Depositional setting of the Lower Old Red Sandstone at Pantymaes Quarry, central South Wales: new perspectives on the significance and occurrence of ‘Senni Beds’ facies

Alluvial deposits of the St Maughans Formation (Lower Old Red Sandstone, Early Devonian) of Tredomen Quarry, near Brecon, southeast Wales, have yielded the oldest known trails of swimming fish as well as body fossils of heterostracans and osteostracans, their inferred producers. Undichna unisulca comprises a single sinusoidal wave (of varying amplitude and wavelength) and is attributed to the caudal lobe or fin of a swimming heterostracan or osteostracan. Variation in the dimensions of U. unisulca trails, together with functional analysis of their inferred producers, suggests different fish sizes and swimming speeds. Undichna cf. simplicitas shows a more complex arrangement of intertwined waves and is interpreted as being produced by a combination of the caudal fin, anal spine and paired pelvic spines of an acanthodian. A new ichnotaxon, Undichna trisulcata isp. nov., consists of three isolated furrows arranged in parallel with associated pectoral fin imprints, and is interpreted as either the trail left by a 'cruising' cephalaspid, intermittently pushing off the substrate with its pectoral fins, or a trail made by a cephalaspid landing on the substrate. The presence of Undichna within these relatively proximal fluvial sediments (displaying no evidence of marine influence) is indicative of an in situ vertebrate freshwater community. Taphonomic constraints on Undichna preservation, in combination with sedimentological analysis, suggest weak bottom currents and/or rapid burial, post-trail formation. Arthropod trackways (Diplichnites gouldi Types A and B, Protichnites isp., and Palmichnium pottsae), a bilobed trail (cf. Cruziana), worm burrows (cf. Cochlichnus) and large meniscate backfilled burrows (Beaconites barretti) contribute invertebrate components to this ichnofauna. The association of Diplichnites trackways on the same surfaces as Undichna supports a semi-aquatic habit of their inferred myriapod producers.

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“…Arthropod trackways and plant remains are also common at this locality (Owen and Hawley 2000;Smith et al 2003).…”

Section: Geological Setting and Stratigraphymentioning

confidence: 95%

“…The overall sequence is similar to that described for similar age sediments at Pant-y-Maes, Powys, where a permanent sandy river system gave way to an ephemeral meandering system with a floodplain. Arthropod trackways and plant remains are also common at this locality (Owen and Hawley 2000;Smith et al 2003).…”

Section: Geological Setting and Stratigraphymentioning

confidence: 95%

Fish trails from the Lower Old Red Sandstone of Tredomen Quarry, Powys, southeast Wales

Morrissey

Braddy

Bennett³

et al. 2004

Geological Journal

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“…are difficult to explain. Owen and Hawley (2000) have advocated tectonic uplift and a change in depositional slope to explain changes from mudstone-prone channel belts to low-sinuosity, multi-storey sandstone bodies within the Senni Beds Formation in central Wales. Tectonic pulses would generate the exposure of a sand-prone provenance either within the inverted Welsh Basin or from more proximal fault blocks.…”

Section: Tectonic Influence On Sedimentationmentioning

confidence: 99%

Variable alluvial sandstone architecture within the Lower Old Red Sandstone, southwest Wales

Williams

Hillier²

2004

Geological Journal

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Sandstone bodies within the Lower Old Red Sandstone (ORS) in southern Pembrokeshire exhibit variability in architecture, sediment grade and composition both spatially and temporally. Four architectural styles are observed, namely decimetre-to metre-thick sheets, metre-thick multi-storey amalgamations, inclined-heterolithic units and ribbon geometries. Sandstone bodies in the Freshwater East Formation are sheet-like, heterolithic units several metres thick. An association with lingulids and wave ripples alludes to a marine influence, possibly estuarine tidal flats or storm washovers. Within the Moor Cliffs Formation, the most common sandstone bodies are centimetre-to metre-thick sheets with high width-to-depth ratios. Fine-grained sandstones represent sheet-flood deposition on unconfined, planar surfaces, whereas coarser-grained sandstones constitute distinctive amalgamations of discrete flood events, reflecting either a change in provenance or tectonic influence. Clear incision of coarse-grained, multi-storey units within the Inter-Tuff Moor Cliffs Formation reflects a change in relative sea-level, possibly tectonically induced.The base of the Conigar Pit Sandstone Member (CPSM) is marked by a distinctive, exotic-clast conglomerate defining the base to heterolithic, lateral-accretion bedsets and sandstone sheets. This association defines a significant influx of coarsegrained sediment post-Chapel Point Calcrete formation, an interval of presumed topographic stability across the Anglo-Welsh Basin. This influx must reflect rejuvenation of source regions, with changes in base-level reflecting either eustatic or tectonic influences. Commonly observed in the CPSM are fine-grained, inclined-heterolithic bedsets recording deposition by highly sinuous rivers with flashy discharge. Up-sequence within the CPSM are metre-thick, multi-storey amalgamations of predominatly trough cross-stratified medium-to coarse-grained sandstone. It is likely that these units are genetically related to contemporaneous decimetre-thick sandstone sheets, the latter being 'splay' events marginal to the main channel axis. The interbedding of multi-storey sandstones and fine-grained laterally accreted units reflects changes in provenance, slope and/or climate.Thickness variations within the Lower ORS detail significant thickening of all units northward into the Benton Fault. It seems likely that this thickening reflects variable accommodation space development associated with active growth along this and other WNW-ESE-trending faults, and migration of channel belts toward the footwall.

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“…Bassett and Owens (1974) reported trackways from the Lower ORS of Krokws (¼ Crwcas) Quarry, near Brecon, attributing them to a scorpion-like arthropod, although reassessment of these together with similar trackways from Pant-y-maes Quarry near Sennybridge (Smith et al 2003), indicates they can be referred to Diplichnites gouldi, produced by myriapods. Owen and Hawley (2000) additionally recorded 'Skolithos-type vertical burrows' and 'endichnial burrows packed with pellets' from siltstone and mudstone horizons in the Lower ORS of Pant-y-maes Quarry.…”

Section: Introductionmentioning

confidence: 99%

Terrestrial trace fossils from the Lower Old Red Sandstone, southwest Wales

Morrissey

Braddy

2004

Geological Journal

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An assemblage of terrestrial trace fossils is described from the Lower Old Red Sandstone of Pembrokeshire, southwest Wales, preserved in mainly fine-grained alluvial facies (channel and overbank sediments, deposited by predominantly ephemeral flows within a semi-arid environment), and thin tuffaceous horizons. The ichnofauna is dominated by an extensive, but low diversity Beaconites ichnocoenosis, comprising the meniscate backfilled burrow Beaconites barretti. Concentrations of these burrows (up to 30 per square metre) show normal size distributions, representing periodic colonization events (inferred as a response to seasonal desiccation) of subaerially exposed (partly indurated) sediments, probably by a population of eoarthropleurid myriapods penetrating the substrate to the level of the water table in order to aestivate and/or moult. Arthropod trackways also characterize an active arthropod epifauna of arachnids (Paleohelcura; first Welsh record) and myriapods (two forms of Diplichnites up to 160 mm wide) and Diplopodichnus. Additional ichnotaxa include arthropod foraging and resting traces (bilobed trails, Tumblagoodichnus and Selenichnites), 'scratch arrays' and worm burrows (Cochlichnus, and Palaeophycus) and faecal pellets all representative of the Scoyenia ichnofacies.

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Depositional setting of the Lower Old Red Sandstone at Pantymaes Quarry, central South Wales: new perspectives on the significance and occurrence of ‘Senni Beds’ facies

Abstract: The 200 m long face of Pantymaes

Cited by 7 publications

References 20 publications

Fish trails from the Lower Old Red Sandstone of Tredomen Quarry, Powys, southeast Wales

Fish trails from the Lower Old Red Sandstone of Tredomen Quarry, Powys, southeast Wales

Variable alluvial sandstone architecture within the Lower Old Red Sandstone, southwest Wales

Terrestrial trace fossils from the Lower Old Red Sandstone, southwest Wales

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