ERTH2003 Pracs

plane bedding with lamination

differential weathering

beds weathering at different rates

ripple cross stratification

lower flow

dune cross stratification

lower flow

antidunes

higher energy

chutes and pools

higher energy

right side up

upside down

wave vs current

wave- symmetrical

current- longer on one side

cross stratification

unidirectional current flow

curves in the direction of the current in tangential

bedding types

hummocky cross stratification

mud cracks

flute casts

load casts

ball and pillow/flame

finer pokes up, denser sinks

soft sediment deformation

mud cracks vs syneresis cracks

S looks more like worms, they’re thinner and have more distinct colour borders

skolithos

septarian nodule

cone in cone structures

quartz

blobby or lumpy, transparent or grey, common, will reflect on rotation

feldspar

pink or blinding white, will have lines

plagioclase is the white one, orthoclase is pink

muscovite

rainbow flakes

biotite

pitch black

lithic fragments

composed of other rocks

a

quartzarenite

b

sublitharenite

c

subfeldarenite

d

feldsarenite

e

lithic arkrose

f

feldspathic litharenite

g

litharenite

matrix

brown-opaque material between grains, arenite if over 10%, dense

cement types under microscope

quartz- overgrowth, kina looks like salt and pepper that will sparkle as you rotate

calcite- bright pastel

clay- bright material, crystal shapes,

fe- brown or red

grain contact types

floating will be without contact

microcline

cross hatching (lines in both directions)

diagenetic features

processes that occur after deposition

compaction, cementation, dissolution, and recrystallization

kaolinite

white and powdery

hematite

red coloured, layered and breaks apart easy

alluvial fan

braided stream

meandering stream

natural levee

courser

crevasse splay

oxbow lake

would start courser at the bottom and would be finer

longitudinal dunes

barchan dunes

open lake

ephemeral lake

courser but plane bedding

allochems

Allochems are recognizable grains in carbonate rocks, such as ooids, peloids, and fossil fragments, that are typically embedded in a matrix of micrite or sparry calcite.

pressure solution

Pressure solution is a geological process where minerals dissolve at points of high stress between grains and are either redeposited in areas of lower stress or removed from the rock entirely.

calcite vs neomorphised

neomorphism retains detail of organism and will shine, calcite will be colourful in matrix. very bland

stylolite

burial

burial- deep water will usually have striations lying over the top, long sutured contacts

micritic envelopes

dark rim

a

mudstone, less that 10% grain

b

wackestone: mud- more than 10% grain

c

packestone- mud but grain supported

d

grainstone- no mud but grain supported

e

boundstone- in growth position, can trap sediment with it

f

crystalisation, no texture recognisable

folk cement options

spary calcite cement- sand

micrite matrix- lime mud

folk allochem options

instraclasts, oolites, fossils, pelletes

and these then combine with the matrix type e.g. oospirite vs oomicrite

folk rock names

Micrite:

micrite—>fossiliferous biomicrite (if there)—>sparse micrite—>packed miicrite

poorly washed biosparite (if both)

Cement:

unsorted—> sorted—>rounded

micrite is based on % of matrix, cement is based on rounding and sorting

turbidity

large amounts of water, clasts are fluid supported, sediment deposited by flow wanes

sole marks at bottom, scoured base, fining up, waning flow

herringbone cross stratification

changes direction

orthoconglomerate

clasts in contact (clast/framework supported)

paraconglomerate

clasts “floating” in matrix (matrix-supported)

diamicrite

paraconglomerate where there are 2 distinct size fractions

oligomict

single clast type

polymict

more than one clast type

quartzrose

more than 90% quartz and chert

petromict

less than 90% quartz and chert

marine burial

needle structures/blades

vadose

pendant, meniscus of fluid contacting grains, concave up

phreatic

blocky, floating contacts

meteroic

floating and tangential contacts,