Major boundary problems—Cambrian/Precambrian, Permian/Triassic, Cretaceous/Tertiary, and Pliocene | Geology Optional Notes for UPSC PDF Download

Archean-Proterozoic Boundary (A-Pr Boundary)

• Eparchean boundary in India is defined by the gap between Archeans and Puranas.
• Greenstone belts in India primarily belong to the Archaean era with some presence in the Proterozoic era.
• Key greenstone belts in India, such as Dharwar in South India, Iron-Ore Group in Eastern India, and Bailadilla Group in Central India, date back to the Late Archaean period and exhibit characteristics transitioning to the Proterozoic era.
• The conclusion of the Archaean era is characterized by a surge in granitic activities.
• Narrow and continuous fold belts like Aravalli, Delhi, and Satpura indicate the convergence of different continental blocks to form the Indian subcontinent.
• The Tirupati-Tirumala Eparchean unconformity distinguishes the Proterozoic Gulcheru Quartzite from the Archean granite.
• The age of the Archean-Proterozoic boundary is established at 2500 Ma, signifying the conclusion of the Kenoran orogeny.

Precambrian-Cambrian (PC-C Boundary)

• Sedimentation in the transition from the late Proterozoic to the Cambrian era began with a widespread marine advance in the northwestern Himalayas due to global warming following the Varangian glaciation around 610-590 million years ago.
• The PC/C boundary is characterized by the Cambrian explosion, signifying significant biological changes including:
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  • The appearance and disappearance of soft-bodied Ediacaran Fossils.
  • The emergence of organisms with hard skeletal structures, along with changes in the isotopic composition of carbonates.
  • In the Proterozoic era, fossils were smooth, while in the Cambrian period, they developed spines.
  • The predominant newly emerged animals were primarily bottom feeders which were builders and binders.
  • The Cryogenian period witnessed extensive glaciations, including the snowball earth phenomenon where ice sheets extended to the equator. Pangea, the supercontinent, formed by the end of the Proterozoic era.
  • The proliferation of multicellular life forms.
  • The significance of trace fossils became pronounced in understanding this boundary, serving as stratigraphic markers. The study of lebensspuren, which are sedimentary structures left by organisms, is crucial for interpreting ancient environments.
  • The oldest known fossils are the stromatolites of blue-green algae discovered in Canada and Australia.
  • Fossils found include:
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    • In the Late Paleozoic era: Trilobites, brachiopods, archaeocyathids, and their trace fossils. This era also encompasses soft-bodied metazoans like the Ediacaran fossils.
    • In the Proterozoic era: Rare trace fossils and stromatolites.

PC/C Boundaries in India

Tethys Himalayan Zone

• Kashmir-Ladakh
• Lahaul-Spiti
• Kumaon
• Krolo

Lesser Himalayan Zone

• Birmania Basin, Rajasthan (Pokhran Boulder Beds)
• Nandadevi: Martoli Formation (Ralam Conglomerates)
• Saline Series (now in Pakistan)

Saline Series consists of gypsum, marl, and salts. Lower Cambrian trilobites are preserved as Neobolus Shale.

Permian Triassic Boundary (P-T Boundary)

• Guruyal Ravine Findings

  • The P-T boundary at Guruyal Ravine is characterized by the extinction of Brachiopod fauna Productus shale.
  • It is marked by the appearance of Triassic Cephalopods (Ottoceras Woodwardi), Conodonts (Hindeodus parvus), and Lower Triassic bivalve Claria.
  • The sequence is arneaceous-argillaceous-calcareous in nature.

• Permian Sequences

  • Permian sequences exhibit widespread red beds due to regression and phases of non-deposition (hiatus).

• Global Boundary Stratotype Point (GBSP)

  • The GBSP of the P-T boundary is identified by the first occurrence of the conodont species Hindeodus parvus.
  • This species marks a transition between Hindeodus and Isarcicella.

Permian Triassic Boundaries in India

• Guruyal Ravines of Vihi District in Kashmir is the prime area for studying the Permian-Triassic (P-T) boundary due to its rich faunal and lithological characteristics.
• Other significant regions for studying the P-T boundary in India include Pahalgam, Pir Panjal, Bhallesh, Zanskar (NW Kashmir), and Kumaon (SE Kashmir).
• The first appearance of the ammonoid Ottoceras Woodwardi marks the beginning of the Triassic period.
• In the Spiti region, the Triassic period is characterized by massive limestone beds known as Otoceras Beds, which are overlain by flaggy limestone beds called Ophiceras Beds.
• The P-T boundary in Spiti is identified lithologically by the presence of carbonate beds with limonitised pebbly rocks in between.
• The P-T boundary is also documented in the Gondwana sequence.
• In the Damuda Group, Permian rocks are unconformably overlain by the Panchet Group.
• The middle Panchet group is recognized as the P-T boundary and is succeeded by the Mahadeva Formation of Triassic age.

