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.

潜穴活动等生物扰动行为可改变底栖有孔虫（benthic foraminiferal）的壳体保存状态，还可通过垂直混合作用引发沉积物均一化，进而改造底栖有孔虫组合。本次研究针对西班牙西南部加的斯省科尼尔-德拉弗龙特拉（Conil de la Frontera）地区的上中新统海相沉积，开展了底栖有孔虫组合与埋藏学（taphonomy）分析。该套沉积以泥灰岩为主，普遍发育两类岩层的交替序列：一类是以Segregatis麻虾迹（Macaronichnus segregatis）为核心的强生物扰动岩层（遗迹组构指数4~5），另一类为无生物扰动岩层。底栖有孔虫组合以小拟卷包虫（Cibicidoides mundulus）和光亮卷包虫（Cibicides refulgens）为优势属种，指示该泥灰岩沉积于贫营养、富氧的上陆坡环境。研究采用Q型聚类分析（Q-mode cluster analysis）检验了潜穴活动对底栖有孔虫壳体保存的影响，结果识别出两组差异显著的样品群：一组对应无生物扰动岩层，另一组涵盖生物扰动岩层。两组样品群的差异主要源于壳体破碎程度与重结晶作用强度，且生物扰动沉积物中的这两项指标均更高。被推断为欧菲虫科（Opheliidae）多毛类蠕虫的Segregatis麻虾迹造迹生物，通过强腐蚀性化学消化作用蚀刻了微体化石壳体，使其更易发生破碎；强烈的生物扰动则促进了孔隙流体循环，加速了重结晶进程。普遍的潜穴活动导致微体化石发生显著的垂向再沉积作用，进而使得生物扰动岩层中的底栖有孔虫组合在混合层（即完全被潜穴改造的最上层基质层）内发生均一化。生物扰动岩层与无生物扰动岩层的交替产出，反映了在整体均一的贫营养海洋环境下，风暴事件引发的食物颗粒从陆架浅水区乃至大陆向研究区坡下间歇性搬运的沉积过程。