Siliciclastic Succession Research Articles

Evolution and palaeoenvironmental migration of a Cambrian undermat miner

Microbial mats sealed the sea bottom, becoming the food supply of many early metazoans, which exploited this resource in multiple ways during the late Ediacaran and earliest Cambrian. The onset of highly penetrative bioturbation in shallow-marine environments later in the early Cambrian removed this seal, resulting in the protracted restriction of microbial mats to marginal- and deep-marine environments. In this study, we demonstrate that the undermat-miner trace fossil Oldhamia followed the pattern of matground restriction to deep-marine environments. This is shown by a dataset compilation of Cambrian Oldhamia based on a comprehensive review of the literature with addition of recently discovered Oldhamia in the Cambrian strata of North and South China. Oldhamia is one of the most distinctive and widely distributed ichnogenera in early to middle Cambrian siliciclastic successions. It consists of semi-permanent, very shallow-tier, undermat-miner structures produced by stationary vermiform organisms. Despite its importance, details of Oldhamia ichnodiversity trajectories at ichnospecies level, environmental trends, and potential palaeogeographic patterns have not been explored. Our results demonstrate that Oldhamia displays high diversification in Fortunian shallow- and deep-marine settings, representing a signal of the Cambrian Information Revolution. Oldhamia alata and O. geniculata only occurred in shallow-marine settings, O. curvata and O. flabellata were restricted to the deep sea, and O. antiqua and O. radiata ranged from shallow- to deep-marine settings. The producers of Oldhamia retreated into deep sea since the end of the Fortunian mirroring the restriction of matgrounds as a response of intense bioturbation in shallow-marine deposits during the Agronomic Revolution. The producers of Oldhamia originated from the Iapetus Ocean and then migrated into other oceans, most likely through dispersal assisted by ocean currents.

The early–middle Cambrian siliciclastic tide‐dominated succession in eastern Korea

AbstractThe basal Taebaek Group (Myeonsan and Myobong formations) illustrates second‐order transgression on the eastern Sino‐Korean Block during the early–middle Cambrian (Stage 3?–Wuliuan). The irregular palaeotopography of Precambrian basement led to the development of localised alluvial fans and fan deltas. As transgression continued, tidally influenced estuarine and associated shallow subtidal flats developed. Continued transgression resulted in a relatively deep subtidal environment, with postulated carbonate shoals serving as barriers. Stacking of facies indicates a general deepening‐upward trend, transitioning from terrestrial–nearshore to marine environments dominated by tidal effects. The study area subsequently experienced shallowing, leading to the emergence of tidal inlet and dune environments. Siliciclastic input was attenuated, facilitating the development of carbonate shoal complexes. The overall transgressive succession of the basal Taebaek Group aligns with similar sequences observed in the Sino‐Korean Block and western Laurentia, where the lowermost Cambrian strata which formed in various depositional environments on the uneven basement rocks were followed by extensive tide‐dominated siliciclastic successions. These successions were then overlain by epeiric carbonate platforms that developed synchronously across the area as siliciclastic input diminished with the continued transgression. This comparison demonstrates that the transgressive sequences in the Sino‐Korean Block and western Laurentia can be understood within a framework that explains how extensive Cambrian carbonate platforms initially developed due to a second‐order eustatic sea‐level rise during the Cambrian greenhouse period.

Tracing uplift and erosion in orogenic settings using quartz luminescence sensitivity: Insights from the Northern Andes uplift

The optically stimulated luminescence (OSL) sensitivity of the fast component in quartz has been increasingly used in provenance analysis of Quaternary sediments. Quartz OSL natural sensitization is thought to be mainly controlled by the formation conditions of the source bedrock and surface processes occurring mainly in sediment source areas. Thus, quartz OSL sensitivity can be linked to distinct sediment source regions, based on their tectonic setting and erosion conditions. In this way, changes in quartz OSL sensitivity within siliciclastic successions would track variations in sediment provenance. So far, few works evaluated how the OSL sensitivity of quartz sand grains varies in sedimentary successions that experienced long-term cycles of deep burial, exhumation, and erosion. Therefore, this work aims to characterize the sensitivity of the fast OSL component of quartz sand grains retrieved from the Cenozoic sedimentary rocks of the Northern Andes basins and assess its spatiotemporal changes. We found that quartz grains with the lowest OSL sensitivity are sourced by crystalline and volcanic rocks related to the Andean Continental Arc emplaced in the Colombian Central Cordillera, reflecting the onset of denudation in orogenic sources during the Paleocene. Subsequently, increasing trends in OSL sensitivity are related to the sedimentary recycling during the Andean orogeny, reaching maximum values as a result of the progressive unroofing of Cretaceous rocks in the Colombian Eastern Cordillera, originally sourced from the low-relief Amazon Craton. Changes in quartz OSL sensitivity measured in the Cenozoic sedimentary basin-fill sequences of the Northern Andes vary according to the shifts in sediment provenance related to the orogenic construction and sediment recycling of the Andean range.

