C. Dewet et al., DISRUPTED COAL AND CARBONATE FACIES WITHIN 2 PENNSYLVANIAN CYCLOTHEMS, SOUTHERN ILLINOIS BASIN, UNITED-STATES, Geological Society of America bulletin, 109(10), 1997, pp. 1231-1248
Two cyclothems contain an unusual suite of disrupted fabrics. This stu
dy's interdisciplinary integration of coal maceral and sedimentologica
l information offers significant new interpretations of coal-limestone
interchange, both depositionally and diagenetically. Disrupted fabric
s within the Herrin Coal and Providence Limestone are interpreted as r
epresenting previously undocumented interactive processes between coal
s and limestones. The Herrin Coal contains brecciated beds that are th
e result of marine transgression over a coastal-plain mire, representi
ng high-energy conditions at the swamp-beach interface. This interface
has rarely been documented in detail. Peat is inherently unstable pri
or to its conversion to coal, and we document this by interpreting con
glomeratic beds in overlying strata. Differential compaction of Herrin
peats generated subaqueous debris flows in the overlying Providence L
imestone. This mechanism for syndiagenetic and early diagenetic sedime
nt deformation has not been previously recognized. In addition, near-s
urface and surface processes produced other disrupted fabrics in the P
rovidence Limestone, such as in situ mosaic breccias, nodular fabrics,
and calcrete horizons. This study also documents that stratigraphical
ly adjacent, alkaline carbonate sediments were further altered by unde
rsaturated acidic pore waters, derived from compacting peats during ea
rly diagenesis. Our interdisciplinary approach to distinguishing and i
nterpreting all of these disrupted fabrics led to a new appraisal of t
he importance of depositional and postdepositional interactions betwee
n coal and limestone. The presence of mire deposits can have a signifi
cant influence on the thickness, distribution, and fabrics in overlyin
g strata. In cyclothems, climatic and eustatic changes may control ove
rall depositional patterns, but peat compaction may determine certain
facies.