Date- 1st February 2020
Location- Along the Raipur – Maldevta Road Section of the eastern Doon Valley
Conducted by- Dr. R.J. Azmi, Former Scientist ‘G’, Wadia Institute of Himalayan Geology, Dehradun
Field Trip Report
The one day geological excursion along the Raipur – Maldevta Road Section of the eastern Doon Valley was organized mainly to demonstrate the different sedimentary and metamorphic rock types with emphasis on its Stratigraphy, Structure and Tectonics.
The field trip was conducted by Dr. R.J. Azmi and along with around 150 students from over 10 national and international colleges like Universiti Teknologi Petronas, Malaysia, UPES, AMU, Delhi University, VELS, GIET, Chandigarh University, etc, the field trip saw the presence of Shri Umesh Pradhan, Former Executive Director, ONGC, Shri Rajesh Sharma, Chief General Manager, Geology, ONGC, Shri RS Modak, SG, ONGC, Smt. Anumita Mondal, Senior Geologist, ONGC, Shri Jagdish Arya, Senior Geologist, ONGC, and Dr. Uday Bhan, faculty advisor of UPES AAPG Student Chapter.
The field trip consisted of the four following stops:
- Baldi River Bridge: The bridge is situated exactly on the MBT. The lower hills on the SW side of the bridge is composed of Siwalik Sandstones of Middle Miocene age (~10 Ma). The higher Lesser Himalayan mountains on the NE of MBT is composed of highly deformed phyllites of ~1800 Ma old, thrust over southward on Siwaliks due to India – Eurasia collision.
- Outcrop of glacial Blaini Boulder Bed (Blaini Tillite) of Marinoan age (650 Ma) on the right bank of Song River, near the Iron Bridge. Here the unconformity between the Nagthat Quartzite (~1800 Ma) and Blaini Tillite (~650 Ma) represents >1 Billion-Year hiatus.
- Outcrop of the Upper Krol Limestone with microbial mats algal laminites and oncolites near the Iron Bridge over the Bandal River, a tributary of the Song River.
- Abandoned PPCL Mine Compound where the discovery of the Lower Cambrian conodonts and other Small Shelly Fossils was made by Azmi et al. (1981) from the Lowest Tal Chert-Phosphorite Member of the Tal Formation
On these stops, students were shown various rock formations, structures, unconformities, etc. Also, students were taught how to use Brunton Compass and find out strike and dip of a rock.
Details of Location
Within about 9 km stretch of this section on the Raipur – Maldevta road between Maharana Pratap Chowk and the abandoned Maldevta PPCL Mine Compound, we will first come across a very young (~10 Ma) Late Tertiary fluvial sequence of sandstone and mudstone of Siwalik Mountain Range of the Outer or Sub-Himalaya, which is tectonically juxtaposed along the Main Boundary Thrust (MBT) with much older (~1800 Ma, Paleoproterozoic) Lesser Himalayan metamorphic rocks of the Chandpur Phyllite and Nagthat Quartzite (Jaunsar Group). In turn, this metamorphosed succession (Jaunsar Group) is overlain, with a major regional unconformity (encompassing more than a Billion-Year Period of non-deposition and/erosion) by unmetamorphosed sedimentary succession of silisiclastics and carbonates of the Mussoorie Group comprising the Blaini – Krol – Tal (BKT) Formations of Terminal Neoproterozoic to Early Cambrian age (650 – 520 Ma).
The discovery of the diverse earliest Cambrian ‘Small Shelly Fossils’ by the author (Azmi et al., 1981) from the Lower Tal Phosphorites of the Maldevta PPCL Mine (now an abandoned mine) proved to be an internationally most famous benchmark discovery in the Lesser Himalayan stratigraphy which not only brought a revolutionary age revision of an over-century held view of Late Paleozoic – Mesozoic age for the BKT succession, but precisely defined the Precambrian – Cambrian Boundary Boundary (542 Ma) event at the base of the Lowes Tal Chert-Phosphorite Member.
The most significant outcome of this discovery was the ‘Blaini Boulder Bed’ which was hitherto considered as a deep rooted evidence of Permo-carboniferous glaciation in Indian geology ultimately turned out to be an important marker of the Latest Precambrian glaciation - Marinoan Glaciation (650 Ma) of global nature whose imprints have been found on all the continents, suggesting this period as an “Snowball Earth”. Ensuing global warming led to deglaciation in which extensive shallow carbonate platforms were formed with rich development of microbial mats and algal structures (Oncolites and Stromatolites), soft-bodied Ediacaran Metazoans and abundant remains of skeletal microfossils or Small Shelly Fossils (SSF), also commonly known as the ‘Cambrian Explosion’ fossils.
Most of these have been nicely recorded from the BKT succession, especially the SSF which have attracted much global attention because of these being the first animals preserving the mineralized hard tissues or the bony material in them – an evolutionary jump from the soft tissues to the hard ones! From the Petroleum perspective, the vast platformal sediments of Terminal Neoproterozoic – Early Cambrian age in the Lesser Himalaya present unprecedented opportunity for extensive exploration of Hydrocarbons in India. In this age framework, successful beginning has already been made by ONGC in the Lower Vindhyans of Nohta wells of Madhya Pradesh.
We, the UPES AAPG Student Chapter, would like to express our sincere gratitude to Dr. R.J. Azmi for guiding us through the field trip and making us understand various aspects of Geology practically. Also, we would like to thank AAPG International for the support that they have provided us throughout.