Geoscience Reference
In-Depth Information
11.3
Cryosols and Correlation of Glacial Deposits
The fact that soils show a regular progression in development with time enables
their use in correlating drifts between or among valleys affected by a similar glacial
sequence. This has enabled us to develop a “master relative chronology” for the
MDV (Table
11.1
). The chronology is based on an examination of 431 sites on
moraines with approximate ages that range from mid-Holocene to Miocene. The
chronology enables investigators to estimate relative ages of landforms based on the
properties listed, which include depths of staining, cohesion, visible salts, and
ghosts (pseudomorphs), depth to ice-cemented permafrost, salt stage, weathering
stage, thickness of salt pan, desert pavement development index, degree of patterned
ground formation, and soil subgroup.
Table
11.2
shows a provisional correlation of drifts in the MDV based on data
contained in Table
11.1
. These data confi rm that the outlet glaciers (Taylor, Wright
Upper, Hatherton, Beardmore) and alpine glaciers (Wright Valley) have acted out-
of-phase with grounded ice in the Ross Sea (Wilson Piedmont Glacier) and that
outlet glaciers in the MDV behaved similarly in response to changes in climate that
accompanied the glacial-interglacial cycles
11.4
Cryosols and Glacier Dynamics
Since the Pliocene most of the glaciers in the MDV have been cold-based (dry-based),
meaning that they are frozen to their bed. These glaciers advance over frozen aprons
at their termini so that they are able deposit drift with minimal impact to the under-
lying surface. Figure
11.7
provides evidence for overriding by cold-based glaciers
in Arena Valley. The upper soil (above the diabase ventifact in the center of the
image) is of Taylor IV age (>1.0 Ma, <7.4 Ma) and the buried soil is of Quartermain
age (>11.3 Ma).
Bockheim (
2010b
) examined soil preservation and ventifact recycling from
dry-based and wet-based glaciers at 609 sites in the central and southern
TAM. Buried soils were most common from deposition by dry-based glaciers
(44 of 51 pedons). Fifteen percent of the pedons contained recycled ventifacts in
relict and buried soils that ranged from late Quaternary to Miocene in age, par-
ticularly in drift from dry-based glaciers (56 of 77 pedons). Overall 84 % of the
buried soils and 78 % of the pedons with recycled ventifacts originated from dry-
based glaciers. The proportion of soils with recycled clasts on a particular drift
was greatest where the ratio of drift thickness to soil thickness (“recycling ratio”)
was the least.
