Ordovicien

The productive layer of the Estonian oil shale deposit as seen in the Põhja-Kiviõli II opencast mine. The productive layer is made up of oil shale layers A through F1 together with the limestone layers in between. However, in some cases, layers F2, G and H (visible in the image, but not labeled) are also mined. The oil shale beds are marked on the image with capital letters, limestone layers are labeled with a combination of two capital letters, indicating at their location within the productive layer. Dashed lines indicate layer boundaries, which are harder to distinguish and are thus approximations. Stratigraphy: the productive layer of the Estonian oil shale deposit is part of the Kiviõli Member of the Viivikonna Formation. The formation belongs to Upper-Ordovician Kukruse Regional Stage (global Sandbian Stage). (Source reference: Heikki Bauert and Olle Hints "XI Baltic Stratigraphical Conference. Abstracts and Field Guide", Stop 4: Põhja-Kiviõli II open-pit mine, page 85, figure 4.4).

The GSSP for the Hirnantian stage in the ICS geological timescale (uppermost Ordovician stage), located in the Wangjiawan profile (an outcrop of black shale, brownishly weathered siliceous shale and chert layers of the Wufeng Formation) along the G241 road, about 40 km north of Yichang, Hubei, China. An exact golden spike is missing in the profile (2025) but a memorial plague marks the place. The GSSP occurs at the first appearance of fossils of the graptolite species Normalograptus extraordinarius. It was ratified in 2006.

Rock from the Skiddaw Group, of Ordovician (Tremadocian) age, at Scawgill Bridge quarry in Cumbria, England, UK.