Interpretation Criteria for Sedimentary Rocks

Rupali Lohani 35th OCG Batch‘F’

Preliminary steps to Distinguish Different Sedimentary Rocks

• Correlation between geology and landform

• Combination of factors : Experience Patience Perception

• Use of photorecognition elements in proper association

• Knowledge of climatic environment

Interpretation Criteria

•a•a

Based on

Photo element

Based on Morphological

Features

• Tone• Texture• Shape• Size• Association

• Landforms • Drainage pattern• Land use and land cover pattern

Intermediate rocks

Limestone, Dolomite,

Rock salt, etc

Carbonates + Evaporites

Coarse Clastics Fine Clastics

Conglomerate, Sandstone,

Quartz-arenite etc

Clay, Shale, etc

Classification of Sedimentary Rocks

Horizontally Bedded Sandstone• Topograhy:

• Bold, massive, flat topped hills of equal elevation• Nearly vertical hill sides

• Drainage• Coarse textured, joint controlled modified dendritic• Often rectangular

• Erosion• Few gullies, V-shaped

• Photo tone• Light due to light colour of the rock• In humid areas dense tree causes dark tone• Red sandstones give dark tone

• Vegetation• Commonly forested in humid while sparse in arid

Horizontally Bedded Shale• Topograhy:

• Minutely dissected with steep stream/gully in arid climate• Gently to moderately sloping softly rounded valleys & hills

• Drainage• Fine textured, dendritic pattern with gently curving streams in

arid climate• Medium to fine in humid climate

• Erosion• Sharp angular in arid terrain• Gullies have gently rounded cross section in humid• Tone• Generally dark tone

• Vegetation• Barren in arid except for desert vegetation• Intensely cultivated in humid areas.

Horizontally Bedded Shale

Arid

Humid

Horizontally Bedded Sandstone

ARID

HUMID

Horizontally Bedded Limestone• Topograhy:

• Karst topography in humid areas • Forms table rocks in arid climate

• Drainage• Internal drainage in humid climate• Angular drainage with medium to fine density in arid terrain

• Erosion• Chemical weathering in humid climate• Erode very little and forms cap or table rocks in arid terrain

• Photo tone• Varies from light to dark depending on cover

• Vegetation• Barren in arid except for desert vegetation• Dense vegetation resulting from clay soil in humid areas.

GSITI HYD

Interbedded Sedimentary Rocks – Flat Lying• Topograhy:

• Terraced hillsides with hilltops at same elevation• Slopes more gradual in humid while sharp in arid

terrain

• Drainage• Dendritic medium to coarse in humid• Dendritic medium to fine in arid

•Photo tone• Varies depending on rock type on cover

• Vegetation• Climate and the lithology

Interbedded Sedimentary Rocks – Tilted• Topograhy:

• Series of parallel ridges with alternating valleys• Slopes and ridges are smooth in humid while

sharp in arid terrain• Drainage

• Trellis and dendritic• Coarse in humid terrain and fine in arid terrain

•Photo tone• Varies depending on rock type on cover

• Vegetation• Climate and the lithology

GSITI HYD

Interbedded Tilted Sequence Sandstone and Shale

Rocktype Topography/Landform

Drainage Tone Gullies Vegetation/Landuse

Sandstone Humid

Arid

Massive,steep slopes.

Flat table

Dendritic course.Angular, dendritic(M-F)

Light.

Light banded

Few (V shaped).

Few to none

Forested.

Barren

Shale Humid

Arid

Soft hills.

Steep rounded hills

Dendrtic (M-F)Dendritic (F)

Mottled- Dull

Light

Soft U shaped.

Steep sided

Cultivated

Barren or badlands

INTERPRETATION CHART- CLASTIC SEDIMENARY ROCKS

Rock type Topography/Landform

Drainage Tone Gullies Vegetation/Landuse

Limestone Humid Arid

Karst topographyFlat table

Internal

Angular, Dendritic (M-F)

Mottled

Light

Fringed

Few to none

Cultivated

Barren

Dolomite Humid

Arid

Hill & Valley

Flat table

Angular, Dendritic M.Angular, dendritic(M-F)

Light grey

Light banded

Soft U shaped

Few to none

Cultivated,Forested

Barren

Interpretation Chart for Carbonate Rich Rocks

Rocktype Topogaphy

Drainage

Tone Gullies Vegetation/Landuse

Flat interbedded(Thick bedded)-Humid

Arid

Terraced hillsides

Terraced hillsides

Dendrtic (M-C)

Dendritic (M-F)

grey

Med light banded

Varies

Varies to few

Cultivated

Barren

Flat interbedded(Thin bedded ) Humid Arid

Uniform slopes

Minor terraces

Dendritic-M

Dendritic F

Medium grey

Faint thin bands

Soft-U shaped

Few to none

Cultivated, forested

Barren

Tilted Interbedded Humid

Arid

Parallel ridgesSaw toothed edges

Trellis-M

Trellis-F

Grey & light bandedBanded

Varies

Varies

Forested,cultivatedBarren

INTERPRETATION CHART-SEDIMENARY ROCKS

GSITI HYD

Thin Interbedded

Flat-Lying Sedimentary

Rocks

GSITI HYD

Interbedded Sedimentary Rocks

– Tilted

Landforms• When the resistant strata are inclined the

ridges eroded from the strata are asymmetrical in cross section

• The slope which has the same direction as the dip is usually a consequent or resequent or dip slope

• The slope opposed to the dip is obsequent slope

• Where dip is less than 30o the obsequent slope is steeper than resequent and the landform is described as Cuesta

• With dip becoming steeper, the ridge becomes symmetrical and are called hog’s back

PLATEAU – MESA - BUTTE

Flatirons – Steeply dipping beds – indicate direction of dip

Landform Analysis Landform Character /

StructureLitho Unit

High Topography

Hard resistance rock

Quartzite/sandstone

Mesa,Butte Horizontal/sub horizontal

Quartzite/sandstone

Cuesta slope Medium dipping bed

Quartzite/sandstone

Flat iron Moderate to steep dipping bedded strata

Quartzite/sandstone

THANK YOU……