Southern Alabama holds one of the world's most complete shallow shelf Cretaceous-Tertiary boundary sections. The boundary is exposed in a sequence of marl-limestone interbeds in a roadcut south-east of Braggs in Lowndes County, Alabama. Benthic foraminifera were extracted in 10cm intervals to obtain a high-resolution record of assemblage succession across this controversial boundary. A local sea level curve was then formulated using previous paleobathymetric foraminiferal assemblage models from the Gulf Coast and the Atlantic Coastal margin. Sea-level fluctuations thus evident have revealed a fourth-order cycle similar to those found by Briskin and Fluegeman (1990) with an average period of around 430 kyr through the Paleocene. This cycle includes a drop from outer slope to middle shelf conditions in the latest Cretaceous and a subsequent increase from inner shelf to outer shelf conditions in the earliest Paleocene. Within this cycle are several fifth-order cycles that are interpreted as having a periodicity of roughly 100 kyr. Sea-level cycles with Milankovitch frequencies occurring on an ice-free Paleocene Earth lend support to the concept of astronomical forcing of climate and thus sea-level. / Department of Geology

Bibliography : leaves 347-364. / xvi, 364, [58] leaves, [15] leaves of plates : ill. (some col.), maps (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / A stratigraphically-based study of the nature of the shelf succession and its relationship to surrounding successions of the central Carpentaria Basin and the Great Artesian Basin as a whole. / Thesis (Ph.D.)--University of Adelaide, Dept. of Geology and Geophysics, 1995

No description available.

Within Big Bend National Park, the unconformable contact between the Buda Limestone and the overlying Boquillas Formation represents the Commanchean-Gulfian boundary. Previous studies of the geochronology of this interval have relied primarily on provincial ammonite faunas rather than foraminifera, and place the Buda and basal Boquillas in the Lower Cenomanian. Because of its indurated nature, a comprehensive foraminiferal biozonation has not been acquired for the Buda Limestone. Recent revisions to Cretaceous foraminiferal biozonations and taxonomies necessitates a new biostratigraphic study of the Buda - Boquillas interval. The overlapping ranges of F. washitensis, G. bentonensis, G. caseyi, P. appenninica, P. delrioensis, P. stephani, and R. montsalvensis place the Buda within the upper portion of the Early to Middle Cenomanian Th. globotruncanoides Zone. Microkarst found on the surface of the Buda Limestone has been interpreted as representing a subaerial exposure and sequence boundary. However, microkarst-like features can result from subaqueous or intrastratal processes. Carbon and oxygen stable isotope analysis of the lower and middle Buda has indicated a mean δ13C value of 1.73‰ VPDB, which is in line with other values reported from the Lower Cenomanian. The top 2.6m of Buda contains a 0.62‰ negative δ13C shift from 1.88‰ VPDB to 1.26‰ VDPB in a 40 cm interval, expected if subaerial exposure occurred. Higher variation in measured carbon isotope values beneath the contact also lend evidence for meteoric alteration. The standard deviation in δ13C values from the top 2.8 m of the Buda is 0.207, which is 2.16 times larger than the rest of the studied section at 0.096. The Buda contains a shallow pelagic-dominated fauna of heterohelicids (45-90%), globigerinellids (3-37%), and hedbergellids (4-22%). Intermediate-depth globigerinellids display an initial increase followed by a marked decrease in abundance upsection, interpreted as sea level transgression and regression, respectively. The lower contact of the Buda with the Del Rio Clay has been previously interpreted as a subaerial exposure, and a P:B break from ~0% planktonics in the upper Del Rio to ~80% in the Buda supports this claim. This study therefore interprets both the upper and lower contacts of the Buda as sequence boundaries. The overlying 1.2 m Boquillas is nearly devoid of benthics and represents a deeper assemblage including the double-keeled Dicarinella sp., as well as several Upper Cenomanian (D. algeriana Subzone) species. Based on foraminiferal data, the duration of the Buda - Boquillas unconformity is roughly equivalent to the missing Th. reicheli and Th. greenhornensis Biozones, or a sizable portion of the Middle Cenomanian. / Systematic paleontology -- Biostratigraphy of the Buda Limestone -- Biostratigraphy of the lowermost Boquillas Formation -- Stable isotope geochemistry. / Department of Geological Sciences

Made available in DSpace on 2014-06-11T19:26:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-05-05Bitstream added on 2014-06-13T19:13:16Z : No. of bitstreams: 1 voltani_cg_me_rcla.pdf: 3761766 bytes, checksum: b819d81d58be398c33a3c1bcd92c037f (MD5) / A Bacia do Araripe é a maior estrutura bacinal interior do Nordeste brasileiro, com História Geológica apresentando registros desde a Era Paleozóica. Mas é do Cretáceo que vem sua notabilidade. O Membro Romualdo da Formação Santana é um autêntico lagerstätten, cujos fósseis estão magnificamente preservados e são muito diversos, especialmente entre os vertebrados. Entre estes estão descritos cerca de 30 morfótipos de peixes. Uma parte significativa desta diversidade encontra-se depositada no Museu de Paleontologia e Estratigrafia “Paulo Milton Barbosa Landim”, UNESP, Campus de Rio Claro. São 13 gêneros representados, distribuídos em 3.119 espécimens. Parte deste material foi analisado, a fim de trazer contribuições sobre a Osteologia de cada grupo, bem como Paleobiogeografia, Paleoecologia, Cronobioestratigrafia / The Araripe Basin is the largest interior basin structure from Northeastern Brazil, which has a Geological History presenting data since the Paleozoic Era. Nevertheless its notability comes from the Cretaceous. The Romualdo Member from the Santana Formation is an authentic largerstätten, containing an excellently preserved diverse fossil assemblage, especially vertebrates. Among those are described about 30 morphotypes of fishes. A meaningful portion of this diversity is found deposited on “Museu de Paleontologia e Estratigrafia “Paulo Milton Barbosa Landim”, UNESP, Rio Claro Campus. There are 13 genera represented, distributed on 3.119 specimens. Part of this material has been analised, in order to contribute with the Osteology of each group, as well as to Paleobiogeography, Paleoecology and Chronobiostratigraphy

PhD (Geology) / Department of Mining and Environmental Geology / Cretaceous-Tertiary Periods marked the break-up of Gondwana, a large landmass composed of most of the present-day southern continents. In understanding the events of the supercontinental break-up, paleoenvironmental studies need to be carried out. In such studies, kaolinites could be used as paleoenvironmental proxies due to their small particle sizes and large surface area. It is in this context that this research sought to reconstruct the paleoenvironments in which selected Cretaceous-Tertiary kaolin deposits in the Douala Sub-Basin in Cameroon formed. To achieve this objective, mineralogical and geochemical characterisations were carried out using x-ray diffractometry, scanning electron microscopy, Fourier transform infrared spectrometry, thermal analyses and x-ray fluorescence spectroscopy. Trace elements and stable isotopes were analysed using mass spectrometries. Ages of zircons in the kaolins were determined using laser ablation magnetic sector-field inductively coupled plasma mass spectrometry (LA-SF-ICP-MS) U-Pb geochronology. Diagnostic evaluation for industrial applications of the kaolins were carried out using particle size distribution, texture, moisture content, pH, and electric conductivity. Six kaolin deposits from Cretaceous-tertiary Formations of the Douala Sub-Basin were studied; namely, Bomkoul (Tertiary), Dibamba (Tertiary), Ediki (Cretaceous), Logbaba (Cretaceous), Missole (Tertiary) and Yatchika (Cretaceous). The nature and occurrences of these kaolin deposits in Cameroon were determined through thorough mineralogical and geochemical characterisations of bulk (< 2 mm size fraction), silt (2-63 μm size fraction) and clay samples (< 2 μm size fraction). By quantifying the mineral phases present, the morphology and the functional groups in the kaolins are presented as the mineralogical characteristics of kaolins of each study site; whereas, the major oxides geochemistry and the micro-elemental composition constitute the geochemical characteristics of these kaolins. The minerals’ geneses were also determined and the prevailing paleoenvironmental and paleoclimatic conditions in which they were formed were reconstructed using trace elements and stable isotopes of oxygen and hydrogen in kaolinite. The maximum age of the kaolins were determined using U-Pb LA-SFICP-MS dating of zircons in the kaolin deposits. Diagnostic