Post-glacial Eustatic Sea-level Rise Research Articles

Working from the Known to the Unknown: Linking the Subaerial Archaeology and the Submerged Landscapes of Santarosae Island, Alta California, USA

Since the collapse of the Clovis-first model of the peopling of the Americas some 30 years ago, there has been growing interest in the Pacific Coast as a potential early human dispersal corridor. With postglacial eustatic sea level rise inundating most New World paleoshorelines older than ~7000 years, however, locating terminal Pleistocene sites along modern coastlines is challenging. Using the distribution and archaeology of subaerial Paleocoastal archaeological sites on California’s Northern Channel Islands as a guide, we developed a Geographic Information Systems (GIS) predictive model to locate and map submerged high probability landforms, which might contain Paleocoastal sites. Our results illustrate how archaeologists can narrow targets in their search for evidence of the first Americans along submerged Pacific Coast paleoshorelines.

The Neoproterozoic succession of the central Rocky Mountains, Canada

Abstract The Neoproterozoic succession exposed in the central Canadian Rocky Mountains comprises a thick (2 to 5 km) sequence of marine clastic rocks deposited after major subsidence associated with continental scale rifting. A major transverse south to north change in lithofacies separates the succession into southern more distal and northern more proximal sequences. The southern sequence (Miette Group) comprises the sandstone-conglomerate dominated McKale Formation (new) overlain by the argillite and siltstone dominated East Twin Formation (new). Locally, black pyritic slate and limestone of the Cushing Creek Formation (new) occurs at the base. The Cushing Creek Formation was deposited in a deep euxinic basin with only minor sandstone turbidite deposition. The lower part of the McKale Formation was deposited in basin-floor turbidite complexes, whereas the upper part, with its thick interlayered argillite intervals and uncommon slump structures, was deposited in lower slope environments. A thick varicoloured argillite unit separates the lower and upper McKale Formation in northeastern exposures. This unit, mappable into the lower part of the Framstead Formation and correlative with the Old Fort Point Formation, records an abrupt reduction in the supply of clastic material associated with the termination of glaciation. The East Twin Formation represents a transition from slope sedimentation at the base to shallow-marine sedimentation at the top. It records the reduction of the supply of coarse clastic material into the basin and the filling of the Neoproterozoic basin. The northern sequence (Misinchinka Group) comprises in succession: diamictite of the Vreeland Formation (new); argillite with local carbonate olistoliths, medial sandstone to conglomerate and, in the east, basal interbedded sandstone and argillite of the Framstead Formation (new); carbonate of the Chowika Formation; and argillite and siltstone of the Cut Thumb Formation (new). Locally interbedded siltstone, argillite and sandstone of the Paksumo Formation (new) occur at the base of the exposed succession. The Paksumo, Vreeland Formation and basal part of the Framstead Formation record glacially influenced slope sedimentation. The Paksumo Formation and basal part of the Framstead Formation are primarily turbidite deposits, whereas diamictites of the Vreeland Formation are primarily resedimented mass flow and glaciogenic ‘rain-out’ deposits. The lower part of the Framstead Formation records an abrupt reduction in the supply of clastic material associated with a post-glacial eustatic sea level rise. Large olistoliths of shallow-water carbonate in both the lower and upper parts of the Framstead Formation indicate deposition in a slope environment and instability of the adjacent carbonate platform. Sandstone to conglomerate turbidite-filled channels in the middle part of the Framstead Formation record a relative sea level drop and a temporary breakdown of the adjacent carbonate platform. The return to fine clastic slope sedimentation in the upper part of the Framstead Formation records a relative sea level rise. The overlying Chowika carbonate platform records a dramatic reduction in clastic sediment supply and a relative sea level drop. The abruptly overlying Cut Thumb Formation represents a relative sea level rise and a change to deeper water siliciclastic shelf sedimentation that is not reflected in the south. Tectonism near the end of Neoproterozoic Windermere sedimentation resulted in the inversion of part of the initial deep basin-floor to form an outboard high on the west and in the reactivation of the transverse facies-change zone, as a north-side-down rather than south-side-down feature.

The evolution of the Dutch and Belgian coasts and the role of sand supply from the North Sea

