Nearshore surficial geology, heavy minerals and geochemistry, Northern Juan de Fuca Strait
| dc.contributor.author | Kilby, Caleen Elaine | en_US |
| dc.date.accessioned | 2024-08-14T18:31:19Z | |
| dc.date.available | 2024-08-14T18:31:19Z | |
| dc.date.copyright | 1991 | en_US |
| dc.date.issued | 1991 | |
| dc.degree.department | Department of Geography | |
| dc.degree.level | Master of Science M.Sc. | en |
| dc.description.abstract | The nearshore surficial geology, heavy mineral distribution and geochemistry of northern Juan de Fuca Strait is examined in this study. Surficial sediments were mapped using analyses of 150 offshore samples along with 382 km of geophysical records including sidescan sonar and high resolution seismic profiling. Grain-size and geochemical analyses were performed on sediment less than 2 mm in size. Heavy mineral separations and heavy mineral identification were performed on the sand fraction of selected samples. Beach and river samples were collected and analysed for heavy mineral content and to trace mineral provenance. Seabed surface samples reveal sediments which are texturally and mineralogically immature. A series of shallow (above 30 m depth) nearshore terraces are covered with a thin veneer (few metres or less) of relict glacial gravel and boulders along with medium to fine sand. Below approximately 80 m depth a muddy sand veneer covers a sediment wedge which thickens towards the centre of the strait. Recent sediments are derived from reworked underlying and adjacent glacial material, erosion of the coastal sandstone facies of the Carmanah Group, and river influx reflecting the adjacent terrigenous lithologies. Sediments are subsequently winnowed and reworked into bedforms such as flow-transverse dunes and oscillation ripples. Comparatively high amounts of heavy minerals, averaging 7%, are found in the sand fraction of the sediments. These concentrations are over twice the levels found in sands of Barkley Sound and five times higher than in sands of the continental shelf northwest of the study area. Heavy minerals consist primarily of amphiboles (hornblende), epidote and lithic fragments. The Metchosin Igneous Complex is the most likely source of the heavy minerals. Magnetite/ilmenite are the predominant opaque minerals. Trace metals show low background levels in the surface sediments in both mud and sand fractions in the offshore and beach sands. Only Ti shows significantly high background levels (0.7%). Enriched cu, Fe, Mn, V, Ti and Cr values are in evidence between China Beach and Sheringham Point. Between these two points a small nearshore heavy mineral placer is identified along Sandcut Beach extending to at least 800 m from shore. The placer has heavy mineral concentrations from 15% up to 45%, and enriched Ti values from 0.75% to as high as 1.4%. Source of the placer is believed to be from former mine tailings dumped at, or below tide-water. Formation of shallow marine or beach placers along the northern strait are most likely limited due to mineral and textural immaturity of the sediments. However, locally beaches may experience sufficient hydraulic reworking and seasonal recycling to create heavy mineral placers. | |
| dc.format.extent | 332 pages | |
| dc.identifier.uri | https://hdl.handle.net/1828/18434 | |
| dc.rights | Available to the World Wide Web | en_US |
| dc.title | Nearshore surficial geology, heavy minerals and geochemistry, Northern Juan de Fuca Strait | en_US |
| dc.type | Thesis | en_US |
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