Lower Colorado Group Research Articles

Preliminary geology, mineral chemistry and diamond results from the C29/30 Candle Lake volcanic complex, Saskatchewan, Canada

The C29/30 kimberlite is one of two diamondiferous kimberlites in the Candle Lake cluster located in east-central Saskatchewan, Canada, approximately 70 km from the Fort á la Corne kimberlite field. The kimberlites are hosted by a Cretaceous sequence of marine mudstone and shale of the Lower Colorado Group, and underlying siltstone and sandstone of the Mannville Group. This sequence overlies Paleozoic carbonates that were deposited over the Proterozoic crystalline basement. Based on the country rock stratigraphy and morphology of the body, C29/30 is inferred to be Cretaceous in age. The elongated kimberlite body has a lateral extent of approximately 2 km with the long axis oriented in a south-east to north-west direction and an estimated surface expression of 75.3 ha. The investigation of 47 drill cores suggests that this body is a single volcanic complex dominated by a single phase of volcaniclastic kimberlite that is characterised by absent to rare phlogopite within the groundmass of preserved juvenile clasts. Minor amounts of at least one other phase of kimberlite containing conspicuous groundmass phlogopite have also been documented. The subsurface shape of C29/30 is complex and is interpreted to result from a combination of explosive volcanic activity that formed two craters from separate feeder vents. The formation of the elongated trough is poorly understood. It may have formed by a fissure style eruption, or erosive processes related to the mass flow of material away from one of the craters or possible the collapse of an eruption column. The C29/30 kimberlite is similar to bodies of the Fort á la Corne kimberlite field with respect to country rock setting, pipe morphology and the dominant textural varieties present. This contribution presents a preliminary geological model of C29/30 based on data obtained from the drilling programmes completed in 2006, 2007 and 2008.

Geology of the Orion South kimberlite, Fort à la Corne, Canada

A wide variety of primary pyroclastic, volcaniclastic and re-sedimented volcaniclastic deposits derived from multiple kimberlite eruptions are exceptionally well preserved at the Orion South kimberlite body in the Fort à la Corne field in central Saskatchewan. Construction of this kimberlite complex involved episodic kimberlite volcanic events punctuated by periods of volcanic quiescence, erosion and sedimentary deposition within the Western Canadian Sedimentary Basin. The Orion South kimberlite complex erupted into deltaic coastal plain/transitional estuarine (Mannville Group: Cantuar and Pense formations) and shallow marine (Lower Colorado Group: Joli Fou, Viking and Westgate formations) environments. At Orion South, eight distinct kimberlite phases erupted over 6 to 7 million years from ca. 106 Ma (Cantuar Formation equivalent) to ca. 99 Ma (Viking Formation equivalent). Detailed core logging, geochemistry, chronostratigraphy, petrography and geophysics were undertaken to define distinct eruptive phases and reconstruct the depositional environment, volcanic styles and 3-D architecture of the complex. The eight main kimberlite deposits record eruptive styles ranging from magmatic, to ‘wet’ and ‘dry’ phreatomagmatic, to submarine eruptions, a consequence of the varying interaction between kimberlite magma and seawater and/or groundwater.

An allostratigraphic correlation of Lower Colorado Group (Albian) and equivalent strata in Alberta and British Columbia, and Cenomanian rocks of the Upper Colorado Group in southern Alberta

