Late Permian Sediments Research Articles

Some Permian glossopterid fructifications and leaves from the Bowen Basin, Queensland, Australia

Three new glossopterid fructifications and a new Glossopteris leaf are described from Late Permian sediments of the southwest and central Bowen Basin, Queensland, Australia. Glossopteris bucklandensis sp. nov. and the female fructification Ottokaria inglisensis sp. nov. are described from the Black Alley Shale, Denison Trough. Cometia biloba gen. et sp. nov. and Senotheca kingii sp. nov. are instituted for new female fructifications from the Burngrove and Fair Hill Formations respectively on the Comet Platform. A collection of female fructifications from the Rangal Coal Measures, Comet Platform, is assigned to Dictyopteridium walkomii (Rigby) comb. nov. Numerous specimens of O. inglisensis and D. walkomii show that receptacle dimension ratios and tubercle (ovule attachment point) densities are useful taxonomic features, whereas wing and stalk vs. receptacle dimension ratios are less consistent. Exceptionally high tubercle densities on some small fructifications possibly reflect limitation of receptacle growth induced by local ecological conditions.

Late Permian glossopteridfructifications from the Bowen and Sydney Basins, eastern Australia

The morphology and taxonomy of several glossopterid reproductive structures, from Late Permian nonmarine strata of eastern Australia, are discussed herein. Plumsteadia jensenii sp. nov. is described from the Black Alley Shale, western Bowen Basin. Plumsteadia microsaccaRigby, 1963 and five other forms tentatively referred to this genus, are recorded from Late Permian sediments of the western and central Bowen Basin; and Plumsteadia sp. cf. P. ampla(White) Rigby, 1969 is recorded from coeval sediments of the Sydney Basin. Additionally reported is a single juvenile or degenerate fructification from the Black Alley Shale attached to the midrib of a Glossopteris leaf. The chronological and geographic distribution of Permian Gondwanic fructifications referable to Plumsteadia is tabulated.

Permo-Triassic Extinctions: Relation to Sea-Floor Spreading

An analysis of the Permo-Triassic fauna and paleogeography on a stage-by-stage basis supports previous more general summaries by concluding that the number of families of marine invertebrates was significantly reduced (essentially halved) during the last three Permian stages (32 m.y.), and that the extinctions were not markedly selective. Shallow marine seas were reduced from a coverage of 40% of their possible distribution in the early Permian to less than 15% coverage in latest Permian, and then were expanded to 34% coverage in the lower Triassic. If this apparent reduction in shallow marine seas is due to selective erosion of late Permian sediments, there seems no way to account for it unless there was significant reduction in sea level. Alternatively, late Permian marine seas may never have been widespread, again due to lowering of sea level. The apparent late Permian marine regression is attributed to water withdrawing into a deepening ocean basin. The basaltic ocean bottom continued to sink during a...

THE DIAGENESIS AND DEPOSITIONAL ENVIRONMENT OF THE PERMIAN RANGER CANYON AND MOWITCH FORMATIONS, ISHBEL GROUP, FROM THE SOUTHERN CANADIAN ROCKY MOUNTAINS

SummaryThe Ranger Canyon and Mowitch Formations are the youngest Permian strata in the Rocky Mountain Front Ranges. They constitute a thin, widespread and clearly defined stratigraphic entity covering approximately 60,000 sq. miles; they occur below Triassic beds and above a major, regional, intra‐Permian unconformity, initiated by a transgression which started in the northwest. Beds of the above entity are therefore diachronous. The erosion surface is overlain by polymict, phosphatic conglomerates containing mature lag gravels and immature breccio‐conglomerates and corrosion breccias.Rock types are either sandstones or silty and sandy cherts, phosphorites and occasionally dolomites. Clastic components are dominantly mature quartz (some pseudomorphs gypsum), phosphate, some feldspar, negligible clay, and stable detrital minerals, necessitating: (1) many cycled, clastic sedimentary rock; (2) local gypsum; and (3) phosphate producing, distributive provinces.Secondary features include primary cementation by quartz, chalcedony, dolomite, sulphate and phosphate, with replacement mainly by chalcedony. Contraction fractures are cemented by quartz (after anhydrite and fluorite), calcite and barite. Accessory authigenic minerals are hematite, sulphates (pseudomorphed by quartz), fluorite, apatite and dolomite. Diagenesis therefore occurred within a chemically active environment.Minerals present indicate: (1) phosphate producing and (2) evaporite producing environments, the components for which may be obtained from sea water by: (a) a biogeochemical phosphate‐fixation cycle; and (b) concentration of brines by interstitial refluxion.A Recent environmental parallel occurs along the coast of Baja, California. Phosphate produced off‐shore contributes to quartz‐rich sediments prograding seawards; evaporitic conditions produce minimum carbonate and maximum sulphate precipitation.The sequence of events envisaged for the Permian rocks started with phosphate corrosion of bed‐rock and cementation of lag gravels; some phosphate was contributed to shoreline, with quartz and gypsum sands, prograding over the basal conglomerate. Sand cementation by carbonate occurred in shoreline and intertidal zones, and by sulphate in the supratidal zones. Concentration of brines by refluxion, and local silica enrichment, facilitated silica precipitation and replacement. Penecontemporaneous silicification of Late Permian sediments was therefore instrumental in their ultimate preservation.