Sedimentology and distribution of late quaternary calciturbidites and calcidebrites in the Mozambique Channel (Southwest Indian Ocean)

Abstract

Submarine gravity flow processes on carbonate platform slopes can lead to the deposition of calciturbidite and calcidebrite beds on the adjacent deep-water seafloor. Such deposits have been previously found to occur more frequently during sea-level highstands, leading to increased export of carbonates to the deep sea during interglacial periods. Here, we document a new occurrence of these types of event beds in cores near a series of volcano-cored carbonate platforms in the Mozambique Channel (SW Indian Ocean), describing them from a sedimentological perspective and analyzing the controls on their distribution. 32 event beds, located near four isolated platforms, are composed primarily of uncoated skeletal grains from primarily shallow-water and planktic taxa. Compositional analysis shows that planktic foraminifera are hydrodynamically sorted such that they form a greater proportion of the upper parts of event beds. Age models based on foraminifer δ18O isotope data allow for precise (ky-scale) dating of each gravity flow event; results show that events occurred with frequencies ranging from 2 to 4 events per 100,000 years over the past ~ 800 kyr regardless of the phase within the sea-level cycle (i.e., transgressive, regressive, highstand or lowstand). However, events were most frequent during periods, both relative and absolute, of highest sea level, and are therefore interpreted to be controlled in part by sea-level status or change, though additional causes are also possible.

Possible Tsunami-Induced Sediment Transport From Coral Reef to Deep Sea Through Submarine Canyons on the Southern Ryukyu Forearc, Japan

“…Sediment core lithology around submarine canyon mouths of the southern Ryukyu forearc varies depending on the connectivity of submarine canyon heads with coral reefs. In pure carbonate and mixed carbonate-siliciclastic settings, sediment exports from shallow carbonate platforms and reefs to the deep-sea is controlled by the carbonate and clastic sediment productivity, type of canyon, and connectivity of shelf channel with the submarine canyon (Mullins, 1983;Eberli, 1991;Jorry et al, 2010Jorry et al, , 2020Puga-Bernabéu et al, 2011, 2014Counts et al, 2018Counts et al, , 2021. First, we will examine the relationship between sediment core lithology and the type and connectivity of submarine canyons.…”

“…Carbonate production on carbonate platform tops and sediment exports from platforms to surrounding deep seas by plumes and gravity flows have been influenced by late Quaternary large scale oscillations of sea level (e.g., Mullins 1983;Droxler and Schlager, 1985;Eberli, 1991;Jorry et al, 2010Jorry et al, , 2020Webster et al, 2012;Counts et al, 2021). In many studies, a general correlation has been found between an increase in calciturbidite frequency and periods of sea-level highstand (Droxler and Schlager, 1985;Jorry et al, 2010Jorry et al, , 2020Webster et al, 2012;Wunsch et al, 2017;Counts et al, 2018Counts et al, , 2021. However, the exact occurrence patterns of calciturbidites are variables, reflecting the bank-top water depths (the timing of the flooding of bank-top), type of submarine canyon, and shelf-edge morphology (Jorry et al, 2010;Puga-Bernabéu et al, 2014).…”

“…Further, Eberli (1991) showed that sediment export from carbonate platform rims, either along a volcanic island or along a continental shelf differs from that from pure carbonate platforms. Several studies on submarine canyons and their role in sediment transport in pure carbonate and mixed carbonate-siliciclastic depositional settings along passive margins such as Bahamas, Great Barrier Reef and Mozambique Channel have been conducted (Grammer and Ginsberg, 1992;Jorry et al, 2010Jorry et al, , 2020Mulder et al, 2012aMulder et al, , b, 2017Webster et al, 2012;Puga-Bernabéu et al, 2014;Wunsch et al, 2017;Tournadour et al, 2017;Counts et al, 2018Counts et al, , 2021. However studies on carbonate sediment export to the deep-sea, from small reefs surrounding a small island along an active margin are still limited.…”

Comment on ‘Going with the flow: Experimental simulation of sediment transport from a foraminifera perspective’ by Ash‐Mor et al. (2022), Sedimentology, 69, 1231–1251

“…Sediment distribution patterns on the shelf slopes and within slope channels demonstrate that the sediment composition of (non‐)skeletal grains present in these environments not only links to the depositional setting itself but also has strong ties to the shallow‐water distribution patterns of the (non‐)skeletal sediments as demonstrated for the Gulf of Aqaba/Eilat (Perl, 1997), but also for numerous carbonate‐dominated environments (e.g. Haak & Schlager, 1989; Reijmer et al ., 1992, 2012, 2015; Jorry et al ., 2020; Counts et al ., 2021). Hence, the statement of Ash‐Mor et al .…”

“…study (2017, section 4.3, last paragraph), the quantity and size of the transported LBF in the individual gravity flows is discussed as an expression of the magnitude of an earthquake. This LBF quantity to earthquake link fully disagrees with what is known from comparable variations in LBF occurrences in carbonate gravity flows – MTDs portrayed for a wide range of tectonic stable depositional environments, for example: (i) general (Spence & Tucker, 1997; Reijmer et al ., 2015); (ii) Bahamas (Crevello & Schlager, 1980; Principaud et al ., 2015; Tournadour et al ., 2015; Wunsch et al ., 2017, 2018; Le Goff et al ., 2020); (iii) Great Barrier Reef (Webster et al ., 2016); and (iv) Mozambique Channel (Counts et al ., 2021). The occurrence of certain LBF in gravity flows – MTDs merely links to a specific location or an assembly of locations within the margin to slope domain from which the sediment‐mass originated in response to destabilization processes.…”