Abstract The Lower Colorado Group (Late Albian—earliest Cenomanian) has been allostratigraphically divided on the basis of regional unconformities and transgressive surfaces, resulting in recognition of an informal Lower Colorado allogroup, comprising the Paddy, Joli Fou, Viking, Westgate and Fish Scales alloformations. The Paddy alloformation forms an eastward-thinning wedge up to 125 m thick, composed of nine allomembers that progressively onlap the basal unconformity PE0 from west to east. Paddy rocks are mainly alluvial in the west, grading into marginal marine in the east and north. Paleo valley-fills are present at the tops of most allomembers. The Joli Fou alloformation transgressively overlies nonmarine Mannville Group rocks, and forms a relatively sheet-like blanket (average 20 m) of marine mudstone that coarsens in the north, where it is assigned to the lithostratigraphic Viking Formation, and in the far south, where it is assigned to part of the lithostratigraphic Bow Island Formation. The Viking alloformation erosively overlies the Joli Fou alloformation at surface VE0 and consists of regional allomembers VA, VB and VD, separated by unconformities VE0, VE1, VE3 and VE4. Allomembers VA and VB (mean 30 m thick) are intensely bioturbated shallow marine silty fine sandstones whereas allomember VD is weakly bioturbated, and includes sandy shoreface deposits in the SW and thick (>50 m) offshore marine mudstone in the north (part of the lithostratigraphic Hasler Formation). Allomember VC is confined to paleovalley deposits below VE3. All regional Viking allomembers can be traced into the lower Bow Island Formation in the south. Marine mudstones of the Westgate alloformation form a wedge thinning from >600 m in the NW to The Paddy alloformation is entirely, or almost entirely older than the Joli Fou alloformation, and hence is much older than the Viking alloformation, with which it is traditionally equated. The new allostratigraphic correlations make it much easier to understand temporal and spatial relationships between the many lithostratigraphic components of the Lower Colorado Group, and of equivalent strata exposed in the Rocky Mountain Foothills. The new allostratigraphy reveals a complex interplay between eustatic changes and more localized flexural tectonic events.

Contrasting eruption styles of the 147 Kimberlite, Fort à la Corne, Saskatchewan, Canada

The Cretaceous Fort à la Corne (FALC) kimberlite field was active over a time span of ~ 20 Ma with contemporaneous terrestrial (Mannville Group) to marine (Lower Colorado Group) background sedimentation. Steep-sided pipes, craters and positive landform volcanoes such as scoria or tuff cones are thought to have formed during that period. The 147 Kimberlite is located in the SE section of the field's main cluster and is part of the large (~ 377.5 ha) Orion North volcanic complex. Based on logging of 25 drill cores, the morphology of the country rock/kimberlite interface suggests excavation of a complex crater field down to the upper portion of the Mannville Group sedimentary deposits. At least two types of volcaniclastic deposits are identified: a main kimberlite unit that is typically characterized by crustal xenolith-poor (1–2%), normal graded beds possibly deposited as turbidites in a subaqueous environment, originating from the nearby 148 tephra cone and infilling the adjacent 147 crater, and a second unit, located on the NE margin of the 147 Kimberlite, that represents a thick (~ 60 m) sequence of large (up to 22 m) sedimentary country rock blocks located at least 60 m above their original stratigraphic position. We suggest the following time sequence of events: Crater excavation as a consequence of a shallow magma fragmentation level within the uppermost country rock sequences, together with several closely spaced eruptive centres initially formed the complex, intercalated crater field. Subsequently, ongoing eruptions with a fragmentation level above the country rock produced the lithic fragment poor main infill of the 148 Kimberlite. Resedimentation from the outer flanks of the 148 tephra cone resulted in the deposition of turbidites in the 147 area. A consolidation phase solidified the lowermost portion of the main infill in 147. A subsequent explosion(s) occurred within the Mannville Group in the 147 area, ejecting large blocks of sedimentary country rocks and fracturing the overlying volcaniclastic main infill. Finally, blocks of the main infill tilted and possibly slumped into the subsidence structure developed above the emptied explosion chamber of 147. The different volcanic deposits reflect a change in eruption style and fragmentation level from highly explosive to spatter activity with little fragmentation potential. Cap rocks to build up the volatile overpressure necessary to blast the craters were not present at the time of emplacement. No diatremes were observed in the study area. Assuming that the magma properties remained constant over time, the change in eruption style has to be attributed to external factors, such as water access to the rising magma. The volcanic behaviour of the kimberlite magma appears to be comparable to that of other magmatic systems, both in eruptive style and production rate. No evidence was found for a high, possibly Plinian production rate or dispersion.

