Cenomanian Dunvegan Formation Research Articles

Reply to the Discussion by Al‐Mufti on “On the origin and significance of composite particles in mudstones: Examples from the Cenomanian Dunvegan Formation” by Li et al. (2021), Sedimentology, 68, 737–754

We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted. The data that support the findings of this study are available from the corresponding author upon reasonable request.

Crocodylian and dinosaur trace fossil assemblages from crevasse splay/levee and floodplain lake environments: middle Cenomanian Dunvegan Formation, northeast British Columbia, Canada

ABSTRACT Delta-plain strata of the Cenomanian Dunvegan Formation, in north-east British Columbia, represent anastomosed rivers that were flanked by vegetated crevasse splays, wetlands and shallow lakes. These rocks preserve a rich record of ankylosaur and ornithopod walking and wading tracks, as well as crocodylian swim traces and tracks. Analysis of depositional, erosional, and trace-making events reveals alternating phases of flooding and emergence that controlled both animal activity (walking, wading, swimming) and mud substrate consistency (firm vs. soupy), and hence fidelity of track preservation. Some tracks resemble those produced by both ankylosaurs and crocodylians, and confident attribution is difficult. The absence of tail drag marks suggests an ankylosaur trackmaker, whereas prominent claw marks might favour a crocodylian origin. Unusually large crocodylian swim traces suggest animals about 9 m, and possibly up to 12 m in length. These large traces may represent a precursor to the giant crocodylian Deinosuchus. Ankylosaur tracks are well-preserved in lake and channel-margin deposits, whereas crocodylian traces are most commonly preserved in firm muddy lake sediments that had experienced previous subaerial exposure and dewatering. Close integration of trace fossils with sedimentary and stratigraphic features makes it possible to reveal a detailed chronology of biotic and sedimentary events on palaeo-surfaces.

On the origin and significance of composite particles in mudstones: Examples from the Cenomanian Dunvegan Formation

AbstractDespite the fact that mud‐dominated composite particles have increasingly been recognized as important components of marine mudstones, the characteristics, types and origins of these composite particles remain poorly understood. This incomplete understanding of critical mudstone parameters (for example, depositional grain size, composition at the particle scale and provenance) severely limits the ability to accurately interpret the conditions (for example, depositional environment and climate) under which these rocks were deposited. Herein, detailed petrographic analysis was conducted in core samples from a transect of contemporaneous proximal to distal deposits from the Cenomanian Dunvegan Formation, a fluvial‐dominated delta system in the Western Canada Sedimentary Basin. Within the well‐developed depositional framework, mud‐dominated composite particles can be tracked along the depositional profile of the Dunvegan Formation from the fluvial to the marine realm (from incised valley to distal prodelta). By following these particles from source (hinterland erosion) to sink (offshore deposition), the origin and dispersal of various types of mud‐dominated composite particles in marine mudstones can be unequivocally determined. Mud‐dominated composite particles derived from a wide range of origins are differentiated. Allochthonous mud‐dominated composite particles, supplied by rivers draining the hinterland, comprise volcanic rock fragments (vitric or felsic in composition), chert fragments, shale lithics (clay‐mineral‐rich or quartz‐rich in composition), metamorphic rock fragments and chlorite/siderite clasts. Autochthonous mud‐dominated composite particles include rip‐up clasts (argillaceous, sideritic or siliceous in composition) formed from intra‐basinal erosion and contemporaneous floccules. The recognition of mud‐dominated composite particles shows that the Dunvegan prodelta ‘mudstones’ are much coarser grained and more heterogeneous in terms of their petrographic composition than the grain size of their component minerals would suggest. Results of this study call for a critical reappraisal of the composition and actual grain size of mudstones in general. Recognition of mud‐dominated composite particles can provide valuable insights to unravel their provenance, transport history and depositional setting, and will greatly enhance their utility as palaeoenvironmental archives.

An ankylosaurian dinosaur from the Cenomanian Dunvegan Formation of northeastern British Columbia, Canada

Abstract. Fragmentary but associated dinosaur bones collected in 1930 from the Pine River of northeastern British Columbia are identified here as originating from an ankylosaur. The specimen represents only the second occurrence of dinosaur skeletal material from the Cenomanian Dunvegan Formation and the first from Dunvegan outcrops in the province of British Columbia. Nodosaurid ankylosaur footprints are common ichnofossils in the formation, but the skeletal material described here is too fragmentary to confidently assign to either a nodosaurid or ankylosaurid ankylosaur. The Cenomanian is a time of major terrestrial faunal transitions in North America, but many localities of this age are located in the southern United States; the discovery of skeletal fossils from the Pine River demonstrates the potential for the Dunvegan Formation to produce terrestrial vertebrate fossils that may provide important new data on this significant transitional period during the Cretaceous.

