Библиотека

Strasser A. (1994) Milankovitch cyclicity and high-resolution sequence stratigraphy in lagoonal-peritidal carbonates (Upper Tithonian – Lower Berriasian, French Jura Mountains). IAS Spec. Publ. 19, 285-301.

Three sections of the Tidalites-de-Vouglans and Goldberg Formations have been studied in the French Jura. The sedimentary record consists of well-stratified carbonates which represent shallow-lagoonal, intertidal and supratidal depositional environments where salinities ranged from normal marine to hypersaline or fresh water. The beds display a hierarchical stacking which is probably related to climatically induced sea-level fluctuations in the Milankovitch frequency band. Elementary sequences (commonly corresponding to an individual bed) would represent the 20-ka precession cycle, larger composite sequences the 100- and 400-ka eccentricity cycles. Elementary and larger sequences can, partly and on a small scale, be analysed in terms of sequence stratigraphy. Sequence boundaries mark the top of the beds and in many cases are erosive. Low-stand deposits comprise calcrete, conglomerates and marls with freshwater fossils, or are missing altogether. Thin transgressive deposits follow a generally well-defined transgressive surface and contain reworked pebbles and mixed marine and freshwater fossils. High-stand deposits make up the bulk of the sequences and generally exhibit a shallowing-upward facies evolution. A large part of the sea-level cycle, however, was dominated by non-deposition, reworking and erosion. The time framework given by the inferred Milankovitch cyclicity permits estimation of rates of sediment accumulation and of diagenetic processes. Detailed analysis of depositional sequences interpreted to have been induced by Milankovitch cycles suggests a duration of about 3 .6Ma for the two formations studied. Larger sequences are difficult to identify, but partial time control by ammonites and charophyte-ostracod assemblages allows for a tentative correlation with the global sea-level chart of Haq et al. (1987). Difficulties with and the validity of such a comparison are discussed.

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