Depositional architecture of the tide-dominated late Oligocene hydrocarbon reservoirs in the Tapti-Daman block, Mumbai Offshore basin, India

The intricate interaction between tidal and river currents across a gently sloping shelf area complicates the geological interpretation of sedimentary deposits in subsurface sections. This study comprehensively analyzes the depositional framework and facies architecture in the late Oligocene siliciclastic succession of the Daman Formation, Mumbai Offshore Basin, which shows subtle changes in depositional stacking pattern in response to shoreline shifts. The late Oligocene siliciclastic succession being a major hydrocarbon producer in the Mumbai Offshore Basin; this research also aims to enhance the optimization of reserve exploitation and prospectivity evaluation. A detailed analysis was conducted using well-logs and seismic data integrated with available geological data. The Oligo-Miocene sequence demonstrates a coarsening-upward facies trend until the late Oligocene, followed by a fining-upward facies trend during the early Miocene and characterized by numerous stacked sandstone layers. The facies distribution pattern, sedimentary characteristics, and progradational geometry suggest a deltaic system dominated by tides for the late Oligocene succession and the latter part of the early Oligocene succession. The early Miocene succession shows a reversal in depositional trend with a retrogradation pattern. The late Oligocene deltaic deposits show a very high sediment load deposited during the peak river discharge from the Narmada-Tapti River system. The gentle depositional slope allowed redistribution of sediments by tidal currents. The deltaic system was further resolved into subaqueous mouth bar, delta front, and prodelta facies associations based on facies modeling. The correlation of the facies model with the regional depositional setup indicates that the late Oligocene succession corresponds to a third-order highstand system tract (HST) cycle.

Tectonostratigraphy of the Upper Jurassic-Lower Cretaceous siliciclastic (Shurijeh Formation) in the eastern Kopeh Dagh fold and thrust belt, Iran

During the Late Jurassic-Early Cretaceous, a significant gas-bearing siliciclastic succession was deposited in the Kopeh Dagh fold-thrust belt in northeastern Iran. Study of the regional evolution of depositional system and geodynamic setting of the red beds continental strata can help in a better understanding of the development of an intracontinental extension in this part of the Eurasia Plate. However, this evolution is driven by faulting events that are not fully understood. Facies analysis in wells and outcrops of the Upper Jurassic-Lower Cretaceous Mozduran and Shurijeh formations in the Saleh Abad area, the easternmost part of the Kopeh Dagh Basin, led to the identification of two fluvial braided river systems in the Shurijeh Formation. Provenance and sedimentological studies indicate that siliciclastic sediments were supplied from the south into the north during the Late Jurassic-Early Cretaceous in the Kopeh Dagh Basin. The higher compositional and textural maturity in the upper part of the Shurijeh Formation relative to the lower part indicate more recycling and more extensive transport of the sediments. Two stages of normal faulting can be identified based on the tectonostratigraphic evolution in this interval: The first phase was initiated with polymictic conglomerates during the Late Jurassic in the lower part of the Shurijeh Formation, while the basin-controlling fault was a buried structure. The second phase started with an influx of quartz conglomerates when the basin-controlling fault reached the surface in the middle part of the Shurijeh Formation. This study integrates new field observations and interpretations to enhance understanding of a complex history of multiphase deformation controlled facies patterns, structural geometries of the Late Jurassic-Early Cretaceous. Renewed Cretaceous extension generated accommodation space for the transgressive Shurijeh Formation.

