Microfossil distribution in the Silurian of Britain and Ireland

Microfossils are diverse, abundant, and well-preserved in the Silurian shelf sediments of the British Isles, but are scarcer in graptolitic shale and greywacke sequences. Most work has concentrated on the Welsh Borderland where acritarchs, miospores, conodonts, and ostracodes have all proved stratigraphically valuable. Acritarchs, chitinozoa, and scolecodonts are all abundant from middle Llandovery to upper Ludlow strata and ostracodes are common from the upper Llandovery to the Downtonian. Conodont abundance is highest in the Whitcliffian, but diversity and biostratigraphical value are greatest in the upper Llandovery. Ostracodes are of particular correlative use from the middle Ludlow to Downtonian and acritarchs are important from the middle Llandovery to the upper Ludlow. Miospores are very scarce in Llandovery sediments but in Ludlow and Downtonian strata they are abundant and diverse. All groups display some facies dependence, but miospores occur in a range of nearshore shelf, estuarine, and alluvial deposits and, of the marine groups, acritarchs show least environmental control. Arenaceous foraminifera, hydrozoa, and melanosclerites are sporadically abundant.