CYCLIC RECORD OF SEA-SURFACE TEMPERATURE AND SEA LEVEL DURING THE VISEAN (CARBONIFEROUS) OF GREAT BRITAIN

Brachiopods with their low-Mg calcite shells are robust archives for recording paleoenvironmental conditions. Shell calcite forms in isotopic equilibrium, and their carbon and oxygen isotope compositions can be used to document changes in sea-surface temperature (SST). The Visean of Great Britain was a time of great tectonic and glacio-eustatic events. We combined our results from the Visean Leete Formation of Llangollen, Wales with results of brachiopods from Derbyshire (Angiolini et al., 2012), and from Llangollen, Anglesey and Bathgate (Popp et al., 1986) to document changes in sea level and SST.

Multiple growth increments (cross-sectional and ontogenetic transects) of the tropical Visean brachiopod Daviesiella llangollensis from Llangollen (Wales) were analyzed for elemental and isotopic compositions. Furthermore, the specimen was screened for diagenetic alteration using cathodoluminescence as well comparative trace chemistry with modern counterparts. Based on the δ¹³C values, the brachiopod exhibits three different growth packages. The first package near the umbo has δ¹³C values ranging from +2.45 to +3.24 ‰ (VPDB). The second package records a steep drop in δ¹³C values to +0.25 ‰. In the third package, the δ¹³C values range from +1.74 to +2.73 ‰. These trends are similar to those observed in the material from Bathgate. Similarly, the samples from Anglesey, Derbyshire, and Llangollen exhibit two growth packages with distinct carbon isotope compositions. The fluctuations in the δ¹³C values observed within the samples represent variations in the carbon reservoir as well as capture sea level changes of rapid transgressions and regressions due to local/global tectonic activity.

When calculating the SST of the Leete Sea, the offshore Llangollen samples record temperatures ranging from 27.7 to 31.6°C (with a δ¹⁸O_SW of -4‰ (SMOW)), and the onshore material record a similar SST range of 28.8 to 31.2°C. Although the samples are from the Leete, Petershill and Monsal Dale Formations of Wales, Scotland, and England respectively, the seawater composition of the near shore locality was isotopically lighter resulting from a higher evaporation rate. We conclude that the δ¹³C and δ¹⁸O values of Daviesiella llangollensis from Great Britain record changes in both seawater temperature and sea levels.