Abstract

Scanning electron microscopic (SEM) analysis of surface features on detrital monocrystalline quartz sand grains is used in conjunction with existing information on hydrology, climate, and depositional environment in an attempt to unravel the history of surface deposits on the Alaskan North Slope and shelf. Samples from along the Colville and Sagavanirktok rivers, ranging from the high-relief headwaters to the subaerial deltas, were analyzed together with a suite of continental shelf samples that form a transect from shallow, submerged deltas across barrier islands, shoals, and out to the shelf break. Twenty to thirty grains from each sample were analyzed and assigned to one of eight grain types. The classification was devised by the authors to represent increasing aquatic and eolian abrasion and resultant destruction of the original grain form and evolution towards a rounded and chemically altered form. Our study leads to the following conclusions: 1) Increasing abrasion occurs with increasing river transport distance, but this pattern does not extend across the shelf, where modern erosion of underlying shelf deposits is believed to mask the riverine influence. 2) A considerable number of freshly fractured grains occur in samples from delta, nearshore, and shelf environments but are completely absent in the fluvial environment, suggesting that the process of refracturing grains is associated with modern littoral or marine processes. 3) The large number of refractured grains in the shoal environment suggests that intense impacting of grains through ice-related sedimentary processes may provide a mechanism for fracturing the grains. 4) Samples from the barrier islands, Stamukhi Shoal, and the general shelf surface are so similar that the question of whether such shoals represent drowned barrier islands or modern constructional features cannot be answered. 5) The similarity between all shelf samples with a preponderance of eolian grain types suggest that sands with similar abrasional histories cover the shelf, and this blanket may have developed from deposits strongly influenced by eolian processes during times when the shelf was subaerially exposed. 6) The extensive chemical features on the surface of many of the grains from the shelf environment suggest a relict or erosional source for the grains.

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