Dgf. Long et al., PALYGORSKITE IN PALEOSOLS FROM THE MIOCENE XIACAOWAN FORMATION OF JIANGSU AND ANHUI PROVINCES, PR CHINA, Sedimentary geology, 112(3-4), 1997, pp. 281-295
Strata associated with Tertiary basalts of the Xiacaowan Formation, in
the North Jiangsu Basin of eastern China, contain mudstones which are
rich in palygorskite and montmorillonite, with lesser concentrations
of dolomite and CT-opal. Massive montmorillonite clays may have develo
ped as vertisols by deep meteoric weathering of underlying basalt flow
s in a sub-humid to semi-arid climatic setting with pronounced seasona
lity. Laminated montmorillonite clays, higher in the sequence, accumul
ated in low-lying areas in inland lakes with poor external drainage. C
limatic fluctuations resulted in periods of increased aridity, during
which falling lake levels exposed montmorillonite-rich vertisols, lake
and playa sediments, to further pedogenesis. Lowering of the water ta
ble and increased rates of evaporation allowed leaching of sodium and
calcium from the soils; this, in conjunction with the introduction of
silica and magnesium by rising ground water, led to the neomorphic dev
elopment of extensive stratiform palygorskite deposits.