Sedimentologic and stratigraphic constraints on emplacement of the Star Kimberlite, east–central Saskatchewan

Diamond-bearing kimberlites in the Fort à la Corne region, east–central Saskatchewan, consist primarily of extra-crater pyroclastic deposits which are interstratified with Lower Cretaceous (Albian and Cenomanian) marine, marginal marine and continental sediments. Approximately 70 individual kimberlite occurrences have been documented. The Star Kimberlite, occurring at the southeastern end of the main Fort à la Corne trend, has been identified as being of economic interest, and is characterized by an excellent drill core database. Integration of multi-disciplinary data-sets has helped to refine and resolve models for emplacement of the Star Kimberlite. Detailed core logging has provided the foundation for sedimentological and volcanological studies and for construction of a regionally consistent stratigraphic and architectural framework for the kimberlite complex. Micropaleontologic and biostratigraphic analysis of selected sedimentary rocks, and U–Pb perovskite geochronology on kimberlite samples have been integrated to define periods of kimberlite emplacement. Radiometric age determination and micropaleontologic evidence support the hypothesis that multiple kimberlite eruptive phases occurred at Star. The oldest kimberlite in the Star body erupted during deposition of the predominantly continental strata of the lower Mannville Group (Cantuar Formation). Kimberlites within the Cantuar Formation include terrestrial airfall deposits as well as fluvially transported kimberlitic sandstone and conglomerate. Successive eruptive events occurred contemporaneous with deposition of the marginal marine upper Mannville Group (Pense Formation). Kimberlites within the Pense Formation consist primarily of terrestrial airfall deposits. Fine- to medium-grained cross-stratified kimberlitic (olivine-dominated) sandstone in this interval reflects reworking of airfall deposits during a regional marine transgression. The location of the source feeder vents of the Cantuar and Pense kimberlite deposits has not been identified. The youngest and volumetrically most significant eruptive events associated with the Star Kimberlite occur within the predominantly marine Lower Colorado Group (Joli Fou and Viking Formations). Kimberlite beds, which occur at several horizons within these units, consist of subaerial and marine fall deposits, the latter commonly exhibiting evidence of wave-reworking. Black shale-encased resedimented kimberlite beds, likely deposited as subaqueous debris flows and turbidites, are particularly common in the Lower Colorado Group. During its multi-eruptive history, the Star Kimberlite body is interpreted to have evolved from a feeder vent and overlying positive-relief tephra ring, into a tephra cone. Initial early Joli Fou volcanism resulted in formation of a feeder vent (∼200 m diameter) and tephra ring. Subsequent eruptions, dominated by subaerial deposits, partly infilled the crater and constructed a tephra cone. A late Joli Fou eruption formed a small (∼70 m diameter) feeder pipe slightly offset to the NW of the early Joli Fou feeder vent. Deposits from this event further infilled the crater, and were deposited on top of early Joli Fou kimberlite (proximal to the vent) and sediments of the Joli Fou Formation (distal to the vent). The shape of the tephra cone was modified during multiple marine transgression and regression cycles coeval with deposition of the Lower Colorado Group, resulting in wave-reworked kimberlite sand along the fringes of the cone and kimberlitic event deposits (tempestites, turbidites, debris flows) in more distal settings.

Revised Stratigraphy of the Lower Colorado Group (Albian To Turonian), Western Canada

