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 …

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 …