Recurrent hardgrounds and their significance for intra-basinal correlations:a case study of upper Bathonian rocks from the western margin of the Indian craton  

作　　者：Dhirendra K.Pandey Franz T.Fürsich Matthias Alberti Jitendra K.Sharma Narendra Swami 

机构地区：[1]Earth and Planetary Sciences Group, Manipal Center for Natural Sciences,Centre of Excellence, Dr. TMA Pai Planetarium Building, Manipal Academy of Higher Education [2]FG Pal?oumwelt, GeoZentrum Nordbayern, Friedrich-Alexander Universit?t Erlangen-Nürnberg [3]Institut für Geowissenschaften, Christian-Albrechts-Universit?t zu Kiel [4]Department of Geology,University of Rajasthan [5]Himalayan Geology Division,Geological Survey of India Northern Region

出　　处：《Journal of Palaeogeography》2019年第1期19-30,共12页古地理学报（英文版）

基　　金：financial support by the Alexander von Humboldt Foundation

摘　　要：A set of two to three prominent hardgrounds can be traced for more than 40 km from east to west within the Jurassic succession of the Jaisalmer Basin at the western margin of the Indian Craton. The hardgrounds started to form under subtidal conditions in a mixed carbonate–siliciclastic setting during the last phase of a transgressive systems tract, i.e. the maximum flooding zone. The age difference between the hardgrounds is very small, but they differ lithologically. Typically, the stratigraphically oldest hardground occurs at the top of a 1-m-thick calcareous sandstone. It is characterized by a spectacular megaripple surface encrusted with oysters and subsequently occasionally bored by bivalves. The hardground is overlain by 10–25 cm of biowackestone to biopackstone, at the top of which another hardground is developed. This second hardground is characterized by abundant bivalve(Gastrochaenolites isp.) and "worm" borings(Trypanites and Meandropolydora isp.) and occasional oyster encrustations. The third hardground can be found within the overlying 60-cm-thick, bioturbated, fossiliferous silty marly packstone. It shows common to abundant oyster encrustations and occasional borings together with reworked concretions. The individual hardground can be well recognized throughout the basin based on lithology and biotic components. The second hardground(biowackestone to biopackstone) with abundant bivalve and worm borings is most prominent and widespread. Lithostratigraphically, these three hardground surfaces belong to the uppermost part of the Bada Bag Member of the Jaisalmer Formation. Based on ammonites, such as Perisphinctes congener(Waagen), brachiopods, and corals, this interval of the Bada Bag Member has been assigned a late Bathonian age. The entire succession above the first hardground is bioturbated up to the overlying marly silt of the Kuldhar Member of the Jaisalmer Formation, which is already Callovian in age. The characteristic hardground lithologies, together with the ammonite record, allow long-disA set of two to three prominent hardgrounds can be traced for more than 40 km from east to west within the Jurassic succession of the Jaisalmer Basin at the western margin of the Indian Craton. The hardgrounds started to form under subtidal conditions in a mixed carbonate–siliciclastic setting during the last phase of a transgressive systems tract, i.e. the maximum flooding zone. The age difference between the hardgrounds is very small, but they differ lithologically. Typically, the stratigraphically oldest hardground occurs at the top of a 1-m-thick calcareous sandstone. It is characterized by a spectacular megaripple surface encrusted with oysters and subsequently occasionally bored by bivalves. The hardground is overlain by 10–25 cm of biowackestone to biopackstone, at the top of which another hardground is developed. This second hardground is characterized by abundant bivalve(Gastrochaenolites isp.) and "worm" borings(Trypanites and Meandropolydora isp.) and occasional oyster encrustations. The third hardground can be found within the overlying 60-cm-thick, bioturbated, fossiliferous silty marly packstone. It shows common to abundant oyster encrustations and occasional borings together with reworked concretions. The individual hardground can be well recognized throughout the basin based on lithology and biotic components. The second hardground(biowackestone to biopackstone) with abundant bivalve and worm borings is most prominent and widespread. Lithostratigraphically, these three hardground surfaces belong to the uppermost part of the Bada Bag Member of the Jaisalmer Formation. Based on ammonites, such as Perisphinctes congener(Waagen), brachiopods, and corals, this interval of the Bada Bag Member has been assigned a late Bathonian age. The entire succession above the first hardground is bioturbated up to the overlying marly silt of the Kuldhar Member of the Jaisalmer Formation, which is already Callovian in age. The characteristic hardground lithologies, together with the ammonite record, allow long-dis

关 键 词：Hardgrounds STRATIGRAPHY PALAEOENVIRONMENT JURASSIC Jaisalmer Basin 

分 类 号：P[天文地球]