Transcript Bowser and Sustut Basins - state of knowledge and new

BOWSER AND SUSTUT BASINS
STATE OF KNOWLEDGE AND NEW INITIATIVES
C.A. Evenchick, Geological Survey of Canada
101-605 Robson St., Vancouver, BC; [email protected]
basin analysis...
mapping...
structural analysis...
Natural Resources Canada
Ressources Naturelles Canada
CAE Apr22/03
Bowser and Sustut Basins - state of knowledge
and new initiatives
OUTLINE
 history of research, quality of coverage
 regional geological framework and terminology
 stratigraphic framework
 structural framework
 new initiatives
… together with discussion of:
Skeena Group (Haggart)
Aeromagnetic … (Lowe)
….will put us in position to discuss:
Thermal Maturation and petroleum systems (Osadetz)
Coal Bed Methane (Ryan)
CAE Apr22/03
REGIONAL GEOLOGICAL
FRAMEWORK - location
 north-central British Columbia
 in Intermontane Belt of the
Canadian Cordillera, a region of
low metamorphic grade relative to
the bounding Omineca Belt
(metamorphic) and Coast Belt
(plutonic and metamorphic
 overlies Stikine Terrane
(Stikinia), a terrane allochthonous
to the North American margin prior
to deposition of Bowser and Sustut
basin strata
 Stikinia and overlap basins are
separated from certain North
American rocks by oceanic Cache
Creek terrane
CAE Apr22/03
… a quick history of research
1944: Bowser and Sustut
basins not known to exist,
although exploration in the
Groundhog Coalfield dates
back to the early 1900’s
1962: parts of northern
Bowser and Sustut basins
recognized in 1956 GSC
mapping;
2 wells drilled 1969, 1972
2003: regional mapping
across most of basin area;
some remains at
reconnaissance level of
knowledge.
7 graduate theses.

CAE Apr22/03
REGIONAL GEOLOGICAL FRAMEWORK - central BC geology
 basins are Jurassic and Cretaceous clastic rocks
 overlie Triassic and lower Jurassic volcanic arc rocks (Stuhini, Hazelton groups)
 deformed in Cretaceous
to form Skeena Fold Belt
that terminates on the NE
in a frontal triangle zone
within Sustut Basin strata
 intruded on west by
early Tertiary plutonic
rocks (Coast Belt), and
locally in southeast by
Cretaceous and early
Tertiary plutons
 overlain by late Tertiary
and Quaternary volcanic
rocks (minor)
modified from Evenchick and Thorkelson, GSC Bull. 577, 2003/in press
CAE Apr22/03
STRATIGRAPHIC FRAMEWORK
Stratigraphy of Spatsizi River
area is typical of other
regions in the vicinity of the
Bowser and Sustut basins:
Table of formations, Spatsizi River map area.
Time scale of Harland et al. (1990).
MESOZOIC BASINS
Cretaceous Sustut Basin;
nonmarine
Jurassic-Cretaceous Bowser
basin; marine and nonmarine
MESOZOIC ARCS
Triassic and lower Jurassic volcanic
arc rocks (plutons, volcanic rocks,
related sedimentary rocks)
STIKINE ASSEMBLAGE
Paleozoic metavolcanic rocks,
metaplutonic rocks, carbonates
modified from Evenchick and Thorkelson, GSC Bull. 577, 2003/in press
CAE Apr22/03
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)
modified from Evenchick and Thorkelson, GSC Bull. 577, 2003/in press
CAE Apr22/03
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
modified from Evenchick and Thorkelson, GSC Bull. 577, 2003/in press
modified from Evenchick etal., 2001, GSC Open File 3956
CAE Apr22/03
STRATIGRAPHIC FRAMEWORK - BOWSER LAKE GROUP
Devils Claw Formation (alluvial, fluvial)
Jenkins Creek assemblage (nonmarine)
Groundhog-Gunanoot assemblage (deltaic)
Skelhorne assemblage (deltaic)
Eaglenest assemblage (deltaic)
Muskaboo Creek assemblage (shelf)
Todagin assemblage (slope)

