• Abrasion, transport and distribution of sediment in selected streams of Southern Ontario and Western New York /

      Kester, Stephen Joseph.; Department of Earth Sciences (Brock University, 1985-06-09)
      The rate of decrease in mean sediment size and weight per square metre along a 54 km reach of the Credit River was found to depend on variations in the channel geometry. The distribution of a specific sediment size consist of: (1) a transport zone; (2) an accumulation zone; and (3) a depletion zone. These zones shift downstream in response to downcurrent decreases in stream competence. Along a .285 km man-made pond, within the Credit River study area, the sediment is also characterized by downstream shifting accumulation zones for each finer clast size. The discharge required to initiate movement of 8 cm and 6 cm blocks in Cazenovia Creek is closely approximated by Baker and Ritter's equation. Incipient motion of blocks in Twenty Mile Creek is best predicted by Yalin's relation which is more efficient in deeper flows. The transport distance of blocks in both streams depends on channel roughness and geometry. Natural abrasion and distribution of clasts may depend on the size of the surrounding sediment and variations in flow competence. The cumulative percent weight loss with distance of laboratory abraded dolostone is defined by a power function. The decrease in weight of dolostone follows a negative exponential. In the abrasion mill, chipping causes the high initial weight loss of dolostone; crushing and grinding produce most of the subsequent weight loss. Clast size was found to have little effect on the abrasion of dolostone within the diameter range considered. Increasing the speed of the mill increased the initial amount of weight loss but decreased the rate of abrasion. The abrasion mill was found to produce more weight loss than stream action. The maximum percent weight loss determined from laboratory and field abrasion data is approximately 40 percent of the weight loss observed along the Credit River. Selective sorting of sediment explains the remaining percentage, not accounted for by abrasion.
    • Algal and protozoan response to Holocene climate change and anthropogenic impact: a case study from Sluice Pond, MA

      Drljepan, Matea; Department of Earth Sciences (Brock University, 2014-07-18)
      Sluice Pond is a small (18 ha) and deep (Zmax 20.0 m) partially meromictic, pond in Lynn, Massachusetts that contains a diverse dinocyst record since the early Holocene. High dinocyst concentrations, including morphotypes not previously described, as well as the preservation of several specimens of cellulosic thecae are attributed to low dissolved oxygen (DO) in the basin. The fossil protozoan record supports the interpretation- thecamoebians were unable to colonize the basin until the middle Holocene and only became abundant when the drought-induced lowstand oxygenated the bottom waters. Protozoans tolerant of low DO became abundant through the late Holocene as water levels rose and cultural eutrophication produced a sharp increase in biochemical oxygen demand (BOD) beginning in the 17th century. Recent sediments contain a dominance of Peridinium willei, indicating cultural eutrophication and the planktonic ciliate Codonella cratera and the thecamoebian Cucurbitella tricuspis in the deep basin. Above the chemocline however, a diverse difflugiid thecamoebian assemblage is present.
    • Analytical modelling of bacterial migration and accumulation with rate-limited sorption in discrete fractures

      Yazicioglu, Meliha Beyza.; Department of Earth Sciences (Brock University, 2002-07-09)
      An analytical model for bacterial accumulation in a discrete fractllre has been developed. The transport and accumlllation processes incorporate into the model include advection, dispersion, rate-limited adsorption, rate-limited desorption, irreversible adsorption, attachment, detachment, growth and first order decay botl1 in sorbed and aqueous phases. An analytical solution in Laplace space is derived and nlln1erically inverted. The model is implemented in the code BIOFRAC vvhich is written in Fortran 99. The model is derived for two phases, Phase I, where adsorption-desorption are dominant, and Phase II, where attachment-detachment are dominant. Phase I ends yvhen enollgh bacteria to fully cover the substratllm have accllillulated. The model for Phase I vvas verified by comparing to the Ogata-Banks solution and the model for Phase II was verified by comparing to a nonHomogenous version of the Ogata-Banks solution. After verification, a sensitiv"ity analysis on the inpllt parameters was performed. The sensitivity analysis was condllcted by varying one inpllt parameter vvhile all others were fixed and observing the impact on the shape of the clirve describing bacterial concentration verSllS time. Increasing fracture apertllre allovvs more transport and thus more accllffilliation, "Vvhich diminishes the dllration of Phase I. The larger the bacteria size, the faster the sllbstratum will be covered. Increasing adsorption rate, was observed to increase the dllration of Phase I. Contrary to the aSSllmption ofllniform biofilm thickness, the accllffilliation starts frOll1 the inlet, and the bacterial concentration in aqlleous phase moving towards the olitiet declines, sloyving the accumulation at the outlet. Increasing the desorption rate, redllces the dliration of Phase I, speeding IIp the accllmlilation. It was also observed that Phase II is of longer duration than Phase I. Increasing the attachment rate lengthens the accliffililation period. High rates of detachment speeds up the transport. The grovvth and decay rates have no significant effect on transport, althollgh increases the concentrations in both aqueous and sorbed phases are observed. Irreversible adsorption can stop accllillulation completely if the vallIes are high.
    • Armor coats, inverse grading, and streambed scour in selected streams of Southern Ontario and Western New York /

