Fossil holoplanktonic mollusks (pteropods and heteropods) are so far little known from Trinidad and have not yet been employed in paleoenvironmental studies in this region. Specimens >125 µm were examined in samples from two sections of the Middle Miocene Brasso Formation of Central Trinidad. Samples from the type section at Brasso Village were younger (planktonic foraminiferal Zones N11–N12) than those from Nollis Tunnel, near Tabaquite (N8). Both sections yielded abundant holoplanktonic molluscs, but all were juveniles. At Brasso Village, yields were highest in samples collected near a bathyal oxygen minimum zone (OMZ) that was revealed using benthic foraminifera. The percentage of the fauna as Vaginella sp. did not vary significantly throughout this section, while Heliconoides sp. was concentrated in rocks deposited near the OMZ base and Creseis spina above the OMZ core. This implies depth stratification among the pteropods that limited the flux of Heliconoides sp. to shallower water samples. The fauna from Nollis Tunnel, where recovery was restricted to eight out of nine samples, was used to infer the position of the OMZ at this site. The assemblage was more abundant at Nollis Tunnel than at Brasso Village. Simultaneous confidence intervals show that the proportional abundance of Vaginella sp. did not vary significantly throughout the Nollis Tunnel section, while Creseis roesti and Heliconoides inflatus inflatus? showed depth stratification. This demonstrates that fossil holoplanktonic gastropods have potential as a tool for paleoenvironmental interpretations, especially in detecting fossil OMZs.

中文翻译：

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千足动物和异足动物（软体动物，腹足纲，Thecosomata）和特立尼达的中新世最低氧区

迄今为止，特立尼达对化石全浮游软体动物（翼足类和异足类）知之甚少，尚未在该地区的古环境研究中使用过。在特立尼达中部中新世中部布拉索斯组的两个部分的样品中检查了大于125 µm的样品。Brasso村类型剖面的样本（浮游有孔虫带N11–N12）比塔巴基特（N8）附近的Nollis Tunnel的样本年轻。两个部分均产生丰富的全浮游类软体动物，但均为幼体。在Brasso村，使用底栖有孔虫显露的海底氧气最小带（OMZ）附近收集的样品中，单产最高。动物群的百分比为Vaginella sp。在本节中没有明显变化，而螺旋螺 集中在OMZ底部附近和OMZ核心上方的Creseis脊柱附近的岩石中。这意味着翼足类之间的深度分层限制了螺线虫的通量。到较浅的水样。来自Nollis隧道的动物区系，只能将九个样本中的八个样本进行恢复，以推断该区域的OMZ位置。在Nollis隧道的人群比在Brasso村庄的人群要丰富。同时置信区间显示，Vaginella sp。的比例丰度。整个Nollis隧道段没有明显变化，而Creseis roesti和Heliconoides inflatus inflatus？显示深度分层。这表明化石全浮游性腹足动物有潜力作为古环境解释的工具，尤其是在探测化石OMZ中。