Enigmatic annular landform on a Miocene planar karst surface, Nullarbor Plain, Australia

Abstract

The Nullarbor Plain is a 200,000 km 2 planar karst surface in southern Australia, underlain by Cenozoic shallow-water limestones. During the Miocene the area was uplifted, and although the plain is generally considered extremely flat, locally, the geomorphology of the Nullarbor Plain retains evidence of earth surface processes across a long, middle Miocene-to-present time span. The accessibility of the recent 0.4 arc-second TanDEM-X digital elevation model (DEM) by the German Aerospace Centre motivated the search for other possible fine-scale landforms that would previously have been unresolvable. The analysis of DEM images revealed an enigmatic annular landform with an outer diameter between 1200 m and 1300 m. It consists of a circular elevated rim and a central dome. Its morphology is distinct from other landforms observed on the plain, and cannot be readily explained as a part of known active or inferred/expected processes on the plain (e.g., fluvial, aeolian, karst, tectonic or extra-terrestrial impact processes).More recent karst processes (dayas formation) overprinting the landform indicates the presence of the annular structure prior to dayas formation. A unique microbial boundstone facies sampled from the bed-rock of the annular structure supports an interpretation of long-lived, at least partial retention of a primary depositional structure. Differential carbonate deposition, especially bioherm growth, was a likely origin of the annular topographical expression of the present-day landform and is comparable to biogenic structures in the modern day deeper Great Barrier Reef.

Karst landform classification considering surface flow characteristics derived from digital elevation models

“…The karst surface morphology records crucial information about the landform's development stages, geomorphic evolution processes, and the forces that shaped them (Guo & Lin, 2016; Waltham & Fookes, 2005; White, 2002; Zhu, 2009). Therefore, the scientific and automatic classification of karst landforms is the basis for conducting related karst research and plays a vital role in uncovering the landform's geomorphic formation mechanism and surface morphology characteristics (Lipar et al, 2022; Miccadei et al, 2011; Nofal & Abboud, 2016). However, due to the extremely complex surface morphology of karst landforms, their automatic classification is quite difficult (Wu et al, 2015).…”