46.60 m thick) sediments from the present delta plain. Sedimentary units of the sediments were classified based on grain size compositions and sedimentary structures: (A) alluvial zone, (B) estuarine zone, (C) shallow marine, (D) prodelta, (E) delta front, and (F) delta plain. The weathered sediment, paleosol, was observed at 43.16 m below the surface. There is an unconformity (43.10 m) to separate a Pleistocene sediment layer in the lowermost part differentiating from a Holocene sediment layer in the upper part of the core. The shallow marine sedimentary unit (32.20~23.50 m), in which grain size decreases upward is overlain by the prodelta unit (23.50~15.10 m), which consists of fine-grained sediments and relatively homogeneous sedimentary facies. The boundary between the delta front unit (15.10~8.00 m) and the delta plain unit (8.00~0.00 m) appears to lie at 8.0 m, and the variation in grain size is different; coarsening upward in the delta front unit and fining upward in the delta front unit, respectively. These sediments are characterized by a lot of sand–mud couplets and mica flakes aligned along with cross-stratification, which may be deposited in relatively high-energy environments. Until 13 cal ka BP, the sea level was 70 m below the present level and the drilling site might be located onshore. At 10 cal ka BP, the sea level was located 50 m below the present level and the drilling site might be moved to an estuarine environment. From 8 to 6 cal ka BP, a transgression phase occurred as a result of coastline invasion by the rapid rise of the sea level. Thus, the drilling site was drowned in a shallow marine environment. After 6 cal ka BP, the sea level reached the present level, and, since then, progradation might begin to form, primarily by more sediment input. After this period, the progradation phase continues as the sediments have advanced and the delta grows.

Geochemical Characteristics, Hydrocarbon Potential, and Depositional Environment Evolution of Fine-Grained Mixed Source Rocks in the Permian Lucaogou Formation, Jimusaer Sag, Junggar Basin

The Permian Lucaogou Formation (P2l) in the Jimusaer Sag, Junggar Basin is an essential source rock and a tight oil-producing layer in China. The source rock of the Lucaogou Formation is characteri...

Early Jurassic palaeoenvironments in the Surat Basin, Australia – marine incursion into eastern Gondwana

AbstractInterpretations of palaeodepositional environments are important for reconstructing Earth history. Only a few maps showing the Jurassic depositional environments in eastern Australia currently exist. Consequently, a detailed understanding of the setting of Australia in Gondwana is lacking. Core, wireline logs, two‐dimensional and three‐dimensional seismic from the Precipice Sandstone and Evergreen Formation in the Surat Basin have been used to construct maps showing the evolution of depositional environments through the Early Jurassic. The results indicate the succession consists of three third‐order sequences (Sequence 1 to Sequence 3) that were controlled by eustatic sea level. The lowstand systems tract in Sequence 1 comprises braidplain deposits, confined to a fairway that parallels the basin centre. The strata were initially deposited in two sub‐basins, with rivers flowing in different orientations in each sub‐basin. The transgressive systems tract of Sequence 1 to lowstand systems tract of Sequence 3 is dominated by fluvio–deltaic systems infilling a single merged basin centre. Finally, the transgressive and highstand systems tracts of Sequence 3 show nearshore environments depositing sediment into a shallow marine basin. In the youngest part of this interval, ironstone shoals are the most conspicuous facies, the thickness and number of which increase towards the north and east. This study interprets a corridor to the open ocean through the Clarence–Moreton Basin, or the Carpentaria and Papuan basins, evidence of which has been eroded. These results challenge a commonly held view that eastern Australia was not influenced by eustasy, and propose a more dynamic palaeogeographic setting comprising a mixture of fluvial, deltaic and shallow marine sedimentary environments. This work can be used to unravel the stratigraphic relationships between Mesozoic eastern Australian basins, or in other basins globally as an analogue for understanding the complex interplay of paralic depositional systems in data poor areas.

Environmental setting of the Cambrian Terreneuvian rocks from the southwestern Yangtze Platform, South China

