Elemental geochemical insights into sediment sources, influx variations and depositional environment changes in the Eocene–Miocene Lark Formation, Danish North Sea

The Lark Formation in the Danish North Sea holds great paleoenvironmental interest for understanding climatic and tectonic impacts on sediment supply and depositional environment during the latest Eocene to the Middle Miocene. This study investigates sediment provenance, variations in sediment flux, chemical weathering intensity, and redox conditions in relation to these climatic and tectonic events. A dataset of 86 cuttings and one core from six wells in the Danish North Sea was analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The recently published maceral composition of these samples was also included in this research.

Provenance investigation indicates that the sediment originated from felsic sources within a continental arc tectonic setting. Such a source area is currently located in southern Norway and Sweden on the southwest margin of the Baltic Shield. During the Eocene–Miocene progressive filling of the eastern North Sea Basin, climatic conditions primarily controlled chemical weathering intensity and sediment influx. This is evidenced by higher Chemical Index of Alteration (CIA) and Zr concentrations in the Lower Miocene compared to other series deposited under cooler and less humid climates. Additionally, elemental proxies (Ce_anom, V/(V + Ni), Th/U), along with organic petrological and geochemical evidence, indicate that the Lark Formation was deposited in dysoxic-anoxic environments. Variations of these proxies further reveal that sea-level changes primarily controlled fluctuations in redox condition, resulting in more oxic environments. Moreover, the impact of marine productivity on U and Mo is revealed by the positive correlations between the enrichment factors of U (U_EF) and Mo (Mo_EF) and the abundances of liptinite and Cd. Increased productivity, combined with bottom water anoxia, led to the enrichment of U and Mo in the sediment, with upwelling further enhancing this process.