Carboniferous Basin Research Articles

Unraveling overprinted formation mechanisms of massive dolostone in the Lower Triassic sequence of an isolated carbonate platform in Nanpanjiang Basin, south China

Massive dolomitization is common in carbonate platforms but determining the causes of dolomitization remains challenging. A particular difficulty lies in identifying cases where petrographic and geochemical attributes of dolostone related to one mechanism could be obscured by a later, different one. To better understand whether traditional approaches are sufficient to unravel the origins of dolostone resulting from successive, different mechanisms, this study investigates the formation mechanism(s) of dolostone along a platform-to-basin transect of a Permian-Triassic isolated platform in the Nanpanjiang Basin. The dolostone in the Lower Triassic succession comprises three dolomite phases that can be distinguished through field relationships, petrography, 87Sr/86Sr ratios, and microthermometry. Dolomite type 1 formed due to the reflux of platform-top evaporated seawater that flowed through the platform interior in the Early Triassic. Dolomite types 2 and 3 are interpreted to have formed at elevated temperatures during or after Late Triassic platform burial and to have played a secondary role in forming the dolostone. The dolomitizing fluids that resulted in the formation of dolomite types 2 and 3 were derived from Early Triassic seawater-like fluid that was expelled from the Lower Triassic basinal carbonate sediments and moved updip to the platform interior. Dolomitized clasts in partially or non-dolomitized slope breccias demonstrate pre-burial timing of dolomite type 1, and distinguish the earlier dolomitization from later, post-burial dolomitization represented by dolomite types 2 and 3. Dolomite type 1 retains its Early Triassic seawater δ13C and 87Sr/86Sr signatures, whereas overlapping geochemical fields of the three types of dolomite (trace element concentration, δ18O) imply that burial dolomitizing fluids locally reset the geochemistry of dolomite type 1. This finding suggests that the same dolomite archive may retain well-preserved or altered data depending on the specific geochemical proxy and that identifying individual dolomitization mechanisms using geochemical proxies is possible only in some cases.

Characterization and evolution of a carbonate basin floor fan on a leeward side of an isolated carbonate platform, Sirte Basin, Libya

The recognition of carbonate basin floor fans and the interpretation of their formation and evolution are extremely crucial to the hydrocarbon exploration since they form important oil and gas reservoirs. There has been little research on the geometries and controlling factors of the carbonate basin floor fans from subsurface three-dimensional (3D) seismic and wireline log data. Most studies have been conducted on siliciclastic basin floor fans. Thus, this study characterizes the internal configuration and processes controlling the deposition of a lower Eocene carbonate basin floor fan system in the Sirte Basin in a sequence stratigraphic context through integrated 3D seismic and wireline log interpretations. The carbonate fan complex shows hummocky to undulated seismic geometries on vertical seismic sections and bounded by an unconformable sequence boundary at the base and a downlap surface at the top. It has an aerial extension of around 9 km from south to north along depositional dip and at least 8 km from east to west along strike. In well data, the fan system predominantly comprises limestone units intercalated with thin shale intervals. Log curves display an overall funnel-shaped trend, suggesting progradational stacking pattern. The vertical thickness of the fan complex varies from 120 to 165 m. The evolution of the carbonate fan was influenced by the interplay of accommodation space and sediment supply. A pre-existing topography, tectonic subsidence, and sea-level rise generated accommodation space for the deposition of the fan system, whereas sediment-gravity flows transported the fan sediments from the platform interior and margin to the basin floor. This study provides sedimentological and stratigraphic criteria to recognize and interpret the evolution of basin floor fans along isolated carbonate platforms from 3D seismic and wireline log data and may serve as an analog for ongoing and future studies on carbonate basin floor fans elsewhere.