Terreneuvian strata from the western Yangtze Platform host diverse assemblages of small shelly fossils (SSFs), which are key for understanding the Cambrian Bioradiation Event and have been the objects of numerous geochemical studies to understand environmental factors during Fortunian and Cambrian Age 2. The region has been proposed to host the vacant stratotype of Cambrian Stage 2. However, a comprehensive study of paleogeography and evolution of sedimentary facies for the Terreneuvian is still lacking. Here we present a detailed sedimentological and petrographic study of six stratigraphic sections from the western Yangtze Platform. Eleven depositional environments (facies associations) are proposed based on the characterization of twenty-five facies. We further reconstruct palaeogeographic model based on the evolution of depositional environments and discuss the formation of phosphorites. The Zhujiaqing Formation deposited diachronously on the Ediacaran strata, and facies associations range from tidal flats, shoal, back-shoal to semi-restricted and energetic subtidal. As sedimentation continued, protected shallow subtidal became widespread. Evidence presented from the Zhujiaqing Formation indicates that strata in the laolin section are more continuous than those on other parts of the Yangtze Platform. However, stratigraphic condensation and the protected and partly restricted environment should be taken into consideration when discussing a proposed global GSSP “Laolinian Stage” (Cambrian Stage 2). In-situ phosphates formed in various environments, which argues against the previous assumption that primary phosphate formed only in isolated embayments. Concentration of granular phosphorites occurred in shoal areas by winnowing and reworking of in-situ phosphate and phosphatized skeletons, while in the intra-platform basin, repeated alternations of syndepositional phosphogenesis, current reworking, and amalgamation of storm-generated phosphatic event beds contributed to the concentration of granular phosphorites.

Comprehensive REE + Y and sensitive redox trace elements of Algerian phosphorites (Tébessa, eastern Algeria): A geochemical study and depositional environments tracking

The Algerian sedimentary phosphorites of marine origin are located mainly in the Tébessa region, which is part of the Eastern Saharan Atlas. These phosphorites are hosted by Paleocene-Eocene series and crop out in two main sedimentary areas: the northern sites (Djebel El Kouif, Djebel Dyr and Djebel Tazbant) and the southern sites, which include the Djebel Onk commercial world-class ore deposits that are represented in this study by the Kef Essenoun sector. This study reports a detailed investigation of these phosphorites at a regional scale and is aimed to characterizing the evolution of their depositional environments. Field and laboratory works consist of a systematic sampling of outcrops, petrographical (OM and SEM-EDS), mineralogical (XRPD) and chemical (major, trace and rare earth elements by ICP-MS) analyses associated with a PCA statistical treatment. The time-wise evolution of the depositional environments was constrained based on rare earth elements (REE) and selected redox sensitive element proxies, such as Ce, Eu, Y, Mn, U and V.The results show that the phosphorites have a granular fabric with variable grain sizes. The grains can contain micro-remains and impurities related to their origin, which was most often fecal pellets. Carbonate fluor-apatite is the main mineral phase in these phosphorites, where P2O5 contents show large variations between different outcrops (average from 18.39 to 30.16 wt%). A marked evolution of depositional environments is observed in their vertical trends from sub-reduced and sub-oxic in the lower beds to rather oxic conditions in the upper layers. This evolution shows a significant shift along the sedimentary profiles reflecting more open connection to Tethyan seawater towards younging trend. These results contrast remarkable changes of depositional conditions during Paleocene–Eocene transition.

Ichnology and depositional environments of the Upper Cretaceous Dinosaur Park – Bearpaw formation transition in the Cypress Hills region of Southwestern Saskatchewan, Canada

The upper Campanian Dinosaur Park Formation (DPF) is a south- and eastward-thinning fluvial to marginal-marine clastic wedge in the Western Canadian Sedimentary Basin. The DPF is overlain by the Bearpaw Formation (BF), a fully marine clastic succession representing the final major transgression of this epicontinental sea across western North America. In southwestern Saskatchewan, the DPF is comprised of marginal-marine coal, carbonaceous shale, and heterolithic siltstone and sandstone grading vertically into marine sandstone and shale of the BF. Historically these deposits have been interpreted as the record of fluvial delta systems along a paleocoastline. This study revisits this interpretation using integration of ichnologic, sedimentologic, and sequence stratigraphic concepts.Detailed facies analysis indicates the upper DPF does not record sedimentation in a delta system, but rather was deposited in a low-relief coastal plain with a wave-dominated, tidally influenced, fluvially modified shoreline. Marginal-marine facies, interpreted as lagoons, tidal flats and estuaries, are bioturbated, showing a typical brackish-water trace-fossil assemblage, including Asterosoma isp., Chondrites isp., Cylindrichnus concentricus, Teichichnus rectus, and Skolithos isp. Fine-grained sandstone was deposited in an estuarine mouth-bar and barrier-island complex that protected the coast from wave reworking. As the seaway transgressed across the coast, fully marine wave-dominated parasequences replaced those of the coastal plain. Typical trace fossils include Asterosoma isp., Chondrites isp., Diplocraterion isp., Nereites missouriensis, Phycosiphon incertum, Planolites isp., Rhizocorallium isp., and Zoophycos isp., reflecting open, fully marine conditions. This study provides new insights into the evolution of depositional environments in the Late Cretaceous of southwestern Saskatchewan, and provides a framework for further geological and paleontological studies ongoing in the region.