Ritchie-Alger assemblage (submarine fan)
sandstone, siltstone, rare
conglomerate; about equal
proportions of sheet-like intervals
up to 50 m thick dominated by
either siltstone and very finegrained sandstone, or by
medium-grained sandstone;
abundant turbidite features (e.g.
Bouma cycles, flame structures,
flute and groove casts);
conglomerate is minor in most
regions, and includes poorly
sorted units considered to be
debris flows; marine fossils
CAE Apr22/03
STRATIGRAPHIC FRAMEWORK - BOWSER LAKE GROUP
Devils Claw Formation (alluvial, fluvial)
Jenkins Creek assemblage (nonmarine)
Groundhog-Gunanoot assemblage (deltaic)
Skelhorne assemblage (deltaic)
Eaglenest assemblage (deltaic)
Muskaboo Creek assemblage (shelf)

Todagin assemblage (slope)
Ritchie-Alger assemblage (submarine fan)
siltstone, fine-grained
sandstone, conglomerate;
mainly laminated siltstone and
fine grained sandstone which is
dark grey to black weathering,
and includes thin orange
weathering claystone beds and
syndepositional faults and folds;
chert pebble conglomerate
occurs as lenses; marine fossils
present
CAE Apr22/03
STRATIGRAPHIC FRAMEWORK - BOWSER LAKE GROUP
Devils Claw Formation (alluvial, fluvial)
Jenkins Creek assemblage (nonmarine)
Groundhog-Gunanoot assemblage (deltaic)
Skelhorne assemblage (deltaic)
Eaglenest assemblage (deltaic)
Muskaboo Creek assemblage (shelf)

Todagin assemblage (slope)
Ritchie-Alger assemblage (submarine fan)
siltstone, fine-grained
sandstone, conglomerate;
mainly laminated siltstone and
fine grained sandstone which is
dark grey to black weathering,
and includes thin orange
weathering claystone beds and
syndepositional faults and folds;
chert pebble conglomerate
occurs as lenses; marine fossils
present
CAE Apr22/03
STRATIGRAPHIC FRAMEWORK - BOWSER LAKE GROUP
Devils Claw Formation (alluvial, fluvial)
Jenkins Creek assemblage (nonmarine)
Groundhog-Gunanoot assemblage (deltaic)
Skelhorne assemblage (deltaic)
Eaglenest assemblage (deltaic)

Muskaboo Creek assemblage (shelf)
Todagin assemblage (slope)
Ritchie-Alger assemblage (submarine fan)
sandstone, siltstone, conglomerate;
primary lithofacies is sandstone
forming laterally continuous thin- to
thick-bedded sheets; less common
are siltstone interbedded with
sandstone, and lenses of
conglomerate; sandstone is thin- to
thick-bedded, locally arranged in
coarsening-up cycles; includes
burrows, bivalve coquina, and other
marine fossils, common ripple marks
and cross bedding, with local
hummocky cross stratification;
conglomerate increases in proportion
and thickness upsection
CAE Apr22/03
STRATIGRAPHIC FRAMEWORK - BOWSER LAKE GROUP
Devils Claw Formation (alluvial, fluvial)
Jenkins Creek assemblage (nonmarine)
Groundhog-Gunanoot assemblage (deltaic)
Skelhorne assemblage (deltaic)

Eaglenest assemblage (deltaic)
Muskaboo Creek assemblage (shelf)
Todagin assemblage (slope)
Ritchie-Alger assemblage (submarine fan)
conglomerate, sandstone, siltstone,
mudstone, and rare coal; arranged in
coarsening- and fining-up cycles of
mudstone to pebble or 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, sets locally
up to 10’s of metres thick; sandstone
has planar cross stratification and
hummocky cross stratification; sparse
marine fossils but abundant plant
fossils, including silicified log fragments
CAE Apr22/03
STRATIGRAPHIC FRAMEWORK - BOWSER LAKE GROUP
Devils Claw Formation (alluvial, fluvial)
Jenkins Creek assemblage (nonmarine)
Groundhog-Gunanoot assemblage (deltaic)

Skelhorne assemblage (deltaic)
Eaglenest assemblage (deltaic)
Muskaboo Creek assemblage (shelf)
Todagin assemblage (slope)
Ritchie-Alger assemblage (submarine fan)
thinly interlayered and vari-coloured
siltstone, sandstone, and conglomerate
(with or without coal), commonly arranged
in coarsening- and thickening-upward
cycles; common features of sandstone
are parallel bedding, cross bedding,
ripples, burrows, bivalve coquina;
conglomerate comprises a lower
proportion of the unit (15 to 30%) than in
the Eaglenest assemblage; conglomerate
units up to 50 m thick cap cycles up to 70
m thick, and tops locally have
megaripples; plant and marine fossils are
ubiquitous, trace fossils including
Skolithus and Diplocraterion are common,
as are log fragments several metres long
CAE Apr22/03
STRATIGRAPHIC FRAMEWORK - BOWSER LAKE GROUP
Devils Claw Formation (alluvial, fluvial)
Jenkins Creek assemblage (nonmarine)
Groundhog-Gunanoot assemblage (deltaic)
Skelhorne assemblage (deltaic)
Eaglenest assemblage (deltaic)
Muskaboo Creek assemblage (shelf)
Todagin assemblage (slope)
Ritchie-Alger assemblage (submarine fan)

