MORPHOLOGY AND SEISMIC STRATIGRAPHY OF THE INNER CONTINENTAL-SHELF OFF NOVA-SCOTIA, CANADA - EVIDENCE FOR A-65-M LOWSTAND BETWEEN 11,650 AND 11,250 C-14 YR BP

Nova Scotia's position near the margin of large Pleistocene ice sheets makes the Scotian Shelf region critical for evaluation of glaciation models and sea-level change. The sea floor of the inner Scotian Shelf was mapped using multibeam bathymetry, a combination of conventional s eismic and sonar techniques, and sampling. Multibeam bathymetry provid es an areal image of the sea floor. Combining this unique image with s ub-bottom seismic imaging, the relationships between sea floor topogra phy and the underlying strata were explored. The inner continental she lf of Nova Scotia can be subdivided into five major terrain ''zones''. These are the: (1) Truncation Zone, (2) Morainal Zone, (3) Outcrop Zo ne, (4) Basin Zone and (5) Scotian Shelf End-Moraine Complex. The Scot ian Shelf End-Moraine Complex and Basin Zone are glacial-depositional zones at the seaward edge of the inner shelf. Landward of these zones is a region of high relief bedrock, with ridges and valleys largely de void of surficial sediments extending from 80 to 120 m water depth (Ou tcrop Zone). This zone is interpreted as a relict bedrock surface, pre served under frozen-bed glacier conditions. To the east of the Outcrop Zone, in similar water depths, are unmodified till ridges overlying b edrock (Morainal Zone). The Truncation Zone is a region of the inner s helf from - 90 m to the present shoreline characterized by muted acous tic topography and planar erosional surfaces truncating bedrock and su rficial sediments. The Truncation Zone is subdivided into the Valley S ubzone, the Transition Subzone, the Platform Subzone and the Estuarine Subzone. The Valley Subzone is typified by sediment-infilled valleys occurring in 75 to 90 m water depths. These valleys contain seismic fa cies with a ponded style of deposition planed off at the sea floor or by erosional unconformities near the sea floor. The Transition Subzone is marked by a relatively steep ''ramp'' and terraces. The ramp at th e type section extends from 75 to 65 m water depth. The surface of the ramp can be either an erosional unconformity or a depositional surfac e formed by clinoform beds. The - 65 m former shoreline is interpreted as the top of the Transition Subzone ramp surface. At one ramp locali ty, clinoform beds form part of a progradational sequence called the S ambro Delta. A mussel valve fragment (Mytilus edulis) was obtained fro m a core in the foresets and radiocarbon dated. An age of 11,650 +/- 1 10 yr B.P. was obtained, adjusted for isotopic fractionation. Above - 65 m the sea floor forms a low relief, gently sloping erosional surfac e (Platform Subzone). Estuarine deposits have been found above - 50 m. The new sea-level curve constructed with the dated - 65 m shoreline a nd recently published data is at variance with calculated RSL curves b ased on geophysical models, primarily in the amplitudes and rates of R SL change. Reasons for the discrepancies may be late-melting ice and r egional variations in lithospheric strength and thickness.