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The Cenomanian–Turonian Oceanic Anoxic Event (OAE 2: 94 Ma) marked one of the most severe episodes of climate and environmental change during the Cretaceous Period. The primary feature of this interval was widespread marine anoxia/euxinia, leading to deposition of organic-rich, thinly-bedded, mudstones across the world’s oceans, which in turn caused a pronounced positive shift in δ13C of seawater that is recorded (and characterizes) OAE 2 strata worldwide. The event was also marked by climate warming (with superimposed cooling pulses), biotic stress, and terrestrial perturbations such as increased continental weathering. However, the majority of studied records of OAE 2 were deposited in deep-marine Atlantic and Tethyan settings or European epicontinental basins. Thus, the record of environmental change in other locations or environments is less clear. The Western Interior Seaway (WIS) represented a marine corridor across North America that connected the Arctic and Atlantic marine realms. Thus, understanding the environmental and oceanographic changes in the WIS during OAE 2 is crucial to resolving the wider impact of the event across the global marine realm. Several previous works have focused on sites towards the southern end of the WIS (e.g., Pueblo, Iona Core). In this study, we present a new multi-proxy geochemical dataset from a site in the central–northern part of the Western Interior Seaway: Pratts Landing (western Alberta, Canada). Previous palynological studies have highlighted a southward migration of boreal dinoflagellates during the Plenus Cold Event midway through OAE 2, as well as increased input of terrestrial organic matter. Here, we correlate these data with information from redox, nutrient, and volcanic proxies, and compare the Pratts Landing record with other deep- and shallow-marine records of OAE 2 to gain a wider perspective over the environmental changes that operated in different settings during that time interval. This viewpoint is key for understanding the differences and complexities in how surface phenomena were disturbed during OAE 2, and interpreting geochemical records of different settings during that time interval.

Previous studies of Cretaceous sedimentary rocks have used multi-proxy correlation methods to suggest eustatic change, modulated by the c. 400 kyr long eccentricity rhythm. Although numerous authors have inferred eustatic changes on shorter timescales, none have demonstrated synchronous sea-level changes in separate basins on different plates, thousands of kilometres apart. Our study integrates basin-scale, three-dimensional sequence architecture, molluscan biostratigraphy, and carbon-isotope chemostratigraphy to demonstrate synchronous sea-level changes in upper Turonian to lower Coniacian shallow-marine clastic successions in the Western Canada Foreland Basin, and the Bohemian Cretaceous Basin. Depositional sequences in both basins are plotted in a common time domain using an astronomically calibrated age model, allowing direct comparison. In both basins, at least seven major transgressive events can be shown to be synchronous within the limits of combined biostratigraphic and chemostratigraphic resolution. ‘Major’ and ‘minor’ sequences of late Turonian age appear to have been paced, respectively, by the long (c. 400 kyr) and short (c. 100 kyr) eccentricity cycles. In contrast, early Coniacian sequences evidence pacing by the c. 38 kyr obliquity rhythm. Stratal architecture suggests that sequences developed in response to eustatic changes of c. 14–20 m at average rates ranging 0.08 to >1.3 m/kyr. At a time of ‘warm greenhouse’ climate, sea-level change of this magnitude and timescale may not be explicable entirely as a result of thermal- and aquifer-eustasy, and hence glacio-eustasy may also have been a contributing factor.

The great Late Cenomanian transgression of the Greenhorn Sea is recorded in western Alberta and adjacacent British Columbia by shallow-marine deposits of the lower Kaskapau Formation that blanket underlying deltaic deposits of the Dunvegan Formation. Overlying the basal ‘A-X unit’ of the Kaskapau are the allostratigraphically-defined Doe Creek and Pouce Coupe units, each of which forms a SW-thickening wedge up to about 100 m thick. The Doe Creek and Pouce Coupe units comprise, respectively, 10 and 8 allomembers, each defined by a marine flooding surface. Doe Creek facies are organized in upward-shoaling successions less than about 10 m thick. Shallow-water marginal-marine facies prevail in the west and north, with transgressive mudstones overlain by thin, sharp-based shoreface sandstones that, in places, contain roots and dinosaur tracks. In some instances, marine mudstone grades directly upward into a rooted, muddy paleosol. Mapped regionally, these facies define a broad, shallow, SE-facing embayment approximately 200 x 200 km. Trace and molluscan fossils suggest that salinity was below normal marine level, and benthic fauna were, at times, stressed by high turbidity and sedimentation rate. The central part of the embayment is dominated by offshore mudstone that encloses isolated, sharp-based lenticular bodies of clean sandstone up to 9 m thick. Sandstones are ovoid to elongate in plan view, and commonly extend many tens of km N-S or NE-SW. These sandstones are interpreted as top-truncated lowstand delta and strandplain deposits that became isolated on the outer ramp following marine transgression. The sharp base of most shoreface sandstones implies that deposition took place during relative sea-level fall. All Doe Creek allomembers thicken into the foredeep, with the tectonically-flexed surface inclined to the SW. Palaeogeographic maps show, however, that lowstand shorelines were oriented approximately NE-SW, and that the depositional surface sloped to the SE. This geometric relationship implies that, despite tectonic subsidence increasing to the SW, the rate of sediment supply and efficiency of redistribution were able to maintain a wave-graded surface sloping to the SE. Because shorelines migrated across, rather than up and down tectonic dip, allomembers are interpreted to have been controlled primarily by high-rate, high-frequency eustatic cycles, rather than by tectonic movements. The Pouce Coupe unit represents a complete reversal of basin paleogeography relative to the Doe Creek. Pouce Coupe shoreface sandstones are stacked in a linear belt just west of 120°W and grade westward into offshore muddy facies that thicken to the WSW. The entire unit is truncated eastward by the K1 unconformity and is absent over most of Alberta. It is postulated that the Proterozoic Kiskatinaw domain acted as a crustal weak zone, forming a hinge that defined the eastern margin of the Pouce Coupe flexural depocentre.

The late Cenomanian Kaskapau Formation records transgression of the Greenhorn Sea over deltaic strata of the Dunvegan Formation. However, stratigraphic and paleogeographic details of the initial stages of this profound reorganization of basin geography have not previously been determined. The basal Kaskapau strata above the Dunvegan Formation are assigned to the informal allostratigraphic ‘A-X unit’. Subsurface and outcrop correlation shows that five regionally-mappable allomembers, bounded by marine flooding surfaces, can be mapped within the A-X unit which, as a whole, forms a wedge that thickens south-westward from

Numerous crocodylian swim tracks occur in the late Early Cretaceous and earliest Late Cretaceous of western North America, in coastal plain deposits marginal to the Cretaceous interior seaways. New assemblages from the lower Albian Gates Formation, within the Tumbler Ridge UNESCO Global Geopark Quintette site (TRUGG-Q) in British Columbia, Canada, resemble those from Albian-Cenomanian Dakota Sandstone sites in Colorado, Kansas and Utah, and facilitate comparative analysis of how such assemblages are registered and preserved. The Gates Formation track assemblage formed on the southwest margin of the ‘Moosebar Sea’ that filled the foredeep of the Western Canada Foreland Basin in the Early Albian. Northeast-prograding sandy deltas were backed by low-lying and heavily-vegetated coastal plains, inhabited by track-making dinosaurs, birds, and crocodylians. The base of a tidal channel-fill at the TRUGG-Q site preserves crocodylian swim traces indicating progression largely parallel to the channel axis, as also inferred for some USA sites. Swim track lengths can be categorized on a short–long spectrum which reflects swimming behavior, with short, wide toe tip traces indicating firm digging-in of toes (‘punting’ or ‘poling’ behavior), and elongate scrape marks indicating light touch-down (or substrate ‘raking’) by buoyant animals making intermittent contact with a subaqueous substrate. The body lengths size of crocodylian trackmakers can be calculated from rare complete ‘walking’ track footprints or from the widths, not lengths, in the case of ‘swim’ traces. The mean size of the Canadian tracks indicates individuals with body lengths in the range of ~1.0 m, with larger trackmakers up to ~4.0 m more common at the USA sites.

