Geomorphological implications of the basement structure in the Krishna-Godavari deltas, India

Summary. A correlation of the morphology of the Krishna-Godavari twin delta region with the tectonic framework of its basement along the east coast of India revealed that the Kolleru Lake in the inter-delta region is situated over a basement graben known as Gudivada Sub-basin, while the vast mudflat to the south of the lake coincides with the Bantumilli Sub-basin. The 8-km-wide beach ridge complex that separates the Kolleru and the southern mudflat largely coincides with the Kaja-Kaikaluru Ridge (horst) that lies in between the Gudivada and Bantumilli Sub-basins (grabens). The anomalous landward meandering of the Vasishta and Vainateyam distributaries close to the coastline and the three-fold widening during the past four decades of the Nilarevu estuary in the Godavari delta are in line with the Matyapuri-Palakollu Fault. Similarly, the 70-km-long straight segment of the delta-front coast between the Gautami and Vasishta distributary mouths in the Godavari delta, which is rather anomalous for a prograding delta, coincides with the landward boundary of the Ravva offshore sub-basin. Swerving of the Krishna River course throughout its deltaic reaches and the clock-wise bending of the active Krishna delta lobe into the Nizampatnam offshore sub-basin appear to be associated with the Krishna Cross Trend fault. Furthermore, the elongated nature of the Krishna delta and its visibly greater seaward bulge than its bigger neighbour (Godavari delta) in spite of the fact that the latter receives higher sediment loads and water discharges, might also be due to tectonic influence. Although the connection between the surface morphology and basement framework is hard to establish for want of detailed shallow subsurface data, the landform anomalies point to the possible influence of neotectonics in shaping the morphologies of the Krishna-Godavari deltas.