Evidence of Palaeoclimatic Fluctuations in Miliolite Rocks of Saurashtra, Western India

Detailed studies of various miliolite occurrences of Saurashtra have revealed fluctuations in the palaeoclirnate witnessed in the course of deposition and consolidation of the dune material during Middle and late Upper Pleistocene. The entire process of formation of miliolite rocks is indicative of alternating arid and humid phases. During protracted arid phases strong wind actions were effective whereas during brief wet phases fluvial erosion & deposition and pedogenesis were brought about. The various evidences in support of palaeoclimatic fluctuations include: (i) the presence of erosional surfaces separating the miliolite deposits by intercalated redsoil horizons, cross-beddedand horizontally bedded miliolite deposits, two cross-bedded miliolite sequences with reversed dips and the two superimposed unidirectional cross-bedded miliolite sequences with different angles of dipin the coastal cliffsections, (ii) the occurrence of intercalated red beds and fluvial debris (sand/silt/gravel) within miliolite sequences as seen in some of the river and well sections, together with slope-wash debris between two miliolite layers substantiating small scale intervening periods of quiescence, (iii) a well defined junction between the two different major cycles of aeolian accumulation marked by the surfaces of non-deposition, erosion and honeycomb weathering at the top of the lower cycle as encothered in some of the well sections, (iv) burial of animal burrows by a younger cycle of miliolites devoid of animal burrows in some exposures and (v) the presence of diagenetically formed coated grains, vadose calcite silt around the ooliths & intraclasts, and its occurrence between two generations of cement in thin section also provide aclue to the minor breaks in diagenetic environment.