Intracanyon flows in the Deccan province, India? Case history of the Rajahmundry Traps

Abstract

The Rajahmundry Traps form small exposures of basaltic flows on either side of the Godavari River near the east coast of India, and they are thought to be late Cretaceous-early Paleocene in age. Because they lie ∼400 km from the nearest surface exposures of the Deccan Traps, their mode of formation remains unknown. Furthermore, the Rajahmundry Traps show normal magnetic polarity, indicating that they cannot be exact time equivalents of the large volumes of the Deccan Traps which show reversed magnetic polarity. Geochemical analyses reveal that the Rajahmundry Traps are of very uniform composition. Geochronological studies suggest an age of ∼64 Ma, marginally younger than the main sections (Western Ghats) of the Deccan Traps. The only section of the main Deccan province that may be stratigraphically equivalent, on the basis of age, geochemical signatures, and magnetic polarity, is the Kolhapur Formation at the southern end of the Deccan province near the west coast, ∼800 km from the Rajahmundry Traps. We suggest that the Rajahmundry Traps and other basaltic material found near the mouth of the Godavari River represent remnants of intracanyon flows that flowed eastward down the ancestral river systems of peninsular India, away from the domed structure caused by the plume that led to the formation of the Deccan Traps. Similar intracanyon flows that have traveled ∼600 km from their source to the Pacific coastline are well documented in association with the Columbia River Basalt province (United States). In the case of the Rajahmundry Traps the distance traveled would appear to be ∼1000 km.