W. D. Nettleton

Late Quaternary, redeposited loess-soil developmental sequences, South Yemen

Abstract Episodic desert loess and paleosol sequences in South Yemen provide a late Pleistocene to Holocene record of climatic change and soil development. At Sana, one paleosol based on its thickness and development formed during mid or early Holocene time in approximately four thousand years. The 2Akb horizon sample of this paleosol has a 14 C age of 7750 ± 300 years. At Ibb the 2ABtb horizon of another paleosol has a 14 C age of > 33,100 years. Deposition (silt + very fine sand + clay) for the Sana site calculates to average 110 g m −2 yr −1 and includes 3.3 g or less of CaCO 3 m −2 yr −1 This rate of desert loess and carbonate deposition is probably 2 to 5 times greater than that in the Lahontan Basin of the United States during the last 13 kyr, and about 2 to 5 times higher than that in the southwestern United States today. It is about the same as the 12 cm kyr −1 (170 g m −2 yr −1 estimated for central North Iran and the 10 cm kyr −1 (0.1 mm yr −1 estimated for the Netivot section of the Negev of Israel but some 7 to 9 times less than the rate estimated for Wisconsinan loess in Iowa. Thickness of desert loess examined and the calculated rate of deposition indicate that the crater has been receiving desert loess for at least 15 kyr, and that the crater is pre Holocene. Pedogenic development of the Camborthids and Haplargids in the ground soils and that of the argillic horizons in the Sana paleosols suggest that these soils formed in a somewhat more humid phase than the present warm-tropical, semi-arid environment. The occurrence of mollic epipedons in the Sana paleosols, but not in the ground soils is evidence of a more humid past climate (mid or early Holocene). The Ibb paleosol, which formed at least partly during a more humid part of the late Pleistocene, is even more strongly developed than the mid or early Holocene Sana paleosols.

Micromorphologic Evidence of Adhesive and Cohesive Forces in Soil Cementation

Cemented soil horizon differentation is based on the material that is dominantly responsible for restricting root growth and retarding porosity. Chemical bonding properties of the cementing material determine whether it coheres to itself or adheres to the s-matrix. the relative amount of adhesion or cohesion of soil cement can be inferred most clearly from fabric arrangements of strongly cemented horizons. Ionicly bonded calcite and gypsum produce open-porphyric related-distribution-patterns in which the primary grains float in the expanding crystal matrix. In contrast, covalently bonded silica, iron, aluminum, and organic matter produce close-porphyric related-distribution-patterns in which isotopic cutans surround grains and fill voids and channels. Whole-horizon chemical data and quantification of cement on thin sections indicate that adhesive cementation requires less cement than cohesive cementation.

Silt flow in soils

Abstract Nettleton, W.D., Brasher, B.R., Baumer, O.W. and Darmody, R.G., 1994. Silt flow in soils. In: A.J. Ringrose-Voase and G.S. Humphreys (Editors), Soil Micromorphology: Studies in Management and Genesis. Proc. IX Int. Working Meeting on Soil Micromorphology, Townsville, Australia, July 1992. Developments in Soil Science 22, Elsevier, Amsterdam, pp. 361–371.

Micromorphological evidence of clay translocation in poorly dispersible soils

Abstract Clay translocation is an important pedogenic process. Field and laboratory studies are used herein to evaluate the process in some Ultisols and Oxisols having horizons with poor dispersion characteristics. Surface areas measured by ethylene glycol monoethyl ether (EGME) and micromorphological studies confirmed the presence of argillic horizons in the Ultisols. Two of the Oxisols also have illuviation argillans, but most of these are below oxic horizons. Staining and cementation by Fe and Al oxides in soils in the oxidic families appear to have masked evidence of clay accumulation except in lower horizons. Because overlying horizons do not disperse well, we conclude that either environmental conditions changed or else weathering became more intense following development of the argillic horizons. Climatic shifts and continued intense weathering apparently are responsible for formation of the low-activity clays, and the iron and aluminum oxide cementation causing the poor dispersion.

Argillic Horizon Formation in late Wisconsinan Eolian Materials in Southwest Colorado, U.S.A

Abstract Argillic horizons with reddish hues were studied in Haplargids and Argiborolls across an elevation transect. The eolian parent materials were deposited in two, or more episodes. The younger deposit, late Wisconsinan, was 14 C dated from a buried musk ox (Symbos cavifrons) at Grass Mesa as beginning about 16,000 ybp. The late Wisconsinan soil at this site and those at lower elevations have illuviation argillans coating and bridging sand grains. Maximum clay content of the late Wisconsinan soil at Grass Mesa is 22% vs. 13% in the eolian parent material. In the bisequal Monticello pedon above Grass Mesa, the late Wisconsinan argillic horizon has common illuviation argillans in channels and voids. In higher upper parts of the transect where the deposits are thin and clay contents reach 35%, plasmic fabrics in the argillic horizons have vosepic, masepic, and skelsepic areas. In the late Wisconsinan soils, depth to carbonate corresponds to the average annual maximum depth of wetting suggesting that these soils could have formed in a climate much like that of todays.

Quantitative relationships between net volume change and fabric properties during soil evolution

Abstract Chadwick, O.A. and. Nettleton, W.D, 1994. Quantitative relationships between net volume change and fabric properties during soil evolution. In: A.J. Ringrose-Voase and G.S. Humphreys (Editors), Soil Micromorphology: Studies in Management and Genesis. Proc. IX Int. Working Meeting on Soil Micromorphology, Townsville, Australia, July 1992. Developments in Soil Science 22, Elsevier, Amsterdam, pp. 353–359.