In north-central Alberta and adjacent British Columbia, clastic strata of the middle to late Albian Peace River and Shaftesbury formations were deposited in alluvial to shallow marine environments across the foredeep of the Western Canada Foreland Basin. A high-resolution, log and core-based allostratigraphic framework for the Paddy Member of the Peace River Formation established nine allomembers, PA to PI, bounded by flooding surfaces and apparently equivalent non-marine surfaces. Within the estimated 2 Myr. duration of the Paddy, allomembers allow the evolving palaeogeography and changing relationship between accommodation and sedimentation rates to be analysed on time-steps on the order of 105 yrs. Paddy strata fill an arcuate depocentre ~ 300 km wide, across which the rocks thin eastward from 125 m to ~ 5-10 m. The northern part of the basin is occupied by muddy, offshore marine deposits that pass abruptly southward into a linear, WSW-ENE-trending body of sandstone deposited in a wave-dominated barrier-strandplain, at least 350 km long. Extending > 200 km to the south of the strandplain was a region of shallow brackish to freshwater lagoons and lakes that graded to the SW into alluvial facies. Within the lagoon region, few m thick, elongate and patchy sandstones represent river dominated deltas. In allomembers PA to PG, these sandstones are concentrated in the west and south, implying supply from the western Cordillera. In allomembers PH and PI, sandstones are mainly in the east and have a distinctive, quartz-rich composition. They can be correlated eastward into the coeval Pelican Formation, and were probably sourced from the Canadian Shield on the opposite side of the basin. In the western foredeep, alluvial rocks comprise aggradational, unconfined floodplain deposits with ribbon sandstones, dissected, on at least nine separate levels, by paleovalleys that are confined to the proximal foredeep. Valleys are 10-20 m deep, few km-wide, and filled with multi-storey channel-bars of pebbly coarse sandstone or conglomerate. Valleys cut down from well-developed interfluve palaeosols that record a falling and then rising water table. Alternating aggradation and degradation, and advance and retreat of the alluvial gravel front is attributed to cycles of varying rainfall intensity, rather than tectonism or eustasy. Apparently coeval transgressive-regressive successions in the lagoon and marine regions are attributed to few-m scale eustatic changes. On the NE margin of the basin, tidal sandstone fills a northward-opening estuary cut on the basal Paddy unconformity. This sandstone contains the first well-documented specimens of Gnesioceramus comancheanus (Cragin), proving contemporaneity with at least part of the marine Joli Fou Formation to the east. Paddy allomembers change shape upward from short blunt wedges, through more acutely tapered wedges, to sheets. This change reflects initially rapid flexural subsidence, attributed to active thickening of the adjacent orogenic wedge. A waning rate of deformation permitted wider dispersal of sediment across the basin, driving broad isostatic subsidence beneath increasingly sheet-like rock bodies. A major hiatal surface, VE3, records non-deposition or subtle erosion attributed to erosional unloading and uplift of the adjacent orogen. A subsequent marine transgression is attributed to renewed thickening of the tectonic wedge that triggered deposition of marine mudstone that thickens westward from 0 to > 110 m over 300 km. A postulated Milankovitch-band climatic control on both local gravel supply (via fluctuating rainfall), and shoreline movement (via ?Antarctic glacio-eustasy or groundwater storage), might account for cycles of alternating incision and aggradation in the alluvial realm. The same mechanism may also explain why shallow marine units such as the Cretaceous Viking and Cardium formations contain abundant conglomerate in lowstand shoreface deposits (higher river discharge), yet have highstand shorelines dominated by sandstone (lower river discharge). This article is protected by copyright. All rights reserved.

The Upper Cretaceous (Coniacian-Santonian) of the Western Canada Foreland Basin, contains a rich record of scaphitid ammonites (scaphites). We describe four species: Scaphites (Scaphites) preventricosus Cobban, 1952, Scaphites (S.) ventricosus Meek and Hayden, 1862, Scaphites (S.) depressus Reeside, 1927, and Clioscaphites saxitonianus (McLearn, 1929). These are widespread index fossils that demarcate the upper lower-middle, middle, and upper Coniacian, and the lower Santonian, respectively. They occur in the lower part of the Wapiabi Formation, Alberta. The Coniacian part of the section has been divided into 24 informal allomembers based on the recognition of marine flooding surfaces, most of which can be traced through the >750 km extent of the study area. The most distinctive feature in the ontogenetic development of scaphites is the change in coiling during ontogeny. At the approach of maturity, the shell uncoils slightly, forming a shaft, which then recurves backward approaching the earlier ...

Inoceramid bivalves are the dominant invertebrate fauna of the Coniacian and basal Santonian of the Western Canada Foreland Basin in western Alberta. In the upper lower Coniacian through to basal Santonian, six successive faunas are recognized, which provide the basis for corresponding, formally defined inoceramid zones. From bottom upward these are the zones of: Cremnoceramus crassus crassus /C. deformis deformis, Inoceramus gibbosus, Volviceramus koeneni, Volviceramus involutus, Sphenoceramus subcardissoides, and Sphenoceramus ex gr. pachti. Particular faunas represent assemblages known widely from the Euramerican biogeographic region, although they characterize mostly its northern, boreal area. The inoceramid-based biostratigraphic scheme allows correlation with other parts of the North American Western Interior and with parts of the Euramerican biogeographic region. The studied succession provides a good record of the Inoceramus gibbosus Zone, which characterizes the topmost lower Coniacian. ...

The biostratigraphy of the uppermost Cenomanian – Lower Turonian succession in the lower part of the Blackstone Formation exposed in the Ram River (Alberta, Canada), is interpreted in terms of the standard inoceramid/ammonite zonation of the interval. Four successive inoceramid zones are recognized, those ofInoceramus pictus,Mytiloides puebloensis,M. kossmati, andM. mytiloides, as established in the stratotype section at Pueblo, Colorado. Their correlation to Pueblo is confirmed by ammonite data.The mid-Early Turonian zone ofM. kossmatiyielded an assemblage ofInoceramus, with species showing close affinity to the latest Cenomanian lineages. This multi-species sample proves the survival ofInoceramuslineages into the otherwiseMytiloides-dominated Early Turonian, and indicates that their disappearance from the record of the North American Western Interior was not because of their extinction. It is suggested that the apparent lack ofInoceramusin Lower Turonian strata is due to an extremely low population abundance in the Early Turonian sea.

In west-central and southwestern Alberta, the lower and upper tongues of the marine mudstone-dominated Bearpaw Formation have a complex lateral relationship with marginal marine and non-marine strata of the Horseshoe Canyon and Blood Reserve formations. Wireline log, core and outcrop data permit the establishment of a regional transgressive-regressive (T-R) sequence stratigraphic framework for the upper Campanian Bearpaw strata. This provides a context within which lithostratigraphic boundaries of the Bearpaw tongues with laterally equivalent and overlying strata can be more rigorously mapped. Maximum flooding (MFS) and transgressive (TS) surfaces were defined on the basis of stratal stacking patterns and inferred lapout relationships wherever possible. Lower Bearpaw tongue and laterally equivalent strata are assigned to four regionally mappable T-R sequences. In the study area the top of the underlying Belly River Group is placed at the MFS in the lowermost of these sequences. In the overlying lower Bearpaw sequences, the TS is generally considered to coincide with the MFS within the limits of wireline log resolution, and the succession consists mainly of stacked regressive systems tracts which usually show a near-parallel internal stratal geometry. Upper Bearpaw tongue and laterally equivalent strata are assigned to three regionally mappable T-R sequences. The basal upper Bearpaw sequence has a well-developed transgressive systems tract consisting of backstepping, individually regressive parasequences, and southeast-prograding clinoform geometry is clear in each of the upper Bearpaw tongue regressive systems tracts. The lithostratigraphic upper boundaries of the lower and upper Bearpaw tongues are time-transgressive facies contacts that step up-section to the southeast (paleoseaward) through the respective regressive systems tracts. The base of the upper Bearpaw tongue steps up-section from the basal TS of the lowermost sequence in the southeast, through the overlying transgressive systems tract, to coincide with the maximum flooding surface to the northwest (paleolandward).

Inclined Heterolithic Stratification, characterized by dipping, interbedded and interlaminated sandstone and mudstone lithosomes comprises a major portion of the Athabasca Oil Sands. Fluvial processes have generally been interpreted to be the major cause of lithological variations and accompanying cyclicity in Inclined Heterolithic Stratification. The objectives of this research are applying quantitative and visual frequency analysis techniques, to determine and interpret the laminae-scale cyclicity of Inclined Heterolithic Stratification lithosomes. The Inclined Heterolithic Stratification in the Pierre River area is subdivided into five lithosomes based on distinct ichnological and sedimentological features. For each lithosome, Continuous Wavelet Transforms, applied to measurements of laminae or bed thicknesses, treated as pseudo time-series, converts these time-series to the frequency domain in order to determine the cyclicity of interlaminated portions of lithosomes. Visual identification of cycle breaks, by splitting series into cycles following troughs and peaks is completed as well. The results from the analysis demonstrate that the interlaminated portions of Inclined Heterolithic Stratification in the Pierre River Area preserve cyclic patterns that are consistent with semidiurnal synodic neap-spring tidal periodicity. Even in bioturbated intervals, interlaminated sandstone and mudstone is indicative of tidal cyclicity. The thicker sandstone or mudstone beds disrupting the tidally interlaminated portions of Inclined Heterolithic Stratification are interpreted to reflect variations in fluvial flux. This study gives a better understanding of the tidal regime during the lower Cretaceous McMurray Formation deposition and of the processes governing Inclined Heterolithic Stratification laminae-scale lithological variability.

