Geology Reference
In-Depth Information
15
Precambrian Tidal Facies
Kenneth A. Eriksson and Edward Simpson
Abstract
The Precambrian stratigraphic record dating back to 3.2 billion years is replete with
examples of interpreted tidal facies. This chapter discusses relevant qualitative as
well as quantitative criteria that support tidal interpretations. Qualitative criteria
include herringbone cross bedding, bimodal-bipolar paleocurrent patterns, tidal
bedding and modified ripples. Quantitative criteria in the form of tidal rhythmites
which display semidiurnal, fortnightly and monthly hierarchical bundling patterns
provide the best evidence for tidal processes during the Precambrian Era. Banded
iron-formations (BIF's), which are unique to the Precambrian rock record,
may record evidence of tidal modulation in the form of Earth-tidal rather than
ocean-tidal rhythms. Preservation of tidal and particularly tidal-flat facies in the
Precambrian was enhanced by sediment stabilization as recorded in microbially
induced sedimentary structures (MISS). Tidal facies in the Precambrian record are
preserved in both transgressive and highstand systems tracts, the latter as progra-
dational delta front-prodelta deposits. Data from the Precambrian record reveal that
despite a closer Earth-Moon distance, at the least in the Archean Era, bedforms
were of comparable scale to those existing today and tidal ranges were probably
mostly macrotidal but not extreme.
15.1
Introduction
opposed to lacustrine conditions in Precambrian
basins. Recognition of marine paleoenvironments is
critical to sequence stratigraphic interpretations of the
Precambrian rock record including construction of
relative sea level curves. Individual qualitative criteria
that have been used in the past in support of a tidal
interpretation are equivocal but in combination may
favor such an interpretation. In contrast, quantitative
data provide better support for tidal processes on
the early Earth and also can be used to constrain
Earth-Moon orbital dynamics. Thus, the purpose of
this chapter is to reevaluate qualitative criteria that
have been proposed in favor of a tidal origin and to
summarize those studies based on quantitative data
In the absence of body fossils, coupled with the dearth
of trace fossils, physical sedimentary structures of
tidal origin provide the best evidence for marine as
