Palynofacies, micropalaeontology, and source rock evaluation of non-marine Jurassic–Cretaceous boundary deposits from northern Germany - Implications for palaeoenvironment and hydrocarbon potential

verfasst von

Anton Christoph Schneider, Jörg Mutterlose, Martin Blumenberg, Ulrich Heimhofer, Friedrich W. Luppold

Abstract

The Jurassic–Cretaceous boundary interval of northern Germany is characterised by non-marine deposits attributed to the Purbeck and Wealden facies. These organic-rich sediments were deposited under restricted, brackish-lacustrine conditions in a palaeogeographically isolated basin (Lower Saxony Basin). Rock-Eval and δ ¹³ C _org measurements were performed to characterise the composition and distribution of the organic matter, to determine the kerogen type chemically, and to define the quantity and maturity of the organic matter. A strong correlation between the optical characteristics, documented by the palynofacies analysis, and the chemical kerogen analyses have led to a better understanding of the palaeoenvironment and the processes which caused the organic matter enrichment. The samples studied from the basin center show a high petroleum generation potential, their estimated maturity is close to the onset of oil generation. Total organic carbon (TOC) concentrations of up to 18% have been measured, hydrogen index values reach up to 1185 mg HC/g TOC. The kerogen assemblages in two basinal successions are dominated by granular amorphous organic material (AOM), dinoflagellate cysts, and Botryococcus algae. In a more marginal succession continent-derived debris (phytoclasts, pollen and spores) is dominant. The AOM is interpreted to have originated either from phytoplankton (probably dinoflagellate cysts and Botryococcus), or its bacterial/archaeal degradation products formed under anoxic conditions. TOC-rich samples which are dominated by these amorphous kerogens show the highest petroleum potential, the AOM therefore plays a key role for the petroleum generation. The long-term climatic and hydrological evolution of the Lower Saxony Basin, which is based on palynomorphs, ostracods, and benthic foraminifera, is here interpreted by a five-stage model. Fluctuations in the salinity of the water bodies are directly reflected by the ratio between different freshwater and brackish-marine organisms as well dinoflagellate cyst diversity; five different cyst morphogroups are used for palaeoenvironmental interpretations. The deposition of TOC-rich beds in the German Wealden can be best explained by both high primary productivity and the establishment of prolonged phases of bottom water anoxia in a brackish-lacustrine depositional environment. Ecological conditions supporting enhanced productivity and preservation of the algal/bacterial-derived organic matter were most favourable during the mid–late Berriasian (Wealden 1–4).

Organisationseinheit(en)

Leibniz Forschungszentrum FZ:GEO
Institut für Geologie
Abteilung Geologie
AG Sedimentologie, Stratigraphie und Palynologie

Externe Organisation(en)

Ruhr-Universität Bochum
Bundesanstalt für Geowissenschaften und Rohstoffe (BGR)
Landesamt für Bergbau, Energie und Geologie (LBEG)

Typ

Artikel

Journal

Marine and Petroleum Geology

Band

103

Seiten

526-548

Anzahl der Seiten

23

ISSN

0264-8172

Publikationsdatum

05.2019

Publikationsstatus

Veröffentlicht

Peer-reviewed

Ja

ASJC Scopus Sachgebiete

Ozeanographie, Geophysik, Geologie, Ökonomische Geologie, Stratigraphie

Ziele für nachhaltige Entwicklung

SDG 14 – Lebensraum Wasser

Elektronische Version(en)

https://doi.org/10.1016/j.marpetgeo.2019.02.016 (Zugang: Geschlossen)