Despite the abundant well-log and core data available for the McMurray Formation, the succession has remained difficult to interpret. Presently, a fundamental aspect of understanding the depositional nature of the McMurray Formation is whether or not the formation is dominantly estuarine or fluvial. Focussing on the informal middle McMurray, our detailed analysis of the McMurray Formation within the Kearl Oil Sands area critically evaluates the utility of collecting high-resolution ichnological and sedimentological data as a means to assess the depositional environments and to evaluate the evidence for an estuarine versus a tidally influenced fluvial depositional setting. This study asserts that the middle McMurray Formation within the Kearl Oil Sands area was deposited on estuarine point-bars. The examined dataset encompasses what are interpreted to be inner to middle estuarine depositional locales within a mesotidal regime. Integration of detailed ichnological and sedimentological data permits recognition of intertidal flat deposits which exist at sea level, and the identification of which provides a locally useful stratigraphic datum. Identification of successions of stacked tidally influenced channels of varying dimensions help identify stratigraphic levels of amalgamated estuarine channel bars and gives an approximation of relative changes in sea level.

An echinoderm association is reported from the ?early late Albian Paddy Member of the Peace River Formation of British Columbia, Canada. The association includes Frasericrinus mauricensis gen. et sp. nov., two additional distinctive crinoid column types, a poorly preserved asteroid, and an umbilical fragment of the cephalopod Stelckiceras. This is the first report of a Cretaceous isocrinid from North America. The echinoderm fossils are from the top of a succession of storm-deposited sandstones and mudstones (Boulder Creek Formation) that can be correlated southward into nearshore and terrestrial facies of the Paddy Member of the Peace River Formation. The echinoderm fossils were buried (and probably lived) about 12–14 km from the contemporaneous shoreline in an estimated water depth of 10–20 m. Integration of biostratigraphic and allostratigraphic schemes suggests that the echinoderms are of earliest late Albian age. The association of the echinoderm fauna with ammonites of Boreal affinity indicates deposition in northern waters, although the presence of Tethyan inoceramids in apparently coeval Paddy Member strata 270 km to the east suggests that northward-advancing water from the Gulf of Mexico had reached northwestern Alberta, if not actually merged with the Boreal embayment. The nearshore occurrence of Cretaceous stalked crinoids is indicative of an asynchronous, gradual migration of stalked crinoids to deep-water habitats, to which they are restricted in modern oceans.

The points raised by Dr. Schieber are most efficiently addressed through a joint Reply from both Plint and Cheadle, who are currently working on Cretaceous mudrocks in the Canadian portion of the Western Interior Seaway. Before making our reply, both Plint and Cheadle, as relative neophytes in the world of mudrock sedimentology, are pleased to acknowledge the guidance and inspiration provided by the numerous, groundbreaking, publications of Juergen Schieber. We hope that our research on Canadian mudrocks can also make some modest contribution to the exciting, tantalizing and sometimes frustrating field of mudrock sedimentology. We thank Dr Schieber for the interest he has taken in the paper by Plint (2014) concerning prodelta mudstone in the Cretaceous Dunvegan Formation. Below, we comment briefly on the main points raised in Schieber’s Discussion.

The middle to upper Albian Peace River Formation was deposited at the southern end of the ‘Hulcross Sea’, an embayment of the Boreal Ocean that occupied the foredeep of the Western Canada foreland basin. The Peace River Formation can be allostratigraphically divided by numerous, regionally-mappable erosion surfaces, recognizable both in wireline logs, core, and outcrop. We propose recognition of the informal Harmon, Cadotte and Paddy alloformations, bounded by four regionally-mappable marine transgressive surfaces, HE0, CE0, PE0 and VE3 in ascending order. The Harmon alloformation consists predominantly of marine mudstone, and is divided into five allomembers bounded by marine flooding surfaces and/or thick bentonites. The Harmon forms a wedge thinning from >145 m in the SW to 5 m in the NE over approximately 300 km. There is no geometric evidence of a sigmoidal geometry, or that allomembers downlap onto a single, distinct surface. Deposition took place on a very low-gradient and low-relief marine ramp, strongly influenced by storms. The Cadotte alloformation consists of well-sorted swaley cross-stratified sandstone and was deposited on a wave-dominated strandplain shoreface. Ravinement surfaces divide the Cadotte into three, sheet-like allomembers, each typically about 10 m thick. Allomembers CA and CB are mainly fine-grained sandstone whereas allomember CC is dominantly medium-grained sandstone with abundant pebble conglomerate. Towards the north, sandstone grades laterally into heterolithic facies indicative of an offshore setting. The Paddy alloformation lies unconformably on the Cadotte, and comprises an array of facies, with alluvial and lagoonal deposits predominant in the south. Further north, sandstone indicative of a wave-influenced strandplain shoreline forms a belt trending WSW-ENE across the middle of the area; heterolithic offshore marine deposits lie to the north. The Paddy alloformation comprises nine allomembers, PA to PI, that onlap progressively onto the basal unconformity PE0 from SW to NE. The pronounced wedge shape and muddy lithology of the Harmon implies rapid flexural subsidence and largely vertical aggradation whereas the sheet shape of the Cadotte suggests a lower rate of subsidence when high-frequency eustatic change may have driven rapid regressions and transgressions. The lower Paddy allomembers PA to PF are strongly wedge-shaped, suggestive of renewed tectonically-driven subsidence whereas upper allomembers PG to PI are more sheet-like, suggesting that a tectonic load exerted a less important influence and instead, more uniform regional isostatic subsidence took place, driven by the load of the eastward-encroaching sediment body. Sandstone-rich Paddy strata are abruptly overlain, at the VE3 unconformity, by a blanket of dark marine mudstone that forms the basal part of the lithostratigraphic Shaftesbury Formation; the mudstone between the VE3 and VE4 surfaces is of upper Viking age, and has a pronounced wedge geometry which implies a major new pulse of flexural subsidence in the west.

Determining sediment transport direction in ancient mudrocks is difficult. In order to determine both process and direction of mud transport, a portion of a well-mapped Cretaceous delta system was studied. Oriented samples from outcrop represent prodelta environments from ca 10 to 120 km offshore. Oriented thin sections of mudstone, cut in three planes, allowed bed microstructure and palaeoflow directions to be determined. Clay mineral platelets are packaged in equant, face-face aggregates 2 to 5 μm in diameter that have a random orientation; these aggregates may have formed through flocculation in fluid mud. Cohesive mud was eroded by storms to make intraclastic aggregates 5 to 20 μm in diameter. Mudstone beds are millimetre-scale, and four microfacies are recognized: Well-sorted siltstone forms millimetre-scale combined-flow ripples overlying scoured surfaces; deposition was from turbulent combined flow. Silt-streaked claystone comprises parallel, sub-millimetre laminae of siliceous silt and clay aggregates sorted by shear in the boundary layer beneath a wave-supported gravity flow of fluid mud. Silty claystone comprises fine siliceous silt grains floating in a matrix of clay and was deposited by vertical settling as fluid mud gelled under minimal current shear. Homogeneous clay-rich mudstone has little silt and may represent late-stage settling of fluid mud, or settling from wave-dissipated fluid mud. It is difficult or impossible to correlate millimetre-scale beds between thin sections from the same sample, spaced only ca 20 mm apart, due to lateral facies change and localized scour and fill. Combined-flow ripples in siltstone show strong preferred migration directly down the regional prodelta slope, estimated at ca 1 : 1000. Ripple migration was effected by drag exerted by an overlying layer of downslope-flowing, wave-supported fluid mud. In the upper part of the studied section, centimetre-scale interbeds of very fine to fine-grained sandstone show wave ripple crests trending shore normal, whereas combined-flow ripples migrated obliquely alongshore and offshore. Storm winds blowing from the north-east drove shore-oblique geostrophic sand transport whereas simultaneously, wave-supported flows of fluid mud travelled downslope under the influence of gravity. Effective wave base for sand, estimated at ca 40 m, intersected the prodelta surface ca 80 km offshore whereas wave base for mud was at ca 70 m and lay ca 120 km offshore. Small-scale bioturbation of mud beds co-occurs with interbedded sandstone but stratigraphically lower, sand-free mudstone has few or no signs of benthic fauna. It is likely that a combination of soupground substrate, frequent storm emplacement of fluid mud, low nutrient availability and possibly reduced bottom-water oxygen content collectively inhibited benthic fauna in the distal prodelta.

