Claudia J. Schröder-Adams

Highstand transport of coastal sand to the deep ocean: A case study from Fraser Island, southeast Australia

Deep-water sands form a new frontier for marine geology and petroleum exploration, but how does sand reach the deep sea? Existing geological models predict that deep-water sands are mainly supplied from rivers during times of low sea level, or by incision of canyons into the shelf to tap river or longshore-transport sand sources. Here, we demonstrate that at high sea level, southeast Australian deep-water sands are delivered by a wave-driven coastal transport system, interacting with estuarine ebb tidal flows, that transports sand over the shelf edge at a change in margin orientation. Discovery of this new process results from an investigation that combines multibeam acoustic, microfaunal, zircon and luminescence dating, oceanographic, Landsat, remotely operated vehicle, and sediment property methods. Our longshore transport–driven model is capable of forecasting new locations for deep-water sand deposits in a predictive paleoclimatic and paleotectonic setting.

Late Cretaceous (Cenomanian to Campanian) paleoenvironmental history of the Eastern Canadian margin of the Western Interior Seaway: bonebeds and anoxic events

Abstract Upper Cretaceous strata in the Pasquia Hills of the northern Manitoba Escarpment, eastern Saskatchewan, Canada provide a detailed paleoenvironmental and sea-level record of the eastern margin of the Western Interior Seaway. Sediments deposited during the Cenomanian/Turonian Greenhorn marine cycle are dominantly black mudstones deposited in a stratified water column, with bottom-water anoxia recurrently reaching into the photic zone. A middle Cenomanian sea-level lowstand event followed by transgression left a series of bonebeds within the Belle Fourche Member of the Ashville Formation, indicating a sedimentary environment starved of coarse siliciclastics. Maximum sea level resulted in the formation of limestone beds within the Favel Formation, further favoured by reduced terrigenous sediment input compared to the western margin. Limestone sedimentation was followed by a phase of increased freshwater input under lower sea level conditions, and reducing zoo- and phytoplankton diversities. During final Greenhorn regression, eastern Saskatchewan probably turned into a restricted basin severely limiting marine circulation. Poor or absent benthic foraminiferal assemblages and biomarker analysis suggest prevailing watermass stratification throughout the Cenomanian/Turonian transgressive/regressive cycle. This was caused either by a freshwater lid, stratification of Boreal and Tethyan-derived watermasses, or both, to various intensities affected by changing sea level. Basin oxygenation during Niobrara time varies between localities along the eastern margin as documented by presence/absence of benthic and planktic foraminifera.

Holocene environmental history of thermokarst lakes on Richards Island, Northwest Territories, Canada: Theocamoebians as paleolimnological indicators

Richards Island, Northwest Territories, Canada, is characterized by thermokarst lakes which record Holocene limnological change. This study is the first report of thecamoebian assemblages and continuous annual lake water temperatures from these Arctic lakes. Ecological environments on Richards Island are influenced by a climatic gradient resulting from the contrasting influences of the cold Beaufort Sea to the north and the warm waters of the Mackenzie Delta to the east and west. This climatic gradient in turn influences modern thecamoebian assemblages, and is an indication of the complexity involved in interpreting past conditions from core material in this area.Population abundance and species diversity of thecamoebian assemblages on Richards Island are not significantly different from those reported from temperate and semi-tropical latitudes. However, certain assemblage characteristics, such as large and coarse agglutinated tests, dominance of assemblages by one or two species and low morphological variation are interpreted to be diagnostic of Arctic conditions. Thecamoebian assemblages in core material from the area indicate that the local paleolimnological conditions may have changed within the last 3 ka, and this is unrecorded in previously reported pollen data.Paleoenvironmental interpretations in a permafrost landscape have to take into account morphological instability of thermokarst lakes, which can be the cause of paleolimnological and consequently faunal change. In this area ecosystem development is clearly related to geomorphology and local climatic effects and is not exclusively controlled by regional climate change.

