The influence of climate,hydrology and permafrost on Holocene peat accumulation at 3500 m on the eastern Qinghai–Tibetan Plateau

Peatland of the eastern Qinghai–Tibetan Plateau lies at the convergence of the East Asian and Indian monsoon systems in eastern Asia. To understand the evolution of this peatland and its potential to provide new insights into the Holocene evolution of the East Asian monsoon a 6 m peat core was collected from the undisturbed central part of a peat deposit near Hongyuan. The age-depth profile was determined using 16 ¹⁴C-AMS age dates, the peat analysed for a range of environmental variables including carbon, nitrogen and hydrogen concentration, bulk density, δ¹³C and the associated spring water analysed for hydrogen and oxygen isotopes. The age-depth profile of the recovered peat sequence covers the period from 9.6 to 0.3 kyr BP and is linear indicating that the conditions governing productivity and decay varied little over the Holocene. Using changes in carbon density, organic carbon content and its δ¹³C, cold dry periods of permafrost characterised by low density and impeded surface drainage were identified. The low δ¹⁸O and δD values of the spring water emanating around the peat deposit, down to ?13.8 and ?102‰ (VSMOW), respectively, with an inverse relationship between electrical conductivity and isotopic composition indicate precipitation under colder and drier conditions relative to the present day. In view of the current annual mean air temperature of 1 °C this suggests conditions in the past have been conducive to permafrost. Inferred periods of permafrost correspond to independently recognised cold periods in other Holocene records from across China at 8.6, 8.2–7.8, 5.6–4.2, 3.1 and 1.8–1.5 kyr BP. The transition to a cold dry climate appears to be more rapid than the subsequent recovery and cold dry periods at Hongyuan are of longer duration than equivalent cold dry periods over central and eastern China. Light–dark banding peat on a scale of 15–30 years from 9.6 to 5.5 kyr BP may indicate a strong influence of decadal oscillations possibly the Pacific Decadal Oscillation and a potential link between near simultaneous climatic changes in the northwest Pacific, ENSO, movement of the Intertropical Convergence Zone and the East Asian Monsoon.     

Alluvial architecture of mid-channel fluvial–tidal barforms: The mesotidal Lower Columbia River,Oregon/Washington,USA

Barforms of mesotidal to macrotidal fluvial–tidal transitions, regardless of fluvial-discharge, are currently thought to display a sedimentary architecture dominated by tidal signatures. Due to the scarcity of observations from modern mesotidal fluvial–tidal transitions, especially those of multi-channelled large-rivers (mean annual discharge ≥7000 m³ s⁻¹ and peak discharges ≥15 000 m³ s⁻¹) with mid-channel bars, this concept remains unproven. The present study analyses data produced by a combination of high-resolution ground penetrating radar and coupled shallow vibracores (<5 m depth), collected from modern fluvial–tidal mid-channel bars of the mesotidal multi-channelled Lower Columbia River, Washington/Oregon, USA, which can experience peak discharges ≥18 000 m³ s⁻¹. These data were used alongside time-sequenced aerial imagery to characterize the spatio-temporal sedimentological evolution of these barforms in singular flows or combined flows consisting of river, tidal and/or wind-wave oscillatory, current components operating in unique fluvial–tidal transition regimes. Results indicate that ca 75% of the Lower Columbia River fluvial–tidal transition produces braid-bars with basal to bar-top sedimentological architectures that are indistinguishable from fluvial-only braid-bars recorded in the literature. Barform stratal characteristics within the fluvial–tidal transitions of mesotidal large-rivers are therefore more likely to be dominated by downstream-oriented currents. Furthermore, a new style of low-angle (<5°) inclined heterolithic stratification found in bar-top accretion-sets within upper-mixed tidal–fluvial regime braid-bars is observed. This common stratification is created by combined-flows characterized by intrabasinal wind-wave oscillatory-currents and bidirectional tidal-currents. This inclined heterolithic stratification marks the initial downstream fluvial–tidal crossover point from Lower Columbia River up-dip fully-fluvial braid-bar architectures, to those possessing bar-top facies produced by the hydraulic-sedimentation response of combined intrabasinal wind-wave and tidal influence. When preserved, this form of mid-channel bar inclined heterolithic stratification provides a unique sedimentological signature of multi-channelled fluvial–tidal transitions that possess an open-water lower basin with intrabasinal wind-waves.     

