Scottish Ordovician ostracodes: a review of their palaeoenvironmental, biostratigraphical and palaeobiogeographical significance

Abstract

Ostracodes have a wide geographical distribution in the Ordovician of Scotland. They are known from the Southern Uplands, the Girvan district, the Highland Border region and the Inner Hebrides. Overall, more than forty species are recorded. They occur in clastic and carbonate rocks indicative of a range of shallow to deeper marine-shelf environments. Though many of the faunas are allochthonous, broad patterns of ostracode palaeoenvironmental distribution can be elucidated, and elements of the shallow marine Leperditella and open marineshelf Anisocyamus associations (previously recorded from N America) are present. Indigenous faunas are absent from the deep marine sediments of the Southern Uplands Northern Belt. Ostracodes are known from the Arenig, Llanvirn, Caradoc and Ashgill series in Scotland; those of the latter two series have widest biostratigraphical value. In the Girvan district the Caradoc species 'Ctenobolbina' ventrospinosa, Krausella variata, Balticella deckeri and Monoceratella teres have correlative value with N America, whilst the Ashgill species Kinnekullea comma appears to be a locum for the anceps graptolite Biozone in Britain, Ireland and possibly the eastern Baltic. The ostracodes are of typical Laurentian affinity, but show progressive generic links with the Baltic region during the late Llanvirn-Caradoc interval, and by Ashgill times display species-level links with southern Britain and Ireland. These distributional patterns suggest approaching geographical proximity for the early Palaeozoic continents of Laurentia, Baltica and Avalonia, and the ability of some Ordovician ostracodes to cross the Iapetus Ocean.

Ostracods from Upper Ordovician (Katian) carbonate lithofacies in southwest Scotland

“…Ostracods preserved as moulds is a common type of preservation in much of the Ordovician succession of Scotland (e.g. Lady Burn Formation, Lower Ardwell Flags, Stinchar Limestone, Balclatchie Group; see Williams et al 2001a;Siveter, 2009) and is also common in England and Wales (see Jones, 1986Jones, , 1987. The ostracods from carbonates of the Craighead Limestone Formation (Fig.…”

“…(Vannier, Siveter & Schallreuter, 1989;Meidla, 1996), late Katian strata of northern England (Williams et al 2001b) and late Katian strata of the Girvan District, Scotland (Floyd, Williams & Rushton, 1999). Balticella species are documented from Sandbian-age strata in the Bromide Formation of Oklahoma (Harris, 1957), the Edinburg Formation of Virginia (Kraft, 1962), the Balclatchie Conglomerate of the Girvan District (Williams et al 2001a) and the Baltic region (Meidla, 1996). Again, the record from the Craighead Limestone Formation extends the range of Balticella into the Katian.…”

“…In part, the lack of study reflects the mostly poor preservation of much of the Scottish fauna and also the difficulty of recovering ‡Author for correspondence: mk241@le.ac.uk ostracods from highly tectonized rocks. Nevertheless, the Ordovician ostracods of Scotland have wide occurrence (Williams et al 2001a), with the most extensive faunas being recorded from the Girvan district in the southwest of the country (Jones, 1879(Jones, , 1893Siveter, 1978;Siveter & Curry, 1984;Floyd, Williams & Rushton, 1999;Williams & Floyd, 2000;Williams et al 2001a). Recent work on the Girvan faunas has documented their biostratigraphic, palaeoecological and palaeogeographic significance (Williams et al 2001a).…”

THE TERGOMYAN MOLLUSC CARCASSONNELLA FROM THE UPPER ORDOVICIAN OF GIRVAN, SCOTLAND

“…Girvan ostracodes show similar biogeographical distribution to that of the brachiopods and trilobites, having mostly Laurentian affinity through the Caradoc with a change towards more genera that had occurred earlier or co‐occurred in Baltica (Williams et al . 2001).…”

“…2001). In the Drummuck Subgroup, the ostracodes Kinnekullea comma and Euprimites from the Lady Burn Formation provide evidence for interaction between Laurentian, Avalonian and Baltoscandian faunas for the first time (Williams et al . 2001).…”