ABSTRACT The sedimentology, biostratigraphy and geochemistry of the Albian to middle (?) Turonian interval of the Colorado Group in Western Canada indicate that four, regionally mappable lithostratigraphic units are present in this marine shale succession. In ascending order, these are: the Westgate Formation, the Fish Scales Formation, the Belle Fourche Formation and the Second White Specks Formation. The Westgate Formation is a laminated-to-bioturbated, heterolithic mudstone to siltstone which thickens from 20 m on the Manitoba-Saskatchewan border to over 120 m in northwestern Alberta. This formation contains an agglutinated foraminiferal assemblage characteristic of the late Albian Miliammina manitobensis Zone. The total organic carbon (TOC) is dominantly Type III (terrestrially derived) organic matter and comprises 2 wt% or less of the rock mass. The Fish Scales Formation is less than 20 m thick and consists of mudstone to claystone with associated sandstone and conglomerate beds. Bioturbation is sparse to absent and foraminifera are not present; the age is bracketed as Early Cenomanian. TOC abundances are variable up to 8 wt% and comprise a mixture of Types II and III. The Belle Fourche Formation is a non- to slightly-calcareous mudstone to siltstone which thickens westward from 20 m to 150 m. Bioturbation is sparse to moderate and in general, grain size coarsens upward culminating in persistent, thin, siltstone to fine-grained sandstones near the top. The foraminiferal assemblage is dominantly agglutinated and characteristic of the middle Cenomanian Verneuilinoides perplexus Zone. TOC abundances are generally less than 2 wt% dominantly consisting of Type III organic matter, but more elevated TOC values and Type II organic matter occur in facies transitional into the overlying Second White Specks Formation. The Second White Specks Formation (SWS) is a non-bioturbated, calcareous, organic-rich claystone to siltstone. The SWS thickens from about 25 m in eastern Saskatchewan to over 90 m in northwestern Alberta with local thickening to 55 m in southeastern Alberta. This unit is distinctive due, primarily, to the abundance and diversity of marine bioclasts, the foraminiferal assemblage, the predominance of Type II organic matter, and the high TOC content (up to 12 wt%). The dominantly planktonic assemblage is characteristic of the late Cenomanian to Turonian Hedbergella loetterlei Zone. Another characteristic of the SWS is the common occurrence of nannofossils, primarily coccoliths. RESUME La sedimentologie, la biostratigraphie et la geochimie de l'intervalle albien a turonien moyen (?) du groupe Colorado dans le Canada occidental indiquent que quatre unites lithostratigraphiques, cartographiables a l'echelle regionale, sont presentes dans cette succession argilleuse marine. En ordre ascendant, celles-ci sont la formation Westgate, la formation Fish Scales, la formation Belle Fourche et la formation Second White Specks. La formation Westgate est un mudstone a siltstone heterolithique, lamine a bioturbe qui s'epaissit de 20 m a la frontiere du Manitoba-Saskatchewan a plus de 120 m dans l'Alberta du nord-ouest. Cette formation contient un assemblage de foraminiferes agglutines caracteristique de la Zone Miliammina manitobensis albienne superieure. La matiere organique est principalement de Type III (terrestre) et le carbone organique total (TOC) represente au plus 2% ponderal de la roche. La formation Fish Scales a moins de 20 m d'epaisseur et comprend des mudstones a claystones avec des lits greseux et conglomeratiques associes. Les bioturbations sont rares a absentes et il n'y a pas de foraminiferes; par End_Page 325------------------------ deduction, l'age est cenomanien inferieur. Les abondances en TOC sont variables jusqu'a 8%, et la matiere organique est un melange des Types II et III. La formation Belle Fourche est un mudstone a siltstone non- a faiblement calcaire qui s'epaissit vers l'ouest de 20 m a 150 m. Les bioturbations sont rares a moderees et, en general, la taille des grains s'accroit vers le haut, et un mince siltstone a gres fin persiste a son sommet. L'assemblage foraminifere est domine par des formes agglutinees et est caracteristique de la zone Verneuilinoides perplexus cenomanienne moyenne. L'abondance du TOC est generalement de moins de 2% et la matiere organique est de Type III, mais des valeurs de TOC plus elevees et de la matiere organique de Type II existent dans le facies transitionel vers la formation Second White Specks surjacente. La formation Second White Specks (SWS) est un claystone a siltstone non bioturbe, calcaire, et riche en matiere organique. La formation SWS s'epaissit depuis environ 25 m dans le Saskatchewan oriental a plus de 90 m dans l'Alberta du nord-ouest avec des epaississements jusqu'a 55 m dans l'Alberta du sud-est. Cette formation est reconnaissable principalement par l'abondance et la diversite des bioclastes d'origine marine, l'assemblage des foraminiferes, la predominance de matiere organique de Type II, et la haute teneur en TOC (jusqu'a 12%). L'assemblage principalement planctonique est caracteristique de la zone Hedbergella loetterlei cenomanienne superieure. Une autre caracteristique de la formation SWS est l'occurrence commune de nannofossiles, principalement des coccolithes. Traduit par Patrice de Caritat

Syndepositional and Postdepositional Salt-Dissolution Structure Traps in Lower Cretaceous Sandstones, Cessford Field, Alberta, Canada: ABSTRACT

