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This dissertation was carried out as part of the international and interdisciplinary graduate school StRATEGy. This group has set itself the goal of investigating geological processes that take place on different temporal and spatial scales and have shaped the southern central Andes. This study focuses on claystones and carbonates of the Yacoraite Fm. that were deposited between Maastricht and Dan in the Cretaceous Salta Rift Basin. The former rift basin is located in northwest Argentina and is divided into the sub-basins Tres Cruces, Metán-Alemanía and Lomas de Olmedo. The overall motivation for this study was to gain new knowledge about the evolution of marine and lacustrine conditions during the Yacoraite Fm. Deposit in the Tres Cruces and Metán-Alemanía sub-basins. Other important aspects that were examined within the scope of this dissertation are the conversion of organic matter from Yacoraite Fm. into oil and its genetic relationship to selected oils produced and natural oil spills. The results of my study show that the Yacoraite Fm. began to be deposited under marine conditions and that a lacustrine environment developed by the end of the deposition in the Tres Cruces and Metán-Alemanía Basins. In general, the kerogen of Yacoraite Fm. consists mainly of the kerogen types II, III and II / III mixtures. Kerogen type III is mainly found in samples from the Yacoraite Fm., whose TOC values are low. Due to the adsorption of hydrocarbons on the mineral surfaces (mineral matrix effect), the content of type III kerogen with Rock-Eval pyrolysis in these samples could be overestimated. Investigations using organic petrography show that the organic particles of Yacoraite Fm. mainly consist of alginites and some vitrinite-like particles. The pyrolysis GC of the rock samples showed that the Yacoraite Fm. generates low-sulfur oils with a predominantly low-wax, paraffinic-naphthenic-aromatic composition and paraffinic wax-rich oils. Small proportions of paraffinic, low-wax oils and a gas condensate-generating facies are also predicted. Here, too, mineral matrix effects were taken into account, which can lead to a quantitative overestimation of the gas-forming character. The results of an additional 1D tank modeling carried out show that the beginning (10% TR) of the oil genesis took place between ≈10 Ma and ≈4 Ma. Most of the oil (from ≈50% to 65%) was generated prior to the development of structural traps formed during the Plio-Pleistocene Diaguita deformation phase. Only ≈10% of the total oil generated was formed and potentially trapped after the formation of structural traps. Important factors in the risk assessment of this petroleum system, which can determine the small amounts of generated and migrated oil, are the generally low TOC contents and the variable thickness of the Yacoraite Fm. Additional risks are associated with a low density of information about potentially existing reservoir structures and the quality of the overburden. Diese Dissertation wurde im Rahmen des internationalen und interdisziplinären Graduiertenkollegs StRATEGy durchgeführt. Diese Gruppe hat sich zum Ziel gesetzt, geologische Prozesse zu untersuchen, die auf unterschiedlichen zeitlichen und räumlichen Skalen ablaufen und die südlichen Zentralanden geprägt haben. Diese Studie konzentriert sich auf die Tonsteine und Karbonate der Yacoraite Fm., die zwischen Maastricht und Dan im kreidezeitlichen Salta-Grabenbecken abgelagert wurden. Das ehemalige Riftbecken liegt im Nordwesten Argentiniens und gliedert sich in die Teilbecken Tres Cruces, Metán-Alemanía und Lomas de Olmedo. Die übergreifende Motivation für diese Studie war es, neue Erkenntnisse über die Entwicklung der marinen und lakustrinen Bedingungen während der Ablagerung der Yacoraite Fm. in den Tres Cruces und Metán-Alemanía Sub-Becken zu gewinnen. Weitere wichtige Aspekte, die im Rahmen dieser Dissertation untersucht wurden, sind die Umwandlung von organischer Materie der Yacoraite Fm. in Öl sowie deren genetische Beziehung zu ausgewählten produzierten Ölen und natürlichen Ölaustritten. Die Ergebnisse meiner Studie zeigen, dass die Ablagerung der Yacoraite Fm. unter marinen Bedingungen begann und sich bis zum Ende der Ablagerung in den Tres Cruces- und Metán-Alemanía-Becken ein lakustrines Milieu entwickelte. Im Allgemeinen besteht das Kerogen der Yacoraite Fm. überwiegend aus den Kerogentypen II, III und II/III-Mischungen. Der Kerogentyp III findet sich vor allem in Proben aus der Yacoraite Fm., deren TOC-Werte niedrig sind. Aufgrund der Adsorption von Kohlenwasserstoffen an den Mineraloberflächen (Mineralmatrixeffekt) könnte der Gehalt an Typ-III-Kerogen mit der Rock-Eval-Pyrolyse in diesen Proben überschätzt werden. Untersuchungen mittels organischer Petrographie zeigen, dass die organischen Partikel der Yacoraite Fm. hauptsächlich aus Alginiten und einigen Vitrinit-artigen Partikeln bestehen. Die Pyrolyse-GC der Gesteinsproben zeigte, dass die Yacoraite Fm. schwefelarme Öle mit einer überwiegend Wachs-armen paraffinisch-naphthenisch-aromatischen Zusammensetzung und paraffinische Wachs-reiche Öle generiert. Geringe Anteile paraffinischer, Wachs-armer Öle und einer Gaskondensat-generierenden Fazies werden ebenfalls vorausgesagt. Auch hier wurden Mineralmatrixeffekte berücksichtigt, die zu einer quantitativen Überschätzung des gasbildenden Charakters führen können. Die Ergebnisse einer zusätzlich durchgeführten 1D-Beckenmodellierung zeigen, dass der Beginn (10 %TR) der Ölgenese zwischen ≈10 Ma und ≈4 Ma stattfand. Der größte Teil des Öls (von ≈50 % bis 65 %) wurde vor der Entwicklung struktureller Fallen gebildet, die während der