Variation of Hg content in low sulfur coals in relation to the coal-forming environment: a case study from Zhuji Coal Mine, Huainan Coalfield, North China

Twenty-nine low sulfur coal samples were selected to determine the magnitude and variability of mercury (Hg) content in a well-documented stratigraphy system including ten continuous coal seams in Zhuji Coal Mine, Huainan Coalfield, Anhui Province, North China. Mercury content of samples was measured on a direct mercury analyzer and confident results were obtained as evaluated by standard references, sample replicates and procedural blanks. The calculated overall mine average Hg content is 71.19 ± 9.28 ng/g based on seam averages and weighting by the estimated reserve of each coal seam. The estimated Hg emission potential for Huainan coalfield is obviously lower than that calculated from coal emission factor in industrial use. An increasing trend of Hg content with the evolution of depositional environment was observed from Nos. 3 to 11-2 coal seams. Combining the evidence of sedimentology and paleontology, a better understanding was gained of the mechanism of Hg sequestration in specific coal benches. A large portion of Hg residing in the low sulfur coals presumably integrated to the functional groups of organic constitution, whereas pyrite was generally abundant in the high sulfur coals.

Structural controls on sedimentation during asymmetric extension: The case of Sorbas Basin (SE Spain)

Understanding the link between sedimentation and fault kinematics is important for reconstructing the evolution of sedimentary basins. The relationship between the mechanics of creating accommodation space and the sediment supply in asymmetric extensional basins is critical for quantifying their syn- and post-rift evolution, but is not yet well understood. One exceptional place to analyze such mechanics of normal faulting and its relationship with the evolution of depositional environments is the Sorbas Basin in the Betic Cordillera of SE Spain. We have analyzed the interplay between extension and deposition by means of a detailed sedimentological and field kinematic study. The results indicate a novel and coupled evolution, characterized by low-order tectonically induced sedimentary successions driven by the change of deformation style and high-order tectonically induced sedimentary successions driven by individual stages of fault activity. Fault mechanics and hanging-wall tilting control the formation of depositional slopes, while footwall exhumation induces enhanced sourcing of coarse sediments that may be stored in proximal areas or recycled in the basin during episodes of fault activity. Following initiation of extension, the subsequent syn-kinematic deposition was characterized by a wide spectrum of subaqueous gravity flows, whose types and transformation mechanisms were controlled by the style of normal faulting, sediment supply and basin physiography. Furthermore, the study quantifies the controls of rheological stratified sediments on normal faulting mechanics and their implications for the spatial and temporal basin evolution.

Early Triassic environmental dynamics and microbial development during the Smithian–Spathian transition (Lower Weber Canyon, Utah, USA)

The Early Triassic biotic recovery following the end-Permian mass extinction is well documented in the Smithian–Spathian Thaynes Group of the western USA basin. This sedimentary succession is commonly interpreted as recording harsh conditions of various shallow marine environments where microbial structures flourished. However, recent studies questioned the relevance of the classical view of long-lasting deleterious post-crisis conditions and suggested a rapid diversification of some marine ecosystems during the Early Triassic. Using field and microfacies analyses, we investigate a well-preserved Early Triassic marine sedimentary succession in Lower Weber Canyon (Utah, USA). The identification of microbial structures and their depositional settings provide insights on factors controlling their morphologies and distribution. The Lower Weber Canyon sediments record the vertical evolution of depositional environments from a middle Smithian microbial and dolosiliciclastic peritidal system to a late Smithian-early Spathian bioclastic, muddy mid ramp. The microbial deposits are interpreted as Microbially Induced Sedimentary Structures (MISS) that developed either (1) in a subtidal mid ramp where microbial wrinkles and chips are associated with megaripples characterizing hydrodynamic conditions of lower flow regime, or (2) in protected areas of inter- to subtidal inner ramp where they formed laminae and domal structures. Integrated with other published data, our investigations highlight that the distribution of these microbial structures was influenced by the combined effects of bathymetry, hydrodynamic conditions, lithology of the substrat physico-chemical characteristics of the depositional environment and by the regional relative sea-level fluctuations. Thus, we suggest that local environmental factors and basin dynamics primarily controlled the modalities of microbial development and preservation during the Early Triassic in the western USA basin.