      Maddalena, Albert L.; Department of Earth Sciences (Brock University, 1984-06-01)
      Surface size analyses of Twenty and Sixteen Mile Creeks, the Grand and Genesee Rivers and Cazenovia Creek show three distinct types of bed-surface sediment: 1) a "continuous" armor coat which has a mean size of -6.5 phi and coarser, 2) a "discontinuous" armor coat which has a mean size of approximately -6.0 phi and 3) a bed with no armor coat which has a mean surface size of -5.0 phi and finer. The continuous armor coat completely covers and protects the subsurface from the flow. The discontinuous armor coat is composed of intermittently-spaced surface clasts, which provide the subsurface with only limited protection from the flow. The bed with no armor coat allows complete exposure of the subsurface to the flow. The subsurface beneath the continuous armor coats of Twenty and Sixteen Mile Creeks is possibly modified by a "vertical winnowing" process when the armor coat is p«natrat«d. This process results in a welld «v«loped inversely graded sediment sequence.vertical winnowing is reduced beneath the discontinuous armor coats of the Grand and Genesee Rivers. The reduction of vertical winnowing results in a more poorly-developed inverse grading than that found in Twenty and sixteen Mile Creeks. The streambed of Cazenovia Creek normally is not armored resulting in a homogeneous subsurface which shows no modification by vertical winnowing. This streambed forms during waning or moderate flows, suggesting it does not represent the maximum competence of the stream. Each population of grains in the subsurface layers of Twenty and sixteen Mile Creeks has been modified by vertical winnowing and does not represent a mode of transport. Each population in the subsurface layers beneath a discontinuous armor coat may partially reflect a transport mode. These layers are still inversely graded suggesting that each population is affected to some degree by vertical winnowing. The populations for sediment beneath a surface which is not armored are probably indicative of transport modes because such sediment has not been modified by vertical winnowing. Bed photographs taken in each of the five streams before and after the 1982-83 snow-melt show that the probability of movement for the surface clasts is a function of grain size. The greatest probability of of clast movement and scour depth of this study were recorded on Cazenovia Creek in areas where no armor coat is present. The scour depth in the armored beds of Twenty and Sixteen Mile Creeks is related to the probability of movement for a given mean surface size.
    • Armourstone revetments : will standard design criteria prevent failure? /

      Van Riezen, Rhonneke Dyann.; Department of Earth Sciences (Brock University, 2005-06-29)
      Bank stabilization structures are used to prevent the loss of valuable land within the urban environment and the decision for the type of structure used depends on the properties of the stream. In the urban areas of Southern Ontario there is a preference for the use of armourstone blocks as bank stabilization. The armourstone revetment is a free standing stone structure with large blocks of stone layered vertically and offset from one another. During fieldwork at Forty Mile Creek in Grimsby, Ontario armourstone failure was identified by the removal of two stones within one column from the wall. Since the footer stones were still in place, toe scour was eliminated as a cause of failure. Through theoretical, field, and experimental work the process of suction has been identified as a mode of failure for the armourstone wall and the process of suction works similarly to quarrying large blocks of rock off bedrock streambeds. The theory of lateral suction has previously not been taken into consideration for the design of these walls. The physical and hydraulic evidence found in the field and studied during experimental work indicate that the armourstone wall is vulnerable to the process of suction. The forces exerted by the flow and the resistance of the block determine the stability of the armourstone block within the wall. The design of the armourstone wall, high surface velocities, and short pulses of faster flowing water within the profile could contribute to armourstone failure by providing the forces needed for suction to occur, therefore adjustments to the design of the wall should be made in order to limit the effect.
    • Assessing environmental controls for candidate microbial ichnofossils in hydrothermally altered basaltic tuffs of Upsal Hogback, NV

