Syn‐deformational and drilling‐induced remanent magnetizations from diamond drill cores of the Mt Eclipse Sandstone, Central Australia

Abstract

Six diamond drill cores of the latest Devonian‐Early Carboniferous Mt Eclipse Sandstone from the Ngalia Basin, central Australia, were oriented using regional bedding strike, core orientation, core/bedding angle and magnetic fabric information. Combined alternating field and thermal demagnetization revealed a predominant drilling‐induced remanence (C1), a syn‐deformational overprint (C2) and a possible primary remanence (C3). The drilling‐induced remanence is most likely a combination of isothermal remanent magnetization and piezo‐remanent magnetization, formed in an axial symmetrically‐distributed strong magnetic field inside the magnetic drill barrel, during the initial drilling process. C1 has almost totally reset the remanences in magnetite and goethite, but has had little impact on hematite. C2 was found in four cores and is a chemical overprint formed during the Alice Springs Orogeny. This chemical event could also have been responsible for the uranium mineralization in the rocks. C2 gives a mid‐ to Late Carboniferous pole at (29.2°S, 148.1°E) with DP = 45.8°, DM = 47.1°. C3 was found in five samples in one core.