Timescale dependent sedimentary record during the past 130 kyr from a tropical mixed siliciclastic–carbonate shelf edge and slope: Ashmore Trough (southern Gulf of Papua)

Abstract

In tropical and sub-tropical mixed siliciclastic-carbonate depositional systems, fluvial input and in situ neritic carbonate interact over space and time. Despite being the subject of many studies, controls on partitioning of mixed sediments remains controversial. Mixed sedimentary records, from Ashmore Trough shelf edge and slopes (southern Gulf of Papua), are coupled with global sea-level curves and anchored to Marine Isotope Stage stratigraphy to constrain models of sediment accumulation at two different timescales for the past 130 kyr: (i) 100 kyr scale for last glacial cycle; and (ii) millennial scale for last deglaciation. During the last glacial cycle, carbonate production and accumulation were primarily controlled by sea-level fluctuations. Export of neritic carbonate to the slopes was initiated during re-flooding of previously exposed reefs and continued during Marine Isotope Stage 5e and 1 interglacial sea-level highs. Siliciclastic fluxes to the slope were controlled by interplay of sea level, shelf physiography and oceanic currents. Heterogeneous accumulation of siliciclastic mud on the slope, took place during Marine Isotope Stage 5d to Marine Isotope Stage 3 sea-level fall. Siliciclastics reached adjacent depocentres during Marine Isotope Stage 2. Coralgal reef and oolitic-skeletal sand resumed at the shelf edge during the subsequent stepwise sea-level rise of the last deglaciation. Contemporaneous, abrupt

Neogene to Quaternary evolution of carbonate and mixed carbonate-siliciclastic systems along New Caledonia's eastern margin (SW Pacific)

“…According to this concept, siliciclastic deposits prevailed on the upper slope during sea-level lowstands and at the beginning of the shelf reflooding, whereas carbonate facies dominate during transgressions and highstand periods. This configuration is currently observed on the platform edge of Quaternary mixed carbonatesiliciclastic systems such as the Australia and Papua New Guinea Reef (Tcherepanov et al, 2008a;Harper et al, 2015;Mallarino et al, 2021) or the Belize Barrier Reef (Esker et al, 1998;Ferro et al, 1999;Gischler et al, 2010;Droxler and Jorry, 2013). However, the reciprocal pattern is not expressed everywhere along the upper slope of the eastern margin.…”

Differentiating reefal ridges from relict coastal ridges: Lessons from the seismic geomorphologic study of buried Miocene buildups (North West Shelf, Australia)

“…Additionally, Ridge 1 is continuous and there are no indicators of sediment flow, such as inter-platform seaway, reef passes or slope debris, in contrast to other reefs described from seismic data (e.g., Courgeon et al, 2016;Posamentier et al, 2010Posamentier et al, , 2022Schlager, 2005). Drowned reefal ridges described in the literature tend to be only a few 100's metres or a few kilometres long (e.g., Jorry et al, 2016;Khanna et al, 2017;Mallarino et al, 2021;Rovere et al, 2018) or to be composed of joint and isolated pinnacles (Abbey et al, 2011), and as such are dissimilar to Ridge 1. Finally, lithological data do not fully support a reefal origin, as no bioconstructed crust, lithified coral conglomerate or other indicators of reefal bioconstruction were observed along the time-equivalent outcrops (Riera et al, 2021) or from well data.…”