Boundaries
Diachronous
History of Stratigraphy
High frequency clastic parasequences of shore
Maximum Flooding surface (mfs)
Parasequence
Parasequence
Set
Walther's Law states that "Facies adjacent to one another in a continuous vertical sequence also accumulated adjacent to one another laterally".
However:
• Walther's Law can only apply to a section without unconformities.
• Walther's Law can only apply to a section without subdividing diachronous boundaries, including transgressive surfaces (TS) and the maximum flooding surfaces (mfs).
Paradoxically, though parasequences,
parasequence sets and sequences are subdivided by diachronous surfaces,
Walther's Law is used to interpret the depositional setting of these parcels
of sediment. The diachronous character of the subdividing surfaces is,
to all intents and purposes, ignored and instead it is assumed that the
packets of sediment forming parasequences, parasequence sets and sequences
accumulated penecontemporaneously. In other words the sediments below
and above the bounding surfaces of the sedimentary units in question are
either older, or conversely younger, than that unit. In other words sediments
of a sedimentary unit (parasequences, parasequence sets and sequences)
are assumed to have accumulated synchronously.
The coupling of the "over simple" generalization of the penecontemporaneous
relationship of sediment accumulation and the application of Walther's
Law have made this law a very POWERFUL tool and all sedimentary stratigraphers
use it! In fact the assumption of the synchronicity of sediment accumulation
coupled to the application of Walther's Law is fundamental to the
interpretation of the sedimentary record.
An example of the application of Walther's Law can be seen in Coe et al's
(2003) interpretion (click on link in the left column) of the depositional
setting of high frequency clastic parasequences from sections measured
in the Book Cliff escarpment. Here eastward prograding clastic wedges
of sands and shales mark the Campanian shoreline of the Uinta and Piceance
Basin of Colorado and Utah (click on link in the left column).
The original Walther's
Law was stated as follows:
"The various deposits of the same facies areas and similarly
the sum of the rocks of different facies areas are formed beside each
other in space, though in cross-section we see them lying on top of each
other. As with biotopes, it is a basic statement of far-reaching significance
that only those facies and facies areas can be superimposed primarily
which can be observed beside each other at the present time." (Middleton,
1973)
References and Links
Middleton, G. V., 1973, Johannes Walther's Law of the Correlation of Facies:
Geological Society of America Bulletin, v. 84, p. 979-988.
http://www.gpc.peachnet.edu/~pgore/geology/historical_lab/stratigraphy.php
http://www.arches.uga.edu/~rfreeman/sed_rocks_questions.html
