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ABSTRACT

Exceptionally thick (over 15 m) deposits of peat which fill the northern end of Sucker Lake basin in northcentral Michigan document the volumetric importance of allochthonous organic material in a modern coal-forming environment. Organic debris that originates in, and is derived from, a highly vegetated floodplain immediately upstream is deposited as a lakeward-prograding lobe that exhibits features typical of most lacustrine Gilbert deltas, but is composed almost entirely of organic material. This system overlies an additional 7 m of nearly pure, brecciated lacustrine carbonate, deposited as shallow lake-margin benches and emplaced into the deep basin centre by gravity sliding prior to deltaic progradation.

In the southern end of the basin, bottomset beds of fine silt-size organic phytoclasts onlap distal facies of progradational bench carbonates, which originate (in shallow water) through calcite encrustation about stems of the dominant macrophyte Chara. With continued sedimentation, a stratigraphic succession in which allochthonous organics will overlie pure, allochthonous lacustrine carbonates and in part be overlain by autochthonous carbonates will characterize the northern end of this Holocene system. In the southern end around the basin margins, however, autochthonous carbonates will entirely underlie allochthonous organics.

Numerous continuous cores (up to 22 m) through these units document: (1) the importance of sources of allochthonous organic debris in modern coal-forming complexes, (2) the genetic relationship between nearly pure calcareous and nearly pure carbonaceous facies within these paludal-lacustrine settings, and (3) the complexity of interrelationships between the several component facies within such continental sedimentary systems.