The Salzgitter-Salder Quarry (Lower Saxony, Germany) and Słupia Nadbrzeżna river cliff section (central Poland): a proposed candidate composite Global Boundary Stratotype Section and Point for the Coniacian Stage (Upper Cretaceous)

Abstract

An integrated account of a candidate composite Global Boundary Stratotype Section and Point for the base of the Coniacian Stage, comprising the Salzgitter-Salder Quarry section (Lower Saxony, Germany) and the Słupia Nadbrzeżna river cliff section (central Poland), is provided. Documented are all the main biostratigraphically significant macrofossil and microfossil groups: ammonites, bivalves (inoceramids and the genus Didymotis), planktonic foraminifera and calcareous nannoplankton. Also provided are correlations based on stable carbon isotope curves. The base of the Coniacian is defined by the first occurrence (FO) of the inoceramid bivalve Cremnoceramus deformis erectus (Meek, 1876), a cladogenetic successor of the C. waltersdorfensis (Andert, 1911) lineage. This event is well above the first appearance of the classic ammonite marker of this boundary, Forresteria petrocoriensis (Coquand, 1859), which is first noted high in the Upper Turonian Mytiloides scupini inoceramid bivalve zone at Słupia Nadbrzeżna. The boundary at Salzgitter-Salder cannot be precisely defined by means of ammonites; however, there is an apparent local change in one scaphitid lineage a short distance below the boundary. In calcareous nannofossil terms, the boundary falls within the interval between the first occurrence of Broinsonia parca parca and the last occurrence (LO) of Helicolithus turonicus. At present, no planktonic species found in both sections can be used as a close proxy for the base of the Coniacian, as defined by the inoceramid bivalve marker. In terms of carbon stable isotopes, the Turonian–Coniacian Boundary lies in the inflection point from falling to rising δ¹³C values. A comparison of the Salzgitter-Salder and Słupia Nadbrzeżna carbon isotope curves indicates a hiatus at the former locality. The base of the Coniacian in the Salzgitter-Salder section is marked by a flood occurrence of Cremnoceramus deformis erectus, constituting the deformis erectus I event. The boundary interval at Słupia Nadbrzeżna is expanded: here the first occurrence of C. deformis erectus is separated from both the terminal Turonian C. waltersdorfensis waltersdorfensis event and the C. deformis erectus I event, also indicating the existence of a hiatus at the boundary in the Salzgitter-Salder section. In view of this hiatus at the critical level, it is proposed that the two sections should constitute a candidate composite Coniacian GSSP.