ABSTRACT The Permian marks a time of substantial climatic and tectonic changes in the late Paleozoic. Gondwanan glaciation collapsed after its earliest Permian acme, aridification affected the equatorial region, and monsoonal conditions commenced and intensified. In western equatorial Pangea, deformation associated with the Ancestral Rocky Mountains continued, while the asynchronous collision between Laurentia and Gondwana produced the Central Pangean Mountains, including the Appalachian-Ouachita-Marathon orogens bordering eastern and southern Laurentia, completing the final stages of Pangean assembly. Permian red beds of the southern midcontinent archive an especially rich record of the Permian of western equatorial Pangea. Depositional patterns and detrital-zircon provenance from Permian strata in Kansas and Oklahoma preserve tectonic and climatic histories in this archive. Although these strata have long been assumed to record marginal-marine (e.g., deltaic, tidal) and fluvial deposition, recent and ongoing detailed facies analyses indicate a predominance of eolian-transported siliciclastic material ultimately trapped in systems that ranged from eolian (loess and eolian sand) to ephemerally wet (e.g., mud flat, wadi) in a vast sink for mud to fine-grained sand. Analyses of U-Pb isotopes of zircons for 22 samples from Lower to Upper Permian strata indicate a significant shift in provenance reflected in a reduction of Yavapai-Mazatzal and Neoproterozoic sources and increases in Grenvillian and Paleozoic sources. Lower Permian (Cisuralian) strata exhibit nearly subequal proportions of Grenvillian, Neoproterozoic, and Yavapai-Mazatzal grains, whereas primarily Grenvillian and secondarily early Paleozoic grains predominate in Guadalupian and Lopingian strata. This shift records diminishment of Ancestral Rocky Mountains (western) sources and growing predominance of sources to the south and southeast. These tectonic changes operated in concert with the growing influence of monsoonal circulation, which strengthened through Permian time. This resulted in a growing predominance of material sourced from uplifts to the south and southeast, but carried to the midcontinent by easterlies, southeasterlies, and westerlies toward the ultimate sink of the southern midcontinent.

ABSTRACT The Colorado Plateau in the southwestern United States is within the Paleozoic transcontinental arch, an area of thin, cratonic strata. The plateau was broken by latest Mississippian to early Permian Ancestral Rocky Mountain orogenesis, which produced bedrock uplifts that influenced lower Mesozoic sedimentation before Jurassic burial. Clastic sediments shed from uplifts interfinger with eolian Permian strata ultimately derived from eastern Laurentia. Triassic and Jurassic strata of the Colorado Plateau are here divided into five depositional systems, each representing a different sedimentary and tectonic setting and forming stratal associations referred to as “deposystems.” The five deposystems, which largely but not entirely correspond to formation or group names, were deposited during northward continental drift from tropical latitudes (fluvial, tidal, and nearshore marine Moenkopi and fluvial Chinle) through desert latitudes (the erg-dominated Glen Canyon and San Rafael) to temperate latitudes (fluvial Morrison). Paleomagnetically determined paleolatitudes, corrected for inclination shallowing due to postdepositional sediment compaction, place the Glen Canyon and San Rafael eolianites firmly within expected latitudes for desert environmental conditions. Lower Triassic strata of the Moenkopi deposystem form a westward-thickening wedge of fluvial and shallow marine strata and are overlain by entirely fluvial strata of the Chinle deposystem. Both contain 240–280 Ma detrital zircon populations derived from the east Mexico magmatic arc, but more northern Chinle fluvial deposits contain a higher fraction of zircons derived from Paleozoic, Neoproterozoic, and Grenville provinces in eastern Laurentia. Westward thickening of Moenkopi strata is attributed to subsidence in the proforeland basin of the east-vergent Sonoma orogeny in central Nevada, whereas accommodation space for Chinle sedimentation was provided by dynamic subsidence above the upper Triassic subduction zone behind the newly established Cordilleran magmatic arc to the southwest. Overlying, largely Jurassic Glen Canyon and San Rafael deposystems are dominantly eolian. Detrital-zircon geochronologic analysis indicates that eolian sands were derived largely from eastern Laurentia. Interbedded marginal marine, ­lacustrine-sabkha, and fluvial strata have been associated with regional unconformities, but evidence for such unconformities is here regarded as indicating facies transgressions without development of plateau-wide unconformities or disconformities. Upper Jurassic northward continental drift carried the plateau out of the desert belt and into the zone of prevailing westerly winds. This coincided with a flare up of magmatism in the Cordilleran magmatic arc, leading to transgression of Morrison fluvial sediments over erg deposits of the San Rafael deposystem. Eastward dispersal of Morrison sediments marked the initiation of the Cordilleran orogen as the dominant topographic feature of the plateau region.

The Arizaro Basin in northwestern Argentina sits today in the western Puna Plateau at elevations of 3800–4200 m along the eastern flank of the Miocene to modern magmatic arc. The basin is roughly circular in plan view and ~100 km in diameter, and it was filled during Miocene time (ca. 21–9 Ma) by >3.5 km of eolian, alluvial, fluvial, and lacustrine sediment in addition to ash-fall tuffs from the Andean magmatic arc. The basin fill was subsequently shortened in its central part, and it has been uplifted and topographically inverted. The Arizaro Basin is not obviously related to known faults, nor does it exhibit a peripheral belt of coarse-grained sedimentary rocks derived from flanking topographically higher regions. Sandstone modal framework compositions are arkosic, but not as rich in volcanic lithic fragments as typical intra-arc basins. Detrital zircon U-Pb age spectra implicate source terranes in locally exposed Ordovician granitoid rocks, more distal Upper Paleozoic–Mesozoic arc terranes in western Argentina and possibly northern Chile, and the local Miocene magmatic arc. Depositional-age zircons are present in most of the sandstones analyzed for detrital zircon U-Pb geochronology, and zircon U-Pb ages from volcanic tuff layers provide independent chronological control. The tectonic component of subsidence initiated at low rates, accelerated to ~0.6 mm/yr during the medial stage of basin development, and tapered off to zero as the basin began to shorten internally and experience topographic inversion after ca. 10 Ma. Together, the data presented here suggest that the Arizaro Basin could have developed in response to the formation and gravitational foundering of a dense Rayleigh-Taylor–type instability in the lower crust and/or mantle lithosphere. Insofar as hinterland basins of uncertain tectonic affinity are widespread in the high central Andes, the model developed here may be relevant for other regions of enigmatic subsidence and sediment accumulation in the Andes and other cordilleran hinterland settings.