Exploring the P-T Boundary

• The Banpetalic nala section in the Gondwana basin of Raniganj (West Bengal) is proposed as the first continental stratotype for the P-T boundary, based on the presence of estheriids, a group of small crustaceans.
• Fossils of two reptiles, Lystosaurus and Proterosuchus, are found in the Panchet Formation.

Floral Changes

• A shift in flora is observed from large leaf genera like Glossopteris to Dicroidium during the transition from the Permian to the Triassic period.
• Spores and pollens are considered reliable indicators for dating the P-T boundary.

Environmental Shifts

• During the early Permian period, the collision of Gondwana and Laurasia formed the supercontinent Pangaea, leading to extreme climates.
• The lush swamp forests of the Carboniferous era were replaced by conifers, ferns, and drought-resistant plants.
• Signs of the P-T boundary include a significant drop in the C13/C12 stable isotope ratio, an increase in CO2 levels (up to 2000ppm), rising global temperatures, and heightened UV radiation exposure.

Mass Extinction Event

• The Permian-Triassic mass extinction, known as "the Great Dying," resulted in the loss of 96% of marine species and 70% of terrestrial species, making it the largest mass extinction event in history.
• This event also led to the extinction of a vast number of insect species.

Cretaceous-Tertiary/Paleogene Boundary (K-T or K-Pg Boundary)

• Great mass extinction: Approximately 75% of species became extinct, including dinosaurs, marine reptiles, and ammonoids.
• Linked to events like the Chicxulub crater asteroid impact, Deccan trap volcanism, or Maastrichtian sea level regression.
• Stratigraphic division between Maastrichtian and Montian beds. The transition between Post-Maastrichtian and Pre-Montian beds is marked by Passage Beds of the Danian Stage.

Passage Beds in India:

• Sind Area, Pakistan
• Tiruchirapalli area, South India
• Assam region, NE India

Sind Area

• Cardita Beaumonti is recognized as the index fossil of the Danian age in the Indian subcontinent.
• Ranikot and Pab sst are predominantly lacking in fossils.

Tiruchirapalli Area

• Divided into Uttatur, Tiruchirapalli, Ariyalur, and Niniyur groups.
• Ariyalur Formation contains foraminiferal assemblages from the Maastrichtian age, with key species like Lepidoobitoides, Siderolites, and Rotalia.
• Niniyur yields a diverse fossil assemblage of gastropods, corals, and lamellibranchs.
• The K-T boundary is located at the contact of the Ariyalur-Niniyur formations.

Assam Region

• The upper Cretaceous rocks of the Assam region consist of the Mahadek Formation, which is overlain by the marine Langpar Formation.
• Langpar Formation has revealed a Danian fossil assemblage and is followed by a significant continental coal-bearing sequence known as the Therria Formation.
• Both Langpar (marine) and Therria formations are grouped as passage beds representing the K-T transition by Rama Rao.

Neogene-Quaternary Boundary (Pliocene-Pleistocene Boundary)

• Definition: The Neogene-Quaternary (N/Q) boundary is an important geological boundary marking a transition in various regions like the Siwaliks, Kashmir, and the Andamans in India.
• Main Criteria for Defining the Boundary:
  • Extinction of Discoasters
  • First appearance of Globorotalia truncatulinoide
  • Extinction of Globigerinoides sacculifer fistulosus above the boundary
  • Change in Globorotalia menardii population coiling patterns
  • Occurrence of the Olduvai Event (1.75–1.91 million years ago) on the magnetic scale
• Geological Features:
  • In the Andaman-Nicobar islands, late Cenozoic deep water marine facies are well-developed.
  • Paralic facies are observed in isolated outcrops along the Kutch-Saurashtra, Kerala, and Coromandel coasts.
• Regional Placement of the N/Q Boundary:
  • In Andaman-Nicobar islands, the boundary aligns with the first appearance of Globorotalia Truncatulinoides.
  • On the Bombay coast, the appearance of the Globigerina calida-praecalida group suggests a planktonic foraminiferal basis for the boundary.
  • Transition in Globorotalia menardii coiling patterns above the Plio-Pleistocene boundary, associated with the Olduvai paleomagnetic event.
• Characteristic Events:
  • The Olduvai Event falls within the Pinjor zone, a significant marker of the N/Q boundary.
  • The event is also marked by the first appearance of Equus and Elephus, along with the disappearance of Hipparion in the Siwaliks.

The Formation of Karewas in the Southwest Kashmir Valley

• Rising of Pir Panjal: During the Pliocene-Pleistocene period, the Pir Panjal mountain range experienced uplift, leading to the creation of large lakes in the Southwest Kashmir Valley.
• Origin of Karewas: Karewas refer to the sedimentary deposits that accumulated in these lake basins over multiple glacial-interglacial cycles.
• Geological Age: The Karewas are attributed to the Pleistocene epoch based on glacial evidence and the presence of specific fossils like Elephas hysudricus and certain diatoms.
• Identification Point: The Pleistocene-Pliocene boundary is identifiable in the Hirpur section of the Karewas, providing a crucial reference point for geological studies.