Substantiation of In Situ Water Shut-Off Technology in Carbonate Oil Reservoirs

The efficient development of carbonate oil deposits with excessive fissuring is a current challenge. Uneven and rapid well stream watering is considered as one of the factors that make the process of the development of carbon deposits more complicated. The purpose of the research is to diagnose and evaluate the mechanisms of well stream watering for carbon deposits and find applicable technology to prevent it. An overview of in situ water shut-off technologies was carried out. A description of the main materials used for water shut-off is presented, and selective methods are studied in more detail. A carbonate basin of an oil field is selected as the object of investigation. The geological and physical characteristics of this deposit are given. Analysis of possible causes and sources of water cut of the fluid is made according to the technique of K.S. Chan, under which the main reason for the watering of the well production is the breakthrough of formation and injection water through a system of highly permeable natural fractures and channels. Matrixes of applicability of in situ water shut-off technologies and polymer compositions are made. The composition based on carboxymethyl cellulose for in situ water shut-off is selected for the chosen deposit.

3-D seismic chronostratigraphy of reefs and drifts in the Browse Basin, NW Australia

Abstract In its subsurface, the Browse Basin on the Australian Northwest Shelf accommodates one of the largest Miocene–Pliocene carbonate platform provinces on Earth. This study presents a comprehensive three-dimensional (3-D) documentation and investigation of the Neogene Browse Basin carbonates based on the analysis of 15 3-D seismic reflection volumes covering ca. 33,000 km2 and 22 industry boreholes. Eight basin-wide seismic marker horizons tied to Sr isotope and biostratigraphic data provide a robust 3-D chronostratigraphic framework that (1) newly documents the occurrence of Miocene to recent carbonate systems in vast inboard basin areas; (2) presents the 3-D distribution and dynamic development of carbonate platforms through time constrained by absolute ages; and (3) supports the detailed 3-D interpretation of Miocene to recent depositional processes and key stratigraphic controls. Around 18.6 Ma, the extent of all Browse Basin carbonate platforms was ca. 8600 km2, rising to >10,000 km2 between 15.6 Ma and 12 Ma. By ca. 9.7 Ma, the total platform extent had decreased to ca. 5700 km2, waning to <2800 km2 in the Pliocene. The observed reef demise is less abrupt than previously thought and comprises two steps, with the first in the late Miocene on the outer shelf and the second in the Pliocene on the middle and inner shelf. The Miocene outer-shelf platform demise coincided with (1) strong subsidence that outpaced sedimentation, (2) an increase in NW–SE-oriented tidal current activity, (3) the development of NNE–SSW-oriented bottom currents, and (4) the onset of drift sedimentation. The Pliocene demise of middle-shelf reefs coincided with (1) an increase of clastic sediment input from land and (2) stalling of the Indonesian Throughflow around 3.7 Ma. The basin-wide, 3-D seismic chronostratigraphic analysis presented supports a re-evaluation of the key controls for Miocene and Pliocene reef growth and decay on the NW Shelf and highlights the complexity of interacting global, regional, and local processes and peculiarities in carbonate platform development.

A composite Llandovery δ13Ccarb record from the Michigan Basin, USA

Abstract A new high-resolution, composite δ13Ccarb curve for the Michigan Basin, USA, was constructed using two stratigraphically overlapping subsurface cores that span the complete Llandovery interval. The Llandovery succession of the Michigan Basin measures between 140 m and 265 m thick and is represented by three lithostratigraphic groups: the Cataract (Manitoulin formation and Cabot Head Shale), the Burnt Bluff (Lime Island, Byron, and Hendricks formations), and the Manistique (Schoolcraft and Cordell formations). The composite δ13Ccarb curve exhibits five positive carbon isotope excursions (CIEs). Conodont and 87Sr/86Sr data suggest that the CIEs correlate with the Hirnantian, Early Aeronian, Late Aeronian, Valgu, and Ireviken global excursions. The new composite δ13Ccarb curve from the Michigan Basin represents the most stratigraphically complete, single-basin Llandovery record worldwide. The composite δ13Ccarb curve permits the ages of three Llandovery lithostratigraphic groups to be chronostratigraphically determined within ca. 1 Ma resolution. The composite δ13Ccarb curve also implies that the Ordovician–Silurian boundary in the Michigan Basin is located at the top of the Manitoulin formation and not at the base of the Manitoulin formation, which is consistent with recent findings from Manitoulin Island, Ontario. From the regional perspective, the high-resolution composite δ13Ccarb curve provides a valuable tool for delineating the depositional history of the Michigan Basin during the Llandovery. From a global perspective, the new composite δ13Ccarb curve sheds light on the dynamics of the global carbon cycle, particularly during the Rhuddanian, which is rarely preserved in other carbonate basins worldwide.