sandstone, siltstone, carbonaceous and
calcareous mudstone, with minor
conglomerate and coal; locally arranged
in fining-up cycles; sandstone is fine- to
medium-grained with planar bedding and
planar tabular cross bedding; most
sandstone is thin- and thick-bedded,
medium-grained, recessive weathering
wacke; resistant weathering arenite is
less common and forms discontinuous
sheets and lenses; finer grained strata are
thinly bedded and locally include densly
packed plant fossils; conglomerate sheets
and lenses, <10% of the unit, include
large scale cross bedding; plant fossils
are common and include in-situ trees;
marine fossils are rare
CAE Apr22/03
STRATIGRAPHIC FRAMEWORK - BOWSER LAKE GROUP
Devils Claw Formation (alluvial, fluvial)
Jenkins Creek assemblage (nonmarine)
Groundhog-Gunanoot assemblage (deltaic)
Skelhorne assemblage (deltaic)
Eaglenest assemblage (deltaic)
Muskaboo Creek assemblage (shelf)
Todagin assemblage (slope)
Ritchie-Alger assemblage (submarine fan)

conglomerate, sandstone,
siltstone; a high proportion of
pebble conglomerate (30-80%) in
laterally continuous sheets with
large-scale cross bedding;
conglomerate forms bases of
fining-up cycles with mediumgrained sandstone, fine-grained
sandstone, carbonaceous
siltstone, and minor coal;
sandstone has platy and trough
cross bedding; fossil plants
common; marine fossils absent
CAE Apr22/03
STRATIGRAPHIC FRAMEWORK - BOWSER LAKE GROUP
Devils Claw Formation (alluvial, fluvial)
Jenkins Creek assemblage (nonmarine)

