Abstract We propose the Psammichnites gigas gigas sub-ichnozone in the Cambrian Kunzam La Formation exposed in the Hojis Valley, Kinnaur, Himachal Himalaya, which indicates a Cambrian Series 2–Stage 4 age for the host sediments. Additionally, the paper also reports eight microbially induced sedimentary structures (MISS) represented by distinctive reticulate (‘Elephant skin' and ‘Kinneyia’ types) and linear patterns with cracked ripple crests, and mat slump structures. These MISS are closely associated with grazing trails of Psammichnites gigas gigas. The preservation in alternating well-sorted and thick (3–20 cm) fine sandstone beds and associated sedimentary structures indicate a shallow marine, nearshore-to-shoreface depositional environment. MISS, ripple marks, and bio-stabilized substrate indicate a limited influx of clastics, with photoautotrophic microorganisms likely contributing to their formation. Research highlights This study presents the first biostratigraphical investigation of the Cambrian Kunzam La Formation in the Hojis Valley, situated within the geologically understudied Kinnaur region of the Tethyan Himalaya. Notably, no body fossils have been documented across the entire Kinnaur region, underscoring the importance of ichnozonation within the area. This study aims to enhance the stratigraphy of Kinnaur region to facilitate regional correlation, bridging the gap between the adjacent Zanskar-Spiti in the North and Kumaon–Garhwal region in the South. Key findings are as follows:<OrderedList> <ListItem> <ItemNumber>1.</ItemNumber> <ItemContent> Age refinement: The identification of the Psammichnites gigas gigas sub-ichnozone within the Cambrian Kunzam La Formation and its correlation with the biostratigraphically well defined analogous Cambrian sections in the Zanskar–Spiti regions, suggests a tentative Cambrian Series 2–Stage 4 age for the host sediments. </ItemContent> </ListItem> <ListItem> <ItemNumber>2.</ItemNumber> <ItemContent> Palaeoenvironmental analysis: The presence of microbially induced sedimentary structures (MISS) near the ichnogenus Psammichnites horizon, along with surrounding depositional features like rock bed thickness (3–20 cm), sediment type (fine sandstone), and associated ripple marks, indicate a shallow marine nearshore to shoreface depositional environment with limited sediment influx. This environment lacks hummocky cross-stratification (HCS), storm tool marks from microbial sand chips, and any significant erosion in microbial mats strata. Moderate reworking by waves and currents, attributed to the biostabilized siliciclastic substrate, suggests a storm-protected, shallow marine depositional system influenced by shallow photoautotrophic microbial mats. </ItemContent> </ListItem> </OrderedList>

Psammichnites gigas gigas sub-ichnozone and microbially induced sedimentary structures (MISS) from Kunzam La Formation (Cambrian), Hojis Valley, Kinnaur, Himachal Himalaya

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发表日期：

2025年2月18日

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Ranveer Singh Negi,
Birendra Pratap Singh,
Om Narain Bhargava,
Bhagya S Dev

摘要

Abstract

We propose the Psammichnites gigas gigas sub-ichnozone in the Cambrian Kunzam La Formation exposed in the Hojis Valley, Kinnaur, Himachal Himalaya, which indicates a Cambrian Series 2–Stage 4 age for the host sediments. Additionally, the paper also reports eight microbially induced sedimentary structures (MISS) represented by distinctive reticulate (‘Elephant skin' and ‘Kinneyia’ types) and linear patterns with cracked ripple crests, and mat slump structures. These MISS are closely associated with grazing trails of Psammichnites gigas gigas. The preservation in alternating well-sorted and thick (3–20 cm) fine sandstone beds and associated sedimentary structures indicate a shallow marine, nearshore-to-shoreface depositional environment. MISS, ripple marks, and bio-stabilized substrate indicate a limited influx of clastics, with photoautotrophic microorganisms likely contributing to their formation.

Research highlights

This study presents the first biostratigraphical investigation of the Cambrian Kunzam La Formation in the Hojis Valley, situated within the geologically understudied Kinnaur region of the Tethyan Himalaya. Notably, no body fossils have been documented across the entire Kinnaur region, underscoring the importance of ichnozonation within the area. This study aims to enhance the stratigraphy of Kinnaur region to facilitate regional correlation, bridging the gap between the adjacent Zanskar-Spiti in the North and Kumaon–Garhwal region in the South. Key findings are as follows: 1.

Age refinement: The identification of the Psammichnites gigas gigas sub-ichnozone within the Cambrian Kunzam La Formation and its correlation with the biostratigraphically well defined analogous Cambrian sections in the Zanskar–Spiti regions, suggests a tentative Cambrian Series 2–Stage 4 age for the host sediments.

Palaeoenvironmental analysis: The presence of microbially induced sedimentary structures (MISS) near the ichnogenus Psammichnites horizon, along with surrounding depositional features like rock bed thickness (3–20 cm), sediment type (fine sandstone), and associated ripple marks, indicate a shallow marine nearshore to shoreface depositional environment with limited sediment influx. This environment lacks hummocky cross-stratification (HCS), storm tool marks from microbial sand chips, and any significant erosion in microbial mats strata. Moderate reworking by waves and currents, attributed to the biostabilized siliciclastic substrate, suggests a storm-protected, shallow marine depositional system influenced by shallow photoautotrophic microbial mats.