Integrated lower Silurian chitinozoan and graptolite biostratigraphy of Buttington Brick Pit, Wales

摘要

The chitinozoans recovered from six graptolitic horizons in the Buttington Brick Pit, Wales, are described. A correlation between the upper Llandovery and lower Wenlock chitinozoan and grap-tolite biostratigraphical schemes is presented. These data are compared with the recently refined chitinozoan biostratigraphical scheme in the nearby Banwy River section, Wales. Chitinozoans from definite turriculatus graptolite Biozone strata are described for the first time from the UK. Chitinozoans indicative of the Eisenackitina dolioliformis Biozone occur in the turriculatus Biozone, although the base of the former biozone probably occurs at a lower stratigraphical level. The Angochitina longicollis chitinozoan Biozone has been identified in middle or probably upper spiralis graptolite Biozone strata. Questionably identified A. longicollis occurs lower, in strata assigned to the middle spiralis Biozone, where it occurs with the short-ranging Conochitina mathrafalensis and Belonechitina cavei. This may indicate that: (1) the base of the longicollis Biozone occurs slightly lower in the Telychian in Buttington Brick Pit than in the more basinal Banwy River section; (2) the specimen assigned to A. longicollis? represents an undescribed species; or (3) C. mathrafalensis and B. cavei occur higher in Buttington Brick Pit than in the Banwy River section. The absence of A. longicollis in the turriculatus and crispus graptolite biozones in Buttington highlights the need to re-examine the specimens assigned to A. longicollis from these levels in Estonia, Sweden and Norway. Chitinozoans indicative of the Margachitina margaritana chitinozoan Biozone occur in murchisoni Biozone strata (the base of the former biozone has not been observed at Buttington), and the occurrence of Conochitina flamma indicates that the highest graptolite bed examined correlates with a level high in the murchisoni graptolite Biozone.