Sedimentation & Stratigraphy Ch. 1-2 VOCAB

Sedimentology

study of the processes of formation, transport, and deposition of material that accumulates as sediment in continental and marine environments

Facies

a body of rock with specified characteristics that reflect the conditions under which it was formed

Terrigenous clastic material

made up of particles or clasts derived from pre-existing rocks

detrital sediments

fragments of pre-existing rocks and minerals produced by weathering and erosion

siliciclastic sediments

silica rich particles weathered from older rocks

What are evaporites

deposits formed ny the precipitation of salts out of water due to evaporation

Volcaniclastic sediments

products of volcanic eruptions or the result of the breakdown of volcanic rocks

lithification

the process of ‘turning into rock’

aggregates

granular material (mud, silt, and sand)

What does the suffix -stone represent?

indication that the material has been lithified (i.e. sand → sandstone)

gravel and conglomerate consist of clasts at what size?

>2mm in diameter

sand-sized grains are at what size?

2mm-1/16mm

mud grains are at what size?

<63 micrometers

What is the Wentworth Scale?

scheme for the classification of aggregates particulate matter

What is the phi scale

numerical representation for the Wentworth Scale in logarithm base two (negative to represent decreasing grain size)

Breccia

commonly used to describe a conglomerate made up of clasts that are angular in shape

Rudite and rudaceous

terms synonymous with conglomerate and conglomeratic

Monomict

clasts in a conglomerate that are all the same material

Polymict

conglomerate contains clasts of many different lithologies

Oligomict

conglomerate that contains 2-3 different clast types

Resistant lithologies

rocks that are less susceptible to breakdown

Matrix

the finer material between large clasts

A rock may be referred to as a sandy conglomerate or muddy conglomerate depending on…?

the grain size of the matrix present

Intraformational conglomerate

composed of clasts of the same material as the matrix

Orthoconglomerate

indicate that a rock is clast-supported

Paraconglomerate

matrix-supported texture in a conglomerate

equant blocks

rocks with equally spaced fracture planes in all directions that form spherical clasts when the edges are rounded off

Oblate or discoid form

rocks that break up into slabs that form clasts with one axis shorter than the other two

Prolate clasts

rod-shaped (less common)

Imbrication

an overlapping, shingle-like arrangement of flat or elongated rock fragments (clasts) stacked in a consistent direction (least resistance to flow way)

if a sandstone is considered acenasceous, it contains…

<15% matrix

Feldspars are only commonly found in circumstances where the chemical weathering of the bedrock…

has not been too intense and the transport pathway to the site of deposition in relatively short

authigenic minerals

these grow as crystals in depositional environments

What does the Pettijohn sandstone classification include?

textural critera, proportion of muddy matrix, composition, percentages of the 3 common components of sandstone: quartz, feldspar, and lithic fragments

if the amount of matrix present is between 15-75% then it is a…

wacke

How much feldspar must be present in a rock for it to be a felspathic or arkose rock?

25%

greywacke

term used in the past for a sandstone that might also be a feldspathic or lithic wacke

Graticule

a scale as an optical feature within the eyepiece of a petrographic microscope

relief

a measure of how strong the lines that mark the edges of the mineral are and how clearly it stands out from the grains around it (reflective index)

Cleavage

a preferred fracture orientation determined by the crystal lattice structure

Pleochroism

a natural phenomena where the color of a mineral changes as light hits it from different angles (the grain is moved with the rotating microscope stage)

Isotropic minerals

have crystal lattices that do not have any effects on the pathway of light passing through them

Anisotropic mineral

the pathway of light is modified when light passes through a crystal of this type (distortion)

birefringence color

appear when anisotropic materials (like certain crystals or minerals) are placed under cross-polarized light, splitting white light into fast and slow rays that recombine out of phase

undulose extinction

as the grain is rotated, different parts go into extinction at different angles

albite plagioclase feldspar

sodium rich

anorthite plagioclase feldspar

calcium rich

placer mineral

minerals that concentrate at the bottom of a flow due to their higher density

chalcedony

form of silica that can be easily identified in thin-section because it has a radial structure when viewed under cross-polars

Clay

a textural term to define the finest grade of clastic sedimentary particles

fissility

a strong tendency to break in one direction, parallel to the bedding

loess deposit

wind-blown silt sediments that cover about 10% of Earth's land

kandite group

crystal layer pattern with two layers

smectite group

crystal layer pattern with three layers

kaolinite

most common member of kandite gorup (2 layer clay)

flocculate

to cause tiny, suspended particles in a liquid to clump together into loose, fluffy clusters or lumps called "flocs"

fabric

a rock’s tendency to break in a certain direction or shows a strong alignment of elongate clasts

granulometric analysis

the measurement and evaluation of the different particle size fractions in a granular material like soil, sediment, or aggregate

Coulter Counter

determines grain size on the basis of electrical properties of grains suspended in a fluid or laser granulometer

skewness

indicator of whether the grain-size histogram is symmetrical or skewed to a higher percentage of coarser or finer material

kurtosis

value that indicates whether the histogram has a sharp peak or flat top

degrees of maturity

refers to the extent to which the material has changed when compared with the starting material of the bedrock it was derived from

compositional maturity

measure of the proportion of resistant or stable minerals present in the sediment

first cycle deposit

material formed by erosion and transportation to the point where they are deposited to form an accumulation of clastic sediment

second cycle deposit

redeposited material