To evaluate the isotopic record of climate change and carbon sequestration in the Late Paleozoic, we have compiled new and published oxygen and carbon isotopic measurements of more than 2000 brachiopod shells from Carboniferous through Middle Permian (359-260 Ma) strata worldwide. We focus on the isotopic records from the U.S. Midcontinent and the Russian Platform because these two regions provide well-preserved marine fossils spanning a broad time interval.
Brachiopod shells were processed and screened for diagenesis by different methods depending on the research group. Some groups crush shells and pick clear crystals under the microscope. Five to ten milligrams of Ca carbonate are analyzed for trace and minor elements (Mg, Sr, Fe, Mn). Other research groups thin-section shells and use cathodoluminscence and plane light microscopy to screen for diagenesis. Nonluminescent shell is microsampled (0.05-0.1 mg) on the thin-section or complementary billet. All research groups use isotope ratio mass spectrometer for carbon (13C/12C) and oxygen (18O/16O) analyses. These data are used to examine paleotemperatures and their relation to climate in the past.
South Wales is characterised by a rich variety of geologic formations and rocks of different ages and periods, and a large asymmetric syncline, as perhaps its most significant structural geological feature, extending from east to west over a length of approximately 96 km and 30 km from north to south, respectively. This oval-shaped syncline is part of the Variscan orogenic thrust and fold belt in Central Europe and covers some 2,700 km2, with coal-bearing rocks from the Upper Carboniferous (Westphalian Stage) deposited in the central syncline and older rocks outcropping in a peripheral belt around it. The coal-bearing sequence begins with Namurian grits and shales, overlain by the more productive Lower, Middle and Upper Coal Measures. A 3D structural geological model has been implemented for the central part of the South Wales Syncline and its bedrock geology. The oldest rocks in the model domain date back to the Pridoli Series from the uppermost Silurian, the youngest to the Westphalian Stage of the Upper Carboniferous. For model implementation, mainly open access data from the British Geological Survey (BGS) has been used.
The final 3D structural geological model covers the entire Central South Wales Syncline and is 32.8 km wide and 36.6 km long. In total, the 3D model includes 21 fault zones and the elevation depth of ten surfaces: (1) Top Upper Coal Measures Formation; (2) Top Middle Coal Measures Formation; (3) Top Lower Coal Measures Formation; (4) Top Millstone Grit Group; (5) Top Dinantian Rocks; (6) Top Upper Devonian Rocks; (7) Top Lower Devonian Rocks (sandstone dominated); (8) Top Lower Devonian Rocks (mudstone dominated); (9) Top Pridoli Rocks; (10) Top Ludlow Rocks (in parts).