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Trace fossils from an upper Maastrichtian cyclic chalk-marl succession, the Rørdal Member, exposed in the Rørdal quarry, Denmark, are analysed in order to test whether the changes in substrate lithology exerted any control over the ichnodiversity, tiering complexity, and density of the infauna. The cyclicity is interpreted as caused by orbital changes within the Milankovitch frequency band. The carbonate content varies between 71 and 82 weight% in the marl and 82-92 weight% in the chalk beds. The material is based on 19 samples collected from six chalk and marl beds. The investigated bedding-normal sample surfaces vary in area between 29 and 155 cm2. Eight ichnogenera and two undetermined ichnogenera are recognised. The member is characterised by three ichnofabrics (A, B and C). The ichnofabric analysis is based on texture and internal structure of the sediments resulting from bioturbation. Ichnofabric A is found only in chalk samples and shows a poor preservation of trace fossils, whereas ichnofabric C is found in a few chalk and all marl samples and comprises a very dense, diverse and well preserved ichnofauna representing a high tiering complexity. Ichnofabric B represents an intermediate situation between ichnofabrics A and C and occurs in chalk samples immediately adjacent to marl beds. The observed changes in ichnofabrics between chalk and marl are related to the amount of clay in the samples and the differences in the occurrence of trace fossils are interpreted as due to differences in the visibility of traces between chalk and marl and not due to differences in ecological stress upon the endobenthic community of the two lithologies. The study thus provides an excellent example of how the effect of taphonomic factors may give a misleading and biased impression of apparent differences in the endobenthic community between chalk and marl. 相似文献
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Characterisation of a Campanian deep-sea fan system in the Norwegian Sea by means of ichnofabrics 总被引：1，自引：0，他引：1
Ichnofabrics are applied in concert with sedimentological data to discriminate sub-environments within a Campanian deep-sea fan system in the Norwegian Sea. Seven ichnofabric types are recognised in the studied cores, which correspond to specific architectural elements of the fan system, including amalgamated channels, lobate sand sheets, proximal and distal overbank, fan fringe, and hemipelagic basin plain environments. A unique observation is an ultra-deep Chondrites ichnofabric, interpreted to result from the activity of a chemosymbiotic tracemaker, possibly utilising hydrothermal vents or hydrocarbon seeps in the near vicinity of an active rift system. Mapping and inter-well correlation of ichnofabrics allow a better control of lateral and vertical facies changes, which are important to exploration and production strategies. This study demonstrates that ichnofabric analysis is proving to be a valuable tool for the characterisation and prediction of reservoir quality, the recognition of potential flow barriers and prediction of lateral depositional trends in deep-sea fan deposits. 相似文献
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Li‐Jun Zhang 《Geological Journal》2014,49(2):177-187
A Lower Devonian (Emsian) tempestite in the western Yangtze plate, China, was studied based on ichnological and stratigraphical features. The results indicated that the local tempestite can be grouped into clastic constituent types, which include bottom erosion structures, graded beds, swaley cross‐stratification (SCS), parallel lamination, bioturbation and the new composition Zoophycos ichnofabrics. Five storm sequences and three Zoophycos ichnofabrics (Zoophycos–Chondrites ichnofabric, Zoophycos–Chondrites–Thalassinoides ichnofabric and Zoophycos–Thalassinoides–Palaeophycus ichnofabric) were discerned. It is demonstrated that the Zoophycos‐producers from the complex types of Zoophycos in storm sequences were opportunistic organisms (r‐strategists). This study reveals storm‐generated physical and biogenic structures and textures and provides a good ichnological method to identify storm deposits. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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