hydro geology slides 11 to 20
TRANSCRIPT
Hydrogeology WorkshopGeological History (3)
Permian and early Triassic times
• (~290 – 230 Ma);
• Surrounded by high ground;
• Arid/desert climate @ 15 - 20 degrees north of the equator;
• Land of braided rivers and flash floods.
•~15 – 20 degrees north of the equator, arid/desert
climate;
•Eroding higher ground to the south and west;
•Subsiding basin north-south oriented basin;
•Huge amounts of material washed down, often as
flash floods;
•Braided rivers system, flowing from south to north,
meanders across the basin floor;
•Pretty inhospitable to life, even ignoring that 95% of
species had just gone extinct.
Hydrogeology WorkshopGeological History (4)
Keep your eye on the
blue line.
• Hills eroding;
• Extension faults cause the
basin to subside;
• Sediments fill subsiding
basin.
All of this and this
ends up in here
Upper Mottled Sandstone
(a.k.a. Wilmslow Sandstone)
Transition Beds (between Upper Mottled
Sandstone and Helsby Sandstone)
Helsby Sandstone
Hydrogeology WorkshopGeological History (5)
Middle Triassic (~230 - 220 Ma)
•Lower relief and low-lying basin
receives mainly fine grained material
(silt and mud);
•Lakes form and evaporate, leaving
gypsum & anhydrite deposits.
•Periodic marine incursions.
Isolated areas of saline water
evaporate to leave extensive
deposits of rock-salt.
•Lower topographic relief, sluggish river system only capable of
transporting fine-grained material silt/mud;
•Lakes form and evaporate;
•Periodic incursion of seawater, followed by evaporations;
•Mudstones and siltstones with evaporites, including significant rock-
salt deposits.
Hydrogeology WorkshopGeological History (6)
Resulting Stratigraphy (handout)
Date (Ma) Period Epoch
Geology Map Formation No.
Old' clasisification New classification
DescriptionGroup Formation Group Formation
~230
Tria
ssic
f6d
Keuper
Keuper Saliferous Beds
Merc
ia M
udsto
ne G
roup
Wlkesley Halite Mainly rock-salt with this red mudstones
f6c
Middle Keuper Marl Middle Mudstone Mostly red-brown silty mudstone with anhydrite nodules. Silstones in lower part.
f6b
Lower Keuper Sailiferous Beds Northwich Halite Thick beds of red-brown rock-salt, separated by this mudstone horizons.
f6a
Lower Keuper Marl Lower Mudstone Alternating beds of musdstones and siltstones. Gypsum present and thin beds of rock-salt toward top.
f5
Keuper Waterstones Tarporley Siltstones Alternating beds dark red and greean shale (mudstone) and pink-red sanstones (fine grained). Silty toward the top.
~240
f4
Keuper Sandsdtones w/ Keuper Sandstone/Conglomerate.
Sherw
ood S
andsto
ne G
roup
Helsby Sandstone Mainly coarse grained, red-brown, grey/buff sandstones with pebbly bands and comnglomerates.
f3
Bunte
r
Upper Mottled Sandstone Wilmslow Sandstone Fine to medium grained soft red-brown sandstones mottled buff and grey. Some mudstones. Few pebbles.
~245
f2
Pebble Beds Chester Pebble Beds Medium and coarse grained red-brown sandstones. Scattered pebbles and some thin conglomerates.
~250
Permian
ef1
Lower Mottled Sandstone Kinnerton Sandstone Fine to medium grained soft red-brown sandstones. Some thin mudstones near top.
~290+ Carboniferous
d6b
Erbistock Beds Upper Coal Measures
Alternating mudstones and seatearths with a few thin sandstones.
Hydrogeology WorkshopGeological History (7)
Then came the Ice Ages.......