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

36 ILLINOIS BASIN COAL RESOURCES
gray, very argillaceous, and contains crinoidal
skeleton elements and bryozoa in abundance.
These beds display no consistent
pattern on electric logs.
8.) In the Ohio-Webster No. 3 drill
hole (sec. 3, T. 5 N., R. 7 E., No. 402)
a caprock limestone, marine shale, black
shale, coal bed, and underclay were found
in the order named beginning 23 feet below
the coal bed described in paragraph 7.
These beds can be identified in all electric
logs represented in the east-west cross-section
for they produce (at the appropriate
position) a pronounced peak opposed by a
small re-entrant in the normal resistivity
curve (pl. 2).
The caprock consists of 3 feet of limestone
which in the upper part is buff to
brown, finely crystalline, and highly fossiliferous.
The fossils consist of encrusting
calcareous algae and crinoidal skeleton elements
which are crowded together in coquina-like
fashion. The basal part of the
limestone is gray to greenish gray, argillaceous,
and includes bryozoa in addition to
algae and crinoids. The limestone is underlain
by 3 feet of gray, calcareous, and very
fossiliferous shale that contains trilobite
fragments and crinoidal remains. This is
followed below by 3 feet of dark gray to
black sheety roof shale with pyritic trails
and ganoid scales, which is underlain by 2
to 3 feet of bony and then clean coal. The
coal bed is underlain by 2 feet of medium to
dark gray calcareous micaceous and pyritic
clay shale that contains medium to dark gray
pyritic limestone nodules. In the southernmost
well of the north-south cross-section
(pl. I), in which this zone was identified
(No. 377) a total of less than 18 inches of
black shale and coal was logged. The black
shale and coal bed can be traced in the northsouth
cross-section southward to the center
of T. 4 N., R. 5 E. (pl. 1, Nos. 121, 377).
It may be represented in the Kenner oil pool
wells (pl. 1, Nos. 495, 398) by a shale 2
feet thick with coalp plant remains found
38 feet below the coal horizon described in
paragraph '7.
9.) A coal bed with overlying black shale
is widespread throughout the areas covered
by the two cross-sectioas (pls. I and 2),
lying generally between 60 to 80 feet below
the bed described in paragraph 8, and 130-
140 feet below the Millersville ( ?) limestone.
In the east-west cross-section the
interval decreases to the east. In the northsouth
cross-section the interval to the next
coal bed above (Paragraph 8) widens to
the south in the area underlain by the overlying
coal zone, as far as the coal zone extends.
The black shale and coal bed together
range in thickness from 1 to 3 feet.
In one well (No. 495)) however, the combined
thickness of the coal and roof shale
amounts to 4 feet, of which 2 feet appear
to be coal, judged on the basis of the drilling
time. A thin caprock limestone 1 foot
thick is locally present, being encountered
in three of the six control wells. The limestone
is buff, brown or gray, finely crystalline,
and locally argillaceous. Fossils, noted
in the cuttings from all three drill holes,
consist of calcareous foraminifera, corals,
brachiopods, and ostracods. The coal bed
is commonly underlain by an underclay or
clap shale which is from 2 to 10 feet thick,
gray to greenish gray, locally calcareous,
and occasionally contains limestone nodules
and siderite spherules.
A limestone I to 6 feet thick is found in
three of the drill holes (Nos. 377, 495, 403)
of the north-south cross-section (pl. 1 ) from
10 to 16 feet below the coal. The limestone
is buff, light gray to greenish gray,
rarely orange, finely granular in some
cuttings and coarsely crystalline in others,
and occasionally argillaceous. The lithologic
character of the cuttings studied by the
writer from one of the wells is that of underclay
limestones, an identification substantiated
by the absence of fossils.
10.) A thin coal bed occurs from 36 to
66 feet below the coal bed described above
(paragraph 9). In the east-west crosssection
(pl. 2)) the interval widens progressively
to the west from 36 to 52 feet,
and in the north-south cross-section (pl. 1 ),
it increases quite irregularly to the south
from 52 to 66 feet. This coal bed is better
identified as the first one above the Shoal
Creek limestone, from which it is separated
by an interval ranging from 43 to 65 feet.