Marine mudstone of the Coniacian Muskiki Member was deposited by storms on a shallow-marine ramp across southern Alberta and northern Montana. The rocks range from the C. crassus crassus Zone of th...

The Cardium Formation is a shallow marine clastic unit of upper Middle Turonian to Lower Coniacian age that was deposited in a ramp setting on the western side of the Western Canada foreland basin. The regional subsurface and outcrop stratigraphy of the Cardium is well-known in northern and central Alberta, but is poorly-known in southern Alberta. A correlation grid of >1200 well logs allowed allomember-bounding erosion surfaces E1 to E7 of the Cardium Formation to be traced across southern Alberta and into northern Montana. Twenty-five outcrop sections in Alberta and Montana were correlated to this stratigraphic framework. Two new bounding unconformities, designated E5.2 and E5.5 were recognized. Both surfaces onlap onto surface E5 towards the NW, showing that the original E5 surface is a composite of three unconformities. The lower Raven River allomember below E5 contains the most basinally-extensive sandstone and is composed of eastward-inclined clinothems indicative of long-term regression. The lower Raven River contains ammonites representative of four Upper Turonian Zones. The overlying upper Raven River and lower and upper Dismal Rat allomembers become progressively muddier upward and form a retrogradational stacking pattern, indicative of long-term transgression. Ammonites and bivalves locate the Turonian-Coniacian boundary just above the E5.5 surface. The E6.5 surface, originally recognized in the Willesden Green area, has been traced over the entire study area, confirming its importance as a major bounding discontinuity. The E7 surface has major erosional relief (>35 m in places) across southern Alberta. Overall, Cardium allomembers between E1 and E5 have a progradational stacking pattern. Allomembers between E5 and E6 are retrogradational whereas those between E6 and E7 are again progradational. Correlation of the Cardium in well logs from Alberta to outcrop of coeval rocks of the Marias River Formation at Ferdig and Deer Creek in Montana, supplemented by biostratigraphic information, suggests that the upper 8–16 m of the Ferdig Member is of Early Coniacian age. The new correlations imply that the top of the Carlile Formation, defined in subsurface, is not the Turonian-Coniacian boundary, as indicated by previous authors, but instead is equivalent to the E7 surface, which defines the top of the Cardium alloformation, and is of Early Coniacian age.

Numerous isolated euselachian teeth were recovered from the early Turonian Kaskapau Formation situated in northwestern Alberta, Canada. This high palaeolatitude assemblage was collected from a sandstone lens along the bank of the Smoky River, and includes 16 species belonging to at least three orders, at least 11 families, and 15 genera. Here we describe Odontaspis watinensis sp. nov. and report the first Canadian occurrence of Polyacrodus sp., Scapanorhynchus sp., and Carcharias aff. C. striatula. The scarcity of benthic taxa in this assemblage supports the previous notion that bottom waters in this region of the Western Interior Seaway experienced enduring anoxic episodes. By comparing the faunal composition of this assemblage with that of middle Cenomanian Canadian assemblages, we show that seven species have a biostratigraphical range that extended across the Cenomanian–Turonian boundary in the northern region of the seaway. Of the taxa described herein, Archaeolamna ex. gr. kopingensis, Cardabiodon a...

During the middle Albian, a southward incursion of the Boreal Ocean flooded northern Alberta and adjacent British Columbia, forming a large embayment known as the Hulcross Sea. Marine mudstones of the Hulcross Formation and Harmon Member of the Peace River Formation record transgression, whereas sandstones of the Cadotte Member of the Peace River Formation record shoreline regression to the north. Abundant hummocky and swaley lamination in the Cadotte sandstone attest to the influence of storms on a shallow shelf. The Cadotte sandstone undergoes a lateral facies change from mud-free shoreface sandstone in the south to heterolithic offshore facies in the north. An articulated crinoid was found within a hummocky sandstone bed about 15 km seaward (north) of the shoreface-shelf facies transition. The articulated state of the crinoid indicates that it was buried very rapidly, and never exhumed. The arms through 20 mm of the column are preserved, but because the details of the aboral cup are not well preserved, this specimen must be left in open nomenclature. The elliptical columnals with a concave latus in the distal portion of the preserved column ally this specimen to the Bourgueticrinida, although with details of the aboral cup lacking and other characters atypical for Mesozoic bourgueticrinids, the Canadian specimen is placed in Bathycrinidae indeterminate. The oldest previously recorded bathycrinids were from the Upper Cretaceous (Maastrichtian), thus this report extends their range to the Lower Cretaceous (Albian).

The stratigraphy of Cretaceous rocks in the Western Canada Foreland Basin is well constrained by dense borehole data that allow three-dimensional mapping of transgressive–regressive events, paleogeography, and subsidence patterns. However, it is difficult to estimate rates of change or to place events in a precise temporal framework because very few of the many bentonite beds have been dated using modern techniques. In this study, two bentonites, of at least regional extent, were dated using isotope dilution – thermal ionization mass spectrometry (ID–TIMS) U–Pb methods on chemically abraded zircon crystals. The older bentonite correlates with the “X” bentonite of the late middle Cenomanian and yields an age of 95.87 ± 0.10 Ma. The Bighorn River Bentonite, which lies just below the Cenomanian–Turonian boundary, yields an age of 94.29 ± 0.13 Ma and is interpreted to equate with the “B” bentonite and bed 80 at Pueblo, Colorado. Both bentonites dated here are older than the previously reported 40Ar/39Ar ages from correlative United States samples, supporting the observation that 40Ar/39Ar ages may systematically underestimate ages of Cretaceous bentonites by ∼1%, as suggested by other recent studies. The X bentonite immediately precedes a major late middle Cenomanian eustatic transgression that inundated the Dunvegan delta complex. The new ages for the X and Bighorn River bentonites indicate an average minimum subsidence rate of ∼0.27 mm/year in the most proximal part of the Cenomanian foredeep in northeast British Columbia during this time. The new age of the Bighorn River Bentonite, coupled with the orbitally tuned time scale of Sageman et al. (2006) , suggests a Cenomanian–Turonian boundary age of 94.12 ± 0.13 Ma.

Large-scale muddy clinoform stratification is rare in Cretaceous marine strata of the Western Canada Foreland Basin; most offshore mudstone units show near-parallel to gently diverging stratification that reflects differential basin subsidence. The early to middle Cenomanian Dunvegan Formation, of broadly deltaic character, is unusual in that it comprises a spectacular set of clinothems. These clinothems have been mapped over a 950 km dip transect, and downlap from NW to SE onto a phosphatic condensed section termed the FSU marker. Our regional mapping shows that the FSU marker is of basin-wide extent and marks the abrupt cessation of deposition for up to about 2 My in the south. In the northwest, the Dunvegan Formation forms a prominent wedge over 300 m thick, interpreted to fill a high-accommodation area. Muddy clinothems in this high-accommodation area are relatively tall (~ 80 m; 115 m decompacted) and extend about 80 km from the delta front to a zero edge at the downlap surface. Wave-rippled and hummocky cross-stratified fine sandstones of the upper delta front record the effects of storms, and extend about 30 m (~ 42 m decompacted) below contemporaneous beach facies, suggesting that effective wave base for sand transport was at about 40 m water depth; mud was transported in deeper water, presumably by storm-driven flows. Towards the SE, the Dunvegan Formation gradually changes from a wedge to a tabular shape, interpreted to indicate deposition in a low-accommodation area. In the transition from high- to low-accommodation areas, clinothems become progressively less tall (50 to about 20 m; 70 to about 29 m decompacted) but longer (150 to > 250 km). The most down-dip “clinothems” are essentially tabular and > 400 km in extent. In the high-accommodation area, offshore mud dispersal is inferred to have been limited by episodic geostrophic flows, and possibly by permanent along-shelf flows that swept mud (probably suspended, flocculated, and pelleted) into a shore-parallel prism, producing relatively short, steep clinothems. Muddy clinothems downlap onto sandy condensed facies of the FSU marker, the latter interpreted to have been deposited in shallow water prior to Dunvegan deposition, but which subsided below wave base in response to loading by the advancing deltaic clinothems. In the southern, low-accommodation area, tabular Dunvegan mudstones suggest that the sea floor was able to aggrade to effective wave base (i.e., about 40 m or less), at which point, wave resuspension of mud became frequent, resulting in efficient off- and along-shore dispersal of mud by geostrophic currents. The initiation of clinothem deposition is interpreted to coincide (a) with a phase of accelerated flexural subsidence in the northwest, related to renewed tectonic loading, and (b) possibly with the onset of large-scale anticlockwise marine circulation at the inception of the Greenhorn Seaway in the early Cenomanian. Together, these tectonic and oceanographic events formed an effective sediment trap along the western margin of the seaway. Only after the western sediment trap had filled, in late Dunvegan time, was mud again dispersed widely across the basin by storm processes in water less than about 40 m deep.