Phyllotheca douroensis sp. nov., a new equisetalean fossil-species from the Douro Carboniferous Basin (Upper Pennsylvanian; NW Portugal): palaeobiogeographical, systematic and evolutionary implications

The first occurrence of the fossil-genus Phyllotheca (Equisetales) from the Carboniferous of Portugal is documented and its palaeobiogeographical, systematic and evolutionary significance is assessed. In this paper, we described this new equisetalean fossil as new species, Phyllotheca douroensis sp. nov., found in the Douro Carboniferous Basin (lower Stephanian C/lower Gzhelian, Upper Pennsylvanian), in northwestern Portugal. P. douroensis sp. nov. represents a convergent form of Phyllothecaceae sensu lato (comprises the Angaran Tchernoviaceae and the Gondwanan Gondwanostachyaceae) with closer affinities to Euramerican floral province.

Joint analysis using geomechanics, computed X-ray tomography and petrography based on coal samples from a carboniferous basin in Poland

Joint analysis using geomechanics, computed X-ray tomography and petrography based on coal samples from a carboniferous basin in Poland

Resedimented limestones in fault-controlled basins (Zorzino Limestone, Southern Alps, Norian, Italy): Facies types and depositional model

The Norian succession of the Southern Alps of Italy stores thick successions of resedimented basinal carbonates (Zorzino Limestone) that were deposited in fault-controlled, anoxic, intraplatform basins developed within a vast inner platform domain (Dolomia Principale). To characterise the basinal facies, to define their distribution within these basins and to identify depositional processes, four stratigraphic logs covering about 2000 m of total stratigraphic thickness from proximal to distal basinal settings were described bed by bed. Eight different lithofacies organised in 11 bed types were identified according to sedimentary structures, texture, and composition: each bed (about 4500 beds in total) was measured individually at cm scale and classified in one of the 11 bed types.Distribution of bed types in terms of events (i.e. number of beds) and cumulative thickness (i.e. volume of sediments produced by the different depositional processes) in the four selected logs change from the proximal to the distal parts of the basin, reflecting the existence of diverse dominant depositional processes at different places within the intraplatform basins. Bed by bed analyses of thick stratigraphic logs provide important hints about the distribution of different types of depositional processes, from proximal to distal basin. Frequent slump folds and mass flow deposits, with clasts mostly deriving from the slope facies itself, indicate instability of the slope. Sediment composition and facies types document a major role played by the reworking of primary deposits formed along the slope: basinal facies mostly consist of resedimented slope deposits, produced by sliding of sediments, rich in lime mud, accumulated along the slope and low-angle proximal basin, whose instability (likely enhanced by seismic activity related to the Norian extensional tectonics) produced most of the recognised facies types. The two-step depositional processes as well as the facies associations and bed types clearly indicate a different behaviour (in terms of prevailing depositional processes and facies associations) of the studied resedimented limestone with respect to siliciclastic deposits.The distribution of facies and the detailed analyses of bed types, recording the distribution of depositional processes at basinal scale, provide a tool for the interpretation of basin morphology, from the study of stratigraphic logs, that can be applied both to outcrop and to subsurface successions.

