A new plant assemblage (microfossil and megafossil) from the Lower Old RedSandstone of the Anglo-Welsh Basin: its implications for the palaeoecologyof early terrestrial ecosystems

Lower Old Red Sandstone deposits penetrated by a series of cored boreholes near Newport (South Wales) have been sedimentologically logged, and recover ed plant assemblages (microfossil and megafossil) investigated. Sedimentolo gical logging indicates that the deposits are typical of the extensive terr estrial-fluviatile floodplain deposits of the Anglo-Welsh Basin. Palynomorp h assemblages have been recovered from a number of horizons and comprise en tirely terrestrial forms (spores and phytodebris). They essentially represe nt a single assemblage, belonging to the middle subzone of the micronatus-n ewportensis sporomorph assemblage biozone, and indicate an Early Devonian ( mid-Lochkovian) age. The new biostratigraphical data enables correlation wi th other Lower Old Red Sandstone deposits of the Anglo-Welsh Basin, and the deposits are assigned to the lower part of the St. Maughan's Group. A plan t megafossil/mesofossil assemblage recovered from one of the spore-bearing horizons includes a zosterophyll assigned to Zosterophyllum cf. fertile. Th is is the earliest reported zosterophyll from the Anglo-Welsh Basin.:The ne w palynological/palaeobotanical data provide important information on the p alaeoecology and palaeobiogeography of the vegetation of the southeastern m argin of the Old Red Sandstone continent during Lochkovian times. Palaeogeo graphical variation in the distribution of plant microfossils and megafossi ls is interpreted as reflecting differences between the flora of the lowlan d floodplain and inland intermontaine basins, although this is to a certain extent overprinted by variation due to localized differences in environmen tal conditions. (C) 2000 Elsevier Science B.V. All rights reserved.