The Santonian-early Campanian Puskwaskau Formation is a prismatic wedge 340 m thick that occupies the foredeep of the Western Canada foreland basin. It is dominated by muddy, offshore sediments deposited by storms in water probably no more than a few tens of metres deep. The Puskwaskau rocks are organized into siltier-upward and sandier-upward successions, bounded by regionally-mappable marine flooding surfaces that permit definition of 14 informal allomembers (labeled A to N in ascending order). These rocks span early Santonian to? early Campanian time and probably represent approximately 2.5 Ma. Only allomember L contains swaley-stratified sandstone bodies (correlative with the Chungo Member in outcrop) that represent at least 40 km of north-eastward shoreface progradation. The upper surface of allomember L is a major, pebble-veneered erosion surface with 15 m of relief that cuts down towards the NE, implying significant relative sea-level fall, followed by subsequent transgressive ravinement. Overlying transgressive mudstone of allomember M onlaps south-westward and appears to fill bathymetric relief cut into the top of allomember L. Allomembers A to L can be grouped into three larger stratigraphic packages, informally termed units, each inferred to represent approximately 750 ka. Each unit is typified by an overall upward-fining succession, followed by an upward-coarsening succession that is capped by a transgressive or flooding surface. Within each unit, facies and small-scale parasequence stacking patterns suggest that accommodation was generated relatively rapidly in the lower part, but accommodation rate diminished towards the top of each unit, possibly even becoming negative. Units 1, 2 and 3 fill discrete arcuate depocentres, the cores of which show abrupt lateral displacement along the orogen by 200–350 km. This is interpreted to record abrupt lateral shifts in the locus of active thrust-sheet advance in the contemporaneous fold-and-thrust belt. These discrete depocentres cannot, however, be discerned in a formation-scale isopach map. In the NW, the base of allomember L is a beveling unconformity that progressively truncates allomembers K to H from the SE towards the NW. Beveling implies gradual tilting and uplift in the NW, prior to and possibly during deposition of allomember L. The initiation of new flexural depocentres took place geologically instantaneously, across the boundaries of individual allomembers (average duration approximately 190 ka); this observation implies that thrust sheets advanced independently, and were separated by major high strain zones.

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.

The Kaskapau and Cardium Formations span Late Cenomanian to Early Coniacian time and were deposited on a low-gradient foredeep ramp. The studied portion of the Kaskapau Formation spans ca 3·5 Myr and forms a mudstone-dominated wedge thinning from 700 to

New allostratigraphic correlations in west-central Alberta show that flooding surfaces in the Sunkay and basal Vimy members of the Blackstone Formation can be traced eastward from Burnt Timber Creek for >500 km to western Saskatchewan, and for 350 km northward into the Dunvegan and Kaskapau formations. At Burnt Timber Creek, a Miliammina manitobensis microfauna in the lowest 1 m of the Sunkay Member indicates equivalence to the Westgate Formation, and an overlying 70 cm conglomerate is correlative with the Fish Scales Formation. Overlying mudstones contain foraminifera of the Verneuilinoides perplexus Zone, indicative of the middle Cenomanian Belle Fourche Formation. The base of the Second White Specks Formation, as currently defined in core in eastern Alberta, equates in outcrop with the lower part of the Sunkay, rather than the base of the Vimy Member as previously thought. The base of the Second White Specks Formation should be placed about 35 m higher in the stratotype core. A bentonite located 9.3 m above the base of the Sunkay Member at Burnt Timber Creek lies near the highest occurrence of Evolutinella sp. aff. E. apricarius, indicating proximity to the "X" bentonite, recognized across the prairies and traceable north into allomember C of the Dunvegan alloformation. A thick bentonite 93.2 m above the base of the Burnt Timber Creek section lies 4 m above the base of the Vimy Member; this bentonite, traceable from northern British Columbia to New Mexico, lies a few metres below the Cenomanian–Turonian boundary and is here formally named the Bighorn River Bentonite.

A black marine mudstone in allomember A of the middle Cenomanian Dunvegan Formation, Alberta, yielded a well-preserved, deep-bodied fish skeleton attributable to a new genus and species, Tycheroichthys dunveganensis, in the Paraclupeidae (Clupeomorpha, Ellimmichthyiformes). This new taxon appears most closely related to members of the subfamily Paraclupeinae, which includes largely freshwater and estuarine or marginal marine species known from South and Central America and China. The Dunvegan Formation represents a large delta complex deposited in the Western Interior Seaway at about 65°N, where mean sea water temperature may have been about 10 °C. The specimen was found about 60 km from the contemporaneous shoreline, and, in life, apparently inhabited a shallow, muddy pro-delta environment characterized by high turbidity and variable salinity. The fish may have died when it was engulfed by brackish floodwater that also introduced suspended mud that rapidly buried the body, preventing physical disarticulation of the skeleton. River outflow probably produced a salinity- and density-stratified water column that limited oxygen transfer to the sea floor, leading to dysaerobic bottom water and an absence of scavengers. High terrestrial phytodetrital content of the sediment also favoured anaerobic conditions that limited bacterial decay.

3-D seismic and log-based mapping of Upper Cretaceous units in the Deep Basin has revealed the presence of fault-related folds in the Cardium Formation and overlying units. The folds formed above low-angle thrust faults that cut clay-rich shales in the lower part of the Kaskapau Formation. Seismic data indicate a fold wavelength of approximately 5 to 8 km at the Cardium level, with fold axes trending NW-SE. Log-based stratigraphic analyses identified fault repeats of Kaskapau allomembers, whereas the 3-D seismic data show details of upward-branching fault splays and related folds. The faults also splay laterally, and transfer strain by overlapping. Post-stack processing of the original 3-D volume, including noise reduction, coherency processing, and volumetric dip analyses significantly improved our ability to image and map these structures. The Cardium Formation produces oil in the study area from fields with orientations that are approximately parallel to the fold axes. These production trends are thought to be related primarily to depositional trends that predate the structural deformation. Nevertheless, the structures we illustrate are fractured, and so they are good analogues for potential drilling targets in similarly-deformed tight-gas reservoirs. Previously published core and borehole breakout studies support these interpretations.

The Middle Turonian Kaskapau Formation in the Rocky Mountain Foothills of northeastern British Columbia comprises up to 950 m of shallow marine sandstones cyclically interstratified with marine mudstones and minor lagoonal deposits. Transgressive surfaces are commonly mantled by thin pebble lags. A transgressive pebble lag exposed in Quality Creek near Tumbler Ridge town site includes rare, well-rounded quartzite cobbles and a quartzite boulder, which were deposited at a paleolatitude of about 67°N. Encrusting organisms are unevenly distributed over five of the largest clasts. Disciniscid brachiopods are abundant on one cobble but are otherwise rare. A conical-shelled lingulate brachiopod with concentric growth lamellae occurs sparsely, and a weakly ribbed lingulate brachiopod is represented by one shell. Serpulid worm tubes, encrusting bryozoans, and possible basal attachments of corals are also present. Attached foraminifera are abundant and distributed over several clasts. Generic diversity an...

