Composition and distribution of sedimentary organic matter in the distal Wealden facies (KB Rehburg-2) of the Lower Saxony Basin, Germany

New insights into the Lower Cretaceous sediments can be gained from a recently drilled core (KB Rehburg-2, Lower Saxony, Germany) covering 180 m of Berriasian strata. Stratigraphic assignment is based on ostracods and indicates Wealden 1-4. Palynofacies analysis was carried out to reconstruct the depositional environment of the sequence studied. This data was complemented by geochemical measurements (TOC, Stot, δ13Corg and RockEval pyrolysis) and sedimentological observations to reconstruct the paleoenvironmental conditions during the earliest Cretaceous in the LSB. The particulate organic matter (OM) shows good to very good preservation and is composed of diverse spores, pollen grains, algae and woody debris; marine particles such as dinoflagellates, acritarchs and prasinophytes occur only sporadically.

Data evaluation and integration reveals a predominantly lacustrine, freshwater to brackish depositional system with high continental OM input. Abundance peaks of Botryococcus algae occur throughout the sequence and indicate freshwater to brackish conditions. The rare occurrence of dinoflagellates and acritarchs can be interpreted as indicators of short-term marine ingressions into the LSB. Prasinophytes point to repeated salinity changes. The scarce abundance of dinoflagellate cysts differs significantly from existing studies in the LSB by Schneider et al. (2017), but correlation with two marine transgressive events is tentatively proposed (TE 1-2). This difference may result from a potentially more terrestrially dominated depositional system represented by the Rehburg-2 core.

References:

Schneider, A.C., Heimhofer, U., Heunisch, C., & Mutterlose, J. 2017. The Jurassic-Cretaceous boundary interval in non-marine strata of northwest Europe – New light on an old problem. Cretaceous Research 87, 42-54.