During the Holocene, the Dutch and Belgian coasts evolved, controlled by post-glacial eustatic sea-level rise, spatially varying vertical subsurface motions (glacio-isostatic crustal rebound, compaction, tectonics) and spatially varying sediment supply (mainly marine sand). The marine sand supply changed as the tidal dynamics and the wave climate changed due to the changing geometry and depth of the North Sea during the Holocene transgression. These changes influenced the coastal evolution. This study compares the results of separate numerical model calculations of the large-scale Holocene tide- and wave-induced sand transport in the southern North Sea with existing geological data of the Dutch and Belgian large-scale coastal evolution, resulting in a qualitatively good correlation. The large-scale coastal evolution is interpreted in terms of the oceanographical forcing, and an integrated conceptual model of the Holocene evolution of the Dutch and Belgian coasts is proposed. The large-scale wave-driven bed-load transport was an order of magnitude smaller than the tidal transports. The modelled tidal transport direction changed from onshore before 6 ka BP to along shore at present for the Zeeland and Holland coasts; the influence that waves may have had on the tidal transport by suspending sand gradually decreased. This change in direction caused the modelled tidal sand supply to the coast to decrease for the Belgian, Zeeland and Holland coasts. While the offshore area of the Holland coast remained a zone of (small) deposition due to decreasing northward sand transports, the offshore area of the Zeeland coast became increasingly erosional after 6 ka BP due to the encroaching divergence of the tidal transports. Due to uncertainty in the magnitude of the modelled sand transports, but robustness in the transport patterns, the focus is on the qualitative rather than the quantitative model results. When compared with the trend of closure, expansion and later erosion and reopening of the coast, the above decrease in sand supply must have been slow enough compared with the decrease in sea-level rise to cause a temporary sand surplus which decayed to a slight deficit as the decrease in supply and the rise in sea level continued. The Wadden Sea coast exchanged little or no sand with the adjacent deeper North Sea throughout the Holocene.

Antarctic Ice-Sheet Volume at 18000 Years B.P. and Holocene Sea-Level Changes at the West Antarctic Margin

AbstractThe Antarctic ice sheet has been reconstructed at 18000 years b.p. by Hughes and others (in press) using an ice-flow model. The volume of the portion of this reconstruction which contributed to a rise of post-glacial eustatic sea-level has been calculated and found to be (9.8±1.5) × 106 km3. This volume is equivalent to 25±4 m of eustatic sea-level rise, defined as the volume of water added to the ocean divided by ocean area. The total volume of the reconstructed Antarctic ice sheet was found to be (37±6) × 106 km3. If the results of Hughes and others are correct, Antarctica was the second largest contributor to post-glacial eustatic sea-level rise after the Laurentide ice sheet. The Farrell and Clark (1976) model for computation of the relative sea-level changes caused by changes in ice and water loading on a visco-elastic Earth has been applied to the ice-sheet reconstruction, and the results have been combined with the changes in relative sea-level caused by Northern Hemisphere deglaciation as previously calculated by Clark and others (1978). Three families of curves have been compiled, showing calculated relative sea-level change at different times near the margin of the possibly unstable West Antarctic ice sheet in the Ross Sea, Pine Island Bay, and the Weddell Sea. The curves suggest that the West Antarctic ice sheet remained grounded to the edge of the continental shelf until c. 13000 years b.p., when the rate of sea-level rise due to northern ice disintegration became sufficient to dominate emergence near the margin predicted otherwise to have been caused by shrinkage of the Antarctic ice mass. In addition, the curves suggest that falling relative sea-levels played a significant role in slowing and, perhaps, reversing retreat when grounding lines approached their present positions in the Ross and Weddell Seas. A predicted fall of relative sea-level beneath the central Ross Ice Shelf of as much as 23 m during the past 2000 years is found to be compatible with recent field evidence that the ice shelf is thickening in the south-east quadrant.

Antarctic Ice-Sheet Volume at 18000 Years B.P. and Holocene Sea-Level Changes at the West Antarctic Margin

AbstractThe Antarctic ice sheet has been reconstructed at 18000 years b.p. by Hughes and others (in press) using an ice-flow model. The volume of the portion of this reconstruction which contributed to a rise of post-glacial eustatic sea-level has been calculated and found to be (9.8±1.5) × 106km3. This volume is equivalent to 25±4 m of eustatic sea-level rise, defined as the volume of water added to the ocean divided by ocean area. The total volume of the reconstructed Antarctic ice sheet was found to be (37±6) × 106km3. If the results of Hughes and others are correct, Antarctica was the second largest contributor to post-glacial eustatic sea-level rise after the Laurentide ice sheet. The Farrell and Clark (1976) model for computation of the relative sea-level changes caused by changes in ice and water loading on a visco-elastic Earth has been applied to the ice-sheet reconstruction, and the results have been combined with the changes in relative sea-level caused by Northern Hemisphere deglaciation as previously calculated by Clark and others (1978). Three families of curves have been compiled, showing calculated relative sea-level change at different times near the margin of the possibly unstable West Antarctic ice sheet in the Ross Sea, Pine Island Bay, and the Weddell Sea. The curves suggest that the West Antarctic ice sheet remained grounded to the edge of the continental shelf untilc. 13000 years b.p., when the rate of sea-level rise due to northern ice disintegration became sufficient to dominate emergence near the margin predicted otherwise to have been caused by shrinkage of the Antarctic ice mass. In addition, the curves suggest that falling relative sea-levels played a significant role in slowing and, perhaps, reversing retreat when grounding lines approached their present positions in the Ross and Weddell Seas. A predicted fall of relative sea-level beneath the central Ross Ice Shelf of as much as 23 m during the past 2000 years is found to be compatible with recent field evidence that the ice shelf is thickening in the south-east quadrant.