Loess Records - Mineral Dust: A Key Player in the Earth System - page 423

the thickest mantles are located in the southern parts of the North Island and the
eastern and southern parts of the South Island (Fig. 16.5 ). On the North Island,
loess deposits are most prominent in the Manawatu region, where old terraces of
cold-climate floodplains have been mantled by dust from nearby braided streambeds
(Molloy 1998 ), and in the inland basins of Hawke's Bay. On the South Island, loess
deposits are most prominent on the high terraces of the Canterbury Plain, the North
Canterbury and South Canterbury downlands, the Banks Peninsula, and the South
Otago downlands and Southland Plains (Molloy 1998 ).
New Zealand loesses tend to exhibit more “classical loess” features: silty loam
texture, pale colors, and weak/massive structure (Fig. 16.2 d). In many localities,
loess facies are characterized by multiple paleosol horizons and/or inclusions of
tephric layers (Eden and Hammond 2003 ), while fragipans are a feature of some
relatively unaltered loess deposits. Common minerals in New Zealand loess deposits
and soil developed therein include quartz, feldspars, micas, vermiculite, kaolinite,
and halloysite. Where volcanic ash has contributed significantly to the loess deposit,
ferromagnesian minerals, allophane, and volcanic glass may be prominent (McCraw
1975 ; Molloy 1998 ; Eden and Hammond 2003 ).
Most loess in New Zealand has been produced by cold-climate processes, such
as freeze/thaw action and glacial grinding, as well as river abrasion, comminution,
and sorting (Eden and Hammond 2003 ). The North Island loess deposits are nearly
all products of fluvial processes and the winnowing of dry streambeds, while in
the South Island cold-climate loess processes operated in the Southern Alps during
the Quaternary glacial periods, supplying silt-sized sediment to the rivers of the
eastern half of the island for eventual winnowing and transport to adjacent plains
and downlands. A further form of loess, tephric loess or volcanic loess, also occurs
in and near the central volcanic region of the North Island (Eden and Hammond
2003 ), but the significance of this tephric parent material is perhaps greatest from a
chronological standpoint. Volcanic ash conveniently identifies (and separates) the
Ohakea loess, which was laid down across the Manawatu between 25,000 and
12,000 years ago and which acts as the parent material for the present-day soils
(Molloy 1998 ). In the South Island of New Zealand, accretion rates and ages of loess
deposits have been estimated through the identification of the Kawakawa Tephra
(deposited 26,0000 years before present), thermoluminescence techniques, and

14 C dating (Eden and Hammond 2003 ).

16.8.5 South America

South American loess presents a broad geographic distribution (Fig. 16.4 b) extend-
ing across the Chaco-Pampean Plain of Argentina and neighboring areas of
Uruguay, southern Brazil (Rio Grande do Sul), Paraguay, and the eastern Bolivia
lowlands (Zárate 2003 ). Loess is extensive in the western Chaco (Iriondo 1997 )
and forms a wide belt in the eastern Pampas, grading into sand mantles and dune