Quartz overgrowth textures and fluid inclusion thermometry evidence for basin-scale sedimentary recycling: An example from the Mesozoic Barents Sea Basin

Sedimentary recycling has the potential to obscure source‐to‐sink relationships, provenance interpretations, burial history reconstructions and robust reservoir quality predictions in siliciclastic sedimentary basins. Here, we integrate petrographic and cathodoluminescence microtextures with fluid inclusion thermometry in quartz overgrowths to identify sedimentary recycling and to constrain the potential provenance candidate for recycled grains in Lower Mesozoic sandstone of the western Barents Sea basin. Four diagenetic imprints were recognized as proof of sediment recycling: (a) microtextural surface properties of overgrowths, (b) the presence of overgrowths at sutured grain contacts, (c) reversed diagenetic sequences and (d) fluid inclusions within quartz overgrowths. The diagenetic imprints confirm delivery of recycled sediments across the western Barents Sea basin. Their widespread distribution across the basin suggest that the recycled grains were derived from a drainage basin with regional‐scale sediment dispersal potential during the latest Triassic. Furthermore, the drainage basin must have contained sedimentary rocks. Prior to surface exposure, the precursor sedimentary basin was subjected to burial temperatures exceeding 130°C, whereby syntaxial quartz overgrowths precipitated. This temperature indicates an uplift of around 3–4 km, which represents a significant tectonic event. Recycled quartz grains can provide insights on their provenance as they retain direct temperature records. The geothermal signatures and geographically widespread distribution of recycled quartz exclude spatially restricted intrabasinal highs and higher‐temperature crystalline rocks as provenance candidates for the recycled grain portion. Our data support the contemporaneous Novaya Zemlya Fold and Thrust Belt as the most likely provenance candidate in the region. The integrated approach demonstrated herein can be used to constrain sediment recycling and partly eroded provenance candidates in sedimentary basins of equivalent setting worldwide, particularly in quartz‐rich strata susceptible to sediment supply from older uplifted sedimentary basins

Anhydrite pseudomorphs and the origin of stratiform Cu-Co ores in the Katangan Copperbelt (Democratic Republic of Congo)

The stratiform Cu–Co ore mineralisation in the Katangan Copperbelt consists of dispersed sulphides and sulphides in nodules and lenses, which are often pseudomorphs after evaporites. Two types of pseudomorphs can be distinguished in the nodules and lenses. In type 1 examples, dolomite precipitated first and was subsequently replaced by Cu–Co sulphides and authigenic quartz, whereas in type 2 examples, authigenic quartz and Cu–Co sulphides precipitated prior to dolomite and are coarse-grained. The sulphur isotopic composition of the copper–cobalt sulphides in the type 1 pseudomorphs is between −10.3 and 3.1‰ relative to the Vienna Canyon Diablo Troilite, indicating that the sulphide component was derived from bacterial sulphate reduction (BSR). The generation of HCO<sub>3</sub>during this process caused the precipitation and replacement of anhydrite by dolomite. A second product of BSR is the generation of H2S, resulting in the precipitation of Cu–Co sulphides from the mineralising fluids. Initial sulphide precipitation occurred along the rim of the pseudomorphs and continued towards the core. Precipitation of authigenic quartz was most likely induced by a pH decrease during sulphide precipitation. Fluid inclusion data from quartz indicate the presence of a high-salinity (8–18 eq. wt.% NaCl) fluid, possibly derived from evaporated seawater which migrated through the deep subsurface. <sup>87</sup>Sr/<sup>86</sup>Sr ratios of dolomite in type 1 nodules range between 0.71012 and 0.73576, significantly more radiogenic than the strontium isotopic composition of Neoproterozoic marine carbonates (<sup>87</sup>Sr/<sup>86</sup>Sr  = 0.7056–0.7087). This suggests intense interaction with siliciclastic sedimentary rocks and/or the granitic basement. The low carbon isotopic composition of the dolomite in the pseudomorphs (−7.02 and −9.93‰ relative to the Vienna Pee Dee Belemnite, V-PDB) compared to the host rock dolomite (−4.90 and +1.31‰ V-PDB) resulted from the oxidation of organic matter during BSR