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K/T Boundary Article

For all of you K/T boundary buffs out there. . .

I haven't seen anything posted on the K/T boundary article that appeared in
the latest issue of Geology (citation and abstract below). In short, Dennis
Terry and his team conclude that a marine K/T boundary sequence is preserved
in South Dakota. Interesting stuff, but I'd like to see some tighter dating.
. .their conclusions should stimulate more research into what was going on
with the Western Interior Seaway at this time.


Geology: Vol. 29, No. 11, pp. 1055–1058.

Marine Cretaceous-Tertiary boundary section in southwestern South Dakota
Dennis O. Terry Jr.*, John A. Chamberlain Jr., Philip W. Stoffer, Paula
Messina, and Patricia A. Jannett


A distinctive zone of disrupted strata, which we interpret as a distal
manifestation of the end-Cretaceous Chicxulub impact event, occurs over 300
km2 in southwestern South Dakota. This disrupted zone is within the Fox
Hills Formation, ranges from 0.5 to 5 m in thickness, and contains
large-scale slump-roll structures, clastic dikes, flame structures, and
massive, homogenized beds. The zone is 0.5 m above a belemnite fauna Sr
dated as 67.6 ± 0.5 Ma, contains scaphitid ammonites characteristic of the
Jeletzkytes nebrascensis ammonite zone of the Fox Hills Formation, and is
capped by a 0.5–4-cm-thick brownish-black mudstone that contains spherules.
Pollen of the late Maastrichtian Wodehouseia spinata palynostratigraphic
zone occurs immediately above and below the disrupted zone. The disrupted
zone is overlain by an additional 25 m of marine Fox Hills Formation. These
stratigraphic relationships suggest that the upper part of the Fox Hills
Formation in this part of South Dakota is Paleocene; that the Western
Interior Seaway was locally present well into the Paleocene; and that
scaphitid ammonites may range the Cretaceous-Tertiary (K-T) boundary.

Andrew A. Farke
South Dakota School of Mines and Technology, Box P404
501 East St. Joseph Street
Rapid City, SD  57701