Albian to Turonian agglutinated foraminiferal assemblages of the Lower Saxony Cretaceous sub-basins – implications for sequence stratigraphy and paleoenvironmental interpretation

Richard M Besen,Ulrich Struck,Ekbert Seibertz

doi:10.5194/fr-24-395-2021

Richard M Besen, Ulrich Struck + Show 1 more

Open Access

https://doi.org/10.5194/fr-24-395-2021

Copy DOI

Abstract

Abstract. Albian to Turonian carbonate deposits at three different locations of the Lower Saxony Cretaceous and thereby of the European mid-Cretaceous epeiric shelf sea were investigated for their fossil agglutinated foraminiferal fauna. In this study, 71 samples from two quarries and three drill cores were treated with formic acid, which enabled the study of agglutinated foraminiferal assemblages even in highly lithified limestones. In total, 114 species were determined and classified as belonging to nine morphogroups. In general, four agglutinated foraminiferal assemblages are distinguished: (1) an uppermost Albian–lowermost Cenomanian assemblage from the Wunstorf drill cores, with the dominant taxa Bathysiphon spp., Nothia spp., Psammosphaera fusca, Reophax subfusiformis, Bulbobaculites problematicus, Tritaxia tricarinata, Flourensina intermedia, Vialovella frankei, Arenobulimina truncata, and Voloshinoides advenus; (2) a Cenomanian assemblage from the Baddeckenstedt quarry and Wunstorf drill cores, with Ammolagena clavata, Tritaxia tricarinata, Vialovella frankei, Arenobulimina truncata, and Voloshinoides advenus; (3) an assemblage related to the Cenomanian–Turonian Boundary Event in Wunstorf and Söhlde dominated by Bulbobaculites problematicus; and (4) a Turonian assemblage in the Wunstorf and Söhlde sections with high numbers of Ammolagena contorta, Repmanina charoides, Bulbobaculites problematicus, Gerochammina stanislawi, and Spiroplectammina navarroana. The latest Albian–earliest Cenomanian assemblage consists of tubular, globular, and elongate foraminiferal morphogroups which are typical for the low- to mid-latitude slope biofacies. All other assemblages are composed of elongate foraminiferal morphogroups with additionally globular forms in the proximal settings of Baddeckenstedt and Söhlde or flattened planispiral and streptospiral forms in more distal settings of Wunstorf. For these assemblages, a new agglutinated foraminiferal biofacies named “mid-latitude shelf biofacies” is proposed herein. Changes in the relative abundance of different morphogroups can often be referred to single features of depositional sequences. Furthermore, classical macro-bioevents, which are often depositional-related, of the Lower Saxony Cretaceous seem to have a micro-bioevent or acme equivalent of the agglutinated foraminiferal fauna.

Highlights

During the mid-Cretaceous, sedimentary sub-basins of Lower Saxony and the Subhercynian were part of a wide epeiric continental shelf sea connected with the Arctic realm, the young North Atlantic Ocean and central Atlantic Ocean, and the Tethys Ocean, which were separated by the MidEuropean Island (Janetschke et al, 2015)
Four agglutinated foraminiferal assemblages are distinguished: (1) an uppermost Albian–lowermost Cenomanian assemblage from the Wunstorf drill cores, with the dominant taxa Bathysiphon spp., Nothia spp., Psammosphaera fusca, Reophax subfusiformis, Bulbobaculites problematicus, Tritaxia tricarinata, Flourensina intermedia, Vialovella frankei, Arenobulimina truncata, and Voloshinoides advenus; (2) a Cenomanian assemblage from the Baddeckenstedt quarry and Wunstorf drill cores, with Ammolagena clavata, Tritaxia tricarinata, Vialovella frankei, Arenobulimina truncata, and Voloshinoides advenus; (3) an assemblage related to the Cenomanian–Turonian Boundary Event in Wunstorf and Söhlde dominated by Bulbobaculites problematicus; and (4) a Turonian assemblage in the Wunstorf and Söhlde sections with high numbers of Ammolagena contorta, Repmanina charoides, Bulbobaculites problematicus, Gerochammina stanislawi, and Spiroplectammina navarroana
During the interval of the Cenomanian Turonian Boundary Event (CTBE), Bulbobaculites problematicus occurs with high relative abundances of usually more than 30 %, and Spiroplectammina navarroana has an acme in the plenus Bed in the Wunstorf 2010/4 core (Figs. 12 and 15)

Summary

Introduction

During the mid-Cretaceous, sedimentary sub-basins of Lower Saxony and the Subhercynian were part of a wide epeiric continental shelf sea connected with the Arctic realm, the young North Atlantic Ocean and central Atlantic Ocean, and the Tethys Ocean, which were separated by the MidEuropean Island (Janetschke et al, 2015). To understand the sea level and depositional sequence coupling and other paleoenvironmental changes in the Lower Saxony Basin, investigations were made for the Albian (e.g. Fenner, 1996; Tyszka, 2009; Bornemann et al, 2017), for the Cenomanian Linnert et al, 2010; Hetzel et al, 2011; Blumenberg and Wiese, 2012; van Helmond et al, 2015), and for the Turonian (Wiese et al, 2015) Most of these studies approach the former conditions in the upper water layers of this Cretaceous shelf sea by focussing on planktic foraminifers and calcareous nannofossils. To get a better understanding of the paleoenvironment of the mid-Cretaceous deposits of Lower Saxony, in particular additional information of the bottom water conditions is necessary

Objectives

Methods

Findings

Conclusion