Trace fossils and ichnofabric in the Kjølby Gaard Marl, uppermost Cretaceous, Denmark
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The Kjolby Gaard Marl (Late Maastrichtian) is a 30 cm-thick, grayish brown, clay-rich, pelagic carbonate rj unit (75 to 85% CaC03) exposed in the Limfjord region of northern Jylland, Denmark. Trace fossil suites and ichnofabric (the sedimentary fabric resulting from all phases of bioturbation) reflect a complex depositional and post-depositional history of the marl unit, which is sandwiched between comparatively pure strata above and below. Initiation of marl deposition occurred gradually and episodically, as indicated by a micro-styolitic fabric resulting from solution-compaction of finely alternating and clay laminae in the basal portion of the bed. During the major phase of marl deposition represented by the middle and upper parts of the unit, the sea floor apparently was very soft and was colonized by an active infauna which produced a low-diversity suite of trace fossils dominated by horizontal burrows. These are now preserved in a highly compacted ichnofabric which is totally bioturbated but contains no easily identifiable trace fossils. As the sedimentary mode returned to deposition, the marl was buried and subsequently strengthened by compaction sufficiently to allow its colonization by a deeper-burrowing infauna that normally preferred somewhat stifter, chalky substrates. Thus, the original ichnofabric was modified by the introduction of late-generation, sharply defined and relatively uncompacted chalk trace fossils (Thalassinoides, Zoophycos and Chondrites, probably appearing in that order). These are superimposed directly on top of the earlier, highly deformed burrows of the initial trace fossil suite.Keywords:
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Kotake, Nobuhiro 1989 07 15: Paleoecology of the Zoophycos producers. Lethaia, Vol. 22. pp. 327–341. Oslo. ISSN 0024–1164. Well-preserved Zoophycos and Spirophyton-like burrows occur in the Upper Pliocene deep-sea sediments exposed along the southern coast of Boso Peninsula, central Japan. They consist of an axial tunnel and helically coiled spreite with fecal pellets. In most cases the two kinds of trace fossil are found separately. In several complete specimens, however, the upper and lower portions represent a Spirophyton-like burrow and Zoophycos, respectively. The downward increase in size of the spreite and fecal pellets in a single burrow suggests that the complete Zoophycos was built successively as the producing animal grew. The occurrence of incomplete Zoophycos may have resulted from post-mortem destruction by echinoid locomotion and turbidity currents. In some cases, the uppermost portion of the axial tunnel is covered with a thin tuff layer. Fecal pellets in such burrows consist of the same tuffaceous material which must have originated from the overlying tuff layer. This fact indicates that the burrow producer did not feed on organic matter within the sediments but foraged detritus on the sea floor. The animal could probably stretch a part of the body from the top of the axial tunnel for feeding and systematically pack the fecal pellets into the sediments. Such segregation between the feeding place and the excretory space is interpreted as an efficient feeding strategy for the detritus-feeding burrowers in the deep sea. D Zoophycos, Spirophyton-like burrow, paleoecology, feeding and excretory behavior, Boso Peninsula, Japan.
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All chalks are fine-grained pelagic sediments derived from calcareous microplankton and nannoplankton. However, chalk (deposited in hundreds of meters of water) differs from chalk (deposited in thousands of meters of water) in several paleontologic and sedimentologic respects. Unlike deep-sea chalk, shelf-sea chalk characteristically contains abundant megafossils, flints, omission surfaces, hardgrounds, borings and early diagenetic mineralization (pyrite, glauconite and phosphate) of trace fossils and clasts. Trace fossil associations are dominated by Thalassinoides and other crustacean burrows in most shelf-sea chalk sections; trace fossil associations in deep-sea chalk cores are dominated by Chondrites, Planolites and Zoophycos.--Modified journal abstract.
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1990, Special Topics in Palaeontology 3,280 pp., E17.95 (pbk), E40.00 (hbk). Unwin Hyman, London. ISBN 004445/6867 (pbk)/3035 (hbk).
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Abstract Infaunal communities in marine environments typically are tiered; that is, different taxa live at different depths within the sediment. Tiered suites of biogenic structures yield complex biogenic sedimentary fabrics (ichnofabrics), with the traces of deep-burrowing organisms overprinted on those of shallow-burrowing organisms. Careful analysis of crosscutting relationships of burrows in such composite ichnofabrics allows reconstruction of the tiered nature of fossil endobenthic communities. It is important to recognize that the best preserved and most prominently displayed trace fossils in most assemblages usually represent the deepest tier. Thus, they were farther removed from the sea floor and therefore less indicative of actual sea floor conditions than the more poorly preserved traces of the shallower tiers, on which the deeper traces are juxtaposed.
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A new scheme for the description and analysis of bioturbation and the resultant ichnofabrics is proposed. This system can be used in core and field-based studies and consists of two parts. (1) A bioturbation index in which a descriptive grade is assigned to the degree of bioturbation. This integrates the sedimentology and ichnology, where the higher grades of bioturbation result from increased burrow overlap and the subsequent loss of the primary sedimentary fabric. (2) An ichnofabric constituent diagram which records the detail of the ichnofabric by graphically plotting the dimensional data of the ichnotaxa and their order of emplacement against their coverage. This scheme differs from previous attempts to characterize bioturbation using semi-quantatitive methods and visually portrays the ichnofabric so that comparative studies can be carried out. This is of particular use in facies analysis, the establishment of the ichnocoenoses and tier diagrams, and within sequence stratigraphic studies so that hiatal surfaces can be recognized.
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Research Article| January 01, 1986 Trace-fossil model for reconstruction of paleo-oxygenation in bottom waters Charles E. Savrda; Charles E. Savrda 1Department of Geological Sciences, University of Southern California, Los Angeles, California 90089-0741 Search for other works by this author on: GSW Google Scholar David J. Bottjer David J. Bottjer 1Department of Geological Sciences, University of Southern California, Los Angeles, California 90089-0741 Search for other works by this author on: GSW Google Scholar Geology (1986) 14 (1): 3–6. https://doi.org/10.1130/0091-7613(1986)14<3:TMFROP>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Charles E. Savrda, David J. Bottjer; Trace-fossil model for reconstruction of paleo-oxygenation in bottom waters. Geology 1986;; 14 (1): 3–6. doi: https://doi.org/10.1130/0091-7613(1986)14<3:TMFROP>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Recognition of fluctuations in the degree of paleo-oxygenation of bottom waters recorded in fine-grained pelagic strata is important for interpretation of paleoceanographic and paleoclimatologic conditions. General sedimentary fabric, composition of trace-fossil assemblages, and burrow size and crosscutting relationships have been incorporated into a trace-fossil tiering model that permits detailed reconstruction of changes in paleo-oxygenation of bottom waters. Applications of this model to the Miocene Monterey Formation (California) and the Cretaceous Niobrara Formation (Colorado) indicate that the ichnologic approach is more sensitive to both magnitude and rates of change in oxygenation levels compared to macrobenthic body-fossil information. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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