subsurface geology and coal resources of the pennsylvanian system ...

EDHiARDS COUNTY 6 1
electric logs is generally indicated by a
fairly sharp reverse peak in both the normal
and the third resistivity curves (Nos. 9,
11, 34, fig.8; Nos. 3,91,fig.9; No. 8, fig.
10). This coal bed is believed to occupy
approximately the stratigraphic position of
the LaSalle (No. 2) coal bed of northern
and western Illinois,l%nd in these reports
it is referred to as "No. 2," with the understanding
that it may not always be applied
to the same bed. Spores isolated from coal
cuttings from coal beds at 1200 feet in hole
No. 9 (fig. 8) and at 1125 feet in hole No.
91 (fig. 9) included forms characteristic
of the LaSalle (No. 2) coal bed.13
The Palzo sandstone is the third of the
prominent members of the Carbondale
group mentioned above. This sandstone
marks the base of the Carbondale group,
and is usually 20 to 70 feet thick. In some
localities it is so thin as to be difficult to
spot, or it may be absent. When the sandstone
is very thick it probably possesses
channel form with an uneven base that truncates
lower beds. At the type locality, the
Palzo sandstone extends to, or nearly to,
the top of the Dekoven coal bed in the upper
part of the Tradewater group.'* However,
in some places it appears to extend below the
position of this bed down to, or nearly to,
the top of the Davis coal bed. On the
other hand, in localities where the Palzo
sandstone is thin and less channel-like a
considerable thickness of shale intervenes
between the base of the sandstone and the
Dekoven coal bed. Furthermore, in localities
where the Palzo sandstone is thin, additional
coal beds seem to occur at one and
possibly more positions between the coal
bed regarded as "No. 2" and the Dekoven
bed. It is not always certain whether or
not such beds lie above or below the Palzo
sandstone.
Identification of the Palzo sandstone in
electric logs is in general based upon the
position of a strong indentation of the normal
resistivity curve about 100 feet below
the "No. I" coal bed or about 200 feet be-
l2 White, David. Paleobotanical work in Illinois in 1908:
Illinois Geol. Survey ,Bu!l. 14, p. 293, 1909.
1Verwnal commun~cat~on from R. M. Kosanke.
1'Weller J Marvin, Geology and oil possibilities of
extreme sokthern Illinois: Illinois Geol. Survey Rept. Inv.
71, p. 36 (footnote 13), 1940.
!ow the No. 5 bed. In general this indentation
in the curve appears to mark the position
of the "No. 2" coal bed, but not in all
drill holes (see No. 9, fig. 8). The top oi the
Palzo sandstone lies 525 to 620 feet (average
560-570 feet; see page 63 for detailed
data) below the top of the West Franklin
limestone, or about 300 feet below No. 6
coal bed. It is usually well defined in the
geological records prepared from drill cuttings
(see figs. 8, 9, lo), and its presence is
usually well marked in electric logs by a relatively
conspicuous pattern indicative of
sandstone. This sandstone member and the
massive sandstone lying between No. 6 and
No. 5A coal beds are the two most conspicuous
sandstone members of the Carbondale
group.
The base of the Carbondale group has
been defined as the base of the Palzo sandstone.15
No definition has been given for
the top of the Tradewater group, and as
the Palzo sandstone lies upon an uneven
surface of Tradewater beds, these may extend
a considerable number of feet above
the Dekoven coal bed in some places. It is
*
possible that, like most Pennsylvanian sandstone
~nembers, there are localities where
there is a complete sedimentary transition
from the Tradewater to the Carbondale
group.
The Dekoven and Davis coal beds and
various other members of the Tradewater
and Caseyville groups, including both thin
coal and thin limestone members, are not
yet definitely identified in Edwards County.
STRUCTURE OF THE
PENNSYLVANIAN BEDS
Hrrrin (NO. 6) coal bed.-The accompanying
map of Herrin (No. 6) coal
bed (pl. 4) shows that the structure of the
Pennsj-lvanian beds in Edwards County is
dominated by the regional eastward rise of
I5 Wellcr, J. Marvin. Henbest, Lloyd G., and Dunbar.
Call 0.. Stlatigraphy of the Fusuline-bearing beds of Illinois
(in Pe~lns~lvanian Fu~ulinidae of Illinois by Carl 0. Dunbar,
and Lloyd G. Henbest) : Illinois Geol. Survey Bull.
67, p. 10. 1912.