Journal of Thermal Analysis and Calorimetry, V ol. 71 (2003) 739–750
THERMAL CHARACTERIZATION OF LACUSTRINE
DOLOMITES FROM THE SAMBHAR LAKE PLAYA,
THAR DESERT, INDIA
R. Sinha
1, 2*
and W . Smykatz-Kloss
2
1
Engineering Geosciences Group, Indian Institute of Technology, Kanpur 208016, India
2
Institute of Mineralogy and Geochemistry, Karlsruhe University, 76131 Karlsruhe, Germany
Abstract
The Sambhar Lake playa sediments in Thar desert, western India, host a variety of evaporite minerals.
Carbonates form a major proportion of the evaporites in a 23 m deep core and several dolomite-rich ho
-
rizons are recorded. Our XRD and DTA based investigations show that these dolomites are
non-stoichiometric and disordered (proto-dolomites) except at one level (4.08 m) from where a
well-ordered dolomite is reported. We also record frequent variation in the characteristics of dolomites
with depth in terms of structural ordering, Ca/Mg ratio and Fe content. Dolomites reported form the
Sambhar Lake playa are interpreted to be authigenic due to the absence of any carbonate rock in the
catchment and seem to be derived from a precursor calcite under (sub-) evaporitic conditions.
Keywords: DTA, lacustrine carbonates, playa sedimentology, Sambhar Lake, Thar desert
Introduction
The occurrence and origin of dolomites has been a subject of interest for over six de-
cades now and probably no other mineral has attracted as much speculation regarding
its origin as dolomite. The so-called ‘dolomite problem’ has been discussed and re
-
viewed by many workers (Usdowski [1], Lippmann [2], Zenger and Dunham [3],
Morrow [4], Last [5], Warren [6, 7]), and the main facets of the problem are: (a) in
spite of a simple composition, CaMg(CO
3
)
2
, it has not been possible to synthesize do
-
lomite under normal sedimentary conditions, (b) despite its abundance in ancient
rocks, dolomite is relatively rare in modern sediments, and (c) the understanding of
the inorganic and organic geochemical factors conducive to form dolomite are still
largely unresolved.
Recent formation of dolomite in coastal sabkhas and in inland lakes and playas has
received a fair attention since the discovery and documentation of Coorong dolomites in
southern Australia (Skinner [8], von der Borch et al. [9]; Rosen et al. [10, 11]). Since then
a number of occurrences of dolomites have been reported and discussed from lacustrine
1388–6150/2003/ $ 20.00
© 2003 A kadémiai Kiadó, Budapest
Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht
* Author for correspondence: E-mail: rsinha@iitk.ac.in