A. Bayet-Goll; R. Moussavi-Harami; A. Mahboubi
Abstract
Trace fossils are abundant in the clastic succession throughout the Shirgesht Formation of Kalmard Block, Central Iran. At certain horizons there are beds full of Cruziana and Rusophycus. This study presents an evaluation of the arthropod ichnotaxa of the Cruziana and Rusophycus from the Ordovician succession ...
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Trace fossils are abundant in the clastic succession throughout the Shirgesht Formation of Kalmard Block, Central Iran. At certain horizons there are beds full of Cruziana and Rusophycus. This study presents an evaluation of the arthropod ichnotaxa of the Cruziana and Rusophycus from the Ordovician succession Shirgesht Formation. Apart from the broad range in morphology and size, Cruziana from Shirgesht Formation show higher behavioral diversity using food sources than has ever been documented in a single section. It consists of a straight, or gently curved, ploughed furrow usually a few centimetres across, which is divided lengthwise into two lobes, each of which is braided transversely by a series of scratches. These vary in arrangement and profile according to ichnospecies. Overall characteristics of recognized ichnospecies suggest that with the exception of C. semiplicata, the ichnofaunas contain all the members of the Cruziana rugosa Group throughout the clastic successions in Shirgesht Formation. It consists of the five members of C. rugosa, C. furcifera, C. goldfussi C. rouaulti and C. yini. The Shirgesht Formation material therefore indicates that these arthropod ichnofossil assemblages are suitable for Cruziana ichnostratigraphy in Shirgesht Formation. Accordingly, the present assemblage could represent the Early to middle Ordovician age. The arthropod traces also, occur with other biogenic sedimentary structures in a fine to medium grained sandstone with minor mudstone interbeds of the Shirgesht Formation. The substrate composition and ichnological evidence places the arthropod ichnofossil-rich unit in the Cruziana ichnofacies.
A. Bayet goll; M. Hosseini-Barzi
Abstract
Geochemical analysis of major elements from 12 sampels from Shirgesht Formation sandstones and shales with Ordovicien age in sections of kuh-Asheghan and Kuh-Rahdar at Kalmard block in Central Iran zone, and plotting these data on silisiclastic rocks classification diagrams, show that they are quartzarenite ...
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Geochemical analysis of major elements from 12 sampels from Shirgesht Formation sandstones and shales with Ordovicien age in sections of kuh-Asheghan and Kuh-Rahdar at Kalmard block in Central Iran zone, and plotting these data on silisiclastic rocks classification diagrams, show that they are quartzarenite and shale. Moreover, the use of discrimination, biplot triangular diagrams determined the quartzose recycled provenance (craton and recycled orogen) and passive margin tectonic setting for these deposites. These data suggest the quartzose sedimentary provenace for sandstones and intermediate to felsic ignious provenance for shale. Furthermore, determination of weathering influence in source area, by using CIA index, indicated that the source area of these deposites has been exposed to intense weathering. This can be explained by humid weather in source area of passive continental margin.
