The Callovian-Oxfordian of the Neuquén Basin (Argentina) is characterized by an extensive marine carbonate system (La Manga Formation) with a predominance of shallow and middle ramp deposits, although locally in tectonically controlled settings, deeper deposits also formed. These middle Oxfordian deeper deposits consist of mudstone-wackestone carbonates alternating with black shales and show marked centimetre-scale rhythmicity, probably controlled by the Earth's orbit parameters, mainly precession and eccentricity. The present study was designed to examine these deposits in terms of their sedimentology, geochemistry, and small-scale stratigraphy in Arroyo Los Blancos, southern Mendoza Province, where they are exceptionally well exposed and preserved. Results indicate that the sediments were deposited in an anoxic to dysoxic, relatively deep, sea-floor environment as revealed by the presence of: a) organic-rich shales, b) undisrupted lamination in most facies, c) pyrite framboids, and d) absence or scarcity of trace fossils and benthic fauna. Thin beds of graded wackestone-packstone and accumulations of thin shells of Bositra bivalves indicate sporadic reworking of the sea floor by weak currents. Organic petrology, Rock-Eval pyrolysis and thermal maturity indicators were used to characterize TOC and different types of organic matter. Low pyrolysis S yields along with low hydrogen indices suggest poor kerogen convertibility. Vitrinite reflectance (%Ro) ranged from 2.39 to 2.97 with an average of 2.70. The thermal alteration index (TAI) was 4+(5), indicating overmaturity. A tectono-sedimentary model is proposed for these deposits. According to this model, the relatively deep, organic-matter rich facies of La Manga Formation would have been deposited in the deepest zones of topographic lows controlled by tilting and differential subsidence of tectonic blocks bounded by normal faults.These faults were probably inherited from previous extensional tectonics of Late Triassic - Early Jurassic age.

The Callovian-Oxfordian of the Neuquén Basin (Argentina) is characterized by an extensive marine carbonate system (La Manga Formation) with a predominance of shallow and middle ramp deposits, although locally in tectonically controlled settings, deeper deposits also formed. These middle Oxfordian deeper deposits consist of mudstone-wackestone carbonates alternating with black shales and show marked centimetre-scale rhythmicity, probably controlled by the Earth's orbit parameters, mainly precession and eccentricity. The present study was designed to examine these deposits in terms of their sedimentology, geochemistry, and small-scale stratigraphy in Arroyo Los Blancos, southern Mendoza Province, where they are exceptionally well exposed and preserved. Results indicate that the sediments were deposited in an anoxic to dysoxic, relatively deep, sea-floor environment as revealed by the presence of: a) organic-rich shales, b) undisrupted lamination in most facies, c) pyrite framboids, and d) absence or scarcity of trace fossils and benthic fauna. Thin beds of graded wackestone-packstone and accumulations of thin shells of Bositra bivalves indicate sporadic reworking of the sea floor by weak currents. Organic petrology, Rock-Eval pyrolysis and thermal maturity indicators were used to characterize TOC and different types of organic matter. Low pyrolysis S yields along with low hydrogen indices suggest poor kerogen convertibility. Vitrinite reflectance (%Ro) ranged from 2.39 to 2.97 with an average of 2.70. The thermal alteration index (TAI) was 4+(5), indicating overmaturity. A tectono-sedimentary model is proposed for these deposits. According to this model, the relatively deep, organic-matter rich facies of La Manga Formation would have been deposited in the deepest zones of topographic lows controlled by tilting and differential subsidence of tectonic blocks bounded by normal faults.These faults were probably inherited from previous extensional tectonics of Late Triassic - Early Jurassic age.

