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Re: Keller keeps punchin'



At 06:13 PM 4/14/2003 -0400, Dinogeorge@aol.com wrote:
In a message dated 4/14/03 12:25:40 PM Pacific Daylight Time,
jbois@umd5.umd.edu writes:

<< Drilling at Yucatan reveal, they say, microfossils 300,000 years after
 supposed extinction: >>

Could have washed back in at the time the crater was made. Also, it now seems
as if Chixculub was just one crater from a nearly simultaneous worldwide
bombardment.


Microfossils in the water column settle according to Stokes settling law, (as does everything) and one must consider factoring in current, both surface, and stratified, as well as Ekman spiral, among other motion in the water column. "Fines" - those particles less than 4-Phi in size, settle very slowly even in a 100% quiet environment (such as a graduated cylinder lab experiment in which one demonstrates how painfully long it takes to settle the fines in a 100% quiet water column) "Washing back in" after the impact doesn't happen exactly the way the mental image the words provide. Such things as palynomorphs & diatoms, since they are in the very small fines, must be looked at in conjunction with additional evidence prior to accepting the date they themselves often provide - why? - because the smallest sedimentary particles are the most easily picked up and reworked, and thus, are not always the most convincing chronostratigraphic indicators when presented by themselves because of the extremely high potential for reworking. I, and a multitude of other scientists, do trust foraminifera for biostratigraphic age dating - many of which made it through the K-T boundary with ease, both sessile and vagrant benthonic forms as well as many planktonic forms. My personal favorite is Neogloboquadrina pachyderma. Albeit a little young for this discussion, it descended from survivors. A lovely little beast prone to switching to sinistral coiling when it gets colder.......

Gerta Keller is one of the top marine microfossil researchers in the world and she is highly respected - I have a suspicion she hammered her data profusely before she published it. I'm dying to read the entire report, not just the "bite" ................

Carry on,


********************************* Marilyn D. Wegweiser, Ph.D. Assistant Professor of Geology Curator, Paleozoic & Mesozoic Collections Department of Biological and Environmental Sciences Georgia College & State University Milledgeville, GA 31061 Office: 478-445-2441 FAX: 478-445-5290

http://www.faculty.de.gcsu.edu/~mwegweis/
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Director: This Side Of Hell, WY Research Project; it's north of Pitchfork Wyoming, north of Hell's Half Acre, Wyoming, west of Hell, North Dakota, and south of Hellroaring Plateau, Montana. Could it get any better than this?