New observations on Rajahmundry Traps of the Krishna-Godavari Basin

Abstract

The Rajahmundry Traps of the Krishna Godavari Basin (K-G Basin) consist of three distinct basalt flows interbedded with two intertrappean sedimentary horizons, which in turn are underlain by the late Cretaceous fossiliferous limestone bed (infratrappean) and overlain by the Cenozoic Rajahmundry Formation (conglomerate/sandstone). Among the three, the lower flow is characterized by the presence of the physical volcanological features such as rootless cones, tumuli and dyke like forms along with single to multitier columnar and radial jointing. The middle and upper flows are simple, massive and vesicular and exhibit spheroidal weathering. Physical volcanological features and lithological attributes indicate that the lower flow was formed by an explosive volcanic activity in hydrous environment, followed by sub aerial eruption to form the middle and upper flows. The fossiliferous limestone bed is a representative horizon for the K-T boundary mass extinction caused due to intense volcanism. Intertrappean sediments exhibit weathered soil profiles (palaeosols) with limestone beds denoting a distinct time gap during various phases of lava eruption. Evaluation of the palaeogeographic scenario of the Krishna and Godavari Rivers does not provide any evidence for the existence of Cretaceous palaeovalley which would have provided pathway for lava transportation from the Deccan volcanic province of western India to the K-G Basin situated along the east coast. The present study opens up an alternative approach to explain the origin of basalt flows at Rajahmundry. In all probability the lavas could be intrabasinal. NW-SE and NE-SW faults or their intersection zones are probable pathways for lava eruption in the K-G Basin.

Nature of Flow Patterns of Rajahmundry Lava, Gowripatnam Area, West Godavari, India:Insights from AMS Studies

“…These traps can be considered as 'materials of prominence' in the geology of Peninsular India as they are the only extensive outcrops of basaltic lava flows along the east coast of India and are almost coeval to the Deccan Traps 14 . Further, Bakshi 3 reported new 40 Ar/ 39 Ar ages for lava flows from the Deccan Traps and Rajahmundry Basalts and critically assessed reliability of other dates available in the published literature.…”

“…The tectonic junction present between the NW-SE trending Godavari Rift and NNE-SSW to NE-SW oriented K-G Basin is known as Godavari Triple Junction (GTJ). Figure 2 provides the disposition of the lineaments in the studied area 14 . The fascinating fact about this terrain is that it preserves the records of geological records of Mesoproterozoic to Neogene 14 .…”

“…Figure 2 provides the disposition of the lineaments in the studied area 14 . The fascinating fact about this terrain is that it preserves the records of geological records of Mesoproterozoic to Neogene 14 . The evidences for Palaeozoic to Mesozoic Gondwana rifting, Cretaceous continental break-up and drifting are provided by the Phanerozoic sediments exposed in this GTJ 16 .…”

“…Earlier researchers) 18,19 opined that this rift commenced in response to collisional events in the adjacent Eastern Ghat Mobile Belt (EGMB) during the Mesoproterozoic and the sedimentation processes continued up till Neoproterozoic. During Carboniferous to Mesozoic, a second phase of rifting took place which led the alluvial lithic fill to get deposited in these basins which came to be known as the continental Gondwana 14 . The alluvial basins of this period constituted a network of radial drainage system of intercontinental Gondwana palaeo-drainage [21][22][23] .…”

“…In the present scenario, two schools of thought exist regarding the explanation of the nature of the basaltic lava at Rajahmundry: the river piracy model and the fissure eruption model [13][14][15] . Here the authors attempt towards the feasibility of the models in explaining the mechanism of lava flow.…”