Digital Database of Modern Evaporites and their Predicted
Distribution Based on Results from an Atmospheric
General Circulation Model Simulation
C. N. Wold, G. J. Schwartz, C. Morrill
1
Introduction
Evaporites are probably the most significant of climatically sensitive sediments,
because they form in only regions where the rate of evaporation greatly exceeds
the rate of rainfall plus runoff. Evaporites, coals, carbonates, tillites, and thick
clastic deposits are among some of the climate-sensitive sediments that have
been used as qualitative and indirect evidence for paleoclimatic conditions.
Several authors have used AGCMs and semi-quantitative methods to explain
the distribution of climatically sensitive sediments for the geologic record. However, only a few models have been based on first principles. Briggs and Pollack
(1967) developed a model to simulate the spatial characteristics of the Late Silurian Salina Formation of the Michigan Basin. Their model had two dimensions
in the horizontal plane, i.e. a Cartesian coordinate map view of the basin. The
rate of evaporation from the surface of the brine was prescribed. They assumed
that water was seeping into the basin radially and were able to simulate a "bull'seye" pattern of evaporites similar to those observed in the Salina Formation.
Pollard and Schulz (1994) developed a proxy formation model for evaporites
that calculated the rate of evaporation over a hypothetical, subaqueous evaporite
basin. In general, a PFM simulates the physical, chemical, and/or biological conditions necessary for the formation of a climatically sensitive sediment (Wold
and DeConto, in press). Pollard and Schulz (1994) applied the PFM for evaporites to the Triassic. The paleoclimate was simulated with GENESIS (Pollard and
Thompson 1995; Thompson and Pollard 1995a; b) using a 4S x 7S grid for the
atmosphere and 2° x 2° grid for the land surface. The experiment of Pollard and
Schulz (1994) did not predict Carnian (225 Ma; Late Triassic) evaporites in the
proto-Atlantic rift. Wold et al. (1994) explained this by the fact that the rift was
not resolved on either the 4.5° x 7.5° or 2° x 2° grids. Wold et al. (1994) increased
the resolution to better resolve the rift valley and mountain flanks. Using the results of the Late Triassic climate simulation (Hay et al. 1994; Wilson et al. 1994)
Wold et al. (1994) then ran the PFM for evaporites and found much better agreement with the observed data.
Wold and DeConto (in press) used the PFM for evaporites (Pollard and Schulz
1994) to predict the potential locations of Late Cretaceous evaporite basins
Distribution Based on Results from an Atmospheric
General Circulation Model Simulation
C. N. Wold, G. J. Schwartz, C. Morrill
1
Introduction
Evaporites are probably the most significant of climatically sensitive sediments,
because they form in only regions where the rate of evaporation greatly exceeds
the rate of rainfall plus runoff. Evaporites, coals, carbonates, tillites, and thick
clastic deposits are among some of the climate-sensitive sediments that have
been used as qualitative and indirect evidence for paleoclimatic conditions.
Several authors have used AGCMs and semi-quantitative methods to explain
the distribution of climatically sensitive sediments for the geologic record. However, only a few models have been based on first principles. Briggs and Pollack
(1967) developed a model to simulate the spatial characteristics of the Late Silurian Salina Formation of the Michigan Basin. Their model had two dimensions
in the horizontal plane, i.e. a Cartesian coordinate map view of the basin. The
rate of evaporation from the surface of the brine was prescribed. They assumed
that water was seeping into the basin radially and were able to simulate a "bull'seye" pattern of evaporites similar to those observed in the Salina Formation.
Pollard and Schulz (1994) developed a proxy formation model for evaporites
that calculated the rate of evaporation over a hypothetical, subaqueous evaporite
basin. In general, a PFM simulates the physical, chemical, and/or biological conditions necessary for the formation of a climatically sensitive sediment (Wold
and DeConto, in press). Pollard and Schulz (1994) applied the PFM for evaporites to the Triassic. The paleoclimate was simulated with GENESIS (Pollard and
Thompson 1995; Thompson and Pollard 1995a; b) using a 4S x 7S grid for the
atmosphere and 2° x 2° grid for the land surface. The experiment of Pollard and
Schulz (1994) did not predict Carnian (225 Ma; Late Triassic) evaporites in the
proto-Atlantic rift. Wold et al. (1994) explained this by the fact that the rift was
not resolved on either the 4.5° x 7.5° or 2° x 2° grids. Wold et al. (1994) increased
the resolution to better resolve the rift valley and mountain flanks. Using the results of the Late Triassic climate simulation (Hay et al. 1994; Wilson et al. 1994)
Wold et al. (1994) then ran the PFM for evaporites and found much better agreement with the observed data.
Wold and DeConto (in press) used the PFM for evaporites (Pollard and Schulz
1994) to predict the potential locations of Late Cretaceous evaporite basins