Depositional facies controls on reservoir rock typing and heterogeneity: Devonian siliciclastic succession, south central Ghadames basin, Libya

The Devonian sedimentary succession hosts the most potential reservoir targets in Ghadames Basin, Northwest Libya. This succession consists of a complex pattern of siliciclastic facies deposited during successive episodes of sea level fall and rise, thereby leading to a large scale heterogeneity in sandstone facies connectivity and distribution. The present study integrates core sedimentology, wireline logs, and routine and special core analysis to establish a framework for predicting the distribution of the best Devonian reservoir rock types (RRTs). A lowstand amalgamated fluvial sandstone bars only exist in the Lower Devonian Tadrart Formation; the other Devonian rock units consist of transgressive and highstand tidally-influenced estuarine and deltaic facies. The pore system characteristics are controlled by initial depositional attributes where open, megapores with entry displacement pressures <10 psi occur in the quartzose, high energy fluvial sandstone bars, delta distributary channels and mouth bars. These facies are classified as RRTI and are mostly associated with lowstand and late highstand facies. In contrast, the other RRTs display tight pore system with elevated irreducible water content >20%. RRTI rocks account for greater than 90% of the fluid flow capacity in the Devonian reservoirs. A link between the facies depositional setting, RRT distribution, vertical amalgamation and lateral compartmentalization of flow conduits, barriers and baffles zones has been proposed, thereby promoting the predictability of the best reservoir targets.

Geochemical fingerprinting of continental crust trapped in Cadomian volcanic arcs along northern Gondwana

During the Ediacaran to Cambrian periods, the extensive Avalonian–Cadomian accretionary orogen formed along the northern margin of the Gondwana (Pannotia) supercontinent. One of the best-preserved magmatic arcs within this orogenic system is the Davle volcanic complex (DVC) in the Teplá–Barrandian unit of the Bohemian Massif. Using detailed field observations, petrography, major/trace element concentrations, Nd–Hf isotopic compositions as well as U–Pb zircon dating, we interpret a complex evolutionary history of the DVC as comprising three main stages. The first stage (∼610–570 Ma) is represented by a volcano-plutonic association of andesite, dacite, rhyolite and tonalite–trondhjemite–granodiorite (metamorphosed to orthogneiss). A wide range of major/trace element contents together with highly variable εNd values (+3.6 to –5.1) suggest derivation from a juvenile (mantle-derived) source with subsequent assimilation of cratonic crust during magma emplacement, also supported by the modelling of the assimilation–fractional crystallization (AFC) process. The second stage (∼580–560 Ma) is characterized by a gradual termination of the volcanic arc activity, followed by a deposition of marine siliciclastic succession comprising, from the bottom to the top, laminated tuffs, silicified black shales (Lečice Member), and a thick turbidite greywacke–shale–conglomerate sequence (Štěchovice Group). The third stage of poorly constrained age (∼570–500 Ma) is represented by an intra-arc extension and intrusion of juvenile trondhjemite and related rhyolite dykes (εNd +4.8 to +8.4). Finally, we compare these findings with zircon U–Pb ages and whole-rock Nd isotopic data from other Cadomian terranes and propose that the cratonic crust played an important role in recycling along the whole orogenic belt. Thus, we conclude that the Cadomian Orogen formed as a collage of fringing (such as modern Japan, Taiwan, or Philippines) and continental (as modern Andes) arcs of variable evolutionary stages rather than as a belt dominated by intra-oceanic island arcs.

The Lower Cambrian deposits of the Le Rozel Formation (Normandy, NW France): Insight into a newly described ichnofossil assemblage

The rise of morphological complexity and taxonomic diversity of trace fossils during the Cambrian Period has been a prominent focus to track the evolution and diversification of early animals. Here, we present a newly described trace fossil assemblage from the lower Cambrian Le Rozel Formation in Normandy (Northwestern France) composed of the following ichnogenera: Archaeonassa, Bergaueria, Helminthoidichnites, Helminthopsis, Nereites, Psammichnites, and Treptichnus. Trace fossils are exquisitely preserved on top of strata (i.e., epirelief), and are distributed through the entire thickness of the siliciclastic succession of about 200 m. This thick sedimentary succession shows sedimentary environments with ripples generated by unidirectional current processes or by oscillatory processes, such as hummocky cross-stratification (HCS) storm facies, tidal facies with flaser stratification, and unidirectional current ripples. In addition, syneresis cracks and microbially induced sedimentary structures (MISS) suggest that the Le Rozel Formation was deposited in a shallow marine shelf environment. New U-Pb dating of detrital zircon grains suggests a late Ediacaran maximum deposition age of 549 ± 3 Ma. This dating is supplemented by the substantial preservation of the three-dimensional burrow systems (Treptichnus pedum) and the large sediment bulldozers (Nereites, Psammichnites). Collectively, our findings suggest that the trace fossils assemblage was deposited during the Terreneuvian Epoch, beneath the first archaeocyaths and the first trilobite-bearing facies from both other lower Cambrian Carteret and Saint-Jean-de-la-Rivière Formation. The ichnofauna described from the Le Rozel Formation complements the worldwide trace fossil record around this critical time of life history.

