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<p>In the present study mineralogy and modal analysis of the Miocene Surma sandstones of the Inner Fold Belt has been analysed to understand their source rock, the tectonic settings and the palaeoclimate. Surma sandstones are angular to subangular in shape, moderately to moderately well-sorted in nature and fine to medium grained in size. In the studied sediments the dominant framework constituent is quartz (avg. 51.67%) where non-undulatory monocrystalline quartz dominates over undulatory quartz. Feldspar (avg. 12.38%), is represented by both, the K-feldspar and the plagioclases. Lithic fragments (avg. 13.59.%) are second in abundance and comprise of metamorphic, sedimentary and volcanic fragments. Mica is in minor quantity (avg. 0.58%). Based on the framework grains sandstones of the study area have been classified as feldspathic litharenite, lithicarkose, litho-feldspatho-quartzose and feldspatho-litho-quartzose. Silica is the dominating cementing material, however at places carbonate and iron cement has also been observed. The transparent heavy mineral assemblage (80%) of Surma sandstones includes garnet, tourmaline, zircon, rutile, chloritoid, kyanite, andalusite, chlorite, staurolite, wollastonite, and phlogopite in their decreasing order of abundance with average ZTR index being 51.46%. Framework constituents coupled with heavy minerals assemblage suggests a mixed provenance where sediments were supplied jointly by metamorphic, sedimentary and igneous sources. Though modal analysis points towards a recycled orogen, however, supply from crystalline sources cannot be ruled out. Presence of high percentage of unstable rock fragments and feldspars suggests high relief, steep slopes, short transportation, and quick burial. On the basis of above observations and the kind of terrain that exists close to the study area, supply from KarbiAnglong Massif lying in the northwest, Indo-Myanmar Range in the east and the rising Himalaya in the north has been visualised.</p>

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Petrography and heavy mineral assemblage of the sandstones of Surma Group (Miocene) from the Inner Fold Belt of Nagaland: implications on provenance, tectonic settings and paleoclimate

  • 期刊论文

  • 发表日期：

    2026年6月30日

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  • Vitholeto Nagi,
  • S. K. Srivastava

摘要

In the present study mineralogy and modal analysis of the Miocene Surma sandstones of the Inner Fold Belt has been analysed to understand their source rock, the tectonic settings and the palaeoclimate. Surma sandstones are angular to subangular in shape, moderately to moderately well-sorted in nature and fine to medium grained in size. In the studied sediments the dominant framework constituent is quartz (avg. 51.67%) where non-undulatory monocrystalline quartz dominates over undulatory quartz. Feldspar (avg. 12.38%), is represented by both, the K-feldspar and the plagioclases. Lithic fragments (avg. 13.59.%) are second in abundance and comprise of metamorphic, sedimentary and volcanic fragments. Mica is in minor quantity (avg. 0.58%). Based on the framework grains sandstones of the study area have been classified as feldspathic litharenite, lithicarkose, litho-feldspatho-quartzose and feldspatho-litho-quartzose. Silica is the dominating cementing material, however at places carbonate and iron cement has also been observed. The transparent heavy mineral assemblage (80%) of Surma sandstones includes garnet, tourmaline, zircon, rutile, chloritoid, kyanite, andalusite, chlorite, staurolite, wollastonite, and phlogopite in their decreasing order of abundance with average ZTR index being 51.46%. Framework constituents coupled with heavy minerals assemblage suggests a mixed provenance where sediments were supplied jointly by metamorphic, sedimentary and igneous sources. Though modal analysis points towards a recycled orogen, however, supply from crystalline sources cannot be ruled out. Presence of high percentage of unstable rock fragments and feldspars suggests high relief, steep slopes, short transportation, and quick burial. On the basis of above observations and the kind of terrain that exists close to the study area, supply from KarbiAnglong Massif lying in the northwest, Indo-Myanmar Range in the east and the rising Himalaya in the north has been visualised.