re: ribbon chert

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From: Eric Muller (emuller@exploratorium.edu)
Date: Sun Jun 02 2002 - 09:11:42 PDT 

Date: Sun, 02 Jun 2002 09:11:42 -0700
From: Eric Muller <emuller@exploratorium.edu>
Subject: re: ribbon chert
Message-id: <002201c20a50$2f806400$6401a8c0@office>

Hey David,
Good question about the ribbon chert in the Headlands.
I found this on the web at http://www.nps.gov/prsf/geology/geoguide.pdf

"Alternatively, the rhythmic bedding may
represent periodic changes in oceanic upwelling
and siliceous productivity, possibly developed in
response to the earth’s orbital cycles (Decker,
1991). A growing body of literature indicates that
the earth’s 21,000, 41,000 and 100,000 year
orbital cycles, as well as others, are reflected in
biogenic sedimentary sequences (Fischer, 1991).
In any case, diagenesis would have enhanced the
cycles produced by either turbidite or productivity
mechanisms."

Eric Muller
Science Educator
Exploratorium
Teacher Institute
3601 Lyon St.
San Francisco, CA 94123
415 561 0386

www.doscience.com

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