Groundhog-Gunanoot assemblage (deltaic)
Skelhorne assemblage (deltaic)
Eaglenest assemblage (deltaic)
Muskaboo Creek assemblage (shelf)
Todagin assemblage (slope)
Ritchie-Alger assemblage (submarine fan)
mudstone, siltstone, fine-grained
sandstone, medium-grained
sandstone, rare conglomerate and
coal; commonly arranged in finingup cycles; sandstone is grey,
green, and brown weathering and
occurs as laterally continuous
sheets, discontinuous sheets, and
lenses; lenses are planar and
trough cross bedded; fossil plants
abundant, including in-situ roots
and plants with delicate structure;
marine fossils absent
CAE Apr22/03
STRATIGRAPHIC FRAMEWORK - BOWSER LAKE GROUP
Bathonian/Callovian
Early Oxfordian
Lithofacies assemblage map of the northern 2/3 of
the Bowser Basin
Middle Oxfordian –
Early Kimmeridgian
Late Kimmeridgian –
Earliest Cretaceous
mid-Cretaceous
CAE Apr22/03
STRATIGRAPHIC FRAMEWORK - SUSTUT GROUP
More than 2000 m of nonmarine clastic strata, divided into two formations:
Brothers Peak Formation
Tango Creek Formation
At least 700 m thick on the SW side
of the basin. It overlies lower units
in angular unconformity. A base of
quartz pebble conglomerate or
coarse fanglomerate is overlain by
primarily sandstone, siltstone, and
mudstone. Sandstone occurs as
sheets and lenses of quartz- and
chert-rich feldspathic arenite.
Sandstone, siltstone, and
mudstone form fining-upward
cycles in the lower member. An
upper member is mudstone, and
calcareous siltstone and sandstone
(Eisbacher, 1974). Detrital micas
distinguish sandstone and siltstone
from otherwise similar Bowser Lake
Group.
Age is Barremian or Early Albian to
Late Campanian
NE
CAE Apr22/03
STRATIGRAPHIC FRAMEWORK - SUSTUT GROUP
Brothers Peak Formation
Tango Creek Formation
Conformably overlies Tango
Creek Fm. Characterized by
polymict conglomerate,
sandstone, and siliceous tuff.
Commonly has a basal
conglomeratic succession more
than 50 m thick which includes
siliceous ash-fall tuff. The
conglomeratic base is overlain
by a succession dominated by
pebbly sandstone, siliceous ashfall tuff, and mudstone, with rare
coal. Sandstone occurs as
sheets and as lenses
(Eisbacher, 1974).
Age is Late Campanian to late
Early Maastrichtian.
SE
KBP
KBP
KBP
KTC
KTC
KTC
CAE Apr22/03
STRUCTURAL FRAMEWORK – THE SKEENA FOLD BELT
REGIONAL RELATIONSHIPS
Location of cross-section
Strata of the 3 main clastic successions,
and underlying Stikinia, are folded and
thrust faulted. Contractional structures
define the Skeena Fold Belt, a thin
skinned fold and thrust belt of Cretaceous
age. The dominant fold trend is northwest,
but domains of northeast trending
structures occur locally on the west side
of the fold belt (Evenchick 1991a,b;
2001).
modified from Evenchick, 2001
CAE Apr22/03
STRUCTURAL FRAMEWORK - SKEENA FOLD BELT
FIRST ORDER FEATURES - GEOMETRY AND SCALE
 dominant structures are folds; they are close to tight, and upright to inclined to the
northeast; they have wavelengths of hundreds of metres to 1 km; larger wavelength folds are
associated with structural culminations of competent volcanic rocks of Stikinia.
NE
NE
Bowser Lake Group
Sustut Group
Bowser Lake Group
Bowser Lake Group
NE
SE
CAE Apr22/03
STRUCTURAL FRAMEWORK - SKEENA FOLD BELT
FIRST ORDER FEATURES - GEOMETRY AND SCALE
 dominant structures are folds; they are close to tight, and upright to inclined to the
northeast; they have wavelengths of hundreds of metres to 1 km; larger wavelength folds are
associated with structural culminations of competent volcanic rocks of Stikinia.
NE
from Evenchick and Thorkelson, GSC Bull. 577, 2003/in press
CAE Apr22/03
STRUCTURAL FRAMEWORK - SKEENA FOLD BELT
FIRST ORDER FEATURES - GEOMETRY AND SCALE
 thrust faults are present but, unless cut-offs are recognized, they are difficult to
recognize because Bowser Lake Group lacks distinctive regional stratigraphic markers
NE
CAE Apr22/03
STRUCTURAL FRAMEWORK - SKEENA FOLD BELT
FIRST ORDER FEATURES - GEOMETRY AND SCALE
 contractional structures affect underlying successions of Stikinia
NE
JHSu
JHSu
JHCu
JHCu
from Evenchick and Thorkelson, GSC Bull. 577, 2003/in press
CAE Apr22/03
STRUCTURAL FRAMEWORK - SKEENA FOLD BELT
FIRST ORDER FEATURES - MAGNITUDE OF SHORTENING
 the fold belt accommodated a minimum of 44% horizontal shortening by folds and thrust faults
 distinctive map units in the northeastern fold belt permit construction of balanced cross sections
NE
modified from Evenchick 1991
Tectonics vol 10
 in the Bowser Lake Group, excellent exposure
permits estimation of minimum shortening
by measuring bed-lengths of local markers
NE
from Evenchick and Thorkelson, GSC Bull. 577, 2003/in press
CAE Apr22/03
STRUCTURAL FRAMEWORK - SKEENA FOLD BELT
FIRST ORDER FEATURES - BOUNDARIES

 the fold belt terminates to the northeast in a
triangle zone within the Sustut Group
 it is interpreted to root to the west in the Coast
Belt, where there are contracrtional structures of
similar age
Triangle zone

