Bowser and Sustut Basins - state of knowledge and new initiatives Outline -regional geological framework and terminology -stratigraphic framework -structural framework -history of research, quality of coverage -new initiatives

1
BOWSER AND SUSTUT BASINS STATE OF KNOWLEDGE AND
NEW INITIATIVES C.A. Evenchick, Geological
Survey of Canada 101-605 Robson St., Vancouver,
BC cevenchi_at_nrcan.gc.ca
basin analysis...
mapping...
structural analysis...
Natural Resources Canada
Ressources Naturelles Canada
2
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)

3

• 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

4
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 1900s
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.
?
5
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
6
STRATIGRAPHIC FRAMEWORK
Table of formations, Spatsizi River map
area. Time scale of Harland et al. (1990).
Stratigraphy of Spatsizi River area is typical of
other regions in the vicinity of the Bowser and
Sustut basins
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
7
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
8
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
9
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
fine-grained 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
10
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
11
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
12
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
13
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 10s of metres
thick sandstone has planar cross stratification
and hummocky cross stratification sparse marine
fossils but abundant plant fossils, including
silicified log fragments
14
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
15
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,
lt10 of the unit, include large scale cross
bedding plant fossils are common and include
in-situ trees marine fossils are rare
16
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 medium-grained sandstone,
fine-grained sandstone, carbonaceous siltstone,
and minor coal sandstone has platy and trough
cross bedding fossil plants common marine
fossils absent
17
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 fining-up 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
18
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
19
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
20
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 ash-fall 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
21
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
22
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
Bowser Lake Group
SE
NE
Bowser Lake Group
Sustut Group
23
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
24
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
25
STRUCTURAL FRAMEWORK - SKEENA FOLD BELT
FIRST ORDER FEATURES - GEOMETRY AND SCALE

• contractional structures affect underlying
  successions of Stikinia

NE
JHSu
JHCu
JHSu
JHCu
from Evenchick and Thorkelson, GSC Bull. 577,
2003/in press
26
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
27
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
KBP
KTC
28
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.
29
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.

30
BOWSER AND SUSTUT BASINS STATE OF KNOWLEDGE AND
NEW INITIATIVES CONCLUSIONS

• Recent work on the geological (stratigraphic/stru
  ctural) 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.

31
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