Ambenali Formation

Ambenali Formation
Name	Ambenali Formation
Type	Geological formation
Period	Maastrichtian
Region	Western Ghats, Maharashtra
Country	India
Unitof	Deccan Traps
Underlies	Harishchandragad Formation
Overlies	Poladpur Formation

Ambenali Formation The Ambenali Formation is a Maastrichtian-aged volcanic and sedimentary succession exposed in the Western Ghats of Maharashtra, India, notable within studies of the Deccan Traps and Cretaceous–Paleogene extinction event. It preserves basaltic flows, intertrappean sediments, and paleobiological assemblages that link regional plate tectonics of the Indian Plate with global geologic and biotic events tied to the Maastrichtian Stage and the end-Cretaceous turnover. The unit is central to correlations between Indian volcanism, regional stratigraphy, and international stratigraphic standards such as the International Commission on Stratigraphy frameworks.

Geology and Stratigraphy

The formation occurs within the Western Ghats escarpment and forms part of the larger Deccan Traps flood basalt province, stratigraphically positioned above the Poladpur Formation and below the Harishchandragad Formation. Regional mapping ties exposures near Mahabaleshwar, Satara, Pune, and the Konkan region into continuous stacks of flows, palaeosols, and intertrappean beds that are correlated with sections at Koyna and Junnar. Correlation studies reference chronostratigraphic markers tied to the Cretaceous and the Paleogene, using magnetostratigraphy comparable to global geomagnetic polarity time scale intervals and chemostratigraphic links to the Hawaii Scientific Drilling Project and other flood basalt provinces.

Lithology and Facies

Lithologically the formation comprises pahoehoe and aa basaltic flows, agglomerates, and intertrappean sediments including siltstone, claystone, lignite, and calcareous horizons. Petrographic analyses reference plagioclase, pyroxene, and olivine assemblages similar to other Large Igneous Province basalts and are compared to mineralogy from the Rajahmundry and Kerguelen Plateau provinces. Facies models integrate preserved palaeosols, paleosurface weathering profiles, and fluvial to lacustrine lenses that echo facies seen in Iberian and Ethiopian flood basalt successions. Geochemical fingerprints use trace-element ratios and isotopic systems analogous to studies at the Siberian Traps and Columbia River Basalt Group.

Age and Paleontology

Radiometric and biostratigraphic work places the Ambenali succession predominantly in the late Cretaceous Maastrichtian, overlapping with the timing of the Deccan Traps eruption pulses contemporaneous with the Chicxulub impact. Fossil assemblages from intertrappean beds include charophytes, pollen and spores assignable to angiosperm and gymnosperm groups comparable with floras from Rajasthan and Gondwana sequences, as well as vertebrate tracks and occasional bone fragments akin to finds from Lameta Formation localities. Palynological correlations reference taxa used in global correlation schemes employed by the International Paleontological Association and compare to Maastrichtian assemblages from Seymour Island and Hell Creek Formation sites for broader biostratigraphic context.

Depositional Environment and Basin Evolution

Sedimentary interbeds record lacustrine, fluvial, and palustrine environments that developed in interflow depressions and half-graben settings influenced by regional uplift of the Western Ghats rifted margin of the Indian Plate. Basin analysis integrates flexural, extensional, and mantle plume-driven models similar to those applied to the Réunion hotspot hypothesis, linking volcanic pulses with transient accommodation changes, drainage reorganization, and palaeoclimate shifts comparable to Maastrichtian global trends discussed in IPCC-era paleoclimate syntheses. The sequence of volcanic-sedimentary cycles documents feedbacks among volcanism, weathering, and biotic responses recorded in contemporaneous successions such as the Deccan Traps elsewhere and the North Atlantic Igneous Province.

Economic Significance and Resources

Intertrappean lignite and clay horizons have local economic relevance for small-scale fuel and brick-making operations near towns such as Mahabaleshwar and Satara, while basalt flows form durable building stone used in regional infrastructure projects tied to Mumbai-area construction. Hydrogeologic studies use the porosity and fracture networks of Ambenali basalts to assess groundwater resources exploited by municipal systems in Pune and surrounding districts; geotechnical properties influence slope stability along the Western Ghats highway corridors and reservoirs such as the Koyna Dam. Mineral exploration has considered trace-metal enrichments analogous to those targeted in other Large Igneous Province settings, though no large-scale ore deposits are documented.

Research History and Dating Methods

Investigation of the formation began with 19th- and 20th-century surveys by geologists affiliated with institutions such as the Geological Survey of India and later academic teams from University of Mumbai and IIT Bombay. Modern studies deploy 40Ar/39Ar and K–Ar radiometric dating, magnetostratigraphy, palynology, and chemostratigraphy to refine chronology and correlate pulses of Deccan volcanism with global events including the Cretaceous–Paleogene extinction event. Recent work integrates high-precision geochronology with sequence stratigraphy and palaeomagnetic polarity records used by the International Union of Geological Sciences community to resolve eruption tempo and palaeoenvironmental change across the Ambenali succession.

Category:Geologic formations of India Category:Deccan Traps Category:Maastrichtian Stage