Browsing by Subject "Late Cretaceous"
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Item Characterization and prediction of reservoir quality in chlorite-coated sandstones : evidence from the Late Cretaceous Lower Tuscaloosa Formation at Cranfield Field, Mississippi, U.S.A.(2013-05) Kordi, Masoumeh; Fisher, W. L. (William Lawrence), 1932-; Hovorka, Susan D. (Susan Davis)The effectiveness of CO₂ injection in the subsurface for storage and EOR are controlled by reservoir quality variation. This study determines the depositional processes and diagenetic alterations affecting reservoir quality of the Lower Tuscaloosa Formation at Cranfield Field. It also determines the origin, time and processes of the grain-coating chlorite and its impacts on reservoir quality. Moreover, by integrating depositional and diagenetic characteristics and by linking them to sequence stratigraphy, the distribution of reservoir quality, could be predicted within a sequence stratigraphic framework. The studied sandstones are composed of medium to coarse-grained, moderately sorted litharenite to sublitharenite with composition of Q76.1F0.4L23.5. Depositional environment of this formation in the Mississippi Interior Salt Basin is interpreted as incised-valley fluvial fill systems. The cross sections and maps at the field show trend of the sandy intervals within channels with a NW-SE paleocurrent direction. During burial of the sandstones, different digenetic alterations including compaction, dissolution, replacement and cementation by chlorite, quartz, carbonate, kaolinite, titanium oxides, pyrite and iron-oxide modified the porosity and permeability. Among these, formation of chlorite coats plays the most important role in reservoir quality. The well-formed, thick and continuous chlorite coatings in the coarser grain sandstones inhibited formation of quartz overgrowth, resulted in high porosity and permeability after deep burial; whereas the finer grain sandstones with the poorly-formed, thin and discontinuous chlorite coatings have been cemented by quartz. The optimum amount of chlorite to prevent formation of quartz overgrowths is 6% of rock volume. The chlorite coats are composed of two layers including the inner chlorite layer formed by transformation of the Fe-rich clay precursors (odinite) through mixed-layer clays (serpentine-chlorite) during early eodiagenesis and the outer layer formed by direct precipitation from pore waters through dissolution of ferromagnesian rock fragments during late eodiagenesis to early mesodiagenesis. In the context of the reservoir quality prediction within sequence stratigraphic framework, the late LST and early TST are suitable for deposition of chlorite precursor clays, which by progressive burial during diagenesis could be transformed to chlorite, and thus results in preserving original porosity and permeability in deep burial.Item Utilizing Vertebrates to Understand the Factors that Influence Terrestrial Ecosystem Structure(2012-07-16) Redman, CoryConserving biodiversity in the current global ecological crisis requires a robust understanding of a multitude of abiotic and biotic processes operating at spatial and temporal scales that are nearly impossible to study on a human timescale and are therefore poorly understood. However, fossil data preserve a vast archive of information on past ecosystems and how they have changed through time. My PhD research is composed of three studies that look at biogeogaphic distribution, ecosystem structure, and trends in richness and diversity. Identifying organisms to the species level is a common practice in ecology when conducting community analyses. However, when species-level identification is not feasible, higher level taxonomic identifications are used as surrogates. This study tests the validity of supraspecific identifications for vertebrates in regional biogeography studies, using the recorded occurrences of terrestrial and aquatic taxa from 16 national parks on the Colorado Plateau and culling the data set based on a series of taphonomic processes to generated fossil assemblages. Changes in community structure as a result of increased magnitude and/or frequency of perturbations have been well documented in terrestrial and marine ecosystems. Unfortunately, the long-term effects of sea-level rise on vertebrate communities in coastal habitats are poorly understood and difficult to study on a human time scale. This study examines the long term effects of relative sea-level change on coastal plain ecosystems of the Belly River Group (Campanian) in southern Alberta using microvertebrate fossils. Most Cretaceous freshwater deposits in North America produce only a couple of articulated fish skeletons. Because of this preservational bias many workers suggested that freshwater teleosts were largely absent from North America until the Eocene or later. Late Cretaceous fish assemblages are of particular interest, because these assemblages undergo a major compositional change. Pre-Cretaceous fish assemblages are dominated by non-teleosts, while Paleogene assemblages are dominated by teleosts that are members of extant families. This study provides a first approach in characterizing long-term trends in richness and the distribution of Late Cretaceous, nonmarine actinopterygians of the Western Interior of North America.