      Pentesco, Justin; Department of Earth Sciences
      Putative biogenic alteration has previously been identified in basaltic glass of the ocean floor, in subglacial hyaloclasts, in meteorite impact glass, and more recently in tuff erupted in a lacustrine environment. Documentation of putative biogenic alteration and characterization of the environments in which they have formed improves understanding of the thermophilic chemotrophic euendoliths to which the ichnofossils are attributed, which may enhance humankind’s understanding of the origins of life on Earth and potential evidence of life elsewhere. Upsal Hogback is a series of monogenetic tuff rings in the topographic low of the Carson Sink in the Lahontan Basin in Western Nevada. These tuff rings erupted into pluvial Lake Lahontan between 19 ka and 33.7 ka. Tufas emplaced on the tuff rings are especially abundant at two elevation intervals, which can be correlated to stillstands of Lake Lahontan, providing the minimum age constraint for the emplacement of Upsal Hogback. Chemical analysis of basalts from each ring indicates a common magmatic source that was likely affected by fractional crystallization of olivine and plagioclase as the rings erupted from north to south. In basaltic tuff of Upsal Hogback, petrographic analysis has revealed the presence of putatively biogenic alteration textures in association with palagonite, calcite, and zeolites. Tuff samples with the most abundant putative biogenic alteration are those from the interior of the tufas. Biogenic origin of the textures is indicated by their size, the log-normal distribution of their sizes, and the complex morphology which cannot readily be explained by known abiogenic processes. Measurement of palagonitization and consideration of zeolite assemblage indicates a hydrothermal fluid of sustained temperature between 40°C and 60°C. Upsal Hogback’s autochthonous carbonates, basaltic tuff, palagonitization, and the emplacement of the tuff rings in an alkaline lake may make it a good analogue for the Mars 2020 landing site in Jezero crater, Mars. The geologic characteristics of Upsal Hogback, including the hydrothermal regime, together with the early stage of putative biogenic alteration identified, provide an instructive example for future work investigating terrestrial and extraterrestrial environments for evidence of life.
    • Atmospheric and environmental interpretations of Early Paleozoic halite (Upper Ordovician, Hudson Bay Basin, & Upper Silurian, Michigan Basin)

      Davis, Alyssa M.; Department of Earth Sciences
      Halite sourced from Upper Ordovician strata (Red Head Rapids Formation) in the Hudson Bay Basin and Upper Silurian strata (Salina Group A-2 and B units) in the Michigan Basin was used to interpret atmospheric and environmental conditions during their respective depositional periods. Primary halite was distinguished from secondary or diagenetically altered halite using screening parameters consisting of petrography, trace element analysis, microthermometry and gas analysis of fluid inclusions. Primary halite preserves liquid and/or liquid-vapour cubic fluid inclusions within chevrons and fluid inclusion bands whereas secondary halite contains large, irregularly-shaped fluid inclusions. Petrographic analysis highlights the coexistence of primary and secondary fluid inclusions within some sample sets. Trace element analysis suggests that the deposits of the Hudson Bay and Michigan Basins were likely affected by periodic freshening that altered the trace element concentrations. Homogenization temperatures of the Upper Silurian halite range from 13.3 – 35.2°C which agree with expected paleoclimatic conditions. The contemporaneous occurrence of primary, depositional halite with secondary, diagenetic halite is noted during the crush fast scan method of gas analysis by mass spectrometry. Diagenetic influences are clearly reflected in the gas analysis results of some halite samples. In part, they reflect the influence of degradation and/or thermal maturation of organic matter and hydrocarbon migration subsequent to halite deposition. Atmospheric oxygen content in the primary halite from the Red Head Rapids Formation (Upper Ordovician) ranges from 13.5 to 19 %, whereas in the Salina Group A-2 and B units (Upper Silurian) it falls between 20 and 26 %. The measured values of atmospheric oxygen based on Upper Ordovician halite overlap with the range of oxygen modelled by Berner (2006) and Algeo & Ingall (2007), and the values of atmospheric oxygen of Upper Silurian halite correspond to values modelled by Berner (2006; 2009).
    • Atmospheric conditions during the Visean (Carboniferous), and post-depositional hydrocarbon generation in the Shubenacadie Basin, Nova Scotia