Lithological–geochemical,petromagnetic, and paleoecological characteristics of the Campanian–Selandian sedimentation conditions in the Ul’yanovsk–Saratov basin

The results of a complex study of the Upper Cretaceous carbonate section in the quarry of the cement plant of the town of Sengilei (Ul’yanovsk district) are presented. The Lower Paleocene cyclic opoka member is described. The formation conditions of the Upper Cretaceous cyclic and cryptocyclic, as well as Lower Paleocene cyclic, rocks are interpreted for the first time on the basis of lithological, petrographic, petromagnetic, geochemical, and paleoecological methods. The cyclicity was formed due to dilution cycles under climate fluctuation and eustatic variations, which were caused by eccentricity cycles of the Earth’s orbit. These cycles are identified in the cryptorhythmic lanceolata sequence of the Lower Maastrichtian rocks.     

Evidence for deep anaerobic biodegradation associated with rapid sedimentation and burial in the Beaufort–Mackenzie basin,Canada

Formation waters of the 14 km thick late Cretaceous–Cenozoic Beaufort–Mackenzie basin were examined as part of a larger project to better understand the petroleum potential of the region, where early exploration defined petroleum reserves of 744 × 10⁹ bbls recoverable crude oil and 11.74 tcf gas. Historical water analyses (2583 samples from 250 wells drilled up to 5 km depth) were compiled and culled to remove incomplete and poor quality samples. The resultant database shows a broad range of salinity and water chemistry that has no systematic relationship with depth. Three main water types are defined, paleo seawater, and freshwaters related to a Miocene age gravity-driven flow system, and low TDS–high alkalinity waters. High alkalinity waters are isolated in overpressured fault blocks that were rapidly buried by post-Miocene Iperk shale deposition. The high alkalinities (up to 9000 mg/L) are interpreted to be related to in situ CO₂ generation through anaerobic methanogenesis in response to freshwater invasion. The dominant control on biogenic gas generation appears to be maximum burial temperature rather than the modern temperature distribution. This is consistent with the paleopasteurization model that suggests once critical burial temperatures are reached, sterilized rocks are inhibited from further biodegradation, even when temperatures subsequently drop back into the habitable zone.     

Response of a dryland fluvial system to climate–tectonic perturbations during the Late Quaternary: Evidence from Rukmawati River basin,Kachchh, western India

Dryland rivers, dominated by short-lived, localised and highly variable flow due to discrete precipitation events, have characteristic preservation potential, which serves as suitable archives towards understanding the climate–tectonic coupling. In the present study, we have investigated the fluvial records of a major, southerly-draining river – the Rukmawati River in the dryland terrain of southern Kachchh, in western India. The sediment records along the bedrock rivers of Kachchh register imprints of the Indian summer monsoon (ISM), which is the major source of moisture to the fluvial system in western India. The Rukmawati River originates from the Katrol Hill Range in the north and flows towards the south, into the Gulf of Kachchh. The field stratigraphy, sedimentology, along with the optical chronology suggests that a braided-meandering system existed during 37 ka period due to an overall strengthened monsoon. A gradual decline in the monsoon strength with fluctuation facilitated the development of a braided channel system between 20 and 15 ka. A renewed phase of strengthened monsoon with seasonality after around 15 ka which persisted until around 11 ka, is implicated in the development of floodplain sequences. Two zones of relatively high bedrock uplift are identified based on the geomorphometry and morphology of the fluvial landform. These zones are located in the vicinity of the North Katrol Hill Fault (NKHF) and South Katrol Hill Fault (SKHF). Geomorphic expression of high bedrock uplift is manifested by the development of beveled bedrock prior to or around 20 ka during weak monsoon. The study suggests that the terrain in the vicinity of NKHF and SKHF is uplifting at around 0.8 and >0.3 mm/a, respectively. Simultaneously, the incision in the Rukmawati River basin, post 11 ka, is ascribed to have occurred due to lowered sea level during the LGM and early Holocene period.     

