Recent investigations indicate that the Cretaceous succession comprises five (rather than 13) formations, with a total thickness which is some 40 percent less than previously supposed. Two major cycles of sedimentation are represented--gray argillites of the Zapata formation which mark the widespread lower Cretaceous transgression in the southern Andes, and the thick sequence of flysch and molasse-type deposits of the Punta Barrosa, Cerro Toro, Tres Pasos, and Dorotea formations, Santonian? to Maestrichtian in age.

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