Petrographic Characteristics and Depositional Environment Evolution of Middle Miocene Sediments in the Thien Ung - Mang Cau Structure of Nam Con Son Basin

DOI: 10.17014/ijog.4.3.143-157This paper introduces the petrographic characteristics and depositional environment of Middle Miocene rocks of the Thien Ung - Mang Cau structure in the central area of Nam Con Son Basin based on the results of analyzing thin sections and structural characteristics of core samples. Middle Miocene sedimentary rocks in the studied area can be divided into three groups: (1) Group of terrigenous rocks comprising greywacke sandstone, arkosic sandstone, lithic-quartz sandstone, greywacke-lithic sandstone, oligomictic siltstone, and bitumenous claystone; (2) Group of carbonate rocks comprising dolomitic limestone and bituminous limestone; (3) Mixed group comprising calcareous sandstone, calcarinate sandstone, arenaceous limestone, calcareous claystone, calcareous silty claystone, dolomitic limestone containing silt, and bitumen. The depositional environment is expressed through petrographic characteristics and structure of the sedimentary rocks in core samples. The greywacke and arkosic sandstones are of medium grain size, poor sorting and roundness, and siliceous cement characterizing the alluvial and estuarine fan environment expressed by massive structure of core samples. The mixed calcareous limestone, arenaceous dolomitic limestone, and calcareous and bituminous clayey siltstone in the core samples are of turbulent flow structure characterizing shallow bay environment with the action of bottom currents. The dolomitic limestones are of relatively homogeneous, of microgranular and fine-granular texture, precipitated in a weakly reducing, semi-closed, and relatively calm bay environment.

Reconstructing the Holocene depositional environments along the northern coast of Sfax (Tunisia): Mineralogical and sedimentological approaches

A sedimentological and mineralogical study of sedimentary cores allowed reconstructing the evolution of depositional environments along the Northern coast of Sfax (Tunisia). The aim of this research work is to identify the factors controlling the sedimentation from the Holocene to the Present time. Three 30-m sediment cores collected by drilling at 30 m water depth were analyzed for their color, magnetic susceptibility signal, grain size by laser diffraction, organic matter content by loss of ignition, carbonate content by calcimetry and mineralogy by X-ray diffraction on bulk powder and clay <2 μm. They broadly present the same sedimentological and mineralogical features. Microscopical observations of petrographic slides allowed identifying six main sedimentary facies. Bulk mineralogical assemblages comprised clay minerals, quartz, calcite, gypsum and K-feldspars were examined. Considerable change was observed in the carbonate content that mimicked the bioclaste abundance and diluted the detrital minerals (clay minerals, quartz and feldspars). The gypsum mainly occurred in the lower sedimentary columns (SC12 and SC9) and in the upper/middle of core SC6. The clay fraction was made of a mixture of kaolinite, illite, smectite and palygorskite with no clear variation through core depth. Both grain-size parameters and magnetic susceptibility profile showed a sharp transition in the upper 2–5 m of the sedimentological columns. Coarse, sandy to gravely sediments characterized by a low magnetic susceptibility signal were replaced by fine bioclastic-rich clayey sediments. The analysis of vertical succession of depositional facies revealed a fluvial depositional environment (coastal plain) basically marked by fluvial channels and inundation plains at the bottom of all cores. However, core-top sediments recorded a littoral marine environment with sand depositions rich in gastropods, lamellibranches and algæ. Depositional facies, sedimentological and mineralogical parameters were consistent with a transition from a fluviatile depositional environment with some emersion phases marked by the gypsum precipitation, to a marine littoral environment. Such evolution was accompanied with a relative sea-level rise which flooded the fluvial system at the coastal plain during the Holocene, in agreement with sea-level fluctuations in southeast Tunisia during the Holocene.

Lithostratigraphy and geochemistry of Upper Vendian‒Lower Cambrian deposits in the northeastern Baltic monocline

The results of investigations of Upper Vendian‒Lower Cambrian deposits in the northeastern part of the Baltic monocline specify views on the evolution of depositional environments of sedimentary successions constituting the basal part of the sedimentary cover in inner areas of the northwestern East European Platform. It is shown that the Late Vendian and initial Cambrian were characterized by the consecutive influx of relatively mature terrigenous detrital material that originated from both the weathering crust of the Baltic Shield and new sources. Its deposition was interrupted by notable, although likely asynchronous, hiatuses, which are registered at the base of the Upper Vendian Vasileostrovskaya and Voronkovo formations and Lower Cambrian Lomonosov Formation. In the Late Vendian, sedimentary material was transported from the Baltic Shield, while beginning from the initial Early Cambrian the additional contribution to the formation of the sedimentary cover of the Baltic monocline was provided by coarse-grained sedimentary material from the Timan margin of the Baltica as follows from U‒Pb isotopic ages obtained for detrital zircons. At the same time, lithogeochemical parameters of fine-grained rocks experienced no substantial changes.