Geology 12: Sedimentary Facies and Structures

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

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

Drill hole Low E High E T = L / H Use note helper WS 6.2A

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

Drill hole Low E High E R = H / L Use note helper WS 6.2A

Transgression/Regression What happened here?

 Go to note helper WS 6.2 A and complete reverse side

a) H L L T Sea Land

b) L L H R Land Sea

c) L H L L L H R T R LandSea

Transgression/Regression H H L L L L T T R

Transgressional Seas

How man got to Australia

140 m lower

65 m higher

 Hand out note helper WS 6.2B  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. sst sh 1 bed Sst from spring runoff or flood (Hi E) Sh from slow periods (low E)

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

Strata/Beds

Varves

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

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

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 b) wave-formed ripple marks = symmetrical Current direction

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 c) Silt/sand is deposited on top & in the cracks preserving the structure. Side view Top view Side view

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

“Jaws” Woolly Mammoth

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

Fossils: Trace Fossil

Coprolites

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

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

Flute Casts / Marks

Do WS 6.2