Palaeomagnetism of red beds from the Kimberley Group, Western Australia: Implications for the palaeogeography of the 1.8 Ga King Leopold glaciation

Phillip W. Schmidt*, George E. Williams

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    26 Citations (Scopus)

    Abstract

    The 1.8 Ga King Leopold glaciation in northwestern Australia is recorded in the Kimberley Basin by subglacial erosional forms cut in an unconformity surface at the top of the Speewah Group and buried by glaciofluvial deposits at the base of the King Leopold Sandstone, the lowest formation of the Kimberley Group. The glaciofluvial deposits are conformably overlain by texturally mature, locally glauconitic quartzarenite of shallow-marine origin, implying that glaciation occurred near sea level. Palaeomagnetic data for five sites (29 specimens) in the hematite-bearing Elgee Siltstone of the upper Kimberley Group in the northeastern Kimberley Basin gave a dip-corrected mean direction of declination D = 95.4°, inclination I = 13.8° (α95 = 9.7°), indicating a palaeolatitude λ = 7.0 +5.3/-5.0°. Results for red beds from five sites (28 specimens) in the conformably overlying Pentecost Sandstone gave a dip-corrected mean direction of D = 94.1°, I = 13.0° (α95 = 11.7°), λ = 6.6 +6.4/-5.9°. Combining our data for the Elgee Siltstone and Pentecost Sandstone with results for the Elgee Siltstone in the southeastern Kimberley Basin [Li, Z.X., 2000. Palaeomagnetic evidence for unification of the North and West Australian cratons by ca. 1.7 Ga: new results from the Kimberley Basin of northwestern Australia. Geophysical Journal International 142, 173-180.] yielded a dip-corrected mean direction for 17 sites of D = 93.5°, I = 15.1° (α95 = 4.4°), palaeolatitude λ = 7.7 ± 2.3°, and an overall pole position at latitude λp = 5.4°S, longitude φp = 211.8°E, with confidence semi-axes dp = 2.3° and dm = 4.5°. A positive fold test at 99% confidence was obtained for the combined data for the 17 sites. The basinwide concordance of results for the Elgee Siltstone and the positive fold test argue for an early magnetisation acquired prior to late Palaeoproterozoic initial folding of the Kimberley Group and close to the time of deposition. Our results imply a low palaeolatitude for the Kimberley Group and the King Leopold glaciation. Palaeomagnetic data for the 1.822 Ga Plum Tree Creek Volcanics in the Pine Creek Orogen to the east of the Kimberley Basin are consistent with northwestern Australia being in low palaeolatitudes during the late Palaeoproterozoic. Hence the enigma of glaciation near sea level in low palaeolatitudes, which marks the Neoproterozoic and early Palaeoproterozoic, applies also to the late Palaeoproterozoic. Red beds from the Lansdowne Arkose of the Speewah Group also were studied, but only directions ascribable to Tertiary regolith weathering processes were found. Similar findings for the late Palaeoproterozoic McArthur Basin in northern Australia suggest some units in that basin also record Tertiary regolith processes. Crown

    Original languageEnglish
    Pages (from-to)267-280
    Number of pages14
    JournalPrecambrian Research
    Volume167
    Issue number3-4
    DOIs
    Publication statusPublished - 10 Dec 2008

    Keywords

    • Elgee Siltstone
    • Hematite
    • Lansdowne Arkose
    • Palaeoproterozoic
    • Pentecost Sandstone
    • Regolith

    Fingerprint

    Dive into the research topics of 'Palaeomagnetism of red beds from the Kimberley Group, Western Australia: Implications for the palaeogeography of the 1.8 Ga King Leopold glaciation'. Together they form a unique fingerprint.

    Cite this