The Callovian-Oxfordian of the Neuquén Basin (Argentina) is characterized by an extensive marine carbonate system (La Manga Formation) with a predominance of shallow and middle ramp deposits, although locally in tectonically controlled settings, deeper deposits also formed. These middle Oxfordian deeper deposits consist of mudstone-wackestone carbonates alternating with black shales and show marked centimetre-scale rhythmicity, probably controlled by the Earth's orbit parameters, mainly precession and eccentricity. The present study was designed to examine these deposits in terms of their sedimentology, geochemistry, and small-scale stratigraphy in Arroyo Los Blancos, southern Mendoza Province, where they are exceptionally well exposed and preserved. Results indicate that the sediments were deposited in anoxic to dysoxic, relatively deep, sea-floor environment as revealed by the presence of: a) organic-rich shales, b) undisrupted lamination in most facies, c) pyrite framboids, and d) absence or scarcity of trace fossils and benthic fauna. Thin beds of graded wackestone-packstone and cumulations of thin shells of Bositra bivalves indicate sporadic reworking of the sea floor by weak currents. Organic petrology, Rock-Eval pyrolysis and thermal maturity indicators were used to characterize TOC and different types of organic matter. Low pyrolysis S yields along with low hydrogen indices suggest poor kerogen convertibility. Vitrinita reflectancia (%Ro) ranged from 2.39 to 2.97 with an average of 2.70. The thermal alteration index (TAI) was 4+(5), indicating overmaturity. A tectono-sedimentary model is proposed for these deposits. According to this model, the relatively deep, organic-matter rich facies of La Manga Formation would have been deposited in the deepest zones of topographic lows controlled by tilting and differential subsidence of tectonic blocks bounded by normal faults.These faults were probably inherited from previous extensional tectonics of Late Triassic - Early Jurassic age.

يتميز Callovian - Oxfordian لحوض Neuquén (الأرجنتين) بنظام كربونات بحرية واسع النطاق (La Manga Formation) مع غلبة الرواسب المنحدرة الضحلة والمتوسطة، على الرغم من أنه محليًا في البيئات التي يتم التحكم فيها تكتونيًا، تشكلت أيضًا رواسب أعمق. تتكون هذه الرواسب الأعمق في أكسفورد الوسطى من كربونات الحجر الطيني المتناوبة مع الصخر الزيتي الأسود وتظهر إيقاعًا ملحوظًا على مقياس السنتيمتر، ربما يتم التحكم فيه بواسطة معلمات مدار الأرض، وخاصة السبق والغرابة. تم تصميم الدراسة الحالية لفحص هذه الرواسب من حيث علم الرواسب والكيمياء الجيولوجية والطبقات الصغيرة في أرويو لوس بلانكوس، مقاطعة ميندوزا الجنوبية، حيث يتم تعريضها وحفظها بشكل جيد بشكل استثنائي. تشير النتائج إلى أن الرواسب ترسبت في بيئة قاع البحر غير المؤكسدة إلى بيئة قاع البحر العميقة نسبيًا كما يتضح من وجود: أ) الصخر الزيتي الغني بالعضوية، ب) التصفيح دون انقطاع في معظم الأوجه، ج) أشباه الإطارات البيريتية، د) غياب أو ندرة الحفريات النزرة والحيوانات القاعية. تشير الطبقات الرقيقة من حجر الواكستون المتدرج وتراكمات الأصداف الرقيقة لثنائيات الصدفة البوسيترا إلى إعادة صياغة متفرقة لقاع البحر بواسطة تيارات ضعيفة. تم استخدام علم البترول العضوي والتحلل الحراري الصخري ومؤشرات النضج الحراري لتمييز TOC وأنواع مختلفة من المواد العضوية. تشير نتائج الانحلال الحراري المنخفضة S جنبًا إلى جنب مع مؤشرات الهيدروجين المنخفضة إلى ضعف قابلية تحويل الكيروجين. تراوح انعكاس الفيترينيت (٪Ro) من 2.39 إلى 2.97 بمتوسط 2.70. كان مؤشر التغيير الحراري (TAI) 4+(5)، مما يشير إلى الإفراط في النضج. ويقترح نموذج تكتوني رسوبي لهذه الرواسب. وفقًا لهذا النموذج، فإن الأوجه العميقة نسبيًا والغنية بالمادة العضوية لتكوين لا مانغا قد ترسبت في أعمق مناطق القيعان الطبوغرافية التي يتم التحكم فيها عن طريق الإمالة والهبوط التفاضلي للكتل التكتونية التي تحدها أخطاء طبيعية. ربما كانت هذه الأخطاء موروثة من التكتونيات الامتدادية السابقة في العصر الترياسي المتأخر - العصر الجوراسي المبكر.