Small planktonic foraminiferal assemblages from the Boreal Aptian Hoheneggelsen KB 9 core (Hannover, northern Germany) - distribution, biostratigraphy and palaeoceanography

摘要

A planktonic foraminiferal biostratigraphy is established for the Boreal Lower to Upper Aptian sediments of the Hoheneggelsen KB 9 core (Lower Saxony Basin, northern Germany) and is correlated to planktonic foraminiferal records of coeval Tethyan sections (Switzerland, southeastern France, Italy, Spain, and Tunisia). Planktonic foraminiferal assemblages of the Hoheneggelsen KB 9 core are characterized by well preserved, small Praehedbergella, Blowiella and Leupoldina specimens and species that are known from the Tethyan Realm and indicate northern Tethyan ingressions during the early Aptian. Planktonic foraminiferal assemblages of the Hoheneggelsen KB 9 core reflect the profound palaeoceanographic change of the marine regime in the Lower Saxony Basin, starting in Lower Aptian sediments older than the 2 m thick mid Lower Aptian Fischschiefer Horizon of the Hoheneggelsen KB 9 core, which is correlated particularly with the Blowiella blowi Zone and considered as the Boreal equivalent of the Lower Aptian Oceanic Anoxic Event (OAE) la of the Tethyan Realm (Selli Level of Italy, Niveau Goguel of southeastern France). Interregional biostratigraphic correlation of the Hoheneggelsen KB 9 core with Tethyan sections is based on first and last occurrences of planktonic foraminiferal zonal marker species (Blowiella blowi, Leupoldina cabri) and suggests that the OAE la interval in the Boreal Hoheneggelsen KB 9 section (northern Germany) and certain Tethyan sections (Roter Sattel, Switzerland; Cassis-La Bédoule, southeastern France; Cau, Spain; Calabianca, Italy) falls within the (upper) Blowiella blowi Zone, whereas the OAE la interval in other Tethyan sections (Jebel Messella and Jebel Ressas, Tunisia; Cismon, northern Italy) falls within the upper Blowiella blowi Zone to lower Leupoldina cabri Zone, or only within the lower Leupoldina cabri Zone (Djebel Serdj, Tunisia; Cismon, northern Italy). The comparison shows that the lower boundary of the Leupoldina cabri Zone needs to be recalibrated if the OAE la period of time is considered as a synchronous time slice.