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Re: Ghosts of New Papers Past



>>Gamma rays?

>What next, death rays? Or machine guns? What does one need that kind of
power for?

     See, this is what happens when paleontologists think that biology is
more important than geology for understanding paleontology!   Gamma ray
logging is one means of better correlating what is going on with strata (or
other rocks) in the subsurface with those seen at the surface.  Quotes:

"Downhole geophysical logging involves lowering a probe down a boring by a
cable to acquire readings which represent the physical properties of the
adjacent rock or earth materials. Natural gamma-ray logs record the
naturally occurring radiation emitted from sediments. A sodium-iodide
detector in the probe registers the natural gamma radiation emitted by
potassium-40 and by the natural radioactive decay of uranium and
thorium...This log is useful for distinguishing aquifer materials from other
sediments." (from
http://www.isgs.illinois.edu/maps-data-pub/geologs/gamma-logs.shtml).

"Identification of distinct, genetically related stratigraphic packages in
the subsurface using conventional water resource data sets (e.g. vague
lithologic descriptions and sparse borehole geophysical logs consisting of
spontaneous potential and resistivity) is difficult and often misleading.
Natural gamma-ray (GR) logs record the total radioactivity emitted by
sediments surrounding a borehole, and spectral gamma-ray (SGR) logs measure
the contribution of radioisotopes, potassium (K), thorium (Th), and uranium
(U). These logs permit a more refined interpretation of lithology and a
proxy for determining depositional environments." (from
http://adsabs.harvard.edu/abs/2006AGUFM.V33B0671S).

"Naturally radioactive elements tend to have a far greater concentration in
shales than in other sedimentary lithologies, and therefore the total
gamma-ray log and, in particular, the corrected gamma-ray log (HCGR and CGR)
and the Th log are frequently used to derive a "shale volume" (see Ellis
1987 and Rider 1996). In addition, the shape of the gamma log curve may be
used to reconstruct downhole fluctuations in grain size, and infer changes
in sedimentary facies: the standard approach is to interpret bell shaped
gamma curves as a fining-upwards sequence and funnel shaped gamma curves as
a coarsening-upward sequence (Serra & Sulpice 1975). However, these methods
are only likely to be of use in simple sandstone/shale formations, and are
subject to error when a significant proportion of the gamma ray
radioactivity originates from the sand sized detrital fraction of the rock
(see Heslop 1974 and Rider 1990).

Gamma ray data may also be used to help interpret the environment of
deposition. Unconformities can result in the accumulation of phosphatic
nodules, which may be evident in the spectral gamma log as an anomalous
spike in U. Increased U values, and in particular low Th/U ratios, may also
be associated with marine condensed sequences (Myers & Wignall 1987).
Doveton (1991) used Th/U ratios to estimate paleo-redox conditions at the
time of deposition, which he used to identify generally transgressive and
regressive intervals." (from
http://www.ldeo.columbia.edu/BRG/ODP/LOGGING/TOOLS/add_gamma/text.html).

And also see http://tinyurl.com/chwqa2. 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jerry D. Harris
Director of Paleontology
Dixie State College
Science Building
225 South 700 East
St. George, UT  84770   USA
Phone: (435) 652-7758
Fax: (435) 656-4022
E-mail: jharris@dixie.edu
 and     dinogami@gmail.com
http://cactus.dixie.edu/jharris/

"It's no wonder that truth is stranger
than fiction. Fiction has to make
sense."
                          -- Mark Twain