Transcript Sedimentary Rocks and Depositional Environments

Sedimentary Rocks and
Depositional Environments
Lab 1
Rock Types - Background
Igneous
 Metamorphic
 Sedimentary


Broken down to form sediments
– Sediments – fragments of rock, individual
mineral grains (quartz), parts of plants or
animals, clay minerals, and other minerals
Minerals - Background

Igneous, metamorphic, and sedimentary rocks
are made of minerals

Minerals – substances that make up rock; the
building blocks of rocks

Example minerals – quartz, potassium feldspar,
biotite mica, muscovite mica, calcite
Sedimentary Rock Characteristics
Grain size
 Rounding
 Minerals
 Matrix
 Color

Grain Size

The average diameter of the particles
Gravel
> 2 mm
Visible to the unaided eye
Sand
< 2mm,
>1/8 mm
Visible to the unaided eye, feels very
gritty
Silt
(mud)
<1/8 mm,
> 1/256 mm
Invisible to the unaided eye, can see
with a hand lens, feels gritty
Clay
(mud)
< 1/256 mm
Cannot be seen without a microscope,
feels smooth, dull luster
Pg. 1-2 of lab manual
** Ruler in Back of AGI Manual **
Minerals

Building blocks of rocks
Mineral
Hardness Cleavage
Color
Distinguishing
Feature
Quartz
7
None
(fractures)
Milky to
Colorless
Hardness and
looks
glassy
Potassium
feldspar
6
2 to 3
planes
Salmon to
Red
Color
Biotite
mica
2.5
1 plane
Black to
dark brown
Black flakes
Muscovite
mica
3
1 plane
Colorless to
light brown
Light colored
flakes; shiny
Calcite
3
3 planes,
rhomb
White to
Gray
Reacts with acid
(HCL)
Pg. 1-3 of lab manual
Matrix
Sedimentary rocks are composed of large
particles (grains) surrounded by smaller particles
 The smaller particles are the matrix
 The fill in between larger grains

None—there
are almost no
open spaces
Much
Some
All
Sedimentary Environments

A rock will display certain characteristics
depending on the environment in which it was
formed

The study of the composition and other
characteristics of the sed. rocks can reveal info.
about the conditions occurring during
deposition (helps determine environment)
Sedimentary Environments







Alluvial Fans
River Channels
Glaciers
Swamps
Deltas
Beaches and Barrier
Islands
Dunes





Lagoons
Tidal Flats
Reefs
Continental Shelf,
Slope, and Rise
Deep marine
environments
Refer to Figure 1.1 pg. 1-2
Alluvial Fan



Rivers in mountainous
areas erode and transport
sediment
When meets flat plain
deposits sediment in fanlike shape
Common rocks:
sandstone, conglomerate,
breccia, diamicton
River Channels




Rivers vary in size and
energy level
Contain various sediment
types (gravel, sand)
Feldspar less common
Common rocks:
sandstone, conglomerate
Glaciers



Not able to sort sediment
size
Glacial sediments (till) are
mixtures of gravel, sand,
silt, and clay
Rock types: diamicton
Swamps




Lots of organic matter
Slow decomposition
Buried and compacted
organic matter hardens to
form coal
Common rocks: coal,
shale
Deltas





Rivers flow into lakes or
oceans
Deposit sediment in a
fan-like shape
Mississippi River Delta,
Nile Delta
Large areas composed of
various environments
(channels, swamps, bays)
Common rocks: shale,
siltstone, sandstone, coal
Beaches and Barrier Islands




Barrier island is like a beach separated from the
mainland by a lagoon
Constant wave action separates sand sized grains from
others
Sediment has traveled far from source, so well rounded
Common rocks: sandstone
Dunes



Form adjacent to beaches and barrier islands
Contain non-marine fossils
Common rocks: sandstone
Lagoons


Low-energy environment
 Fine grain sizes settle and
accumulate (silt, mud)
 Common rocks: shale,
siltstone

Behind a barrier island or
reef
Barrier island/reef act as
breakwaters protecting
the lagoon from wave
action
Tidal Flats




Broad, flat areas that are periodically covered in water
when tide rises and dry when tide is low
Variable energy levels
Alternating layers of coarse and fine sediment
Common rocks: siltstone, shale, limestone
Reefs




Organisms build large, rocky accumulations by
cementing their shells or other structures
Common in tropical regions (warm water)
Calcite precipitates
Common rocks: limestone
Continental shelf, slope, and rise


Shallow marine: extend from beach to water depths of
100 m; low energy; fine grains settle; common rocks are
sandstone, siltstone, shale
Deep marine: extend down to thousands of meters; low
energy; fine grains settle; fossils are rare; common rocks
are shale, sandstone
Today’s Lab!!

List properties of unknown sedimentary
rocks

Identify the unknown rock specimens
(rock name)

Determine possible depositional
environment(s) where the rock formed
Rock Names
Shale
 Siltstone
 Sandstone
 Conglomerate
 Breccia
 Diamicton
 Limestone
 Coal
