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 Himalaya. Spicules include cross-shaped as well as single-rayed forms, and occur sporadically in a chert or phosphatic groundmass. Scanty records of siliceous sponge spicules in the Proterozoic sedimentary rocks and their abundance and rapid proliferation during the Early Cambrian are interpreted as a result of major change in seawater chemistry due to enhanced availability of nutrients, leading to progressive evolution of siliceous biological forms and phosphatic shelly faunas.