Quaternary Depositional Episodes, Western Spitsbergen, Norway: Aminostratigraphy and Glacial History

Abstract

Quaternary events interpreted from deposits along the central west coast of Spitsbergen are subdivided and correlated by amino acid enantiomeric ratios in enclosed molluscan fossils. Deposition is characterized by relatively short episodes of rapid sedimentation associated with glacial activity and high relative sea level. Depositional episodes are separated by relatively longer periods of subaerial exposure and pedogenesis. At least five major depositional episodes, each terminated by an emergence cycle, are identified by characteristic isoleucine epimerization ratios (alle/Ile) in Mya truncata and Hiaiella arctica. Absolute age limitations are derived by calibrating the alle/Ile ratios against radiometrically dated samples and diagnostic faunal communities. Glacial activity and sea-level change are inferred from the facies relationships within each depositional episode.

The oldest recognized unit, episode H, is characterized by alle/Ile Total ratios of 0.15 ± 0.02. At least three emergence cycles and two distinct glacial events are recorded within deposits of this episode. The absolute age is estimated to be between 300 and 1000 ka.

The next younger episode, D, is represented at only one site, although reworked shells with the same ratios were also found. Total alle/Ile ratios are ca. 0.08 and the age is estimated to be between 170 and 480 ka.

Deposits of the three youngest depositional episodes, C, B, and A, are widespread throughout the study area, and are characterized by Total alle/Ile ratios of 0.051 ± 0.006, 0.033 ± 0.0022, and 0.019 ± 0.001, respectively. Episode C deposits represent the last major regional glaciation of the area, an event estimated to have occurred between 90 and 260 ka ago. Episode B deposits are associated with a restricted regional glaciation estimated to have occurred between 40 and 130 ka ago. The associated fauna indicates marine conditions as warm or warmer than present. Episode A deposits are related to a latest Weichselian/earliest Holocene marine transgression/regression cycle during a period of restricted local glacier expansion, ca. 9 to 12 ka ago.

These findings place constraints on the timing and extent of Spitsbergen/Barents Sea glacial events. The 18 ka BP open-ocean δ¹⁸O minimum is not associated with extensive glacierization of the Forlandsund region of western Spitsbergen, nor did outlet glaciers of the postulated Barents Sea ice sheet reach the study area in the last 40 ka or more.