evaluation of the kaolins was carried out, and involved the determination of physical characteristics (particle size, texture, colour and moisture content) and physico-chemical characteristics (pH and electrical conductivity). Results showed that kaolinite and quartz (as major phases), smectite and/or illite (as minor phases), anatase and rutile (as minor or trace phases), goethite and hematite (as trace viii phases) were the mineral phases present in bulk and silt samples. Whereas, in the < 2 μm fractions, the mineral phases are made up of kaolinite and smectite (as major phases), smectite and/or illite (as minor phases), anatase and rutile (as minor or trace phases), goethite and hematite (as trace phases). The kaolins are mostly made up of thin platy or pseudo-hexagonal particles or flakes, books or stacks of kaolinite. The Dibamba, Logbaba and Missole II kaolins have well-ordered structures. Exothermic peak temperatures were generally between 943-988oC. The most abundant major oxides are silica and alumina, followed by iron oxide and titania; though Logbaba and Missole II had higher titania than iron oxide. 85% of the kaolins, portrayed extreme silicate weathering (chemical index of alteration > 80%) and are compositionally mature (index of compositional variability > 0.78). The geochemical composition of the kaolins showed that source rocks of these kaolins vary between rhyolite/granite and rhyolite/granite + basalt. The geochemistry also suggested that the kaolins formed in a marine environment (except Logbaba samples). Trace elements results revealed that Cretaceous-Tertiary kaolins in the Douala Sub-Basin are mainly enriched in rare earth elements compared to the upper continental crust, and have negative Eu anomaly. Large ion lithophiles (mainly Rb and U) were highly enriched in samples, high field strength elements (Y and Nb) were enriched in studied samples of all fractions; and transition trace elements generally had concentrations quite similar to upper continental crust values. Stable isotopes showed that the kaolins were formed in a supergene environment; and temperatures of kaolinitisation (assuming equilibrium with the global meteoric water line) were 26.58oC ± 9.65oC for Cretaceous kaolins and 29.40oC ± 7.22oC for Tertiary kaolins. Assuming equilibrium with the local (Douala) meteoric water line, the temperatures of kaolinitisation were 24.64oC ± 9.48oC for Cretaceous and 27.42oC ± 7.08oC for Tertiary kaolins. Four main zircon populations were identified from radiogenic dating: the 1st between 550 and 650 Ma, the 2nd between 950 and 1050 Ma, the 3rd around 1600 Ma and the 4th between 2800-3200 Ma. These four zircon populations belong to the Proterozoic (Neo-, Meso- and Paleoproterozoic) and the Archean. The maximum depositional ages of the kaolins, reflected by the youngest weighted averages of zircon populations varied between 588 ± 2 Ma and 612 ± 2 Ma, all belonging to the Ediacaran Period (Neoproterozoic). The diagnostic evaluation of the kaolins revealed that the kaolins are very sandy, with 50% of the samples having a sandy loamy clay or sandy loam texture. The colour of the samples varied considerably from white to darker colours (dark grey); with 15% of the kaolins being light reddish brown. The moisture content was generally very low (< 2 wt %) in all size fractions, except in Yatchika samples (moisture content > 2 wt %). The kaolins are generally acidic, with ix a pH(KCl) varying between 3.06 and 3.81, except in Missole I samples, which had a pH (KCl) < 2. The electrical conductivity (EC) generally varied between 20 to ~ 50 μS/cm, except Dibamba and MSL II 01 samples which had EC values in the interval 50 μS/cm < EC < 80 μS/cm; and Missole I samples having an EC > 7500 μS/cm. In conclusion, no great distinction was found between Cretaceous and Tertiary kaolins of the Douala Sub-Basin based on their mineralogy and geochemistry. The best kaolins in terms of these characteristics, and in comparison with the Georgia Kaolins (known for their high kaolinite quality), were the Dibamba (Tertiary), Logbaba (Cretaceous) and Missole II (Tertiary) kaolins. Based on their compositional maturity and mineralogical characteristics, these three kaolins are considered to be second cycle sediments; unlike Bomkoul, Yatchika and Ediki kaolins, which are believed to be first cycle sediments. Based on the trace elements and stable isotopes composition, Cretaceous and Tertiary kaolins of the Douala Sub-Basin