Karbonatplattformentwicklung im Indischen Ozean: Strömungen, Monsun und Meeresspiegel (IndoCarb)
Zusammenfassung der Projektergebnisse
The carbonate edifice of the Maldives bears an exceptional record of the Neogene global climate and ocean current reconfigurations that resulted in the present-day global climate system. The evolution of the carbonate edifice of the Maldives is subdivided into seven stages separated by six turning points of platform growth. The turning points are reliably recorded in the stratigraphy of the carbonates. The first four turning points during the early and middle Miocene are related to sea-level changes. Phases of aggradational platform growth are consistent with long-term sea-level high stands during the early Miocene and the early to middle Miocene Climate Optimum that is dated here between 17 to 15.1 Ma. The sedimentological and ichnological data show that from the Oligocene (~25.5 Ma) to the end of the Middle Miocene Climate Optimum the slope deposits of the Maldives were poorly oxygenated. The change in platform architecture from aggradation to progradation marks a turning point at 15.1 Ma. This change in platform-slope geometries from well-defined bank edges to sigmoidal clinoforms coincides with the global decline of coral reefs during the Middle Miocene Climate Transition around 15 Ma and a general sea-level lowering. In the Maldives, it is also recorded by the backstepping of the outer margin of the carbonate platform. The associated slope deposits have ichnofabrics pointing towards a good oxygenation of the sea-floor. A sudden change of the sedimentation pattern occurred 12.9–13 Ma when the platform sedimentation switched to a current-controlled mode when the monsoon-wind-driven circulation started in the Indian Ocean. The similar age of the onset of drift deposition from monsoon-wind-driven circulation across the entire Maldives archipelago indicates an abrupt onset of monsoon winds in the Indian Ocean. This process went hand into hand with initiation of several steps of platform contraction through drowning events which terminated ca. 3.6-3.9 Ma. In areas where reef growth persisted after the first drowning, the deposits show a change in the fossil assemblage with progressive less corals and more coralline algae and large benthic foraminifera as Amphistegina, Lepidocyclina, Operculina, Borelis, and Marginopora. Ten unconformities dissect the drift sequences in the Maldives, attesting changes in current strength or direction that are likely caused by the combined product of changes in the monsoon-wind intensity and sea level fluctuations in the last 13 Ma. The complete drift succession is intensily bioturbated and characterized by the Zoophycos ichnofacies. This seems to be typical of carbonate drifts as deduced from the comparison with such deposits of Bahamas, Australia, Cyprus and Dennmark. The first three drift sequences in the Maldives correspond to a delta drift, a recently-discovered type of sediment-body that results of the action of bottom currents, pelagic settling and gravity flows, as well as in-situ carbonate production by shallow-water organisms, mainly large benthic foraminifera. A major shift in the drift packages occurred at 3.6-3.9 Ma that coincides with the end of stepwise platform drowning and a reduction of the oxygen minimum zone in the Inner Sea. The study of the granulometry of the most recent drift sediments shows that variability of the lithogenic grains in the sediment is likely an input-related signal, controlled not by current-sorting and winnowing of fine particles, but by the time-variable input of coarser (> 10 µm) dust particles. It is proposed that these grain-size variations thus directly trace past changes in wind intensity over the Indian Ocean.
Projektbezogene Publikationen (Auswahl)
- (2018) Carbonate delta drifts: a new drift type. Mar. Geol., 401, 98-111
Lüdmann, T., Betzler, C., Eberli, G.P., Reolid, J., Reijmer, J.J.G., Sloss, C.R., Bialik, O.M., Alvarez-Zarkikian, C.A., Alonso-Garcia, M., Blatter, C.L., Guo, J.A., Haffen, S., Horozal, S., Inoue, M., Jovane, L., Kroon, D., Lanci, L., Laya, J.C., Mee, A.L., Nakakuni, M., Nath, B.N., Niino, K., Petruny, L.M., Pratiwi, S.D., Slagle, A.L., Su, X., Swart, P.K., Wright, J.D., Yao, Z. and Young, J.R.
(Siehe online unter https://doi.org/10.1016/j.margeo.2018.04.011) - (2018) Ichnofabrics logs for the characterization of the organic content in carbonates. Mar. Petrol. Geol., 95, 246-254
Reolid, J. and Betzler, C.
(Siehe online unter https://doi.org/10.1016/j.marpetgeo.2018.04.019) - (2018) Refinement of Miocene sea level and monsoon events from the sedimentary archive of the Maldives (Indian Ocean). Progress in Earth and Planetary Science 5
Betzler, C., Eberli, G.P., Lüdmann, T., Reolid, J., Kroon, D., Reijmer, J.J.G., Swart, P.K., Wright, J.D., Young, J.R., Alvarez-Zarikian, C.A., Alonso-García, M., Bialik, O.M., Blättler, C.L., Guo, J.A., Haffen, S., Horozal, S., Inoue, M., Jovane, L., Lanci, L., Laya, J.C., Mee, A.L.H., Nakakuni, M., Nath, B.N., Niino, K., Petruny, L.M., Pratiwi, S.D., Slagle, A.L., Sloss, C.R., Su, X. and Yao, Z.
(Siehe online unter https://doi.org/10.1186/s40645-018-0165-x)
