SEDIMENTARY STRUCTURES

• UPPER BEDDING : Rain print, Ripple marks, Mud cracks

• LOWER BEDDING - (Erosional structures)

  • Scour marks :

    • Flute cast : have a bulbous nose at their upstream end helps to infer paleocurrent direction

    • Obstacle scour / Current crescent

    • Longitudinal scour ,

    • Gutter casts

  • Tool marks :

    • Groove cast,

    • Chevron marks,

    • Prod casts,

    • Bounce marks,

    • Skip marks (Can’t identified in vertical section)

• SYN-DEPOSITIONAL : Graded bedding, Cross bedding

• POST DEPOSITIONAL/DEFORMATIONAL

  • Load cast - gravitational instability

  • Convolute bedding

  • Dish and pillar structure - water escape structures, fluidisation

  • Ball and pillow structure

  • Slump structure

BASED ON ENVIRONMENT

• Tidal : Herringbone,

• Sub-tidal : Double mud drapes

• Inter-tidal : Rain print, Mud crack, Adhesion ripple

• Storm : Hummocky cross

• Fluvial : Epsilon cross stratification

TOP AND BOTTOM CRITERIA

• Oscillation ripple

• Load cast - soft sediment deformation

• Graded bedding

• Mud crack

• Rain print

PALEOCURRENT DIRECTION

• Current ripples : unidirectional

• Ladder-back ripple: bidirectional

• Parting lineation

• Current crescent

• Flute cast - have a bulbous at upstream e

• Groove cast

• Cross bedding

• Herringbone CS - bimodal-bipolar, bidirectional

• Trough CS - Unidirectional

DIFFERENT TYPES OF CROSS BEDDING

1) PLANAR TABULAR CROSS BEDDING : Upper and lower bounding surfaces are planar and parallel

2) WEDGE SHAPED : Upper and lower bounding surfaces are planar and but not parallel

3) TROUGH SHAPED : Upper and lower bounding surfaces are curve and but not parallel

OTHER TYPES CROSS BEDDING

• HERRINGBONE : Bimodal and bipolar, Tidal environment

• Hummocky Cross: Convex up, storm environment

• Trough cross : Concave up, truncated towards the top and tangential towards the bottom

• Swaley cross : Concave up

• Lenticular : Sets bounded by converging surfaces

• Festoon : Mounded dunes and ripples cutting with each other

• Reactivation surface : formed when one tidal current is dominated, an erosional surface that formed within cross stratified strata

BASED ON ENERGY CONDITION

• Flasher bedding : mud in sand, sand % > clay % - high energy env

• Lenticular bedding : sand in mud , clay % > sand % - low energy env

• Wavy bedding : Sand % = Clay % (alternate traction and suspension load)

MATURITY OF SANDSTONES

Maturity depends upon:

1) Textural maturity - amount of clay, sorting and roundness

2) Mineralogical maturity - Quartz and feldspar content

TEXTURAL MATURITY

• with increasing clay content : maturity decreases

• with increasing sorting : maturity increases

• with increasing roundness : maturity increases

TEXTURAL INVERSION

• Two textural parameter indicating opposite maturity

  Ex: Rounded grains in clayey matrix , Rounded and poorly sorted grains

• Interclast: before diagenesis

• Intraclast: after diagenesis

GOLDICH DISSOLUTION SERIES

• Tells about stable and unstable minerals

• Opposite of Bowen’s reaction series

STABILITY SERIES

According to Bowen’s reaction series:

• Olivine - most susceptible and least stable

• Quartz - most stable and least susceptible

According to Goldich stability series

• Halite : least stable

• Hematite : most stable