| Popis: |
The multistoried siliciclastic succession at the base of basal Kerur Formation of the Neoproterozoic Badami Group shows ample variations in sequence building pattern within the ambit of the Precambrian fluvial sedimentation system. Detailed facies, architectural element, paleocurrent as well as stratigraphic architectural analysis invariably revealed a frequently avulsive braided pattern, with flashy discharges, for the paleoriver system; which is consistent with the basic tenet of the Precambrian alluvial sedimentation. Rare eolian features suggest seasonal flow fluctuations, referring to the semiperennial nature of the fluvial system. The studied interval represents a single valley fill, internally constituted by seven vertically juxtaposed channel belts. Each channel belt is fining upward along with the overall grain-size reduction up the succession. While the older channel belts inferred to be braided, channels possibly become more sinuous towards the top of the succession, as inferred from the appearance of bank-attached bars along with the omnipresent longitudidal bars. Flow durability within channel also increases with time, as the lower two belts appear to be ephemeral with highest energy flashy discharges, changing into semiperennial to perennial one upward. Bounded between an unconformity below and a thoroughly wave-featured limestone unit above, the coarse and poorly sorted clastic sedimentary rocks at the base of the basal Kerur Formation are interpreted as a base-level lowstand product, indicating gradual filling of the paleoriver valley under the backdrop of slow rise in base profile. Tectonics-related generation of accommodation space as well as the rejuvenation of slope along and across the basin-margin dictated the sediment distribution and sequence building pattern primarily. The increase in channel sinuosity up-the-succession is governed by the raised rate of base profile rise, which ultimately leads to termination of the terrestrial depositional system by complete marine inundation. |
