The Holocene neritic carbonates of Western Mediterranean Sea
Zusammenfassung der Projektergebnisse
The oligotrophic to slightly mesotrophic cool-water carbonate factories of the Alboran Ridge, the bay of Oran, and the southern shelf of Mallorca in the Western Mediterranean Sea are dominated by red algae. The geometry of the deposits is that of a highstand wedge which thins out towards deeper water; The position of the top of the wedge is controlled by wave base. Sediments unconformably overlie Miocene - Pliocene or older rocks. This shows that older Pleistocene shelf sediments were eroded, probably during sea-level lowstands, and that the highstand wedges are ephemeral sediment accumulations in times characterized by a regime of high-amplitude sea-level fluctuations. Reworked sediments were probably accumulated in wedge-shaped sediment bodies, which are presently lying in water depths of around 120 m. Some intervals in the recovered cores are richer in mollusks. In water depths shallower than 70 m, the sediment surface is covered by a 10 to 20 cm thick veneer which formed during the last 800 to 1000 years. Cool-water carbonates contain up to 53 % aragonite and up to 83 % HMC, each of the areas analyzed has a distinct carbonate mineralogical composition There are no significant downcore trends of enrichment in LMC or in reduction of aragonite. Although the mollusk debris in particular is heavily bored by microendoliths, no micritic rims occur around these components. This corroborates the notion that a lack of micritic rims is indicative for recognizing cool-water carbonates in the stratigraphic record. The benthic foraminiferal faunas from modern cool water carbonate environments of the Western Mediterranean display a distinct bathymetric zonation, mainly attributed to the distribution of rhodoliths and related substrates, and the specific food availability. Based on these observations, transfer functions for paleowater depth reconstructions have been developed and applied to fossil faunas from sediment cores of the study areas. Among various statistical methods tested, the Weighted Averaging-Partial Least Square (WA- PLS) method showed the best performance with a precision of approximately 11 m. On the Alboran Platform and the Mallorca Shelf, relative sea-level rose by approximately 50 m during the past 12 kyr, resembling the global and regional Mediterranean sea-level histories. On the shelf off southwest Mallorca, low stable oxygen isotope values of surface dwelling planktonic foraminifera and a change in sediment facies and benthic ecosystems indicate a local freshening and eutrophication of near-coastal surface waters between approximately 9.6 and 5.5 kyr BP. This interval corresponds to the formation of sapropel S1 in the Eastern Mediterranean Sea and documents enhanced precipitation on Mallorca Island and links to the large-scale northern Hemisphere atmospheric circulation.
Projektbezogene Publikationen (Auswahl)
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2009. Distribution of recent benthic foraminifera in shelf carbonate environments of the Western Mediterranean Sea. Mar. Micropal., 73: 207-225
Milker, Y., Schmiedl, G., Betzler, C., Römer, M., Jaramillo-Vogel, D., Siccha, M.
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2011. Erosion of continental margins in the western Mediterranean due to sea-level stagnancy during the Messinian reflooding. Geo-Marine Letters, 31: 51-64
Just, J., Hübscher, C., Betzler, C., Lüdmann, T., Reicherter, K.
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2011. Late Pleistocene and Holocene cool-water carbonates of the Western Mediterranean Sea. Sedimentology, 58: 643-669
Betzler, C., Braga, J.C., Jaramillo-Vogel, D., Römer, M., Hübscher, C., Schmiedl, G., Lindhorst, S.