Geology, geochemistry, mineralization and fluid inclusion characteristics of the SW of Hormuz Island banded iron formations, southern Iran

The Hormuz Island banded iron formations (HIBIFs) are situated at the Zagros Folded Zone in southern Iran. The BIFs occur intercalated with the Neoproterozoic Hormuz series, an evaporite and siliciclastic succession with pyroclastic rocks, and were deposited on the continental rift margin of the Arabian plate. The HIBIFs are banded rocks consisting of the alternation of dark Fe-rich and reddish-brown Si-rich layers, and belong to oxide facies iron formations. The post-Archean Australian shale normalized rare earth elements and yttrium patterns of HIBIFs have the characteristics of both hydrothermal solutions and seawater. The sharp positive Eu anomaly (2.10–6.90) may be inherited from high-temperature hydrothermal solutions, while slightly negative Ce anomalies (0.57–0.82) are inherited from seawater. The homogenization temperature and salinity of primary fluid inclusions range from 180.7 to 474.3°C and from 2.24 to 12.85 wt% NaCl, respectively, which suggests that intermediate- to high-temperature hydrothermal fluids and seawater contributed to the formation of the HIBIFs. The Eu/Sm and Sm/Yb ratios in BIFs are between the values of hydrothermal fluids and seawater. In summary, all geological and geochemical data suggest that the HIBIFs are a post-great oxidation event iron formation pulse at the end of the Ediacaran period. However, this is actually not similar to Neoproterozoic syn-glacial iron formations. Instead, this is a new occurrence of iron formation in an overlooked/understudied time period when either global or local conditions were conducive to iron deposition. The iron deposition on Hormuz Island does not appear to be triggered by fluctuating atmospheric oxygen or sea-level variations, but instead may be related to syn-basinal volcanism in the active continental rift margin environment in anoxic submarine condition. Thematic collection: This article is part of the Geochemical processes related to mined, milled, or natural metal deposits collection available at: https://www.lyellcollection.org/topic/collections/geochemical-processes-related-to-mined-milled-or-natural-metal-deposits

A shift in redox conditions near the Ediacaran/Cambrian transition and its possible influence on early animal evolution, Corumbá Group, Brazil

The Ediacaran–Cambrian transition witnessed some of the most important biological, tectonic, climatic and geochemical changes in Earth’s history. Of utmost importance for early animal evolution is the likely shift in redox conditions of bottom waters, which might have taken place in distinct pulses during the late Ediacaran and early Paleozoic. To track redox changes during this transition, we present new trace element, total organic carbon and both inorganic and organic carbon isotopes, and the first iron speciation data on the Tamengo and Guaicurus formations of the Corumbá Group in western Brazil, which record important paleobiological changes between 555 Ma to < 541 Ma. The stratigraphically older Tamengo Formation is composed mainly of limestone with interbedded marls and mudrocks, and bears fragments of upper Ediacaran biomineralized fossils such as Cloudina lucianoi and Corumbella werneri. The younger Guaicurus Formation represents a regional transgression of the shallow carbonate platform and is composed of a homogeneous fine-grained siliciclastic succession, bearing meiofaunal bilateral burrows. The new iron speciation data reveal predominantly anoxic and ferruginous (non-sulfidic) bottom water conditions during deposition of the Tamengo Formation, with FeHR/FeT around 0.8 and FePy/FeHR below 0.7. The transition from the Tamengo to the Guaicurus Formation is marked by a stratigraphically rapid drop in FeHR/FeT to below 0.2, recording a shift to likely oxic bottom waters, which persist upsection. Redox-sensitive element (RSE) concentrations are muted in both formations, but consistent with non-sulfidic bottom water conditions throughout. We interpret the collected data to reflect a transition between two distinct paleoenvironmental settings. The Tamengo Formation represents an environment with anoxic bottom waters, with fragments of biomineralized organisms that lived on shallower, probably mildly oxygenated surficial waters, and that were then transported down-slope. Similar to coeval successions (e.g., the Nama Group in Namibia), our data support the hypothesis that late Ediacaran biomineralized organisms lived in a thin oxygenated surface layer above a relatively shallow chemocline. The Guaicurus Formation, on the other hand, records the expansion of oxic conditions to deeper waters during a sea level rise. Although the relationship between global biogeochemical changes and the activities of early bioturbators remains complex, these results demonstrate an unequivocal synchronous relationship between oxygenation of the Corumbá basin and the local appearance of meiofaunal bioturbators.

