Ichnology and biostratigraphic significance of Cambrian trace fossils from the lowest stratigraphic level of Kunzam La Formation, Chandra Valley, Lahaul and Spiti, India

Abstract

Abstract Trace fossils are abundant in the Cambrian Kunzam La Formation in the Lahaul and Spiti regions of the Himalaya. All previously known records belong stratigraphically to the upper part of the Cambrian Series 2/Stage 4 to the Miaolingian Series. In the present work, 15 ichnogenera comprising 26 recorded ichnospecies come from the lower part of the Kunzam La Formation exposed in the Chandra Valley, eastern Lahaul and Spiti, Himachal Pradesh. Three trace fossils associations, based on their sequence of appearance, are: (i) the Treptichnus pedum association (trace fossil association–I)-, a low diversity association, containing Planolites beverleyensis, Palaeophycus isp., and Treptichnus pedum, (ii) the Monomorphichnus association (trace fossil association–II) characterized by a sudden increase in trace fossil diversity and traces of arthropod/trilobite origin comprising Cruziana problematica, Cruziana isp., Catenichnus contentus,? Diplocraterion isp., Dimorphichnus obliquus, Dactylophycus isp., Lockeia siliquaria, Monomorphichnus multilineatus, M. lineatus, Planolites annularis, P. montanus, P. beverleyensis, Palaeophycus imbricatus, P. tubularis, Rusophycus didymus, R. leifeirikssoni, R. dispar, Rusophycus isp., Saerichnites abruptus, and serially repeated Rusophycus and Cruziana, Treptichnus pollardi and arthropod resting traces, and (iii) the Psammichnites association (trace fossil association–III) characterized by a dominant presence of large burrowing systems of Psammichnites gigas and traces of Diplichnites isp. and Ctenopholeus kutcheri. Considering the same rate of sedimentation for these deposits determined in the >50 km distant Parahio Valley and the stratigraphic position of the Psammichnites gigas assemblage zone in the Himalaya, these trace fossil associations probably fall within Cambrian Series 2, Stage 4, though the sudden increase in diversity and complexities of traces suggest an older age. Stratigraphically, the trace fossils presently described are the oldest yet recorded from the Cambrian of the Lahaul and Spiti regions.