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Lesser Himalayan Strata
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Lesser Himalayan Strata
One of the major depositional strata in the Himalaya is the Lesser Himalayan Strata from the Paleozoic to Mesozoic eras. It had a quite different marine succession during the Paleozoic, as most parts of it are sparsely fossiliferous or even devoid of any well-defined fossils. Moreover, it consists of many varied lithofacies, making correlation work more difficult. This article describes the major formations of the Paleozoic – Mesozoic Lesser Himalayan Strata, including the Tal Formation, Gondwana Strata, Singtali Formation and Subathu Formation.
The Himalayan mountain chain is a fold and thrust belt that can be divided into four units bounded by thrusts from south to north: the Sub-Himalaya, Lesser Himalaya, Greater Himalaya and Tethyan Himalaya. The Lesser Himalayan Zone has a lower relief and elevation of the mountains compared to Greater Himalaya. The Lesser Himalaya Sequence (LHS) is bounded by two main thrusts: the Main Central Thrust (MCT) in the north and the Main Boundary Thrust (MBT) in the south.
The main layers of the LHS includes non-fossiliferous, low-grade, metasedimentary rocks, metavolcanic strata and augen gneiss. These have been dated as an age ranging from 1870 Ma to 520 Ma (i.e. Proterozoic to Cambrian). Near the end of the Early Cambrian, there was a regional diastrophism (i.e. deformation of the Earth's crust) or crustal movement that heaved up the Indian subcontinent, interrupting the sedimentation in the Lesser Himalaya and causing a widespread unconformity in Nepal. This is known as the Great Lesser Himalayan Unconformity, which separates the older LHS from the overlying younger LHS that has an age of Permian to Middle Eocene.
During the Paleozoic and Mesozoic, the LHS starts from the basal Tal Formation, which is part of the Outer Lesser Himalayan sequence in the Garhwal Himalaya. The Tal was deposited between the period of the Late Proterozoic to Palaeozoic Cambrian. After that, there was a great hiatus between the Middle Proterozoic rocks and the overlying Palaeocene-Eocene strata. This indicates that the LHS experienced a long period of denudation or non-deposition in the Western Himalaya (e.g. in the Jumla area), resulting in missing Gondwana Strata in Jumla during the Mesozoic (see more in the table of "Gondwana Strata of LHS in Western and Central Nepal"). In the Central and Eastern Himalaya, Gondwana strata from the Permian to Paleocene were preserved unconformably onto the older LHS. The next succession of the LHS in the Garhwal Himalaya comes to the Singtali Formation, which was deposited from the Late Cretaceous to Palaeocene, followed by the Subathu Formation, which was deposited from the Late Palaeocene to Middle Eocene, marking the start of Cenozoic Era.
Table showing the major formations discussed in the following sections:
The Tal Formation belongs to the Mussoorie Group of Outer Lesser Himalaya of Garhwal in northwestern India. It is well exposed along the Krol Belt, and is overlying the Precambrian Krol Group.
The Tal in the Mussoorie Synform can be divided into the Lower Tal and Upper Tal. For the Lower Tal, there are four subdivisions: the Chert, Argillaceous, Arenaceous and Calcareous Units. The basal black shale succession with sandy limestone represents a depositional environment of a protected lagoon or embayment, while the overlying siltstone is deposited in a mud flat of an intertidal zone.
The Upper Tal can be subdivided into lower quartzitic sequence and upper thick calcareous sequence containing abundant fragmentary shells of bivalves, gastropods, bryozoa, etc. The Phulchatti quartzite succession represents the deposits of a shoal environment, while the uppermost shell limestone sequence indicates an increasing energy of the shallow tidal sea, and a marine transgression in the Cretaceous.
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Lesser Himalayan Strata
One of the major depositional strata in the Himalaya is the Lesser Himalayan Strata from the Paleozoic to Mesozoic eras. It had a quite different marine succession during the Paleozoic, as most parts of it are sparsely fossiliferous or even devoid of any well-defined fossils. Moreover, it consists of many varied lithofacies, making correlation work more difficult. This article describes the major formations of the Paleozoic – Mesozoic Lesser Himalayan Strata, including the Tal Formation, Gondwana Strata, Singtali Formation and Subathu Formation.
The Himalayan mountain chain is a fold and thrust belt that can be divided into four units bounded by thrusts from south to north: the Sub-Himalaya, Lesser Himalaya, Greater Himalaya and Tethyan Himalaya. The Lesser Himalayan Zone has a lower relief and elevation of the mountains compared to Greater Himalaya. The Lesser Himalaya Sequence (LHS) is bounded by two main thrusts: the Main Central Thrust (MCT) in the north and the Main Boundary Thrust (MBT) in the south.
The main layers of the LHS includes non-fossiliferous, low-grade, metasedimentary rocks, metavolcanic strata and augen gneiss. These have been dated as an age ranging from 1870 Ma to 520 Ma (i.e. Proterozoic to Cambrian). Near the end of the Early Cambrian, there was a regional diastrophism (i.e. deformation of the Earth's crust) or crustal movement that heaved up the Indian subcontinent, interrupting the sedimentation in the Lesser Himalaya and causing a widespread unconformity in Nepal. This is known as the Great Lesser Himalayan Unconformity, which separates the older LHS from the overlying younger LHS that has an age of Permian to Middle Eocene.
During the Paleozoic and Mesozoic, the LHS starts from the basal Tal Formation, which is part of the Outer Lesser Himalayan sequence in the Garhwal Himalaya. The Tal was deposited between the period of the Late Proterozoic to Palaeozoic Cambrian. After that, there was a great hiatus between the Middle Proterozoic rocks and the overlying Palaeocene-Eocene strata. This indicates that the LHS experienced a long period of denudation or non-deposition in the Western Himalaya (e.g. in the Jumla area), resulting in missing Gondwana Strata in Jumla during the Mesozoic (see more in the table of "Gondwana Strata of LHS in Western and Central Nepal"). In the Central and Eastern Himalaya, Gondwana strata from the Permian to Paleocene were preserved unconformably onto the older LHS. The next succession of the LHS in the Garhwal Himalaya comes to the Singtali Formation, which was deposited from the Late Cretaceous to Palaeocene, followed by the Subathu Formation, which was deposited from the Late Palaeocene to Middle Eocene, marking the start of Cenozoic Era.
Table showing the major formations discussed in the following sections:
The Tal Formation belongs to the Mussoorie Group of Outer Lesser Himalaya of Garhwal in northwestern India. It is well exposed along the Krol Belt, and is overlying the Precambrian Krol Group.
The Tal in the Mussoorie Synform can be divided into the Lower Tal and Upper Tal. For the Lower Tal, there are four subdivisions: the Chert, Argillaceous, Arenaceous and Calcareous Units. The basal black shale succession with sandy limestone represents a depositional environment of a protected lagoon or embayment, while the overlying siltstone is deposited in a mud flat of an intertidal zone.
The Upper Tal can be subdivided into lower quartzitic sequence and upper thick calcareous sequence containing abundant fragmentary shells of bivalves, gastropods, bryozoa, etc. The Phulchatti quartzite succession represents the deposits of a shoal environment, while the uppermost shell limestone sequence indicates an increasing energy of the shallow tidal sea, and a marine transgression in the Cretaceous.