Integrated middle-upper Homerian (Silurian) stratigraphy of the Vidukle-61 well, Lithuania

Integrated lithostratigraphical, cyclostratigraphical, graptolite and conodont biostratigraphical and chemostratigraphical (C-13) data are presented from the upper Jaagarahu, Geluva and Dubysa regional stages, including the lundgreni Event (middle Homerian) in the Vidukle-61 well, Lithuania. The Vidukle-61 well is located in the west of Lithuania in the deep-water facies zone. Because of its completeness, this section is the keystone for middle-upper Homerian stratigraphy that allows us to combine different kinds of data into a coherent picture of large-scale biotic and environmental turnover. Three formations are distinguished: the upper part of the Riga Formation, with the Ania Member in the uppermost part, the Siesartis Formation and the lower part of Dubysa Formation. The Grotlingbo bentonite is in the upper part of Ania Member. In the Geluva regional stage, two 4th-order and six 5th-order cycles have been distinguished. In the studied interval of the Vidukle-61 core, the following graptolite biozones were recognized: lundgreni (upper part), parvus, nassa, praedeubeli, deubeli, ludensis and nilssoni (lower part). Conodonts enabled recognition of the bohemica longa Biozone. A single find of Ctenognathodus murchisoni Pander in the nassa graptolite interzone indicates an earlier than previously thought origin of this species.