Non-Classical Types of Loess

IRIONDO, MARTIN; KRÖHLING, DANIELA

SEDIMENTARY GEOLOGY

Elsevier Science Ltd.

Lugar: Oxford; Año: 2007 vol. 202 p. 352 - 368

0037-0738

The purpose of this contribution is to describe the sequence of physical and chemical processes resulting in the sediment-type named loess, a fine grained sediment deposit of universal occurrence. Owing to historical causes, loess has been (and still is) implicitly linked to glacial / periglacial environments among most naturalists. However it is known today that most eolian dust is deflated from tropical deserts. Hence, that sequence of processes is more comprehensive than the former narrow cold scenario. Six examples of different "non classical" cases (from South America and Europe) that fit well to the loess definition are developed. 1) Volcanic loess in Ecuador: pyroclastic eruptions / valley wind / mountain praire / silica structuring. 2) Tropical loess in northeastern Argentina, Brazil and Uruguay: deflation of river and fan splays / savanna / iron sesquioxide structuring. 3) Gypsum loess in northern Spain: destruction of anhydrite / gypsiferous layers in a dry climate / valley wind / Saharian shrub peridesert / gypsum structuring. 4) Tradewind deposits in Venezuela and Brazil: deflation in tidal flats / trade wind into the continent / savanna / iron hydroxide structuring. 5) Anticyclonic gray loess in Argentina: continental anticyclone on plains / anticlockwise winds and whirls / steppe / carbonate structuring. All these non-classical types conform to the accepted loess definitions and they also share the most important field characteristics of loess such as grain size, friability, vertical or sub-vertical slopes in outcrops, subfussion and others. Other cases can probably be recognized when systematically scrutinized.