Allochthonous, seaward-dipping deposits that flank reef-rimmed carbonate platforms (reef-rimmed carbonate foreslopes) display a spectrum of deposit types, seismic-scale stratal architecture, and bed-scale heterogeneity due to diverse sediment sources and resedimentation processes. This variability has resulted in a lack of consistent characterization approaches, and has made the development of predictive models that link carbonate foreslope deposit types to stratal architecture challenging. This study uses data from outcrops, including the Upper Devonian of the Canning Basin, Western Australia and the Upper Permian of the Delaware Basin, West Texas, and examples from literature to provide 1) an approach for characterizing reef-rimmed carbonate foreslopes in terms of deposit types and architecture, 2) conceptual models that outline the variations that exist, and 3) discussion of the intrinsic and extrinsic factors that control the observed variations. The primary depositional elements that construct reef-rimmed carbonate foreslopes can be categorized as 1) debris elements (breccias and blocks) from brittle reef failure, 2) grain-dominated elements (grainstones and rudstones) from offbank transport of sand and gravel, and 3) mud-dominated elements (mud-dominated fabrics) that record relative foreslope quiescence and fine-grained periplatform shedding. The fundamental stratal geometries observed are 1) accretionary margins, characterized by margin-toforeslope interfingering and clinoforms, and 2) escarpment margins, characterized by aggrading-retrograding margin architecture and foreslope onlap. The combinations of element proportions, element distribution, stratal geometry, bed- to bedset-scale architecture, and depositional profile scale that exist in carbonate foreslopes range widely, warranting multiple depositional models. The deposit type and architectural variations observed in detail from Upper Devonian and Upper Permian outcrops of the Canning Basin, Western Australia, and the Delaware Basin, West Texas, respectively, are linked to differing scales of superimposed accommodation change and reef faunal assemblage. Observations from other outcrops and extensive literature review display further controlling factors that affect carbonate foreslope development, such as platform morphology, oceanographic conditions, slope height, tectonic setting, and siliciclastic input, suggesting a multi-variable interplay of controls. These controls dictate the productivity and resedimentation of the contributing sediment factories, and/or influence the development of the carbonate platform system as a whole. Knowledge and classification of carbonate foreslope deposit types, architecture, and controls not only improve understanding of these complex systems, but also allow for the development of predictive relationships for economic purposes. / text

The scarcity of carbonate on Mars has been difficult to reconcile with the morphologic evidence for a wet epoch in Martian history, and has weakened early interpretations of a water-rich Noachian. Limited soil carbonate from pre-Silurian Earth has created a similar conundrum, and in both instances this paradox has likely led to overreaching interpretations about past climates. To better understand the formation of carbonate on Mars, early Earth, and in present day hyperarid climates, we examined the distribution of carbonate in the Atacama Desert—a region that spans multiple climate regimes and allows us to isolate the effects of precipitation and plant cover on soil mineralogy. To better quantify the influences of vegetation on carbonate we utilized a simple one-dimensional precipitation model and simulated carbonate formation with or without plant cover under a range of relevant climatic conditions and soil morphologies. In the Atacama we found two distinct zones with only trace (<5%) carbonate: the "absolute desert" with precipitation too low to sustain plant life, and the high Andes where precipitation was significantly higher, but where the low mean annual temperature (MAT) inhibits plants. The fog-supported, low-elevation coastal "lomas" below approximately 800 meters above sea level (masl) and the higher elevations between approximately 2500-4500 masl are variably vegetated and contain abundant carbonate within the soils. Plants increase total evapotranspiration and its distribution with depth, weathering rates, and total pCO₂. Our model results show that all of these factors increase the formation of pedogenic soil carbonate. Without the influence of vegetation the diminished carbonate that is produced is flushed through the shallow soil, where it eventually precipitates in the deep vadose zone or is entrained by groundwater.

The Canterbury Basin is located on a passive margin on the east coast of the South Island, developed by the rifting of the New Zealand continental fragment from Antarctica in the Late Cretaceous. Well cuttings produced during petroleum exploration in the offshore Canterbury Basin have been examined for secondary minerals and textures. Minerals and textures have been identified primarily from optical examination in reflected light, with a particular focus on producing high-resolution images. Additional identifications are made using thin sections, SEM, XRD and XRF analysis. The focus of this study is the Clipper-1 well in the Clipper sub-basin as it contains the most abundant mineralisation and covers the full depth of the Canterbury Basin sedimentary sequence. Examination of cuttings from this well has revealed intrusive igneous carbonates and native metals including iron, aluminium and copper. The trace element concentrations in the igneous carbonates indicates they are derived from crustal material. Textures indicating fluidisation and recrystallisation of sedimentary material are also present. The proposed mechanism for producing these unusual mineral assemblages is a late Pliocene or younger mafic intrusion into the schist basement of the Canterbury Basin. The igneous carbonates are inferred to be derived from melting of carbonates in the schist. The native metals have been produced from melt due to highly reducing conditions produced by interaction of the intrusion with coal and limestone. The combination of native metals and igneous carbonates with a conspicuous absence of typical silicate igneous rocks is inferred to represent a new type of intrusive environment that has not previously been described in the scientific literature.

