Seismic-based geomorphology of a mixed carbonate siliciclastic shelf-to-basin submarine drainage system, Miocene, Browse Basin, Northwest Shelf of Australia

Abstract

Recent studies revealed that carbonate slopes can have similar architectural elements as their siliciclastic counterparts. This study uses a large regional 3D seismic dataset to map and quantify carbonate and mixed carbonate-siliciclastic slope architectural elements to generate an updated model of these slope systems. The research area of this project is the upper slope to toe-of-slope region of Miocene carbonates in the Browse Basin of the NW Shelf of Australia covering a total of over 25,000 km² in area. This slope can be divided into three components: (1) a low angle transition between carbonate platform margins and the upper slope; (2) a steep upper slope riddled with low-sinuosity, line-fed canyons; and (3) a low angle lower slope with a mix of sinuous channel-levee systems, mass transport deposits, and slope fans. The slope channels were sourced from large carbonate platforms along the shelf. Slope architectural elements, such as canyons, channel-levee systems, mass transport deposits, and fans, were imaged to extract geomorphic data such as length, gradient, aspect ratio, and sinuosity. Canyons are defined as channels between 0.5 to 1.5 km wide and 80 to 250 m deep that are relatively straight (sinuosity of 1.00-1.14) and set upon the steeper gradients of the upper slope (2.4° - 11°). Some canyons transformed downstream into channel-levee systems, which are narrower and shallower and more sinuous (1.05-1.30), developing on a slope angle of 1.2° - 4.6°. In many cases, the evolution of canyons into channel-levee systems can be clearly observed in seismic data in the middle-outer slope. The development of the channel-levee systems in the lower slope is controlled by slope gradient and concavity. The channel-levee system can be eroded by large mass transport deposits. This high-resolution regional 3D seismic dataset provides an excellent example of a carbonate slope to toe-of-slope morphology that can be used to generate an updated model of such systems and provide a new analogue for exploring other carbonate slope and basin environments.