      Shaver, Kristen; Department of Earth Sciences
      Halite has become of particular interest recently due to its potential to preserve ancient air and provide the first paleoatmospheric composition data that is not reliant on proxies. As halite precipitates, fluid inclusions become trapped within the crystal structure. Some of which also capture miniscule gas bubbles of the air present during precipitation. This study presents the first results of Visean (Carboniferous) paleoatmosphere captured in the Shubenacadie Basin, Nova Scotia. To ensure the gas-hosting fluid inclusions are of primary origin, strict screening parameters must be applied. Those deemed adequate from visual and petrographic examinations, had reasonable homogenization temperatures, argon concentration between 0.8 and 1.0 mol %, contained a sum of methane and carbon dioxide below 10 mol %, and displayed minimal gas variation within samples were used for paleoatmospheric interpretation. Trace element concentrations (Mg, K, Ca) of halite were also examined to determine if they could provide further confirmation of primary origin but further work is required to determine its viability. The few halite samples that met all the screening parameters originated from the upper MacDonald Road formation and yielded an O2 window of 11 to 16 mol %. The failed samples in the upper formations contained visible and olfactible hydrocarbons while the lower formations contained elevated methane. This hydrocarbon generation is consistent with and increasing thermal alteration index with depth due to heat generated by the underlying Mississippi Valley-Type deposit in the basin.
    • Biogeochemistry of Paleozoic brachiopods from New York State and Ontario

      Bates, Nicholas R.; Department of Earth Sciences (Brock University, 1989-07-09)
      A comprehensive elemental, isotopic and microstructural analyses was undertaken of brachiopod calcites from the Hamilton Group (Middle Devonian), Clinton Group (Middle Silurian) and Middle to Upper Ordovician strata of Ontario and New York State. The majority of specimens were microstructurally and chemically preserved in a pristine state, although a number of specimens show some degree of post-depositional alteration. Brachiopod calcites from the Hamilton and Clinton Groups were altered by marine derived waters whereas Trenton Group (Middle Ordovician) brachiopods altered in meteorically derived fluids. Analysis of the elemental and isotopic compositions of pristine Hamilton Group brachiopods indicates there are several chemical relationships inherent to brachiopod calcite. Taxonomic differentiation of Mg, Sr and Na contents was evident in three co-occuring species from the Hamilton Group. Mean Mg contents of pristine brachiopods were respectively Athyris spiriferoides (1309ppm), Mucrospirifer mucronatus (1035ppm) and Mediospirifer audacula (789ppm). Similarly, taxonomic differentiation of shell calcite compositions was observed in co-occuring brachiopods from the Clinton Group (Middle Silurian) and the Trenton Group (Middle Ordovician). The taxonomic control of elemental regulation into shell calcite is probably related to the slightly different physiological systems and secretory mechanisms. A relationship was observed in Hamilton Group species between the depth of respective brachiopod communities and their Mg, Sr and Na contents. These elements were depleted in the shell calcites of deeper brachiopods compared to their counterparts in shallower reaches. Apparently shell calcite elemental composition is related to environmental conditions of the depositional setting, which may have controlled the secretory regime, mineral morphology of shell calcite and precipitation rates of each species. Despite the change in Mg, Sr and Na contents between beds and formations in response to environmental conditions, the taxonomic differentiation of shell calcite composition is maintained. Thus, it may be possible to predict relative depth changes in paleoenvironmental reconstructions using brachiopod calcite. This relationship of brachiopod chemistry to depth was also tested within a transgressiveregressive (T-R) cycle in the Rochester Shale Formation (Middle Silurian). Decreasing Mg, Sr and Na contents were observed in the transition from the shallow carbonates of the Irondequoit Formation to the deeper shales of the lowest 2 m of Rochester Shale. However, no isotopic and elemental trends were observed within the entire T-R cycle which suggests that either the water conditions did not change significantly or that the cycle is illusory. A similar relationship was observed between the Fe and Mn chemistries of shell calcite and redox/paleo-oxygen conditions. Hamilton Group brachiopods analysed from deeper areas of the shelf are enriched in Mn and Fe relative to those from shallow zones. The presence of black shales and dysaerobic faunas, during deposition of the Hamilton Group, suggests that the waters of the northern Appalachian Basin were stratified. The deeper brachiopods were marginally positioned above an oxycline and their shell calcites reflect periodic incursions of oxygen depleted water. Furthermore, analysis of Dalmanella from the black shales of the Collingwood Shale (Upper Ordovician) in comparison to those from the carbonates of the Verulam Formation (Middle Ordovician) confirm the relationship of Fe and Mn contents to periodic but not permanent incursions of low oxygen waters. The isotopic compositions of brachiopod calcite found in Hamilton Group (813C; +2.5% 0 to +5.5% 0; 8180 -2.50/00 to -4.00/00) and Clinton Group (813C; +4.00/00 to +6.0; 8180; -1.8% 0 to -3.60/ 00) are heavier than previously reported. Uncorrected paleotemperatures (assuming normal salinity, 0% 0 SMOW and no fractionation effects) derived from these isotopic values suggest that the Clinton sea temperature (Middle Silurian) ranged from 18°C to 28°C and Hamilton seas (Middle Devonian) ranged between 24°C and 29°C. In addition, the isotopic variation of brachiopod shell calcite is significant and is related to environmental conditions. Within a single time-correlative shell bed (the Demissa Bed; Hamilton Group) a positive isotopic shift of 2-2.5% 0 in 013C compositions and a positive shift of 1.0-1.50/00 in 0180 composition of shell calcite is observed, corresponding with a deepening of brachiopod habitats toward the axis of the Appalachian Basin. Moroever, a faunal succession from deeper Ambocoelia dominated brachiopod association to a shallow Tropidoleptus dominated assocation is reflected by isotopic shifts of 1.0-1.50/00. Although, other studies have emphasized the significance of ±20/oo shifts in brachiopod isotopic compositions, the recognition of isotopic variability in brachiopod calcite within single beds and within depositional settings such as the Appalachian Basin has important implications for the interpretation of secular isotopic trends. A significant proportion of the variation observed isotopic distribution during the Paleozoic is related to environmental conditions within the depositional setting.
    • Bioindication of ozone using milkweed plants in Southern Ontario