Upper Cambrian–Lower Ordovician conodonts from the southern margin of the Kopet-Dagh Basin, Saluk Mountains, Iran

A detailed Furongian to Tremadocian conodont biostratigraphy is established from the Saluk Mountains located in southern Kopet-Dagh, northeast Iran. Thirty species assigned to 17 genera were recovered from decimetre-scale limestone beds in a fine-grained siliciclastic succession, deposited in an intraplate rift system. The following biozones are established for the region, in ascending order: Proconodontus muelleri, Eoconodontus, Cordylodus intermedius, Cordylodus lindstromi, Cordylodus angulatus, Paltodus deltifer and Acodus triangularis interval zone. This low-to medium-richness conodont fauna comprises cosmopolitan euconodont species of Proconodontus, Eoconodontus, Cordylodus, Teridontus nakamurai, Semiacontiodus nogamii and a few long- ranging proto- and paraconodont species, which inhabited a narrow marine basin flanked by landmasses and formed by active rifting. It lacks shallow water tropical taxa and probably belongs to the Cold Domain of the Shallow Sea Realm. The occurrence of conodonts of the Paltodus deltifer Biozone in the uppermost part of the Qyzlar Formation in the Ghelli section suggests that the major episode of flood basalt volcanism in south Kopet-Dagh commenced in the late Tremadocian. Hadi Jahangir [Jahangir.hadi@nigpas.ac.cn] and Guanzhou Yan [gzyan@nigpas.ac.cn], State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, PR China.

Deciphering influencing processes in a tropical delta system (middle-late Eocene? to Early Miocene, Colombian Caribbean): Signals from a well-core integrative sedimentological, ichnological, and micropaleontological analysis

Deltaic depositional systems are characterized by a complex interaction of physical, chemical, and biological factors. Although fluvial-, wave- and tidal-dominated deltaic environments have been extensively studied, evaluation of the processes in tropical mixed sedimentary systems has not been fully documented. Tropical regions with active margins are tectonic environments where these multiple factors act on the development of coastal systems. An onshore well-core from this tropical setting (Sinú-San Jacinto Basin, Colombian Caribbean) revealed that a middle-upper Eocene?-lower Oligocene coarse-grained deltaic setting is replaced by a thick coal-bearing mixed-energy fine-grained deltaic succession from the Oligocene to Early Miocene. The integrated analysis of facies associations, ichnological data, and terrestrial/marine micropaleontological assemblages (palynomorphs, foraminifera, and calcareous nannofossils) of this well-core allowed us to identify changes in dominance and influence of coastal processes (fluvial-, wave- and tide) and shoreline evolution. Using this information, as well as the sediment supply and accommodation space ratio, we were able to distinguish three intervals from the bottom to the top of the siliciclastic succession: (i) middle-late Eocene?–early Oligocene, prograding, fluvial-dominated, wave- and tide-influenced coarse-grained deltas with amalgamation of hyperpycnal-dominated mouth bars with hyperconcentrated flow input, (ii) Oligocene, retrograding to prograding, hyperpycnal-dominated heterolithic delta deposits punctuated by transgressive pulses, and (iii) late Oligocene to Early Miocene, aggradational, coal-bearing fine-grained delta plain with a higher proportion of transgressive phases over the continental environment. The complete succession represents long-term (∼14 Myr) mixed-energy nearshore siliciclastic systems, showing different lithological arrangements and sedimentation styles. A long-term evolution is observed from a middle-late Eocene? steep, short and coarse-grained sedimentary system with tropical humid lowland forest and punctual development of macrobenthic tracemaker communities (Interval I) to an Early Miocene gently (poorly drained), well-developed delta plain with mangroves and wave- and storm-influence record through trace fossils assemblages (Interval III). A combination of factors, including subsidence, relief uplifting, and possible relative sea level changes, are interpreted as the main controls on the stratigraphic evolution of sedimentary styles throughout the entire succession. Minor-order sedimentary successions into each interval (e.g., prograding distributary mouth-bar channel) revealed short-term cycles presumably controlled by an internal delta dynamic. Multidisciplinary analysis is essential for recognizing the influence of fluvial, wave, and tidal processes on tropical deltas, where high spatial and temporal variability makes it difficult to determine dominant processes for long periods of time.