Channel incision into a submarine landslide on a Carboniferous basin margin, San Juan, Argentina: Evidence for the role of knickpoints

AbstractEmplacement of submarine landslides, or mass‐transport deposits, can radically reshape the physiography of continental margins, and strongly influence subsequent sedimentary processes and dispersal patterns. Typically, progressive healing of the complicated relief generated by the submarine landslide occurs prior to progradation of sedimentary systems. However, subsurface and seabed examples show that submarine channels can incise directly into submarine landslides. Here, the evolution of a unique exhumed example of two adjacent, and partially contemporaneous, submarine channel‐fills is documented. The channels show deep incision (>75 m), and steep lateral margins (up to 70°), cut into a >200 m thick submarine landslide. The stepped basal erosion surface, and multiple terrace surfaces, are mantled by clasts (gravels to cobbles) reflecting periods of bedload‐derived sedimentation, punctuated by phases of downcutting and sediment bypass. The formation of multiple terrace surfaces in a low aspect ratio confinement is consistent with the episodic migration of knickpoints during entrenchment on the dip slope of the underlying submarine landslide. Overlying sandstone‐rich channel‐fills mark a change to aggradation. Laterally stacked channel bodies coincide with steps in the original large‐scale erosion surface, recording widening of the conduit; this is followed by tabular, highly aggradational fill. The upper fill, above a younger erosional surface, shows an abrupt change to partially confined tabular sandstones with normally graded caps, interpreted as lobe fringe deposits, which formed due to down‐dip confinement, followed by prograding lobe deposits. Overlying this, an up‐dip avulsion induced lobe switching and back‐stepping, and subsequent failure of a sandstone body up‐dip led to emplacement of a sandstone‐rich submarine landslide within the conduit. Collectively, this outcrop represents episodic knickpoint‐generated incision, and later infill, of a slope adjusting to equilibrium. The depositional signature of knickpoints is very different from existing models, but is probably reflective of other highly erosional settings undergoing large‐scale slope adjustment.

Effects of Magmatic Fluids in Coals of São Pedro da Cova Coalfield, Douro Carboniferous Basin, Portugal: Insights from Inorganic Geochemistry

The Douro Carboniferous Basin (DCB), aged from Gzhelian, is an important coal-bearing basin occurring in Northern Portugal. While the coals and the sedimentary sequence of the DCB have been deeply studied, the inorganic geochemical data are scarce. This study intends to provide major and trace element contents and discuss their modes of occurrence and origins using a set of twenty-four coal samples from the São Pedro da Cova Coalfield taken from different sectors/outcrops. Thus, an integrated approach using petrographic, geochemical, both organic and inorganic, and mineralogical data was used to achieve these purposes. The main results demonstrated that these coals are anthracite A and vitrinite is the main organic component. Most of the elements have inorganic affinities and are associated with aluminosilicates, while the other elements have affinities with sulfides. Illite and muscovite are the main phyllosilicates occurring in these coals and pyrite is the most common sulfide. However, cinnabar, together with phosphates (fluorapatite, monazite, xenotime and gorceixite), were also identified. The enrichment of most elements as well as a heterogenous rare earth elements (REE) distribution pattern in the tectono-sedimentary unit (TSU) samples are related to magmatic fluids. On the other hand, on the Eastern Outcrop (EO), a tectonic slice, the subparallel trend of the REE distribution patterns, and a depletion of all the elements are related to the sedimentary contribution. The occurrence of cinnabar and gorceixite epigenetic mineralizations is interpreted as the action of a porphyry intrusion identified in this area of the DCB, between the TSU B1 and TSU D1.

Ferns and lycophytes in coal mining waste and tailing landfills.

