Abstract
Abstract. Species of Aulacodiscus and Trinacria, two important marine diatom genera with biostratigraphic utility in offshore North Sea exploration and onshore correlation, are identified, described and emended and the North Sea microfaunal zonation scheme is revised accordingly. Occurring mainly as pyritised diatom moulds or steinkerns, detailed scanning electron microscope (SEM) analysis of several specimens, formerly in open nomenclature, has allowed the correct taxonomic identification of pyritised morphologies found to belong to the genus Aulacodiscus, including A. allorgei, A. heterostictus, A. insignis, A. singilewskyanus, A. subexcavatus and A. suspectus. The important marker species Trinacria regina is emended. SEM studies, using specimens preserved in pyrite and original silica, have shed further light on the varying forms and frustule morphology of Trinacria regina so that valves and frustules formerly thought to represent separate species are now found to be grouped within this taxon; SEM studies have shown that many of these variations represent different valves within a chain, whilst others may signify ecophenotypic variants. Emendments are therefore made to clarify the taxonomic status of different variants within T. regina, important in the Palaeocene–Eocene boundary interval onshore and offshore such as the Sele and Balder formations and the Fur Formation diatomite of Jutland, Denmark. Species of taxa formerly in open nomenclature are now assigned to Aulacodiscus insignis, which are important offshore markers in offshore late Oligocene to early Miocene sediments in northwest Europe.
Highlights
This paper examines species from Aulacodiscus Ehrenb. and Trinacria Heiberg which occur within these intervals and are important in offshore exploration biostratigraphy
Difficulties in distinguishing species were commented on in the extensive review of Burke and Woodward (1963–1974), in particular the fact that some species, including those encountered in North Sea Palaeogene and Neogene sediments, possess dissimilar valves, which has caused taxonomic problems where whole frustules are not preserved intact
The taxonomic identity of these taxa was revealed through scanning electron microscope (SEM) studies and comparisons with specimens held in the collections of the Natural History Museum by Mitlehner (1994), refining the earlier work of King (1983) which highlighted their importance as stratigraphic markers in the Oligocene and Miocene but which had them left in open nomenclature (e.g. “Diatom spp. 3, 4 & 5”)
Summary
Marine diatoms have long been known to occur, often in large numbers, at various intervals in the Late Cretaceous to Neogene offshore sedimentary sequences of the North Sea Basin and related onshore sediments in northwest Europe (Heiberg, 1863; Grunow, 1866; Shrubsole and, Kitton, 1881; Wick, 1943–1950; Benda 1965, 1972; Egger et al, 2000; Homann 1991; King and Hughes, 1983; Malm et al, 1984; Mitlehner, 1994, 1996; Thyberg et al, 1999; Van Eetvelde et al, 2004; Richardt and Sheldon, 2014; Sheldon et al, 2018), Russia (Glezer et al, 1974; Oreshkina and Oberhänsli, 2003; Strel’nikova et al, 2004; Aleksandrova et al, 2012; Oreshkina and Radionova, 2014), the North Atlantic (Thomas and Gradstein, 1981), the Norwegian Sea (Scherer and Koç, 1996), and Arctic Canada (McNeill, 1990). This paper redresses this issue, building on previous studies by Mitlehner (1994, 1996), Mitlehner and Hart (2010), and Bidgood et al (1999)
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