An Early Carboniferous paleomagnetic pole for Gondwanaland: New results from the Mount Eclipse Sandstone in the Ngalia Basin, central Australia

Abstract

Paleomagnetism of fourteen diamond‐drill cores from the uppermost Devonian‐Lower Carboniferous Mount Eclipse Sandstone in the Ngalia Basin, central Australia, has been studied. The samples were oriented using the borehole directions, bedding planes identified in the drill cores, and regional bedding attitudes. Three magnetic remanent components have been revealed: (1) a drilling‐induced, low‐ to moderate‐temperature remanence (C1) from all the drill cores, which is oriented parallel to the drill cores and is most likely a combination of isothermal remanent magnetization and piezoremanent magnetization; (2) a moderate‐ to high‐temperature, syndeformational overprint (C2: D = 226.7°, I = 82.3°, α95 = 6.2°, k = 68.9) in 65 samples from nine drill cores, which was probably acquired during the mid‐ to Late Carboniferous Mount Eclipse movement; and (3) a moderate‐ to high‐temperature, likely primary remanence (C3: D = 057.1°, I = −36.9°, α95 = 9.6°, K = 29.6) from 64 samples in nine drill cores, which exhibits a positive fold test. C2 and C3 are found only in reddish siltstones and sandstones, whereas C1 is best developed in grey reduced sandstones and siltstones. A palynological examination gives an early to mid‐Viséan (Early Carboniferous) age of deposition for samples carrying the interpreted primary component. C2 gives a mid‐ to Late Carboniferous pole at 32.1°S, 119.5°E with A95 = 11.9°, which is in agreement with results of a previous study on surface outcrops. C3, when combined with results from one drill core in a previous study, gives a Viséan pole at 37.6°S, 52.6°E with A95 = 8.7°. This pole suggests a south polar position for central Africa during the Early Carboniferous and therefore indicates the existence of a large ocean between Gondwanaland and Laurussia at that time. The paleo‐south pole shifted from central Africa in the Early Carboniferous (∼340±5 Ma) to East Antarctica in the mid‐ to Late Carboniferous (∼310±10 Ma) with a minimal continental drifting rate of 15–20 cm/yr.