Sequence
Stratigraphy of the lower portion of
the Upper Trissic Chinle
Formation, southcentral Utah, USA
Joseph Beer, University of Minnesota
Duluth,
Department of Geological Sciences, Duluth, MN, [email protected]
Field and
well
log
data
from central Utah
identify three
sequence
bounding unconformities in the lower portion of the Chinle (Shinarump, Monitor Butte,
Temple Mountain, and Moss Back Members) which
function to divide these deposits into three periods of incision and subsequent
valley fill. The initial period of degradation is marked by interfluve
paleosols and truncation of the underlying Moenkopi Formation creating a paleovalley
which constrains the deposition of these four members. The first paleovalley fill, represented by the Shinarump
Member, is interpreted as a confined sandy low-sinuosity river system. A second
period of incision is marked by truncation of the Shinarump
and correlative paleosols and pedogenically
modified strata. The Monitor Butte and correlative Temple Mountain Members overlie
this unconformity and consist of mudstones and sandstones representing fluvio-lacustrine deposition and vertisols
and interbedded mudstones and sandstones deposited in
a high-sinuosity river system. A final cut and fill within the pre-Shinarump paleovalley is filled
by the high- and low-sinuosity fluvial deposits of the Moss Back Member.
Truncation of the Monitor Butte and Temple Mountain Members and the Moenkopi Fm. and interfluve pedogenesis mark the preceding surface of degradation.