- Copyright © 2009, SEPM (Society for Sedimentary Geology)
Upper Miocene mudflat and marginal lacustrine sediments were deposited on the fringes of an alluvial-fan system in the low-gradient, endorheic southern Teruel Basin, northeast Spain. The 147-m-thick Prado succession consists of 55 meter-scale sedimentary cycles, displaying a clastic-rich and a carbonate-rich interval. The clastic-rich parts are weakly pedogenically modified, red to yellow-orange mudstones and are interpreted as deposits of a well-drained mudflat. The carbonate-rich sediments consist of calcretes, marls, and muddy limestones. The calcretes range from dispersed nodules to massive nodular and are interpreted to be of pedogenic or phreatic origin. The marls and muddy limestones are light- to dark-gray and rich in organic matter, shell fragments, and gastropods. They are interpreted as ephemeral pond to marginal lacustrine deposits. A composite sedimentary cycle model is presented summarizing the different facies and their vertical distribution throughout the Prado area. On a 10 m scale, distinct stratigraphic intervals show lithologic trends representing alternating wetter and drier paleoenvironments. Cycle characteristics are laterally consistent, whereby limestone beds pinch out towards the basin margin and thicken towards the central parts of the 10-km-wide and 20-km-long subbasin.
The high-resolution magnetostratigraphy resolves four normal-polarity and four reversed-polarity intervals that are straightforwardly correlated to chron interval C5n.2n to C5Ar.1r in the ATNTS04 time scale. The resulting age control indicates a duration of 19 to 23 kyr for the meter-scale lithofacies cycles, suggesting control by precession-driven climate change. An astronomical tuning is established by correlating each cycle to the La2004 precession curve using recently recalibrated ages for the polarity reversals as a starting point. The resulting astronomical ages for the reversals in the Prado section are consistent with the astronomically calibrated magnetostratigraphy and cyclostratigraphy of the marine Monte dei Corvi section in Italy. At Prado, three intervals with thicker-than-average cycle thickness most likely reflect obliquity influence during 405 kyr eccentricity minima when precession amplitudes are low. This corroborates the orbital forcing hypothesis of the lithofacies cycles and the astronomical tuning of the Prado succession. The combined magnetostratigraphy and cyclostratigraphy method applied in this study shows the high potential of this method for detecting orbital climate forcing in continental successions.