Paleobiology Commons^™

Complex Unicellular Microfossils From The 1.9 Ga Gunflint Chert, Canada, Ana L. González Flores

Electronic Thesis and Dissertation Repository

The presence of eukaryotic life during the early Paleoproterozoic has been a matter of debate because well-preserved fossils older than 1.8 Ga rarely exhibit eukaryotic cellular microstructures. In this study, microfossils from the 1.9 Ga Gunflint Chert were studied using the extended-focal-depth imaging technique, combined with scanning electron microscopy, resulting in recognition of three types of large (10–35 μm diameter) complex unicellular bodies (CUBs) and one type of “multicellular body” (< 50 μm diameter). The CUBs show the following eukaryotic cyst-like structures: (1) radially arranged internal strands similar to those in some acritarchs and dinoflagellates; (2) regularly spaced long tubular processes, stubby pustules, and/or robust podia on the cell surface; (3) reticulate cell-wall sculpturing such as pits, ridges, and scale-like ornaments; and (4) internal bodies that may represent membrane-bounded organelles. These morphological features provide strong evidence for the presence of protists in the late Paleoproterozoic.

Among the three types of CUBs from the Gunflint microbiota, a new species, Germinosphaera gunflinta sp. nov., was recognized. This species has the diagnostic characteristics of Germinosphaera, such …

Stratigraphy Of The Upper Silurian To Middle Devonian, Southwestern Ontario, Shuo Sun

Electronic Thesis and Dissertation Repository

The upper Silurian–Middle Devonian succession was dominated by carbonate and evaporite deposits, with minor siliciclastic sedimentation, and a significant hiatus across the Siluro-Devonian (S-D) boundary in southwestern Ontario. The stratigraphic units include, in ascending order: Late Silurian Bass Islands/Bertie formations and Salina G Unit, the Devonian Oriskany Formation, Bois Blanc Formation (including Springvale Member), Detroit River Group (including the Lucas, Amherstburg and Sylvania formations), Onondaga Formation, and Dundee Formation.

Below the S-D unconformity, the upper Silurian Bass Islands/Bertie formations are predominantly dolostone of peritidal-sabkha origin and episodic subaerial exposure. Revised stratigraphic correlation shows that the Bertie Formation is older than …

Ordovician Continental Paleogeography And Paleoenvironment For The Michigan Basin From Paleomagnetic Analysis, Michelle Macrae

Electronic Thesis and Dissertation Repository

This study investigates the paleomagnetic record of Paleozoic rocks from two Michigan basin localities in southwestern Ontario to help close the 40 myr gap in Paleozoic paleomagnetic data. Paleomagnetic data from the Queenston (Upper Ordovician) formation consistently exhibits easily removed viscous remanence, an intermediate and a high temperature component consistent with the unblocking temperatures of magnetite and hematite respectively. Alternating-field and thermal demagnetization in 16–20 steps up to 670º C typically reveal a southeastern, shallow up direction removed from magnetite, and a southwestern, steep up direction removed from hematite. A Late Paleozoic overprint was preserved in the magnetite and a …

Paleogeography Of Early Paleozoic Laurentia And Meguma, Avalonia Terranes Via Paleomagnetism And Faunal Review, Halima S. Warsame

Electronic Thesis and Dissertation Repository

Paleomagnetic assessment of 821 Cambrian to Silurian-aged rock specimens of igneous and sedimentary origin was used as a means to provide insight on the ancient geographies of the region in which these rocks are currently found. The Earth’s magnetic field direction can be recorded at the time of rock formation and/or at a later significant event by magnetic minerals, allowing these signatures to be used to track the past motions of the continents. Stepwise demagnetization of the Port au Port, St. George and Table Head Groups in western Newfoundland, and the Mavillette gabbro (426 +/- 2 Ma, U-Pb baddeleyite) of …

Giant Beaver (Castoroides) Palaeoecology Inferred From Stable Isotopes, Tessa Plint

