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3.3. Troodos Cover: S Side (Gypsum Tbcs (Swallowtails will break up when…
3.3.
Troodos Cover: S Side
Gypsum
Maroni Quarry
A.
Alabastrine Gypsum
Beige, mm-laminated rock displaying razor weathering
Fining upwards of packages
Turbidites ? Fining upwards & periodicity
B.
2° selenite
Chaotically arranaged blades (fishtail)
Diagenetic, 2° given chaotic arrangement
1° selenite would have vertical arrangement
Formed by dissolution of alabastrine
C.
Jumble
Mix of cm-scale selenite fragments
On top of outcrop
Big sutures
2 bands selenite meet in centre
Gypsum Sequence
Pakhna marl
Low ρ gypsum turbidite
Mass flow from basin margin
Gypsum Tbcs
Swallowtails will break up when flow down slope
Palaeoslope w gypsum source downslope
Slope becomes unstable
Gypsum cascaded down into basin forming turbidites
Turbidites form nr depocentre - deeper centre of basin
Mass flow deposits of gypsum on margin
What prompted reprecipitation?
Seawater influshing dissolves gypsum if crystals = fine enough
∴ Alabastrine --> 2° selenite
Selenite 'vein'
Evidences conduit for fluid flow
Crack opens - selenite nucleates on valley wall
With further opening, selenite blades nucleate
Suture forms when selenite crystals meet in centre of crack
Extension required
Crack w bladed crystals growing toward centre
Diagenesis alabastrine
Evap seawater once overstep solubility
Start to precipitate crystals throughout water column
V unstable
Lotsa randomly oriented crystals pushed together
If energy added
System looks to reduce energy & disorder in system
Water flushed through system
Dissolves crystals
Nucleates in more stable orientation around water source
Celestite
=
Sr sulphate mounds
Swirly lamination, fine grained parts of block
Strontium enrichment via seawater evap
Stromatolite
Water fountains form due to algal activity
Result from
gwater seeps & bacterial activity
Formation
Precipitation of Sr enriched gwater
Trapping of sediment by bacterial mounds
Dissolve gypsum @ Z - release Sr - remobilise to precip @ surface
Source Sr
Diagenesis of gypsum @ depth
2° selenite has lower Sr
Upward gwater flow
Groundwater carries Sr rich water upward
Only possible if gwater pools = punctured i.e. by faults
Upward artesian flow recharges aquifer on palaeoslope
Order of precip if evap seawater
Carbonate conc
Dolomite conc
Strontium conc (last to precip)
Stromatolite Formation
= Semihemispheric radiating accumulation
Water seeps out, Sr precipitates on surface
Thin algae cover trapps material
More water seeps out & so on...
Kalavassos
(U. Miocene)