NE
KTC

KBP
NE
NE

KBP
KBP
KTC
KTC
KBP
CAE Apr22/03
STRUCTURAL FRAMEWORK - SKEENA FOLD BELT
FIRST ORDER FEATURES - TIMING
Relationships between structures and stratigraphic units indicate that orogenic
shortening began prior to Albian time, and continued into the Maastrichtian or later.
The youngest rocks deformed below
the sub-Sustut angular unconformity
are Oxfordian. The youngest deformed
rocks in the fold belt are late Early
Maastrichtian age (Brothers Peak Fm).
KTC
KBP
The Sustut Group and Devils Claw Formation are
inferred to be synorogenic clastic basin fill associated
with formation of the Skeena Fold Belt (e.g. Evenchick,
2000); the Sustut Group formed in the foreland (basin)
to the Skeena Fold Belt, whereas the Devils Claw
formed in a piggy back basin within the fold belt.
CAE Apr22/03
BOWSER/SUSTUT BASINS - NEW INITIATIVES
Thermal mat. pre- 2002
Thermal maturation July 2002
 spring 2002: GSC began a
joint project with the BC MEM
New Ventures Branch to study
the thermal history of the
northern 2/3 of the Bowser and
Sustut basins
from GSC/BCMEM Open File 4343
 fall 2002 to present: project proposal to GSC to continue
joint project with the BC MEM New Ventures Branch on energy
resource potential of the Bowser and Sustut basins. Work to
focus on energy resource studies and increased knowledge of
the geological framework (stratigraphy, structure, basin
architecture and history). Region extended to encompass
entire basin area. Intended final product is Basin Atlas with
unified, pan-basin terminology and interpretations.
Proposed length of project is 4 years.
“conditional” project approval granted by GSC early April ’03.
CAE Apr22/03
BOWSER AND SUSTUT BASINS
STATE OF KNOWLEDGE AND NEW INITIATIVES
CONCLUSIONS
 Recent work on the geological (stratigraphic/structural) framework vastly
improves understanding of where to explore for particular types of plays by
identifying and mapping lithofacies assemblages, and identifying primary
structural characteristics of a regional fold and thrust belt, including the
frontal triangle zone.
 Although significant improvements have been made, there is much
additional work required because large parts of the basin remain at
reconnaissance level of knowledge.
 The revised geologic framework reduces exploration risk, and will be used
in future resource assessments.
 The geologic framework serves as a base for beginning to understand the
new thermal maturity model and exciting new petrographic and chemical
work; the subjects of following presentations.
CAE Apr22/03
Cited references and recent publications
Eisbacher, G.H. (1974): Sedimentary history and tectonic evolution of the Sustut and Sifton basins, north-central British
Columbia; Geological Survey of Canada, Paper 73-31, 57 p.
Evenchick, C.A. (1991a): Geometry, evolution, and tectonic framework of the Skeena Fold Belt, north-central British
Columbia; Tectonics, v. 10, p. 527-546.
Evenchick, C.A. (1991b): Structural relationships of the Skeena fold belt west of the Bowser Basin, Northwest British
Columbia. Canadian Journal of Earth Sciences 28, 973-983.
Evenchick, C.A. (2000): Evolution of the Bowser Basin / Skeena Fold Belt: implications for tectonic models of the Rocky
Mountain Fold and Thrust Belt and Omineca Belt; GeoCanada 2000 – the millenium geoscience summit, May 29-June 2,
Calgary, Alberta.
Evenchick, C.A. (2001): Northeast-trending folds in the western Skeena Fold Belt, northern Canadian Cordillera: a record
of Early Cretaceous sinistral plate convergence; Journal of Structural Geology v. 23 p. 1123-1140.
Evenchick, C.A., Poulton, T.P., Tipper, H.W., and Braidek, I. (2001): Fossils and facies of the northern two-thirds of the
Bowser Basin, northern British Columbia; Geological Survey of Canada, Open File 3956.
Evenchick, C.A., Hayes, M.C., Buddell, K.A., and Osadetz, K.G.(2002): Vitrinite reflectance data and preliminary organic
maturity model for the northern two thirds of the Bowser and Sustut basins, north-central British Columbia. Geological
Survey of Canada, Open File 4343 and B.C. Ministry of Energy and MInes, Petroleum Geology Open File 2002-1.
Osadetz, K.G., Evenchick, C. A. , Ferri, F. , Stasiuk, L. D., and Wilson, N. S. F. (2003): Indications for effective petroleum
systems in Bowser and Sustut basins, north-central British Columbia. in Geological fieldwork, 2002; B. C. Ministry of
Energy and Mines, Paper 2003-1.
Evenchick, C.A. and Thorkelson, D.J. (2003/in press): Geology of the Spatsizi River map area, north-central British
Columbia, Geological Survey of Canada Bulletin 577. As of early April 2003 this publication is in editorial review by GSC
editors; preliminary copies of the text will be provided by the author upon request.
…….. Many more Bowser/Sustut/Skeena references are cited within these publications
CAE Apr22/03