The Kaskapau Formation is mudstone-dominated, ranges in age from Late Cenomanian to Middle Turonian, and records a phase of rapid flexural subsidence of the Western Canada foreland basin. The Late Cenomanian portion of the formation that lies above the Dunvegan Formation and below a regional beveling unconformity (the 'K1' surface) is here divided into three informal allostratigraphic units bounded by regional transgressive surfaces. Each unit comprises several upward-shoaling allomembers, bounded by transgressive or flooding surfaces. The units in ascending order are named the A–X, Doe Creek and Pouce Coupe; only the latter two are discussed here. The Doe Creek unit is a wedge that thins eastward from approximately 115 m to less than 5 m over approximately 400 km. The Doe Creek unit was deposited in a broad, very shallow embayment, open to the southeast. Waters were initially brackish, but became more marine over time. In the west, a series of prograding sandy deltaic shorelines and intervening transgressive mudstones can be traced for tens of kilometres into the basin. About 200 km to the east, Doe Creek strata deposited on the eastern margin of the embayment are much muddier but also contain evidence of emergence. In the central part of the embayment, allomembers shoal upward and locally are capped by laminated to bioturbated, lenticular sandstone bodies up to 9 m thick and tens of kilometres long. These sandstones, which preserve no subaerial facies, are detached from shoreline deposits to both west and east and are interpreted as basinally-isolated lowstand delta-front deposits. The Pouce Coupe unit is a wedge that thins eastward from approximately 105 m in the Foothills to zero near the Alberta-British Columbia border. In the east, lower allomembers are bioturbated mudstones and muddy sandstones; higher allomembers are dominated by clean fine-grained marine sandstone that form N–S elongate bodies up to 9 m thick, and tens of kilometres long, arranged in a westerly-prograding stacking pattern. In the west, the Pouce Coupe unit is mudstone-dominated. The Pouce Coupe unit was deposited in a N–S elongate marine basin, bounded in the east by a hinge zone located at about 120°W longitude; the western margin of this basin now lies beneath over-thrust rocks. To the east of the hinge lay an extensive, low-relief land area where upper allomembers of the Doe Creek unit (and possibly older rocks) were subaerially exposed and eroded. The detritus was transported westward and incorporated into the Pouce Coupe unit. The hinge zone appears to coincide with a tectonic domain boundary in the Precambrian basement, which may have localized and amplified flexural deformation during Late Cenomanian time.

The Kaskapau Formation is a mudstone-dominated wedge up to 950 m thick that spans late Cenomanian to middle Turonian time. The formation has a prominent wedge geometry and was deposited in the foredeep of the Western Canada Foreland Basin. In outcrop in northeast British Columbia, nearshore sandstones are locally well developed and include rare wedges of nonmarine strata. On Quality Creek, near Tumbler Ridge, 11 m of nonmarine strata contain abundant dinosaur tracks and the first in situ dinosaur bone reported from British Columbia. This site, at a paleolatitude of about 67°N, preserves a rare glimpse of Turonian terrestrial environments during global eustatic highstand. Three main dinosaur habitats are recognized: strandplain and beach-ridge; freshwater lake; and brackish lagoon. Back-beach sandstone has a relief of about 2.5 m, interpreted as beach ridges; sandy coals containing abundant dinosaur tracks represent inter-ridge slough deposits. Overlying lake deposits comprising laminated muds with freshwater molluscs grade up into rooted muddy siltstone and locally, dinoturbated sandstone. Lake deposits are capped by lagoonal mudstone with abundant brackish-water molluscs, locally including a dinosaur-trampled oyster bioherm. The upper parts of sandy lagoonal deltas are pervasively dinoturbated. Sandstone filling a tidal channel contains logs, oyster shells, and bones of dinosaurs, turtles, and crocodiles, as well as fish scales. The lagoonal succession is erosively overlain by offshore sandy mudstones. Various lines of evidence suggest that the mean annual temperature at this sea-level location was about 14 °C, with a cold-month mean no less than 5.5 °C. The high-latitude location implies a significant period of winter darkness, and correspondingly diminished plant productivity.

The Kaskapau Formation is a major, mudstone-dominated syntectonic wedge deposited in Late Cretaceous time in the foredeep of the Western Canada foreland basin. This study addresses the middle and upper parts of the formation (Late Cenomanian–Middle Turonian), embracing the uppermost part of the Sunkay, Vimy, Haven, and lower part of the Opabin members, which thin eastward from 700 to about 50 m over 250 km. A regional (35,000 km2) subsurface allostratigraphic framework based on 756 well logs and six cores has been extended into 16 major outcrop sections in the British Columbia Foothills and the Peace River valley in Alberta. The lower and upper boundaries of the study interval are defined allostratigraphically at two regional erosion surfaces, the K1 (base) and Granular Siderite (top). In the west, the Kaskapau Formation is divided into five units (I–V), each defined by a major transgressive surface. Each unit contains a major tongue of stacked shoreface sandstones that are named, in ascending order the Dickebusch, Trapper, Tuskoola, Wartenbe and Mount Robert sandstones. All the shoreface sandstones grade eastward over a distance of about 20 to 40 km into heterolithic and muddy facies. Each unit comprises five to seven informal allomembers, each of which shoals upward and is bounded by a flooding or ravinement surface. Most of the 28 allomembers have a wedge shape, thinning to the east, although allomembers 1 and 4 pinch out to the west. Westward-thickening wedges of nonmarine deposits up to 40 m thick are present in units IV and V in the far northwest. In the northeastern part of the study area, three, 3 to 5 m thick sandstone bodies are present at the tops of allomembers 1, 4 and 6. These are named the Erin Lodge, Howard Creek and Josephine Creek sandstones. Their distribution suggests that each sandstone was supplied from the northeast. In the eastern part of the study area, a mudstone package approximately 40 m thick, characterized by high radioactivity forms the basin-wide log marker known as the Second White Speckled Shale. Log correlation shows that this organic-rich mudstone is a diachronous facies which formed during rapid proximal subsidence when sand and silt were trapped in the western foredeep. Units I to III of the Kaskapau Formation taper dramatically to the east whereas units IV and V taper less strongly. These geometric changes are interpreted to record a progressively decreasing rate of flexural subsidence during middle-late Kaskapau time. The limited progradation of shorelines (

A basic sedimentological and palaeopedological framework is now in place for non-marine sequence models. The variability of interfluve palaeosols has not, however, been systematically documented, nor have the stratigraphic implications of that variability been incorporated into sequence models. Interfluve palaeosol variability in the deltaic Dunvegan Formation, NE British Columbia, Canada, is investigated, for which a detailed allostratigraphic and palaeogeographic framework has been developed, based on abundant well (> 2300 logs) and outcrop (> 60 sections) control. Regionally extensive valley fills and interfluves have been mapped in coastal plain deposits over an area of about 50 000 km 2 . This palaeogeographic framework permits interfluve surfaces exposed in outcrop to be located in terms of distance from the margins of coeval valleys. The micromorphological, geochemical and mineralogical characteristics of five representative sequence-bounding palaeosols located from 250 m to more than 15 km from coeval valley margins are described. These interfluve palaeosols are similar to modern Alfisols and all record (i) aggradation on an alluvial/coastal plain; (ii) a subsequent static and/or degradational phase related to valley incision, nondeposition and soil thickening; and (iii) a final aggradational phase related to valley filling and renewed sedimentation across the coastal plain. Within this overall template, however, variations in palaeosol thickness, redoximorphic features, illuvial clay content and geochemistry suggest developmental control by hydrological characteristics that were influenced by both the nature of the underlying alluvial sediments and distance from the valley margin. The presence of mature interfluve palaeosols with complex developmental histories suggests that landscape dissection may have been related to terrace development associated with valley incision. Palaeosols closer to valley margins are thicker, contain more illuvial clay and display characteristics suggesting better drained conditions relative to those palaeosols that developed further from valley margins. Subsequent deposition on interfluves also reflects distance from valleys, with those sites close to valleys accumulating cumulic soils with evidence of brackish groundwater, whereas far from valleys (> 10-15 km), groundwater was fresh and clastic supply minimal, encouraging peat formation. Variations in drainage and palaeotopography during landscape dissection resulted in different palaeosol development styles on interfluve surfaces that can be shown, on the basis of physical correlation, to have the same geomorphic age. These observations support the concept of the soil-forming interval as a basis for pedostratigraphic correlation in ancient terrestrial deposits. Palaeosol variability on interfluves is to be expected, and recognition and documentation of this variability is an important prerequisite to palaeogeomorphological, palaeoclimatic and sequence stratigraphic interpretations.

