sedimentary rocks and surface processes

ow

A Sedimentary rock is:

is: rock formed from the lithification or crystallization of: minerals

in solution, organic remains, materials produced by living things (biochemical) or clastic

sediments (rock fragments of all sizes)

Lithification

to harden and form rock. Lithification is the three step process

(deposition, compaction, and cementation) that that forms sedimentary rocks

Crystallization

process by which mineral sediments in solution solidify either by

evaporation of chemical reaction.

clastic

made of fragments of other rocks

chemical

made from dissolved minerals precipitating out of solution

biochemical

made by living things, but was never a live (such as seashells)

organic

made of the organic remains of living plants and animals

Sediments

all types of consolidated materials that form sedimentary rocks.

Fragments of other rocks, chemical precipitants, and remains of plants and animals

clastic sediments

fragments of pre-existing rocks

chemical sediments

mineral in solution in water

organic sediments

remains of the living tissues of plants and animals

biochemical sediments

nonliving remains of plants and animals

How Sedimentary Rocks are identified

Sedimentary rocks are identified by their horizontal layers called Beds or Strata

How Sediments are classified

1. Origin and Composition (what they are made of )

2. Size of the sediment (clastic sediments range in the size from clay to boulders)

size of sediments largest to smallest

Boulders, cobbles, gravel, pebbles, sand, silt, mud, clay

How sediments are produced

(1) Weathering (breaking down) and Erosion (transport) of

Parent material and (2) Chemical and Physical processes

Types of Weathering

Biophysical, Physical, Biochemical, chemical

Physical weathering

wind, water, ice (repetitive cycle of freezing and thawing of water that

seeps into cracks of rocks), glaciers, exfoliation

Biomechanical weathering

weathering by living things such as plants growing in rock cracks

that continue to further break down a rock into smaller fragments

Chemical weathering

water and or acid rain that causes some existing rock to by dissolved.

Biochemical weathering

weathering of living things, plants that grow on the surface of rocks. The plants extract minerals necessary for growth which then causes the rock to break

down into smaller fragments.

Erosion/Transport

movement from source to location of deposition

transport agents

wind, water, glaciers, ice, and volcanic eruptions

Clastic Sedimentary rocks are classified based upon their

grain size and grain shape.

Jagged clastic sediments produce rocks called

breccias

Rounded clastic sediments produce rocks called

conglomerates

Complete Sedimentary rock forming Process

Step 1. Sediment Production: forms of weathering

Step 2. Sediment Transport: forms of transport

Step 3. Shaping the sediments

Step 4. Sorting of the sediments

Step 5. Deposition

Step 6. Compaction

Step 7. Cementation

Gravel-sized sediments form the clastic sedimentary rock called

conglomerate

Jagged, gravel-sized sediments form the clastic sedimentary rock called

breccias

Sand-sized sediments form the clastic sedimentary rock called

sandstones

Jagged, sand-sized sediments form the clastic sedimentary rock called

arkrose

Silt, mud and clay-sized sediments form clastic sedimentary rocks such as

siltstone and shale

Examples of Evaporites (formed by the evaporation of water that is carrying dissolved

minerals) include

gypsum__, halite_, and travertine.

whats an evaporite

sedimentary rocks formed by the evaporation of water that is carrying dissolved

whats an inorganic carbonate

sedimentary rocks made of mostly calcium carbonate

Examples of Inorganic Carbonates (made of mostly Calcium Carbonate) include

travertine__ and inorganic limestone_.

Examples of Silica-based Chemical Sedimentary rocks would be

chert and quartz.

Examples of Biochemcial Carbonates (mix of shells and inorganic carbonate “glue”)

stromatolitic limestone, biochemical limestone, coquina and chalk.

Biochemcial Carbonates

mix of shells and inorganic carbonate “glue”

examples of Organic Sedimentary rocks

coal (plant material), coquina (shell fragments), chalk (plankton shells), and diatomite

graded bedding

exists where a transporting agent loses the ability to transport

increasingly lighter sediments. This often occurs in repeated cycles.

cross bedding

occurs when sediments are deposited at angles to one another. This

often occurs with sand (sand dunes) in beach and desert environments.

ripple marks

are created when flowing (in one direction, or back and forth)

shapes sand. Beach ripples are symmetrical, while stream ripples are

asymmetrical.

mudcracks

are created when silt and clay sediments dry and contract. Why are

fossilized mudcracks geologically valuable? They can indicate periods of extensive

dryness (droughts)

molds

fossils are holes left in rock.

casts

fossils are created when minerals fill a mold fossil.

Abrasion

: the wearing away of rock material by grinding action

Exfoliation

: the peeling of surface layers from exposed bedrock

Hydrolysis

: the chemical reaction of water with other substances

Erosion

: The removal and transport of materials by natural agents.

Weathering

: The breakup of rock due to exposure to processes that occur at or near

Earth’s surface.

Soil

combination of highly weathered clastic sediments (mostly sand, silt, and

clay), chemical sediments and organic material in which plants can grow.

soil has 2 types

transported and residual

The material from which soil is formed is called

parent material

Residual Soil

: soil whose parent material is the bedrock beneath it.

Transported soil

: soils formed from sediments that were produced elsewhere

(examples: Glacial and Alluvial soils)

How fast can soil be created depends on four things:

1. The rock type of the parent material (ex. Some rocks are more chemically

stable than others)

2. Climate (high rainfall and/or hot temperatures increase the rate of soil

formation)

3. Plant and Animal Activity (biochemical and biomechanical weathering)

4. Slope (a deep soil cannot form of a slope)

Soil Fertility

: The ability of a soil to grow plants

Salinization

: the build-up of dissolved minerals that are concentrated in lower soil

horizons and are brought to the surface through irrigation.

Talus

: rock fragments that have been weathered from a cliff and pulled down by

gravity.

Land Slide

: movement of mass of bedrock or loose soil and rock down a slope of a

hill, mountain, or cliff.

o Usually occur on steep slopes after heavy rains or when large amounts of

snow melts.

Creep

: slow, gradual movement of soil down a slope.

o Objects fixed in soil (fence) will lean downhill.

o Presence of water in soil contributes to creep.

Slump

blocks of land tilt and move downhill along a surface that curves into the

slope.

o Occurs because the top of the slope is too steep, and the bottom cannot

support it.

Mudflows

: rapid movement of water that contains large amount of suspended clay

and silts.

o Can travel up to 100 km/hour.

o Can move rock, boulders, trees, and houses.

o Occurs in drier regions that get infrequent but heavy rainfall.

Earthflows

: mass of weathered materials saturated with water flows downhill

o Slower and less fluid than a mudflow

o Speed depends on the amount of water in the soil, composition of the soil,

and steepness of the slope.

o Can last a couple of days to years.

Lahar

: mudflow that accompanies a volcanic eruption

o Heat from the erupted material melts the snow on top of a volcano and

which then moves down the side of the volcano.