High‐frequency sequences within a retrogradational deltaic succession: Upper Cenomanian Dunvegan Formation, Western Canada Foreland Basin

AbstractAfter prograding for several hundred kilometres during Middle Cenomanian time, the Dunvegan delta complex in north‐west Alberta and adjacent British Columbia experienced stepwise transgression, commencing at about the Middle to Late Cenomanian boundary. Progressive drowning of the delta complex is recorded by Dunvegan allomembers B and A, each comprised of three simple depositional sequences, bounded by composite subaerial unconformity/flooding surfaces. Each sequence represents an array of deltaic depositional environments. Delta‐front sandstones preserve little evidence, such as hummocky cross‐stratification, for powerful storm wave action, although wave and combined‐flow ripples are common. Delta‐front sandstone bodies tend to be smaller and lobate in the lower part of the studied interval, and larger and more linear near the top. This suggests increasingly effective wave‐driven redistribution of sand as more open‐marine conditions were gradually established. The top surfaces of allomembers B and A are locally incised by sandstone‐filled palaeovalleys up to 19 m deep; river incision may have been a response to relative sea‐level fall and/or a change in the ratio of discharge to sediment load. Overall, the shoreline described a broad arc, open to the south east, with the sense of shoreline migration north‐west to south‐east. For each sequence, the shoreline migrated an average of 80 km between transgressive and regressive limits. The transgressive limit shows a progressive landward offset of about 15 km per sequence, culminating in complete drowning of the delta system above sequence A3. Isopach maps show that syn‐depositional tectonic subsidence rotated the basin down to the south‐west; palaeogeographic maps show, however, that the sea floor sloped to the south‐east, implying that sediment redistribution effectively filled all tectonically generated accommodation and maintained a south‐east inclined depositional surface. Transgressions and regressions across this surface were therefore driven primarily by eustasy rather than pulses of tectonic subsidence. Simple calculations based on inferred alluvial gradients of 10–20 cm/km suggest that eustatic excursions of ca 8–16 m would have been sufficient to generate sequence thicknesses on the order of 10 m. Limited geochronologic and biostratigraphic control suggests that the six simple sequences that form Dunvegan allomembers B and A each represent an average of about 41 kyr, suggesting that the orbital obliquity cycle was the primary control on high‐frequency sea‐level cycles.

Predicting sediment discharges and erosion rates in deep time—examples from the late Cretaceous North American continent

AbstractDepositional stratigraphy represents the only physical archive of palaeo‐sediment routing and this limits analysis of ancient source‐to‐sink systems in both space and time. Here, we use palaeo‐digital elevation models (palaeoDEMs; based on high‐resolution palaeogeographic reconstructions), HadCM3L general circulation model climate data and the BQART suspended sediment discharge model to demonstrate a predictive, forward approach to palaeo‐sediment routing system analysis. To exemplify our approach, we use palaeoDEMs and HadCM3L data to predict the configurations, geometries and climates of large continental catchments in the Cenomanian and Turonian North American continent. Then, we use BQART to estimate suspended sediment discharges and catchment‐averaged erosion rates and we map their spatial distributions. We validate our estimates with published geologic constraints from the Cenomanian Dunvegan Formation, Alberta, Canada, and the Turonian Ferron Sandstone, Utah, USA, and find that estimates are consistent or within a factor of two to three. We then evaluate the univariate and multivariate sensitivity of our estimates to a range of uncertainty margins on palaeogeographic and palaeoclimatic boundary conditions; large uncertainty margins (≤50%/±5°C) still recover estimates of suspended sediment discharge within an order of magnitude of published constraints. PalaeoDEMs are therefore suitable as a first‐order investigative tool in palaeo‐sediment routing system analysis and are particularly useful where stratigraphic records are incomplete. We highlight the potential of this approach to predict the global spatio‐temporal response of suspended sediment discharges and catchment‐averaged erosion rates to long‐period tectonic and climatic forcing in the geologic past.

