Abstract

The Upper Cretaceous-lower Paleocene terrestrial formations from the Aix-en-Provence basin offer a high-resolution record of the effects of climate changes. These units were deposited in a basin with low topographic relief under climate conditions that varied from subhumid to semiarid. Sedimentation during subhumid periods was characterized by accumulation of carbonate mud in the main lake and aggradation of floodplains during overbank floods. Carbonate-rich paleosols, which occur throughout the subhumid succession, contain authigenic minerals with interstratified illite–smectite and smectite.

Although subhumid conditions were dominant during deposition, the occurrence of five semiarid episodes can be documented on the basis of facies, paleomagnetic signal, and mineralogic associations of rocks deposited across the paleolandscape. The lake-margin environment was most sensitive to climate change. Dolomite and gypsum crystals, authigenic smectite and palygorskite, and secondary fine-grained hematite grew within rocks deposited along the lake margin under semiarid conditions. The mineralogic transformations resulted in a distinct paleomagnetic record composed of a It component (200 to 400°C) and an associated chemo-detrital ht component (up to 600°C). During the semiarid episodes, sedimentation in floodplain environments was reduced, allowing development of mature smectite or smectite–palygorskite paleosols.

Semiarid episode 1 occurs within the Calcaire de Rognac Formation, semiarid episodes 2 and 3 lie within the Upper Argiles Rutilantes Formation, and semiarid episodes 4 and 5 are just below and within the Calcaire de Vitrolles Formation. Recognition of correlative deposits with a distinct paleomagnetic signal allows correlation between the continental successions of Provence and the geomagnetic polarity time scale. The lithostratigraphic units, as well as the distribution of dinosaur oospecies are largely diachronous, representing a few millions of years.

Semiarid episodes 1 to 3 occurred during the Early Maastrichtian. No semiarid episodes are recorded for the cooler interval that defined the Middle–Late Maastrichtian. Semiarid episodes 4 and 5 correspond to the warmer periods that preceded and followed the 500-ky-long interval containing the Cretaceous–Tertiary boundary.

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