Sedimentology, stratigraphy, and tectonic implications of a paleo-Proterozoic continental extensional basin: the El Sherana – Edith River groups, Northern Territory, Australia

Abstract

The ca. 1.83 Ga El Sherana – Edith River basin of Northern Territory, Australia, contains terrestrial sedimentary and volcanic rocks deposited during continental extension or transtension. Braid-plain sandstones and conglomerates, turbiditic sediments, and interbedded mafic and felsic volcanics, including ignimbrites, filled the basin. Alluvial fans and rock avalanche breccias are locally developed. Prebasinal structure controlled antecedent topography and influenced drainage patterns, thickness changes, and facies distribution.Unconformities bound all formations of the El Sherana and Edith River groups, revealed by beveled and incised strata, reversals in paleocurrent trends, sharp discordance in juxtaposed facies, and paleovalleys filled with unique sediments. Scarp-derived sediments are preserved only in a small, transfer-related strike-slip basin within the larger basin environment. Unconformities are regional and are interpreted as time lines throughout the basin. These unconformities developed during regrading of slopes forced by active tectonism, accompanied by syntectonic sedimentation and basin depocenter migration.The El Sherana – Edith River strata overlie older sediments (~2.1–1.88 Ga) of the Pine Creek orogen, which formed during a period of global orogeny related to continental assembly. Development of the El Sherana – Edith River basin began substantially (40–50 Ma) after denudation of the Pine Creek orogen belt, and is related to regional postcollisional extension. This extension is recorded by basin formation, bimodal tholeiitic and alkalic magmatism, and elevated geotherms. Other paleo-Proterozoic basins of northern Australia show a similar history of rift deposition above a fossil compressional belt.