      Department of Earth Sciences (Brock University, 2010-03-09)
      Ambient (03) ozone concentrations were compared to ozone damage on milkweed plants to determine if there was a correlation. Eight survey sites of at least 100 plants each were located within 5 kilometers of Air Quality Index (AQI) stations in southern Ontario. Sites were visited nine times from June-September (2007) and milkweed leaves from 75 plants were assessed using methods pioneered in the United States. Ambient 0 3 results were calculated into SUM65, seasonal cumulative 0 3, and total 03. The 0 3 exposure indices SUM65 and cumulative 0 3 were tested statistically to determine which index is biologically relevant to milkweed as an 0 3 damage indicator species. The milkweed damage indices were incidence of leaves damaged per plant, incidence of plants damaged per site, and total 0 3• The incidence of plants injured per site was the best damage parameter with an F(1,28)=17.37, p=0.0003 for SUM65 and F(1,28)=7.5, p=O.0106 for cumulative 03 .. Milkweed plants showed quantifiable ozone damage with minimal spatial differences in damage and thus have potential use as a biomonitor species in southern Ontario.
    • The Cenozoic Gonyaulacacean Dinoflagellate Genera Operculodinium Wall, 1967 and Protoceratium Bergh, 1881 and Their Phylogenetic Relationships

      Paez-Reyes, Manuel; Department of Earth Sciences (Brock University, 2014-05-13)
      The palynology of Ocean Drilling Program Site 1007, leeward of the present Bahamas Bank, provides insights into upper Oligocene–lower Pleistocene dinoflagellate cyst associations in the tropical Americas. These associations are reviewed along with the sedimentary paleoenvironment to provide context for a morphological study of the cystdefined dinoflagellate Operculodinium bahamense and its comparison with the thecadefined dinoflagellate Protoceratium reticulatum which produces a cyst assignable to the cyst-defined genus Operculodinium. Detailed reconstructions of the tabulation in both species reveal strong similarities, having a sexiform hyposomal tabulation and L-type or modified L-type ventral organization. Protoceratium reticulatum has dextral torsion of the hypotheca, requiring assignation of the genus to the subfamily Cribroperidinioideae, whereas Operculodinium bahamense has neutral torsion requiring assignation to the subfamily Leptodinioideae. Results either imply polyphyletic origins for the genus Operculodinium or that combinations of ventral organization and torsion cannot always be applied rigidly to subdivide the family Gonyaulacaceae.
    • Central North Atlantic (IODP Site U1313) paleoceanography based on a high-resolution dinoflagellate cyst record across the Early–Middle Pleistocene boundary (Marine Isotope Stages 20–18, ~810–741 ka)

