Sand supply, sources and evolution of the mid-Carboniferous Clare Basin, western Ireland: insights from multi-proxy provenance approaches
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Sedimentary provenance analysis aims to improve the understanding of all factors associated with sediment production, transport and deposition. This has implications for a wide range of geosciences, helping towards reconstructing palaeogeography, palaeodrainage, and palaeoenvironment. However, multiple factors hinder optimum interpretation of provenance signals in sediments and sedimentary rocks. Some of these factors are investigated in this study, including the impacts of sedimentary recycling and sediment storage in the hinterland, prior to final deposition. This project applies a multi-proxy provenance approach to ancient sandstones from the mid-Carboniferous Clare Basin, western Ireland, to answer key provenance analysis questions and also to better constrain sedimentary routing and sources, basin infill, and palaeogeographic evolution. A large provenance dataset is presented here, comprising zircon U-Pb geochronology data from 13 samples (1624 grains), apatite U-Pb geochronology and trace element results from 10 samples (587 grains), heavy mineral analysis of 31 samples and standard petrographic analysis of 57 samples. The use of zircon and apatite U-Pb geochronology, heavy minerals analysis, apatite trace elements, and petrographic analysis is proven a powerful combination in the identification of sedimentary recycling in mineralogically mature sandstones. The results enable the identification of multiple source terranes supplying the sandstones of the Clare Basin. A major first cycle southern peri-Gondwanan associated input is identified. Additionally, polycyclic zircon (of Laurentian and Caledonian affinity) and apatite (Caledonian affinity) are established as ultimately being derived from the north but recycled through Old Red Sandstone sedimentary basins to the south (e.g. Dingle and Munster basins). Sedimentary recycling is therefore clearly favoured over intensive first cycle chemical weathering, to explain the mineralogical maturity of sandstones in the Clare Basin. The multi-proxy provenance approach identifies sedimentary sourcing in the Clare Basin as being continuously from the WSW-SSW throughout the entire sampled stratigraphy. Comparing provenance signals from the entire basin, both temporally and spatially, using detrital geochronology and heavy mineral indices, enables a better understanding of hinterland and shelf configuration evolution. Furthermore, southern hinterland uplift, linked with the Variscan Orogeny, is envisaged to impact supply during the later infill of the Clare Basin. In addition, heavy mineral indices in Tullig Cyclothem deltaic sandstones indicate a link between detrital mineralogy, sedimentary facies and sediment pre-depositional history. Relatively higher apatite-tourmaline index values are seen in channelised sandstones compared to sandstones associated with mouth bar and interdistributary bay facies. The apatite-tourmaline index highlights variations in the extent of chemical weathering experienced by the sediment prior to deposition. Such findings likely indicate that chemical weathering occurring prior to deposition is dependent on the sediment residence time in the hinterland and this signal appears to carry through to ultimate deposition. This highlights the potential of this specific index for use in reconstructing palaeoweathering and palaeoclimate at a deep-geological time scale. This project advances the utility of provenance analysis and highlights the need for a multi-proxy provenance approach to fully understand sedimentary routing. For the first time, the Clare Basin infill has been fully constrained through a multi-proxy provenance approach. Learnings from this case study from a well-known Irish sedimentary basin can be applied to other sedimentary successions, with a specific applicability to quartz-rich sedimentary rocks.