Lateral Variations of P-Wave Velocity from Deep Borehole Data in the Southern Apennines, Italy

We have selected 28 deep wells in the Southern Apennine area, most of which are located along and around the Val d’Agri Basin. The Southern Apennines, one of the most seismically active regions of the Italian peninsula, is a NE-verging fold-and-thrust belt characterised by the Meso–Cenozoic Apulia carbonate duplex system overlain by a thick column of Apennine carbonate platform and Lagonegro basin units. These units are unconformably covered by Neogene siliciclastic successions. Among the many Quaternary tectonic basins in the area, the Val d’Agri Basin is the most important intramontane depression, and is bordered by a ~ NW–SE-trending active fault system that represents one of the main seismogenic structures of the region. Moreover, the Val d’Agri Basin is the largest onshore oil field basin in Europe. In this context, we have analysed sonic log records from 28 deep wells and compared them with the corresponding stratigraphy and the other geophysical logs. We have obtained detailed measurements of the P-wave velocity (Vp) for each well from 0 to ~ 6 km depth, and found important lateral variations of Vp over very small distances. From these values, we have retrieved the densities of the main units crossed by the wells and the range of the overburden gradient in this area.

Detrital modes of buried Permian sandstones of the Puglia 1 well (Puglia Region, Southern Italy)

Permian siliciclastic input, around Mediterranean region, recorded a frame of Pangaea supercontinent breakup. Apulia region had registered it in a sedimentary cycle during final Paleotethys closure and subsequent Neotethys opening, after Variscan orogenesis. Here is provided a compositional insight of Permian siliciclastic succession intercepted in an explorative well log, Puglia 1 well, up to 6110 m till 7070 m in depth, of ENI’s property. The succession, about 760 m in thickness, consists of sandstone, mudstone and breccia. Sandstones are quartzolithic with quartz and metasedimentary lithic fragments abundance, while diagenetic minerals consist of ankerite, dolomite and calcite cements (related to dedolomitization-calcitization processes of the first carbonates), with iron oxides. The resultant provenance is related to eroded Devonian-Carboniferous Variscan orogen, where metasedimentary rocks occur both in Calabria-Peloritani, southern Alps and internal domains of the Circum-Mediterranean orogenic belts.

Post-depositional history of the lower Palaeocene interval using petrographic, CL and geochemical data in the East Tethys: Kopet-Dagh Basin, northeast Iran

AbstractThis study investigates the Danian siliciclastic successions in the East Tethys in the Kopet-Dagh Basin, NE Iran, which are composed of conglomerates, sandstones, shales and mudstones. The studied interval includes significant changes in sedimentary environments from alluvial to fluvial systems. The Danian siliciclastic formation is sandwiched between two marine carbonate sequences. The effects of the late Palaeocene sea transgression can be traced back to the precipitation of several types of carbonate cement in the studied siliciclastic formation. Several diagenetic features have been identified in the studied successions. The most observed features comprise physical and chemical compaction, cementation, alteration, dissolution, fractures and fillings. Some of the mentioned diagenetic processes, such as cementation, may be seen in a range of diagenetic environments and phases, such as early meteoric, low depth and deep burial, and late meteoric after the tectonic uplifting. The calcite cements considered in this study have been subdivided into four types. Some of the calcite cements, such as the rim, gravity pendant and meniscus, are classified as type one. They have formed around the rock grains and show no luminescence. The blocky and poikilotopic types have been grouped in type two. They are deposited between grains and exhibit dark luminescence. Type three cement consists of some of the blocky and poikilotopic cements that have formed amid grains and present a bright luminescence. Finally, type four comprises filled fractures which display a dark luminescence (blocky cement). Geochemical data revealed that the categorized cement types were precipitated in three diagenetic environments: early meteoric; burial; and late meteoric after the uplifting. The meteoric diagenetic environment is subdivided into vadose and phreatic meteoric. The burial diagenetic environment is subdivided into shallow burial and deeper burial. The qualitative petrographic method contributed to the initial recognition of the diagenetic features. The semi-quantitative cathodoluminescence method, the quantitative major and trace elements, and oxygen and carbon stable isotope analysis were utilized to evaluate the exact diagenetic processes and environments. Finally, the diagenetic sequence was reconstructed and depicted as diagenetic models and a paragenesis sequence. The data of this study can lay the foundation for future studies on the siliciclastic diagenesis in the studied basin.

