No description available.

No description available.

Ph.D., Faculty of Science, University of the Witwatersrand, 2011 / The Wahweap Formation is an ~400 m thick clastic sedimentary succession of fluvial and estuarine channel sandstones and floodbasin mudrocks that was deposited in western North America during the Late Cretaceous. It preserves important mammal, dinosaur, crocodile, turtle and invertebrate fossils that have been the subject of recent palaeontological investigations. The Wahweap Formation can be divided into lower, middle, upper, and capping sandstone members based on sand:mud ratios and degree of sandstone amalgamation. Facies analysis reveals the presence of ten facies associations grouped into channel and floodbasin deposits. Facies associations (FAs) from channels include: (1) single-story and (2) multistory lenticular sandstone bodies, (3) major tabular sandstone bodies, (4) gravel bedforms, (5) low-angle heterolithic cross-strata, and (10) lenticular mudrock, whereas floodbasin facies associations include: (6) minor tabular sandstone bodies, (7) lenticular interlaminated sandstone and mudrock, (8) inclined interbedded sandstone and mudrock, and (9) laterally extensive mudrock. The lower and middle members are dominated by floodbasin facies associations. The lower member consists dominantly of FA 8, interpreted as proximal floodbasin deposits including levees and pond margins, and is capped by a persistent horizon of FA 3, interpreted as amalgamated channel deposits. FAs 4 and 6 are also present in the lower member. The middle member consists dominantly of FA 9, interpreted as distal floodbasin deposits including swamp, oxbow-lake and waterlogged-soil horizons. FAs 1, 2, 5, 6, 7, 8, and 10 are present in the middle member as well, which together are interpreted as evidence of suspended-load channels. The upper member is sandstone-dominated and consists of FAs 1, 2, 3, 5, 7, and 8. FAs 5 and 7, which occur at the base of the upper member, are interpreted as tidally influenced channels and suggest a marine incursion during deposition of the upper member. The capping sandstone is characterized by FAs 3, 4, and 6, and is interpreted to represent a major change in depositional environment, from meandering river systems in the lower three members to a low-accommodation, braided river system. Combined results of facies and palaeosol analyses suggest that the overall climatic conditions in which the Wahweap Formation was deposited were generally wet but seasonally arid, and that iv conditions became increasingly moist from the time of lower member deposition up to the time of middle member deposition. Improved age constraints were obtained for the Wahweap Formation by radiometric dating of two devitrified ash beds (bentonites). This allowed for deposition to be bracketed between approximately 81 Ma and 76 Ma. This age bracket has two important implications: firstly, it shows that the Wahweap Formation is synchronous with fossiliferous deposits of the Judithian North American Land Mammal Age, despite subtle differences in faunal content. Secondly, it shows that the middle and upper members were deposited during the putatively eustatic Claggett transgression (T8 of Kauffman 1977) in the adjacent Western Interior Seaway. This is consistent with facies analysis which shows a marked increase in tidally-influenced sedimentary structures and trace fossils at the top of the middle and base of the upper members. Following recent alluvial sequence stratigraphic models, the middle member is interpreted as the isolated fluvial facies tract, while the upper member represents the tidally influenced and highstand facies tracts. Maximum transgression occurred during deposition of the lowest part of the upper member, synchronous with the Claggett highstand in other parts of the Western Interior Basin. The sequence boundary is placed at the base of the overlying capping sandstone member, diagnosed by a major shift in petrography and paleocurrent direction, as well as up to 4 m of fluvial incision into the underlying upper member. The capping sandstone member is interpreted as the amalgamated fluvial facies tract of an overlying sequence. Analysis of the western-most exposures of the Wahweap Formation on the Markagunt and Paunsaugunt plateaus shows facies variations in the proximal and distal parts of the central Western Interior Basin. The inconsistent thickness and variations in fluvial architecture, as well as the presence of unconformities and generally poor exposure in the west, hinder correlation attempts and also prevent the subdivision of the Wahweap Formation into members. Only the capping sandstone, which can be positively identified west of the Paunsaugunt fault, has a consistent thickness and fluvial architecture across the west-east extent of the Wahweap Formation. The capping sandstone also bears remarkable lithological similarity to the Tarantula Mesa Formation which is exposed to the east in the Henry Mountains Syncline, and it is suggested that these two units be equated under the name “Tarantula Mesa Formation”, which has precedence.

