Transcript Northern Resources Development Overview of the Stratigraphy Earth Sciences Sector and Sedimentology of the Bowser, Sustut and Skeena Groups Northern Resources Development Peter Mustard Carol Evenchick Margo McMechan David.

Northern Resources Development
Overview of the Stratigraphy
Earth Sciences Sector
and Sedimentology of the Bowser,
Sustut and Skeena Groups
Northern Resources Development
Peter Mustard
Carol Evenchick
Margo McMechan
David Ritcey
Fil Ferri
Gareth Smith
Northern Resources Development
REGIONAL STRATIGRAPHIC SUMMARY
 basins span most of middle Jurassic to Late Cretaceous (with gaps)
 overlie Triassic and lower Jurassic volcanic arc rocks (Stuhini, Hazelton groups)
• in total >7 km of maximum
stratigraphic thickness
• most major siliciclastic
environments of deposition –
alluvial fan to deep marine
slope / fan complexes
• 2 (or 3) separate basins of
deposition
• locally sourced, mostly
from NE, East and (minor)
South
modified from Evenchick and Thorkelson, GSC Bull. 577, in press
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STRATIGRAPHIC
FRAMEWORK
MESOZOIC BASINS
Late Cretaceous
Sustut Basin
• nonmarine
Table of formations, Spatsizi River map area.
Time scale of Okulitch et al. (1999).
1.7
5.3
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MESOZOIC ARCS
Triassic and lower Jurassic
volcanic arc rocks (plutons,
volcanic rocks, related
sedimentary rocks)
145
157
178
200
251
STIKINE ASSEMBLAGE
Paleozoic metavolcanic rocks,
metaplutonic rocks, carbonates
modified from Evenchick and Thorkelson, GSC Bull. 577, 2003/in press
Group
Jurassic-Cretaceous
Bowser Basin (+Skeena
Group)
• marine and nonmarine
Skeena
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STRATIGRAPHIC FRAMEWORK - BOWSER LAKE GROUP
Lithofacies assemblages
 new stratigraphic approach to better deal with the Bowser Basin on regional
scale and provide conceptual tools for interpreting basin architecture and
depositional history (when integrated with regional fossil distribution)
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STRATIGRAPHIC FRAMEWORK - BOWSER LAKE GROUP
Lithofacies assemblages
•
integrating distribution of
lithofacies assemblages with
fossil data gives a general
picture of depositional history
of the basin on a regional
scale
•
Jurassic- earliest K: overall
progradation of shelf and
non-marine successions to
southwest over deeper
marine strata
•
“mid”- Late K –: reactivation
of isolated and mostly nonmarine basin fills related to
compression of older strata
(forms Devils Claw Fm and
Sustat Basin)
modified from
Evenchick et al.,
2001, GSC Open
File 3956
modified from Evenchick and Thorkelson, GSC Bull. 577, in press
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STRATIGRAPHIC FRAMEWORK - BOWSER LAKE GROUP
•Basin stratigraphy reflects
changes in deposition from deep
water to shelf to nonmarine
environments.
•A general progradation with time
though with lots of lateral
complexities
modified from Evenchick and Thorkelson, GSC Bull. 577, in press
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Submarine Fan to Slope deposition
Ritchie-Alger assemblage
(submarine fan)
 sandstone, siltstone, rare
conglomerate - > 1000 m thick
dominates much of west of
basin
 sheet-like intervals up to 50m
thick dominated by fine- to
medium-grained sandstone
sheets
 abundant turbidite features
 minor conglomerate debris
flows

Todagin assemblage (slope)
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Todagin assemblage (slope)
Ritchie-Alger assemblage (submarine fan)
 100’s to > 1000’s m
mudstone/siltstone > finemedium sandstone,
conglomerate
 mainly dark gy laminated
siltstone and fine grained
sandstone, few current
structures
 syndepositional minor
faults + extensive slump
folds common
chert pebble conglomerate
occurs as lenses –
commonly 100’s m extent
and 10’s m thick