Mineral coal extraction in Santa Catarina State (Brazil) Carboniferous Basin has degraded the local ecosystem, restricting the use of its areas. One of the biggest environmental impacts in the mining areas is the uncontrolled disposal of waste and sterile mining with high concentrations of pyrite, which in the presence of air and water is oxidized promoting the formation of acid mine drainage (AMD). These contaminants can be leached into water resources, restrict the use of water and soil, and cause threats to fauna and flora. This study aimed to characterize these areas as to the content of Cd, Pb, Ni and Zn metals in the tailings and waste resulting from coal mining and to survey the species of ferns and lycophytes present. Wastes and tailing samples and specimens of ferns and lycophytes were collected in 23 landfills in six municipalities in the region and in four underlying areas used as controls. Chemical and physical analyses (pH in water and pH in KCl, Ca, Mg, P, K, Na, Mn, Fe, Al, clay and OM contents) were carried out and the total contents of heavy metals Cd, Pb, Ni and Zn were determined. Sampling of ferns and lycophytes was carried out by walking. The levels of heavy metals, Cd, Ni and Zn, were below the prevention concentrations established by CONAMA Resolution 420/2009. Pb levels were above prevention values in four landfills. Sixteen species of ferns and one lycophyte were found, with hemicryptophytes the most frequent and helophytes the most adapted to the environment. Of the species found, Pteridium esculentum (G. Forst.) Cockayne, Pityrogramma calomelanos (L.) Link and Telmatoblechnum serrulatum (Rich.) Perrie, DJ Ohlsen & Brownsey demonstrated resistance to degraded and contaminated environments with Pb, which may constitute an alternative for project monitoring and environmental recovery.

The first poroblattinid roachoid from the uppermost Carboniferous of Portugal

ABSTRACT Poroblattina anadiensis sp. nov., first record of the roachoid family Poroblattinidae from Portugal, is described from the upper Gzhelian Vale da Mó ‘Formation’ of Buçaco Carboniferous Basin. The genus Poroblattina was previously known by numerous records from the Moscovian and the Asselian (time range between 306.95 and 295.0 Ma) in Euramerica, showing a high forewing venation variability. The new species is most similar to the French Moscovian Poroblattina duffieuxi, but it differs from this species in having a larger forewing, more irregularly anterior pectinate RP, and more forked branches. Poroblattina anadiensis sp. nov. supports the links between the entomofaunas of North America and Western Europe during the late Carboniferous and early Permian. Despite the intense exploration of the Buçaco Carboniferous Basin units in the nineteen-century and mid-20th century, the new discovery highlights the potential of palaeontological studies now resumed in this region.

A new species of Lesleya (Spermatopsida) from the Carboniferous of Iberia and its palaeoecological and evolutionary significance

ABSTRACT Plant adaptations to environmental and climatic changes in Pangaean intramontane basins are poorly understood. Here, we document a previously unknown primitive gymnosperm species, Lesleya ceriacoi sp. nov., from the Douro Carboniferous Basin (DCB; lower Gzhelian, Upper Pennsylvanian; NW Portugal) of the Variscan Iberian Massif (Iberia). This new species is described from a 303 million-years-old fossil rediscovered at the U.Porto’s Herbarium PO, stored at the Museu de História Natural e da Ciência da Universidade do Porto (MHNC-UP; Portugal). L. ceriacoi sp. nov. displays an exquisite leaf shape with morphological traits adapted to specific ecological conditions of the DCB. These leaf morphological traits comprise toothed and dissected margins, which represent specialised adaptations to drier (xerophytic) conditions of the DCB during the Gzhelian (ca. 304–299 Ma), at the end of the Late Pennsylvanian. The xeromorphic traits of the new species represent an evolutionary novelty for the Pennsylvanian Euramerican dry-climate adapted floras, and are evidence of evolutionary adaptation to environmental and climatic change in intramontane basins like DCB within central tropical Pangaea. Such an adaptation occurred during an interval of wet to dry climate transition after the end of one late Palaeozoic Gondwana Ice Age (glaciation) in Gzhelian time.