An early Late Cretaceous (Cenomanian) sturgeon (Acipenseriformes) from the Dunvegan Formation, northwestern Alberta, Canada

A recent survey of the middle Cenomanian Dunvegan Formation along the Peace River, Alberta, has yielded a partial skull of a large acipenseriform fish. The fossil was from an animal approximately 5 m in length, based on comparisons with living relatives. Though incomplete, this represents an important record of mid-Cretaceous fish from northern North America, as formations of this age are virtually unexplored in northern regions. This fossil is the oldest acipenserid from North America, and one of the most northerly known.

Probable ankylosaur ossicles from the middle Cenomanian Dunvegan formation of northwestern Alberta, Canada.

A sample of six probable fragmentary ankylosaur ossicles, collected from Cenomanian deposits of the Dunvegan Formation along the Peace River, represent one of the first dinosaurian skeletal fossils reported from pre-Santonian deposits in Alberta. Specimens were identified as ankylosaur by means of a palaeohistological analysis. The primary tissue is composed of zonal interwoven structural fibre bundles with irregularly-shaped lacunae, unlike the elongate lacunae of the secondary lamellar bone. The locality represents the most northerly Cenomanian occurrence of ankylosaur skeletal remains. Further fieldwork in under-examined areas of the province carries potential for additional finds.

Hyperpycnal Rivers and Prodeltaic Shelves in the Cretaceous Seaway of North America

Abstract Despite the historical assumption that the bulk of marine “shelf” mud is deposited by gradual fallout from suspension in quiet water, recent studies of modern muddy shelves and their associated rivers show that they are dominated by hyperpycnal fluid mud. This has not been widely applied to the interpretation of ancient sedimentary fluvio-deltaic systems, such as dominate the mud-rich Cretaceous Western Interior Seaway of North America. We analyze two such systems, the Turonian Ferron Sandstone Member of the Mancos Shale Formation, in Utah, and the Cenomanian Dunvegan Formation in Alberta. Paleodischarge estimates of trunk rivers show that they fall within the predicted limits of rivers that are capable of generating hyperpycnal plumes. The associated prodeltaic mudstones match modern hyperpycnite facies models, and suggest a correspondingly hyperpycnal character. Physical sedimentary structures include diffusely stratified beds that show both normal and inverse grading, indicating sustained flows that waxed and waned. They also display low intensities of bioturbation, which reflect the high physical and chemical stresses of hyperpycnal environments. Distinct “mantle and swirl” biogenic structures indicate soupground conditions, typical of the fluid muds that represent the earliest stages of deposition in a hyperpycnal plume. Hyperpycnal conditions are ameliorated by the fact that these rivers were relatively small, dirty systems that drained an active orogenic belt during humid temperate (Dunvegan Formation) to subtropical (Ferron Sandstone Member) “greenhouse” conditions. During sustained periods of flooding, such as during monsoons, the initial river flood may lower salinities within the inshore area, effectively “prepping” the area and allowing subsequent floods to become hyperpycnal much more easily. Although shelf slopes were too low to allow long-run-out hyperpycnal flows, the storm-dominated nature of the seaway likely allowed fluid mud to be transported for significant distances across and along the paleo-shelf. Rapidly deposited prodeltaic hyperpycnites are thus considered to form a significant component of the muddy shelf successions that comprise the thick shale formations of the Cretaceous Western Interior Seaway.

Clinoforms, Paleobathymetry, and Mud Dispersal Across the Western Canada Cretaceous Foreland Basin: Evidence from the Cenomanian Dunvegan Formation and Contiguous Strata

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.

A middle Cenomanian euselachian assemblage from the Dunvegan Formation of northwestern Alberta

A euselachian assemblage was recovered from the middle Cenomanian Dunvegan Formation situated in northwestern Alberta. This assemblage is the most northern described within the Western Interior Seaway and provides an important insight into the euselachian faunal diversity of this little-known region of the seaway. Despite its high paleolatitude, the assemblage contains a number of elasmobranch taxa, including Hybodus , Squalicorax , Archaeolamna , Cretodus , Dallasiella , and Cretoxyrhina . The Dunvegan assemblage also contains the first known reports from Canada of the odontaspid shark Johnlongia parvidens , the cretoxyrhinid shark Protolamna carteri , and the ray Pseudohypolophus mcnultyi . This assemblage extends the northern geographical range of all taxa. Preliminary comparisons with other middle Cenomanian Western Interior Seaway assemblages show that the core composition of the Dunvegan assemblage is remarkably similar to that of other time-equivalent assemblages; however, conspicuously absent are species that are exceedingly common in other localities situated farther south. We suggest that absence of these taxa from the Dunvegan localities may be caused by a temperature intolerance associated with latitude and sea-water circulation patterns, or by an inability to inhabit environments that exhibit salinity variation.

