Origin and character of loesslike silt in unglaciated south-central Yakutia, Siberia, U.S.S.R.

Abstract

Loesslike silt mantles upland terraces and low plateaus throughout unglaciated south-central Yakutia but is thickest along the south side of the lower Aldan River valley and the east side of the Lena River valley. The silt is probably loess deposited during glacial advances by winds blowing southward from the Verkhoyansk Range and eastward across the broad vegetation-free flood plain of the braided Lena River.The well-sorted uniform tan silt is well displayed along the Aldan and Lena Rivers; the thickest exposure measured, more than 60 m, is on the Tyungyulyu Terrace on the east side of the Lena River. On the west side of the valley, it is 10-25 m thick but thins rapidly to a featheredge west of Yakutsk. Almost all scarps along the south side of the Aldan River are capped by 10-35 m of silt.The texture and mineral composition of the loesslike silt are uniform throughout south-central Yakutia, whether it overlies limestone, poorly consolidated sandstone, alluvium, and glacial outwash. All silt samples examined contained a high percentage of quartz and feldspar. The silt stands in sheer cliffs and is massive, with little or no stratification.The origin of the loesslike silt has been ascribed to disintegration in place of country rock by a marine, estuarine, lacustrine, fluvial, residual, or eolian source, or to a combination of these processes. The marine and estuarine hypotheses have never had strong support, but the lacustrine, fluvial, and residual hypotheses have been advanced by many Soviet workers.The most widely accepted explanation of the origin of the upland silt is that it is a combination of lacustrine and alluvial deposits formed on great flood plains and marshy plains. This origin is unlikely, however, because there are no shorelines, wave-cut beaches, deltas, mudcracks, or ripple marks. Neither distinct stratification nor an appreciable amount of clay exists in the silt. Moreover, there is no definite upper boundary to the deposits, as would be expected of lacustrine deposits.The loesslike silt has also been described as a residual deposit formed by the breakdown, by freezing and thawing, of the underlying rocks. The silt bears no chemical, mineralogic, or textural relation to the underlying strata, however, and it is too thick to represent only breakdown of rocks in place.The widespread mantle of uniform loesslike silt is here considered to be windblown, derived from glacial outwash in braided streams and on broad plains, because: (1) it occurs as a surficial mantle; (2) it is lithologically independent of the underlying material; (3) it is stratified indistinctly or not at all, except in retransported material; (4) it is associated with sand dunes; (5) it contains fossils of land animals; (6) its sorting and texture are similar to that of loess and windblown dust from many places elsewhere in the world; (7) its grains are angular and relatively unweathered.

Permafrost carbon: Stock and decomposability of a globally significant carbon pool

“…The existence, spatial distribution, and carbon (C) concentrations of these sediments are well documented in the Russian literature but there has been only one preliminary estimate of their C stock [ Zimov et al , 1997], so they have never been considered in global C inventories. Similar deposits occur less extensively in Alaska [ Pewe and Journaux , 1983]. Estimates of high‐latitude soil C stocks are based largely on studies of the top 1–2 m of soils, predominantly in North America [ Batjes , 1996; Gorham , 1991; Melillo et al , 1995; Prentice et al , 2001; Smith et al , 2004].…”

Iron Redistribution Upon Thermokarst Processes in the Yedoma Domain

“…Yedoma deposits were, at first, characterized as homogeneous silty fine, ice-and organic-rich sediments with primary or secondary aeolian processes being the main contributor during the time of formation. Hence, Yedoma deposits were and still are often defined as loess or loessrelated deposits (Pewe and Journaux, 1983;Tomirdiaro and Chernen'kiy, 1987;Murton et al, 2015). However, in addition to the established aeolian contribution to these ice-rich sediments, additional contributions from fluvial, colluvial, alluvial local sedimentation processes are identified in many regions of the Yedoma domain (e.g., Schirrmeister et al, 2020).…”

Sulfur Isotope Geochemistry of Ice‐Wedges in Yakutia, East Siberia

“…The Central Yakutia lowland remained unglaciated and accumulated a thick loess‐like sequence during the last glacial period [35, 36]. There are three study sites: Cyuie, Churapcha, and Syrdakh, all located within 150 km of each other.…”