Geology Reference
In-Depth Information
near-shore marine depositional environment may have a better chance of
recording an astronomically forced signal than the discontinuous sedimenta-
tion expected for a continental, fluvial depositional environment. However, if
Milankovitch-scale cycles are identified in an ancient fluvial environment, the
timescale of potential shredding processes is constrained and more is learned
about Earth processes.
In this chapter, the case studies will be presented back through geologic
time with the youngest studies first. We will cover rock magnetic cyclostrati-
graphic studies of Plio-Pleistocene marine sediments at the Stirone River
section, northern Italy, Eocene marine marls of the Arguis Formation,
Spanish Pyrenees, Cretaceous platform carbonates of the Cupido Formation,
northeastern Mexico, Triassic platform carbonates of the Latemar, in the
Dolomites of northern Italy, Triassic marine limestones and shales of the
Daye Formation, South China, Mississippian fluvial red beds of the Mauch
Chunk Formation, northeastern Pennsylvania, and the siltstones and car-
bonates of the Neoproterozoic Rainstorm Member of the Johnnie Formation,
Death Valley, California.
6.2
Stirone River Section, Northern Italy
The Stirone River section exposes over 600 m of Plio-Pleistocene marine
sediments in the Po Valley in the Apennines of northern Italy. The section
includes three formations (Colombacci Fm., Argille Azzurre Fm., and
Stirone Fm.) in a coarsening upward sequence of growth strata. Lithologically,
the Stirone River section is comprised of marine mudstones, siltstones, and
sandstones. The rock magnetic cyclostratigraphy was completed by
Gunderson et  al. (2012) on the 342 m of the Stirone Formation which is
composed primarily of fossiliferous silty mudstones. Mary et al. (1993) and
Channell et al. (1994) previously studied the magnetostratigraphy and rock
magnetism of the Stirone River section. In addition to finding a reversal
stratigraphy of Plio-Pleistocene age, they found significant evidence of
secondary iron sulfides as well as primary depositional magnetite. Fossils in
the section also help pinpoint the rock's age.
The Gunderson et al. (2012) study had two parts: 74 oriented samples were
collected at 21 horizons for a magnetostratigraphic study and unoriented
samples were collected every meter from 311 m of section for a rock magnetic
cyclostratigraphic study. The ultimate goal of the cyclostratigraphic study
was to provide a high-resolution age model for the growth strata. The age
model of the growth strata would time the folding of the Salsomaggiore anti-
cline which, in turn, would give a high-resolution measure of fault slip for the
blind thrust driving the anticline upward.
Alternating field demagnetization of the oriented samples revealed a N-R-
N-R-N polarity stratigraphy that could be correlated to the youngest part of the
Gauss (Chron C2A) and the oldest part of the Matuyama (Chron C2) with the
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