Geology 12 Sedimentary Facies and Structures Facies distinctive

Geology 12: Sedimentary Facies and Structures

• Facies: distinctive body of sediment Gravel On-shore fluvial Chert Near-shore marine High Off-shore marine Energy Low

Facies

• Marine Environments – Changes in sea-level due to ice ages, warm oceans, or rising & sinking plates. – 1. Marine Transgression “sea trespasses” • Sea-level rises (buried by water and marine sediments) • Buried docks, cities, beaches, trees • Shoreline moves inland • Marine facies moves inland • Some facies deposited over very large areas

Use note helper WS 6. 2 A Low E Drill hole High E T = L/ H

– 2. Marine Regression “sea retreats” • Sea-level falls • exposed docks, beaches, marine fossil above sealevel • Shoreline moves seaward • Marine facies moves seaward • Some facies deposited over very large areas

Use note helper WS 6. 2 A High E Drill hole Low E R = H/ L

What happened here? Transgression/Regression

Ø Go to note helper WS 6. 2 A and complete reverse side

a) Sea Land L L T H

b) Land H Sea L L R

c) Land H L Sea R L L T H L R

Transgression/Regression L L H T R T

Transgressional Seas

• How man got to Australia

• 140 m lower

• 65 m higher

Ø Hand out note helper WS 6. 2 B Ø Remainder of Chp 6 notes to be completed on note helper.

• Fluvial (river) Environments – Tend to be regressional (coastline moves seaward) as delta builds out – Cross-section of a river’s delta Meandering/wandering river beds

Fluvial Environments

• Sedimentary Structures: features that form as a result of physical and biological processes. 1. Strata/Beds: distinct layers (mm to m thick) that vary in colour, grain size, or composition. sh sst 1 bed Sst from spring runoff or flood (Hi E) Sh from slow periods (low E)

• Ex: Varves: 1 year Silt-clay: (springsummer Clay (fall-winter) (used to determine age of glacial lake’s existence)

Strata/Beds

Strata/Beds

Varves

Varves

Varves

Varves

2. Graded Bedding: grain size decreases upward in a single bed. silt sand gravel 1 bed Form a) at end of stream flood (where waters slow) b) from turbidity currents (underwater flows/landslide of sediments)

• How it forms: – 1. Large current moves materials of various sizes – 2. current slows – 3. large sediment drops out first, then progressively smaller and smaller material

Graded Beds

Graded Beds

Graded Beds

3. Cross-bedding: inclined bedding within a thicker sedimentary layer (mainly sand). Direction of flow 1 bed Successive layers of sediments

Cross Bedding

• What happened? • Cross bedding is common in sand dunes, stream channels & shallow marine environments (shifting beach sand) • Paleo-currents = ancient current directions

Cross Bedding

4. Ripple Marks: ridges within a bed (fine to med’ sediments). 2 types a) current ripple marks = asymmetrical Current direction b) wave-formed ripple marks = symmetrical Current direction

Ripple Marks

Ripple Marks

Ripple Marks

5. Mud Cracks: fine (clay) sediments that dry & shrink in the sun forming polygonal shapes • Indicative of tidal flats and dried lake bottoms • From in 3 steps: a) Mud deposited in low E environment

b) mud dries, shrinks & cracks Top view Side view c) Silt/sand is deposited on top & in the cracks preserving the structure. Side view

Mud Cracks

Mud Cracks

Mud Cracks

6. Fossils: remains or traces of ancient organisms (or old teacher). • 3 types: a) Body Fossil: i) Unaltered: original remains of organism Ex: Wooly Mammoth, Sabre-toothed Tiger ii) Altered: altered or replaced remains or organism Ex: wood replaced by silica = petrified wood Ex: leaves preserved as thin carbon film Ex: calcite shell replaced by iron sulfide

Fossils: Body Fossils

Fossils: Body Fossil

Fossils: Body Fossil Woolly Mammoth “Jaws”

b) Trace Fossil: indication of past organic activity. Ex: tracks, trails, burrows, borings Ex: coprolites (fossilized feces = dino dung)

Fossils: Trace Fossil

Fossils: Trace Fossil Coprolites

c) Mold/cast: shape of organism. Mold 1. Shell buried 2. Shell dissolved (void space) Cast 3. Rock split to reveal mold 4. Rock split 3. 2. Shell to reveal cast sediment/precipitate 1. Shell dissolved buried (void space) deposited in mold) Lots more on fossils in chapter 8

Fossils: Cast & Mold

7. Sole Marks: marks on which was originally the under surface of a bed • Include various marks produced by animals and objects moving on the surface on which the sediment was deposited. • Ex: a filled in scratch left by a moving boulder.

Sole Marks

Sole Marks

8. Flute Casts/Marks: elongated depressions that form at the base of a river channel Current direction

Flute Casts / Marks

Flute Casts / Marks

Do WS 6. 2