Shallow lacustrine carbonate microfacies document orbitally paced lake-level history in the Miocene Teruel Basin (North-East Spain)
by H.A. Abels (Utrecht University), H.A. Aziz (Geophyics LMU Munich), J.P. Calvo (Instituto Geologico y Minero de Espana), E. Tuenter (KNMI),
Results are presented of a detailed carbonate petrographic study of an UpperMiocene lacustrine mixed carbonate–sili ciclastic succession in the TeruelBasin (Spain) with the aim of constraining lake-level variability at differentstratigraphic scales. Regular alternations of red to green mudstone an dlacustrine limestone, termed the ‘basic cycle’ , reflect lake-level variations atthe metre-scale. In an earlier study, the basic cycle was shown to be controlledby the climatic precession cycle. Petrographic analysis made it possible todistinguish two main carbonate microfacies groups characteristic of veryshallow transient and shallow permanent lake env ironments, respectively. Inaddition to the basic cyclicity, the microfacies analysis reveals lake-levelvariations on a larger scale. As a consequence, the astronomical forcinghypothesis of the cyclicity in the Cascante section is explored further. Aclimate modelling study of orbital extremes indicates that high lake levelscould relate to enhanced net winter precipitation and runoff during precessionminima, consistent with Mediterranean geological data. Using this phaserelationship, an astro nomical tuning of the cycles is established starting fromastronomical ages of magnetic reversal boundaries. Subsequently, successivebasic cycles are correl ated to precession minima. The tuning reveals anidentical number of basic cycles in the Cascante section as precession-relatedsapropel cycles in the deep marine succession at Monte dei Cor vi (Italy),corroborating the precessional control of the basic cycles at Cascante. Lake-level highstands in the large-scale cycle identified by the microfacies analysisrelate to maxima in both the ca 100 and 405 kyr eccentricity cycles, againconsistent with Mediterranean geological data. Subtraction of the identifiedastronomically related (lake-level) variations from the palaeoenvironmentalrecord at Cascante indicates a shift to deeper and more permanent lacustrineenvironments in the upper half of the section. The cause of this shift remainsunclear, but it may be linked to tectonics, non-astronomical climate, long-period astronomical cycles or autogenic processes.
Abels, H.A., H.A. Aziz, J.P. Calvo and E. Tuenter, Shallow lacustrine carbonate microfacies document orbitally paced lake-level history in the Miocene Teruel Basin (North-East Spain)