The effect of bioturbation by polychaetes (Opheliidae) on benthic foraminiferal assemblages and test preservation

Abstract

Biological activity such as burrowing can alter benthic foraminiferal shell preservation and may also modify benthic foraminiferal assemblages by vertical mixing, inducing sediment homogenization. Here, we analyse benthic foraminiferal assemblages and taphonomy of upper Miocene marine deposits from Conil de la Frontera (C adiz, south-western Spain). The deposits consist of marls displaying a pervasive alternation of intensively bioturbated beds dominated by Macaronichnus segregatis traces (ichnofabric index 4-5) and non-bioturbated beds. Benthic foraminiferal assemblages are dominated by Cibicidoides mundulus and Cibicides refulgens, indicating that the marls were deposited on an oligotrophic, well-oxygenated upper slope. The impact of burrowing on the preservation of benthic foraminiferal tests was tested using Q-mode cluster analysis, which found two well-differentiated groups of samples, one including the non-bioturbated beds and the other encompassing the bioturbated ones. Fragmentation and recrystallization account for the differentiation of these groups, both being higher in the bioturbated sediments. Aggressive chemical digestion by the Macaronichnus trace-makers, assumed to be a polychaete worm of the family Opheliidae, etched the microfossil shells, making them more vulnerable to fragmentation. Intense bioturbation favoured the circulation of pore fluids, encouraging recrystallization. Pervasive burrowing resulted in significant vertical reworking of microfossils. As a consequence, benthic foraminiferal assemblages in the bioturbated beds were homogenized in the mixed layer; that is, the uppermost layer of the substrate totally burrowed. The alternation of bioturbated and non-bioturbated beds reflects episodic transfer of food particles down slope from shallower parts of the shelf as well as from the continent due to storms under otherwise homogeneous oligotrophic marine conditions.

High‐frequency cycles of brachiopod shell beds on subaqueous delta‐scale clinoforms (early Pliocene, south‐east Spain)

“…The abundance of the benthic foraminifera Cassidulina carinata , Bolivina spp., Bulimina aculeata and Globocassidulina subglobosa (Fig. ) is consistent with the organic enrichment associated with siltation (Jorissen et al ., ; Abu‐Zied et al ., ; Goineau et al ., ; Pérez‐Asensio et al ., ). Ichnoassemblages support the interpretation of high sedimentation rates and nutrient contents, although there are variations in a proximal to distal gradient, with increasing ichnodiversity and density of traces towards distal positions.…”

Mixed carbonate-siliciclastic contourite drift deposits associated with the entrance of an Atlantic-Mediterranean corridor (late Miocene, southwest Spain)

“…Estimated water depths based on benthic foraminiferal assemblages from the two silt beds within Unit 1 suggest a deep environment with palaeo-water depths ranging from around 220 to 550 m (Table 1). The abundance of the deep-water species C. wuellerstorfi and C. mundulus supports this water depth range (van Morkhoven et al, 1986;Holbourn et al, 2013;Pérez-Asensio et al, 2017). Preferential destruction of less-resistant planktonic foraminiferal shells by the action of energetic bottom currents might explain the anomalously low P/B ratio values (Table 1), which are much lower than values recorded in deep settings (van der Zwaan et al, 1990;Murray, 1991Murray, , 2006.…”

Linkages Between East China Sea Deep‐Sea Oxygenation and Variability in the East Asian Summer Monsoon and Kuroshio Current Over the Last 400,000 years

“…Oridorsalis umbonatus is a cosmopolitan species present over a range of water depths and trophic levels (Gupta et al, 2006;; R. K. Singh et al, 2021;Takata et al, 2019). It has also been reported as a suboxic and shallow infaunal to epi- Oxic Species Epifaunal Cibicidoides mundulus (Kaiho, 1994;Pérez-Asensio et al, 2017) Epifaunal Cibicidoides wuellerstorfi (Das et al, 2017;De & Gupta, 2010;Kaiho, 1994) Epifaunal Epistominella exigua (Bhaumik et al, 2007;De & Gupta, 2010) Epifaunal Gavelinopsis sp. (Akimoto & Hasegawa, 1989;Takata et al, 2018) Epifaunal Globocassidulina subglobosa (Araújo et al, 2018;Kaiho, 1994;Kaminski, 2012;Singh et al, 2021;Verma et al, 2013) Epifaunal Quinqueloculina seminulum (Das et al, 2017;Hayward et al, 1997;Kaminski, 2012;Laprida et al, 2007) Epifaunal Sigmoilopsis schlumbergeri (Kaminski, 2012;Mackensen et al, 1995;Saravanan et al, 2019) Suboxic Species…”