Page 66 - Carbonate Facies in Geologic History

Use of Cycles in Chronostratigraphic Correlation 53

Stage 1

Stage 2

Stage 3

Surface of next • rapid ' ransgressoo

Fig. I1-26. Construction of single sedimentary sequence (upward shoaling cycle) by prograda-
tion or seaward outbuilding of carbonate-evaporite facies

In any event, cyclic sedimentation and sea level fluctuation independent of
local tectonics are both the rule in geologic history. The causes of both may be
sought in normal uniformitarian processes and not in any special conditions in
time and space.

Use of Cycles in Chronostratigraphic Correlation

Rock unit correlation is facilitated by grouping beds into cyclothems, but many
geologists have also employed cyclic sedimentary patterns as a valuable tool in
chronostratigraphic correlation. (For an extended criticism of this method, see
Shaw, 1964, TIme and Stratigraphy.) Following principles stated by Coogan (1972,
p. 5-16) and Krumbein and Sloss (1963), the succeeding arguments may be cited
as support for the proper use of cyclical units as "time markers" (Fig. 11-26).