Submarine Fan to Slope deposition
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Open Shelf Deposition
Cranberry River assemblage
(sub-wavebase shelf)
10’s to 100’s m thick unit transitional
below shoreface sandstone of
Muskaboo assemblage
Silty mudstone and siltstone with
<5% fg sandstone
Massive to faintly laminated, locally
pyritic, locally bioturbated
Sandstone as distal turbidite thin
beds or massive to vaguely rippled
sandstone

Muskaboo assemblage (shoreface)
Open Shelf Deposition
Muskaboo assemblage (shoreface)
Cranberry River assemblage
(sub-wavebase shelf)
 med-fg sandstone > siltstone >>
conglomerate;
 sst commonly in laterally
continuous thin- to thick-bedded
sheets and bedsets
locally arranged in coarsening-up
cycles
 common traces, bivalve coquina,
and other marine fossils,
 common ripple marks and cross
bedding, with local hummocky cross
stratification; flaser / lenticular bedding
etc.
 wide range of shallow shelf
shoreface environments
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Deltaic to transitional fluvial assemblages
Groundhog-Gunanoot assemblage (deltaic)
Skelhorne assemblage (deltaic)
Eaglenest assemblage (deltaic)
 conglomerate, sandstone, siltstone,
mudstone, rare coal
 coarsening- and fining-up cycles of
mudstone to pebble-cobble conglomerate
 prominently rusty weathering, and 30
to 80% conglomerate; sheets of
conglomerate to 50 m thick include
planar beds, tabular planar cross
stratification and trough cross
stratification
 sparse marine fossils but abundant
plant fossils, including silicified log
fragments

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Deltaic to transitional fluvial assemblages
Groundhog-Gunanoot assemblage (deltaic)
Skelhorne assemblage (deltaic)
Eaglenest assemblage (deltaic)
 thinly interlayered and vari-coloured
siltstone, sandstone, and conglomerate
(with or without coal)
 coarsening- and thickening-upward
cycles, stacked 10’s m successions
with sandstone >> conglomerate
 plant and marine fossils are
ubiquitous, trace fossils including
Skolithus and Diplocraterion are
common, as are log fragments several
metres long

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Deltaic to transitional fluvial assemblages
Groundhog-Gunanoot assemblage (deltaic)
Skelhorne assemblage (deltaic)
Eaglenest assemblage (deltaic)
 fine-medium sandstone,
siltstone, carbonaceous and
calcareous mudstone, minor
conglomerate and minor to
significant coal
10’s m fining-up cycles
 finer grained strata are thinly
bedded and locally include
densely packed plant fossils;
conglomerate sheets and lenses
plant fossils are common, and
include in-situ trees; marine
fossils are rare