Controls on Barite Mineralization in a Major Intracontinental Shear Zone: Carboniferous of the Cobequid Highlands, Nova Scotia

Prominent veins of late Carboniferous barite, associated with fluorite and calcite, outcrop close to older granite plutons along an intracontinental shear zone that was active throughout the Carboniferous in southeastern Canada. Some barite is stratigraphically constrained to younger than 315 Ma and final mineralization is constrained by a published Rb–Sr isochron of 300 ± 6 Ma. Barite occurrences in the Carboniferous basins of central Nova Scotia, 50 km to the south, are synchronous with or post-date ankerite-siderite-magnetite-pyrolusite and Pb-Zn mineralization, which was facilitated by fluid interaction with thick evaporites. This study aims to determine controls on the distribution of barite in the shear zone, from field relationships, vein petrography and isotope geochemistry of minerals. The isotope chemistry of shear zone barite is similar to that occurring in Pb-Zn-Mn-Ba mineralization to the south, suggesting a common origin. Veins of barite, associated with fluorite, represent the youngest and regionally coolest phase of a 70 Ma history of Carboniferous mineralized veins along the Minas Fault Zone. Their prominence close to granite plutons reflects brittle deformation of the deeply-rooted granites in a complexly deforming fault zone, but the origin of abundant F remains uncertain.

Newly discovered late Devonian and early Carboniferous ophiolite fragments in the Diyanmiao mélange in southeastern Inner Mongolia: Implications for the late Paleozoic tectonic evolution of the southeastern Central Asian Orogenic Belt

The Late Paleozoic tectonic evolution of the southeastern Central Asian Orogenic Belt (CAOB) has long been controversial, and one of the most contentious issues has been whether there was a collisional orogenic event during the Middle Paleozoic. Here we report the discovery of a Late Devonian (373.5 ± 6.8 Ma) ophiolite fragment in the Diyanmiao mélange of southeastern Inner Mongolia. This fragment, coupled with previously reported Carboniferous ophiolites in the same region, confirm the former presence of a Late Devonian ocean basin that evolved into the Carboniferous basin. The geochemical characteristics of the Devonian and Carboniferous mafic rocks in the ophiolites are consistent with evolutionary trends from mid-ocean ridge (MOR)-like to supra-subduction zone (SSZ) compositions. The presence of a Late Devonian-Carboniferous trench-arc-basin system in the region, which is represented by the Daqing-Diyanmiao and Bayan'aobao-Hongger ophiolite belts, the Baolidao arc, and the Erenhot-Hegenshan Oceanic Basin (EHB), confirms the presence of a late Devonian-Carboniferous orogenic belt in the southeastern CAOB. The western segment of the Baolidao arc was developed on continental basement (the Xilin Gol complex), whereas the eastern segment was formed on oceanic basement. This tectonic configuration is similar to that of the modern Aleutian arc, Kamchatka-Kuril Islands and Japan-Ryukyu arc system in the northern and western Pacific Ocean. During the early Permian the oceanic basin represented by the Erenhot-Hegenshan basin closed, and the Baolidao arc was accreted onto the southern continental margin of the Southern Mongolian continental block.

Holocene sediment distribution in the Al Wajh platform lagoon (northern Red Sea, Saudi Arabia), a modern analogue for large rift basin carbonate platforms

