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Organic-rich biolaminated facies from a Kimmeridgian lagoonal environment in the French southern Jura mountains: a way of estimating accumulation rate variations

Published inPalaeogeography, palaeoclimatology, palaeoecology, vol. 99, no. 1-2, p. 163-177
Publication date1992
Abstract

During Kimmeridgian times, the present-day Southern Jura was a carbonate platform. In the palaeolagoon at the village of Orbagnoux, organic matter was deposited, giving birth to calcareous laminites, with organic carbon reaching 12%. Three facies may be distinguished; two types of laminites are encountered: one made of parallel laminae and the other made of undulating laminae. The laminites alternate with massive limestone beds, in which no internal structure may be seen. The lithology, sedimentology and the faunal, floral and organic content of laminites and of massive limestones was thoroughly investigated at different scales using various methods: field observation, transmitted-light and scanning electron microscopy, Rock Eval pyrolysis, biomarkers, infrared study of kerogen, palynofacies observation. It is suggested that the different types of laminites (parallel or undulating) may reflect variations in the accumulation rates, linked with the carbonate and organic matter productions. Undulating laminae would correspond to periods of lack of sedimentation whereas parallel laminae would reflect alternations of periods of sedimentation and periods of non-sedimentation. These variations might in turn reflect climatic changes affecting the emerged lands supplying the lagoon with detrital products (organic or inorganic). The accumulation and preservation of organic matter were made possible by the development of microbial mats, building “oxygen-tight” barriers at the water-sediment interface. These barriers separated overlying, oxygenated water from anaerobic sediments. These phenomena may explain one way in which potential hydrocarbon source-rocks can form under a (poorly ?) oxygenated water column.

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Citation (ISO format)
TRIBOVILLARD, Nicolas Pierre et al. Organic-rich biolaminated facies from a Kimmeridgian lagoonal environment in the French southern Jura mountains: a way of estimating accumulation rate variations. In: Palaeogeography, palaeoclimatology, palaeoecology, 1992, vol. 99, n° 1-2, p. 163–177. doi: 10.1016/0031-0182(92)90013-U
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