Mississippian sedimentary facies belts in east-central California, occurring primarily in the autochthon (lower plate) of the Last Chance Thrust, are consistently oriented in a northeast–southwest direction. The boundary of one belt is marked by the depositional limit of the Osagean to Meramecian Santa Rosa Hills Limestone; a second belt farther to the northwest is bordered by the erosional truncation of the Kinderhookian to Osagean Tin Mountain Limestone. Two additional facies belts, both in the Meramecian to Chesterian Kearsarge Formation, also are present in the area; one near Jackass Flats is marked by the presence of limestone and quartzite olistoliths, and the other in the Last Chance Range includes abundant chert–pebble conglomerates. These two facies of the Kearsarge Formation also occur to the southwest at and near Mazourka Canyon in the allochthon (upper plate) of the Last Chance Thrust. The great similarity and near alignment of these facies belts in both the allochthon and the autochthon can be explained by clockwise rotation of ~55° of the allochthon around a pivot point in the west-central Inyo Mountains. In this model, displacement on the Last Chance Thrust increases from zero at the pivot point to 75 km for rocks exposed in the northern White Mountains. Reconstruction of the paleogeography suggests that the Last Chance Thrust is not part of a major fold and thrust belt but is a major structure limited to a relatively small area along the continental margin where the leading edge of an allochthonous terrane (possibly the Northern Sierra Terrane) impinged against the North American plate.

The concept of the Permian Last Chance Thrust has passed through many stages. Here we point out which critical observations have led to changes in the way this important feature has been interpreted.

ABSTRACT The Sierra Nevada batholith of California represents the intrusive footprint of composite Mesozoic Cordilleran arcs built through pre-Mesozoic strata exposed in isolated pendants. Neoproterozoic to Permian strata, which formed the prebatholithic framework of the Sierran arc, were emplaced against the tectonically reorganized SW Laurentian continental margin in the late Paleozoic, culminating with final collapse of the fringing McCloud arc against SW Laurentia. Synthesis of 22 new and 135 existing detrital zircon U/Pb geochronology sample analyses clarifies the provenance, affinity, and history of Sierra Nevada framework rocks. Framework strata comprise terranes with distinct postdepositional histories and detrital zircon provenance that form three broad groups: allochthonous Neoproterozoic to lower Paleozoic strata with interpreted sediment sources from Idaho to northern British Columbia; Neoproterozoic to Permian strata parautochthonous to SW Laurentia; and middle to upper Paleozoic deposits related to the fringing McCloud arc. Only three sedimentary packages potentially contain detritus from rocks exotic to western Laurentia: the Sierra City mélange, chert-argillite unit, and Twin Lakes assemblage. We reject previous correlations of eastern Sierra Nevada strata with the Roberts Mountains and Golconda allochthons and find no evidence that these allochthons ever extended westward across Owens Valley. Snow Lake terrane detrital ages are consistent with interpreted provenance over a wide range from the Mojave Desert to central Idaho. The composite detrital zircon population of all analyses from pre-Mesozoic Sierran framework rocks is indistinguishable from that of the Neoproterozoic to Permian SW Laurentian margin, providing a strong link, in aggregate, between these strata and western Laurentia. These findings support interpretations that the Sierran arc was built into thick sediments underpinned by transitional to continental western Laurentian lithosphere. Thus, the Mesozoic Sierra Nevada arc is native to the SW Cordilleran margin, with the Sierran framework emplaced along SW Laurentia prior to Permian–Triassic initiation of Cordilleran arc activity.

Abstract The most comprehensive summary available on the stratigraphic occurrence, geographic distribution, phylogeny, and taxonomy of Early Permian colonial rugose corals that occupied the Cordilleran–Arctic–Uralian (CAU) Realm, along the northwestern and western marine shelves and accreted terranes of the ancient supercontinent Pangaea. It is based on all previous studies by other coral specialists, a thorough review of all published data, and on information from a very large number of new collections from new areas. This book contains a new classification and phylogenetic scheme, based on critical restudy of the entire coral fauna at all taxonomic levels

The Bird Spring Shelf in southeastern California, along with coeval turbidite basins to the west, records a complex history of late Paleozoic sedimentation, sea-level changes, and deformation along the western North American continental margin. We herein establish detailed correlations between deposits of the shelf and the flanking basins, which we then use to reconstruct the depositional history, paleogeography, and deformational history, including Early Permian emplacement of the regionally significant Last Chance allochthon. These correlations are based on fusulinid faunas, which are numerous both on the shelf and in the adjoining basins. Study of 69 fusulinid species representing all major fusulinid-bearing Pennsylvanian and Lower Permian limestone outcrops of the Bird Spring Shelf in southeastern California, including ten new species of the genera Triticites , Leptotriticites , Stewartina , Pseudochusenella , and Cuniculinella , forms the basis for our correlations. We group these species into six fusulinid zones that we correlate with fusulinid-bearing strata in east-central and southern Nevada, Kansas, and West Texas, and we propose some regional correlations not previously suggested. In addition, we utilize recent conodont data from these areas to correlate our Early Permian fusulinid zones with the standard Global Permian Stages, strengthening their chronostratigraphic value. Our detailed correlations between the fusulinid-bearing rocks of the Bird Spring Shelf and deep-water deposits to the northwest reveal relationships between the history of shelf sedimentation and evolution of basins closer to the continental margin. In Virgilian to early Asselian (early Wolfcampian) time (Fusulinid Zones 1 and 2), the Bird Spring Shelf was flanked on the west by the deep-water Keeler Basin in which calcareous turbidites derived from the shelf were deposited. In early Sakmarian (early middle Wolfcampian) time (Fusulinid Zone 3), the Keeler Basin deposits were uplifted and transported eastward on the Last Chance thrust. By middle Sakmarian (middle middle Wolfcampian) time (within Fusulinid Zone 4), emplacement of the Last Chance allochthon was complete, and subsidence caused by thrust loading had resulted in development of a new turbidite basin (Darwin Basin) along the former western part of the Bird Spring Shelf. At the same time, farther east into the craton, paralic facies began prograding westward, so that the youngest fusulinid-bearing limestones on the shelf in this area become progressively younger to the west. Eventually, in Artinskian to Kungurian (late Wolfcampian to Leonardian) time (Fusulinid Zones 5 and 6), deposition of fusulinid-bearing limestone on the shelf was restricted to a marginal belt between the prograding paralic facies to the east and the Darwin Basin to the west. Development of the Keeler Basin in Pennsylvanian to earliest Permian time was approximately coeval with collision between South America-Africa (Gondwana) and North America (Laurentia) on the Ouachita-Marathon orogenic belt. This basin developed inboard of a northwest-trending, sinistral fault zone that truncated the continental margin. Later, in the Early Permian, the Last Chance allochthon, which was part of a northeast-trending belt of deformation that extended into northeastern Nevada, was emplaced. This orogenic belt probably was driven by convergence at the continental margin to the northwest. This work adds significant detail to existing interpretations of the late Paleozoic as a time of major tectonic instability on the continental margin of southeastern California as it changed from a relatively passive margin that had characterized most of the Paleozoic to an active convergent margin that would characterize the Mesozoic.