Paleoenvironmental, paleoclimatic, and organic matter assessment of the hybrid Kharita Formation (Albian) in the Abu Gharadig Basin, Egypt: Integration between palynology, organic petrography, and organic geochemistry

The Early Cretaceous (Albian) was a time of equatorial to polar temperature warming and increased environmental perturbations of the global carbon cycle and oceanic anoxia, which resulted in the widespread accumulation of organic carbon-rich sediments. During the Albian, the southern margin of the Tethys Ocean was characterized by marginal to shallow water conditions with minor phases of enhanced stratification and bottom water anoxia in northern Egypt. At this time, accumulation of the thick siliciclastic succession of sandstones versus shale intercalations of the Kharita Formation took place in the Abu Gharadig Basin. The Kharita Formation is investigated for palynological composition and palynofacies analysis, organic matter characterization, hydrocarbon generation potential, and thermal maturity assessment based on 30 and 26 drill cuttings samples from the BED2-3 and BED2-1x wells, respectively. A rich palynological assemblage of herbaceous hygrophilous plants, including pteridophyte spores and water ferns, along with Elaterates and Afropollis pollen indicated warm humid climate conditions. Furthermore, abundant occurrences of Araucariaceae and Cheirolepidiaceae, including Araucariacites, Inaperturopollenites, and Classopollis, reinforcing warm climatic conditions and their climax in areas near coastal vegetation. Statistical cluster analysis identified two palynofacies assemblages (PFA) based on stratigraphic variation in the particulate organic matter (POM). The PFA-1 characterized all samples of the BED2-3 and some intervals of the BED2-1x wells and comprised moderate abundances of phytoclasts and amorphous organic matter (AOM) that defined a kerogen Type II, whereas the PFA-2 was recorded only in the BED2-1x well and is dominated by phytoclast fragments of kerogen Type III. The geochemical screening revealed, based on the low average values of TOC (1.2 wt%), S2 (1.8 mg HC/g rock), and HI (146 mg HC/g TOC), that the Kharita Formation is characterized by a kerogen Type III of gas-prone hydrocarbon but with low generation potential. Tmax and vitrinite reflectance measurements along with greenish-to golden-yellow liptinite macerals indicated that the thermal maturity of preserved organic matter is still in the immature to the early mature stage of the oil window. Inconsistency in kerogen types between PFA-1 and geochemical deductions was interpreted in terms of microscopic investigations of the recovered AOM. Morphologic characteristics observed that most AOM particles were of terrigenous origin due to the impact of biodegradation and transformation of phytoclast particles into AOM, confirming a kerogen Type III of gas-prone hydrocarbons instead of Type II that was elucidated by palynofacies ternary diagrams. The occurrence of coaly matter in the BED2-1x infers closer proximity to fluvio-deltaic sources during deposition of the lower part of the Kharita Formation than in the BED2-3.

Deformation history and processes during accretion of seamounts in subduction zones: The example of the Durkan Complex (Makran, SE Iran)

The Durkan Complex is a tectonic element of the Makran Accretionary Prism (SE Iran) that includes fragments of Late Cretaceous seamounts. In this paper, the results of map- to micro-scale structural studies of the western Durkan Complex are presented with the aim to describe its structural and tectono-metamorphic evolution. The Durkan Complex consists of several tectonic units bordered by mainly NNW-striking thrusts. Three main deformation phases (D1, D2, and D3) are distinguished and likely occurred from the Late Cretaceous to the Miocene–Pliocene. D1 is characterized by sub-isoclinal to close and W-verging folds associated with an axial plane foliation and shear zone along the fold limbs. This phase records the accretion of fragments of the seamount within the Makran at blueschist facies metamorphic conditions (160–300 °C and 0.6 – 1.2 GPa). D2 is characterized by open to close folds with sub-horizontal axial plane that likely developed during the exhumation of previously accreted seamount fragments. An upper Paleocene – Eocene siliciclastic succession unconformably sealed the D1 and D2 structures and is, in turn, deformed by W-verging thrust faults typical of D3. The latter likely testifies for a Miocene – Pliocene tectonic reworking of the accreted seamount fragments with the activation of out of sequence thrusts. Our results shed light on the mechanism of accretion of seamount materials in the accretionary prisms, suggesting that seamount slope successions favour the localization and propagation of the basal décollement. This study further confirms that the physiography of the subducting plates plays a significant role in the tectonic evolution of the subduction complexes.

