Re: Re(3): All kinds of odd observat...

From
Date
Reply-To
The Brazos River K/T section is in my back yard, so I will answer Anthony
Martin's question on how far apart the iridium anomalies are in the section. I
have examined the lithostratigraphy and depositional environments of that
interval. There are 3 Brazos sections for which iridium analyses have been
published: Brazos 1, Brazos 2, and CM-4. In Brazos 1 (the main river bank
section, near the bridge), there are two anomaly peaks about 20 cm apart, the
lower in calcareous mudstones immediately above the HCS sands of the boundary
complex deposits and the upper one in mudstones just above the paleontological
boundary in that section. In Brazos 2 (the downstream river bank section, now
mostly covered by a sand bar), there is one iridium anomaly, shown as a plateau
of similar values over 40 cm, with the top undefined. In CM-4 section (upper
part of Cottonmouth Creek), there are two anomalies about 20 cm apart, one
immediately above the HCS sands and the upper one in a level of mixed mudstone
and sandy mudstone.

The K/T boundary complex at the Brazos sites does contain burrows, both small
and large, including Thalassinoides. The Thalassinoides burrows may be the lower
parts of burrows that originated from higher levels, since much of the overlying
2 metres of Paleocene sediments is conspicuously burrowed. Some lithologies
within the K/T boundary complex are more strongly burrowed than the HCS sands,
which have sparse small and large burrows.

_________________________________________________________________________
Thomas E. Yancey
Dept. Geology & Geophysics
Texas A&M University, College Station, TX 77843-3115
Voice: 409 845 0643    Fax: 409 845 6162
email: tyancey@tamu.edu
                     ---------------------                      (misquoted from)
Complex problems have simple, straightforward, wrong solutions.  (H.L. Mencken)