JOUR.GEOL.SOC.INDIA, VOL.72, OCT. 2008 458 BHAWANISINGH G. DESAI AND OTHERS Analysis of Ichnoguilds and their Significance in Interpreting Ichnological Events: A Study from Jhuran Formation (Upper Jurassic), Western Kachchh BHAWANISINGH G. DESAI 1 , SATISH J. PATEL 2 , RAJITA SHUKLA 2 and DIVYESH SURVE 2 1 Institute of Petroleum Technology Gandhinagar; Raisan Village, Gandhinagar - 9 2 Department of Geology, M.S.University of Baroda, Vadodara - 390 002 Email: bhawanigd@rediffmail.com; sjpatel_geol@rediffmail.com Abstract: The ichnological study of the Jhuran Formation (Kimmerdgian-Tithonian) exposed at Jara Dome of Western Kachchh has revealed the presence of twenty-two ichnospecies. These ichnofossils are typically well expressed at bed transitions, especially at intercalated shale–siltstone–sandstone sequences. The Jhuran Formation is divided into seven lithounits represented by six ichnoguilds exhibiting four distinguishable ichnological events. These events can provide important information on palaeoenvironment, depositional cyclicity and behaviour of the trace making communities. This is illustrated by the quantitative analysis of ichnoguilds in the intercalated sequence. The recurring patterns of the ichnoguilds reveal activity levels within the substrate, feeding style and also reflect colonization events at different beds. The dominance of structures produced by specialized organisms is consistent with an open marine unconsolidated substrate setting. The typical features of each ichnoguild allow characterization and comparison of local palaeoenvironmental conditions (depth, hydrodynamic condition, etc) which mark different ichnological events in the upper Jurassic sequence of the Western Mainland Kachchh basin. Keywords: Trace fossils, Ichnoguilds, Ichnological events, Jara Dome, Jhuran Formation, Western Kachchh. Fürsich and Pandey, 2003) and biostratigraphy (Krishna et al. 2000; Prasad, 1998). However, studies concerning ichnology of Western Kachchh are sparse (Badve and Ghare, 1978).The purpose of this paper is to illustrate ichnoguilds from intercalated shale-siltstone-sandstone sequences of the shallow marine environment and to demonstrate that they can reflect high benthic food contents probably related to organic matter input and also variation in other environmental factors such as oxygenation and sedimentation rate. Previous workers have dealt on more general aspect of ichnology of different parts of the Kachchh Basin (Badve and Ghare, 1978; Fürsich, 1998; Ghare and Kulkarni, 1986; Kulkarni and Ghare, 1991 Patel et al. 2008). We however, try to offer an integrated approach to the ichnoguilds of the shallow marine environmental setting and their significance in depicting the ichnological events of the Rudramata Shale Member and Upper Member of the Jhuran Formation (Kimmerdgian-Tithonian). LOCATION AND GEOLOGICAL SETTING Jara dome (Fig.1) situated in the western part of the INTRODUCTION Ichnology has become an important tool for environmental analysis (Savrda, 1995). The most significant advantage of trace fossils is that they are autochthonous indicators of ecological conditions. As a result, the bio- turbated zone is subdivided into a vertical sequence of habitats occupied by different organisms. The resultant traces are defined as tiers. Tiering structures can be demarcated on the basis of similar sort of behaviour and occupation of a similar niche or location within the sub- strate. The tiering communities reveal a number of recurring patterns involving such parameters as trace fossil types, activity levels within the substrate and feeding style. Trace fossils are further grouped in this way into guild group of species that exploit the same class of environmental resources in a similar way. The purpose of guild analysis is to examine the habitat structure in the alternating shale- siltstone-sandstone sequences resulting from episodic deposition and longer-term palaeoceanographic cycles. The Upper Jurassic rocks of Western Kachchh have been extensively studied for their stratigraphy (Rajnath, 1932; Biswas, 1978), depositional environment (Bose et al. 1986; JOURNAL GEOLOGICAL SOCIETY OF INDIA Vol.72, October 2008, pp.458-466 0016-7622/2008-72-4-458/$ 1.00 © GEOL. SOC. INDIA