Remagnetization of mesozoic limestones from the Jaisalmer basin, NW India

Abstract

High coercivity but low unblocking (LB) temperature components (∼-80-100 °C) demonstrate that goethite is the principal carrier of the natural remanent magnetization (NRM) in Jurassic and Cretaceous limestone from the Jaisalmer basin (Rajasthan, NW India). Goethite-bearing components (declination = 359.9°, inclination = 46.0°, α95 = 4.0°, N = 10 sites) plot close to the present day field direction. High unblocking (HB) components (declination = 172.0°, inclination = -45.6°, α 95 = 9.1°, N = 7 sites) are carried by haematite, mostly with reverse polarity directions, but undoubtedly not primary. This remagnetization event, mostly within a period of reverse magnetic polarity, occurred after 35 Ma and before 780 000 yr (the last known reversal). Only palaeomagnetic data from a single Cretaceous site (declination = 302.0°, inclination = -47.2°, α 95 = 14.0°, N = 10 samples) has potentially preserved a primary magnetization (carried by normal polarity magnetite); if correct, this site substantiates a mid-southerly palaeolatitude for India during mid-Aptian times (∼117 Ma). © 2005 RAS.