Re: "Meteor theory gets rocky ride from dinosaur expert"

[jrc <jrccea@bellsouth.net>]

----- Original Message ----- 
From: "Phil Bigelow" <bigelowp@juno.com>
To: <dinosaur@usc.edu>
Sent: Friday, May 27, 2005 1:09 AM
Subject: Re: "Meteor theory gets rocky ride from dinosaur expert"


> If the southern end of the seaway was closed, ....

PALEONTOLOGY OF THE K/T BOUNDARY INTERVAL: BADLANDS NATIONAL PARK, SOUTH 
DAKOTA


JOHN A. CHAMBERLAIN, JR .(1), DENNIS O. TERRY, JR. (2), PHILIP W. STOFFER 
(3), MARTIN A. BECKER (4)

Abstract-We have documented a distinctive zone of disrupted sediments over 
300 km2 in the Badlands area of South Dakota. This Disrupted Zone (DZ) is 
located in the Maastrichtian Fox Hills Formation about 20 meters above its 
transitional contact with the Pierre Shale, and ranges from 0.5 to 5 meters 
in thickness. Based on Sr age dates, sedimentary features, and impact 
ejecta, we interpret the DZ as a distal manifestation of the end-Cretaceous 
Chicxulub Impact Event. The DZ occurs in an interval with uncommon, but 
significant fossil content. Scaphitid ammonites characteristic of the 
Jeletzkytes nebrascensis ammonite zone occur below and within the DZ, but 
not above it. In addition, the sections, including the DZ itself, contain 
nuculid and inoceramid bivalves, osteichthian and chondrichthian remains, 
crustacean crawling traces, leaf fragments, and disseminated, and sometimes 
carbonized, plant debris. Compared to earlier late Cretaceous faunas of the 
Western Interior, the Badlands K/T fauna is impoverished in that it contains 
relatively few species. This impoverishment is unrelated to the end-K 
impact, and is more likely the result of environmental conditions in the 
Seaway coupled with the high-stress conditions of local environments within 
which the Badlands fauna lived.

____________________


INTRODUCTION
     Figure 1. Paleogeography of North America at the end of the Cretaceous 
Period based on recent ammonite biostratigraphy. WIS _ Western Interior 
Seaway. BNP _ Badlands National Park. Modified from Fig. 1 of Terry et al. 
(in review). Paleogeographic data from Kennedy et al. (1998).

During late Cretaceous time the Western Interior Seaway, an epeiric sea of 
considerable extent, covered much of the mid-continent region of North 
America. Kennedy et al. (1998) suggest that during the Jeletzkytes 
nebrascensis zone of the Late Maastrichtian the Seaway extended northward 
from the Cretaceous Gulf of Mexico to North Dakota (Figure 1). However, the 
absence of marine sections that can be unequivocally dated to the latest 
Maastrichtian or to the Cretaceous/Tertiary transition (e.g. Obradovich, 
1993) has generally been interpreted to mean that the Seaway had retreated 
completely from the northern plains region of the United States by the end 
of the Cretaceous. In this scenario, marine rocks of early Tertiary age, the 
Cannonball Formation for example, necessarily imply the temporary return of 
marine conditions during the early Tertiary.

The late Cretaceous succession exposed in and near Badlands National Park in 
southwestern South Dakota contains evidence that challenges this view. In 
two recent papers (Stoffer et al. 2001; Terry et al., in review), we 
describe a zone of distorted bedding in the marine rocks of the Badlands 
area (referred to here as the DZ) which resembles the highly contorted, 
chaotic bedding seen in some Gulf of Mexico K/T boundary sections 
(summarized in Smit et al. 1996). Moreover, the Badlands DZ interval 
contains impact ejecta and fossil occurrences which suggest association with 
biotic and geologic events that mark the end of the Cretaceous. The Badlands 
DZ is conformably overlain by a considerable thickness of what thus would be 
earliest Paleocene marine sediments. In suggesting continuous marine 
deposition across the K/T boundary in the Badlands area, this interpretation 
implies that the Seaway had not disappeared from the northern plains at the 
end of the Cretaceous, but was a significant paleogeographic feature in this 
area well into the Paleocene


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