The Cambrian – Lower Ordovician Potsdam Group is a mostly siliciclastic unit that provides important insight into the paleoenvironmental, geologic and tectonic history of Early Paleozoic Laurentia. Nevertheless, in spite of 178 years of study the Potsdam in the Ottawa Embayment and Quebec Basin remains poorly understood. Also poorly understood is how the Potsdam relates with coeval strata regionally. In this work six siliciclastic paleoenvironments are recognized: (a) braided fluvial, (b) ephemeral fluvial, (c) aeolian, (d) coastal sabkha, (e) tide-dominated marine and (f) open-coast tidal flat. Fluvial strata were examined in particular detail and interpreted to consist of two end-member kinds. Braided fluvial deposits are dominated by low-relief bars formed in wide, shallow channels; however where basement structures limited the lateral growth of channels, flows were deeper and bar deposits thicker and higher angle. In contrast, ephemeral fluvial strata are dominated by sheetflood splay sedimentation with rare preservation of scour-filling supercritical bedform strata – all later subjected to aeolian reworking. In the upper Potsdam, alternating ephemeral and braided fluvial strata provide a record of climate change, which, respectively, correlate with documented global cool (arid) and warm (humid) periods during the Late Cambrian and Early Ordovician. Three allounits are recognized in Potsdam strata, recording regional episodes of sedimentation and facilitating correlation with coeval strata throughout eastern North America. These correlations, aided with provenance data from detrital zircons, show that changes in the areal distribution of sediment supply, accommodation and deposition/erosion were principally controlled by episodic reactivation of the Neoproterozoic Ottawa graben, which then periodically modified the stratigraphic expression of the ongoing Sauk transgression. Specifically, episodes of tectonic reactivation occurred during late Early to Middle Cambrian (allounit 1), late Middle to early Late Cambrian (allounits 2 – 3 unconformity), and Earliest Ordovician (allounits 3 – 4 unconformity). The earliest episode is correlated to regional extension of southern Laurentia, whereas the latter two are linked to peri-Laurentian accretion events that triggered reactivation of the Ottawa graben via the Missisquoi oceanic fracture zone.

<p> The Ontario shoreline of Lake Huron is one of the most populated areas, with reference to recreational purposes, in Ontario. However, with the rising water levels of the Great Lakes during 1972 and again in 1973, serious problems of beach erosion have resulted, particularly in the area of Grand Bend and Port Franks. This loss of sand has threatened cottages built on the dunes in addition to destroying breakwalls, steps, and boat launching ramps along the beach. It was with the idea of learning more about the beach, and possibly suggesting some methods of beach protection, that the research for this thesis was initiated. During the course of study, the author also became interested in the Ausable River and the associated flooding and erosion problems, with reference to past, present, and future attempts to solve or at least alleviate these difficulties. Thus, one section of the thesis is concerned with the Ausable River alone. </p> <p> The beach studied is actually the culmination of a series of raised beaches, formed during higher post-glacial lake stages. These raised beaches formed a bar separating the now non-existent Ausable Bay from Lake Huron, forming a lagoon eastward of the beach. This bar extends from Grand Bend, in a southwest direction, and culminates at Kettle Point. However, for the purposes of this thesis, that section between Grand Bend and Port Franks received the greatest amount of concentrated study. Over the years, the lagoon, formed by the growth of the bar has silted up, and is now drained for agricultural purposes. </p> <p> The modern beach was observed during the summer of 1972. This involved, profiling of a portion of the shore and offshore topography, procuring beach samples for later analysis, the use of sequential air photographs for observing changes over time, and the analysis of wind and wave data, along with many conversations with local residents and personal observations. </p> <p> The subsequent study of the above factors revealed several major conclusions regarding the beach. First, that it has good natural protection against erosion due to the abundance of sand s tored by the dunes. Second, the beach appears to be in an equilibrium state, however as lake levels fluctuate, so must the beach level, thus destroying the equilibrium for a period of time. With the lowering of the water level, the beach will become wider, exposing sand to the onshore winds, which will in turn rebuild the dunes with the blowing sand. Finally, because of the prximity of man-made structures to the beach, on the unstable dunes, some method of stabilizing the beach is necessary. That suggested is a groin system, designed and constructed by the local authorities. This would help prevent erosion and would eliminate the often vain and possibly dangerous, (to the natural environment), attempts by individuals to halt erosion. </p> <p> This is by no means a complete study of the area and its problems. Further consideration should be given to proposals which have been presented to the local conservation authority, and which were designed to alleviate some of these problems, particularly at Port Franks. The suggestions made here should also be given further thought. In addition to these practical problems, the actual growth of the original bar would provide an interesting subject for study. </p> / Thesis / Bachelor of Arts (BA)