2. Evidence of Former Depositional Environments Deep Marine Black Shales Pelagic Muds/Oozes...
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Transcript of 2. Evidence of Former Depositional Environments Deep Marine Black Shales Pelagic Muds/Oozes...
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