Rare preservation of Triassic pedorelicts with biogenic traces from a hot semi-arid upland palaeoenvironment at Portishead, SW England

Pedorelicts occur sporadically in coastal exposures of Middle to Late Triassic continental sediments, at Portishead, SW England. The clasts include aeolian and bedrock constituents, calcrete textures, vesicles other pedogenic features reflecting a hot semi-arid palaeoenvironment. Interpreted as being derived from an upland soil, they are classified palaeosol terms Calcic Protosol. In the most significant exposure, cryptic tubular trace fossils branching networks within these pedorelict localised fluvial deposit. This extremely rare palaeoecological archive offers glimpse into life Pangaean desert landscape. It is documented for its own merit, support continuing studies palaeobiology prompt investigation comparable deposits. pedorelicts Mercia Mudstone Marginal Facies (MMMF), close basal unconformity with underlying Paleozoic strata, margin Somerset Basin. soil which interpreted have developed regolith over Tournaisian interbedded limestone siltstone. These weathered and, dust containing calcite iron minerals siliciclastic sand, formed structured soil. was aided by intermittent light moderate rainfall that promoted mainly vadose calcretization displacive crystallisation grain breakage. places, vesicular, ‘Av’ horizon, others, it bioturbated development calcite-lined tubules unlined tunnels. At intervals perhaps 104 105 years, catastrophic deluges eroded transported downslope towards basin form onlapping coarse clastic beds typical MMMF. structure disintegrated but fragments became were segregated fault-controlled palaeo-valley, possibly partly debris-flow, be deposited conglomeratic lenses sand. After burial further sedimentation, this deposit underwent diagenetic cementation baryte mineralisation before present exposure erosion.