CLASSIFICATION OF SEDIMENTARY ROCKS

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 CLASSIFICATION OF SEDIMENTARY ROCKS


SANDSTONE CLASSIFICATION

  • Arenite < 15% matrix

  • Wacke > 15% matrix

  • Mudstone > 75% matrix

  • Arkose > 25% feldspar

  • Quartz arenite > 95% quartz



BASED ON MATURITY

  • Quartz wacke : Mineralogically mature but texturally immature

  • Quartz arenite : Both mineralogically and texturally mature

  • Feldspathic wacke : Both mineralogically and texturally immature


CONGLOMERATE CLASSIFICATION

Conglomerates are rounded grains belongs to Rudaceous rocks

  • Oligomict : Clasts are of single rock type

  • Polymict : Clasts are of different rock type

  • Diamict : Matrix % is high (Clasts are completely surrounded by matrix)

  • Petromict : Unstable or metastable clasts

OTHER TERMS

  • Agglomerate : volcanic origin

  • Fanglomerate : found in case of alluvial fan


DUNHAM’S CLASSIFICATION

MUD SUPPORTED

  • Mudstone < 10 % grain

  • Wackestone > 10% grain

GRAIN SUPPORTED

  • Grainstone < 10% grain

  • Packstone > 10 % grain

FOLK CLASSIFICATION

  • Oolite : Spherical grains with internal structure ( < 2 mm)

  • Pisolite : Concentric layers without internal structure ( > 2mm)

  • Cortoids : Rounded grains

  • Oncoids : Grains containing nucleus surrounded by irregular, non-concentric laminae

  • Peleods : Small micritic grains without internal structure

HJULSTROM DIAGRAM

  • The Hjulström Curve shows the linkage between sediment size and the velocity needed to erode, transport or deposit.

  • The upper line shows the erosional velocity or critical erosion velocity needed to initiate sediment erosion.

  • The lower line shows the fall or settling velocity

  • In between the two there is the transportation of sediments.

  • Filip Hjulström’s curve implies that sediments such as sand need low velocities to be dislodged from the bed. This is because sand particles are incohesive; they don’t stick together.

  • Critical velocity of silt and clay is greater than sand.

BATHYMETRY

Sequence of increasing depth

  • Littoral zone : Skolithos

  • Sublittoral zone : Cruziana

  • Neritic zone

  • Bathyal zone : Zoophycus

  • Abyssal zone : Nereites

  • Hadal zone

Sequence of inceasing depth

  • Continental shelf

  • Continental slope

  • Continental rise

  • Abyssal plain

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