Stratigraphical and sedimentological analyses of Late Neoproterozoic successions in Lesser Himalaya are combined herein with palaeogeographical considerations and comparisons with equivalent successions in India and South China. The succession starts with the Hazara Formation, which contains complete and incomplete Bouma sequences suggesting its deposition in deep marine turbidite settings. The overlying Tanawal Formation, rich in massive sandstone, shale and siltstone, was deposited in shallow marine conditions, as indicated by the presence of parallel lamination, large scale tabular, trough cross-and hummocky cross-stratifications. The Tanawal Formation facies shift laterally from proximal (south-southeast) to distal (north-northwest). The glaciogenic Tanaki Boulder Bed, overlying the Tanawal Formation, was deposited during the Maronian glaciation. It is equivalent to the Blaini Formation of India, and to the Sinian diamictites of South China. The Abbottabad Formation of Cambrian age overlies the Tanaki Boulder Bed, and is composed of dolomite, chert nodules and phosphate-rich packages; similar successions are documented in India and South China at the same stratigraphical interval. The similarities of the Neoproterozoic successions of Lesser Himalaya (both in Pakistan and India) and South China suggests their possible proximity during the break-up of Rodinia and the assembly of the Gondwana Supercontinent.
The tommotiids are an important group of Cambrian small shelly fossils, primarily retrieved from the carbonate rock by acid process. Herein, the abundant isolated sclerites of
Tannuolina
are recovered from the siltstone-dominated upper part of the Hazira Formation in the eastern Hazara Basin, North Pakistan. This discovery of tommotiids preserved in the siltstones not only suggests their occurrences in a variety of sedimentary lithofacies, but also provides the opportunity to look for the sclerites or scleritomes (even soft-tissue) of tommotiids in much wider taphonomic windows. The sclerites include two morphs, i.e. mitral and sellate types. Through morphological comparison, they can be identified as
Tannuolina zhangwentangi
Qian & Bengtson, 1989. The large mitral and sellate sclerites (about 1 cm) illustrated herein manifest a relatively consistent morphology during the size increasement. The sellate sclerites may contain two sub-types, the larger sellate sclerite with sella on the sellate side and the smaller convex sellate side without sella on either sides. In the original scleritome, the two sub-types of sellate sclerites probably combine as a composite with the duplicatural side of the smaller one attached on the sella area of the large one. For the first time,
T. zhangwentangi
has been recovered from the Indian subcontinent, previously unknown outside South China. The middle and upper part of the Hazira Formation exclusively bearing
T. zhangwentangi
can directly invite correlation with the
S. flabelliformis
–
T. zhangwentangi
Assemblage Zone of South China representing the uppermost Cambrian Stage 2. This new palaeontological finds not only signifies the utility of
T. zhangwentangi
for intercontinental biostratigraphical correlation, but also suggests that the Terreneuvian SSF biostratigraphy between the Indian subcontinent and South China are quite consistent, comprising of three (at least two) correlative SSF Assemblage Zone (Zone Ⅰ, possible Ⅲ, and Ⅳ of South China). Additionally, our result may also support a relatively close palaeogeographical linkage between these two regions in early Cambrian.
Thematic collection:
This article is part of the Advances in the Cambrian Explosion collection available at:
https://www.lyellcollection.org/topic/collections/advances-in-the-cambrian-explosion
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