      Abomriga, Walid; Department of Earth Sciences
      A dinoflagellate cyst (dinocyst) study of 102 samples from Integrated Ocean Drilling Program Site U1313 in the central North Atlantic Ocean represents the most detailed dinocyst record yet available for Marine Isotope Stage (MIS) 19, which spans the Lower–Middle Pleistocene boundary. A published ultra-high-resolution δ18O record constrains the study. The following paleoenvironmental indicators were among those used: Operculodinium centrocarpum sensu Wall & Dale (North Atlantic Current [NAC]), Nematosphaeropsis labyrinthus (sub-polar water masses), total Impagidinium spp. (subtropical gyre), and total protoperidiniacean cysts and total cyst concentrations (productivity indicators). Cooling just prior to Termination IX suggests a Younger-Dryas type event. An early arrival of the North Atlantic Current at ~797 ka and then warm subtropical gyre waters at 793.58 ka, presage the arrival of oligotrophic waters at 790.5 ka. The onset of peak interglacial conditions at 790.5 ka is delayed relative to the benthic δ18O signal, which has a midpoint age for Termination IX at ~793 ka, and presumably reflects the persistence of ice sheets to the north. Peak interglacial conditions terminated at 784 ka with a duration of ~6500 years. This is shorter than the 10.5–12.5 kyr extent of full interglacial conditions recorded elsewhere and based on different criteria. Dinocyst transfer functions give August sea-surface temperatures of ~20°C for peak interglacial conditions, a few degrees cooler than at present. Subpolar water masses occupied Site U1313 in late MIS 19, but at 750.89 ka (early MIS 18) a return of the North Atlantic Current was followed by further warming, with an August sea-surface temperature of 20 °C for the highest sample at 741.41 ka.
    • Central North Atlantic paleoceanography during the Late Early Pleistocene (spanning Marine Isotope Stage 21) based on a high-resolution dinoflagellate cyst record

      Dube, Mukudzei Mswazi; Department of Earth Sciences
      A high-resolution dinoflagellate cyst record from Integrated Ocean Drilling Program Site U1313, constrained by an ultra-high resolution δ 18O record from the same sample set, is established to enhance our understanding of the paleoceanography and structure of Marine Isotope Stage (MIS) 21 in the central North Atlantic. Changes in cyst abundance, composition of cyst assemblages, and their diversity reflect major regional shifts in climate and ocean circulation for this time interval (866–814 ka). The following paleoenvironmental indicators are used: Operculodinium centrocarpum sensu Wall & Dale (North Atlantic Current), Nematosphaeropsis labyrinthus and Impagidinium pallidum (subpolar gyre), total Impagidinium species (subtropical gyre), and protoperidiniacean cysts (biological productivity). The integration of stable isotope and the generated dinoflagellate cyst data shows MIS 21 to have been climatically unstable and interrupted between 830 and 840 ka by two significant cool episodes. These are resolved using the relative abundance of cooler-water species and by tracking the abundance of O. centrocarpum. During MIS 21, Site U1313 was predominantly under the influence of the subtopical gyre until after 835 ka when the NAC was re-established until the end of MIS 21. This study also extends the stratigraphic range of Fibrocysta? fusiforma from its previously documented range top in the Lower Pleistocene at 2.3 Ma to ~812 ka in the present study. An unnamed Spiniferites species (Spiniferites sp. 1) is confined to the latest phase of MIS 22. Two unidentified acritarchs (Acritarch spp. 1 and 2) occur throughout MIS 21 and merit further investigation.
    • CENTRAL NORTH ATLANTIC PALEOCEANOGRAPHY DURING THE MIDDLE PLEISTOCENE (ca. 726–603 ka): INSIGHTS FROM THE DINOFLAGELLATE CYST RECORD

      Mantilla Duran, Fernando; Department of Earth Sciences (Brock University, 2013-08-07)
      Integrated Ocean Drilling Program (IODP) Site U1313, located at the northern boundary of the subtropical gyre in the central North Atlantic, lies within the southern part of the ice-rafted debris belt. Seventy-three palynological samples were studied from an uninterrupted interval ca. 726–603 ka (upper Marine Isotope Stage [MIS] 18 through lower MIS 15) to resolve conflicting paleoceanographic interpretations. Glacial stages were characterized by high productivity surface waters reflecting a southward shift of the Arctic Front. Sea surface salinities (SSSs) and sea surface temperatures (SSTs) were obtained by transfer functions using the Modern Analogue Technique. The lowest SSTs of 9ºC (±1.3) and 10ºC (±1.3) were recorded in glacial MIS 16 and MIS 18 respectively. However, these reconstructions are influenced by abundant heterotrophic taxa and may reflect elevated nutrient levels rather than lowered temperatures. Reworked palynomorphs uniquely indicate a Cretaceous as well as Paleozoic provenance for the first Heinrich-like events.
    • Chemostratigraphy of the Uppermost Cambrian Below the Ordovician GSSP

      Wang, Lisha; Department of Earth Sciences
      Chemostratigraphy is an important tool for correlating layered sedimentary rock successions. Preserved/near primary carbon isotope signatures in marine carbonates can provide high-resolution profiles for sedimentary sequences supplementing the need for distinguishing fossils from different depositional environments and those lacking fossil materials. The Global Boundary Stratotype Section and Point (GSSP) of the Cambrian‒Ordovician boundary is located at Green Point in the Green Point Formation of the Cow Head Group in western Newfoundland, Canada. To reconstruct a continuous and high-resolution chemostratigraphy from the Cambrian‒Ordovician boundary to the Furongian Series Stage 10, we included the δ13C results of the Green Point Formation covering the Ordovician GSSP interval (Azmy et al., 2014). The Green Point Formation through the base of Ordovician GSSP consists of alternating dark gray to black shale and thin ribbon limestone rhythmites, with few fossils. The samples are micritic limestone, dolomitic limestone, and dolostone. They were determined to be in primary to near-primary condition based on multiple screening tests. Cathodoluminescence screening reveals dull to bright luminescence of the samples indicative of good preservation for many of them. The δ13Ccarb and δ18O values of the Green Point carbonates range from -6.44‰ to +0.33‰ (VPDB) and from -8.63‰ to -5.67‰ (VPDB), respectively, with poor correlation. Mn/Sr ratios range from 0.63 to 9.82, with no correlation to δ13Ccarb, but with ratios supporting the near primary nature of the δ13C values. Carbon isotope compositions of the Green Point Formation below the Ordovician GSSP fluctuate but remaine essentially invariantly negative. The δ13C values reveal a negative excursion at and below the Cambrian‒Ordovician boundary, which may correlate with the Top of Cambrian Carbon Isotope Excursion (TOCE) and its significant negative excursion. A nadir of -6.44 ‰ at the base of the Eoconodontus conodont zone marks the proposed GSSP for the base of the Furongian Series Stage 10. The lower excursion may be correlated with the Hellnmaria-Red Tops Boundary (HERB) carbon isotope excursion found in sequences in the United States of America, Australia, and north China. Without an adequate record of conodonts, high-resolution chemostratigraphic trends of carbon isotope compositions facilitate the correlation of intercontinental and intracontinental sequences.
    • Continental margin architecture : the palynological signature of glacioeustasy /

      Gostlin, Kevin Earl.; Department of Earth Sciences (Brock University, 1999-05-21)
      Palynomorphs from two siliciclastic margins were examined to gain insights into continental margin architecture. Sea level change is thought to be one of the primary controls on continental margin architecture. Because Late Neogene glacioeustasy has been well studied marine sediments deposited during the Late Neogene were examined to test this concept. Cores from the outer shelf and upper slope were taken from the New Jersey margin in the western North Atlantic Ocean and from the Sunda Shelf margin in the South China Sea. Continental margin architecture is often described in a sequence stratigraphic context. One of the main goals of both coring projects was to test the theoretical sequence stratigraphic models developed by a research group at Exxon (e.g. Wilgus et al., 1988). Palynomorphs provide one of the few methods of inferring continental margin architecture in monotonous, siliciclastic marine sediments where calcareous sediments are rare (e.g. New Jersey margin). In this study theoretical models of the palynological signature expected in sediment packages deposited during the various increments of a glacioeustatic cycle were designed. These models were based on the modem palynomorph trends and taphonomic factors thought to control palynomorph distribution. Both terrestrial (pollen and spores) and marine (dinocysts) palynomorphs were examined. The palynological model was then compared with New Jersey margin and Sunda Shelf margin sediments. The predicted palynological trends provided a means of identifying a complete cycle of glacioeustatic change (Oxygen Isotope Stage 5e to present) in the uppermost 80 meters of sediment on the slope at the New Jersey margin. Sediment availability, not sea meters of sediment on the slope at the New Jersey margin. Sediment availability, not sea level change, is thought to be the major factor controlling margin architecture during the late Pleistocene here at the upper slope. This is likely a function of the glacial scouring of the continents which significantly increases sediment availability during glacial stages. The subaerially exposed continental shelf during the lowstand periods would have been subject to significant amounts of erosion fi:om the proglacial rivers flowing fi-om the southern regions of the ice-sheet. The slope site is non-depositional today and was also non-depositional during the last full interglacial period. The palynomorph data obtained fi-om the South China Sea indicate that the major difference between the New Jersey Margin sites and the Sunda Shelf margin sites is the variation in sediment supply and the rate of sediment accumulation. There was significantly less variation in sediment supply between glacial and interglacial periods and less overall sediment accumulation at the Sunda Shelf margin. The data presented here indicate that under certain conditions the theoretical palynological models allow the identification of individual sequence stratigraphic units and therefore, allow inferences regarding continental margin architecture. The major condition required in this approach is that a complete and reliable database of the contemporaneous palynomorphs be available.
    • DEFORMATION OF INTERIOR LAYERED DEPOSITS (ILD) AND THEIR ASSOCIATED LANDFORMS IN WEST CANDOR CHASMA, MARS: IMPLICATIONS FOR THE TIMING OF ILD DEPOSITION