The phosphatic chalks of the Anglo-Paris Basin are granular phosphorites of Santonian to early Campanian age. They were deposited in erosional cuvettes up to 1 km long, 250 m wide and 30 m deep, incised into white chalks. Most are situated in the Picardy region of northern France. Cuvettes are floored by strongly indurated and mineralized basal hardgrounds developed in intraclastic sediments. The hardgrounds are penetrated by prominent phosphatic-chalk filled Thalassinoides burrows and overlain by intraclast-pebble lags containing 'Terebella' phosphatica Leriche, Diblasus arborescens Parent and Lopha semiplana (J. Sowerby). Lithification occurred a few centimetres below the sediment/water interface in a sediment of increased permeability, and is geochemically discernible ~90 cm below the hardground surface. Glauconitization was restricted to replacement of clay minerals during the early development of the hardground, later phosphatization replacing carbonate. Actinocamax verus Miller occurs in basal phosphatic chalks and a bed of Gonioteuthis quadrata quadrata (Blainville) occurs at the summit. The Gonioteuthis Bed is commonly underlain by, but separated from, a bed of Offaster pilula (Lamarck). The proportion of faecal pellets, phosphatic ooliths, echinoderm fragments and benthonic foraminiferans decline above the basal hardgrounds as the phosphorites become finer-grained and less phosphatic. Inoceramid prisms or pelagic foraminiferans are the dominant component of poorer phosphatic chalks. Intraformational slump folds and hardground mélanges occur at the base of some successions. The palaeobiology of belemnites is considered in detail and it is concluded that the Gonioteuthis Beds were the products of massmortalities accompanying reproduction. Pelletal phosphate was formed by the replacement of carbonate during early diagenesis in an organic-rich, anoxic environment and water depths of <150 m. Current activity and subsurface anoxia were intermittent; colonization, bioturbation and winnowing alternating with quiescent, anoxic phases of mineralization. Phosphatic chalk cuvettes were eroded by a proto-Gulf Stream during a eustatic regression. Upwelling of this current was the main source of phosphate in the phosphatic chalks.

No description available.

A DISSERTATION SUBMITTED TO THE FACULTY OF SClENCE, UNIVERSITY OF THE WITWATERSRAND, JOHANNESBURG, FOR THE DEGREE OF DOCTOR OF PHILOSOPHY. / An assemblage of Cretaceous, Diptera, recovered from the sediments of the Orapa Diamond mine, Botswana, is described. The fossil Diptera are placed In the following families: Tipulidae, Empididae, Hybotidae, Bibionidae, and possibly the Mycetophilidae, Rhagionidae and Anisopodidae. A new pulid species, Helius botswanensis (Tipulidae, subfamily Limoniinae), is described; it is the oldest representative of the subfamily. (Abbreviation abstract) / Andrew Chakane 2019

Four new lepidosaurs from the Early Cretaceous deposits of the Tlayua Quarry, Central Mexico are described, establishing their phylogenetic relationships using cladistic methodology. These lepidosaurs have unique characters never present in related forms suggesting that they have evolved in isolated environments far from immediate ancestors, indicating the insular nature of the quarry. The sphenodontid Pamizinsaurus tlayuaensis is covered with unique rows of small rounded osteoderms that could have protected it against predation in open environments. Ankylosphenodon pachyostoseus has unusual teeth ankylosed deep into the dentary with probable continuous growth, which combined with propalinal action of a deep lower jaw suggest herbivory. Unique pachyostotic ribs and vertebrae, delay in the ossification of the epiphyses, and zygapophyses horizontally oriented to stiffen the vertebral column could be related to aquatic behavior. The unique morphology of Pamizinsaurus and Ankylosphenodon argue against the concept of low morphological diversification of sphenodontians. / The lizard Huehuecuetzpalli mixtecus shows most iguanian features, but still retains a divided premaxilla, amphicoelous vertebrae, thoracolumbar intercentra, and the second distal tarsal, supporting a phylogenetic position as sister-group of squamates. Although late in the fossil record, Huehuecuetzpalli provides important information on early transformation of characters in lizard evolution. Tepexisaurus tepexii is an early scincomorph relatively more primitive to all known scincoids. The lack of osteoderms indicates that Tepexisaurus and some paramacellodids are not scincoids, suggesting that the Paramacellodidae is not monophyletic. The relative primitive morphology of Tepexisaurus in Albian deposits can be correlated with the late presence of sphenodontians and the relictual nature of Huehuecuetzpalli in Tlayua. This suggests that TIayua was a refuge for archaic terrestrial forms. / Character transformation at the origin of the Squamata was explored through a phylogenetic analysis including basal lepidosauromorphs, the best known early squamates, and extant squamate "families". Results using a rigorously reviewed data set, show that many characters suggested to be squamate autapomorphies are certainly along a lineage basal to the Squamata, which includes Marmoretta, Tamaulipasaurus, the Ardeosauridae (redefined to include Bavarisaurus), and Huehuecuetzpalli. The name Squamatoidea to group all taxa basal to Squamata + squamates is suggested. The Total Branch Support index obtained falls between values of other published phylogenies. The low values seem to be affected by the inclusion of several fossil taxa with incomplete information and the redistribution of a limited number of characters in a greater number of branches.

