Sedimentology- Kuliah 2- Unconsolidated Sedimen

27
Applied Sedimentology & Sequence Stratigraphy STAG6433 Unconsolidated clastic sediments

description

sedimentologi

Transcript of Sedimentology- Kuliah 2- Unconsolidated Sedimen

Unconsolidated clastic sedimentsParticles (or ‘clasts’) are the basic elements of any sediment
Clastic (terrigenous clastic or siliciclastic) sediments (80-85% of the stratigraphic record) consist of particles derived from pre-existing rocks, as opposed to non-clastic sediments
Texture is the size, shape and arrangement of constituents. Specific features include;
- Grain (particle) size
- Fabric
Lithology is the general characterization of a sediment or a sedimentary rock (e.g., coarse sand, mudstone)
EaES 350-2
to the base 2 of the particle diameter
Udden-Wentworth scale most commonly used.
Useful in interpreting depositional environments and in term of depositional mechanisms.
EaES 350-2
Grain-size (particle-size, granulometric) analysis
Presentation of grain size data
From the cumulative frequency probability curve, we can calculate mean, sorting (standard deviation), skewness & kurtosis.
EaES 350-2
Sediment highly sorted
Turbulence range narrow
Velocity changes narrow
Playtkurtic curves mean the following:
Sediment poorly sorted
Turbulence range wide
Velocity changes wide
Kurtosis
+0.30
+0.10
EaES 350-2
Tail of fines
The range of sizes in the fine fractions are greater than the range of sizes in the coarser fractions.
Negatively skewed curves mean the following:
Tail of coarse
The range of sizes in the coarse fractions are greater than the
range of sizes in the fine fractions.
skewness
EaES 350-2
EaES 350-2
EaES 350-2
EaES 350-2
Grain shape
Most popular method is visual by comparison with Zing diagram (1954).
Significance of shape – reflects internal structure, jointing of original rocks, bedding, lithology, hardness, fracture and transportation.
EaES 350-2
Roundness – ratio of average radius of curvature of corners so that of largest inscribing circle
well rounded to very angular
Grain shape - roundness
EaES 350-2
Sphericity – measure of the degree to which a particle approaches the shape of a sphere.
High or low.
Grain shape - sphericity
EaES 350-2
Grain orientation
Tells us about current direction or geogmetry; affects permeability (flow of gas, oil or water)
Beach – perpendicular to wave action
Alluvial – parallel to current
Lithic fragments (polymineral grains or rock fragments)
Detrital mineral grains dominate in silts, lithic fragments dominate in gravels
EaES 350-2
EaES 350-2
Sediment maturity (degree of change compared to original bedrock: provides evidence on the history of a sediment)
Textural (mud content, sorting, grain shape)
Mineralogical (proportion of stable or resistant minerals)
Sediment maturity
EaES 350-2
EaES 350-2
Kandite group (two layers): kaolinite
Smectite group (three layers): montmorillonite, illite, chlorite
Clay minerals
EaES 350-2
EaES 350-2
EaES 350-2
EaES 350-2
THANK YOU
EaES 350-2