Calcareous Algal Association from the Lower Paleozoic Tethyan Sedimentary Sequence of the Shiala Formation, Indian Gondwana

Abstract

The Lower Paleozoic rocks of the Shiala Formation of the Tethyan-Tibetan sedimentary sequence of Uttarakhand Garhwal region reveals rich and moderately diverse assemblages of calcareous algae. These assemblages include Dysoporelleae, Cyclocrinitids, Solenoporaceans, Microproblematica and cyanobacteria. Seven species have been identified. Most of the taxa described here are reported for the first time from the Shiala Formation. This formation exposes six different microfacies types. Some of the calcareous algal association occurs in different microfacies types and they are not generally facies dependent. The presence of calcareous algal age marker forms in the Shiala Formation brackets the upper age limit as Silurian and it is consistent with earlier age as assigned by acritarch biostratigraphy. The recovered flora is broadly comparable with that of the Tarim basin of China, Uzbekistan, Ontario, Scotland, Kazakhstan, Poland, Baltica etc. A possibility of regional link between the present study area and Tarim basin during Ordovician-Silurian time can not be envisaged based on floral similarity of the two basins due to their cosmopolitan affinity in Gondwana, Laurentia, Siberia, Kazakhstania etc. The recovered flora is basically from the euphotic zone(within few dozen meters) of coastal to lagoonal, low to high energy marine waters of deposition in a tropical to warm-temperate palaeoprovince of Ordovician-Silurian time.

Calcareous algae from the Ordovician succession (Thango Formation) of the Spiti Basin, Tethys Himalaya, India

“…The distribution of these algae in the Ordovician, particularly in India, the Tarim Basin, Kazakhstan, Baltica and North America indicates that all these areas were on the 0-30° latitudinal belt during the Ordovician, reflecting continental reconstruction. It has also been observed that the latitudinal positions of India and the Tarim Basin were adjacent to each other, possibly due to plate reconstruction during Ordovician-Silurian times (Smith 2001, Sinha & Trampisch 2013. The floristic similarities between these widely separated regions indicates that these algal structures developed through the Ordovician and further to the end of the Permian, and were cosmopolitan.…”

A new cryptostome bryozoanPtilotrypafrom the Upper Ordovician Yong Limestone Formation: Tethyan sequence of Kumaun Higher Himalaya, India

“…The greenish-grey silty shale of the lower part of the Shiala succession has yielded well-preserved chitinozoans, melanosclerites, and acritarchs, which suggest Middle to Late Ordovician age whereas, based on calcareous algae, the upper age limit extends into the Middle Silurian. Hence, the Ordovician–Silurian boundary lies within the Shiala Formation (Sinha et al, 1998, 2011; Sinha and Trampisch, 2013; Sinha and Verniers, 2016). On the other hand, Khanna et al (1985) and Bhargava (2008, 2011) assigned a Late Ordovician age to the Yong limestone and placed the Ordovician-Silurian boundary within the Yong Limestone Formation.…”