Mid-Cretaceous High Arctic stratigraphy, climate, and Oceanic Anoxic Events

Over the past decades, much research has focused on the mid-Cretaceous greenhouse climate, the formation of widespread organic-rich black shales, and cooling intervals from low- to mid-latitude sections. Data from the High Arctic, however, are limited. In this paper, we present high-resolution geochemical records for an ~1.8-km-thick sedimentary succession exposed on Axel Heiberg Island in the Canadian Arctic Archipelago at a paleolatitude of ~71°N. For the first time, we have data constraints for the timing and magnitude of most major Oceanic Anoxic Events (OAEs) in brackish-water (OAE1a) and shelf (OAE1b and OAE2) settings in the mid-Cretaceous High Arctic. These are consistent with carbon-climate perturbations reported from deep-water records of lower latitudes. Glendonite beds are observed in the upper Aptian to lower Albian, covering an interval of ~6 m.y. between 118 and 112 Ma. Although the formation of glendonites is still under discussion, these well-dated occurrences may support the existence of cool shelf waters in the High Arctic Sverdrup Basin at this time, coeval with recent geochemical data from the subtropical Atlantic indicating a drop in seasurface temperature of nearly 4 °C.

Thecamoebians in Lake Winnipeg: a tool for Holocene paleolimnology

Holocene sediments in Lake Winnipeg are expressed in the lower Lake Agassiz sequence which is unconformably overlain by the Lake Winnipeg sequence. Nine sites, covering the North and South basins and the connecting Narrows, were selected for analysis of Holocene changes in thecamoebian faunae. Only the Lake Winnipeg sequence contains thecamoebians. This study indicates that biologic productivity and consequently the type of organic material in the sediments is the main control on thecamoebian taxa in Lake Winnipeg. Other factors controlling the distribution of thecamoebians are water chemistry and turbidity. Inorganic sediment geochemistry and water temperature do not appear to significantly influence the thecamoebian fauna of Lake Winnipeg. Variations in the abundance of key thecamoebian species along a north-south transect divide Lake Winnipeg into three distinct areas. The North Basin has remained relatively unchanged since the retreat of Lake Agassiz as indicated by the domination of Difflugia manicata throughout its history. This species appears to prefer Cyanophyta and diatoms as its food source. In the Narrows harsh conditions created by turbid waters and lack of algal food taxa result in Centropyxis aculeata replacing Difflugia manicata as the dominant species. In the South Basin three thecamoebian assemblages are recognized. Cucurbitella tricuspis, indicative of eutrophic conditions, dominates the most recent sediments of the South Basin. The underlying sediments are characterized by Difflugia globulus. In Lake Winnipeg this species is not a cold climate (arctic) indicator as suggested elsewhere but instead seems to prefer sediments containing green and yellow-green algal material. A Centropyxis-Arcella Assemblage occurs only at the base of the southernmost core where it is indicative of an early phase of hyposaline conditions as developed in shallow pools during the southward transgression of Lake Winnipeg. This study illustrates the usefulness of thecamoebians as paleolimnological indicators. Environmental changes are more significant in the restricted South Basin resulting in distinct thecamoebian assemblages. In contrast, the North Basin provided a stable environment throughout the late Holocene reflected in only subtle faunal changes.

A New Stratigraphic Framework for the Upper Colorado Group (Cretaceous) in southern Alberta and southwestern Saskatchewan, Canada

ABSTRACT Extensive marine shales and shallow-marine sandstones of the Cretaceous Upper Colorado Group represent one of the last thick, informally named, stratigraphic intervals in the southern part of the Western Canada Sedimentary Basin. Two regionally-mappable formations in southern Alberta and southwestern Saskatchewan are introduced: The Carlile Formation (Turonian) overlying the Second White Specks Formation, and the Niobrara Formation (Coniacian-Santonian) underlying the Milk River Formation. Both names are extensions of lithologically-similar and laterally-equivalent strata in adjacent parts of the Interior Seaway in Canada and the United States. The boundary between the Carlile and Niobrara formations is recognized at a distinct zone (3 to 15 m thick) of 17 bentonites in the lower part of the Niobrara Formation, whereof two are argon-argon dated to 89.19 (± 0.51) and 89.40 (± 0.31). Regional variations in lithology, petrophysics and geochemistry of the two new formations make it possible to further subdivide these into formal subunits. The Carlile Formation is subdivided into the informal lower, middle and upper units. The Niobrara Formation is formally subdivided into three mappable members in ascending order: the shaly, non-calcareous Verger Member, the sandstone-rich Medicine Hat Member, and the shaly calcareous First White Specks Member. An outcrop reference section of the Carlile Formation is designated at Deer Creek (east of West Butte) in the Sweetgrass Hills of north-central Montana. The single core cut from the Carlile Formation in southern Alberta and southwestern Saskatchewan is located at 13-20-17-7W4 and includes twelve metres of the upper part of the formation. It is used as a reference section for the boundary between the Carlile and Niobrara formations. A reference core of the Niobrara Formation is located at 4-16-22-15W4, which also is designated as the type section of the Verger, Medicine Hat and First White Specks members. An outcrop section at the Ghost River Dam Spillway, west of Calgary, serves as the outcrop reference section for the Medicine Hat Member and is correlated to the subsurface using wireline logs and foraminiferal biostratigraphy. End_Page 304------------------------

An organic geochemical study of Cenomanian-Turonian sediments from the Western Interior Seaway, Canada

Abstract Bulk-geochemical and biomarker data were collected for three Cenomanian-Turonian (Late Cretaceous) sections in the Western Canada Sedimentary Basin (Western Interior Seaway, Canada). Rock-Eval and biomarker analyses indicate an east-west thermal maturity trend due to progressive deeper burial associated with the tectonic flexure of the foreland basin. The source of extractable organic matter is dominantly marine with a minor terrestrial contribution. A pseudohomologous family of 2,2-dimethylalkanes (2,2-DMAs), in the C 16 –C 28 range with an even number of carbon atoms exclusively, was tentatively identified from mass spectral data in samples from the Pasquia Hills region (easternmost section). The specific origin of 2,2-dimethylalkanes remains unclear. The presence of isorenieratene derivatives indicates that the northern part of the Western Interior Seaway experienced photic zone euxinic events throughout the transgressive, highstand, and regressive phases of the Greenhorn Cycle. The differential occurrence of isorenieratane between the Canadian sections and the United States transect at maximum sea-level high stand indicates that the water column of the northern part of the WIS was less oxygenated, whereas the water column in the southern WIS was more dynamic and well-mixed.

A variable lacustrine environment in Lake Winnipeg, Manitoba: Evidence from modern thecamoebian distribution

Thecamoebians (testate protozoan) were examined in 18 surface sediment samples from the North and South basins and the Narrows of Lake Winnipeg, Manitoba. Significantly higher numbers of thecamoebians and tintinnids in the North Basin compared to the Narrows and South Basin are attributed to the effects of urban development around the South Basin of Lake Winnipeg. Human population growth in this area has led to increased nutrient concentration in runoff, causing eutrophication of the southern lake, which in turn allows for increased algal productivity. Cucurbitella tricuspis is found in large abundances in the South Basin, particularly close to the inlet of the Red and Assiniboine rivers. High abundances of this species have been attributed to eutrophic conditions, which this species appears to withstand more successfully than other species. Increases in domestic waste output, that have led to elevated heavy metal concentrations in lake bottom sediments of the South Basin, may have resulted in lower abundances of thecamoebians, further reducing competition.Strong currents in the Narrows cause a slightly coarser substrate and sweep away food sources such as phytoplankton. This results in a lower faunal abundance and slightly lower species richness of thecamoebians. Robust species such as the coarse-grained Difflugia viscidula and species which feed on bacteria such as Centropyxis aculeata show increased abundances.Modern thecamoebian assemblages are comparable to Late Holocene faunal associations in terms of species composition. Individual species abundances, however, have changed. For example, in the North Basin the Late Holocene dominance of Difflugia manicata is replaced by various strains of Difflugia oblonga during recent times. A common species of the South Basin from Late Holocene to recent times is Difflugia globulus. It would appear that faunal differences between basins are the result of differences in algal food sources.

