Grupo Corumbá representa um dos mais completos registros sedimentares do Ediacarano na América do Sul, com afloramentos de rochas siliciclásticas e carbonáticas ao longo da Faixa Paraguai Sul. Estas rochas contêm um rico conteúdo fossilífero, com ocorrências dos primeiros organismos com estruturas biomineralizadas (Cloudina sp). Este trabalho apresenta o estudo faciológico e quimioestratigráfico da Formação Tamengo, Grupo Corumbá na mina Laginha, sucessão carbonática de 130 metros de espessura, em contato erosivo na base com brechas calcárias e no topo com os pelitos da Formação Guaicurus. Para a Formação Tamengo foram descritas 4 fácies sedimentares: brecha calcária intraformacional (F1), grainstone oolítico (F2), packstone/grainstone oolítico (F3) e ritmito (F4), as quais representam a evolução de uma rampa interna-média com geração de barras oolíticas, submetida à ação de correntes e ondas de alta energia. Os dados geoquímicos e isotópicos dos carbonatos mostram as condições geoquímicas dessa rampa carbonática depositada em ambiente marinho de águas rasas. Análises isotópicas de carbono e oxigênio foram realizadas em 130 amostras de rocha, coletadas a cada um metro. Com base nos teores de Rb e Sr determinados por FRX, as 10 amostras com altas concentrações de Sr foram selecionadas para análise isotópica de Sr e geoquímica elementar. Na base da sucessão, os carbonatos oolíticos mostram valores de ?13C (V-PDB) de cerca de -3,5 ?, aumentando para +6,0 ? nos primeiros 70 metros basais da sequência. O aumento nos valores de ?13C é interpretado como resultado do aumento da taxa de matéria orgânica soterrada. Acima desse intervalo, observa-se uma tendência homogênea dos valores ?13C, oscilando entre 1,7 e 3,4 ?. A estabilidade nestes valores positivos pode estar relacionada ao equilíbrio entre a taxa de matéria orgânica soterrada e a reciclagem do carbono pela degradação da matéria orgânica. Os valores de ?18O (V-PDB) são todos negativos e mostram uma tendência progressiva em toda a seção, de -1,8 na base a -9,3 ? na parte superior. Os valores de ?18O provavelmente não refletem as composições isotópicas primárias devido à alteração pós-deposicional. As razões 87Sr/86Sr variaram entre 0,7085 e 0,7089, as quais são concordantes com a evolução global para o final do Ediacarano. Os resultados obtidos permitem inferir que estas razões representam a composição isotópica da água do mar na época da deposição. A presente investigação contribui para o conhecimento das condições geoquímicas presentes nos ambientes marinhos rasos da rampa carbonática onde as rochas da Formação Tamengo foram depositadas e suas implicações no desenvolvimento das comunidades biológicas que evoluíram no final do Ediacariano. / The Corumbá Group represents one of the most complete sedimentary records of the Ediacaran in South America, with outcrops of siliciclastic and carbonate rocks along the southern Paraguay Belt. These rocks contain a rich fossiliferous content, with occurrences of the first organisms with biomineralized structures (Cloudina sp). This work presents the faciologic and chemostratigraphic study of the Tamengo Formation, Corumbá Group, at the Laginha mine, a 130 - m thick carbonate succession, in erosive contact at the base with carbonate breccias and at the top with pelites of the Guaicurus Formation. Four sedimentary facies have been described in the Tamengo Formation: intraformational breccia (F1) oolitic grainstone (F2) oolitic packstone/grainstone (F3) and rhythmites (F4), which represent the evolution of an inner-mid ramp with oolitic bars generation, subjected to the action of currents and waves of high energy. Elementar and isotope geochemistry of carbonates show the chemical conditions in the shallow-water marine environments of this carbonatic ramp. Carbon and oxygen isotopic analysis were performed on 130 calcareous samples, collected each meter. Based on the Rb and Sr contents determined by XRF, ten samples with high Sr concentrations were selected for Sr isotope and elemental geochemical analysis. The ?13C (V-PDB) values start with -3.5 ? at the base of oolitic carbonates, increasing to +6.0 ? in the first 70 meters at the base of the sequence. The increase in ?13C values is preliminarily interpreted as a result of the increase in the organic matter buried. Above this interval, a homogeneous trend is observed in the ?13C values, oscillating between 1.7 and 3.4 ?. The stability of these positive values can be related to a balance between the buried organic matter and carbon recycling by organic matter degradation. The ?18O (V-PDB) values are all negative and show a progressive trend throughout the section, from -1.8 at the base to -9.3 ? at the top. This trend of the ?18O values probably do not reflect the primary isotopic composition due to post-depositional alteration. 87Sr/86Sr ratios ranged between 0.7085 and 0.7089, which are in accordance with the global Sr isotope evolution of the late Ediacaran seawater. The obtained results allow us to infer that these ratios represent the isotopic composition of seawater at the time of deposition. The present study contributes to the knowledge of the geochemical conditions of the shallow marine environments of the Tamengo Formation, which has implications in the development of the biological communities that evolved at the end of the Ediacaran.

