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Cyclicities in Triassic platform carbonates: synchronizing radio‐isotopic and orbital clocks
Author(s) -
Mundil Roland,
Zühlke Rainer,
Bechstädt Thilo,
Peterhänsel Arndt,
Egenhoff Sven O.,
Oberli Felix,
Meier Martin,
Brack Peter,
Rieber Hans
Publication year - 2003
Publication title -
terra nova
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.353
H-Index - 89
eISSN - 1365-3121
pISSN - 0954-4879
DOI - 10.1046/j.1365-3121.2003.00475.x
Subject(s) - milankovitch cycles , geology , cyclostratigraphy , paleontology , sedimentary depositional environment , riphean , magnetostratigraphy , sedimentary rock , carbonate , paleomagnetism , glacial period , materials science , structural basin , metallurgy
Sedimentary cycles recorded in young sediments are often attributed to fluctuations of the Earth's climate on a 10 4 −10 6 ‐year scale which in turn is governed by periodic variations in solar insolation linked to orbital (Milankovitch) parameters. A spectacular example of cyclic stratal patterns in ancient deposits is the Middle Triassic Latemar carbonate platform (W Dolomites, N Italy). Based on spectral analyses from previous studies, a superimposition of precession (∼20 ka) and eccentricity (∼100 ka) controlled sea‐level fluctuations has been suggested to account for the stacking hierarchy at Latemar, with ∼20 ka being assigned to each highest‐order depositional cycle. Zircon U–Pb isotopic ages from volcanic‐ash layers within the cyclic succession, corroborated by biostratigraphic constraints, suggest that the average time interval for every individual cycle is significantly smaller than the shortest Milankovitch period and therefore challenge previously published interpretations relating distinct spectral peaks to the above mentioned hierarchy. However, our new spectral data indicate that cyclicities resembling Milankovitch characteristics might exist, but on an entirely different scale. Our findings show that frequency spectra should only be interpreted in combination with robust age control. They also encourage the search for complementary mechanisms controlling carbonate deposition.