Coastal products of marine transgression in cold-temperate and high-latitude coastal-plain settings: Gulf of St Lawrence and Beaufort Sea

Abstract

Cold climate exerts a clear influence on the processes of marine transgression in midand high-latitude coastal-plain settings, but its signature in the depositional record is much clearer at high latitude. Both cases selected for this study are influenced by the legacy of past glaciation and the pervasive effects of ongoing Holocene marine transgression. Both are affected by sea ice. The high-latitude site lies within the zone of continuous permafrost and the abundance of excess ground ice along the Beaufort coast is the dominant factor distinguishing it from the mid-latitude Gulf of St Lawrence (GSL) setting and standard models of transgressive coasts elsewhere. In the southern GSL, the transgressive unconformity (TU) is at the seabed (or buried by a very thin veneer) across the inner shelf; shoreface sand moves landward, keeping pace with the transgressive front through deposition in barriers, dunes and estuaries. The pace of transgression in the Beaufort Sea is influenced by a number of distinctive periglacial erosion processes, including thermal abrasion and thaw subsidence. Marine transgression across this landscape creates intricate breached-lake estuaries and low sandy barrier beaches with limited dunes, leaving distinctive facies suites and geometry, while seaward sediment transport buries the TU on the inner shelf.

Sediment characteristics of a thermokarst lagoon in the northeastern Siberian Arctic (Ivashkina Lagoon, Bykovsky Peninsula)

“…This salinization probably contributes to further ground ice thaw followed by subsidence that eventually allows full marine inundation. We may thus expect some sedimentary record of marine transgression such as an unconformity described by Forbes et al [10], although marine influence has probably varied in intensity or been intermittent, depending on climatic shifts in sea ice and storm tracks. Tiksi Bay is connected to Ivashkina Lagoon through the lagoon opening.…”

Submarine Permafrost Map in the Arctic Modeled Using 1‐D Transient Heat Flux (SuPerMAP)

“…By back‐calculating sediment accumulation during transgressive and regressive periods, onlapping marine transgression sediment strata and disconformities were created within the model domain, which affected the amount of ice frozen during sea level low‐stand ground cooling. In transgressive environments, terrestrial strata typically terminate with an erosional marine ravinement surface called a transgressive nonconformity (Forbes et al, ). Such alternating terrestrial and marine sediment layers are strongly suggested by the few cored and well‐described offshore cores on the Arctic shelf, which encounter alternating strata of saline and freshwater permafrost (e.g., Blasco et al, ; Ponomarev, , ; Rachold et al, ).…”

Anthropogenic, Direct Pressures on Coastal Wetlands

“…Permafrost extends to about 60 m depth in Holocene delta sediments, with many thaw taliks beneath lakes or channels that do not freeze completely in winter (Todd and Dallimore, 1998). There is higher ground to the east and west of the outer delta, with permafrost extending to a depth of 500-700 m. Erosional breaching of thaw lake basins has created a highly indented coast with eroding bluff headlands, local dunes, low spits and barrier islands, and shallow estuaries with supratidal Puccinellia phryganodes flats and accumulations of driftwood from the Mackenzie River (Ruz et al, 1992;Forbes and Hansom, 2011;Forbes et al, 2014). The delta is micro-tidal (range <0.5 m), but storm surges of up to 2.5 m cause extensive flooding (Manson and Solomon, 2007;Lamoureux et al, 2015).…”