Abstract: Sedimentologic Characterization of the Noyon Uul Syncline, Mongolia
BECK, M. A., University of Montana, Missoula.
The Noyon Uul syncline, southern Mongolia, is an east-west trending structure which provides excellent exposure of Permian through lowermost Jurassic non-marine strata. In the summer of 1997, field work was conducted to evaluate the character of basin sedimentation and its tectonic implications. Five stratigraphic sections, each about 3 kilometers thick, were measured to document stratigraphy, paleoflow and provenance of Mesozoic strata exposed along the flanks of the syncline.
Stratigraphy of the Noyon Uul syncline is characterized in terms
of five facies related to depositional environment. Coarse-grained,
braided fluvial facies consists of coarse sand and pebble to cobble
conglomerate and makes up 25-30% of the Noyon Uul Triassic-Jurassic
record. Large bar sets, up to 10 meters in relief, and large, braid
plain intervals are common. The meandering fluvial facies is
composed of channelized, thick, cross
-stratified sand and
interbedded shale with local caliche and redbed horizons and
comprises 35-40% of the total measured
section
. The shallow
lacustrine facies consists of green and gray shale with thin, cm to
dm scale interbedded sand and massive carbonate layers with
meter-scale thickness. Lacustrine deltaic facies includes dm to m
scale lenticular,
cross
-stratified, channelized sandstone with
abundant soft sediment deformation interbedded with
planar-laminated shale. The deep lacustrine facies consists of
organic-rich, laminated carbonate.
Felsic to intermediate composition volcanic detritus is the
dominant clastic component of sandstone and conglomerate at the
base of the section
, generally comprising over 50% of total clast
content. An increasing component of granite clasts and K-feldspar
grains upsection suggests unroofing of granitic source regions.
Paleocurrent measurements indicate predominantly west-directed
flow, consistent with an axial drainage pattern in front of an
east-west trending highland source region.
The character of depositional environments, paleodispersal patterns and thicknesses of Noyon Uul Mesozoic strata is consistent with the interpretation of a syntectonically developing foreland basin in front of a north-verging thrust system. Such a Mesozoic contractile deformation system has been reported from northern China, 100 km south of Noyon Uul.
AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah