Geology Reference
In-Depth Information
some limestones in which pressure dissolution
formed in response to burial stress. Structural
geologists recognize that different rocks will pro-
duce different tectonic cleavage with different
spacings, fabrics and forms. Sedimentologists
should recognize that burial stresses, which will
produce dissolution surfaces parallel to primary
bedding, can sometimes produce spaced false
stratifi cation and nodular fabrics where there
originally were none.
(4) Recognize that diagenesis and pressure disso-
lution can accentuate, modify, and even fabricate
layering. Although much of the pressure dissolu-
tion research was done 25 years ago, that does not
mean it is out of date.
ACKNOWLEDGEMENTS
We thank you, Bob, for your stimulating interaction
with us over the years.
DISCUSSION
REFERENCES
This paper has presented examples of the improved
knowledge of what layering means from the expe-
rience of the author as well as that of students and
colleagues with whose work the author is inti-
mately familiar. Other scientists and groups have
also made signifi cant contributions in advancing
our understanding of layering.
Since Ginsburg fi rst asked 'Layering - what
does it mean?' over 40 years ago, signifi cant pro-
gress has been made. Pursuit of this question has
helped sedimentologists fi gure out how modern
environments work and reconstruct the environ-
ments and dynamics of ancient layered sediments
now frozen in stone. However, communicating
this information to other disciplines may not have
been so effective. For example, coastal engineers
and beach managers are commonly still putting
sand that is mostly less than 200 μm on beaches,
wasting taxpayers money and degrading offshore
marine habitats and waters. Sedimentologists
need to do a better job of communicating.
In fi nding these answers many new questions
have emerged, questions for the next generation
of sedimentologists to enjoy. The new generation
can start by carefully questioning our interpreta-
tions and then consider the following important
problems. (1) Tackle the complicated question
of differentiating the several types of layering
that presently are grouped under that heading of
tempestites or hummocky stratifi cation through
careful work in modern and ancient deposits.
(2) Seek improved criteria for differentiating the
fl uvial-tempestite-turbidite-tsunamiite group
of very similar fi ning-upwards sequences (as
Jackson (1976) showed, there is very signifi cant
variabilitywithin these sedimentary deposits).
(3) Be prepared to use textural characteristics and
biological structures in reconstructing physical
processes, as that is commonly all that is available.
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