Mineralogy and grain size variations along two carbonate margin-to-basin transects (Pedro Bank, Northern Nicaragua Rise).

Reijmer, John and Andresen, Nils (2007) Mineralogy and grain size variations along two carbonate margin-to-basin transects (Pedro Bank, Northern Nicaragua Rise). Sedimentary Geology, 198 (3-4). pp. 327-350. DOI 10.1016/j.sedgeo.2007.01.018.

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Abstract

The analysis of nine periplatform cores in the surrounding of the Pedro Bank carbonate platform showed the presence of characteristic depositional environments during the last 300 ky. This subdivision is based on mineralogical and grain size variations in space and time.

Along the leeward, downcurrent transect the fine sediment fraction (< 63 μm) dominates the periplatform sediments during interglacial highstands in sea level, and no spatial variations in the fine sediment concentration could be observed within 100 km offbank distance. The sediments are mainly of neritic origin preferentially fine aragonite needles. With increasing distance from the margin (> 40 km) aragonite is still the most abundant mineral, but the percentage decreases, while the pelagic carbonate mineral content (LMC) increases. Within the subordinate coarse-fraction classes (> 63 μm) the very fine sand-fraction dominates at proximal sites (< 20 km) as a result of the influence of fine neritic sediments shed offbank. More distal sites (> 20 km) show a more bimodal distribution pattern in the coarse grain sizes with maximum percentages within the very fine and medium sand-fraction, indicating a mixed neritic/pelagic signal.

During glacial lowstands in sea level a twofold division in the spatial distribution of the periplatform sediments is evident. A proximal environment (< 28 km) with enhanced coarse-fraction percentages vs. a distal environment (> 28 km) showing a strong dominance of the fine fraction (> 90%). The increased coarse-fraction percentage during glacials at proximal sites results from various interacting processes: (1) lower input of fine neritic sediments, (2) increased current winnowing, and (3) redepositional processes at the upper slope during lowered sea level, and the export of this material to “proximal basinal” sites (< 28 km).

At upcurrent sites the mineralogy displays a similar spatial evolution as seen along the downcurrent margin, but with overall reduced percentages. This is the result of the lower export potential of the platform against the main direction of the Caribbean Current, the most important factor for neritic sediment dispersal in the study area. The coarse-fraction content is slightly higher during interglacials compared to the downcurrent margin. During glacials a similar reduction in the percentage of the coarse-fraction is evident in a spatial context. This also substantiates the reduced sediment export and redeposition potential at the upcurrent margin.

Document Type: Article
Keywords: Carbonate platform, Caribbean Sea, Sea level, Carbonate export, Quaternary, Carbonate mineralogy, Grain size distribution
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.sedgeo.2007.01.018
ISSN: 0037-0738
Date Deposited: 03 Dec 2008 16:52
Last Modified: 19 Jul 2018 11:52
URI: http://oceanrep.geomar.de/id/eprint/5407

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