Not available / text

Not available / text

This study examines the regional stratigraphic architecture, depositional systems, and petrographic characteristics of the South Texas Pearsall shale-gas system currently developed in the Indio Tanks (Pearsall) and Pena Creek (Pearsall) fields. The Pearsall Formation was deposited as a mixed carbonate-siliciclastic system on a distally steepened ramp over a period of 11.75 million years. It was deposited between maximum floods of two second-order sequences and contains at least five third-order cycles. Up to three Oceanic Anoxic Events (OAE 1-A, Late Aptian Regional Event, and OAE 1-B) figure prominently in the deposition of the Pearsall sediments, and during these intervals, depending on the location within the Maverick Basin, sedimentation rates were between 0.5 and 2 cm/ky. Facies in the Pearsall section arise from interactions between pre-existing topography, oxygenation regime, eustatic sea-level fluctuation, and depositional processes. In the Pearsall Formation, OAEs affected depositional environments and resulting facies patterns during several time periods. The OAEs occurred in association with transgressions but not necessarily in concert with them. Outer ramp OAE facies are siliciclastic-dominated, TOC-rich, and little-bioturbated. Conversely the outer ramp facies deposited under normally oxygenated paleoenvironmental conditions tend to be carbonate-rich, TOC-poor, and are more prominently bioturbated. / text

No description available.

Cretaceous bauxite deposits from Hall and Veneer mines, Wilkinson County, Georgia are composed of kaolinite, gibbsite, goethite, anatase, nordstrandite and bohemite. Quartz and micas are absent in the samples. The presence of boehmite and goethite are evidence of intense weathering forming the bauxite deposits. The extremely high values of the Chemical Index of Alteration (CIA) which is over 99, and the low values of the alkali metals and alkali earth metals, support an intense weathering origin for the bauxite deposit. There is evidence of deposition in the mines based on the presence of pisoids in the bauxite samples and the composition of the parent materials, which vary markedly by the non-uniform TiO2/Al2O3 values which represent the accumulation of transported materials from contrasting source areas. Kaolin minerals were first produced by the hydrolytic weathering of aluminous sediments and then gibbsite was formed as early kaolin was desilicated.

No description available.

An unusual turtle fauna from Lightning Ridge, New South Wales (Albian) reveals that Australian turtles had a more extensive Mesozoic history than previously indicated. Reevaluation of several primitive groups provides novel information on turtle evolution in the southern hemisphere. Seven turtle taxa are identified at Lightning Ridge. Two are Testudines indet. and two indeterminate chelid groups are evinced by isolated elements. Three new taxa are assigned to the new family Spoochelyidae in the superfamily Meiolanoidea. Spoochelys ormondea n. fam., gen. et sp., Sunflashemys bartondracketti n. gen. et sp. and Opalania baagiwayamba n. gen. et sp. are predominantly land-living turtles with high-domed shells and short manus and pes. The sister-group relationship with the Meiolaniidae, supported by a suite of cranial and postcranial synapomorphies, increases the stratigraphic range of the horned turtles by around ~ 50 my. Primitive structures in Spoochelys (postparietal, supratemporal and interpterygoid vacuity), occur with derived features that are variably developed across Triassic and Jurassic turtles. Phylogenetic analysis precariously resolves the meiolanoids as sister group to a clade containing Palaeochersis and Proterochersis. Limited pleurodiran attributes suggest that meiolanoids may be pleurodiromorphs, closer to primitive pleurodires than to cryptodires. As basal ‘side-necked’ turtles, the Lightning Ridge meiolanoids permit first insights into cranial and postcranial progressions in pleurodiran stem taxa. Evidence of diverse meiolanoids in Early Cretaceous Australia and ancient radiations of meiolanoid-like turtles in southern Pangea, suggest that the horned turtles are a Triassic group and that the dichotomy between Pleurodira and Cryptodira occurred well before the Late Triassic. Early Cretaceous chelids at Lightning Ridge occur at higher palaeolatitude than in South America. The temporal range of Australian chelids is extended by ~ 50 my, demonstrating that chelids had a Jurassic history in Australia, with broad diversifications across the polar supercontinent. The palaeoecological setting of Lightning Ridge is comprehensively described for the first time. Diverse invertebrates and vertebrates include terrestrial, freshwater aquatic and rare marine forms that are anomalous at this near-polar palaeolatitude (~65-70oS). The anachronistic occurrence in Early Cretaceous Australia of distinctive radiations of ‘Triassic-type’ turtles, and other relic groups, implies prolonged intervals of biogeographic isolation in the eastern provinces of Pangea.

An unusual turtle fauna from Lightning Ridge, New South Wales (Albian) reveals that Australian turtles had a more extensive Mesozoic history than previously indicated. Reevaluation of several primitive groups provides novel information on turtle evolution in the southern hemisphere. Seven turtle taxa are identified at Lightning Ridge. Two are Testudines indet. and two indeterminate chelid groups are evinced by isolated elements. Three new taxa are assigned to the new family Spoochelyidae in the superfamily Meiolanoidea. Spoochelys ormondea n. fam., gen. et sp., Sunflashemys bartondracketti n. gen. et sp. and Opalania baagiwayamba n. gen. et sp. are predominantly land-living turtles with high-domed shells and short manus and pes. The sister-group relationship with the Meiolaniidae, supported by a suite of cranial and postcranial synapomorphies, increases the stratigraphic range of the horned turtles by around ~ 50 my. Primitive structures in Spoochelys (postparietal, supratemporal and interpterygoid vacuity), occur with derived features that are variably developed across Triassic and Jurassic turtles. Phylogenetic analysis precariously resolves the meiolanoids as sister group to a clade containing Palaeochersis and Proterochersis. Limited pleurodiran attributes suggest that meiolanoids may be pleurodiromorphs, closer to primitive pleurodires than to cryptodires. As basal ‘side-necked’ turtles, the Lightning Ridge meiolanoids permit first insights into cranial and postcranial progressions in pleurodiran stem taxa. Evidence of diverse meiolanoids in Early Cretaceous Australia and ancient radiations of meiolanoid-like turtles in southern Pangea, suggest that the horned turtles are a Triassic group and that the dichotomy between Pleurodira and Cryptodira occurred well before the Late Triassic. Early Cretaceous chelids at Lightning Ridge occur at higher palaeolatitude than in South America. The temporal range of Australian chelids is extended by ~ 50 my, demonstrating that chelids had a Jurassic history in Australia, with broad diversifications across the polar supercontinent. The palaeoecological setting of Lightning Ridge is comprehensively described for the first time. Diverse invertebrates and vertebrates include terrestrial, freshwater aquatic and rare marine forms that are anomalous at this near-polar palaeolatitude (~65-70oS). The anachronistic occurrence in Early Cretaceous Australia of distinctive radiations of ‘Triassic-type’ turtles, and other relic groups, implies prolonged intervals of biogeographic isolation in the eastern provinces of Pangea.

No description available.

Rocks of Late Cretaceous age in the central part of Utah are dominantly elastic. In general, the sediments in the west are of conglomerate and sandstone of continental origin; the sediments in the east are of sandstone and shale of marine origin, These rocks were deposited at or near the western shore of a sea which extended from the Arctic to the Gulf of Mexico. The strand line lay in a general northern direction through Utah with land to the west and marine water to the east.