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Sedimentological evidence for rotation of the Early Permian Nambucca Block (eastern Australia)

Christopher R. Fielding, Uri Shaanan and Gideon Rosenbaum
Sedimentological evidence for rotation of the Early Permian Nambucca Block (eastern Australia)
Lithosphere (December 2016) 8 (6): 684-698

Abstract

The Early Permian tectonic history of eastern Australia led to the formation of several orogenic curvatures termed the New England oroclines. How these oroclines formed is a controversial issue that is crucial for understanding the paleo-Pacific subduction dynamics at the Gondwanan margin and the formation of curved orogenic belts in general. Here we present new constraints on the role of vertical-axis block rotations in the New England oroclines using paleocurrent indicators from the core of the oroclinal structure (the Nambucca block). Focusing on the lower sedimentary succession within the Nambucca block (Kempsey beds), we recognize two facies associations. Facies association A comprises conglomerate and gravelly sandstone with minor sandstone, collectively interpreted as the deposits of coastal to subaqueous marine fans. Facies association B is made of heterolithic intervals of sandstone and mudrock that are interpreted as the products of deposition on a marine continental slope. Younging directions suggest that facies association A represents the basal part of the succession that is overlain by the more heterolithic association. The paleogeographic position of the Nambucca block, in conjunction with its stratigraphy and geochronological provenance, suggests that it formed as part of a large, deep-marine backarc basin. Paleocurrent and paleoslope directions are north to northeast, inconsistent with the present understanding of the Permian paleogeography that involved an approximately north-south-oriented continental margin (in present coordinates) and an eastward-deepening marine surface. This supports previous paleomagnetic interpretations of counterclockwise rotations of adjacent blocks. In conjunction with recently published structural, paleomagnetic, and geochronological constraints, our data suggest that counterclockwise rotations occurred between 285 and 275 Ma in the course of the formation of the southern segment of the New England oroclines (Manning orocline). The rotation incorporated both continental and marine plate margin segments of eastern Gondwana, thereby deforming the deep backarc basin that is partially represented by the Nambucca block. Our data thus provide constraints both on the kinematics and on the timing of the much-debated southern segment of the New England oroclines.


ISSN: 1941-8264
EISSN: 1947-4253
Serial Title: Lithosphere
Serial Volume: 8
Serial Issue: 6
Title: Sedimentological evidence for rotation of the Early Permian Nambucca Block (eastern Australia)
Affiliation: University of Nebraska at Lincoln, Department of Earth and Atmospheric Sciences, Lincoln, NE, United States
Pages: 684-698
Published: 201612
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 76
Accession Number: 2017-005930
Categories: Structural geologySedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, geol. sketch maps
S31°30'00" - S30°00'00", E151°45'00" - E153°19'60"
Secondary Affiliation: University of Queensland at St. Lucia, AUS, Australia
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201705
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