2. Evidence of Former Depositional Environments

Deep Marine

•Black Shales

•Pelagic Muds/Oozes

•Greywackes

•Mature

•Immature

•Laminations

•Graded Bedding ( some evidence of cross bedding & ripple marks)

•Sole Marks

•Graptolites

•Slow build up of sediment apart from turbidites

Carboniferous 360 – 290 MYA

Carboniferous Limestone

Brachiopods

Crinoids

Ammonoids

Colonial coral

Upper Carboniferous

limestonemudstone

sandstone

Delta top / swamp

Fluvial channel fill

Delta front

Prodelta

Offshore

Upper Carboniferous

Delta top / swamp

Fluvial channel fill

Delta front

Prodelta

Offshore

Turbidity currents

Upper Carboniferous

Carboniferous Limestone

Brachiopods

Crinoids

Ammonoids

Colonial coral

Millstone Grit (ssts)

Medium-grained Arkose

Quartz

FeldsparWeak cross bedding

Mudstones

Shales

Suggest the environment of deposition of the sediments shown in Fig. 1c and give evidence for your conclusion. (5)Environment:

Deltaic (1)

Evidence:

Coal swamp/rootlets/complete fossil plants (1)Coarsening up sequence (1)Cross-bedded sands (1)Marine sediments/bivalves (1)Marine to freshwater (1)Shallowing of water (1)

363 Ma

290 Ma

325 Ma

315 Ma

Devonian 409 – 360 MYA

Sandstones & conglomerates

Limestones & Marine fossils

Devonian - 400 mya

South of equator 10-20ºArid/desert climate – similar to SW USA (New Mexico/Texas)Old Red Sandstone (ORS) ContinentRapid erosion of Caledonian mountains (Caledonian orogeny)Rivers & lakes in basins between mountainsTropical ocean to south (Rheic Ocean)

Desert sandstones – lack of fossilsAlluvial sandstones – river depositsLimestones – brachiopodsShales – lake deposits, primitive fish, land plants, insects on land & first winged insects

Alluvial Environments (meandering rivers)Lithology:

Texture:

Mineralogy:

Structures:

Fossils:

• conglomerates

• well-sorted red sandstones

• desiccation cracks & calcrete

• cross bedding

• repeated cycles

• alluvial fan deposits formed at edge of Caledonian mountain area

Old Red Sandstone Deposits

1 cm

ORS sandstone, Orkney

Medium to fine grained red sandstone with cross bedding

50 cm

ORS conglomerate, Aberdeen

Boulder sized clasts of quartzite, granite, rhyolite & andesite

Devonian Marine Deposits