No description available.

Evidence of the Cretaceous-Paleogene (K-Pg) extinction can be seen across the Mississippi Embayment, however research examining the K-Pg boundary in the state of Mississippi is lacking. The objective of this study addresses how macrofauna changed across the K-Pg boundary in Oktibbeha County, Mississippi and subsequent comparison to other Early Paleogene and Late Cretaceous benthic marine macrofaunal localities. Comparison included previously collected material as well as specimens collected during this study in order to reconstruct the biological community living on the seafloor in the earliest Paleocene Mississippi Embayment. The primary fauna present after the K-Pg extinction was mainly composed of small suspension and deposit feeding oysters and clams as well as carnivorous gastropods. New Paleocene fauna and survivor species exhibited drastically smaller body sizes than organisms in the Cretaceous; postulated to be due to a relative decrease in primary producers and environmental nutrients.

Several questions regarding the nature of extinction in the fossil record of marine invertebrates were investigated using statistical methods and familial diversity data. First, a series of analyses were performed to determine whether the magnitudes of mass extinctions were statistically distinguishable from the magnitudes of background extinctions. The expected proportions of familial extinction for each order in a stage (based on an estimate of the ordinal probability of familial extinction for each of 134 orders) were compared to the observed proportions of familial extinction in the stage using a simple X2 goodness-of-fit test. The results indicate that eight stages in the Phanerozoic had a statistically significant excess of extinction. A second set of X2 analyses was done using estimates of per taxon familial extinction rates for the orders, rather than familial extinction probabilities. The X2 tests resulted in four additional stages that contained a statistically significant surplus of familial extinction. To test the results further, a set of bootstrapping analyses was done for each of five different extinction metrics. Two stages, the Ashgillian and the Dzhulfian, had a statistically significant excess of extinction in both Xl analyses and in four out of five of the bootstrapping analyses. Two additional stages, the Guadelupian and the Maestrichtian, had a statistically significant magnitude of extinction in every analysis. Thus, the results provide strong support for the argument that mass extinctions comprise a distinct group of evolutionary phenomena. Familial extinction rates have declined from the early Phanerozoic to the Recent. Some have suggested that familial extinction rates have been constant through time within most major taxonomic groups and that the decline in familial extinction rates is the result of the successive elimination of groups with relatively high familial extinction rates (a process referred to as taxon sorting). A model of total familial extinction rates through time based on stationary probabilities of familial extinction within orders closely mimics the observed decline in total familial extinction rates supporting the taxon sorting hypothesis. Linear regressions of the familial extinction probabilities of orders versus the geologic time of both their first and their last occurrences suggest that the observed decline in extinction rates resulted from the early elimination of orders with characteristically high probabilities of extinction, and the later origination of orders with relatively low probabilities of extinction. In addition, a statistical analysis comparing the evolutionary volatility of extinct versus extant taxa suggests that extinct orders had greater volatility in their diversity histories which may have contributed to their early demise. The taxonomic selectivity of both background and mass extinctions was investigated using simple X2 analyses. The results suggest that familial extinction during mass extinctions was taxonomically more selective than extinction during background extinctions. In addition, the magnitude of familial extinction experienced by an order in a stage was compared to the familial extinction probability estimated for the order using the binomial theorem. Then, those orders that suffered an unusual excess of familial extinction during particular stratigraphic stages were separated from the remaining orders in the stage. The results suggest that sessile filter feeders (particularly those groups important in ancient reefs) and pelagic groups suffered the greatest during intervals of mass extinction. Finally, the potential relationship of familial diversity to both sea level and I7Sr/86Sr ratios was statistically examined using linear regression techniques. No statistically significant correlation was found between sea level and familial diversity. However, a significant correlation was discovered between diversity and I7Sr /86Sr ratios. Strontium ratios are believed to be an indirect measure of the aerial extent of exposed continental crust. Thus, the relationship between 17 Sr/86Sr ratios and diversity suggests that familial diversity has been a function of 1) the aerial extent of epeiric seas and 2) the amount of clastic material being supplied to these seas. The last factor could have affected familial diversity by restricting normally diverse, shallow carbonate environments. / Master of Science