were derived from felsic rocks. However, Cretaceous kaolins were formed in a cooler anoxic reducing environment; whereas the Tertiary kaolins were formed in a warmer oxidising environment, with higher precipitation. Ages of zircons in Cretaceous-Tertiary kaolins suggested that the zircon formed during two main tectonic events: the Eburnean orogeny, during which older zircons crystallised and the Pan-African orogeny, during which younger zircons crystallised. The maximum depositional ages of the kaolins varied between 588 ± 2 Ma and 612 ± 2 Ma. The main identified sources of these zircons are the Archean Ntem Complex, the Paleoproterozoic Nyong Group and the Neoproterozoic Yaounde Group. The diagnostic evaluation indicated that the particle size greatly influences the mineralogy and geochemistry of the kaolins because the finer particles (< 2 μm) have higher amounts of kaolinite and Al2O3. The moisture content of the kaolins makes them suitable as paint fillers and in soap production. Paper coating, paper filler, ceramics, pharmaceutics and cosmetics are potential applications for the kaolins, though particle size reduction and beneficiation will give them a higher quality. However, because these kaolin deposits are not big and extensive, they cannot be recommended for large scale industrial applications; but they can be used for bricks, pottery and stoneware manufacturing.

[Truncated abstract] The Tintina Gold Province (TGP) comprises numerous (<15) gold belts and districts throughout interior Alaska and Yukon that are associated with Cretaceous plutonic rocks. With a gold endowment of ∼70Moz, most districts are defined by their placer gold contributions, which comprise greater than 30 Moz, but four districts have experience significant increases in gold exploration with notable discoveries at Fort Knox (5.4 Moz), Donlin Creek (12.3 Moz), Pogo (5.8 Moz), True North (0.79 Moz), and Brewery Creek (0.85 Moz). All significant TGP gold deposits are spatially and temporally related to reduced (ilmenite-series) and radiogenic Cretaceous intrusive rocks that intrude (meta-) sedimentary strata. The similar characteristics that these deposits share are the foundation for the development of a reduced intrusion-related gold deposit model. Associated gold deposits have a wide variety of geological and geochemical features and are categorized as intrusion-centered (includes intrusion-hosted, skarns and replacements), shear-related, and epizonal. The TGP is characterized by vast, remote under-explored areas, unglaciated regions with variable oxidation depths and discontinuous permafrost, which, in combination with a still-evolving geological model, create significant exploration challenges. Twenty-five Early and mid-Cretaceous (145-90 Ma) plutonic suites and belts are defined across Alaska and Yukon on the basis of lithological, geochemical, isotopic, and geochronometric similarities. These features, when combined with aeromagnetic characteristics, magnetic susceptibility measurements, and whole-rock ferric:ferrous ratios define the distribution of magnetite- and ilmenite-series plutonic belts. Magnetite-series plutonic belts are dominantly associated with the older parts of the plutonic episode and comprise subduction-generated metaluminous plutons that are distributed preferentially in the more seaward localities dominated by primitive tectonic elements. Ilmenite-series plutonic belts comprise slightly-younger, slightly-peraluminous plutons in more landward localities in pericratonic to continental margin settings. They were likely initiated in response to crustal thickening following terrane collision. The youngest plutonic belt forms a small, but significant, magnetite-series belt in the farthest inboard position, associated with alkalic plutons that were emplaced during weak extension. Intrusion-related metallogenic provinces with distinctive metal associations are distributed, largely in accord with classical redox-sensitive granite-series. Copper, Au and Fe mineralisation are associated with magnetite-series plutons and tungsten mineralisation associated with ilmenite-series plutons. However, there are some notable deviations from expected associations, as intrusion-related Ag-Pb-Zn deposits are few, and significant tin mineralisation is rare. Most significantly, many gold deposits and occurrences are associated with ilmenite-series plutons which form the basis for the reduced intrusion-related gold deposit model