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Lab #3
Terms from lab 3
46
Geology
Undergraduate 1
03/06/2012

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Term
limestone
Definition

Most common limestones are biogenic. 

 

 

Term
Types of Carbonates
Definition

Limestone

Dolomite

Caliche

 

Carbonates come from animals and algae

Term
Organisms that secrete calcium carbonate skeletons
Definition

foraminifera

coccolithophores

molluscs

corals

echinoderms

certain types of algae

 

Term
chalk
Definition

very fine-grained limestones

 

light-colored

Term
marl
Definition
muddy limestones
Term
coquina
Definition
very coarse limestone composed of shell hash
Term
Dolomite
Definition

Originially laid down as limestone, but due to long periods of exposure to groundwater additional magnesium and sulfur were brought into the beds.

 

In EXTREMELY evaporitic conditions, dolomite may be able to precipitate directly from seawater.

 

 

Term
ooids
Definition

Subspherical grains of calcium carbonate fored in agitated water conditions.

 

Associated with shallow, tropical seas. 

 

Formed when calcium carbonate begins to build up in layers around a nucleus such as a sand grian, or shell fragment.

 

Frequently have biogenic cores

 

Currents move the cores back and forth

 

algae may coat them and help carbonate accumulate

Term
oolite
Definition
a rock composed entirely of ooids
Term
Caliche
Definition

a non-biogenic carbonate formed by the precipitation of calcium carbonate in soils.

 

NON-CLASTIC!

 

In arid environments it's caused by water evaportating from the ground bringing carbonates with it.

Term
Types of Evaporites
Definition

halite, gypsum and anhydrite

 

Form from drying water concentrated as salts

 

May have many compositions

Term
evaporites
Definition
formed by precipitation of mineral as a consequence of the evaporation of seawater.
Term
halite
Definition
can accumulate in very thick beds of rock salt.
Term
clastic sedimentary rocks
Definition

typically formed in terrestrial environments but may also be deposited in marine settings, typically on the shelf.

 

Defined by clast size and composition

 

ROUNDING is important

Term
clasts
Definition
fragments of pre-existing rock that have been eroded from a parent rock, transported, deposited, and finally cemented together.
Term
conglomerate/breccia
Definition

clastic rocks made of grains greater than 2mm in diameter. 

grains: heavily rounded and smooth in conglomerate

 

Breccia: clasts are angular. 

Term
sandstone
Definition

clastic rocks composed of grains between 2mm and .125mm in diameter

 

grains: particularly quartz; grains can be seen with the naked eye.

Term
arkose
Definition
a variety of sandstone that has very high feldspar content
Term
siltstone
Definition

made up of grains between .125mm and .004mm.

 

grains are commonly made of quartz

 

small amount between teeth will feel gritty.

 

Term
mudstone/shale/claystone
Definition

clastic mud is formed from clay minerals (similar in structure to tiny mica crystals)

 

grains are generally smaller than .044mm.

 

Break along flat planes

 

will feel smooth against your teeth.

 

Formed by solution of minerals and precipitation as clay

Term
suspended load
Definition
travels up in the fluid without contacting the substrate below
Term
bedload
Definition
sediment grains that are moved by rolling or saltation
Term
(Wind or Water) saltation
Definition

sediment grains that bounce or jump

 

Term
Fluid viscosity
Definition

as viscosity increases, the size of the particles that can be transported increases.

 

Water can transport larger particles than air at the same flow velocity.

Term
flow velocity
Definition

as speed of flow (and turbulence) increases, the size of particles that can be transported also increases.

 

As speed (and therefore energy) drops, so does the max particle size in transport.

Term
 bedforms
Definition

Dependent on flow velocity, viscosity, fluid depth, and grain size, particles may create ripples, sand waves, dunes, and antidunes.

 

as fluid velocity increases, so does the scal of the bedform.

Term
ripples
Definition

relatively small features creaed at relatively low velocities and shallow depths by sand or silt sized particles.

 

Asymmetrical if formed by unidirectional flow, and symmetrical if formed in oscillating current.

 

Move with currents and can indicate old current types

Term
sand waves
Definition

broad, low bedforms that range in wavelength from  tens of cm to nearly a 100 m wide.

 

Straight-crested to highly sinuous in shape.

Term
Dunes
Definition
common bedforms, ranging in size from tens of cm to 100 m in height (only wind-formed dunes, though). May have either straight or sinuous crests.
Term
stoss
Definition
the UPSTREAM side of the bedform
Term
crest
Definition
the top of the bedform
Term
lee
Definition
the downstream side of the bedform
Term
crossbeds
Definition
as a bedform moves downstream, its "tail" is overridden by the next bedform behind it, preserving some traces of the angles lee faces within the layer of sediment.
Term
graded bedding
Definition

deposition of suspended sediment; as long as flow is turbulent, smaller particles will remain in suspension, while larger particles fall out of suspension. The resulting sedimentary layer will be graded, with coarser grained material at the bottom that grades into finer and finer particles toward the top. Such deposits occur when muddy water settles.

 

 

Term
reverse graded bedding
Definition
Smaller particles sink to the base of the bed, while larger particles work their way to the top 
Term
postdepositional structures
Definition
mudcracks, sole marks, toolmarks, raindrop imprints, burrows, footprints/trackways
Term
mudcracks
Definition
irregular, polygonal shapes formed by the drying, shrinking, and cracking of mud.
Term
sole marks
Definition
come in two forms; load casts and flute casts
Term
load casts
Definition
irregularly shaped features that form when denser sediment is deposited above less dense sediment
Term
flute casts
Definition

oblong, raised bulges on the underside of siltstones or sandstones

 

formed by turbulent, sediment-laden currents scouring a muddy bottom.

Term
toolmarks
Definition
indentations formed when currents dragged an object (tree branch, etc.) across sediment
Term
raindrop imprints
Definition

only preserved in finer-grained sediments

 

small impact craters left by raindrops

Term
burrows
Definition

very common in marine mud; trace fossils created by organisms (often worms) digging through soft sediment.

 

trace of feeding activity

 

Skolithos burrow: Vertical burrow type

 

Diptocraterion Burrow: Dish-shaped infillings in vertical burrows

Term
footprints/trackways
Definition
tracks left in sediment by organisms walking or crawling across the surface.
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