A new paraclupeid fish (Clupeomorpha, Ellimmichthyiformes) from a muddy marine pro-delta environment: middle Cenomanian Dunvegan Formation, Alberta, Canada

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.

A review of nonmarine turtles from the Late Cretaceous of Alberta

The Late Cretaceous of Alberta preserves one of the most complete records of fossil turtles within a single geographic area in North America. The Cenomanian Dunvegan Formation contains the earliest record of the family Trionychidae in North America. The Santonian Milk River Formation contains a minimum of ten taxa with Adocus, a small trionychid, and a member of the Solemydidae being the most abundant. Diversity remains high in the mid-Campanian Judith River Group. The solemyidid last occurs in the basal beds of the Judith River Group. A member of the Macrobaenidae first occurs in the Dinosaur Park Formation, the uppermost formation in the Judith River Group. Turtles diversity is low in the late Campanian lower Horseshoe Canyon Formation, and they are absent in the early Maastrichtian upper Horseshoe Canyon Formation. Diversity increases in the late Maastrichtian Scollard Formation, although it is much less than in the contemporaneous Hell Creek Formation of Montana. Two of the taxa present in the Scollard Formation, Compsemys and Plastomenus, occur in late Campanian or early Maastrichtian formations in more southerly areas of North America. The changes in turtle diversity through the Campanian and Maastrichtian are interpreted as a result of shifts in a latitudinal turtle diversity gradient resulting from changes in climate. Based on this interpretation a decrease in temperature from the mid-Campanian to early Maastrichtian, followed by a rapid increase at the beginning of the late Maastrichtian is supported.

Clastic Sediment Partitioning in a Cretaceous Delta System, Western Canada: Responses to Tectonic and Sea-Level Controls

The early–mid Cenomanian Dunvegan Formation represents a largedelta complex that prograded at least 400 km from NW to SE. Aregional stratigraphy based on marine transgressive surfaces andequivalent subaerial interfluves allows the formation to be subdividedinto ten transgressive–regressive allomembers, labelled J to A inascending order, each with an average duration of < 200 ky. Analysisof stacking patterns and facies distributions of parasequenceswithin allomembers allows transgressive, highstand, falling stageand lowstand systems tracts to be identified. Extensive valley systemsthat average 1–2 km wide and 21 m deep can be traced for up to320 km across the top surfaces of allomembers H to E. In their lower20–40 km, valleys are filled with muddy heterolithic tidal facies butthis changes to fluvial-dominated multi-storey channel-fills furtherup-valley. Interfluve surfaces are marked by palaeosols, the characterof which indicate a protracted hiatus with extensive physical, chemicaland biological modification of the parent material.Changes in flexural subsidence rate are indicated by isopach patterns.Allomembers J–F have a sigmoidal prismatic geometry, successivelyofflapping to the SE. There is no evidence of thickening towardthe orogen. In contrast, overlying allomembers E–A show progressivedevelopment of a depocentre along the western margin of the basin.The increasing accommodation rate on the updip coastal plain causedmarine deltas to be starved of sediment, leading to progressive backstepof shorelines. Simultaneously, alluvial deposits within the depocentreshow an upward increase in the proportion of subaqueous tosubaerial facies, culminating in the incursion of brackish and finallymarine waters. Thus tectonic subsidence rate had a first-order affecton both the volume of sediment available to build marine deltas andalso on the local character of facies that accumulated on the coastalplain. The onset of flexural subsidence in allomember E appears tohave resulted in subtle uplift of a forebulge, resulting in dramaticdeflection of river systems.Despite the clear tectonic signature, successive transgressions andregressions involved similar horizontal displacements of the shoreline,regardless of subsidence rate. This suggests that modest eustaticchanges also influenced the accommodation available. Based on themeasured horizontal excursions of the shoreline, the vertical thicknessof alluvial strata, and realistic alluvial gradients, an average eustaticexcursion of about 24 m is calculated. The incision of valley systemsis attributed in part to periods of eustatic fall. However, valleys seemtoo long to be explained by eustasy alone, and hence secular changesin discharge are postulated as an additional forcing factor. Climaticcycles in the Milankovitch band may have been responsible for botheustatic and discharge variations.

