Diss. (sammanfattning) Uppsala : Uppsala universitet, 2005. / Härtill 6 uppsatser.

The end-Triassic Mass Extinction (ETME) was one of the "Big 5" mass extinctions of the Phanerozoic and is thought to have been caused by a series of environmental changes triggered by the emplacement of the Central Atlantic Magmatic Province (CAMP). While the overall driver of the ETME is well-accepted, the specific roles of subsequent environmental changes in driving the extinction remain unresolved due to both spatial and temporal biases within existing geochemical records. Additionally, recent studies suggest that environmental deterioration may have preceded the emplacement of both CAMP and the ETME. Here, we present nitrogen isotope (δ15N) and iron speciation data from a sedimentary succession located in Grotto Creek, Alaska in order track changes in the marine nitrogen cycle and redox across the upper Norian Stage of the Triassic through lower Hettangain Stage of the Jurassic (~215 to 198 million years ago). The geologic succession at Grotto Creek represents deeper water marine deposition in eastern equatorial Panthalassa, likely capturing regional oceanic redox trends. δ15N records from Grotto Creek show a pronounced positive excursion of +3‰ that initiates in the upper Norian, peaks near the Norian-Rhaetian boundary (NRB; ~208.5), and declines through the ETME and into the Hettangian. Throughout this interval, iron speciation data show persistent anoxic conditions and occasional euxinia occurred in the local bottom waters. We propose that the positive δ15N and iron speciation data from Grotto Creek reflect a progressive deoxygenation of the upper water column with the expansion of the equatorial oxygen minimum zone (OMZ). Specifically, the δ15N excursion reflects a shift in the dominant processing of bioavailable nitrogen from uptake and nitrification under oxic conditions to incomplete denitrification followed by complete denitrification as deoxygenation progressed. Records from existing study sites in other regions of the Panthalassa reflect similar redox fluctuations and support that this deoxygenation was a regional phenomenon. Other recent studies of the Late Norian and Rhaetian also document declines in biodiversity that predate the ETME, as well as, carbon isotope excursions, likely reflecting perturbations to the carbon cycle. Together, this evidence suggests that increasingly low-oxygen conditions initiated at least ~8 Ma before the emplacement of CAMP and likely paved the way for the ETME. / Master of Science / The end-Triassic mass extinction (ETME) occurred ~ 201 million years ago and was associated with a large drop in global diversity. The extinction is thought to be due to a warming climate resulting from greenhouse gasses released during the eruption of the Central Atlantic Magmatic Province (CAMP). Although the ETME is one of the largest extinction events of the last ~500 million years, the environmental changes leading to the extinction, and before the CAMP eruption, are not well understood. We studied the Grotto Creek section in Alaska which is a sequence of sedimentary rocks that record the deep ocean environment from the ancient Panthalassa or Paleo-Pacific Ocean. This section also provides a relatively complete record of the time before, during, and after the ETME. Here, we present the stable isotopes of nitrogen (δ15N) from these rocks that show disturbances to the nitrogen cycling that occurred in the ocean more than ~ 8 million years before the ETME. We show that δ15N and iron data from Grotto Creek document falling ocean oxygen levels before the ETME. We also find that our δ15N agrees with other environmental proxies that also reflect declining oxygen levels in the oceans along with decreases in marine animal diversity well before the ETME. These geochemical records help to show a more complete picture of how environments changed in the Panthalassa before the ETME

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The present dissertation aims to present the osteological anatomy of an early sauropodomorph found in Triassic rocks from the municipality of Agudo, Rio Grande do Sul (RS), Brazil. In addition, it aims to tests the biostratigraphic utility of this specimen. CAPPA/UFSM 0002 is composed of postcranial elements from the locality called Sítio Wachholz, ascribed to the Caturrita Formation. Some typical features present in prosauropods are verified in the specimen. For instance, the concave caudal margin of the neural spines of the medial trunk vertebrae, the convex proximal surface of the metacarpal V, and the distal end of the ischium higher than two times the width. On the other hand, typical features of more derived groups than Plateosauridae are absent and the slender shape of the first phalanx of the digit I of the foot corresponds to a common state of basalmost sauropodomorphs. A comparative and phylogenetic analysis among several early sauropodomorphs suggests affinities with Unaysaurus tolentinoi, the only unequivocal sauropodomorph from Caturrita Formation. Based upon such results, a biostratigraphic framework is proposed, which includes the Wachholz, Botucaraí Hill (Candelária, RS), and the Água Negra sites (São Martinho da Serra, RS), this last one so far producing the only record of U. tolentinoi. This corresponds to the first biostratigraphic framework proposed based on fossil vertebrates for the type locality of U. tolentinoi. Considering the presence of the genus Jachaleira in the Los Colorados Formation (Argentina) and in the Botucaraí Hill Site, an early Norian age is suggested to the correlated sites, as recent studies point this age to the portion that yielded Jachaleria in the Los Colorados Formation. Such age places U. tolentinoi and the other sauropodomorphs evaluated here in a unique position regarding the evolutionary history of the sauropodomorphs, suggesting that they lived in a transitional moment, between a period of low representativeness to an of extreme abundance of the group on Earth. / A presente dissertação tem como objetivo principal apresentar a anatomia óssea de um sauropodomorfo primitivo descoberto em rochas Triássicos no município de Agudo, Rio Grande do Sul (RS), Brasil. Além disso, objetiva-se testar o espécime em estudos de correlação bioestratigráfica. O espécime CAPPA/UFSM 0002 é composto por elementos pós-cranianos recuperados na localidade conhecida como Sítio Wachholz, atribuída à Formação Caturrita. É possível verificar a presença de características consideradas típicas dos prossaurópodes . Por exemplo, a forma côncava da margem caudal dos processos espinhosos das vértebras mediais truncais, a superfície convexa da extremidade proximal do metacarpal V e a extremidade distal do ísquio com altura maior do que duas vezes sua largura. Por outro lado, feições típicas de grupos mais derivados do que Plateosauridae não foram encontradas e a primeira falange do digito I do pé apresenta morfologia delgada, comum em sauropodomorfos mais basais. Uma análise comparativa e filogenética dentre diversos sauropodomorfos primitivos sugere afinidades com Unaysaurus tolentinoi, até o momento o único sauropodomorfo inequivoco da Formação Caturrita. Com base em tais resultados, é proposto um esquema de correlação entre os sítios Wachholz, Botucaraí (Candelária, RS) e Água Negra (São Martinho da Serra, RS), este último tendo produzido o único registro de U. tolentinoi até o momento. Assim, esta é a primeira proposta bioestratigrafica envolvendo a localidade tipo de U. tolentinoi com base em vertebrados fósseis. Dada a presença do gênero Jachaleria na Formação Los Colorados (Argentina) e no Sítio Cerro Botucaraí, é sugerida idade Noriana inicial para os sítios correlacionados neste esquema, uma vez que estudos recentes apontam a mesma idade para a porção com registro do gênero na Formação Los Colorados. Esta idade coloca U.tolentinoi e os outros espécimes avaliados aqui em uma posição única na historia evolutiva dos sauropodomorfos, sugerindo que eles viveram em um momento de transição de um período de baixa representatividade para um de extrema abundância do grupo na Terra.