Biostromes and low-relief bioherms, some of which are characterized by exceptionally large, flat specimens of larger benthic foraminifera, are common in Palaeogene and Miocene carbonates, most notably those deposited along the Neotethys Seaway and tropical Pacific islands. By incorporating insights from palaeoceanographic research and the biology of living larger benthic foraminifera, a scenario is proposed that can account for palaeontological and sedimentological features while augmenting previous interpretations. Sexual reproduction by gamete broadcasting is common in foraminiferal taxa, including extant Nummulitidae and Amphisteginidae. Resultant zygotes can develop into tiny, resistant, easily dispersed propagules that recruit in suitable benthic-environmental conditions. The role of algal symbiosis in the biology of larger benthic foraminifera is well-documented. Palaeoceanographically, such taxa proliferated during times of reduced thermal stratification of the oceans. In regions with exceptionally clear, nutrient-depleted waters, ‘twilight-zone’ light penetration was sufficient, at least intermittently, to support some photosynthesis. On outer-shelf or promontory sites at depths of ca 100 to 200 m, the tiny propagules of larger benthic foraminiferal species, incorporating algal symbionts with the lowest light requirements, could have settled and recruited, growing very slowly, nourished by feeding on bacteria and the limited photosynthate produced by their algal symbionts. Under such conditions, thin microspheric individuals of one or two larger benthic foraminiferal taxa could have survived and grown slowly over several years to very large shell diameters, seldom reproducing asexually. Resulting carbonate accumulation rates would have been very slow, such that even rare disturbances by currents, major storms or internal waves could have produced evidence of winnowing and sedimentary structures. The fossil evidence of such habitats should include biostromes or possibly low-relief bioherms of low diversity assemblages characterized by abundant, exceptionally large, flat, microspheric larger benthic foraminifera.

中文翻译：

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为什么一些较大的底栖有孔虫会变得如此大而扁平？

生物群落和低地势生物礁，其中一些以较大的底栖有孔虫的超大扁平标本为特征，在古近纪和中新世碳酸盐岩中很常见，最显着的是那些沉积在新特提斯海道和热带太平洋岛屿上的生物群落。通过结合古海洋学研究和大型底栖有孔虫生物学的见解，提出了一种可以解释古生物学和沉积学特征同时增强先前解释的方案。通过配子广播的有性繁殖在有孔虫类群中很常见，包括现存的 Nummulitidae 和 Amphisteginidae。由此产生的受精卵可以发育成微小的、有抵抗力的、容易分散的繁殖体，在合适的底栖环境条件下进行繁殖。藻类共生在较大底栖有孔虫生物学中的作用已得到充分证明。从古海洋学上讲，这种分类群在海洋热分层减少的时期增殖。在海水异常清澈、营养耗尽的地区，“暮光区”的光线穿透足以支持一些光合作用，至少是间歇性的。在外大陆架或海角处的深处钙在 100 到 200 m 处，较大的底栖有孔虫物种的微小繁殖体，结合了对光要求最低的藻类共生体，可能已经定居和招募，生长非常缓慢，通过以细菌和藻类共生体产生的有限光合产物为食。在这种条件下，一个或两个较大的底栖有孔虫类群的薄微球个体可能存活下来并在几年内缓慢生长到非常大的壳直径，很少无性繁殖。由此产生的碳酸盐积累速度将非常缓慢，以至于即使是由洋流、大风暴或内波引起的罕见干扰也可能产生风选和沉积结构的证据。