Mesozoic collision-related magmatism and crust–mantle interaction along the Anhui segment of the Yangtze River Valley,east-central China

The middle segment of the Yangtze River Deep Fault Belt, located in the foreland of the Dabie orogen, contains widely exposed volcanic–intrusive complexes that formed during two episodes of magmatism (post-collisional and post-orogenic), reflecting crust–mantle interactions during the Late Jurassic (J₃) to Early Cretaceous (K₁). This article summarizes research on the Mesozoic igneous suites and xenolith suites in the area along the Yangtze River. ‘Post-collisional magmatism’ occurred during lithospheric extension at ～145–130 Ma. Its beginning and end are marked by gabbroic xenoliths and pyroxene cumulates within intrusions at Tongling, and by alkali-rich magmatic rocks. The association includes peraluminous silicic rocks and metaluminous mafic–felsic igneous suites, ranging from medium-K to high-K calc-alkaline to shoshonitic compositions. Taking the Tongling region as an example, quartz monzodiorite yields a sensitive high resolution ion microprobe (SHRIMP) zircon U–Pb age of 139.5 ± 2.9 Ma, and granodiorite yields an age of 135.5 ± 4.4 Ma. These intrusive rocks contain 52.79–66.46 wt.% SiO₂, 13.12–17.73 wt.% Al₂O₃, 1.37–4.62 wt.% MgO, 3.86–6.84 wt.% FeO^T, and 4.71–7.87 wt.% total alkalis (Na₂O?+?K₂O). ACNK values range from 0.62 to 1.20, and ANK values from 1.45 to 3.48. ‘Post-orogenic magmatism’ occurred during lithospheric delamination at ～130–120 Ma. The start of magmatism was marked by the formation of gabbro containing spinel lherzolite xenoliths in the Nanjing–Wuhu Basin (NWB), and its end was marked by the generation of feldspathoid phenocryst-bearing phonolite in the NWB and the Lujiang–Zongyang Basin (LZB), respectively. The association that formed during this episode ranges from alkaline to peralkaline. Taking the Niangniangshan Formation in the NWB as an example, the Nosite phonolite yields a whole-rock monomineral Rb–Sr isochron age of 120 ± 9 Ma, and contains 49.92–60.09 wt.% SiO₂, 17.67–20.65 wt.% Al₂O₃, 0.08–2.45 wt.% MgO, 1.32–6.62 wt.% FeO^T, and 9.24–13.92 wt.% total alkalis (Na₂O?+?K₂O). ACNK values range from 0.72 to 1.24, and ANK values from 1.03 to 1.35.

The two magmatisms correspond to two episodes of crust–mantle interaction. The first involved intensive interaction between middle–lower crust and underplated basaltic magma derived from the upper mantle lithosphere, whereas the second involved minor interaction between the middle–lower crust and basaltic magma derived from the lower lithospheric mantle.     

The First Reconstructions of Vegetation and Climate Changes in the Central Part of the Oka Plateau (East Sayan Mountains) in the Middle–Late Holocene

Doklady Earth Sciences - The Central part of the Oka Plateau lying in the East Sayan Mountains is still a poorly studied area of southern Siberia as regards its paleogeography. This gap can be...     

The role of evaporites in the formation of magnetite–apatite deposits along the Middle and Lower Yangtze River,China: Evidence from LA-ICP-MS analysis of fluid inclusions

