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Temporal facies and diagenetic evolution of the mixed siliciclastic-carbonate Jajiya Member (Callovian–Oxfordian), Jaisalmer Formation, West India

Bhat G. M., Ahmat A. H. M.

Volumina Jurassica

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2013

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Vol. 11, no. 1

147–-162

EN

Three broad lithofacies – bioturbated packstone- to rudstone, calcareous sandstone and cross-bedded rudstone to packstone are recognized within the Jajiya Member. The facies architecture and stalking pattern suggests deposition related to TST, HST and TST events punctuated by MFZ events in sequence stratigraphic terms. The 11.4 m thick sequence represents two fining upward and three coarsening upward cycles representing bar-bank depositional settings. The framework constituents of these facies were mainly controlled by the depositional conditions through space and time and have greatly influenced their diagenetic evolution. The main diagenetic features observed within the facies include compaction, early cementation and porosity reduction, micritization and neomorphism representing early or syn-depositional and post-depositional changes. Two phases of early mechanical compaction have largely governed porosity development in these facies. However, cementation, micritization and neomorphism have also contributed significantly in this respect. Evidence suggests that marine phreatic and fresh water phreatic environments dominated the diagenetic evolution of these facies. Calcite cementation was first formed, followed by iron oxide, while silica cementation occurred probably at a late stage.

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Sedimentary cycles in the Callovian-Oxfordian of the Jaisalmer Basin, Rajasthan, western India

Pandey E., Sha J., Choudhary S.

Volumina Jurassica

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2010

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Vol. 8, no. 1

131-162

EN

The Callovian and Oxfordian marine sediments of the Jaisalmer Basin constitute the uppermost part of the Jaisalmer Formation, which comprises the Kuldhar and Jajiya members. In the present paper the authors illustrate retrogradational-progradational, more or less symmetrical cycles representing low- to high-energy marine environments. Despite an incomplete sedimentary record in a profile disrupted by a number of omission surfaces, it is possible to distinguish seven such sedimentary cycles in less than 24 m of sedimentary succession. The cycles, often bearing in their upper parts a thick-bedded well-cemented calcareous sandstone/pack- to rudstone, or hummocky cross-stratified beds indicative of storm events, are occasionally topped by hardgrounds. Hardgrounds provide well-defined boundaries useful for delineating correlative/bounding surfaces, identified here with sequence boundaries (3rd order cycles). Maximum flooding surfaces characterized by richly fossiliferous marly wackestones provide additional correlative horizons. Within these sequences, subordinate cycles can be tentatively distinguished, some of them may represent parasequences. The stratigraphical significance of correlative surfaces and sequences is tested by their fossil content, and these surfaces can be used for regional correlations with neighbouring basin.

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Cyclostratigraphic analysis of Upper Jurassic marly formations (Bure, eastern Paris Basin): comparison of different tools, record of sedimentary gaps and implications for regional correlations

Huret E., Galbrun B., Collin P-Y., Boulila S., Hinnov L., Elion P., Ravenne Ch.

Volumina Jurassica

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2006

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Vol. 4, no. 1

173-174

EN

This study integrates research conducted by ANDRA at the Underground Research Laboratory of Bure (Meuse, France) to investigate the feasibility of a deep geological waste repository in clay for high-level and long-lived intermediate-level radioactive waste. The aim of this study is to detect possible sedimentary gaps, by comparison of different tools (well logging/laboratory measurements) in the Upper Callovian – Lower Oxfordian homogeneous marly formation where the laboratory is located, and to estimate the duration of stages and biostratigraphic zonation by comparison with a basin sequence from the southeast of France that is presumed to have accumulated continuously. The search for hiatuses was made using a high resolution cyclostratigraphic approach based on the study of magnetic susceptibility (MS) and gamma ray (GR) fluctuations. Four ANDRA boreholes (EST 342, EST 322, EST 103 and EST 312) oriented on a SW-NE transect (40 km) were analyzed. Magnetic susceptibility measurements were made on core samples with a Bartington Instruments MS2E1 sensor every 4 cm. Gamma Ray Measurements are realised by well logging (measurement interval: 15.2 cm). Sedimentological data suggest that variations of the clay content influence the long term evolution of MS and GR. The high frequency variations in MS and GR were subjected to spectral analysis. Composite cycles of 0.5, 1 and 2.5 m thickness were recognized on the basis of frequency ratio and correspond to the frequency ratio of orbital Milankovitch cycles. The duration of the Mariae ammonite Zone in the Paris Basin was estimated by counting the cycles, to be between 2.4 and 2.6 My š0.3 ky (borehole EST 322 and EST 103). The amplitude spectrum shows sedimentation rate variations in particular in the Lower Oxfordian and interruptions in cycle evolution correlated to sequential limits. We interpret these zones as short condensed levels. The same methods were applied to sections from the southeast of France (Aspres-sur-Buëch, Thuoux), and the Mariae ammonite Zone estimated to be between 2.3 and 2.8 My of age. By comparison of this biostratigraphic zone between the two studied regions, sedimentary hiatuses of a few hundreds of thousands of years appear to affect the Oxfordian marly formation of the Paris Basin. MS and GR records as laboratory measurements and well logging provide an excellent means for regional stratigraphic correlations, and are especially promising in high resolution cyclostratigraphic studies. Hiatus detection and estimation of their durations can also be considered by this approach.