Melanosclerites from the Late Ordovician strata of the Shiala Formation, Indian Gondwana Hareshwar N. Sinha a,⇑ , Claudia Trampisch b a University Department of Geology, Vinoba Bhave University, Hazaribag 825 301, India b University of Greifswald, Institute of Geography and Geology, Department of Palaeontology and Historical Geology, F.L. Jahnstr. 17a, 17487 Greifswald, Germany article info Article history: Received 6 November 2012 Received in revised form 6 May 2013 Accepted 20 June 2013 Available online 4 July 2013 Keywords: Melanosclerite Tethys Garhwal Himalaya Ordovician Shiala Formation Indian Gondwana abstract Melanosclerites, organic-walled microfossils of problematic affinity, are recorded herein from the lower to middle part of the Shiala Formation of Late Ordovician age and is situated below Ordovician–Silurian boundary established previously by acritarchs data. The assemblages recovered yielded the melanoscle- rites taxa Melanoporella clava, Melanoporella bulla?, Melanoporella polonica, Melanoporella sp. 1, Melanop- orella sp. 2 and Melanosteus sp. The Ordovician–Silurian sedimentary sequence discussed herein was a part of the Gondwanan palaeocontinent situated at 25 to 30°S. The melanosclerite assemblage recov- ered herein from the Shiala Formation is broadly comparable with the Öjlemyr Cherts of Sweden, situated at high palaeolatitude and also of Late Ordovician age. Melanosclerites have not previously been studied in detail from Indian Gondwana and published records on this fossil group are rare in general. The present findings improve our knowledge on this group. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Eisenack (1942) described a problematic rod-shaped organic- walled microfossil from the Ordovician and Silurian glacial erratics of the Baltic region, introducing the term ‘melanosclerite’ (derived from the Greek ‘melanos’, meaning ‘black’, and ‘skleros’, meaning ‘hard’). The melanosclerite ‘skeletons’ are made up of sclerites which vary in length between 60 lm and 2000 lm. Well-preserved specimens appear opaque and dark brown in colour under a trans- mitted light microscope. Due to their close similarity in size and nature of silhouette, the chance of erroneous identification be- tween melanosclerites and chitinozoans is high when examined under a conventional light microscope. The subtle and minor dif- ferences between these two groups of microfossil are apparent, however, when using a scanning electron microscope (SEM), mel- anosclerites are thicker-walled, and generally not hollow (e.g. Górka, 1971; Schallreuter, 1981; Sinha et al., 1996a). The surface of the sclerites is generally rough and dull, but smooth and striated forms are also found. Eisenack (1942) recognised two different types of sclerites. The first type has been identified as a ‘skeleton’, i.e. the main ‘body’ of the melanosclerite, and the second repre- sents appendices protruding outward from the ‘skeleton’. The appendices are termed ‘pleuridien’ (singular ‘pleuridie’) for all mel- anosclerites (Trampisch, 2007). The pleuridien vary in shape from being rod, bulb, or cone shaped. The pleuridien possess two distinct layers, an ‘internal’ and an ‘external’. The internal layer is spongy in character and termed ‘spongiosa’, while the external layer is hard and termed ‘kompakta’ (Trampisch and Butcher, 2010). Some of the morphological features of pleuridien have been shown in Plate 1 (Trampisch, 2007). The biological affinity of melanosclerites is still not fully re- solved, perhaps as a consequence of the limited attention paid to them. Eisenack (1942) and Pichler (1971) considered them as derivatives from hydrozoans (Cnidarian). Górka (1971) described their similarity to the thallus of dasycladacean algae, whereas Dunn (1959) speculated on their being thecamoeba. Cashman (1992) found that some melanosclerites share common morpho- logical features with the planula and early polyp stages of certain modern coelenterates and placed them within the Cnidaria. In the present work the melanosclerites have been considered to be Cnidaria also. Melanosclerites have been reported previously from Laurentia, Baltica and Gondwana (see below). They are exclusively marine, and found in rocks of Cambrian to Devonian age. Cashman (1992) recovered melanosclerites throughout the Gaspe Lime- stone, Quebec, Canada. Sinha et al. (1996a, 1998) found melano- sclerites from the Shiala and Yong Limestone formations of the Tethyan Garhwal Himalaya but they (op.cit.) did not carry out any morphological or biostratigraphical study. Trampisch (2007) described a rich and well preserved melanosclerite assemblages from the Öjlemyr Cherts of Gotland, Sweden, which has improved the taxonomy of this group and added new biostratigraphical data. Trampisch and Butcher (2010) described well preserved melano- sclerites from the Lower Silurian Wilhelmi Formation of Illinois, 1367-9120/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jseaes.2013.06.010 ⇑ Corresponding author. Tel.: +91 6546272665; fax: +91 6546270104. E-mail address: hnsinha2003@gmail.com (H.N. Sinha). Journal of Asian Earth Sciences 75 (2013) 13–18 Contents lists available at SciVerse ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes