GEOL 340 Sedimentology and Stratigraphy
Lecture 2
1. Sedimentary Rock Samples
2. Fundamental Physical Components
3. Fundamental Physical Properties
Sedimentary Rock Samples
Field Photographs
Hand Samples
a rock sample ranging from ~1 cm to several cm's in diameter
Rock Chips
A rock sample generally ~ 0.25 to 1 cm in diameter
Thin Sections
~ 30 micron thick wafer of rock glued to a piece of glass
Fundamental Physical Components
1. Grain = particles comprising a sediment and/or sedimentary rock
2. Porosity = void space between grains (generally ranges from 0% to 45%)
3. Permeability = interconnected porosity, hydrolic connectivity
4. Matrix = fine-grained "background" sediments filling-in
between grains
(matrix supported versus grain supported)
5. Cement = crystals that grow into void spaces between grains
6. Replacement Crystals = crystals that physically replace
a precursor grain,
matrix or cement component via dissolution/precipitation
Fundamental Physical Properties
Texture
a. grain size (Table 4.1, p. 81) Standard, Wentworth, and
Phi (f = -log2d)
clay = < 0.0039 mm = < 3.9 mm
silt = 0.0039 mm to 0.0625 mm = 3.9 mm to 62.5 mm
sand = 0.0625 mm to 2.00 mm
gravel (granule, pebble, cobble, boulder) = > 2.00 mm
b. grain sorting = measure of the range of grain sizes present (Fig. 4.4, p. 88)
c. grain form = overall shape and variations in proportions
sphericity - comparison to a sphere
d. grain roundness = smoothness of individual corners of a grain (Fig. 4.13, p. 99)
e. grain surface texture = small scale microrelief of grains (i.e. pits, etches)
f. Fourier shape analysis = periodic mathematical functions
as a function of
summed sine and cosine terms
Fabric
a. grain orientation box diagrams
imbrication = overlapping and shingling of grains
b. grain packing = spacing and density patterns of grains
c. grain contacts
tangential
long
concavoconvex
sutured
Quantitative Analysis of Grain Size and Sorting
1. Graphical Analysis
a. Histogram or Frequency Curve
b. Cummulative Curve
2. Statistical Analysis
a. Standard Deviation
b. Skewness
This approach fails to work consistently for identifying depositional environments.