Many Cretaceous structure-stratigraphic traps in the Western Canada sedimentary basin formed through regional tilting and/or local salt dissolution (subrosion). Hydrocarbons are trapped in Cretaceous sandstones: (1) along updip pinch-outs as a result of regional tilting, (2) in sediment sinks created by local synsedimentary subsidence due to subrosion, and (3) on local structural highs isolated by subrosion. Cessford field lies over an area of local salt removal and contains a variety of traps in different Lower Cretaceous stratigraphic zones. Regional pinch-outs and local structural highs in marine shelf sandstones of the lower Colorado Group have been exploited since the early 1950s. Renewed exploration in the last decade resulted in the discovery of several pools in fluvial sediments of the underlying Mannville Group in areas characterized by synsedimentary subsidence. A seismic line across a portion of Cessford field reveals the presence of a narrow graben bounded by normal faults reaching from Precambrian basement into the Cretaceous section. Salt solution in the vicinity of the graben is demonstrated by thinning of a Devonian salt formation toward the fault. Structure and isopach maps of several Cretaceous markers show that solution proceeded episodically along elongate zones oriented normal to the graben. Episodic salt solution ismore » interpreted to have been controlled by movement of water along basement isostatic faults in response to Cordilleran thrusting and loading of the foreland basin.« less

Use of Trace Elements for Classification of Crude Oils into Families--Example from Alberta, Canada

This study shows that a combination of instrumental neutron-activation analysis and stepwise multiple-discriminant function analysis is equally successful and valuable in correctly classifying crude oils which had previously been grouped into families based on organic geochemical analysis. In the present study, 11 trace elements were determined by instrumental neutron-activation analysis in 75 Alberta crude oils from similar lithostratigraphic situations and the samples grouped into the same families, plus an ungrouped data set. Stepwise multiple-discriminant function analysis shows that only S, Co, Se, V, and Br are significant discriminators of the three grouped data sets. Further, the efficacy of the discriminant analysis is confirmed using multiresponse permutation procedures. Among the grouped data, 89.1% of the crude oils were correctly classified on the basis of their trace-element content, 70% of which were at a probability level of more than 90%. For some misclassified samples, information from the statistical analysis together with knowledge of the local lithostratigraphy and hydrodynamics can be used to indicate mixing or migration phenomena. For example, crude oil in the Lower Cretaceous Basal Colorado Sandstone at Cessford appears to be a mixture from sources within the lower Colorado Group and in the underlying Mannville Group; in contrast, the only source of crude oil in the Upper Devonian Winterburn Group at Youngstown appears to be the overlying Lower Cretaceous Mannville Group. Among the ungrouped data, the trace-element classification for four Triassic crude oils suggests a source in the overlying Lower Cretaceous Mannville Group. The results for crude oils from Carboniferous and Upper Devonian Wabamun Group strata, far below the sub-Cretaceous unconformity, suggest further work is required before a specific source can be identified. In the structurally separated Turner Valley field, the crude oil in Lower Cretaceous Blairmore Group strata seems to have originated from the overlying Colorado Group, whereas that from Carboniferous rocks shows mixed characteristics. Crude oil from the Athabasca oil sand deposit exhibits enigmatic features.--Modified journal abstract.

Recurrent species groupings in fossil microplankton assemblages

The Binomial Test is used to demonstrate the presence and distribution of recurrent species groups in fossil microplankton assemblages. These assemblages were recovered from deposits of the lower Colorado Group, Late Albian in age, from central Alberta, Canada. The composition of the recurrent groups differs at two localities investigated in detail. In both instances, however, evidence indicates that the recurrent groups are responsive to changes in the sedimentary or environmental regime. The sequential appearance and development of the recurrent groups may be related to changes in lithology, fluctuations in the total miospore/total microplankton ratio, and proximity of ancient shoreline. Certain of the groupings were established under transgressive conditions, while others became established under more stable conditions. Recurrent groups have value in that they allow a more refined correlation of species occurrence data with other palynological indices. They do not have stratigraphic value in themselves but may have value in the selection of local biostratigraphic markers.