The Middle Devonian lower Prairie Evaporite Formation of central Saskatchewan
Date
1970-04-01
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Degree Level
Masters
Abstract
The lower Prairie Evaporite of central Saskatchewan consists
of three distinct members, which are named, in ascending order,
the Ratner, Whitkow and Shell Lake Members. The Ratner Member
consists of interlaminated and interbedded carbonate and anhydrite,
the Whitkow Member of halite with anhydrite in the lower part, and
the Shell Lake Member of anhydrite with a medial carbonate unit
called the Quill Lake marker beds.
The carbonate platform of the lower Winnipegosis member is
overlain locally by carbonate banks with up to 300 feet of relief,
which are included in the upper Winnipegosis member. Basinal areas
between these banks became the sites of accumulation of the
lower Prairie Evaporite which reached a maximum thickness of 350
feet. The upper 20 feet of the carbonate banks consist of algal-derived
pisolitic and stromatolitic material, and of some pisolitic
and stromatolitic material which probably formed in the vadose zone
during subaerial exposure. These shallow water and supratidal-subaerial
carbonates extend into the adjacent anhydrite of the Shell
Lake Member in off-bank areas. Thus, the upper portions of the
Winnipegosis banks appear to be equivalent to the uppermost part of
the lower Prairie Evaporite.
The Ratner Member averages 45 feet in thickness and contains
eight distinct units with laminated carbonate and, or, anhydrite,
which can be traced throughout the northern part of the study-area.
Sub-millimeter carbonate laminae, in one of the units, can be
correlated exactly over a distance of two miles. The remarkable uniformity and lateral continuity of layers in the Ratner Member
suggest deposition in a basinal environment with relatively quiet
water conditions. This is contrary to previous investigations which
have inferred a supratidal origin for these sediments. Layers rich
in organic matter have been preserved in these sediments by precompaction
calcitization and dolomitization.
Thick sequences of nodular mosaic and massive anhydrite, of the
Shell Lake and Whitkow Members, formed on the flanks of carbonate
banks. These anhydrites accumulated preferentially on the southeast
sides of carbonate banks. If the regional flow was from the northwest,
maximum evaporite deposition occurred on the leaward sides of banks.
These thick anhydrites are lateral equivalents of, and interbedded
with halite of the Whitkow Member. The relationship of nodular mosaic
and massive anhydrite (Shell Lake-Whitkow Member) on bank-flanks, and
interlaminated carbonate and anhydrite (Ratner Member), and halite
(Whitkow Member), in basinal areas, is analogous to other ancient
evaporite-carbonate occurrences, such as the Zechstein of Germany.
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Degree
Master of Arts (M.A.)
Department
Geological Sciences
Program
Geological Sciences