Heavy mineral variations in mid‐Carboniferous deltaic sandstones: Records of a pre‐depositional sediment history?

Abstract

Sandstone composition is influenced by multiple factors, including acidic weathering, occurring during storage in the hinterland, prior to deposition. This study aims to better understand and constrain how the nature and duration of such pre‐depositional factors might impact the final sediment composition. Mid‐Carboniferous deltaic sandstones from the Clare Basin, western Ireland, for which depositional environments and provenance are well constrained, are the target of this study. Conventional heavy mineral analysis and specific heavy mineral ratios, such as the apatite–tourmaline index are utilised to examine these phenomena. Relatively high apatite–tourmaline index values observed in channelised sandstones contrast with lower values seen in sandstones associated with mouth bar and interdistributary bay facies. These variations are not linked to changes in provenance and thus potentially indicate differences in weathering intensity due to variable duration of alluvial storage. These changes are probably linked with shorter hinterland residence time in the channelised than in mouth bar and interdistributary bay sandstones. Variations are seen in the rutile‐zircon index without any clear link with facies. These fluctuations could be ascribed to variable supply from a source, which is relatively rich in rutile but poor in zircon and apatite. Despite the apatite component in these sandstones being partially derived from recycled sources, the apatite–tourmaline index stills appears to hold information on the last sedimentary cycle.

High‐frequency temporal variability of provenance signal in the submarine fan with the narrow shelf: Insights from sediment delivery and formation of late Triassic Zhuoni fan in the northeastern Paleo‐Tethys Ocean

“…The Zhuoni fan, however, could be easily connected with the river mouth through the plunge of hyperpycnal flows during the lowstand period, which is subject to a lower degree of weathering as a reactive source‐to‐sink system. Conversely, the ATi ratios were relatively lower when sediments were strongly reworked in the shelf region due to sediment buffering during the highstand period (Nauton‐Fourteu et al., 2021). The most robust interpretation was the highstand temporal storage in the shelf region owing to the chemical weathering of apatite within a slightly longer residence time.…”

Rutile to tourmaline index – a tool for the recognition of the hydrodynamics of the depositional environment; a case study from the Campanian Szozdy Delta System, SE Poland

“…Heavy mineral sorting is supported by several examples both in the geological record and in recent environments (e.g., Komar and Wang 1984;Morton and Hallsworth 1994Cascalho and Fradique 2007;Frihy 2007;Garzanti 2017;Nauton-Fourteu et al 2021). As an example, we provide along-profile variations in heavy-mineral percentages in the swash zone of an Oregon beach (Komar and Wang 1984;Text-fig.…”

“…Heavy mineral analysis is amongst the most sensitive and commonly used techniques in the determination of provenance in sandstone and siliciclastic-rich deposits, revealing the depositional and pre-deposi-tional sediment history (e.g., Morton and Hallsworth 1994Frihy 2007;Nauton-Fourteu et al 2021). The composition of heavy mineral assemblages is influenced by three key processes: physical sorting, mechanical abrasion, and dissolution.…”

“…Dissolution, on the other hand, results in the partial or complete loss of heavy minerals under various geochemical conditions at different stages of the sedimentation cycle. These stages include weathering at the source, subaerial exposure in non-marine depositional settings, burial, and, finally, weathering at the outcrop (e.g., Morton and Hallsworth 1994Frihy 2007;Garzanti and Andò 2007;Nauton-Fourteu et al 2021).…”