SILURIAN (TIPPECANOE) CARBONATE ENVIRONMENTS
AND SABKHA EVAPORITES IN CENTRAL NORTH AMERICA
Isopleths of Salt Concentrations
Evaporite
Sequence
(Repeated
many times)
NaCl
NaCl +
CaSO4
75
would require
evaporation of 1000
50
Michigan
Basin
25
Illinois
Basin
SW
Reef
Pinnacle
Michigan Basin
(Barrier)
Reef
1500 m 750 m dolomite
750 CaSO4- NaCl
(Stratigraphic Basin:
Subsidence = Deposition)
NE
CaSO4 H 2O
CaMgCO3
100%
91%
85% CaSO4
10% NaCl
All CaCO3 precipitated
81% 1/3 CaSO
4 precipitated
KCl/MgCl
NaCl
NaCl
57%
CaSO4
CaSO4 H2O
31%
7%
CaCO3
523
457
Dens
i
ty si
nking
of
OF
Normal Salinity
199
332
NaCl brines
accumulating
brines
High Salinity
ENLARGEMENT
Illinois
Basin
Shelf + Patch Reefs
MICHIGAN BASIN SHOWING PROCESSES
AND DOLOMITE GENERATION
72
34 o/oo
Sill
li
Lo w S a
OF
nit
M g r i ch b r i n e
s
y
EVAPORITE DEPOSITION
dolomitization by
refluxing Mg rich brines
spilling over sill after
basin filled