I. Three Rock Types: Sedimentary, Metamorphic, Igneous

II. Types of Sedimentary Rocks: clastic (fragmental) vs. chemical (precipitate)

III. Clast sizes:

gravel - from fracturing/jointing of parent rock

sand - from disaggregating of individual minerals in the parent rock

clay - formed from silica residue after unstable elements weathered out of parent rock

silt - a special case (i.e. less abundant) formed from either abrasion of sand or from a parent rock whose individual minerals are small

IV. Grain size classification: log-normal grain size distribution resulting from crushing of large blocks of quartz and granite

CLICK FIGURE TO ENLARGE (then click it to return) Upper diagram shows the frequency (as weight percent of total sample) of different grain sizes (measured in mm using a sieve) of a crushed granite block. To convert this raw data into something resembling a 'normal distribution' (i.e. normal probability for which standard parametric stratistics can be used), replot the data on the lower diagram which has a logarhythmic (base 2) scale. The result looks more 'normally' distributed.

CLICK FIGURE TO ENLARGE (then click it to return) My class sketch of how I'd plot up the data. Note the red is the histogram of the data and the yellow is an smoothed approximation of the grain size distribution (i.e. eyeballed smooth curve through the data). Note how yellow curve looks like a normal distribution (it is really a log-normal distribution).

V. Sediment vs, Sedimentary rock:

gravel vs. conglomerate sand vs. sandstone silt vs siltstone clay vs claystone (or shale) fine grained (silt and mud) units often referred to more generally as mudstone

SHALE

VI. Sorting: refers to range of sizes in a rock. Well sorted vs. moderately sorted vs poorly sorted

VII. Rounding: angular vs. subangular vs subrounded vs rounded

VIII. Composition of different grain sizes

Conglomerate is typically composed of large chunks of source rock (i.e. lithic grains)

Sandstone usually made of minerals from source area (e.g. quartz, feldspar, small lithic fragments)

Mudstone is made of silt grains and/or clay minerals

IX. Sandstone Composition

A. Triangular (ternary) diagrams

CLICK FIGURE TO ENLARGE (then click it to return) Standard Q (quartz), F (feldspar), L (lithic grains) diagram.
CLICK FIGURE TO ENLARGE (then click it to return) Same as above except four points are plotted. Arrow shows the 'trend' of the four points going from arkosic (points a and b) to quartzite (point d) composition.

B. Field composition terms for sandstone:

Quartzite (>50% quartz grains),

Arkose (or feldspathic) (<50% quartz, but more feldspar than lithic grains);

lithic sandstone (<50% quartz, but more lithic grains than feldspar).

C. provenance (determining source areas)

1. granitic source vs basaltic source

2. weathering of a granitic source area

3. unroofing sequence of a continental volcanic arc yields inverted stratigraphy

D. EXAMPLE 1: Unroofing sequence in Spain

CLICK FIGURE TO ENLARGE (then click it to return) Shows idealized unroofing sequence off of sequential, basinward stepping thrust faults in northeastern Spain. Colombo, F., 1994, Normal and reverse unroofing sequences in syntectonic conglomerates as evidence of progressive basinward deformation: Geology, v. 22, p. 235-238.

E. EXAMPLE 2: Paleogeographic reconstruction of central Alaska in Mesozoic time.

CLICK FIGURE TO ENLARGE (then click it to return) Example of triangular diagrams from Mesozoic sandstones of central Alaska showing changes in composition. Johnsson, M. J., 2000, Tectonic assembly of east-central Alaska: Evidence from Cretaceous-Tertiray sandstones of the Kandik River terrane: Geological Society of America Bulletin, v. 112, no. 7, p. 1023-1042.
CLICK FIGURE TO ENLARGE (then click it to return) Paleogeographic reconstructions of central Alaska based, in part, on determining source areas from sandstone provenance.

F. Sandstones in Thin section

CLICK HERE to view movie of making a thin section

CLICK HERE to view slide show of sand grains in thin section

X. Cementation: converts sediment into sedimentary rock

A. Lithification: turning loose material into rock

B. Cement vs Matrix: cement forms a mineral out of precipitation (usually by ground water) vs. matrix which is fine grain sediment, clay usually, which deposits along with coarser grains (sand and gravel) that holds the rock together.

CLICK HERE to view movie of sandstone cementation in thin section

C. Cementation is a function of local pH, temperature, concentrations of key elements, rates of precipitation, and time.

D. Typical cementing materials include: carbonate cement (most common), silica cement, hematite cement.

XII. Chemical Sediment

A. Mostly limestone (CaCO₃), also chert (SiO₂) and phosphate (PO₃), and others

B. Limestone - Calcium comes from Ca⁺² weathered from bedrock and carried in solution by rivers.

CO₂ and O₂ come from atmospheric gas captured by wave action and dissolved into sea water.

CaCO₃ = calcite (mineral) which makes up thelimestone (rock).

C. Process facilitated by critters, which leads to an association of limestone with fossils

D. Carbonate Compensation Depth (CCD) - depth in ocean below which no carbonate is deposited.

E. Similar processes (but less abundant) take place for chert (SiO₃)