Exposed upper Proterozoic and Cambrian rocks in the Caborca region, Sonora, Mexico, consists of a shallow-water miogeoclinal sequence quartzite, siltstone, dolomite, limestone, minor amounts conglomerate greenstone.A revised stratigraphic is divided into 14 formations, 11 which have been previously named 3 are here.The as much 3,300 m thick rests unconformably on basement terrane 1,600-to l,750-m.y.-old metamorphic igneous rocks, intruded by l,400-m.y.-old porphyritic granite l,100-m.y.-old...

Abstract Reports of diverse vermiform and peloidal structures in Neoproterozoic to Mesozoic open marine peritidal carbonates include cases interpreted be keratose sponges. However, living sponges have elaborate, highly elastic skeletons spongin (a mesoscopic end‐member a hierarchical assemblage collagenous structures) lacking spicules, thus poor preservation potential contrast the more easily fossilized spicule‐bearing Such fossil comprise layered, network, amalgamated, granular variegated...

The Ediacaran biota is the earliest diverse community of macroscopic animals and protoctists. Body trace fossils in Clemente Formation northwestern Sonora extend downward geologic range forms. Taxa present include cf. Cyclomedusa plana, Sekwia sp., an erniettid (bearing air mattress-like "pneu" body construction), Lockeia ichnosp. Palaeophycus tubularis. confirm presence sediment-dwelling this shallow marine community. are headless, tailless, appendageless. Some may be but others large These...

Research Article| October 01, 1995 Are Neoproterozoic glacial deposits preserved on the margins of Laurentia related to fragmentation two supercontinents?: Comment and Reply Ian W. D. Dalziel; Dalziel 1Institute for Geophysics, University Texas, 8701 N. Mopac Expressway, Austin, Texas 78759-8397 Search other works by this author on: GSW Google Scholar Mark A. S. McMenamin; McMenamin 2Department Geology & Geography, Mount Holyoke College, South Hadley, Massachusetts 01075 Grant M. Young...

Two new species of worm tubes referable to the genus Onuphionella occur in Lower Cambrian strata eastern California and western Nevada. durhami n. sp. is found Campito Formation (in pre-trilobite strata, Fallotaspis and, possibly, Nevadella Zones) O. claytonensis occurs Middle Member Poleta ( Zone). The unusual are armored with an imbricated coat mica flakes, reminiscent modern Owenia. lowest occurrence North America corresponds closely Baltic region, indicating that correlations between two...

Research Article| April 01, 1983 Precambrian-Cambrian transition problem in western North America: Part II. Early Cambrian skeletonized fauna and associated fossils from Sonora, Mexico Mark A. S. McMenamin; McMenamin 1Department of Geological Sciences, Preston Cloud Laboratory, University California, Santa Barbara, California 93106 Search for other works by this author on: GSW Google Scholar Stanley M. Awramik; Awramik John H. Stewart 2U.S. Survey, 345 Middlefield Road, Menlo Park, 94025...

A giant fossil amphipod Rosagammarus minichiellus n. gen., sp. occurs in a Triassic limestone (Luning Formation, west-central Nevada) association with ichthyosaurs (Shonisaurus sp.) and the deep-water trace Protopaleodictyon ichnosp. Fossil pereion pereiopod morphology suggest affinities Acanthogammaridae, freshwater family largely endemic to Lake Baikal. The large size |$(17\;{\rm{cm}})$| of shows that supergiant, deep marine amphipods comparable modern Alicella giganteaChevreux, 1899 were...

The Lower Cambrian sequence south of the town Caborca in northwestern Sonora, Mexico, has yielded trilobites Nevadia ovalis n. sp. and Judomia orbis sp., plus an incomplete fallotaspid cephalon. Nevadella Zone Fritz (1972) can now be recognized Puerto Blanco Formation, fossils from middle part formation strongly suggest presence Fallotaspis Zone. new permit improved correlation Mexican to sections United States stages China Soviet Union.

The proposition that glaciation may not have occurred before the Cenozoic--albeit yet a consensus position--nevertheless raises for reconsideration surface temperature history of earth. Glacial episodes, from Huronian (2.3 billion years ago; BYA) through late Paleozoic (320 to 250 million MYA) been critical constraints on estimation upper bounds (Crowley 1983, Kasting and Toon 1989). Once removed, few if any limit other than life remain. Walker (1982) recognized provides an in Precambrian....

Recent advances in our understanding of the Cambrian evolutionary diversification event (Cambrian Explosion) show that although eumetazoan stem taxa were present late Proterozoic, a tremendous burst macroevolutionary change occurred near beginning Cambrian.Explanations relying on paleoecological feedback are insufficient to explain patterns observed, particularly those associated with near-simultaneous appearance new higher taxa.The diversity biomineralization types among small shelly...

M. A. S. McMenamin and colleagues described a unique crustacean fossil from the Triassic Luning Formation in west-central Nevada as new genus species of amphipod, Rosagammarus minichiellus McMenamin, Zapata Hussey, 2013. The amphipod identity caused an over-150-million-year ghost range connecting R. with next-oldest amphipods Eocene amber. nevertheless failed to stand up closer scrutiny. Additional preparation fossil, coupled examination using polarized light electron microscopy revealed...