Tc. Safarudin,"moore, The history and architecture of lacustrine depositional systems in the northern Lake Michigan basin, J PALEOLIMN, 22(4), 1999, pp. 475-496
The post-glacial history of the Great Lakes has involved changes in lake le
vels that are equivalent in vertical extent to the Pleistocene changes in g
lobal sea level and changes in sediment accumulation by at least two orders
of magnitude. In the sediments of the northern Lake Michigan basin, these
radical changes in base level and sediment supply are preserved in detailed
records of changing depositional environment and the impact of these chang
es on depositional architecture. The seismic sequences of the sediment fill
previously described in Lake Huron have been carried into northern Lake Mi
chigan and used to map the history and architecture of basinal deposition.
As the Laurentide Ice Sheet retreated northward in the early Holocene, it o
pened progressively deeper channels to the east that allowed the larger lak
es to drain through the North Channel, Huron, and Georgian Bay basins. At t
he end of the Main Algonquin highstand, about 10,200 (radiocarbon) yrs ago,
the eastern drainage passage deepened in a series of steps that defined fo
ur seismic sequences and lowered lake levels by over 100 m. Near the same t
ime a new source of sediment and meltwaters poured across the Upper Peninsu
la of Michigan and into the northern Lake Michigan basin from the Superior
basin ice lobe. A marked increase in deposition is seen first in the northe
rn part of the study area, and slightly later in the Whitefish Fan area at
the southern end of the study area. Accumulation rates in the area graduall
y decreased even as lake levels continued to fall. Drainage directly from t
he Superior basin ended before the beginning of the main Mattawa phase abou
t 9,200 (radiocarbon) yrs ago.
Although individual lowstand systems tracts are at the most a few hundred y
rs in duration, their geometries and seismic character are comparable to ma
rine systems tracts associated with sea level falls of similar magnitudes.
In some of the thicker lowstand deposits a second order cyclicity in sedime
ntation can be detected in the high resolution seismic records.