Geology Reference
In-Depth Information
Fig. 16.3 Outcrop of
heterolithic rhythmites from
western Kentucky (see Greb
and Archer 1995, 1998 ).
( a ) Roadcut exhibiting lateral
continuity of mm- to
cm-scale rhythmites and low
angle, large-scale
reactivations. Exposure is
5 m thick. ( b ) Closeup of
planar to rippled lamina that
exhibit prominent dm-scale
bundling. The more sand-rich
zones are less deeply
weathered than the
intervening shale-rich zones.
Scale is 10-cm long
units can contain abundant, well-preserved, carbonized
plant fossils. Many of the shale units are heterolithic
and exhibit a variety of lenticular, wavy, and flaser
bedding (Kvale and Archer 1990 ). Economic coals are
also commonly overlain by heterolithic facies.
of coalified and fragmentary plant materials (“coffee
grounds”) (Fig. 16.4a ). Conglomeratic lags are common
within the lower parts of IVF sandstones. For the EIB,
the conglomerates can include extrabasinal vein-quartz
pebbles. Conversely, in the WIB, the clasts consist of
intrabasinal facies, such as limestone, sandstone, and
sideritic clay chips (Fig. 16.4b ).
In some cases, however, the upper parts of fluvial
sandstones may contain tidal features indicative of
estuarine influences, or the sandstones may be over-
lain by heterolithic facies of coastal-estuarine origin.
In the EIB and WIB, fluvial facies may be overlain by
heterolithic tidal channel or heterolithic tidal flat
facies. In some cases, apparently fluvial channels
are bordered by gray shale wedge facies, which have
tidal indicators.
16.2
Facies Containing Tidal Rhythmtes
16.2.1 Range of Associated Lithofacies
Many of the incised valley-filling sandstones are ori-
ented downdip, which is generally south to southwest,
and are interpreted as fluvial in origin (Potter 1962 ;
Wanless and Wright 1978 ; Archer et al. 1995a ). Cross
bed foresets are sometimes delineated by thin drapes
 
Search WWH ::




Custom Search