Numerous magnetite–apatite deposits occur in the Ningwu and Luzong sedimentary basins along the Middle and Lower Yangtze River, China. These deposits are located in the contact zone of (gabbro)-dioritic porphyries with surrounding volcanic or sedimentary rocks and are characterized by massive, vein and disseminated magnetite–apatite ± anhydrite mineralization associated with voluminous sodic–calcic alteration. Petrologic and microthermometric studies on multiphase inclusions in pre- to syn-mineralization pyroxene and garnet from the deposits at Meishan (Ningwu basin), Luohe and Nihe (both in Luzong basin) demonstrate that they represent extremely saline brines (~ 90 wt.% NaCl_equiv) that were trapped at temperatures of about 780 °C. Laser ablation ICP-MS analyses and Raman spectroscopic studies on the natural fluid inclusions and synthetic fluid inclusions manufactured at similar P–T conditions reveal that the brines are composed mainly of Na (13–24 wt.%), K (7–11 wt.%), Ca (~ 7 wt.%), Fe (~ 2 wt.%), Cl (19–47 wt.%) and variable amounts of SO₄ (3–39 wt.%). Their Cl/Br, Na/K and Na/B ratios are markedly different from those of seawater evaporation brines and lie between those of magmatic fluids and sedimentary halite, suggesting a significant contribution from halite-bearing evaporites. High S/B and Ca/Na ratios in the fluid inclusions and heavy sulfur isotopic signatures of syn- to post-mineralization anhydrite (δ³⁴S_Anh = + 15.2 to + 16.9‰) and pyrite (δ³⁴S_Py = + 4.6‰ to + 12.1‰) further suggest a significant contribution from sedimentary anhydrite. These interpretations are in line with the presence of evaporite sequences in the lower parts of the sedimentary basins.The combined evidence thus suggests that the magnetite–apatite deposits along the Middle and Lower Yangtze River formed by fluids that exsolved from magmas that assimilated substantial amounts of Triassic evaporites during their ascent. Due to their Fe-oxide dominated mineralogy, their association with large-scale sodic–calcic alteration and their spatial and temporal associations with subvolcanic intrusions we interpret them as a special type of IOCG deposits that is characterized by unusually high contents of Na, Ca, Cl and SO₄ in the ore-forming fluids. Evaporite assimilation apparently led to the production of large amounts of high-salinity brine and thus to an enhanced capacity to extract iron from the (gabbro)-dioritic intrusions and to concentrate it in the form of ore bodies. Hence, we believe that evaporite-bearing sedimentary basins are more prospective for magnetite–apatite deposits than evaporite-free basins.     

Understanding the controls on sediment-P interactions and dynamics along a non-tidal river system in a rural–urban catchment: The River Nene

The release of Phosphorus (P) from river sediments has been identified as a contributing factor to waters failing the criteria for ‘Good Ecological Status’ under the EU Water Framework Directive (WFD). To identify the contribution of sediment-P to river systems, an understanding of the factors that influence its distribution within the entire non-tidal system is required. Thus the aims of this work were to examine the (i) total (P_Total) and labile (P_Labile) concentrations in sediment, (ii) the sequestration processes and (iii) the interactions between sediment P and the river water in the six non-tidal water bodies of the River Nene, U.K. Collection of sediments followed a long period of flooding and high stream flow. In each water body, five cores were extracted and homogenised for analysis with an additional core being taken and sampled by depth increments. Comparing the distribution of sediment particle size and P_Total data with soil catchment geochemical survey data, large increases in P_Total were identified in sediments from water body 4–6, where median concentrations of P_Total in the sediment (3603 mg kg⁻¹) were up to double those of the catchment soils. A large proportion of this increase may be related to in-stream sorption of P, particularly from sewage treatment facilities where the catchment becomes more urbanised after water body 3. A linear correlation (r = 0.8) between soluble reactive phosphate (SRP) and Boron in the sampled river waters was found suggesting increased STW input in water bodies 4–6.P_Labile concentrations in homogenised cores were up to 100 mg kg⁻¹ PO₄–P (generally < 2% of P_Total) and showed a general increase with distance from the headwaters. A general increase in Equilibrium Phosphate Concentrations (EPC₀) from an average of 0.9–∼1.7 μm L⁻¹ was found between water bodies 1–3 and 4–6. Fixation within oxalate extractable phases (Al, Fe and Mn) accounted for ∼90% of P binding in water bodies 4–6, but only between 31 and 74% in water bodies 1–3. Statistical models predicting P_Total (R² = 0.78), oxalate extractable P (R² = 0.78) and Olsen P (R² = 0.73) concentrations in river sediments identified Mn oxy-hydroxides (MnO_x) as a strong predictive variable along with the location within the river system. It is suggested that MnO_x within model predictions is identifying a pool of mixed Fe–Mn oxy-hydroxides (MnO_x–FeOOH) or Fe oxy-hydroxide (FeOOH) from the wider Fe_Oxalate pool that are particularly effective at sorbing and fixing P. The findings demonstrate how sediment and P may accumulate along a 100 km non-tidal river system, the extent to which a range of processes can fix P within mineral phases and how natural flooding processes may flush sediment from the river channel. The processes identified in this study are likely to be applicable to similar river systems over their non-tidal water bodies in eastern England.     

The Holocene climatic optimum and pollen records of sapropel 1 in the eastern Mediterranean, 9000–6000 BP

The most recent sapropel in the deep eastern Mediterranean Sea has been deposited between 9 and 6 ka bp. Climate conditions, as revealed by the pollen records of this sapropel in marine cores, were most favorable for temperate deciduous trees, which is in agreement with the inferences from records of peripheral land pollen sites. The abundance of deciduous oak pollen is much higher than that of Artemisia (sage-brush), indicating that annual precipitation in the mid-elevation borderlands was at least 550 mm without summer drought, but more probably in the range 800–1300 mm. The pollen of Pistacia, which formed a savanna at low elevations, is also at its highest abundance and signals the absence of frost in winter, while being capable of withstanding summer drought. The early Holocene therefore appears as the post-glacial climatic optimum with the highest moisture and mildest winters. In southwest Asia, this is also the time of the Neolithic population explosion with incipient domestication of cereals, possibly following natural selection of the ‘tough rachis’ mutation in wheat and barley by the extreme aridity of the preceding Younger Dryas.     

The Bonneville Estates Rockshelter rodent fauna and changes in Late Pleistocene–Middle Holocene climates and biogeography in the Northern Bonneville Basin,USA

Excavations at Bonneville Estates Rockshelter, Nevada recovered rodent remains from stratified deposits spanning the past ca. 12,500 ¹⁴C yr BP (14,800 cal yr BP). Specimens from horizons dating to the late Pleistocene and early Holocene include species adapted to montane and moist and cool habitats, including yellow-bellied marmot (Marmota flaviventris) and bushy-tailed woodrat (Neotoma cinerea). Shortly after 9000 ¹⁴C BP (10,200 cal yr BP) these mammals became locally extinct, or nearly so, taxonomic diversity declined, and the region became dominated by desert woodrats (Neotoma lepida) and other species well-adapted to xeric, low-elevation settings. The timing and nature of changes in the Bonneville Estates rodent fauna are similar to records reported from nearby Homestead and Camels Back caves and provide corroborative data on terminal Pleistocene–early Holocene environments and mammalian responses to middle Holocene desertification. Moreover, the presence of northern pocket gopher (Thomomys talpoides) at Bonneville Estates adds to a sparse regional record for that species and, similar to Homestead Cave, it appears that the ca. 9500 ¹⁴C yr BP (10,800 cal yr BP) replacement of the northern pocket gopher by Botta's pocket gopher in the Great Salt Lake Desert vicinity was also in response to climate change.     

Palaeogeography of Neogene red bed sequences along the Aksa-Ata River in the Parkent–Nurekata intermontane basin (Tien Shan Mountains,Uzbekistan): With special reference to the magnetic susceptibility of siliciclastic rocks

Siliciclastic red beds formed by stream action in the Parkent–Nurekata intermontane basin of the Tien Shan Mountains, E Uzbekistan. The sedimentary rocks were cross-sectioned in the field and subject to heavy mineral, clay mineral and thin section analyses in the laboratory. In addition to these conventional methods, a survey into the variation of the magnetic susceptibility was conducted. During the Paleogene, calcareous rocks (unit A) developed in a subtidal through supratidal environment of deposition. Subsequently, tectonic disturbances tilted the Paleogene carbonate rocks and triggered the formation of an unconformity during the Oligocene. The Miocene to Pliocene red beds have the hallmarks of a delta-like wedge actively prograding over near-shore marine deposits. Two progradational stages (units B and C) were substituted for by a more regressive event (unit D). During deposition and burial the siliciclastics were percolated by strongly alkaline pore fluids under semi-arid climatic conditions. The joint action of rapid uplift in the hinterland and the afore-mentioned hydrological processes were instrumental for heavy minerals such as epidote and staurolite to survive and some peculiar phyllosilicates such as smectite and palygorskite to precipitate. Debris from metamorphic and igneous rocks were delivered from the rising hinterland. The petrographic and magnetic records of red beds are a mirror image of the unroofing of a magmatic edifice in the provenance area between 11 and 3 Ma.     