Electronic Thesis and Dissertation Repository

Stable isotope analysis was used to explore unresolved questions about the palaeoecology of the extinct Pleistocene giant beaver (Castoroides). The δ¹³C, δ¹⁵N, and δ¹⁸O of bone collagen and structural carbonate from enamel served as proxies for palaeodiet and palaeoclimate. A new baseline for freshwater and terrestrial plant δ¹³C and δ¹⁵N was utilized in a mixing model (SIAR) to assess rodent feeding niche. SIAR analysis indicated that Castoroides’ consumed a diet of predominantly macrophytes, making them reliant on wetland habitat for food. Based on isotopic data for potential …

First Major Appearance Of Brachiopod-Dominated Benthic Shelly Communities In The Reef Ecosystem During The Early Silurian, Cale A.C. Gushulak

Electronic Thesis and Dissertation Repository

The early Silurian reefs of the Attawapiskat Formation in the Hudson Bay Basin preserved the oldest record of major invasion of the coral-stromatoporoid skeletal reefs by brachiopods and other marine shelly benthos, providing an excellent opportunity for studying the early evolution, functional morphology, and community organization of the rich and diverse reef-dwelling brachiopods. Biometric and multivariate analysis demonstrate that the reef-dwelling Pentameroides septentrionalis evolved from the level-bottom-dwelling Pentameroides subrectus to develop a larger and more globular shell. The reef-dwelling brachiopods in the paleoequatorial Hudson Bay Basin were more diverse than contemporaneous higher latitude reef-dwelling brachiopod faunas, with ten distinct …

Carbon And Nitrogen Isotopic Investigations Of The Late Pleistocene Paleoecology Of Eastern Beringia, Yukon Territory, Using Soils, Plants And Rodent Bones, Farnoush Tahmasebi

Electronic Thesis and Dissertation Repository

During the late Pleistocene (130-12 ka), Beringia, a largely ice-free land located in the Mammoth Steppe Ecosystem, was home to a large grazing community of megafauna. Many of these animals, including the woolly mammoth, became extinct at the terminal Pleistocene. Assessment of the paleoenvironment, nutrient cycling and foraging ecology in Beringia should help to understand the role of climate change in their extirpation. Such information might also help to explain the curiously higher δ¹⁵N of woolly mammoths relative to other coeval herbivores.

This study assessed eastern Beringian paleoecology using stable nitrogen (N) and carbon (C) isotopic analyses of …

Evolution Of The Late Ordovician Plaesiomyid Brachiopod Lineage In Laurentia, Colin D. Sproat

Electronic Thesis and Dissertation Repository

During the Late Ordovician, a transgression flooded much of Laurentia. The fauna of these intracratonic basins became differentiated from the fauna of the pericratonic shelves and platforms, typically displaying gigantism and coarser shell ornamentation. In this study, 509 specimens from 11 species of the Plaesiomyidae brachiopod family from the Katian and Hirnantian were measured, of which 198 included in principal component analysis to quantify morphological changes over this interval. Three trends were revealed: 1) increasing globosity and dorsal convexity from the early to late Katian, 2) coarser, but fewer ribs on species from the paleoequatorial intracratonic seas compared to species …

Late Archean Oceans: A Laboratory Model Of Oxygen Oases, Maija J. Raudsepp

Electronic Thesis and Dissertation Repository

A cyanobacterial mat, including associated aerobic and anaerobic heterotrophs, was grown in an airtight chamber to simulate the formation of an oxygen oasis in two different Archean-like environments. In the first experiment, methane added to the ecosystem was rapidly oxidized and then O_2(g) increased to 10%. Photosynthesis resulted in a pH of 9.5 and the precipitation of magnesium-manganese carbonates within the mat. In the second experiment, daily additions of ferrous iron were rapidly oxidized, resulting in ferric hydroxide encrusted mat. The growth of cyanobacteria and iron reducing bacteria resulted in an active redox cycle between ferrous and ferric iron. …