| [Thread Prev] | [Thread Next] | [Thread Index] | [Date Prev] | [Date Next] | [Date Index] |
> It's interesting that you bring this point up, since we have this very situation in the K/T boundary sections in New Jersey. Testing for Iridium revealed several spikes, however the section is extensively burrowed by Ophiomorpha nodosa. You can actually see the bright green glauconite of the Hornerstown formation going down into the Maastrichtian Navesink formation through the Ophiomorpha tubes. Oddly, the highest levels were well above this burrowed zone, which is normally considered to be the K/T boundary. Are there any exposures of the K/T boundary in Georgia, as I am not aware of any? Steve Kurth The "piping" of overlying material caused by _Ophiomorpha_ and other trace fossils is a subject that I have been interested in because of the havoc it can cause with fine resolution of boundaries (and in the light of neocatastrophism, boundary events)that are defined by chemical and biostratigraphic markers. What you've described is a great example of how geologically younger sediment can be leaked into underlying layers through burrows or simply mixed into a broad zone by bioturbation. It is a little odd that the highest levels of iridium are above the burrowed zone, though. Here are a few curiousity questions for you, Steve: Is there any evidence of pelletization of the glauconite and subsequent hydrodynamic concentration of pellets into distinctive layers (i.e., flasers)? Is the iridium mostly in the clays (or glauconite)? Most mud in modern environments is deposited as the hydrodynamic equivalent of sand in the form of feces and pseudofeces, so I wonder if the iridium distribution could have been reworked that way, too. After all, you do have evidence of the critters burrowing there, so some of the sediment had to pass through their guts (especially considering that _Ophiomorpha_ is, by definition, a pellet-reinforced burrow). Your question about the K/T boundary in Georgia stumped me for a second because I couldn't remember where there were exposures of it. I checked a Georgia Geological Society field guidebook from 1991 (The Stratigraphic Framework of the Fort Valley Plateau and the Central Georgia Kaolin District: Huddleston & Hetrick) and it has information on exposures. The uppermost Maastrichtian formation in Georgia is the Providence Sand, which pinches out from western to eastern Georgia. However, there's also an unconformity between it and the overlying Lower Paleocene Clayton Formation that becomes more pronounced toward the east; no Maastrictian strata are preserved in east Georgia, as far as I can find in the literature. Anthony J. Martin Geosciences Program, Emory University Atlanta, Georgia USA -- /========/ LearnLink: Expanding Educational Horizons !! !! !! Internet/Telnet: bbs.learnlink.emory.edu !! !! !! For information, mail Info@learnlink.emory.edu /========/ "Minds are like parachutes, they must be open to function."
Partial index: