THE INDONESIAN CYCLOTHEM: MODERN ANALOGUE FOR THE CARBONIFEROUS
D. R. CHESNUT Jr., J. C. COBB and S. F. GREB
Kentucky Geological Survey, 228 Mining and Mineral Resources Building, University of
Kentucky, Lexington, KY 40506-0107, U.S.A.

   The Central Sumatra Basin and adjacent shelf areas contain a record of transgressions and
regressions related to Pleistocene glacio-eustatic sea-level fluctuations. Preliminary analysis of
drill cuttings, hand auger and surface samples, seismic data, and radiocarbon dating was used
to reconstruct a series of buried peats and marine and terrestrial strata in the basin and shelf. The
buried peats appear to be overlain by marine sediment. The radiometric dates of the buried peats
when compared to known sea-level stages indicate that they were formed during lowstand. These
observations suggest that lowstand peats covered by transgressing sediments are most likely to
be preserved. The modern coastal, domed peat of Indonesia is commonly cited as an analogue
for the extensive, low-ash, low-sulfur coals of the Appalachian Basin. This peat, more than 15
meters thick in some places, was first deposited about 7 ka, which corresponds to a glacio-eus-
tatic highstand. However, this peat body is unlikely to be preserved when sea level drops. In fact,
the peat is currently undergoing rapid erosion in some areas.
  In the Eastern Kentucky Coal Field (part of the Appalachian Basin), all of the major coal beds
are overlain by widespread marine and brackish-water strata. The Indonesian coastal, domed
peats deposited at lowstand are more likely analogues for these Appalachian coal beds. The
modem Indonesian highstand peat still serves as a useful example for coal-forming processes.
The transgressive and regressive sediments overlying buried peats in Indonesia constitute probable Pleistocene cyclothems. Whereas the Indonesian cyclothems were modulated by periodicities on the order of 10-3 to 10-4 years, the Appalachian cyclothem were controlled by periodicities on the order of 10-5 years.