Upper Ordovician ostracods from the Cautley district, northern England: Baltic and Laurentian affinities

Abstract

The Cautley Mudstone Formation and Cystoid Limestone Member of the Ashgill Formation (Windermere Supergroup; Ashgill Series), from the Cautley district of northern England, has yielded an ostracod fauna of more than 30 species. Many of these have short ranges, permitting recognition of stratigraphically successive Pusgillian-lower Cautleyan, middle-upper Cautleyan, and Rawtheyan ostracod faunas. Several species are also known from the upper Ordovician of North America (Anticosti Island), Scotland (Girvan district) and the Baltic region (Estonia, glacial erratic boulders of northern Germany), providing evidence to correlate upper Ordovician successions in these areas. The ostracods include abundant podocopes, at some horizons accounting for more than 80 % of the fauna. Binodicopes are also common, but palaeocopes are rare. Assemblages are typical of a clastic dominated open marine shelf setting. Diversity at most horizons is low (c. 3-5 species), but reaches a peak of between 13-14 species in middle Cautleyan horizons. Lower diversity at Pusgillian and Rawtheyan horizons coincides with the encroachment of deeper marine-shelf facies which were probably hostile to Ordovician benthonic ostracods. Some of the ostracods (particularly Aechmina) have distributions suggesting tolerance of a range of mid-to deep shelf benthonic palaeoenvironments, but none were pelagic. During Ashgill times the Cautley district (part of palaeocontinental Avalonia) was replete with ostracod genera and species which also occur in the Baltic region (palaeocontinental Baltica; more than 90 % generic similarity) and to a lesser, but nonetheless significant extent in North America and Scotland (parts of palaeocontinental Laurentia). Such trans-Tornquist Sea and Iapetus Ocean distributional patterns add to previous ostracod data that support models which show palaeogeographical proximity of Avalonia and Baltica, and Avalonia and Laurentia, by Ashgill times. The widely cited observation, that trans-Iapetus ostracod faunas remained strictly provincial until the midor late Silurian, cannot be sustained. § Author for correspondence: m.williams@bgs.ac.uk

Upper Ordovician chitinozoan biostratigraphy from the type Ashgill area (Cautley district) and the Pus Gill section (Dufton district, Cross Fell Inlier), Cumbria, Northern England

“…The most recent revision is that of Rickards (2002), to which we refer for a historical overview of the graptolite biostratigraphy. Williams et al (2001) wrote about the ostracods from the Cautley district. Williams et al (2001) wrote about the ostracods from the Cautley district.…”

Middle Katian/lowermost Hirnantian ostracods from the Prague Basin (Czech Republic): Diversity responses to the climatic changes

“…Williams et al (2001) documented ostracod assemblages of Avalonia (Pusgillian-Rawtheyan Stage) from the Cautley Mudstone Formation of northern England. The comprehensive study on Late Ordovician ostracod faunas of England was also provided by .…”

“…The Bohemian ostracod fauna reflects the diversity of binodicopes and palaeocopes in shaly layers below the Perník Bed as being higher than in the carbonate-rich Perník Bed, with the prevalence of binodicopes. The widespread binodicope genera such as Pseudulrichia, Warthinia, Spinigerites and Aechmina are considered to be typical of deep shelf settings and cooler-water benthic palaeoenvironments (Meidla 1996;Copeland 1977;Williams et al 2001Williams et al , 2003. The occurrence of the eridostracan genus Cryptophyllus is often associated with shallow-marine marginal environments (Olempska 2012 and references therein) which is supported by Bohemian material recorded from the carbonaceous Perník Bed.…”

“…There are three ostracod genera common for all studied regions, two of them are geographically widespread binodicopes, namely Aechmina and Pseudulrichia, and one is the palaeocope genus Platybolbina. Another conspecific binodicope ostracod recorded from both Avalonia (Williams et al 2001) and Laurentia (Copeland 1973) is the species Spinigerites unicornis (Ulrich, 1879) sensu Copeland (1973). Williams et al (2001) also consider British species Warthinia cf.…”

“…Another conspecific binodicope ostracod recorded from both Avalonia (Williams et al 2001) and Laurentia (Copeland 1973) is the species Spinigerites unicornis (Ulrich, 1879) sensu Copeland (1973). Williams et al (2001) also consider British species Warthinia cf. nodosa (Ulrich, 1890) to be probably conspecific with Warthinia nodosa established from North America (e.g.…”