Pore systems in the Middle Permian Phosphoria Rock Complex (PRC), Rocky Mountain Region, USA, evolved with biotic and chemical dynamics in a shallow epicontinental seaway undergoing extreme environmental shifts. Biochemical responses to environmental changes directly affected pore systems and controlled diagenetic pathways through burial. Petrographic methods and spatially resolved measurements of δ 18 O in sequence stratigraphic context allow characterization of pore systems and their evolution in heterogenous biochemical sediments. Pore systems vary regionally and across systems tracts on second-order (9–10 million years [MY]) and third-order (2–5 MY) timescales. Minimal porosity occurs in transgressive mudrocks rich in organic matter (OM), phosphorites, and carbonates. Cool, acidic, low-oxygen, nutrient-rich basinal waters interacted with warm open to restricted shelfal waters in transgressions. This resulted in accumulation and microbial decay of S-rich OM, phosphatization, carbonate precipitation, silicification, as well as deposition of calcitic-biotic debris (bryozoans, brachiopods, and crinoids) and micrite. Relative to landward and highstand marine components, transgressive basinal marine carbonates and silica are δ 18 O depleted due to microbial decay of OM. Extensive cementation coupled with near-surface compaction and recrystallization of micrite occluded large portions of porosity in transgressive phosphorites and carbonates. Porosity in these rocks is dominated by interparticle and, to a lesser degree, intraparticle microporosity in microbored phosphatized and micritized grains. Phosphorites are compacted where cements are not pervasive. OM-rich sediments host minimal volumes of interparticle nanoporosity due to mechanical compaction and incursion of secondary OM (bitumen) during burial. PRC OM is S-rich, due to sulfate-reducing bacterial enrichment, and locally abundant. This drove early generation of secondary OM and inhibited OM-hosted porosity development through thermal maturation. Large volumes of porosity accumulated in highstand sediments and varied with transitions from silicisponge spicule cherts and calcitic-biota carbonates to pervasively dolomitized micritic, peloidal, aragonitic mollusk, and peritidal microbial sediments. These biochemical transitions, and ultimately pore-system evolution, were driven by interaction between oxygenated open marine waters, eolian siliciclastic debris, and increasingly restricted shelfal waters. Marine carbonate and silica δ 18 O are consistent with Middle Permian open marine waters but are enriched landward and through highstands with evaporative fractionation. This δ 18 O-enriched authigenic silica in carbonates and evaporite replacements, as well as δ 18 O enrichment through silica precipitation, suggest dolomitization and silicification were driven by evaporitic processes. In spiculitic cherts and siltstones, silicification and carbonate diagenesis resulted in small volumes of intraparticle, interparticle, and moldic porosity, as well as increased susceptibility to fracturing and associated permeability enhancement. Chalcedony in spiculites and silicified carbonates host minor volumes of porosity where moganite crystallites dissolved during hydrocarbon migration. Highstand dolomites host abundant intercrystalline, moldic, fenestral, and interparticle macroporosity and microporosity, especially in peloidal wackestones, mollusk debris, ooid grainstones, and peritidal microbialites. Dolomitization resulted in dissolution of aragonitic mollusk and ooids, cementation, and preservation of primary porosity. Porosity loss through burial in dolomites occurs through mechanical compaction, and to a lesser degree, precipitation of zoned carbonate cements that are δ 18 O depleted relative to earlier dolomite. Compaction strongly decreases intercrystalline porosity in dolomitized peloidal wackestones. Secondary OM related to hydrocarbon migration coats surfaces and fills small pore volumes, inhibiting burial cementation.

Abstract Joseph Mawson, a nineteenth-century British railway engineer and businessman in Brazil, discovered fossils from the Cretaceous of Bahia that were described by E. D. Cope and Arthur Smith Woodward. A biographical outline of Mawson is presented. Mawson’s discoveries (especially the giant coelacanth fish Mawsonia , named after him by ASW) are interpreted today in the light of modern geological investigations. Mawsonia apparently lived in fluvial, lacustrine and brackish-water habitats in western Gondwana at the time South America separated from Africa. From the Late Jurassic until the Barremian, Mawsonia was widespread across western Gondwana, but its Aptian–Cenomanian records in South America are restricted to northeastern Brazil (including the Borborema tectonic province and adjacent areas to its north). In contrast, Mawsonia remained widespread in the Aptian–Cenomanian of Africa. Recently published data suggest that northeastern Brazil was still contiguous with Africa in the Aptian/Albian, although it was probably separated from the rest of South America by an epicontinental seaway that apparently followed an unconventional course across the Brazilian interior rather than along the present-day coastline. Aptian–Cenomanian records of Mawsonia and other non-marine taxa (including tetrapods) in northeastern Brazil may therefore represent ‘African’ rather than ‘South American’ biotas.

The record of dinosaurs over the last 10 m.y. of the Cretaceous, as well as surrounding the Cretaceous-Paleogene boundary, helps to define extinction scenarios. Although Late Cretaceous dinosaur fossils occur on all present-day continents, only in North America do we find a terrestrial vertebrate fossil record spanning the Cretaceous-Paleogene boundary, although promising work may yield comparable records in South America, India, China, and Europe. For the present then, the North American record represents the proxy for our knowledge of dinosaur extinction. Over the last 10 m.y. of the Cretaceous (late Campanian to late Maastrichtian) in the northern part of the western interior of North America, the number of nonavian dinosaur species dropped from 49 to 25, almost a 50% reduction, even though a 16% greater extent of fossil-bearing exposures record the last dinosaurs in the latest Cretaceous in the western interior. Important, but less-well-exposed, nonavian-dinosaur–bearing units suggest this drop occurred around, or at least commenced by, the Campanian-Maastrichtian boundary. These losses began during climatic fluctuations, occurring during and possibly in part caused by the last major regressive cycle of the Cretaceous, which also reduced the expanse of the low coastal plains inhabited by nonavian dinosaurs. The pulse of Deccan Trap emplacement that began some time later in the latest Cretaceous was also likely a major driver of climatic change. As for the dinosaur record near the Cretaceous-Paleogene boundary, even the best-known records from North America remain enigmatic and open to interpretation. Newer studies suggest some decline in at least relative abundance approaching the Cretaceous-Paleogene boundary, but the cause (or causes) for the final extinction (if it was the case) of non-avian dinosaurs remains unresolved, although the Chicxulub impact undoubtedly played a major role.

ABSTRACT New data and review of classic sections from the Middle and Upper Ordovician North American Midcontinent in the Upper Mississippi Valley provide a refined picture of the age, stable isotope geochemistry, faunal composition, and—ultimately—origin of this epeiric ramp succession. Sequence stratigraphic analysis reveals a series of unconformity-bounded, genetically related facies packages. Shallowing and deepening trends are sometimes difficult to resolve due to a paucity of hydrodynamic indicators, yet unconformity surfaces are well marked by hardgrounds and confirmed by negative C-isotope spikes. Recent conodont biostratigraphy, new U-Pb radioisotopic ages for K-bentonites, and correlation of C-isotope profiles to global trends suggest that the succession spans the Darriwilian to Hirnantian epochs. Focus on Platteville to lower Galena Group strata (Sandbian to early Katian) provides a temporally high-resolution look at the onset and evolution of a long-term (>2 m.y.) positive carbon-isotope excursion, short-term perturbations in that record, and relationship to the preservation and diversity of the enclosed fauna and strata. Major changes in authigenic mineral suites and organic carbon content throughout the Upper Ordovician Upper Mississippi Valley suggest at least three major redox cycles. The combined evidence for globally recognized, positive carbon-isotope excursions coincident with these redox cycles, as well as high-frequency, sea-level fluctuations and successive faunal turnover events, suggests far-field responses to multiple global oceanic anoxic events.

Numerical models of the ocean-climate system indicate that during the early Late Ordovician, water from the higher southern latitudes flowed north toward the equator. The cold-water masses welled up into and penetrated the epicontinental sea of Laurentia. The “cold-water conditions” existed despite high levels of pCO 2 (~15× preindustrial atmospheric levels) and did not necessarily indicate the onset of glaciation during the early Late Ordovician; rather the cold-water conditions may indicate the onset of a cooling event that plunged the Ordovician Earth system toward ice-house conditions that would lead later to the end-Ordovician (Hirnantian) glaciation. Furthermore, the observed distribution of cold-water masses across the southeastern margin of Laurentia is consistent with the interpretation that a cold-water event caused a regional extinction in the Mohawkian of eastern Laurentia.