Society of Petroleum Geophysicists (SPG) and Association of Petroleum Geologists (APG) India organized a geological field excursion to Lesser Himalayas in Rishikesh-Shivpuri-Simthali-Singtali-Kaudiyalaghat area from 01-02 April, 2023.

A total of 39 geoscientists from different work-centres of ONGC Dehradun led by Shri. Vishal Shastri, ED-HoI GEOPIC and President SPG, India along with Shri. Jayanta Sarkar, CGM-Geol. and Secretary APG, India participated in the geological field excursion. Dr. D.C. Srivastava, Emeritus professor, IIT Roorkee, with more than 40 years of experience in Advanced Structural Geology and Stratigraphy of India guided the participants during field trip. The team assembled in front of GEOPIC on the morning of 01st April and the field trip was flagged off by Shri Vishal Shastri. The geological excursion aimed at field familiarization of geological sequences in Lesser Himalayas. The idea behind was to make the geoscientists study the outcrops and visualize the scale of workstation seismic sections in real-life scenarios.

Geologically the Himalayan Mountain chain has been divided into four longitudinal lithotectonic zones bounded by major thrusts namely HFF, MBT, MCT, and STD. From South to North these zones are as follows: Sub-Himalayan Zone or the Himalayan Foothills that comprises mainly the Molasse sediments, the Lesser Himalayan zone comprising low grade metamorphic rocks, the Higher Himalayan Crystalline complex which includes high-grade metamorphic rock and the Tethyan Himalayan sedimentary sequence that encompasses Proterozoic, Palaeozoic and Mesozoic sequences. These zones are longitudinally oriented in West-East direction and extend from Nanga Parbat to Arunachal Pradesh.

The team reached Chandi Ghat, Haridwar where Prof. D.C. Srivastava joined them. He was warmly welcomed by Shri Vishal Shastri with a shawl. Prof. Srivastava addressed the participants and briefed them about the planned excursion. He emphasized on the beauty of the geology of Himalayas and the evolution of different yet alike synclines within Lesser Himalayas such as Mussoorie Syncline, Garhwal Syncline.

Prof. Srivastava informed the participants that we were standing close to the contact between Sub-Himalayas and Lesser Himalayas which is known as the Main Boundary Thrust (MBT). This first stop marked the beginning Sub-Himalayas (Middle Siwaliks) which is evident from the change in topographic elevation as well as the difference in the dominant lithology of the rocks (Sandstone and Quaternary alluvium).The section represents the juxtaposition of Middle Siwalik sandstones against the Quaternary alluvium across the MFT.

Stratigraphically, the Lesser Himalayas comprises of Blaini, Krol and Tal Formations ranging in age from Neo Proterozoic (Ediacarian) to Early Cambrian.The Blaini Formation is characterized by the presence of diamictite layers inter-bedded with greenish and grey shale and graying white, greenish to purple quartz arenite, topped by a pinkish lenticular dolomite (Cap rock). It is followed by the Krol Group dolomitic shales which are often folded and faulted. Krol Group is divided into three sub-units (A, B & C or Lower, Middle and Upper Krol). The transition from Krol to Tal formation is characterized by dolomitic shales of Krol juxtaposed against dark shales of Lower Tal containing a few limonitic beds with occasional occurrences of phosphatic lenses. The argillaceous facies of Lower Tal grade into the arenaceous facies of Upper Tal which is made up of moderately thick bedded, overall coarsening up sandstones.

During the two days field excursion, the participants traversed along the Garhwal Syncline of Lesser Himalayas visualizing the dominant sedimentary rocks from the Indian platform. The participants were throughout guided by Prof. Srivastava explaining the structural and tectonic aspects of the study area.

After breakfast at Chandi Ghat, the team moved towards Rishikesh and took the traverse from Ram Jhula to Lakshman Jhula. At Jonk area,the participants observed the Blaini, Infra Krol and Lower Krol sequences. The Blaini formation at bottom was characterised by diamictites, indicating cold glacial environment which is further overlain by pink coloured dolomite cap rock suggesting a warmer climatic conditions. Several outcrop scale brecciated fault zones within Blaini formation were observed indicating the intense brittle deformation. Interestingly mesoscopic brittle-ductile deformation was shown and mechanism of this type of deformation was explained by Prof. Srivastava.One can observe several discontinuities within the Krol limestones often filled by secondary minerals.

Calling it a day, the participants moved towards Shivpuri where the accommodation had been arranged by SPG and APG India. Along the traverse from Tapovan to Shivpuri, Lower, Middle and Upper Krol and the Lower Tal formations were observed along the road-sections. This traverse marks the south-eastern limb of Garhwal Synclineand bedding planes have dip in the range 50° to 60° towards NE.

The following day i.e. 2nd April, 2023, the team started the traverse from Shivpuri towards Kaudiyala ghat area. The team stopped at the site where the silty shales of Lower Tal have been exposed on the roadside. The bedding planes were dipping at 55° to 65° towards SW. The rocks were intensely jointed with more than three joint sets. The participants observed the minerological variation as the black shales often turned into red due to the presence of Iron content.

The next stop was the exposure of black shales of Tal Formation. The carbonaceous content mainly contributed the blackish appearance of the shales. It was informed by Prof. Srivastava that Precambrian =.Cambrian (PC-C) boundary is placed within this unit by the geo scientists.

The next stop was near Kaudiyala ghat area which marks the North-Western limb of Garhwal Syncline. The participants observed the outcrops of shell limestones. The shell limestone is sandy with terrigenous influxes. Shri Srivastava explained that it was deposited in supratidal to subtidal environment under medium to high energyconditions.

The team started moving back towards Rishikesh. At the lunch stop, a small felicitation ceremony was arranged for Prof. D.C. Srivastava. Shri Jayanta Sarkar, Secretary APG and Shri Vishal Shastri, President SPG thanked Prof. Srivastava for his efforts in guiding the geoscientists and sharing his knowledge. He was presented a memento on behalf of SPG and APG, India. Shri Srivastava thanked SPG and APG for giving him this opportunity to lead an enthusiastic group in the field.

On the way back, the team stopped at one last point where Flower Structure was exposed in the Lower Krol sequence. A flower structure is a geologic structure that results from strike-slip movement associated with convergence (producing a positive flower structure) or divergence (a negative flower structure) generally showing as an upward-widening cone containing a number of faults. The participants were fascinated by such large scale outcrop which they’ve been interpreting on seismic sections. Post this, the teams headed straight back to Dehradun.

The central executive bodies of SPG and APG, India under the guidance of Smt. Sushma Rawat, Director (Exploration) meticulously planned this field excursion. The two day field excursion gave great insight to the geology of the Himalayas, which has fascinated earth scientists of all generations. The on-field experience gained by the participants will undoubtedly be immensely useful in their respective G&G assignments.