Juan A. Pineda, Marcos Comerio, Eduardo G. Ottone, Joaquín Salduondo, Gastón Otegui, Georgina Erra
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Palynofacies II and III occur in laminated shales rich in amorphous organic matter (AOM) and freshwater algal material (Botryococcus) respectively, which were deposited under oxygen-depleted conditions. In general, the detrital material present suggests an input derived from fluvial discharges; however, interbedded tuffs altered to analcime and smectite suggest the transformation of vitric material in pyroclastic ash under saline to alkaline water conditions. Kerogen Types II/III and III with high total organic carbon values indicate a moderate oil- and gas-prone source rock whose thermal maturity varies from immature to the early oil window (T<sub>max</sub>: 430-438 °C; vitrinite reflectance: 0.59-0.67 % VR<sub>o</sub>; and thermal alteration index: 2-2<sup>+</sup>).</p><p>This study demonstrates the importance of palynofacies analyses for the interpretation of depositional changes and associated controls in lacustrine shale successions. 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引用次数: 0
摘要
本研究介绍了对阿根廷西部库约盆地上三叠统波特里略斯-卡丘塔湖沼源岩的综合调查。数据来自于古生界分析、有机岩石学、Rock-Eval 热解和基于 X 射线衍射分析的矿物学研究。对一个 80 米厚的露头断面进行了研究,该断面被解释为代表从受河流排放影响的浅湖积沉积物(最上层的波特里略斯地层)向永久性深湖沉积物(卡丘塔地层)的过渡。共界定了三种古生界。第 I 组古生界的特点是由浅入深的上升循环,含有丰富的木质物质,沉积于缺氧、受干扰的水体中。第二和第三古生界分别出现在富含无定形有机质(AOM)和淡水藻类(Botryococcus)的层状页岩中,沉积于缺氧条件下。一般来说,存在的碎屑物质表明其来源于河水排放;然而,层间凝灰岩蚀变为安山岩和闪长岩表明,在盐碱水条件下,火山碎屑灰中的矾质物质发生了转变。具有高总有机碳值的Ⅱ/Ⅲ类和Ⅲ类岩浆源表明这是一种中等油气易生源岩,其热成熟度从未成熟到早期石油窗口不等(最高温度:430-438 °C;矾土反射率:0.59-0.67 % VR):0.59-0.67%;热蚀变指数:2-2+):2-2+).
PALYNOFACIES AND ORGANIC GEOCHEMISTRY OF LACUSTRINE SOURCE ROCKS: THE POTRERILLOS – CACHEUTA SOURCE ROCK SYSTEM IN THE TRIASSIC CUYO BASIN, WEST-CENTRAL ARGENTINA
This study presents an integrated investigation of the Upper Triassic Potrerillos – Cacheuta lacustrine source rock in the Cuyo Basin of western Argentina. Data came from palynofacies analyses, organic petrography, Rock-Eval pyrolysis and mineralogical studies based on X-ray diffraction analyses. An 80 m thick outcrop section was studied and is interpreted to represent the transition from shallow-lacustrine sediments influenced by fluvial discharges (uppermost Potrerillos Formation) to the deposits of a deep, permanent lake (Cacheuta Formation). Three palynofacies were defined. Palynofacies I is characterized by shallowing-upward cycles with abundant woody material, and was deposited under an oxic, disturbed water column. Palynofacies II and III occur in laminated shales rich in amorphous organic matter (AOM) and freshwater algal material (Botryococcus) respectively, which were deposited under oxygen-depleted conditions. In general, the detrital material present suggests an input derived from fluvial discharges; however, interbedded tuffs altered to analcime and smectite suggest the transformation of vitric material in pyroclastic ash under saline to alkaline water conditions. Kerogen Types II/III and III with high total organic carbon values indicate a moderate oil- and gas-prone source rock whose thermal maturity varies from immature to the early oil window (Tmax: 430-438 °C; vitrinite reflectance: 0.59-0.67 % VRo; and thermal alteration index: 2-2+).
This study demonstrates the importance of palynofacies analyses for the interpretation of depositional changes and associated controls in lacustrine shale successions. When integrated with data from organic geochemistry, palynofacies analysis is an important tool in the evaluation of a source rock's thermal maturity and hydrocarbon generation potential.
期刊介绍:
Journal of Petroleum Geology is a quarterly journal devoted to the geology of oil and natural gas. Editorial preference is given to original papers on oilfield regions of the world outside North America and on topics of general application in petroleum exploration and development operations, including geochemical and geophysical studies, basin modelling and reservoir evaluation.