THE COSHESTON GROUP (LOWER OLD RED SANDSTONE) IN SOUTHWEST WALES - AGE, CORRELATION AND PALEOBOTANICAL SIGNIFICANCE

Upper Silurian-Lower Devonian 'Lower Old Red Sandstone' facies deposit s cropping out in southwest Wales are poorly age-constrained and diffi cult to correlate. Spore assemblages have been recovered from sequence s of these deposits belonging to the lower part of the Cosheston Group . The spore assemblages are equated with the breconensis-zavallatus an d polygonalis-emsiensis Spore Assemblage Biozones and indicate an earl y Devonian age (late Gedinnian (late Lochkovian)-Siegenian (Pragian)). The new biostratigraphical data enable correlation of the lower part of the Cosheston Group with the Senni Beds from the main outcrop of th e Lower Devonian in South Wales and the Welsh Borderland. In addition, the new age data and stratigraphical correlation place important plan t megafossil assemblages from the Cosheston Group and Senni Beds in a more secure stratigraphical framework, thus facilitating comparisons w ith other Lower Devonian plant megafossil assemblages and enhancing pa laeobotanical understanding. Evidence from palynofacies analysis suppo rts sedimentological interpretations which suggest that the 'Lower Old Red Sandstone' facies deposits belonging to the Cosheston Group accum ulated in a continental fluviatile environment.