The geochemical study of siliciclastic rocks from the Lower Cambrian of Parahio Valley has been studied to describe the provenance, chemical weathering and tectonic setting. The K 2 O/Al 2 O 3 ratio and positive correlation of Co (r = 0.85), Ni (r = 0.86), Zn (r = 0.82), Rb (r = 0.98) with K 2 O reflects that the presence of clay minerals control the abundances of these elements and suggests a warm and humid climate for this region. The chondrite normalized REE pattern of the samples is equivalent to upper continental crust, which reflects enriched LREE and flat HREE with negative Eu anomaly. The tectonic setting discriminant diagram log[K 2 O/Na 2 O] vs. SiO 2 ; [SiO 2 /Al 2 O 3 ] vs. log[K 2 O/Na 2 O]; [SiO 2 /20]-[K 2 O+Na 2 O]-[TiO 2 +Fe 2 O 3 +MgO] indicates transitional tectonic setting from an active continental margin to a passive margin. The discriminant function plot indicates quartzose sedimentary provenance, and to some extent, the felsic igneous provenance, derived from weathered granite, gneissic terrain and/or from pre-existing sedimentary terrain. The CIA value indicates low to moderate degree of chemical weathering and the average ICV values suggests immature sediments deposited in tectonically active settings. The A-CN-K diagram indicates that these sediments were generated from source rocks of the upper continental crust.
The calcareous algae Dasyporella silurica, Moniliporella multipora and Vermiporella fragilis are reported for the first time from the Middle Ordovician (Dapingian to Darriwilian) Thango Formation of the Spiti Basin of northern India (Pin Valley, Tethys Himalaya). Moniliporella multipora is reported for the first time from the entire Spiti Basin. This algal assemblage is broadly comparable to that of the directly overlying Takche (=Pin) Formation in the Spiti Basin, as well as that reported from the Ordovician succession of the Tarim Basin and from Kazakhstan. The presence of these calcareous algae is of biogeographical and biostratigraphical significance as it indicates a shallow marine depositional environment for the Thango Formation of the Spiti Basin.
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