An upper Paleozoic sedimentation cycle is represented by the rocks of the Sabaneta and Palmarito Formations of the Merida Andes, southeast of Lake Maracaibo. The Sabaneta is a terrestrial deposit, whereas the overlying Palmarito is marine. Both formations were deposited on older, mainly Paleozoic strata in the Mucuchachi basin, south and east of Lake Maracaibo. This basin, which occupied approximately the present area of the Venezuelan Andes, is believed to have existed since Middle Ordovician time. Continued uplift and progressive denudation of the basin rims produced the sediments that comprise the two formations. Marked changes of depositional environments, from subaerial to fluvio-marine and eventually holomarine, occurred.

The upper Paleozoic sedimentation cycle is associated closely with the structural and sedimentational history of the Mucuchachi basin during the earlier, preceding two-thirds of the time when the basin existed. Intermittent uptilt of the basin rim, balanced by depression of the trough area, is believed to have been the basic mechanism controlling sedimentation. The recurrent active tilting movements created a hinge zone, a structural feature of primary importance during the two distinct sedimentation cycles which represent the 200-million-year period of the basin's existence.

During earlier Paleozoic time, the hinge zone separated an area of trough deposition, where monotonous, fine, terrigenous clastic material accumulated, from an area where a coarse shelf facies was deposited. The hinge zone also may separate metamorphic from non-metamorphic sequences. During a period of tilting that occurred before the upper Paleozoic sedimentation cycle began, the hinge zone is thought to have been a structural axis along which all Devonian and Carboniferous strata of the shelf facies were removed. It probably is significant that later, during Sabaneta time, the inner-basin side of this structural axis was the locus of deposition of the thickest Sabaneta sections.

Structural characteristics of the Sabaneta-Palmarito sedimentary rocks indicate that compressional stresses acted from southeast to northwest, tending to narrow the basin. The trough deposits of the older Paleozoic were deformed by stresses with a similar orientation, but the resulting structural style is different. The differences in structural style between the two depositional cycles are attributed to the superior thickness, greater homogeneity, and probably more plastic behavior of the older Paleozoic rocks, and to differences in the depths at which the deformations took place. Thus, the slates of the older Paleozoic have been thrown into wide, gently folded synclines seemingly separated by narrow, steeply overthrust anticlines. In contrast, because of marked variations in thickne s and facies, the upper Paleozoic cover has deformed asymmetrically and, in the course of deformation, internal detachment planes developed, particularly within the thinner frontal edges of the cover, causing local imbrication.