plio-pleistozänen Diaguita Deformatiosphase gebildet wurden. Nur ≈10 % des insgesamt generierten Öls wurde nach der Entstehung struktureller Fallen gebildet und potentiell darin gefangen. Wichtige Faktoren in der Risikobewertung dieses Erdölsystems, welche die geringen Mengen an generiertem und migriertem Öl bestimmen können, stellen die allgemein niedrigen TOC-Gehalte und die variable Mächtigkeit der Yacoraite Fm. dar. Weitere Risiken sind mit einer niedrigen Informationsdichte über potentiell vorhandene Reservoirstrukturen und die Qualität der Deckgesteine verbunden. This dissertation was carried out within the framework of the international and interdisciplinary research training group StRATEGy whose aim is to study geological processes occurring at different times and spatial scales that have shaped the southern Central Andes. The study focuses on the shales and carbonates of the Yacoraite Fm. deposited in the Salta rift basin (NW Argentina) during the Maastrichtian to Danian, and is divided into the Tres Cruces, Metán-Alemanía, and Lomas de Olmedo sub-basins. The Yacoraite Fm. is considered the potential source rock for most oil fields in NW Argentina. The overall motivation for this research was to provide new insights into the occurrence of marine and lacustrine settings during the deposition of the Yacoraite Fm. in the Tres Cruces and Metán-Alemanía sub-basins. Other important aspects assessed in this research are the likely transformation of organic matter of the Yacoraite Fm. into oil as well as its genetic relation to selected produced oils and natural oil seep samples. Fifty-two outcropping samples from the Yacoraite Fm. collected in the Tres Cruces and Metán-Alemanía sub-basins, seven oil seep samples from the Tres Cruces and Lomas de Olmedo sub-basins and eight produced oils from the latter sub-basin were evaluated. Characterization of the depositional environment and kerogen types of the Yacoraite Fm. was performed using various geochemical analyses encompassing pyrolysis, chromatography, spectrometry and petrography. Minerals were analyzed by X-ray diffraction. The elemental composition of rock samples was determined by X-ray fluorescence and more precise quantification was done by ICP-MS analysis. The study of the hydrocarbon potential of the Yacoraite Fm. was addressed by the following analyses of its organic matter and modeling procedures: • The assessment of the amount, quality, and thermal maturity of the organic matter; • Measurement of the rate of thermal cracking (bulk kinetics) of the organic matter into oil; • The extrapolation of high heating rate kinetics to low heating rates at geological conditions using the first-order kinetic approach provided by the Arrhenius equation; • The prediction of the composition (compositional kinetics) and the phase behavior of its first-formed petroleum; • The specific activation energy distribution of the bulk kinetics of representative samples collected in the Tres Cruces sub-basin were used in the 1D-basin modeling, enabling a comparison between the timing of oil generation and the timing of the formation of structural traps. Subsequently, the implications of these variables on the accumulation of oil in the Tres Cruces sub-basin were assessed. The characterization of produced oils and oil seep samples was carried out by chromatographic and spectrometric techniques. Genetic relationships (source rock-oil correlation) of the oil seep samples in the Tres Cruces sub-basin was studied by comparing their compositional affinities to rock extracts from outcropping samples of the Yacoraite Fm. in the same sub-basin. Since no rock samples were available from the Lomas de Olmedo sub-basin, the source-rock correlation for the oil seep samples and the produced oils assume that the Yacoraite Fm. in this sub-basin has similar organofacies as in the Tres Cruces and Metán-Alemanía sub-basins. The results of this research indicate that the deposition of the Yacoraite Fm. began in marine environments. Lacustrine settings developed during the middle part and predominated towards the end of the deposition in the Tres Cruces and Metán-Alemanía sub-basins. In general, the kerogen of the Yacoraite Fm. is predominantly composed of Type II, II/III, and Type III kerogens. The latter is largely found in samples from the Yacoraite Fm. whose TOC values were low. In these samples, the content of Type III kerogen could be overestimated with Rock-Eval pyrolysis due to hydrocarbon adsorption on mineral surfaces (mineral-matrix effect). Organic petrography showed that the organic particles of the Yacoraite Fm. correspond mainly to alginites and some vitrinite-like particles. Pyrolysis-GC of whole-rock samples indicated that the Yacoraite Fm. generates low sulphur oils with a mainly Paraffinic-Naphthenic-Aromatic Low Wax composition and Paraffinic High Wax oils. Minor contributions of Paraffinic Low Wax Oil and Gas condensate-generating facies are also predicted. Mineral-matrix effects can lead to an overestimation of the gas-prone character and were considered. Extrapolation of bulk kinetics experiments to a geological heating rate of 3 K/Myr reveals that the oil generation from the Yacoraite Fm. in the Tres Cruces sub-basin occurs in a range of approximately 60 °C. The onset (10%TR) of oil generation occurs at geological temperatures from 108 °C to 132 °C. The complete transformation of the organic matter into oil (90%TR) is reached at temperatures between 142 °C and 169 °C. The gas exsolution from the oil occurs at pressures below 200 bar as predicted from PVT-compatible compositional kinetics with subsequent separation of two phases and the increase in liquid viscosity at depths |