Middle Mississippian ramp carbonates in Kentucky (Fort Payne to Salem interval) form a large scale depositional supersequence (0 to 500 feet thick, approximately 8 m. y. duration). It formed on and in front of the abandoned Early Mississippian Borden deltaic marine paleoshelf, which had up to 100 m of relief above the adjacent starved basin. Major facies consist of marine quartz sandstone and shale; peritidal carbonates; high-energy ramp margin, crinoidal-bryozoan grainstones; deeper ramp mounds, skeletal grainstone/packstone sheets and channel-fills interlayered with shale or calcisiltite; and slope deposits of siliceous calcisiltite. Regional slopes on the paleoshelf edge and ramp margin are 0.5 to 2.5 mIkm (less than 0.25 degrees), although clinoforms of 2 to 10 degrees occur locally associated with mounds and depositional lobes. The supersequence LST is dominated by mounds interlayered with green shaly, deeper ramp facies. The mounded units are located in a fairway that is normal to the Borden margin but parallel to the Appalachian Grainger deltaic shelf. No TST is evident, except for a glauconite horizon capping the Borden paleoshelf. The supersequence HST consists of at least eight third-order sequences (each approximately 1 m.y. duration), the older ones downlapping onto the shelf 20 to 30 m deep, the younger ones downlapping into the deeper basin (over 150 m water depth). Sequences show marked toplap with the upper sequence boundary. The third-order sequences locally have lowstand sands, some of which may be associated with a paleodrainage system off the Borden paleo shelf. They lack recognizable TSTs, but have well-developed prograding HST units of nearshore shale and peritidal dolomite, skeletal packstone/grainstone banks, and siliceous calcisiltite slope facies. The supersequence correlates with a global sea level cycle in the lower Visean terminating in a major sea-level fall. The highly clinofonned toplapping supersequence reflects this long term, sea-level fall which prevented space from being created on the old delta top. The third-order sequences, although mappable between the sections, are not easily correlated with global third order cycles. / Master of Science

Phylloid-algal mounds form heterogeneous hydrocarbon reservoirs in the southeastern portion (Blanding sub-basin) of the Paradox Basin. Well-studied Lower Ismay mounds exposed along walls of the San Juan River gorge in the vicinity of Eight Foot Rapids, the west limb of the Raplee Anticline, and at the classic Honaker Trail locality (southwestern Paradox Basin) have often been cited as outcrop analogs of productive subsurface mounds. Until now, however, there has not been a complete description of the distribution, size, and spacing of outcropping algal mounds at the classic Eight Foot Rapids locality. The Lower Ismay sequence was analyzed in the context of a build-and-fill model of deposition. There are three facies associations within the sequence: 1) a basal lowstand to middle highstand pre-mound facies association, 2) a late highstand to middle falling stage phylloid algal-dominated relief-building facies association, and 3) a late falling stage, post-mound relief-filling facies association. Above the basal maximum flooding surface (Gothic Shale), the facies succession displays a distinct shallowing upward trend through the Lower Ismay sequence. Mound dimensions and facies stacking patterns permit evaluation of two depositional models. The first is a traditional, moderate- to low-energy model of vertical and radial mound accumulation of phylloid algal plates. The second is a high-energy, tidally influenced model of accumulation wherein mounds become hydrodynamically elongate. Outcrop data indicate that algal-dominated buildups are domal in shape with no preferred axis of elongation. These patterns do not support a hydrodynamic accumulation of loose algal plate fragments. The absence of in-situ algal thalli in all but the upper few tens of centimeters of the mounds, however, argues against a purely biological/ecological origin of mounds. A down-stepping ramp model is proposed wherein a muddy algal facies was deposited at the base of the mounds in the low energy of the outer ramp, followed by a grain-rich algal core in the mid-ramp environment. Mounds tops accumulated in an algal bafflestone facies in the inner ramp setting. Restriction of energy due to basinward algal buildup may have also contributed to deposition of algal bafflestone. Mounds accumulated radially at differential rates and were influenced by these variations in energy. This differential deposition of microfacies and subsequent diagenetic alteration have produced heterogeneities in algal reservoir rock, producing algal mound reservoirs that have a high potential for compartmentalization.

The Pennsylvanian Marble Falls Formation in the Llano Uplift region of the southern Fort Worth Basin (Central Texas) is a Morrowan-Atokan mixed carbonate-siliciclastic unit whose deposition was influenced by icehouse glacioeustatic sea-level fluctuations and foreland basin tectonics. Previous interpretations of the Marble Falls Formation focused on outcrop data at the fringes of the Llano Uplift. This study uses a series of 21 cores to create a facies architectural model, depositional environmental interpretation, and regional sequence stratigraphic framework. On the basis of core data, the study area is interpreted to have been deposited in a ramp setting with a shallower water upper ramp area to the south and a deeper water basin setting to the north. Analysis of cores and thin sections identified 14 inner ramp to basin facies. Dominant facies are: (1) burrowed sponge spicule packstone, (2) algal grain-dominated packstone to grainstone, (3) skeletal foraminiferal wackestone, and (4) argillaceous mudstone to clay shale. Facies stacking patterns were correlated and combined with chemostratigraphic data to improve interpretations of the unit’s depositional history and form an integrated regional model. The Marble Falls section was deposited during Pennsylvanian icehouse times in a part of the Fort Worth Basin with active horst and graben structures developing in response to the Ouachita Orogeny. The resulting depositional cycles reflect high-frequency sea-level fluctuations and are divided into 3 sequences. Sequence 1 represents aggradational ramp deposition truncated by a major glacioeustatic sea-level fall near the Morrowan-Atokan boundary (SB1). This fall shifted accommodation basinward and previously distal areas were sites of carbonate HST in Sequence 2 deposition following a short TST phase. Sequence 3 represents the final phase of carbonate accumulation that was diachronously drowned by Smithwick siliciclastics enhanced by horst and graben faulting. These findings contribute to our understanding of the depositional response to glacioeustatic sea-level changes during the Pennsylvanian and can also form the basis for constructing a sedimentological and facies analog for Morrowan to Atokan shallow- to deepwater carbonates in the Permian Basin and the northern Fort Worth Basin. / text