Stable isotopic investigation of clay minerals and pedogenesis in an interfluve paleosol from the Cenomanian Dunvegan Formation, N.E. British Columbia, Canada

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 <2-μm size-fraction, including ‘intergrade’ clays that range from swelling chlorite to hydroxy-interlayer vermiculite. Dioctahedral ‘intergrade’ clays consisting mostly of randomly interstratified illitic and hydroxy-interlayer vermiculitic layers comprise the <0.2-μm size-fraction. TEM observations suggest that the <2-μm size-fraction comprises a mixture of detrital and pedogenic clays, whereas the <0.2-μm size-fraction consists almost entirely of clays formed during pedogenesis. Using the stable isotopic compositions of the pedogenic clays and temperatures inferred from paleobotanical and micromorphological data, δD values of −93‰ to −81‰ and δ 18O 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.

Paleovalley systems in the Upper Cretaceous Dunvegan Formation, Alberta and British Columbia

ABSTRACT 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------------------------

Micromorphology and development of interfluve paleosols: a case study from the Cenomanian Dunvegan Formation, NE British Columbia, Canada

Research Article| March 01, 2002 Micromorphology and development of interfluve paleosols: a case study from the Cenomanian Dunvegan Formation, NE British Columbia, Canada P.J. McCarthy P.J. McCarthy Department of Geology and Geophysics and Geophysical Institute, University of Alaska, Fairbanks, AK 99775–5780, USA. Search for other works by this author on: GSW Google Scholar Bulletin of Canadian Petroleum Geology (2002) 50 (1): 158–177. https://doi.org/10.2113/50.1.158 Article history received: 18 May 2001 accepted: 15 Sep 2001 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation P.J. McCarthy; Micromorphology and development of interfluve paleosols: a case study from the Cenomanian Dunvegan Formation, NE British Columbia, Canada. Bulletin of Canadian Petroleum Geology 2002;; 50 (1): 158–177. doi: https://doi.org/10.2113/50.1.158 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of Canadian Petroleum Geology Search Advanced Search Abstract An obvious use of paleopedology for sequence stratigraphic analysis lies in the demarcation of erosional discontinuities or major pauses in sedimentation that allow us to recognize and map stratigraphically important surfaces, both in outcrop and subsurface. Many interfluve surfaces may be apparent on the basis of sedimentology and regional stratigraphy alone; however, their appearance can change markedly across a study area, making correlation difficult. A pedosedimentary approach has been utilized to reconstruct the sequence of pedogenic and sedimentary events recorded by the development of stratigraphically significant interfluve surfaces. This was based upon sets of closely-spaced thin sections taken from interfluve sequence-bounding paleosols exposed at Beatton River canyon, British Columbia, Canada. Micromorphology, field morphologies, and major physicochemical characteristics of three interfluve paleosols reveals a complex sequence of soil development related both to normal floodplain sedimentation and to periods of prolonged stasis resulting from valley incision. Two main pedosedimentary stages, related to regional changes in rates of generation of accommodation, are recorded at each interfluve, although the resolution, processes, and resultant features vary in a manner reflecting local differences in hydrology, topography, initial parent material composition, and time. These processes have operated through various pedogenic development pathways to produce polygenetic paleosol profiles on these Cretaceous interfluves. The pedosedimentary approach followed in this case study provides a means of deciphering the development of interfluve paleosols based upon detailed microstratigraphic associations and depth functions of their pedogenic features, in conjunction with ancilliary geochemical, mineralogical, sedimentological, and stratigraphic evidence. Consequently, potential sequence boundaries, identified on the basis of regional stratigraphic patterns, can be determined with a high degree of confidence on the basis of intrinsic evidence derived from the record of ancient landscape processes preserved within the interfluve paleosols. This content is PDF only. Please click on the PDF icon to access. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Nonmarine sequence stratigraphy: Updip expression of sequence boundaries and systems tracts in a high-resolution framework, Cenomanian Dunvegan Formation, Alberta foreland basin, Canada