No description available.

Diagenetic histories of Proterozoic and Paleozoic carbonate strata on Victoria Island, in the Canadian arctic, are poorly understood, and their potential to be associated with base metals or petroleum is unknown. Using fluid inclusion and geochemical techniques, it was determined that the diagenetic fluid compositions of two major carbonate units, the Wynniatt Formation and the “Victoria Island formation”, were largely controlled by fluid-rock reactions in reservoirs and by mixing of multiple fluids. Diagenesis of the Wynniatt Formation resulted from the progression from a shale-dominant fluid mixture to a meteoric-dominant mixture. Fluid composition of “Victoria Island formation” was a shale-dominant mixture. A change in fluid:rock from low to high was recorded during diagenesis of both units. Metals and hydrocarbons transported to the study sites were ac-quired by the fluids during interaction with the respective source reservoirs. Mixing of diagenetic fluids follows the established ‘mixing model’ used to explain many other min-eralised locations. The diagenetic fluids that affected the strata in this study were compa-rable to those that produced the Polaris Zn-Pb deposit. This similarity suggests that there is potential for mineralisation on Victoria Island.

The Late Devonian was a significant period in Phanerozoic reef evolution. Reef complexes reached their acme in the Middle Devonian and then declined in numbers and complexity thereafter. This change was accompanied by a shift in reef composition characterized by an increase in calcified microbes in the reef milieu. Late Devonian Nisku Formation reefs in the Cynthia Basin at Meekwap, Alberta are composed of calcimicrobes (Renalcis, Epiphyton, Girvanella, Rothpletzella, and Wetheredella), stromatoporoids, and corals. Accessory organisms include brachiopods, benthic foraminifera, molluscs, sponges, bryozoans, and crinoids. Calcimicrobes generate dorsal or ventral crusts on stromatoporoids, and form oncolites in open marine facies. Dorsal crusts are either Girvanella and Rothpletzella, or non-calcimicrobial, spongiostromate or cemented calcisilt encrustations. Ventral crusts are cryptic and composed of Renalcis and Epiphyton. Oncolites comprise layers of Girvanella and Rothpletzella and occur in lagoon and upper-foreslope facies. Girvanella and Rothpletzella are thought to have been photosynthetic because of their preference for interpreted well-lit settings (oncolites and dorsal surfaces) and possible competition for light as expressed by alternating layers of Girvanella and Rothpletzella as well as domal, accretionary growths of either Girvanella or Rothpletzella in oncolites. Renalcis and Epiphyton are viewed as non-photosynthetic or light sensitive because they are rare on upper surfaces and are instead found in cryptic environments. The abundance of calcimicrobes in Meekwap limestones is interpreted to have reflected elevated nutrient levels. Nutrients were likely terrestrially sourced and brought onto the shelf via fluvial runoff and submarine groundwater discharge. Geometry of the Cynthia Basin, as well as the presence of local nutrient sources at Meekwap is thought to have enhanced more regional nutrification via ocean upwelling. The change in the composition of reefs throughout the Late Devonian is attributed to paleoenvironmental changes, such as a colder climate and falling ocean temperatures, as well as increasing nutrient levels, prior to the Late Devonian mass extinction. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2010-12-21 12:24:17.569

No description available.

No description available.

No description available.

In the mid-Cenozoic, New Zealand underwent slow subsidence interspersed with unconformity development, however significant controversy exists around both the extent of submergence below sea level during this period of maximum drowning, as well as the causes of these unconformities. Detailed field observations, combined with extensive petrographic analyses, stable isotopes, cathodoluminescence, and thin section staining were used to develop lithofacies, depositional, and sequence stratigraphic models of the mid-Cenozoic succession in the Waitaki region, South Island, to address these controversies. Twelve facies types have been described for Late Eocene-Early Miocene sedimentary rocks, leading to the identification of two major (Mid Oligocene & Early Miocene) and one minor (Late Oligocene) sequence boundaries. Surtseyan volcanism in the east produced a palaeohigh, resulting in a submerged rimmed cool-water carbonate platform, with low-lying land to the west. This eastern palaeohigh developed karst during sea-level lowstands, which correlate with silty submarine bored hardgrounds in the west. Glauconitic and phosphatic facies deposited during early marine transgression suggest an authigenic factory supplied by terrigenous clays existed during lowered sea level that was progressively shut down in favour of a carbonate factory as sea level rose and terrigenous supply decreased. The eastern palaeohigh served to nucleate this carbonate factory by raising the sea floor above the influence of siliciclastic sediment supply and providing a shallow substrate for marine colonisation. The higher energy eastern facies display dissolution of aragonitic taxa, while deeper western facies retained an aragonitic assemblage. This early bathymetric high created a barrier to submarine currents, but was gradually reduced by erosion during subsequent lowstands. Calcareous facies were often subjected to minor seafloor cement precipitation to shallow burial diagenesis, while eastern facies developed some meteoric cement during subaerial exposure. Comparisons between sea-level change in the study area and the New Zealand megasequence indicate eustatic changes as the primary driver of water depth in the Waitaki region until the development of the modern plate boundary in the Early Miocene.