India’s Eparchean unconformity- A 500 Million year gap in history!

Eparchaean Unconformity (Tirupati hills), a notified National Geo-heritage Monument is a major discontinuity of stratigraphic significance that represents a period of remarkable serenity in the geological history of the earth.

The Tirupati hills are situated at the foot of a range of hills known by several names, including ‘Seshachala’, ‘Venkatachala’ and ‘Balaji’.

The boundary is between sedimentary rocks of the Cudappah Supergroup, 1600 million years in age, and Archaean rocks comprising granites, gneisses and dolerite dykes that are more than 2100 million years old, a 500 million year gap of deposition! Sudden changes and discontinuity in the rock layers in earth’s crust provides an insight into the formation of the subcontinent, the orogeny, the paleoenvironment and the exotic collection of paleo-flora and fauna.

What is an Unconformity?

An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous.

Examples of different types of Unconformities-

There is a billion-year gap in the geologic record where this 500-million-year-old dolomite nonconformably overlies 1.5-billion-year-old rhyolite, near Taum Sauk Hydroelectric Power Station, Missouri.

 

The Taconic Unconformity near Catskill, New York. This angular unconformity separates the Austin Glen Formation (Ordovician) from the overlying Rondout Formation (Silurian) and Manlius Formation (Devonian).
Eemian disconformity in a fossil coral reef on Great Inagua, The Bahamas. Foreground shows corals truncated by erosion; behind the geologist is a post-erosion coral pillar which grew on the disconformity after sea level rose again.
Hutton’s angular unconformity at Siccar Point where 345-million-year-old Devonian Old Red Sandstone overlies 425-million-year-old Silurian greywacke.
Disconformity with the Lower Cretaceous Edwards Formation overlying a Lower Permian limestone; hiatus is about 165 million years; Texas.
Nonconformity between the Pennsylvanian Fountain Formation (left) and Precambrian gneiss (right) at Red Rocks Park, near Golden, Colorado.
Disconformity (at the hammer) between underlying Mississippian Borden Formation and overlying Pennsylvanian Sharon Conglomerate, near Jackson, Ohio.
Angular unconformity of Shawangunk Formation overlying Martinsburg Formation at railroad cut near Otisville, New York.

Access to Eparchean Unconformity

Eparchean Unconformity- Location of the Geological Monument, India.

The nearest railhead to Tirumala hills is Tirupati. The geological monument is located 10 kilometres (6.2 mi) northwest of Tirupati town, at the 12 kilometres (7.5 mi) point on the Tirupati – Tirumala Ghat road. From Tirupati railway station the approach to the Tirumal temple is only by road, a distance of 10 kilometres (6.2 mi). The nearest airport is located at Renigunta, about 15 kilometres (9.3 mi) away from the Tirupati city, which connects to Chennai, Hyderabad and Bangalore airports. Regular bus services (both private and government) are operated by all the states bordering Andhra Pradesh.Bounded between- 13°30′00″N 79°22′30″E / 13.50°N 79.375°E / 13.50; 79.375 and 13°27′N 79°45′E / 13.45°N 79.75°E / 13.45; 79.75)

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