10.6084/m9.figshare.3454940.v1 Thomas H.P. Harvey Thomas H.P. Harvey Mark Williams Mark Williams Daniel J. Condon Daniel J. Condon Philip R. Wilby Philip R. Wilby David J. Siveter David J. Siveter Adrian W.A. Rushton Adrian W.A. Rushton Melanie J. Leng Melanie J. Leng Sarah E. Gabbott Sarah E. Gabbott A refined chronology for the Cambrian succession of southern Britain Geological Society of London 2016 succession Caerfai Bay Shales Formation dates Ma basal Quarry Ridge Grits trilobite 238 U decay Comley Sandstone Formation Shropshire tracer calibration Upper Comley Sandstone Formation Pembrokeshire Cambrian Stages 3 Cambrian Stages 4 Geology 2016-06-21 12:27:25 Dataset https://geolsoc.figshare.com/articles/dataset/A_refined_chronology_for_the_Cambrian_succession_of_southern_Britain/3454940 <p>Three dated (U–Pb, zircon) ash beds from biostratigraphically constrained Avalonian successions of Shropshire (England) and Pembrokeshire (Wales) delimit the traditional ‘Lower'–‘Middle' Cambrian boundary and resolve a problematic regional correlation. In Shropshire, a date of 514.45 ± 0.36 [0.81 including tracer calibration and <sup>238</sup>U decay constant errors] Ma from near the top of the Lower Comley Sandstone Formation provides a maximum age for the boundary between Cambrian Stages 3 and 4, and a date of 509.10 ± 0.22 [0.77 including tracer calibration and <sup>238</sup>U decay constant errors] Ma from the basal Quarry Ridge Grits, Upper Comley Sandstone Formation, provides a minimum age for the boundary between Cambrian Stages 4 and 5 (and thus Series 2 and 3). These dates offer a calibration of early metazoan evolution by directly constraining the age of the intervening Comley Limestones, which contain diverse small shelly fossils in addition to trilobites, and also a key early occurrence of exceptional, three-dimensionally preserved arthropods. In Pembrokeshire, an ash bed from the Caerfai Bay Shales Formation dates to 519.30 ± 0.23 [0.77 including tracer calibration and <sup>238</sup>U decay constant errors] Ma, equivalent to a horizon low in the Lower Comley Sandstone Formation of Shropshire, possibly around the level at which trilobites make their first local appearance. </p>