The relationship between geology and rock weathering on the rock instability along Mugling–Narayanghat road corridor, Central Nepal Himalaya

The present study was conducted along the Mugling–Narayanghat road section and its surrounding region that is most affected by landslide and related mass-movement phenomena. The main rock types in the study area are limestone, dolomite, slate, phyllite, quartzite and amphibolites of Lesser Himalaya, sandstone, mudstone and conglomerates of Siwaliks and Holocene Deposits. Due to the important role of geology and rock weathering in the instabilities, an attempt has been made to understand the relationship between these phenomena. Consequently, landslides of the road section and its surrounding region have been assessed using remote sensing, Geographical information systems and multiple field visits. A landslide inventory map was prepared and comprising 275 landslides. Nine landslides representing the whole area were selected for detailed studies. Field surveys, integrated with laboratory tests, were used as the main criteria for determining the weathering zones in the landslide area. From the overall study, it is seen that large and complex landslides are related to deep rock weathering followed by the intervention of geological structures as faults, joints and fractures. Rotational types of landslides are observed in highly weathered rocks, where the dip direction of the foliation plane together with the rock weathering plays a principle role. Shallow landslides are developed in the slope covered by residual soil or colluviums. The rock is rather fresh below these covers. Some shallow landslides (rock topples) are related to the attitude of the foliation plane and are generally observed in fresh rocks. Debris slides and debris flows occur in colluviums or residual soil-covered slopes. In few instances, they are also related to the rock fall occurring at higher slopes. The materials from the rock fall are mixed with the colluviums and other materials lying on the slope downhill and flow as debris flow. Rock falls are mainly related to the joint pattern and the slope angle. They are found in less-weathered rocks. From all these, it is concluded that the rock weathering followed by geological structures has prominent role in the rock slope instability along Mugling–Narayanghat road section and its surrounding regions.     

Initiation of left-lateral deformation along the Ailao Shan–Red River shear zone: new microstructural,textural, and geochronological constraints from the Diancang Shan metamorphic massif,SW Yunnan,China

The Diancang Shan metamorphic massif, the northwestern extension of the Ailao Shan Massif, is a typical metamorphic complex situated along the NW–SE-trending Ailao Shan–Red River shear zone. Diancang Shan granitic and amphibolitic mylonites collected from sheared high-grade metamorphic rocks were studied using petrographic and electron-backscatter diffraction techniques. Sensitive high-resolution ion microprobe U–Pb dating of zircon grains from the granitic mylonites constrains the timing of shearing. Macro- and microstructural and textural analysis reveals intense plastic deformation of feldspar, quartz, and amphibole under amphibolite-facies conditions, all consistently document left-lateral shearing. Porphyritic monzogranitic mylonite within the shear zone possesses evidence supporting a sequential, progressive process from crystallization during magma emplacement, through submagmatic flow to solid-state plastic deformation. We suggest that the early-kinematic pluton subsequently underwent strong left-lateral strike–slip shearing. The development of complex textures of quartz, feldspar, and amphibole from the granitic and amphibolitic mylonites apparently records successive variation of conditions attending coherent, solid-state high-temperature ductile deformation during regional left-lateral shearing. All magmatic zircons from the mylonitized porphyritic monzogranite give U–Pb ages of 30.95 ± 0.61 million years for the crystallization of the granite. This age provides the timing of onset of left-lateral shearing along the Ailao Shan–Red River shear zone in the Diancang Shan high-grade metamorphic massif.     

The genetic relationship between hydrocarbon systems and Mississippi Valley-type Zn–Pb deposits along the SW margin of Sichuan Basin,China

