Niebuhr B.,Senckenberg Naturhistorische Sammlungen Dresden |
Hampton M.J.,Network Stratigraphic Consulting Ltd |
Gallagher L.T.,Network Stratigraphic Consulting Ltd |
Remin Z.,University of Warsaw
Acta Geologica Polonica | Year: 2011
Results of detailed multistratigraphic analyses of the campanian-Maastrichtian boundary section at Kronsmoor in northern Germany are summarised and calibrated with the Gssp at Tercis les Bains, southwest France. Additional markers for the definition of the boundary in the Boreal Realm are proposed, and a detailed carbon isotope curve around the campanian-Maastrichtian boundary in the chalk facies of the Boreal epicontinental sea is presented. The c isotopic Gssp marker for global correlation is the markedly abrupt decrease of c. 0.7 ‰ δ13C directly at the campanian-Maastrichtian boundary as dated by ammonites. In electronic borehole measurements the Kronsmoor section covers the sp peaks 53 to 64 and the base of the Maastrichtian being situated just below sp peak 60. The first occurrence (Fo) of the ammonite Pachydiscus neubergicus, which corresponds to biohorizon 1 at Tercis, falls in the upper part of nannofossil Zone uc15, at both localities. Biohorizon 3 is the Fo of the ammonite Diplomoceras cylindraceum, which first appears in the upper campanian of Tercis and at Kronsmoor enters significantly above the Fo of Belemnella lanceolata, the conventional Boreal belemnite marker for the base of the Maastrichtian stage. Based on ammonite evidence, the internationally accepted base of the Maastrichtian at Kronsmoor is located between the Fos of Diplomoceras cylindraceum (upper campanian) and Pachydiscus neubergicus (Lower Maastrichtian) c. 11 m above flint layer F 600, at which the first representatives of the belemnite genus Belemnella, in particular Bn. lanceolata occur. The latter thus is a Late campanian species, appearing c. 450 ky prior to the ammonite-based boundary. The Fos of Belemnella pseudobtusa (sensu schulz) resp. Belemnella obtusa (sensu Remin) directly at the boundary can be use as the coleoid proxy for the definition of the base of the Maastrichtian in the Boreal Realm. To define the boundary by benthic foraminifera the last occurrence (Lo) of Neoflabellina praereticulata is suitable. Biohorizon 12, as defined at Tercis, involves the nannofossilUniplanarius trifidus, however, at Kronsmoor this species is rare, occurs only sporadically and also significantly lower in comparison to Tercis. It is possible though to compare and correlate nannofossil events between Kronsmoor and Tercis using cosmopolitan taxa such as Broinsonia parca constricta and Eiffellithus eximius. The Lo of the latter appears to be situated just above the boundary in both sections; it follows from this that the top of nannofossil Zone uc15 is of early Maastrichtian age.
Hampton M.J.,Network Stratigraphic Consulting Ltd |
Bailey H.W.,Network Stratigraphic Consulting Ltd |
Petroleum Geology Conference Proceedings | Year: 2010
A biostratigraphic review, conducted on 34 wells from the chalk of the Eldfisk Field, Norwegian Central Graben, has been integrated with petrophysical, geophysical and sedimentological information resulting in a revised lithostratigraphic framework for the chalk on this structure. Chalk of Danian to Turonian age is divided into five formations: the established Ekofisk Formation of Danian age and Tor Formation of Maastrichtian age, together with a new three-fold division of the Hod Formation, namely the Magne Formation of Campanian age, the Thud Formation of Santonian age and Narve Formation of Coniacian to Turonian age. This work demonstrates the application of this three-fold division of the Hod Formation. Internal field specific subdivisions of all formations are also presented for the Eldfisk Field. This lithostratigraphic framework is applied across the Eldfisk Field, together with the recognition of erosional features, unconformities, areas of non-deposition, reworking and lateral changes in biofacies. The results have also allowed recognition of the following regionally synchronous tectonic phases for the first time on a Norwegian chalk structure: Stille's Ilsede phase (Late Turonian-Coniacian) and Wernigerode phase (Late Santonian-'earliest' Campanian), Mittel-Santon phase (Middle Santonian) of Niebuhr et al. and Reidel's Peine phase ('latest' Early Campanian), together with un-named phases of 'latest' Campanian, intra Mid Maastrichtian and (previously unrecognized?) intra Danian age. Evidence for these tectonic phases is compared with work from Denmark, Germany and the Anglo-Paris Basin. An innovative approach to mapping lateral biofacies (principally water depth) variations has been applied using the microfaunal database. This enhances understanding of the timing of structural phases when integrated with time lines generated by nanoplankton data. Biofacies proxies for silica content in the sediment may also correlate with changes in reservoir quality. Biofacies interpretations have also facilitated the identification and mapping of allochthonous bioclastic rich debris flow deposits. The fully calibrated biostratigraphic, lithostratigraphic and tectonostratigraphic frameworks presented can be applied to chalk structures regionally. © Petroleum Geology Conferences Ltd. Published by the Geological Society, London.