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

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 (Cádiz, 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.