AbstractSedimentary patterns and hydrodynamic transport processes on modern carbonate platforms in arid climates are understudied compared to platforms in humid‐tropical climates. The Al Wajh platform – located in the Arabian–African desert belt – is a large land‐attached carbonate platform in the Red Sea providing an excellent opportunity to fill this gap. The platform covers some 1800 km2 and is almost completely enclosed by a 115 km long reef‐shoal belt. More than 200 sediment surface samples were analyzed in order to investigate the lateral sediment distribution within the lagoon. The seafloor map was refined integrating sample depths with previous published bathymetric information. Conductivity and temperature profiles were measured to study the lagoonal water body. The lagoon is dominated by poorly sorted, sand‐sized sediments with low total organic carbon content, while carbonate fines content shows significant lateral variation. Aragonite dominates sediment mineralogy with high‐Mg calcite and low‐Mg calcite being significant admixtures. Fine‐grained siliciclastics are found across the entire lagoon, with angular quartz locally enriched in nearshore and distal areas. Seven component assemblages are defined ranging from benthic foraminifera and mollusc‐rich to reef debris‐rich component assemblages. Platform‐interior ooids are for the first time documented from the modern Red Sea. The heterogeneous distribution of carbonate fines shows no water depth related trends, while the component assemblage arrangement is depth related. Hydrodynamics are interpreted to be the main mechanism controlling carbonate fines distribution in the lagoon. A nearshore enrichment of angular sand‐sized quartz suggests influx through wadis during flash floods, while an almost even distribution of fine‐grained siliciclastics possibly indicate aeolian import. These findings provide new insights to the importance of hydrodynamic transport processes for sediment distribution in a land‐attached platform lagoon in an arid climate. Finally, this study presents a comparison with other modern platforms and discusses implications for improving strategies of hydrocarbon field development in rift‐basin carbonates.

Dolomitization of Late Norian carbonate deposits of restricted basin facies in the Keszthely Mts., Transdanubian Range, Hungary

In the Transdanubian Range (Hungary), a wide spectrum of Triassic dolomites is known. Mechanism of dolomitization of the platform carbonate successions was subject of a number of studies but the study of dolomitization of basinal carbonates is very limited. Petrographical and isotope–geochemical characteristics of the Upper Triassic dolomitized carbonate deposits, formed in a fault-controlled intraplatform basin, and interpretation of the dolomite-forming processes are presented in the current paper. From the latest Carnian to Middle Norian under semi-arid climatic conditions density-driven flux of seawater derived mesohaline fluids was the dominant mechanism of the near-surface pervasive dolomitization of the thick platform carbonate succession. In the late Middle Norian incipient rifting of the Alpine Tethys led to establishment of an extensional structural regime and onset of the formation of the Kössen Basin. In the study area, above the dolomitized platform carbonate succession, platform-derived carbonate sediments were accumulated in a fault-bounded, semi-restricted sub-basin of the Kössen Basin, whereas talus breccias and debrites were deposited near a basin-bounding master fault. The basin deposits (lower and upper members of the Rezi Dolomite Formation) were subject of early diagenetic dolomitization in shallow burial setting. Enhanced salinity seawater was the dolomitizing fluid; the synsedimentary fracturing may have promoted the fluid flow and thereby the dolomitization. Thick-bedded carbonates (middle member of the Rezi Dolomite Formation) representing a progradational tongue of the ambient platform are intercalated between the basin deposits. The dolomitization of this unit can be explained by the reflux model.

Carboniferous high-Mg andesitic and dioritic rocks in the Aqishan-Yamansu belt: Implications for mantle metasomatism and tectonic setting of the Eastern Tianshan

The Aqishan-Yamansu belt, Eastern Tianshan is characterized by voluminous Late Paleozoic intermediate–felsic igneous rocks and magmatic–hydrothermal Fe (–Cu) deposits. This study presents zircon U–Pb ages and whole-rock geochemistry of newly identified high-Mg andesitic and dioritic rocks (HMAs and HMDs) within the Hongshanliang copper district in the Aqishan-Yamansu belt, Eastern Tianshan to investigate their petrogenesis and constrain the Carboniferous tectonic setting of the Eastern Tianshan. Zircon U–Pb dating of the HMAs and HMDs yielded ages between 336.9 ± 1.9 Ma and 329.0 ± 4.2 Ma. The HMAs and HMDs show calc-alkaline affinities, and exhibit weak Rb, Ba, U, and Pb enrichment and Nb and Ta depletion, with minor negative Eu anomalies. Moreover, the positive εNd(t) values (+6.4 to +6.6), low Th and (La/Sm)N contents/ratios, as well as relatively low and variable εHf(t) values (−3.71 to +1.55) indicate that they were probably sourced from a depleted mantle wedge with negligible to minor crustal contamination. They have low Ba/Th ratios (10.8–93.3), minor negative Eu anomalies, high and variable (La/Sm)N and Th/Yb ratios, which are comparable to the well-known sanukites of the Setouchi volcanic belt, suggesting involvement of sediment-derived magmas during their formation. Integrating published regional mafic–intermediate rocks from the Aqishan-Yamansu belt and this study, we propose that the Hongshanliang high-Mg rocks formed in a continental arc-related setting in the Carboniferous and the belt underwent a sharp tectonic transition event (ca. 330–322 Ma) from the Kangguer oceanic slab steepening to breakoff, corresponding to the Late Carboniferous basin inversion.

