Page 68 - Carbonate Facies in Geologic History

Use of Cycles in Chronostratigraphic Correlation 55

It is obvious that such chronostratigraphic correlation is essentially intraba-
sinal, although certain thin, lithic units have been carried great distances across
several tectonic provinces (see Wanless, 1972, on coals).
Arguments for the time stratigraphic use of these cycle boundaries and thin
markers are mainly deductive and they should be tested wherever possible against
as much detailed paleontology as is available. Shaw's system (1964) of statistical
treatment of sequence of faunal zones, related to a composite standard, offers a
hope of providing the kind of paleontology zonation needed for this. However,
the requisite biostratigraphic detail with which to check our cyclic correlations is
generally missing. For example: The Late Devonian beds of the Williston Basin
contain perhaps between 25-30 cycles, unusually regular and widespread. At best,
our paleontologic zonation provides only a half dozen zones, whether based on
goniatites, conodonts, or brachiopods, for these Frasnian and Fammenian beds
(estimated time, 15-20 million years). The same duration can be estimated for
Late Paleozoic cycles in New Mexico. The Late Pennsylvanian and lowest
Permian of the Sacramento Mountains, (narrow east shelf of the Oro Grande
basin) consist of approximately 50 cycles through beds in which the best fusulinid
experts can at present find only about 5 or 6 subdivisions of the zones Triticites
and Schwagerina. Time involved in this case must be about 15 million years.
Estimated times (Duff et aI., 1967, p.246) for Late Paleozoic cyclothems range
from 30000 to 300000 years each. Fischer (1964) and Zankl (1971) stated that the
duration of the 300 Triassic Dachstein cyclothems was from 20000 to 100000
years each, deposited within a period of 15 million years.
Therefore, whereas at present the most detailed correlatable paleontologic
zones embrace about one to two million years or so (Hay, 1972), the sedimentary
cycles discussed above were probably deposited in as little as 1/10 to 1/20 of this
time!