Chapter 7: Sediments and Sedimentary Rocks

Section 7.2

• sediments: unconsolidated particles/pieces that form by

  1. weathering and erosion of preexisting rocks (detrital & siliciclastic sediments)

  2. precipitation from solution (chemical sediments)

  3. secreted by organisms (biochemical sediments)

• sediments undergo diagenesis after burial

  • after burial, including compaction & cementation happens to sedimentary rocks

• lithification: process that forms sedimentary rocks

different sediments result in different sedimentary rocks: (slide 4)

Section 7.3

• Weathering, Erosion, Transportation, Deposition, Burial = Diagenesis and lithification

Section 7.4

Weathering: general process that breaks up rocks into fragments

2 categories:

• physical: mechanical processes (ice, biological activity) break rocks into smaller pieces

  • no change in chemical composition (ex. freeze wedging, rock falls)

• chemical: rocks & minerals reacting with air & water, decomposing into new products (ex. feldspar + acid = clay, gravestones)

Section 7.5

Current: form and speed of transport

• the stronger the water/wind current, the larger the material that can be carried

• deposition starts when transport stops (when ice or speed of current isn’t there or slows)

• different speed currents causing sorting (well-sorted = smaller pieces with smaller pieces, poorly sorted = larger pieces mixed with small pieces)

size sorting - characteristics of sediments vary with distance from source area and current velocity

• water: current speed; faster when steeper, storms

• wind: speed, varies by location and season

• ice: can carry ANY size; limited to high latitudes an elevations

rounding: abrasion (phys weathering) and dissolution (chem weathering) break down sediment, making it more round as transport distance increases

• increase travel time = decreased grain / clast size, increased roundness, increased sorting, increased silica content, increased by clay content

• = more texturally and compositionally mature

dependent on mineral:

1. hardness

2. cleavage (if angular, then it’s harder to round sharp edges)

3. composition

Section 7.6

sedimentary environments: places & conditions under which sediment can accumulate

major environments of deposition: non-marine & marine

aeolian: desert environments, wind driven

alluvial fans: short-lived streams deposit poorly-sorted sed. on flatheads in front of mountains in arid climates

fluvial environments: rivers, large fraction of terrestrial sed. rocks created by rivers

• channel: conglomerates and sands with sediments aligned in one main direction (slide 14)

• floodplain: thin-bedded shales with mud-cracks, fossil tracks

deltas: rivers empty into a sea, lake or other still water

• finer material goes further out, sandstone to siltstone to shale; swampy areas = fossils & coals, further from the mouth: marine fossils, clay

coastline environments: interface btwn marine & terrestrial conditions, constantly changing

dunes-beach-barrier island: well-sorted, well-rounded sandstones, marine fossils

lagoons: low energy; fine-grained shales, carbonates; hypersaline

• reefs: structure constructed by living organisms (corals); abundant marine fossils

shallow marine-shelf: sandstones & siltstones; abundant marine fossils

• deep marine: fine-grained sediments, siliceous oozes; clays; continues until another continent

Section 7.7

Sedimentary Structures: