James M. White

An 18 million year record of vegetation and climate change in northwestern Canada and Alaska: Tectonic and global climatic correlates

Abstract We reconstruct long-term vegetation/paleoclimatic trends, spanning the last 18 million years, in Alaska, Yukon and far western Northwest Territories. Twenty-one average percentage spectra for pollen and spores are assembled from eight surface/subsurface sections. The sections are dated independently or by correlation. Pollen and spore ratios indicate the direction of change in vegetation and climatic parameters — growing season temperature (Test), tree canopy density (Cest) and paludification at study sites (Pest). A global warm peak ca. 15 Ma is shown by the abundance of thermophilous taxa, including Fagus and Quercus. A temperature decline immediately following 15 Ma parallels climatic reconstructions based on marine oxygen isotopes. Subsequent declines correlate to the Messinian event and the onset of late Pliocene-Pleistocene glaciation. After 7 Ma herbs and shrubs become more important elements of the palynological assemblages, suggesting a more continental, colder/drier climate. However, a late Pliocene warm interval is evident. Vegetation/climatic changes during the early to late Miocene show synchrony with, and are most economically attributable to, global events. After 7 Ma, vegetation/climate change is attributed primarily to latest Miocene-to-Pleistocene uplift of the Alaska Range and St. Elias Mts. The continuing influence of global climatic patterns is shown in the late Pliocene warm interval, despite uplift to the south. The opening of the Bering Strait ca. 3 Ma may have moderated the climate in the study area.

An extensive late Cenozoic terrestrial record of multiple glaciations preserved in the Tintina Trench of west-central Yukon: stratigraphy, paleomagnetism, paleosols, and pollenThis is a companion paper to Barendregt et al., also in this issue.Geological Survey of Canada Contribution 20100035.

The Tintina Trench in west-central Yukon is a late Miocene graben formed along the antecedent early Tertiary Tintina fault. Since its formation the trench has served as a sediment trap for alluvial and glacial deposits. An extensive record of preglacial, glacial, and interglacial sediments spanning the late Pliocene to late Pleistocene has been preserved and is exposed today in modern landslide scars. This sedimentary record comprises multiple sequences of tills, outwash, mudflows, loess, and paleosols. The glacial sediments are the product of both local (montane) and regional (Cordilleran) ice advances that channeled into the trench, while loess and well-developed paleosols (brunisols and luvisols) reflect nonglacial and interglacial conditions, respectively. The Tintina Trench exposures provide the most complete record of glaciations for the region. Paleomagnetism, paleosols, and palynology provide age constraints for the geological events. A formal stratigraphic nomenclature is proposed for this region...

Late Quaternary Palaeoenvironment of Spring Lake, Alberta, Canada

Palaeoenvironmental investigations based upon sediment cores taken from Spring Lake in the Peace River District of Alberta, Canada (latitude 55° 31′ N; longitude 119° 35′ W) show that the sedimentary record spans the Holocene period. Chemical and diatom changes coincide with regional climatic change since deglaciation (about 11 000 yr. B.P.). Calcite laminations in the basal 3 metres of the cores are evident, and were probably formed through elevated water temperature although photosynthetic removal of CO2 undoubtedly contributed. The disappearance of the laminations, and concurrent decrease in calcite X-ray diffraction peaks ca. 5000 yr. B.P. may have been caused by a change from a partially meromictic to a dimictic lake as the climate changed. Benthic and alkaline diatoms dominate before 5000 yr. B.P., while the planktonic Stephanodiscus hantzschii dominated between 5100 and 4200 yr. B.P. probably owing to increased nutrient levels. From ca. 4200 yr. B.P. until the present, benthic Fragilaria spp. and more circumneutral diatoms were dominant. Palaeoproduction, as measured by chlorophyll derivates, was highest in the early developmental stages of the lake, decreased coinciding with a major disturbance of the sediments and lowered water levels, and then gradually increased again until present. Only during the earlier period of peak production does biogenic calcite formation appear more important than calcite deposition caused by high water temperatures.

Miocene and Pliocene lacustrine and fluvial sequences, Upper Ramparts and Canyon village, Porcupine river, east-central Alaska

Abstract Cenozoic strata exposed along the Porcupine River between the Upper Ramparts and Canyon Village, Alaska, can be divided into five unconformity-bounded units (sequences) which are: lower and middle Miocene unit A, the white sandy fluvial sequence with peat beds; middle Miocene unit B, the basalt sequence—part B1 is basalt, and part B2 is organic-rich sedimentary beds; upper Miocene unit C, mudrock-dominated lake sequence; late Miocene or Pliocene to Pleistocene unit D, terrace gravels, detrital organic matter and associated sediments, and Holocene unit E, mixed sand and gravel-rich sediment and other sedimentary material including peat and eolian silt. The sequence (unit A) of lower and middle Miocene fluvial deposits formed in streams and on flood plains, just before the inception of local volanism. Fossil pollen from unit A suggests conifer-dominated regional forests and cool temperate climates. Peat beds and lake deposits from unit B contain pollen that indicates a warmer temperate climate coinciding with the middle Miocene thermal maximum. The lake deposits (unit C) downstream from the basalts accumulated in a small basin which resulted from a hydrologic system that was dammed in the late Miocene but breached soon thereafter. The lower part of the terrace gravels (unit D) expresses breaching of the dammed hydrologic system (of unit C). The Porcupine River became a major tributary of the Yukon River in late Pleistocene time when Laurentide ice blocked drainage from the Yukon interior basins causing meltwater to spill over the low divide separating it from the Porcupine River drainage initiating erosion and capture of the Yukon interior basins.

Stratigraphic framework and estuarine depositional environments of the Miocene Bear Lake Formation, Bristol Bay Basin, Alaska: Onshore equivalents to potential reservoir strata in a frontier gas-rich basin

The Miocene Bear Lake Formation is exposed along the coast and mountains of the central Alaska Peninsula and extends offshore as part of the Bristol Bay Basin. The Bear Lake Formation is up to 2360 m (7743 ft) thick in an offshore well and is considered to have the highest reservoir potential in this gas-rich frontier basin. Our new macrofossil and palynological data, collected in the context of measured stratigraphic sections, allow us to construct the first chronostratigraphic framework for this formation. Biostratigraphic age assignments for the numerous, commonly isolated, onshore exposures of the Bear Lake Formation show that deposition initiated sometime before the middle Miocene (15 Ma) and extended to possibly the earliest Pliocene. The bulk of the Bear Lake Formation, however, was deposited during the middle and late Miocene based on our new findings. We interpret the Bear Lake Formation as the product of a regional transgressive estuarine depositional system based on lithofacies analysis. The lower part of the formation is characterized by trough cross-stratified sandstone interbedded with coal and pedogenic mudstone deposited in fluvial and swamp environments of the uppermost parts of the estuarine system. The lower-middle part of the formation is dominated by nonbioturbated, wavy- and flaser-bedded sandstone and siltstone that were deposited in supratidal flat environments. The upper-middle part of the Bear Lake Formation is characterized by inclined heterolithic strata and coquinoid mussel beds that represent tidal channel environments in the middle and lower tracts of the estuarine system. The uppermost part of the formation consists of tabular, bioturbated sandstone with diverse marine invertebrate macrofossil faunas. We interpret this part of the section as representing the subtidal tract of the lower estuarine system and possibly the adjacent shallow inner shelf. A comparison of our depositional framework for the Bear Lake Formation with core and well-log data from onshore and offshore wells indicates that similar Miocene depositional systems existed throughout much of the Bristol Bay Basin. The documented changes in depositional environments within the Bear Lake Formation are also important for understanding upsection changes in the geometries of potential reservoirs.

Depicting biostratigraphical data from palynodata: Experiments and questions in data presentation and manipulation

Abstract Experiments are presented here in analysis and depiction of Palynodata records. Palynodata, a database of pre-Quaternary records of fossil palynomorphs compiled from global literature, is now available as Geological Survey of Canada (GSC) Open File 5793. Palynodata is a non-random sample of the distributions of palynomorphs. Hence, for any taxon, occurrence records in Palynodata serve as a proxy for its ‘real’ distribution in geological time and paleogeographical space. These experiments may be useful starting points for students of palynology in their exploration of Palynodata records. Palynoplot software bins and plots Palynodata taxa retrievals by time, and by the modern latitude of the study sites. It uses geographical co-ordinates for the study localities in Palynodata and the geological time scale. Such plots reveal temporal and latitudinal distribution patterns, and potential taxonomic and data problems such as outliers and inconsistent taxonomy. Taxonomic studies can be supported by considering time by latitude distributions, in addition to traditional morphology and priorities. The modern latitude of the sites studied gives increasing distortion with geological age. Palynodata output and the study locality file was input for PaleoGIS software to depict occurrence records on paleogeographical maps. PaleoGIS software showed changing occurrence patterns on rotated plates. An experimental trend surface model of the Jurassic-Cretaceous transition used binned records of common filicale genera which were evolutionarily sensitive between 180 and 100 Ma. The results demonstrate potential for the technique, and lessons for interpretation and future refinement. Common taxa may become useful for biostratigraphical problems and, by calibration against reference sections, this technique might be refined to provide a useful biostratigraphical standard for geological system boundaries. These manipulations of Palynodata records are a ‘proof-of-concept’ demonstration of techniques that may help to reveal the biostratigraphical, paleoecological, and paleoclimatological significance of fossil palynomorphs. Such work also reveals desirable improvements in Palynodata. The precision of indexing species in Palynodata may limit the potential level of chronostratigraphical resolution.

Population-based analysis and graphic interpretation of fossil palynomorph records from Palynodata: taxonomic and biostratigraphic implications

Abstract Palynodata is a comprehensive database of the occurrences of pre-Quaternary palynomorphs, encompassing over 20 000 publications. Taxa are assumed to have distributions in time and space which are localized to a region around a central point, and, in the idealized case, can be visualized as a bell-shaped curve. A palynological study can be imagined as drawing a sample from each taxon’s time/space distribution. The probability of recording any taxon is partly a function of its abundance at the sampled point in the distribution. A comprehensive database such as Palynodata should allow approximation of the underlying population distribution of the taxon. Retrievals show that useful information is recovered from Palynodata, although there are errors and inadequacies in the database, of which the chief is the generalized study locality record. A computer program, Palynoplot, produces graphic plots of retrievals from Palynodata, allowing improved recognition of the patterns and problems in the database. Images of the database may have future applications for palynological taxonomy, paleoclimatology, paleoecology, modelling of palynomorph distributions, and possibly plate tectonic reconstruction.