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
Delta top /
swamp
Fluvial
channel fill
Delta front
sandstone
Prodelta
Offshore
mudstone
limestone
Upper Carboniferous
Delta top /
swamp
Fluvial
channel fill
Turbidity
currents
Delta front
Prodelta
Offshore
Upper Carboniferous
Millstone Grit (ssts)
Medium-grained Arkose
Quartz
Feldspar
Weak cross
bedding
Mudstones
Shales
Carboniferous Limestone
Brachiopods
Crinoids
Ammonoids
Colonial coral
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)
limestone
290 Ma
Coal Measures
315 Ma
Millstone Grit
325 Ma
Carboniferous Limestone
363 Ma
shale & siltstone
sandstone
conglomerate
coal
Texture
Crystalline, finegrained, chemical
bioclastic
Fragmental, finegrained, well sorted
Fragmental, coarse
sand, moderately
sorted, sub-rounded,
smooth surface
Fragmental, coarsegrained, poorly
sorted, sub-rounded,
smooth surface
Chemical
Mineralogy
CaCO3
clay & silt
Quartz, feldspar
rock fragments
organic material
Structures
Bedding
Tectonic joints
cross bedding
coarsening upwards
imbrication
Seat earth
(fossil soils)
Fossils
Goniatites
Corals
Crinoids
Brachiopods
Marine bivalves
Freshwater bivalves
Texture
Fragmental, coarse
sand, moderately
sorted, smooth
surface, sub-rounded
Mineralogy
Quartz, feldspar
Structures
Cross-bedding
Fossils
Freshwater bivalves
Texture
Crystalline
fine-grained,
chemical, bioclastic
Mineralogy
CaCO3
Structures
Bedding, tectonic
joints
Fossils
Goniatites
Corals
Crinoids
Brachiopods
Giant lycopods
(Lepidodendron)
Tree ferns
Amphibians, early
reptiles
Spiders, giant
flying insects
Devonian 409 – 360 MYA
Sandstones &
conglomerates
Limestones &
Marine fossils
Devonian - 400 mya
South of equator 10-20º
Arid/desert climate – similar to SW USA (New Mexico/Texas)
Old Red Sandstone (ORS) Continent
Rapid erosion of Caledonian mountains (Caledonian orogeny)
Rivers & lakes in basins between mountains
Tropical ocean to south (Rheic Ocean)
Desert sandstones – lack of fossils
Alluvial sandstones – river deposits
Limestones – brachiopods
Shales – lake deposits, primitive fish, land plants, insects on land &
first winged insects
Alluvial Environments (meandering rivers)
Lithology:
Texture:
Mineralogy:
Structures:
Fossils:
Old Red Sandstone Deposits
• conglomerates
• well-sorted red sandstones
• desiccation cracks & calcrete
• cross bedding
• repeated cycles
• alluvial fan deposits formed at edge
of Caledonian mountain area
ORS sandstone, Orkney
1 cm
Medium to fine grained red
sandstone with cross bedding
ORS conglomerate, Aberdeen
Boulder sized clasts of
quartzite, granite,
rhyolite & andesite
50 cm
Devonian Marine Deposits