The mid-Cenomanian Dunvegan Formation represents a delta complex deposited on a foreland basin ramp over about 2 my. The Dunvegan is divided into 10 transgressive-regressive allomembers, labelled J-A in ascending order, each defined by regional marine transgressive surfaces. Parasequences within allomembers show an aggradational to offlapping stacking pattern that reflects alternate generation and removal of accommodation. The upper surfaces of allomembers H-E are incised by extensive valley systems traceable for up to 320 km and over about 50 000 km 2 . Valley depths range up to 41 m and can change significantly over short distances. However, the average depth of incision (mean 21 m) shows no systematic variation in longitudinal profiles and no evidence of headward shallowing. Valleys are typically 1-2 km wide, but locally widen to about 8 km. Widening is sometimes associated with confluence zones, but elsewhere it is not. Updip reaches of valleys are dominated by crossbedded fluvial sandstone forming multistorey point-bar deposits. Sandstones contain widespread but uncommon paired carbonaceous drapes recognizable as tidal bundles. Inclined heterolithic stratification is locally well developed at the top of the valley fill. Downdip reaches of valleys, typically within 50 km of the lowstand shoreline, have a sandstone-dominated lower part and, locally, a mud-rich upper portion consisting of a variety of laminated heterolithic facies with a clear tidal signature. These heterolithic deposits may represent central basin, tidal flat, bayhead delta and point-bar environments. Valley filling took place mainly during the transgressive systems tract (TST) when tidally influenced environments migrated upvalley. Semi-diurnal tidal backwater effects extended at least 30 km landward of the regional maximum transgressive marine shoreline. The aggradational late TST and highstand systems tract (HST) includes deltaic and coastal plain deposits comprising lake and anastomosed river deposits that suggest a very low gradient ( 1:3000). Delta parasequences of the falling stage systems tract (FSST) offlap seaward and have no equivalent coastal plain deposits. The FSST has an average width of 60 km and an inferred gradient of 1:2500. The upper surfaces of the HST and FSST are extensively incised by valleys. The lowstand systems tract (LST) is subtly aggradational, lacks valleys and is characterized by large delta lobes fed by major distributaries. The width and inferred slope of the FSST, coupled with the thickness of aggradational TST and HST deposits on the coastal plain, suggest a vertical accommodation of about 35 m per transgressive event. About 11 m of this is attributed to isostatic subsidence resulting from water and sediment loads; the residual 24 m is attributed to eustatic rise. This sea-level change is of the same order of magnitude as the valley depths. The length of valleys, however, does not seem to be explicable solely in terms of downstream forcing by sea-level change, and an additional, upstream-forcing mechanism, possibly related to precipitation cycles in the Milankovitch band, might be inferred.

In this paper we describe little-studied exposures of the Upper Cretaceous Cardium Formation in the northern Foothills and Peace River Plains, located north of Twp. 58. We correlate sixteen principal outcrop sections along the Foothills and across the northern escarpment of the Cardium as far east as the Smoky River. Correlations are based on tracing bounding erosion surfaces, initially observed in well logs and cores, and later extended into outcrop. The Kakwa Member is conglomeratic in many of these sections. The member displays a spectrum of conglomerate types, of both shallow marine and fluvial origin. Depositional environments are differentiated on the basis of stratigraphic context, conglomerate texture, sedimentary structures, stratification style and paleogeographic setting. We describe in detail four localities exemplifying the main paleoenvironments. At Bay Tree, a 12 m thick section consists primarily of clast-supported conglomerates representing a wave-dominated shoreface and beachface. This environment is dominated by broadly horizontal stratification with horizontal facies heterogeneity on a metre scale. At Cutbank Lake, swaley-stratified shoreface sandstones contain pebble-lined scours that show an upward increase in thickness and lateral continuity and represent rip current deposits. At Mount Niles, conglomerate forms a 2-6 m thick, >200 m wide, channelized body consisting of heterolithic matrix-supported conglomerates and pebbly sandstones capped by gravel wave ripples. Deposition may have been in a river-mouth setting. At 'Horseshoe Mountain', the upper part of the Kakwa Member consists of metre-scale crossbedded pebbly sandstone and matrix-supported conglomerate deposited in a pebbly fluvial system lacking marine influence. For the entire study area, paleocurrent observations indicate a strong NW to SE alongshore transport of gravel, with storm waves approaching from the NE. Fluvial crossbedding is directed towards the NE. Some of the outcrop facies can also be recognized in core from the adjacent subsurface. Our descriptions of conglomerate facies in outcrop facilitate interpretation of the depositional environment of comparable units in subsurface. Unfortunately, the limited extent of exposures does not allow us to determine with precision the geometry of conglomeratic units. However, a broad conglomerate-rich zone >90 km in dip extent and 10-20 km in strike extent can be traced across the northern outcrop belt and probably records the position of a major and long-lasting pebbly fluvial system. Subsurface analogs would be "exploration fairways". At the reservoir scale, conglomerate bodies showing greater influence of wave reworking would tend to be more elongate, and have greater facies continuity/permeability, in a shore-parallel direction. The outcrops display lateral textural heterogeneity at scales of metres to 10s of metres. This heterogeneity would affect reservoir performance, but could not be captured (for reservoir modeling) using typical development well spacing. End_Page 437

Mineralogical and stable hydrogen and oxygen isotopic compositions have been obtained for clay minerals comprising an interfluve paleosol (Clayhurst CH 2 ) from the early to middle Cenomanian Dunvegan Formation, British Columbia, Canada. This paleosol provides a special opportunity to determine the stable isotopic composition of early Late Cretaceous paleoprecipitation on the western coast of the Western Interior Seaway at a very northerly paleolatitude (65°). Detrital kaolinite and illite, and complex dioctahedral mixed-layer clay minerals of pedogenic origin are abundant throughout the paleosol in the δ D values of −93‰ to −81‰ and δ 18 O values of −12.9‰ to −11.6‰ were generally obtained for the ancient soil water, and hence paleoprecipitation. For one thin interval near the top of the paleosol, higher δ -values are indicated for the ancient soil water. These results may indicate processes arising from a westward transgression of the Western Interior Seaway.

The Cenomanian Dunvegan Formation is divided into ten regressive-transgressive allomembers designated J-A in ascending order, and represents a large delta complex deposited over about 2 m.y. Valley systems were mapped on the upper surfaces of allomembers H to E, using 4800 well logs and 40 outcrop sections distributed over 50,000 km2. Valleys trend broadly NW to SE across a delta plain that expanded in width from 150 to over 300 km during progradation of the deltas that comprise allomembers H to E. The longest valley can be traced for up to 330 km. A few valleys can be traced seaward into low-sinuosity distributaries feeding delta lobes. Most other valleys disappear within 20-30 km of the lowstand delta front, at a point interpreted to separate the falling stage from the lowstand systems tract. Most valley systems have a dendritic pattern, although an apparently anastomosed pattern is observed in some areas. Individual valley reaches have a strong NW-SE and NE-SW preferred orientation, with abrupt, approximately right-angle bends and junctions. These valley trends mimic those of faults in the underlying Carboniferous rocks. Valley depths range between 15 and 40 m, and average depths range from 19.1 to 23.8 m, with an overall average of 21.3 m. There is no systematic variation in depth along the length of individual valleys. Valleys are typically 1 to 2 km wide, but can expand to a maximum of 10 km, sometimes, but not always in the vicinity of confluences. Valley-fills are dominated by fine- to medium-grained sandstone, up to 97% in some wells. Sandstone probably represents multi-storey point bars. Mudstone tends to form a greater part of the fill (up to 50%), in more seaward reaches. Muddy deposits are generally concentrated in the upper 5-15 m of valley-fills, where muddier-upward units might represent heterolithic point-bars and/or tidal flats whereas sandierupward units could represent bay-head deltas. Valley incision is considered to be most probably attributable to eustasy coupled with climatically driven changes in the ratio of sediment load to discharge. Neither tectonic tilting, nor changes in the rate of subcrustal loading appear to provide plausible explanations for incision and filling. End_Page 277

Lower to upper Coniacian rocks in the foredeep of the Western Canada Foreland Basin are dominated by mudstone and subordinate sandstone and were deposited on a very low-gradient, storm-dominated marine ramp. The rocks are organized into several scales of upward-coarsening, upward-shoaling succession, bounded by marine flooding surfaces. Abundant, publicly available wireline log data permit flooding surfaces to be traced for hundreds of kilometers in subsurface. Flooding surfaces can be considered to approximate time surfaces that allow the subsidence history of the basin to be reconstructed. Particularly widely traceable flooding surfaces were chosen, on pragmatic grounds, as the boundaries of 24 informal allomembers, most of which can be mapped along the foredeep for >750 km. Allomembers can also be traced westward into the fold-and-thrust belt to outcrop in the Rocky Mountain Foothills. Some flooding surfaces are mantled with intra- or extrabasinal pebbles that imply a phase of shallowing and, ...

