SILICEOUS SPONGE SPICULES IN THE EARLY CAMBRIAN CHERT-PHOSPHORITE MEMBER OF THE LOWER TAL FORMATION, KROL BELT, LESSER HIMALAYA

We present the first record of siliceous hexactinellid and demo-sponge (?) spicules from lower Tommotian chert and phosphorite of the Lower Tal Formation of the Mussoorie and Garhwal synclines in the Lesser Him alaya. Spicules include cross-shaped as well as single-rayed forms, an d occur sporadically in a chert or phosphatic groundmass. Scanty recor ds of siliceous sponge spicules in the Proterozoic sedimentary rocks a nd their abundance and rapid proliferation during the Early Cambrian a re interpreted as a result of major change in seawater chemistry due t o enhanced availability of nutrients, leading to progressive evolution of siliceous biological forms and phosphatic shelly faunas.