Poladpur Formation

Poladpur Formation
Name	Poladpur Formation
Type	Geological formation
Period	Maastrichtian
Lithology	Basalt, intertrappean sedimentary rocks
Region	Western Ghats, Maharashtra, India
Namedfor	Poladpur

Poladpur Formation is a Maastrichtian volcanic and intertrappean sequence exposed in the Western Ghats near Poladpur, Maharashtra, India. The unit records alternating Deccan Traps flood basalts and thin sedimentary horizons that preserve plant remains, vertebrate fragments, and paleosols associated with the latest Cretaceous. Studies of the formation have linked it to regional magmatism contemporaneous with major events such as the K–Pg boundary, the Reunion hotspot activity, and Gondwanan breakup episodes.

Geology and Lithology

The formation primarily comprises tholeiitic basalt flows interbedded with silty, claystone, and lignitic horizons that include paleosols and ferruginous layers. Field descriptions note columnar jointing reminiscent of other Deccan Traps sections and vesicular amygdaloidal textures comparable to flows at Mahabaleshwar and Lonar, while pelletal lapilli and hyaloclastite facies occur locally. Petrographic studies report plagioclase, clinopyroxene, olivine microphenocrysts, and interstitial glass, with alteration products such as chlorite, iddingsite, and zeolites consistent with subaerial weathering documented at Neral and Koyna.

Stratigraphy and Age

Stratigraphically the unit lies within the uppermost sequence of Deccan Traps successions and is correlated with the Wai and Poladpur groups recognized in Konkan–Western Ghats stratigraphy. Radiometric ages using ^40Ar/^39Ar and paleomagnetic polarity stratigraphy align with late Maastrichtian chronostratigraphy near 66–67 Ma, coeval with the main phase of Reunion plume volcanism that produced the main Deccan eruptive pulses. Correlations have been attempted with distal marine sections such as the El Kef and Gubbio records to tie volcanic stratigraphy to the K–Pg extinction interval.

Paleontology and Fossil Content

Fossil content in sedimentary interbeds includes fragmented plant macrofossils, charcoalified wood, pollen and spores assemblages, and rare vertebrate remains. Palynological assemblages list genera comparable to Cretaceous floras recorded in Peninsular India and Gondwana localities, with angiosperm pollen linked to families found in Deccan flora studies and gymnosperm traces analogous to Cycadophyta and Coniferales remains described from Intertrappean deposits. Vertebrate fragments reported from nearby intertrappean horizons have been compared to Titanosauria limb elements and theropod teeth known from other Indian Maastrichtian localities. Charcoal and fusain occurrences suggest wildfire events contemporaneous with emplacement of basalt flows, a phenomenon paralleled in contemporaneous sites near Karnataka and Maharashtra.

Depositional Environment and Paleoenvironment

Interpretations propose a predominantly subaerial flood basalt environment punctuated by short-lived lacustrine, palustrine, and fluvial episodes that produced the sedimentary interbeds. Paleosol horizons and root traces indicate intervals of landscape stability and colonization by pioneer vegetation analogous to successional communities documented after volcanic eruptions in modern analogs such as Mount St. Helens and Kilauea. Geochemical proxies, including stable isotopes and paleosol clay mineralogy, indicate seasonally wet tropical conditions similar to Maastrichtian paleoclimates reconstructed for Peninsular India, with local redox fluctuations reflected in iron oxide and pyrite distributions.

Regional Distribution and Outcrops

Exposures occur along the Konkan coast and Western Ghats escarpment, notably in sections near Poladpur, Raigad district, and contiguous plateaus including Mahad and Roha. The formation is traceable in river-cut cliffs, roadcuts, and quarry exposures that have been mapped by regional geological surveys and documented in field campaigns associated with institutions such as the Geological Survey of India and regional universities. Correlative Deccan sequences crop out across Maharashtra, Karnataka, and Goa, enabling basin-scale stratigraphic correlation with sections at Panhala and Purandar.

Economic Significance and Uses

Basaltic units of the formation serve as local aggregate for construction projects in the Konkan region, supplying crushed stone for roads and buildings in municipalities like Ratnagiri and Raigad. Intertrappean lignitic horizons, though typically thin and discontinuous, have been assessed for low-grade fuel potential and for palaeobotanical resource value in museum and educational collections. Basalt weathering profiles contribute to lateritic soil development that supports agriculture in plateau margins near urban centers, and some basalt exposures have been evaluated for groundwater aquifer properties relevant to regional water management.

Research History and Studies

Investigations began with early 20th-century geological mapping by colonial-era surveys and advanced through mid-20th-century stratigraphic syntheses by Indian geologists. Modern work integrates field mapping, petrography, geochronology, paleomagnetism, and palynology from research groups at institutions including the Indian Institute of Science, University of Pune, and the National Geophysical Research Institute. High-resolution studies linking eruptive pulses to the K–Pg boundary used ^40Ar/^39Ar dating and geochemical fingerprinting that compared Poladpur flows with other Deccan units, while multidisciplinary projects have assessed the role of volcanism in late Cretaceous biotic change documented in global records such as Gubbio and El Kef.

Category:Geologic formations of India Category:Deccan Traps