TELYCHIAN-EARLY SHEINWOODIAN (EARLY SILURIAN) CONODONT-, GRAPTOLITE-, CHITINOZOA-, AND EVENT-BASED CHRONOSTRATIGRAPHY DEVELOPED USING THE GRAPHIC CORRELATION METHOD

Graphic correlation of several previously uncompiled stratigraphic sections with the Silurian Composite Standard of Kleffner and Barrick (2007) results in recognition, and “filling in,” of a Telychian unconformity in the Standard Reference Section (Cellon, Austria), and a revised Telychian-early Sheinwoodian (Early Silurian) Composite Standard (CS) that has worldwide applicability as a high-resolution chronostratigraphy. The Early Silurian CS is divisible into 12 conodont chronozones, 12 graptolite chronozones, and seven chitinozoa chronozones, most of which are defined in the same manner as previously recognized biozones for those taxa. The Telychian-early Sheinwoodian CS includes 28 bentonites, 17 of which occur in at least two sections belonging to the CS. Because only one bentonite has yielded a reliable radiometric date, the new CS cannot be scaled relative to absolute ages. In the Telychian-early Sheinwoodian CS, correlation of the conodont, graptolite, and chitinozoa chronozones comprising the CS compares favorably to recent correlation of Telychian-early Sheinwoodian conodont and graptolite zones (Männik, 2007) and conodont and chitinozoa zones (Kiipli et al., in press). The level for the base of the Wenlock in the Global Boundary Stratotype Section and Point for the base of the Wenlock, the Hughley Brook, Leasows, Great Britain section, graphically correlates to a position in the upper part of the Cyrtograptus murchisoni Chronozone, within the Upper Pseudooneotodus bicornis Chronozone (just above Datum 2 of the Ireviken Event), within the upper part of the Margachitina margaritana Chronozone, and just above the Ireviken Bentonite.