Abstract
Palaeomagnetic, mineralogical and geochemical investigations have been carried out to estimate the origin and age of the Mn-Fe ore of Um Bogma formation of the early Carboniferous. Oriented samples were collected from 26 sites in the Mn-Fe ore and host rocks of Um Bogma formation and the overlying sandstone of Abu Thora formation. The palaeomagnetic pole, determined from the characteristic remanent magnetization of the Mn-Fe ore from 20 sites and the hosting rocks of Um Bogma formation, is located at 22 degrees S, 97 degrees E. This palaeomagnetic pole position falls close to the Carboniferous poles of Africa, suggesting that the Mn-Fe ore and associated rocks of Um Bogma formation were deposited during the Carboniferous. Furthermore, the palaeolatitude determined for these rocks, based on the mean palaeomagnetic inclination, suggests that the Mn-Fe ore of Um Bogma was deposited at a latitude 10 degrees S of the equator, i.e. in tropical conditions. Mineralogical and geochemical investigations support the palaeomagnetic results. Samples from the overlying Abu Thora sandstone yield a mean palaeomagnetic direction which provides a palaeomagnetic pole position at latitude 59 degrees , longitude 302 degrees . This magnetization is significantly different from that of the Mn-Fe ore and host rocks and is assigned a Cretaceous age. The porous sandstone acquired its magnetization long after deposition, most likely by diagenetic chemical processes associated with red pigmentation.