Desert crusts and rock coatings - Arid Zone Geomorphology - page 161

age - Dorn (1998) identifies eleven factors other than
time that lead to darkening. Attempts have been made to
date rock varnish using the 230 Th/ 234 U technique corrob-
orated with 231 Pa/ 235 U (Knauss and Ku, 1980), as well as
cation-ratio (K + +

north of South Australia. Journal of the Geological Society
of Australia , 24 , 107-116.
Alonso-Zarza, A.M. (1999) Initial stages of laminar calcrete
formation by roots: examples from the Neogene of central
Spain. Sedimentary Geology , 126 , 177-191.
Alonso-Zarza, A.M. (2003) Palaeoenvironmental significance of
palustrine carbonates and calcretes in the geological record.
Earth-Science Reviews , 60 , 261-298.
Ambrose, G.J. and Flint, R.B. (1981) A regressive Miocene lake
system and silicified strandlines in northern South Australia;
implications for regional stratigraphy and silcrete genesis.
Journal of the Geological Society of Australia , 28 , 81-94.
Amit, R. and Gerson, R. (1986) The evolution of Holocene reg
(gravelly) soils in deserts - an example from the Dead Sea
region. Catena , 13 , 59-79.
Amit, R. and Yaalon, D.H. (1996) The micromorphology of
gypsum and halite in reg soils - the Negev Desert, Israel.
Earth Surface Processes and Landforms , 21 , 1127-1143.
Andrews, J.E., Singhvi, A.K., Kailath, A.J. et al. (1998) Do
stable isotope data from calcrete record Late Pleistocene
monsoonal climate variation in the Thar Desert of India?
Quaternary Research , 50 , 240-251.
Arakel, A.V. (1980) Genesis and diagenesis of Holocene evap-
oritic sediments in Hutt and Leeman Lagoons, Western Aus-
tralia. Journal of Sedimentary Petrology , 50 , 1305-1326.
Arakel, A.V. (1982) Genesis of calcrete in Quaternary soil pro-
files, Hutt and Leeman Lagoons, Western Australia. Journal
of Sedimentary Petrology , 52 , 109-125.
Arakel, A.V. (1986) Evolution of calcrete in palaeodrainages of
the lake Napperby area, central Australia. Palaeogeography,
Palaeoclimatology, Palaeoecology , 54 , 283-303.
Arakel, A.V. (1991) Evolution of Quaternary duricrusts in
Karinga Creek drainage system, central Australian ground-
water discharge zone. Australian Journal of Earth Sciences ,
38 , 333-347.
Arakel, A.V. and McConchie, D. (1982) Classification and gen-
esis of calcrete and gypsum lithofacies in palaeodrainage
systems of inland Australia and their relationship of
carnotite mineralization. Journal of Sedimentary Petrology ,
52 , 1149-1170.
Arakel A.V., Jacobson G., Salehi M. and Hill C.M. (1989) Sili-
cification of calcrete in palaeodrainage basins of the Aus-
tralian arid zone. Australian Journal of Earth Sciences , 36 ,
73-89.
Aref, M.A.M. (2003) Classification and depositional environ-
ments of Quaternary pedogenic gypsum crusts (gypcrete)
from east of the Fayum Depression, Egypt. Sedimentary Ge-
ology , 155 , 87-108.
Aristarain, L.F. (1971) On the definition of caliche deposits.
Zeitschrift f ur Geomorphologie , NF 15 , 274-289.
Armenteros, I., Bustillo, M.A. and Blanco, J.A. (1995) Pedo-
genic and groundwater processes in a closed Miocene basin
(northern Spain). Sedimentary Geology , 99 , 17-36.
Bachman, G.O. and Machette, M.N. (1977) Calcic soils and
calcretes in the southwestern United States , US Geological
Survey, Open File Report 77-794.

Ca 2 + /Ti 4 + ) and radiocarbon methods
(Dorn et al. , 1986, 1989). These techniques, and partic-
ularly the cation-ratio method, have been the subject of
debate concerning their accuracy, comparability and relia-
bility (Bierman and Gillespie, 1991, 1992a, b, 1994, 1995;
Dorn, 1992, 1995; Cahill, 1992; Harrington and Whitney,
1995). Perhaps the greatest potential application for rock
varnish is through the analysis of varnish microlamina-
tions (Dorn, 2007). The basic assumption of the technique
is that varnish microstratigraphy is influenced by regional
climatic variations; black Mn-rich layers record wet in-
tervals, while orange and yellow Mn-poor layers indicate
drier periods (Dorn, 1990; Jones, 1991; Liu and Dorn,
1996; Liu, 2003). The climatic signals recorded in var-
nish have been proven to be regionally contemporaneous
(Liu and Dorn, 1996; Liu et al. , 2000), such that varnish
microstratigraphy now has the potential to be used as a
dating tool in a similar way to tephrachronology.

References

Abdel Jaoued, S. (1987) Calcretes and dolocretes of Upper
Palaeocene-Miocene (Bou-Loufa Formation) in southern
Tunisia. Bulletin de la Societ´eGeologique de France , 3 ,
777-781.
Al Juaidi, F.A., Millington, A. and McLaren, S. (2003) Evaluat-
ing image fusion techniques for mapping geomorphological
features on the eastern edge of the Arabian Shield (Central
Saudi Arabia). Geographical Journal , 169 , 117-131.
Alexander, G.B., Heston, W.M. and Iler, R.K. (1954) The sol-
ubility of amorphous silica in water. Journal of Physical
Chemistry , 58 , 453-455.
Alexandre, A., Meunier, J.D., Llorens, E. et al. (2004) Method-
ological improvements for investigating silcrete formation:
petrography, FT-IR and oxygen isotope ratio of silcrete quartz
cement, Lake Eyre Basin (Australia). Chemical Geology ,
211 , 261-274.
Ali, Y.A. and West, I. (1983) Relationships of modern gypsum
nodules in sabkhas of loess to composition of brines and sed-
iments in northern Egypt. Journal of Sedimentary Petrology ,
53 , 1151-1168.
Allen, C.C. (1978) Desert varnish of the Sonoran Desert - op-
tical and electron probe analysis. Journal of Geology , 86 ,
743-752.
Alley, N.F. (1973) Landscape development of the mid-north of
South Australia. Transactions of the Royal Society of South
Australia , 97 , 1-17.
Alley, N.F. (1977) Age and origin of laterite and silcrete duri-
crusts and their relationship to episodic tectonism in the mid-