lecture 2 stratigraphic data n.
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Lecture 2: Stratigraphic data. Boris Natalin. Stratigrapher uses - Data from surface outcrops - Subsurface data such as cores, well logs, and seismic data Today’s topics are sedimentary rocks and their structures

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Stratigrapher uses

- Data from surface outcrops

- Subsurface data such as cores, well logs, and seismic data

Today’s topics are sedimentary rocks and their structures

Classification of sedimentary rocks:- Clastic (Siliciclastic)- Biogenic- Chemical

Sedimentary structures



  • Clastic sedimentary rocks consist of rock and mineral grains derived from the chemical and mechanical breakdown (weathering) of pre-existing rock. They contain rock fragments and more commonly, particles of quartz and feldspar. Clastic rocks are further classified on  the basis of grain size.



φ= -log2 diameter (in millimeters)

0.0625 mm

  • Conglomerates (> 2mm) is consolidated gravel
    • Boulder (>256mm)
    • Cobble (65-256 mm)
    • Pebble (4-64 mm)
    • Granule (2-4 mm)
  • Sandstones (0.062-2 mm) consolidated sand
    • Very coarse (1.0 - 2.0 mm)
    • Coarse (0.5 - 1 mm)
    • Medium (0.25 - 0.5 mm)
    • Fine (0.125 - 0.25 mm)
    • Very fine (0.0625 - 0.125 mm)
  • Shales (<0.0062 mm) is consolidated mud, rich in organic matter.
    • Silt (0.0039 - 0.0625 mm)
    • Clay (0.0002 - 0.0039 mm)
shape and roundness
Shape and Roundness
  • The degree of abrasion of sedimentary particles
mudrocks or mudstone 0 06 mm
Mudrocks or mudstone (<0.06 mm)
  • Silt
  • Shale (lithified clay)
  • Bedded silt or bedded shale (>10 mm)
  • Laminated silt or laminated shale (<10 mm)
  • Chemical/Biochemical
  • Limestone
  • Dolomite
chemical sedimentary rocks
Chemical sedimentary rocks
  • Evaporates
  • Siliceous sedimentary rocks (cherts)
  • Phosphorites
sedimentary structures
Sedimentary structures
  • A geologic structure is a geometric feature in rock whose shape, form, and distribution can be described
  • Large scale feature of sedimentary rocks
  • Information on origin of rocks
  • Information on younging direction
  • Information on paleocurrent direction
Beds, or strata are tabular or lenticular layers of sedimentary rock that have lithologic, textural, or structural unity that clear distinguishes them from layers above and bellow
Bedding planes
  • Groups of similar beds or cross beds are called bedsets
  • Bed termination may occur: - merging of bedding planes (pinch-out)- lateral gradation of composition (die out)- meeting of crosscutting features such as channel or unconformity
three mechanisms are responsible for the formation of bedding planes
Three mechanisms are responsible for the formation of bedding planes

1) Sedimentation from suspension

2) Horizontal accretion from a moving bed load

3) Encroachment into the lee of an obstacle

  • Bed load is a part of the stream load that moves on or immediately above the stream bed
  • Streamload is all material that is transported by a stream
Lack of bedding means:(1) bioturbation(2) deposition from highly concentrated stream load(3) rapid deposition from suspension.
graded bedding
Graded bedding
  • Commonly produced by turbidity currents
  • Turbidity current is poorly sorted material suspended in water. When flow begins to slow down, material settles according to the grain size.
bed and bedforms
Bed and bedforms
  • Bed – the smallest lithostratigraphic unit, commonly ranging in thickness from a centimeter to a meter or two and distinguishable from beds above and below (3D)
  • Bed (in sedimentology) – the floor of a body of water (2D)
  • Bed form or bedform – any deviation from a flat bed, generated by stream flow on the bed of a channel (2D)
cross stratification
Cross stratification
  • Cross stratification from Jurassic age Navajo sandstones. Wind direction is from left to right

Load casts

Flame structures

Extend downward from a sand layer into an underlying mud or very fine sand layerYounging direction

bedding plane structures
Bedding plane structures
  • Groove cast; striations, bounce, brush, prod, and roll mark
  • Flute cast
  • Parting lineation
  • Track, trails burrows
  • Mudcracks and syneresis cracks

Grooves (Oluk yapıları)


(Buzul kertikleri)


Flute marks

Load casts

Groove casts