Measurements on modern coral reefs at Lee Stocking Island(Bahamas) illustrate that boring cyanobacteria species make a major contribution to microboring bioerosion rates. Borings attributed to cyanobacteria also occur in fossil environments. Bioerosional studies on Permian and Triassic reefs show similar intensities to those observed on modern equivalents. The importance of borings assigned to cyanobacterial activity is even more apparent in paleobathymetry. Comparison of the bathymétrie ranges known from modern and fossil microborings demonstrates a preference of boring cyanobacteria for shallow marine environments. Furthermore, some traces are linked to distinct portions of the shallow euphotic zone. They significantly contribute to characterize typical microboring assemblages, which are used for paleodepth reconstructions. In contrast to these stenobathic species, one cyanobacterial species turned out to be eurybathic. It has been recorded as deep as the dysphotic zone but may even extend to the aphotic zone.
Late Quaternary dead molluscan shells off Mauritania (West Africa) from the intertidal zone to 220–300 m water depth were studied for microborings. The study gives preliminary data on microborings in upwelling areas and their implications for the fossil record. In total 18 ichnotaxa are described. They are considered to be produced by cyanobacteria, green algae, red algae, fungi and foraminifera. The ichnotaxonomic composition shows minor differences relative to tropical/subtropical areas of investigation. No ichnotaxa are believed to be specific to upwelling areas. Bathymetrical distribution patterns revealed different depth ranges for individual ichnotaxa. Relative to areas with similar latitude but not influenced by upwelling, the absolute depth of the photic zone is shallower. The majority of ichnotaxa observed are already known from the fossil record (tropical and subtropical study areas) and should also be expected from ancient upwelling areas.
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