Allogene Kontrolle der Sedimenterzeugung und der Erosionsraten im höchsten Küstengebiet der Erde: die Sierra Nevada de Santa Marta (Nordost Kolumbien)
Zusammenfassung der Projektergebnisse
A detailed morphotectonic analysis integarated to a robust compositional database including optical petrography (11,463 grains), Raman heavy mineral analysis (44,782 grains), detrital geochronology (apatite, titanite, and zircon – 6,378 grains), apatite (1,159 grains) and titanite (1,571 grains) geochemistry and bulk-rock and silt-clay geochemistry, allowed to quantify of tectonic, climatic, and lithological controls on (i) Denudation rates, and (ii) the generation of sand and silt/clay in 17 drainages of the Sierra Nevada de Santa Marta (SNSM). Denudation rates based on cosmogenic nuclides range between and 0.094 ± 0.006 and 0.511 ± 0.054 mm/yr for the SNSM. Rares are relatively low considering that the SNSM has a very high relief and is located in a (sub-)tropical region. Compositional signatures are biased and strongly dependent on lithology and resulting sand texture. The grain-size windows used for the analysis of heavy minerals show that their abundance is markedly controlled by inherited texture, with amphibole, titanite, and epidote concentrated in the 63-125 and 125-250 µm fractions, while zircon, titanite, and apatite, (the accessory phases employed for U-Pb dating), are unusually found in the silt (32-63 µm) grain-size window. The detrital geochronology signatures and apatite and titanite geochemistry are also grain-size dependent. A brand-new linear log-ratio mixing model integrating sand and silt bulk-rock and single-grain compositions, and lithological areal distribution, allowed quantifying sediment generation for each lithology. The results indicate that volcanic rocks are systematically underrepresented (up to 40% dilution of compositional signatures), granitic rocks are slightly underrepresented (up to 10%), while metamorphic rocks are overrepresented. The latter is overrepresented due to the coarse nature of the sand generated in the SNSM which is mostly made of rock fragments. The combination of differential sand inputs and mineral fertility of different lithologies is likely the reason explaining the surprisingly low denudation rates. The combined effect of rock avalanche and chemical weathering produce a riverbed that contains pebbles, boulders and some sand, but from different sources recording different erosion rates: sand formed by weathering and supplied by overland flow erosion where erosion rates are usually <0.2 mm/yr, and pebbles and boulders supplied by rock avalanches/landslides where erosion rates could be higher (if measured). In such a case, quartz grains in riverine sediments could record low denudation rates despite the occurrence of a boulderly bedload, abundant rock avalanche deposits in the landscape and steep to oversteepened hillslopes.
Projektbezogene Publikationen (Auswahl)
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Geothermal energy as a means to decarbonize the energy mix of megacities. Communications Earth & Environment, 3(1).
Vargas, Carlos A.; Caracciolo, Luca & Ball, Philip J.
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Lithologic, geomorphic, and climatic controls on sand generation from volcanic rocks in the Sierra Nevada de Santa Marta massif (NE Colombia). Sedimentary Geology, 429, 106076.
Hatzenbühler, D.; Caracciolo, L.; Weltje, G.J.; Piraquive, A. & Regelous, M.
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Multidimensional Scaling of Varietal Data in Sedimentary Provenance Analysis. Journal of Geophysical Research: Earth Surface, 128(3).
Vermeesch, P.; Lipp, A. G.; Hatzenbühler, D.; Caracciolo, L. & Chew, D.
