Contusotruncana contusa abundances and morphotypes in the cretaceous mid-latitude South Atlantic

Spatial and temporal patterns in test size and shape (test conicity and spiral roundness) and absolute abundance (accumulation rate) of the planktonic foraminifer Contusotruncana contusa were studied in the South Atlantic Ocean (DSDP sites 356, 516, 525 and 527) during an interval corresponding to the last 800 kyr of the Cretaceous. The variation in absolute abundance of C. contusa was characterised by alternating periods of high and low abundance; some of these periods were traceable across the entire mid-latitude South Atlantic Ocean. While the mean spiral roundness did not show any interpretable patterns, a sudden increase of the mean test size and mean test conicity occurred between 65.3 and 65.2 Ma (based on linear interpolation within the Cretaceous part of Subchron C29R) at all sites studied, indicating a poleward migration followed by rapid withdrawal of the low-latitude C. contusa morphotypes from the mid-latitude South Atlantic Ocean. We suggest that this event was caused by a short period of surface-water warming in the southern mid-latitudes corresponding to the brief high-latitude warming event and associated faunal migrations in the Boreal and Austral realms.

本研究分析了白垩纪最后800千年期间，南大西洋（深海钻探计划DSDP站位356、516、525及527）中浮游有孔虫Contusotruncana contusa的壳体大小与形态（壳体锥度及螺旋圆度）、绝对丰度（堆积速率）的时空分布模式。C.contusa的绝对丰度变化表现为高低丰度期交替出现的特征，其中部分时期可在整个南大西洋中纬度区域追溯。尽管平均螺旋圆度未呈现任何可解释的模式，但所有研究站位在65.3至65.2百万年前（基于亚时C29R白垩纪部分的线性插值）均出现平均壳体大小及锥度的突然增加，这表明低纬度C.contusa形态型先向极地迁移，随后迅速撤离南大西洋中纬度区域。我们认为，该事件由南中纬度表层水温短期升高所致，这与北方及南方生物区系中短暂的高纬度升温事件及相关动物群迁移相对应。