The early to middle Cenomanian Dunvegan Formation represents a major deltaic complex that, within the study area, prograded 400 km from NW to SE, parallel to the Cordillera, over about 2 m.y. The formation ranges from about 90 to 270 m thick, being thickest in the NW, in the vicinity of Chetwynd B.C. The formation has been divided into ten allomembers, broadly comparable to transgressive-regressive sequences, labeled J to A in ascending order. Updip, allomembers are bounded by erosional valleys and interfluve surfaces whereas downdip, they are bounded by regionally-traceable marine ravinement and flooding surfaces. The geometry and facies distribution of the ten allomembers has been mapped over an area of about 80 000 km2 using 2340 well logs and 63 outcrop sections. Twelve log cross-sections summarize regional facies distribution and thickness, and key surfaces are correlated into 28 outcrop sections around the northern and western margins of the basin. Allomembers are composed of "shingles" that represent individual upward-shoaling delta lobes. The updip, sandy parts of shingles are attributed to the lithostratigraphic Dunvegan Formation, whereas muddy downdip parts are assigned to the Shaftesbury Formation. Allomembers downlap onto a prominent condensed section, rich in fish scales (the radioactive, "Fish Scales Upper" log marker), that in this study defines the base of an informal Dunvegan alloformation. A prominent marine to lagoonal flooding surface on top of Dunvegan allomember A, traceable throughout the study area, is considered to mark the top of the alloformation. Marine flooding surfaces that bound allomembers in downdip areas can be traced updip into surfaces that define the tops of interfluve paleosols that separate 20-35 m deep valleys. Because they provide evidence of alternating deposition and erosion, allomembers can be interpreted as transgressive-regressive sequences reflecting relative sea level oscillations. Only two of the allomembers display a recognizable downward shift in facies and onlap that typifies classical Exxontype sequences. Allomembers J-F have a sigmoidal-prismatic geometry, thickest in the marine delta-front area and thinning up- and down-dip. They show no significant thickening along-strike towards the Cordillera, suggesting no differential subsidence in that direction. In contrast, allomembers E to A show progressive updip thickening of alluvial facies in the NW, adjacent to the Cordillera, and concomitant decrease in volume of marine deltas downdip. This probably reflects progressive sediment partitioning in response to renewed updip flexural subsidence. Paleogeographic maps for allomembers J-C reveal a series of lobate to cuspate deltas indicating significant fluvial influence. Local facies successions are, however, dominated by wave-formed structures which could, in the absence of paleogeographic information, be misinterpreted to represent linear coastal systems. A summary paleogeographic map of the basal 15-50 m of the overlying Kaskapau Formation shows a 400 km shoreline backstep from Dunvegan allomember C, with the formation of a broad embayment fringed by low-energy, shoal-water deltas in the north. Coeval, wave-dominated sandbodies to the SE are isolated in shelf mudstone and might represent lowstand shoreline deposits. Within the lower Kaskapau Formation, an unconformity, termed "K1", locally truncates several tens of m of strata from W to E. In the east, the K1 unconformity is correlative with a Glossifungites firmground, overlain by up to 1 m of ooidal ironstone. Mudstone-encased SCS (swaley cross stratification) and HCS (hummocky cross stratification) sandstones within this interval, including the Doe Creek and Pouce Coupe sandstones are partially truncated by the K1 unconformity; these sands pass westward into mudstones and may have been shed from a rising forebulge in the east. Stratigraphically-equivalent marine sandstones on the western margin of the basin have no physical connection with Doe Creek and Pouce Coupe sandstones. The Howard Creek and other unnamed sandstones overlie the K1 surface; they appear to be associated with another erosion surface at the base of the highly radioactive Second White Speckled Shale that approximates the Cenomanian-Turonian boundary. End_Page 43------------------------- RESUME La Formation de Dunvegan du Cenomanien inferieur-moyen represente un complexe deltaique majeur qui, dans la region d'etude, a progresse sur 400 km du NW ou SE, parallelement a la Cordillere, pendant environ 2 m.a. La formation mesure de 90 a 270 m d'epaisseur, etant a son plus epais au NW, dans les environs de Chetwynd, C.-B. La formation a ete divisee en 10 allomembres, generalement comparables a des sequences transgressives-regressives, etiquetes J a A en ordre ascendant. En amont-pendage, les allomembres sont limites par des vallees erosionnelles et des surfaces interfluves alors qu'en aval-pendage, ils sont limites par des surfaces de ravinement marin et d'inondation que l'on peut suivre a l'echelle regionale. La geometrie et la distribution des facies de ces dix allomembres ont ete cartographiees sur une region d'environ 80 000 km2 en utilisant les diagraphies de 2340 puits et les coupes de 63 affleurements. Douze coupes de diagraphies resument la distribution regionale et l'epaisseur des facies, et des surfaces reperes sont correlees avec 28 coupes d'affleurements au pourtour des marges septentrionale et occidentale du bassin. Les allomembres sont composes de "bardeaux" qui representent des lobes de delta individuels d'eau moins profonde vers le haut. Les parties sablonneuses, en amont-pendage, sont attribuees a la formation lithostratigraphique de Dunvegan, alors que les parties en aval-pendage sont assignees a la Formation de Shaftesbury. Les allomembres forment un biseau de progradation dans une coupe condensee proeminente, riche en ecailles de poisson (le marqueur diagraphique "Fish Scales Upper", radioactif), qui dans cette etude defini la base d'une alloformation informelle de Dunvegan. Une surface d'inondation marine a lagunaire en saillie au sommet de l'allomembre A de Dunvegan, qui peut etre suivie a travers toute la region d'etude, est consideree comme le marqueur du sommet de cette alloformation. Les surfaces d'inondation marine qui limitent les allomembres dans les regions en aval-pendage peuvent etre suivies, en amont-pendage, dans des surfaces qui definissent les sommets de paleosols interfluves qui separent des vallees profondes de 20 a 35 m. Parce qu'ils fournissent une preuve de l'alternance de depot et d'erosion, les allomembres sont interpretes comme des sequences transgressives-regressives refletant des oscillations du niveau marin relatif. Seul deux allomembres montrent un deplacement vers le bas, reconnaissable en facies et en recouvrement, qui est typique des sequences classiques du type Exxon. Les allomembres J-F ont une geometrie sigmoide-prismatique, sont plus epais dans la region du front deltaique marin et s'amincissent vers le haut et en aval-pendage. Ils ne montrent aucun epaississement significatif parallelement a la direction, vers la Cordillere, ne suggerant aucune subsidence differentielle dans cette direction. En contraste, les allomembres E a A montrent un epaississement progressif vers l'amont-pendage des facies alluvionnaires du NW, a proximite de la Cordillere, et une decroissance concomitante en aval-pendage du volume des deltas marins. Ceci reflete probablement le cloisonnement progressif des sediments en reponse a une subsidence flexurale renouvelee en amont-pendage. Les cartes paleogeographiques des allomembres J-C revelent une serie de deltas lobes ou indentes indiquant une influence fluviale significative. Les successions de facies locaux sont toutefois dominees par des structures formees par les vagues, ce qui, en l'absence d'information paleogeographique, pourrait etre interprete, a tort, comme representant des systemes lineaires cotiers. Une carte paleogeographique de sommaire des 15-50 m de la base de la Formation de Kaskapau susjacente, montre un recul de 400 km d'une ligne de rivage sur l'allomembre C de Dunvegan, accompagne de la formation d'une large baie bordee par des deltas de faible energie et de faible profondeur au nord. Des corps sablonneux contemporains, domines par les vagues au SE, sont isoles dans du mudstone de plate-forme et representent peut-etre des depots de rivage de faible niveau marin. A l'interieur de la partie inferieure de la Formation de Kaskapau, une discordance, appelee "K1", tronque localement plusieurs dizaines de metres de strates de l'ouest a l'est. A l'est, la discordance K1 est correlee avec un sol de terre compactee a Glossifungites, recouvert par jusqu'a un metre de roche ferrugineuse a ooides. Les gres SCS et HCS enfermes dans le mudstone a l'interieur de cet interval, incluant les gres de Doe Creek et de Pouce Coupe, sont partiellement tronques par la discordance K1; ces gres deviennent vers l'ouest des mudstones et peuvent avoir ete derives de l'erosion d'un soulevement frontal a l'est. Les gres marins, stratigraphiquement equivalents sis sur la marge ouest du bassin, n'ont aucune connexion physique avec les gres de Doe Creek et de Pouce Coupe. Les gres de Howard Creek et d'autres gres sans nom recouvrent la surface K1; ils semblent etre associes avec une autre surface d'erosion a la base du Shale Second White Speckled, hautement radioactif, qui se rapproche de la limite Cenomanien-Turonien. Traduit par Lynn Gagnon