Ten allomembers, labeled J-A, have been mapped in the deltaic Dunvegan Formation using 2340 wells and 63 outcrop sections. Each allomember spans about 200 k.y., is bounded by regional transgressive surfaces, and consists of 3-10 component shingles, apparently of autogenic origin. Allomembers H-E are discussed in this article. Their internal stacking patterns and bounding surfaces permit interpretation as depositional sequences. Sequences H-F have a sigmoidal-prismatic geometry, downlap to the southeast, and thin northwest onto the coastal plain. No differential thickening exists toward the orogen in the southwest. In contrast, sequence E thickens markedly toward the northwest. The tabular geometry of sequences H-F suggests accommodation was controlled by sea level change, whereas the wedge geometry of sequence E suggests significant tectonic tilting. Subaerial unconformities that bound valleys and extend onto adjacent interfluve paleosols can be traced 120-330 km updip into outcrop. The base of each sequence is characterized by shoreline backstep of 80-150 km. Transgressive and highstand shingles in each sequence comprise marine deltaic deposits that pass landward into coastal plain strata. Falling-stage shingles offlap seaward with little or no nonmarine equivalents updip, whereas lowstand shingles show renewed coastal onlap. In outcrop, three nonmarine systems tracts are recognized: (1) A channel-dominated, low-accommodation systems tract fills valleys up to 35 m deep and is equivalent to the early transgressive systems tract. (Begin page 1968) (2) A lacustrine-dominated, high-accommodation systems tract comprises mudstone enclosing ribbon channel sandstones, blankets interfluves, and forms the bulk of each sequence. It is equivalent to late transgressive and early highstand systems tracts. (3) A paleosol-dominated, low-accommodation systems tract occupies the upper part of each sequence and is capped by the sequence boundary. It is equivalent to the late highstand systems tract. Sequence-bounding interfluve paleosols represent tens of thousands of years of pedogenesis related to slow aggradation, followed by fluvial entrenchment and clastic bypass, and represent the late highstand, falling-stage, lowstand, and early transgressive systems tracts. Coastal plain deposits record only part (perhaps

Sequence stratigraphy and paleogeography of a Cenomanian deltaic complex: the Dunvegan and lower Kaskapau formations in subsurface and outcrop, Alberta and British Columbia, Canada

Sequence stratigraphy and paleogeography of a Cenomanian deltaic complex: the Dunvegan and lower Kaskapau formations in subsurface and outcrop, Alberta and British Columbia, Canada

Evolution of an ancient coastal plain: palaeosols, interfluves and alluvial architecture in a sequence stratigraphic framework, Cenomanian Dunvegan Formation, NE British Columbia, Canada

To date, discussion of changes in alluvial style and in the character of palaeosols in relation to changes in accommodation and sediment supply on floodplains has primarily been from a conceptual standpoint: few case studies are available against which to test ideas. One hundred and thirty metres of non‐marine strata of the Dunvegan Formation were examined in 14 closely spaced sections in the canyon of the Kiskatinaw River, NE British Columbia, Canada. This site was located about 120 km inland from the transgressive limit of the contemporary marine shoreline and represents almost exclusively freshwater environments. Fluvial channels in the Kiskatinaw River section are of two types. Small, single‐storey, very fine‐ to fine‐grained sandstone ribbons with W/T ratios &lt;30, encased in fine‐grained floodplain sediments are interpreted as anastomosed channels. Fine‐ to medium‐grained, laterally accreted point‐bar deposits forming multistorey sand bodies with individual W/T ratios &gt;30 are interpreted as the deposits of meandering rivers filling incised valleys. Interchannel facies include the deposits of crevasse channels and splays, lakes, floodplains and palaeosols. Floodplain palaeosols consist of laterally heterogeneous, simple palaeosol profiles and pedocomplexes similar to modern Entisols, Inceptisols and hydromorphic soils. Interfluve, sequence‐bounding palaeosols adjacent to incised valleys are laterally continuous, up to 3 m thick and can be reliably identified using a combination of (1) stratigraphic position; (2) field observations, such as thickness, structure, colour, degree of rooting; and (3) micromorphological features, such as evidence of bioturbation, clay coatings, ferruginous features and sphaerosiderite. Interfluve palaeosols are similar to modern Alfisols and Ultisols. Correlation of the local stratigraphic succession with the regional sequence stratigraphic framework, based on 2340 well logs and 60 outcrop sections, shows that the vertical changes in coastal plain character (more coals and lakes vs. more pedogenesis) can be related to relatively high‐frequency base level cycles (eustatic?) that are expressed as transgressive–regressive marine cycles in downdip areas. Regional isopach maps show that these cycles were progressively overprinted and modified by an increasing rate of tectonic subsidence in the north and west. The character of palaeosols developed on aggrading floodplains primarily reflects local sediment supply and drainage. In contrast, well‐developed interfluve palaeosols record pedogenesis during periods of reduced or negative accommodation (base level fall). Vertical changes in floodplain palaeoenvironments and palaeosol types reflect changes in accommodation rate. The detailed micromorphological analysis of interfluve palaeosols represents a powerful application of an under‐used technique for the recognition of key surfaces in the geological record. This has broad implications for non‐marine sequence stratigraphy.