Biostratigraphy and palaeogeographic implications of Ordovician and Silurian chitinozoa from the High Zagros Mountains, Northern Persian Gulf, Iran

A siliciclastic succession is exposed at the Faraghan mountain, northern Persian Gulf, southeastern Iran. A detailed, high-resolution palynological analysis was performed on the Zardkuh, Seyahou, Dargaz, and Sarchahan formations to verify the exact age and palaeogeographic position of the High Zagros Mountains. Two hundred surface samples from this succession were collected and analysed. Most samples yielded abundant and well-preserved chitinozoans, acritarchs, scolecodonts, and cryptospores. Fifty-three chitinozoan species (21 genera) were identified that permitted to establish the Eremochitina brevis, Desmochitina ornensis, Belonechitina henryi, Siphonochitina formosa, Belonechitina robusta, Tanuchitina fistulosa, Acanthochitina barbata, Armoricochitina nigerica, Ancyrochitina merga, Tanuchitina elongata, Spinachitina oulebsiri, and Spinachitina fragilis biozones in ascending stratigraphic order as was previously established for the North Gondwana Domain. These results indicate that the Zagros Mountain Belt of Iran was part of the North Gondwana palaeo-province during the Ordovician-Silurian. On the other hand, these chitinozoan biozones and other associated fauna (e.g. graptolites, trilobites, brachiopods, and conodonts) suggest a late Early Ordovician (Floian) to Early Silurian (Rhuddanian) age range, with unconformities, for this succession. Based on chitinozoan biozones, a distinctive hiatus is present between the Zardkuh and Seyahou formations at Faraghan mountain, which corresponds to the absence of jenkinsi-tanvillensis chitinozoan biozones, encompassing the latest Middle Ordovician (latest Darriwilian: stage slice Dw3) and the early Late Ordovician (Sandbian: the stage slices Sa1 to Sa2 and time slices 5a to 5b). Two chitinozoan species were erected: Belonechitina bifurcaspina sp. nov., Angochitina persianense sp. nov., and Eremochitina cf. brevis was left in open nomenclature.

Sequence Stratigraphy of Miocene Mixed Carbonate-Siliciclastic in Fold and Thrust Belt System, Banggai Basin

This study was specifically analyzed in the southern part of the Banggai Basin, precisely in the TKA Field. In the Tertiary, regional stratigraphy reveals, the Banggai Sula microplate comprises carbonate shelf and siliciclastic sequence. Several previous studies had been concluding, the tertiary limestone was deposited during the Early Eocene to Middle Miocene. Carbonate formations which has been known by Tomori and Minahaki Formation. Meanwhile, their siliciclastic dominated is Matindok Formation and Celebes Mollase. These sequences formed a distinct stratigraphic style in the geophysical well log and seismic data. Four cycles are distinguished, the lower part of Tomori Formation at the outer shelf and directly overlying by the upper part of inner shelf Tomori Formation. it was superimposed by siliciclastic sediments that have been deposited in the outer litoral during regressive phase. Whereas during rising sea level or highstand, the litoral system migrated to basinward wherein Minahaki Formation was deposited. Sequence stratigraphy provides a reliable methodology for correlate both carbonate and siliciclastic successions. It was analyzed based on 4 wells, 2D, and 3D seismic data which has been available. Sequence stratigraphy analysis using T-R sequence concept by Embry and Johanessen. Trasngressive and regressive phases were obviously determined by lithofacies, coral colony and foram that were recorded on biostratigraphic analyses. In this study, cyclic sea-level change will be recognized as system tract record of mixed carbonate-siliciclastic sequence.

Depositional and thermal history of a continental, coal-bearing Middle Jurassic succession from Iran: Hojedk Formation, northern Tabas Block

AbstractDuring the early Bajocian, a conspicuous coal-bearing siliciclastic succession was deposited in the northern Tabas Bock, which is important for understanding the regional geodynamics of the Central-East Iranian Microcontinent (CEIM) as well as for the Jurassic coal genesis in this part of Laurasia. Sedimentary facies analysis in a well-exposed section of the lower Bajocian Hojedk Formation (Kalshaneh area, northern Tabas Block) led to the recognition of ten characteristic sedimentary facies and three facies associations, representing channels with point bars and floodplains of a Bajocian meandering river system. Modal analysis indicates that the mature quartz arenites and quartzo-lithic sandstones of the Hojedk Formation originated from the erosion and recycling of older, supracrustal sedimentary rocks on the Yazd Block to the west. The coal petrography and maturity show an advanced maturation stage, whereas the great thickness of these continental strata points to a pronounced extension-related subsidence in the northern Tabas Block. The rapid rate of differential subsidence can be explained by accelerated normal block-faulting in the back-arc extensional basin of the CEIM, facing the Neotethys to the south. Compared to the thick Jurassic, the post-Jurassic strata are relatively thin and played a limited role in the thermal history of the coal in the northern Tabas Block. A relatively high geothermal gradient in the tectonically highly mobile area of the northern Tabas Block and/or heating by regionally widespread Palaeogene intrusions were most probably the key drivers of the thermal maturation of the Middle Jurassic coals.