The model-based acoustic impedance inversion shows that low impedance at the BSR marks the base of the hydrate stability zone, confirmed by the well logs.
In the Cisuralian Series the first appearance of Streptognathodus isolatus marks the base of the Asselian Stage, the first appearance of Sweetognathus merrilli marks the base of the Sakmarian, Sweetognathus whitei and Mesogondolella bisselli mark the base of the Artinskian, and Neostreptognathodus pnevi and N. exculptus mark the base of the Kungurian.
This boundary marks the base of the Tremadoc Series in the Ordovician System.
The GSSP has been placed in a thin shale seam amid the limestone, which marks the base of the Lower Leintwardine Formation.
T. pedum, which initially appears in Cambrian deposits and marks the base of the period, demonstrates the first regularly branching burrow pattern.
The emergence of Clarkina postbitteri marks the base of the Wuchiapingian Stage in the Lopingian Series; and the first appearance of Clarkina wangi characterizes the base of the Changhsingian.
The first appearance of Jinogondolella nankingensis specifies the base of the Roadian Stage in the Guadalupian Series, the first appearance of Jinogondolella aserrata indicates the base of the Wordian, and the first appearance of Jinogondolella postserrata marks the base of the Capitanian.
This small unit consists of a massive sandstone layer that marks the base of the Couches de Pechelbronn supérieures.
This sequence, Bf_Hsd17β4, marks the base of the vertebrate Hsd17β4 enzymes (fig. 2; supplementary fig. S1, Supplementary Material online; NJ, 100; ML, 1,000) hence indicating that this SDR family might have already been present at the dawn of chordate diversification.
Today the base of the graptolite zone of Monograptus uniformis is regarded as marking the base of the Devonian.
