352
W. L. Watney . J. Kruger· J. c. Davis· J. Harff . R. A. Olea, . G. C. Bohling
The overall lithofacies and stratigraphic pattern in the Nuyaka Creek GS suggests transgression-regression. Transgressive clastics dominate the base of the
genetic unit shelfwide, with larger amounts of clastics supplied early and late in
the cycle along the landward (northwestward) end. This also suggests a proximal
source of clastics at this location. The pattern suggests a probable relative rise
and fall in sea level. Previous studies demonstrate that these landward clastics
are comprised of mixed red and green silty deposits with considerable evidence
for episodic subaerial exposure (Watney 1980; Watney et al. 1997). In contrast,
the lower clastic section is thicker on the lower shelf and basin margin, dominating the lithofacies in this region up through the Hushpuckney GSu. The thicker
lower clastics on the lower shelf are possibly the result of sustained deeper water
that precluded development of carbonate sediments.
4.2
Munice (reek Genetic Set
In general, the Muncie Creek GS exhibits much more variation in thickness and
lithofacies than the Nuyaka Creek GS in the area of the cross-section. Thicknesses increase markedly from shelf to toward the basin. The base of the Muncie
Creek GS is a prominent condensed section of the Muncie Creek Shale. Carbonate facies of the lower Munice Creek GS are displaced landward some 100 km
from the carbonate bank margin of the underlying Nuyaka Creek GS to near
SAR boundary D (Fig. 5). The backstepping is also associated with landward displacement of more carbonate-dominated lithofacies compared to the Nuyaka
Creek GS. The landward mixed clastic-carbonate lithofacies appears to have
been removed from the area of the cross section. The carbonate margin is very
abrupt occurring in less than 2 km with an estimated slope of 3°. The carbonate
GSUs thicken at the margin before downlapping into the basinward clastics. The
exact horizon of downlap of each GSU is conjectural until more biostratigraphic
data are obtained.
Clastic proportions increase toward the top of the lower carbonate-dominated Muncie Creek GS. The lower carbonate interval is abruptly overstepped by
clastics that extend considerably landward, thinning and lapping out slightly
landward from the SAR A boundary. This lapout is 200 km landward from the
carbonate bank margin in the Nuyaka Creek. Backstepping and inferred relative
sea-level rise was interrupted by fluctuations in sea level resulting in accumulation of sandstone in front of the lower Muncie Creek GS carbonate bank
(Winchell 1957). This has been effectively described as low-stand deposition, in
part, the result of sediment bypassing through incised valleys cut into the shale
succession on other parts of this shelffarther to the east (Archer et al. 1994). Also, the Douglas Limestone appears to represent sea-level fluctuation, lapping out
onto the mid-shelf position as sediment accommodation is apparently lost.
The geometry of the Douglas Limestone and the lower reaches of the Toronto
Limestone parallel each other and could also be described as offlap, suggesting
that they represent lateral accretion events (GSU scale?) within the upper
W. L. Watney . J. Kruger· J. c. Davis· J. Harff . R. A. Olea, . G. C. Bohling
The overall lithofacies and stratigraphic pattern in the Nuyaka Creek GS suggests transgression-regression. Transgressive clastics dominate the base of the
genetic unit shelfwide, with larger amounts of clastics supplied early and late in
the cycle along the landward (northwestward) end. This also suggests a proximal
source of clastics at this location. The pattern suggests a probable relative rise
and fall in sea level. Previous studies demonstrate that these landward clastics
are comprised of mixed red and green silty deposits with considerable evidence
for episodic subaerial exposure (Watney 1980; Watney et al. 1997). In contrast,
the lower clastic section is thicker on the lower shelf and basin margin, dominating the lithofacies in this region up through the Hushpuckney GSu. The thicker
lower clastics on the lower shelf are possibly the result of sustained deeper water
that precluded development of carbonate sediments.
4.2
Munice (reek Genetic Set
In general, the Muncie Creek GS exhibits much more variation in thickness and
lithofacies than the Nuyaka Creek GS in the area of the cross-section. Thicknesses increase markedly from shelf to toward the basin. The base of the Muncie
Creek GS is a prominent condensed section of the Muncie Creek Shale. Carbonate facies of the lower Munice Creek GS are displaced landward some 100 km
from the carbonate bank margin of the underlying Nuyaka Creek GS to near
SAR boundary D (Fig. 5). The backstepping is also associated with landward displacement of more carbonate-dominated lithofacies compared to the Nuyaka
Creek GS. The landward mixed clastic-carbonate lithofacies appears to have
been removed from the area of the cross section. The carbonate margin is very
abrupt occurring in less than 2 km with an estimated slope of 3°. The carbonate
GSUs thicken at the margin before downlapping into the basinward clastics. The
exact horizon of downlap of each GSU is conjectural until more biostratigraphic
data are obtained.
Clastic proportions increase toward the top of the lower carbonate-dominated Muncie Creek GS. The lower carbonate interval is abruptly overstepped by
clastics that extend considerably landward, thinning and lapping out slightly
landward from the SAR A boundary. This lapout is 200 km landward from the
carbonate bank margin in the Nuyaka Creek. Backstepping and inferred relative
sea-level rise was interrupted by fluctuations in sea level resulting in accumulation of sandstone in front of the lower Muncie Creek GS carbonate bank
(Winchell 1957). This has been effectively described as low-stand deposition, in
part, the result of sediment bypassing through incised valleys cut into the shale
succession on other parts of this shelffarther to the east (Archer et al. 1994). Also, the Douglas Limestone appears to represent sea-level fluctuation, lapping out
onto the mid-shelf position as sediment accommodation is apparently lost.
The geometry of the Douglas Limestone and the lower reaches of the Toronto
Limestone parallel each other and could also be described as offlap, suggesting
that they represent lateral accretion events (GSU scale?) within the upper