The Chipu Mississippi Valley-type (MVT) deposit is located on the southwest (SW) margin of the Sichuan Basin. Occurrence of plentiful organic matter (bitumen) at this deposit and abundant hydrocarbon reservoirs in the SW Sichuan Basin implies a link between lead–zinc mineralization and hydrocarbon systems in this area. The high δ³⁴S values of most metal sulphides from the different ore stages suggest that H₂S-bearing gases and/or thermochemical sulphate reduction (TSR) by organic matter could have been the source of reduced sulphur involved in ore formation. Sulphides with small positive to negative δ³⁴S values can be attributed to organically bound sulphur at the Chipu deposit. Carbon and oxygen isotopic compositions from sparry carbonates suggest mixing of organic carbon with seawater-derived carbon in the mineralization process. From the early to the later ore stages, δ¹³C_PDB values of ore-hosting carbonates are increasingly more negative, which indicates strengthening of the TSR role during mineralization. Hydrogen and oxygen isotopes in fluid inclusions in the quartz gangue indicate the provenance of the ore-forming fluids in the hydrocarbons. Moreover, some extremely low hydrogen isotope values suggest the addition of hydrogen from the same source. The low H/C ratios and high non-hydrocarbon component of the bitumen (Zhang et al. 2010 Zhang, C.Q., Yu, J.J., Mao, J.W., Yu, H. and Li, H.M. 2010. Research on the biomarker from Chipu Pb-Zn Deposit, Sichuan. Acta Sedimentologica Sinica, 28: 832–844. v.p.in Chinese with English abstract [Google Scholar]) also suggest that the organic matter may have been involved in TSR and subjected to a strong oxidation by ore-bearing fluids. This study attempts to explain the lead–zinc mineralization process and the role of organic matter in it. As there is a demonstrable relationship between the evolution of the hydrocarbons and regional lead–zinc mineralization along the SW edge of the Sichuan Basin, we propose a possible model in which the MVT mineralization coincided with the degradation of hydrocarbon reservoirs due to the large-scale migration of basinal fluids, most likely driven by the late Indosinian orogeny in response to the closure of the Palaeo-Tethys Ocean.     

The Relationship between Granitic Rock and Skarn Fe Deposit: A Case Study from the Chengchao Fe Deposit, Edong Ore District, Middle–Lower Yangtze River Valley Metallogenic Belt, Eastern China

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Magnetostratigraphy of Upper Cretaceous strata in Grand Staircase-Escalante National Monument,southern Utah: The Santonian–Campanian Stage boundary,reassessment of the C33N/C33R magnetochron boundary,and implications for regional sedimentation patterns within the Sevier Foreland Basin

Samples were collected for magnetostratigraphic analysis from the Upper Cretaceous Straight Cliffs and Wahweap formations within Grand Staircase-Escalante National Monument, southern Utah, in an attempt to locate the C34n–C33r and C33r–C33n boundaries; the former approximates the Santonian–Campanian Stage boundary. Locating both of these horizons within the Monument provides for refined temporal resolution of the many new fossil localities discovered in these units, while also adding to our understanding of the overall Straight Cliffs–Wahweap sequence stratigraphic architecture. Results indicate that the John Henry and Drip Tank members of the Straight Cliffs Formation are of normal polarity, and represent the later part of C34n, the Cretaceous Normal Polarity Super-Chron. The C34n–C33r boundary apparently resides in a significant hiatus determined to occur between the Drip Tank Member of the Straight Cliffs Formation and the lower part of the overlying Wahweap Formation. In stratigraphically ascending order, the informally named lower, middle, and most of the upper members of the Wahweap Formation are of reversed polarity. The C33r–C33n polarity change occurs in the upper part of the upper member, and C33n continues stratigraphically upward through the capping sand member of the Wahweap Formation and into the overlying Kaiparowits Formation. The presence of over 200 m of reversely magnetized strata above a level in the lower part of the middle member dated to 79.9 ± 0.3 Ma, which coincides with the GTS2012 date for the C33r–C33n boundary of 79.9 Ma, suggests that the published age of that boundary may be in error. A new date of approximately 78.91 Ma is proposed, in turn allowing for the thick sequence of reversely magnetized strata above the 79.9 Ma level. Age revision of the Kaiparowits Basin's Late Cretaceous record demonstrates that during late Santonian through early middle Campanian time, except in central Utah, a close correlation in time and facies successions with other successions throughout the Western Interior Basin suggests a eustatic influence on the depositional patterns. Starting in the late middle Campanian, the Kaiparowits record, along with those both to the north and south, appear to diverge in style and facies successions. We consider this to have resulted from a fundamental change in depositional controls triggered by the Laramide Orogeny. The anomalous central Utah record appears to have been profoundly influenced by a massive salient (Nebo-Charleston thrust system) in the Sevier Fold and Thrust belt that was active for much of the Late Cretaceous.