      Birnie, Colin; Department of Earth Sciences (2013-02-22)
      On Mars, interior layered deposits (ILD) provide evidence that water was once stable at the surface of the planet and present in large quantities. In West Candor Chasma, the ILD and their associated landforms record the depositional history of the chasma, and the deformation of those deposits provide insight into the stresses acting on them and the chasma as a whole. The post ILD structural history of West Candor is interpreted by analyzing the spatial relationships and orientation trends of structural features within the ILD. Therecording of stresses through brittle deformation of ILDs implies that the ILD had been lithified before the stress was imposed. Based on the prominent orientation trends of deformation features, the orientation of the stress regime acting upon the ILD appears to be linked to the regime that initially created the chasma-forming faults. An additional minor stress orientation was also revealed and may be related to large structures outside west Candor Chasma. The late depositional history of Ceti Mensa is herein investigated by examining the attributes and spatial relationship between unique corrugated, linear formations (CLF). The CLFs appear to be aeolian in origin but display clear indications of brittle deformation, indicating they have been Iithified. Evidence of lithification and the mineral composition of the surrounding material support the interpretation of circulating water in the area.
    • Detecting spatial variation in hydrology and carbon export across a lake-rich permafrost landscape, Old Crow Flats, Yukon, Canada

      Hughes, Daniel; Department of Earth Sciences
      Lake-rich permafrost landscapes are widespread across northern regions and provide refuge for abundant wildlife and resources for local communities. Evidence suggests that these landscapes are highly sensitive to changes in climate. The traditional territory of the Vuntut Gwitchin First Nation, Old Crow Flats (OCF), YK, is a vast 5600-km2 lake-rich landscape that is internationally recognized for its ecological and cultural integrity. Pronounced changes in lake and river water levels and land cover compositions have been observed during recent decades by local community members and in scientific studies. Research presented here focuses on enhancing our understanding of spatial patterns in hydrology and carbon export across OCF, using a suite of water chemistry parameters, carbon concentrations and water and carbon isotope tracers. The spatial patterns detected are providing an important reference for ongoing investigations of how changing climate and lake-rich landscapes are influencing water and carbon balances.
    • Determining rotational direction of rotation structures using prolate shaped grains within till

      Mandri, Christina M.; Department of Earth Sciences (2013-04-09)
      Micromorphology is used to analyze a wide range of sediments. Many microstructures have, as yet, not been analyzed. Rotation structures are the least understood of microstructures: their origin and development forms the basis of this thesis. Direction of rotational movement helps understand formative deformational and depositional processes. Twenty-eight rotation structures were analyzed through two methods of data extraction: (a) angle of grain rotation measured from Nikon NIS software, and (b) visual analyses of grain orientation, neighbouring grainstacks, lineations, and obstructions. Data indicates antithetic rotation is promoted by lubrication, accounting for 79% of counter-clockwise rotation structures while 21 % had clockwise rotation. Rotation structures are formed due to velocity gradients in sediment. Subglacial sediments are sheared due to overlying ice mass stresses. The grains in the sediment are differentially deformed. Research suggests rotation structures are formed under ductile conditions under low shear, low water content, and grain numbers inducing grain-to-grain interaction.