| dc.description.abstract | The study interpreted depositional environments from sedimentological data present
in metasedimentaiy rocks of the Neoarchean Shebandowan Group of the Wawa
Subprovince. Outcrops in the study area contained sedimentary structures and bed
sequences consistent with shallow water, coastal sedimentation, and represents an
Important record of Archean depositional processes. Three depositional environments
are represented In the rock record; tidal strandline, the shoreface, and the offshore. The
tidal strandline was further divided Into the tidal flat and tidal channel sub-environments.
The presence of these three environments provides unequivocal evidence for the
existence of shallow-water shelves In the Archean; a period during which sedimentation
was dominated by deposition in alluvial fan, fluvial environments and deep water settings.
The three environments and associated sub-environments record processes reflective
of differing current activity which controlled and Influenced deposition. The tidal
environment was dominated by bidirectional tidal currents. Deposition In the shoreface
was predominated by unidirectional wave-produced currents which overprinted prevailing
tidal current activity, in the distal portions of the shoreface environment though,
deposition was once again controlled by tidal currents. In the offshore, deposition was
controlled by storm currents which generated distinctive beds of hummocky cross-stratification.
The tidal environment Is composed of many sedimentary structures similar to those
present In Phanerozoic and present-day tidal sequences. In the tidal flat sub-environment,
vertical sequences of flaser, lenticular, wavy and coarsely interlayered
bedding reflect current velocity fluctuations Intimately tied to spring - neap tidal cycles.
The tidal channel sub-environment lacks many of the features characteristic of tidal
channels described In the literature; such as extensive point bar development. Instead
the tidal channels of the study area appear to represent sequences deposited In relatively
straight channels.
Migration of sandwaves and dune fields deposited the cross-stratified lithofacies of
the shoreface environment. Similar to a high-energy non-barred coastline, the proximal
portion of the shoreface lacks any evidence of beach development. Instead, the
shoreface records a rapid and discontinuous transition from the tidal strandline
environment.
Hummocky cross-stratification (HCS), parallel laminated and massive sandstone beds
as well as slltstone and mudstone beds typify the offshore environment. The HCS differs
greatly In thickness and intemal structure from HCS described In the literature. The HCS
In the study area reflects restricted and/or variable sediment supply and flow conditions.
A paleotidal range was determined from the sediments of the tidal environment. The
range Indicated a mesotidal environment and is comparable to Precambrian tidal ranges
reported In the literature. Tidal rhythmites, present on the tidal flats, suggest a length of
26 days for the NeoArchean lunar month. Currents which deposited the tidal rhythmites
produced both semidiumal and diurnal sediment sequences. | |
