U-Pb zircon geochronology of volcaniclastics and encasing sandstones from the Chhoti Khatu section: Bearing on the Neoproterozoic Marwar Supergroup stratigraphy and its global implications

Abstract

An isolated ∼40 m thick outcrop section, namely the Chhoti Khatu section, containing an embedded volcaniclastic layer, in the southeast of the Marwar Basin, western India (erstwhile stratigraphically correlated with the Jodhpur Group of the Marwar Supergroup) has drawn attention from geoscientists in recent time for fixation of geochronologic age and time bracketing of the basin succession. A detail petrography of suggestive volcaniclastic unit reveals dominance of detrital sedimentary clasts over volcaniclastic fragments. An admixture of silt and sand-sized highly angular clasts of quartz, feldspar, volcanic crystal, and lithic fragment; delicate-shaped glass/pumice shards and mica grains in fragmentary texture either in grain-supported mode or as floating clasts within glassy, microlitic matrix represent the volcaniclastic layer present at the Khatu section. An epiclastic origin is inferred for the unit, instead of a felsic tuff, as inferred earlier. A comparison between U-Pb zircon age data from the epiclastic unit and its encasing sandstones allowed interpretation of a ∼1000 Ma crystallization age for the igneous body from where volcanic clasts were derived in the Khatu epliclastics. The youngest zircon peak of ∼870 Ma at the Khatu section indicates the maximum depositional age for Khatu sedimentation. A comparison between Khatu detrital zircon geochronology data and published zircon geochronology data from the Jodhpur Group of the Marwar Supergroup allowed us to infer a pre-Jodhpur depositional history for the Chhoti Khatu section. This raises a need to reappraise the earlier proposed stratigraphic correlation between the Khatu succession and the Jodhpur Group of rocks form the Marwar Basin.

Keywords

• Volcaniclastic
• U-Pb geochronology
• Chhoti Khatu
• Marwar Supergroup
• Neoproterozoic