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Non Marine Alluvial to floodplain
Devils Claw Formation (alluvial, fluvial)
Jenkins Creek assemblage (nonmarine
floodplain fluvial)
 mudstone, siltstone, med-fg
sandstone, rare conglomerate
and coal; commonly arranged
in fining-up succesions
 grey, green, and brown
weathering siltst/sst as
laterally continuous sheets,
discontinuous sheets, and
channelized lenses
fossil plants abundant,
including in-situ roots and
plants with delicate structure;
marine fossils absent
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Non Marine Alluvial to floodplain
Devils Claw Formation (alluvial, fluvial)
Jenkins Creek assemblage (nonmarine
floodplain fluvial)
 conglomerate, sandstone, siltstone
 30-80%) pebble conglomerate in
laterally continuous sheets with largescale cross bedding
 conglomerate forms bases of
fining-up cycles with medium-grained
sandstone, fine-grained sandstone,
carbonaceous siltstone, minor coal
 fossil plants common; marine
fossils absent
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STRATIGRAPHIC FRAMEWORK - SUSTUT GROUP
> 2000 m of nonmarine clastic strata, divided into two formations:
Brothers Peak Formation
Tango Creek Formation
• unconformably overlies
Bowser Lake Group or older
units on NE and East side of
basin
• Early to Late Cretaceous
age (early Albian to
Maastrichtian)
• internally conformable
prograding successions of
floodplain, braided fluvial and
alluvial fan sedimentary
rocks
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STRATIGRAPHIC FRAMEWORK - SUSTUT GROUP
Tango Creek Formation
 > 700 m thick - Albian to Late Campanian
 overlies lower units (including BLG) with angular unconformity
base of quartz pebble conglomerate or coarse fanglomerate
 overlain by primarily sandstone, siltstone, and red/green/gray mudstone.
 Sandstone occurs as sheets and lenses of quartz- and chert-rich feldspathic
arenite, with detrital white mica (differs from BLG sst)
 floodplain deposits with generally westerly directed paleoflow
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STRATIGRAPHIC FRAMEWORK - SUSTUT GROUP
Brothers Peak Formation
 Conformably overlies Tango Creek Fm; Late Campanian to Maastrichtian age.
>
1000 – 1500 m thick in many places
 Characterized by polymict conglomerate, sandstone, and siliceous tuff.
 Commonly basal conglomeratic succession more than 50 m thick which includes
siliceous ash-fall tuff (but some tuffs in Tango Crk too!).
K BP
K TC
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STRATIGRAPHIC FRAMEWORK - SUSTUT GROUP
Brothers Peak Formation
 overlain by a succession dominated by pebbly
sandstone, siliceous ash-fall tuff, and mudstone, with
rare coal.
 deposited as fluvial and debris flow deposits in
various alluvial fan environments transition to
floodplains
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Skeena Group
• Early K succession
preserved along the
present southern margin
of “Bowser Basin”
• mapped as separate,
overlying sedimentary
succession in 60’s/70’s
(e.g. Tipper and
Richards, 1976), but only
mapped at “recon” scale
Skeena Group
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 > 1-1.5 km thick composite
stratigraphy
 mix of non-marine and
marine shelf mudstone,
sandstone, conglomerate and
coal
Modified from
Bassett, 1995
Skeena Group
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 includes significant
intrabasinal Albian volcanic
event (not present in classic
Bowser Basin)
 capped by Cenomanian fluvial
chert pebble conglomerates
derived from east
Modified from
Bassett, 1995
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Skeena Group
Stratigraphy
Previous formations
names not widely
accepted (except Rocky
Ridge Fm volcanic unit)
 generally interpreted
as separate from
Bowser Lake Group
units though in part
overlaps in time with
upper BLG
Modified from Bassett and
Kleinspahn, 1997
Stratigraphic scheme
from Bassett, 1995, PhD
thesis
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There is a Bowser to
Skeena Group
transition
 now can document 3
separate and somewhat
different types of
transitional contacts
between marine strata
typical of BLG Muskaboo
Crk assemblage and
non-marine strata
typically called Skeena
Group in these areas
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There is a Bowser to Skeena Group transition
Needs confirmation from biostratigraphic
or geochronologic age control, but
appears to suggest a southern margin
transition from marine to non-marine
Bowser Basin rather than separate
stratigraphies.
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There is a Bowser to Skeena Group transition
Suggests the Skeena Group
represents a southern margin
to the Bowser Basin during
Cretaceous time
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BOWSER - SUSTUT – SKEENA STRATIGRAPHY
KNOWLEDGE AND GAPS
 use of lithostratigaphic
assemblage units and
increasing biostratigraphic
database is working as a “basinscale” method of dealing with a
complex stratigraphy lacking
obvious regional markers
 formal stratigraphic schemes
that can be applied consistently
are increasingly apparent
need a lot more work / data; in
terms of both fundamental
mapping and age controls to
erect formal stratigraphy