High resolution stratigraphy and paleoenvironmental changes in the southern North Sea during the Neogene : an integrated study of Late Cenozoic marine deposits from the northern part of the Dutch offshore area

Abstract

This thesis is the result of a multidisciplinary study on the prograding marine Neogene sedimentary succession of the southern North Sea Basin. To date, sediment material available from the Neogene North Sea is very scarce. Its location between 400 and 1500 m below the seabed in the depocentre of the basin is usually to deep for conventional scientific drilling campaigns. These sediments, on the other hand, are situated far above economically interesting hydrocarbon occurrences and are thus not of primary interest for oil companies that usually focus on deeper targets. Recent shallow gas findings in the Netherlands offshore sector, however, spurred exploration activity by Wintershall Noordzee B.V. and the Nederlandse Aardolie Maatschappij (NAM) within Neogene sediments. The generated high quality exploration data enabled the detailed analysis of the marine sediments above the Middle Miocene unconformity (MMU) in the northern Dutch offshore sector presented in this thesis. The extensive data compilation and comprehensive interpretation contribute to a better understanding of the paleoenvironmental history of the Late Neogene North Sea in relation to climate change. Because of the importance of adequate time control, the first aim of this thesis is to find appropriate dating methods and to establish a chronology for the marine sediments above the Middle Miocene unconformity in the northern Dutch offshore sector. Based on a firm chronology, this thesis further aims to contribute to a better understanding of the paleoenvironmental development of the Late Neogene North Sea in relation to climate changes. Information about the marine sediments from the Neogene North Sea Basin is mostly based on indirect, geophysical methods including well-log analyses and seismic interpretation of conventional 2D seismic data. Specific sedimentological investigations of the sediments are scarce and if available, only from locations at more coastal or onshore parts of the basin. Furthermore, it is difficult to tie these sedimentological data to geophysical data. The results of this thesis are obtained from geophysical data including conventional 2D-seismic data, 3D-seismic data and well-log data as well as from sedimentological analyses on discrete sediment samples (cores samples, side wall core samples and cutting material). The sediments have been analysed on the faunal and floral elements (dinocysts, pollen and foraminifers). In addition, measurements on grain-size, clay mineralogy and samarium-neodymium (Sm-Nd) isotopes were performed. These analyses depict the sediment characteristics directly and the imprint of the interacting environmental factors has been independently derived. The multidisciplinary approach of this thesis, combining well-dated climate proxy records and sedimentological data with geophysical data has been used to portray the geological development for the Pliocene North Sea as complete as actually possible.