The effect of paleotopography on the late Albian and Cenomanian sea-level record of the Canadian Cretaceous interior seaway

In western Canada, a major paleoenvironmental change at the Albian-Cenomanian boundary is related to a eustatic sea-level rise overprinted by a relative sea-level fall in conjunction with preexisting topography within the basin. This paper shows the lateral variability of sedimentology, paleoecology, and biostratigraphy of the latest Albian to Cenomanian interval along the Canadian western margin of the Cretaceous interior seaway. This paper (1) provides an integrated depositional and paleoecological examination of the Albian and Cenomanian lithologic units in the northern Western Interior Seaway; (2) demonstrates the effect of antecedent paleotopography within the basin at the time of the transgression; (3) documents the variability in sedimentary facies and paleoecology controlled by paleorelief; and (4) demonstrates the diachroneity, lateral extent, and extremity of the multiple unconformities controlled by this paleorelief. An enigmatic aspect of the lowermost Cenomanian Fish Scales Formation has been the regional occurrence of chert, quartz, and bioclastic pebbles associated with black anoxic shale. A regional north-south traverse across Alberta provides insight into this problem. In southwestern Alberta, chert- and quartzite-pebble conglomerate and sandstone that are equivalent to the Fish Scales Formation—known as Barons Sandstone (subsurface) and Blairmore Grits (outcrop)—represent proximal shelf sedimentation. This coarse-grained sediment was flushed out during sea-level lowstand and then reworked by a subsequent transgression associated with the Belle Fourche Formation. A large paleohigh existed in southwesternmost Alberta at this time. Northward, the Fish Scales Formation is bounded top and bottom by unconformities and conglomerate, indicating multiple sea-level fluctuations and deposition in a wave-influenced shelf environment. In west-central Alberta, preserved deposits of the Fish Scales Formation indicate deposition in a nearshore setting. Farther to the north and, most distally, in northwestern Alberta and elsewhere to the east, the coarse component of the Fish Scales Formation is predominantly gravel-sized fish and other vertebrate debris with significantly less siliciclastic detritus. Regionally, the unconformity at the base of Fish Scales–Barons becomes more pronounced southward and westward where the underlying shale of the Westgate Formation (or Westgate Member) has been eroded or was never deposited. The regional paleogeographic setting for the Barons Sandstone and Fish Scales Formation indicates greater amounts of erosion and coarser-grained deposition in the southwest associated with the paleohigh. Northward and eastward, there was greater accommodation space, less erosion associated with the unconformity, and finer-grained sediment.

An Ornithomimid (Dinosauria) Bonebed from the Late Cretaceous of Alberta, with Implications for the Behavior, Classification, and Stratigraphy of North American Ornithomimids

Bonebeds can provide a wealth of anatomical, taphonomic, and ontogenetic information about the specimens preserved within them, and can provide evidence for inferred behavior. The material described here represents the first known bonebed of ornithomimids in North America, and the fourth record of an ornithomimosaur bonebed in the world. Partial skeletons representing three individuals are preserved in this assemblage, each comprising primarily portions of the posterior postcrania (pelvis, hind limbs and tail). All three individuals are morphologically similar, although one is larger in overall size. Given the stratigraphic position of the site, and the morphology of the postcrania, the preserved material represents a taxon from the clade containing Ornithomimus and Struthiomimus. Pedal ungual morphology is examined and found to be too variable to be useful in distinguishing these species taxonomically. This site provides additional evidence of gregarious behavior in ornithomimids and the first probable record of that behavior in North American forms.