Spatial variation in provenance signal: identifying complex sand sourcing within a Carboniferous basin using multiproxy provenance analysis

Multiple factors (e.g. source rock composition, climate, nature/scale of sedimentary system) influence the volume and composition of sediment delivered to basins. Fluctuations in these parameters produce cryptic source signals which can vary within the same sedimentary system. Bespoke multi-proxy provenance approaches, targeted at minerals of variable stability, allow for an assessment of natural biasing (recycling) and intra-basinal spatial variations. Provenance of fluvial/deltaic sandstones (Mullaghmore Sandstone Formation) in the NW Carboniferous Basin, Ireland, has been constrained using zircon and apatite U–Pb geochronology, trace elements in apatite and Pb-in-K-feldspar analysis. Zircon U–Pb grain populations are consistent with feldspar data, suggesting Proterozoic basement highs offshore Ireland and Scotland were the main contributor with minor supply from Archean–Paleoproterozoic rocks of Greenland/NW Scotland and Caledonian-aged rocks. However, apatite data show a much larger proportion of Caledonian-aged grains of metamorphic origin, suggesting significant sediment was recycled from Neopropterozoic metasedimentary rocks. The spatial variation in provenance indicates that, at onset of clastic input, sediment was being routed to the basin through a complex drainage system, comprising several discrete hinterland catchments, rather than supply from a single, large interconnected sedimentary system. Such complexities can only be identified with the careful application of a bespoke multi-proxy provenance approach. Supplementary material: Tables 1-5 and individual Pb-in-K feldspar plots are available at https://doi.org/10.6084/m9.figshare.c.5536691

Investigation of origin, sedimentary environment and preservation of organic matter: A case study in Garau Formation

Knowing the characteristics of suitable environments for precipitation of oil prone source rocks facilitates oil explorations and leads to development of oil fields. The current study investigates the organic matter properties and sedimentary environment conditions of the Garau Formation in various outcrop sections in Lurestan province from south-west of Iran (High Zagros) with using elemental analysis, visual kerogen analysis and Rock-Eval pyrolysis data. The geochemistry parameters indicate that the Garau Formation is an excellent oil prone source rock and composed of kerogen type I and II. The oxygen index (OI) is very low which reveals that organic matter deposited in an anoxic sedimentary environment and suitable for the preservation of organic matter and hydrocarbon generation. The visual analysis of isolated kerogens from source rock samples indicates the abundance of dark amorphous organic matter (AOM) with small amounts of phytoclasts and pyrite with no palynomorphs. Sedimentation seems to have occurred in deep and reduced parts of a carbonate basin during a rapid transgression. In addition, due to the effect of thermal maturation, the color of amorphous organic matter has darkened. The elemental analysis and Van-Krevelen diagram was shown that the type of organic matter and reveals the thermal maturity of the oil window. Moreover, amount of pyritic sulfur (Sp) and organic sulfur (So) contents have been calculated, and it was reveals that the high content of organic sulfur is a key element in the structure of organic matter.