Calcareous dinoflagellates in Cretaceous to Recent sediments of DSDP Hole 39-356@en

Calcareous dinoflagellates often dominate the dinoflagellate cyst assemblage in Cretaceous to Recent oceanic sediments. However, their distribution in Paleogene sediments has scarcely been studied. The investigation of samples from DSDP Site 356 for their calcareous dinoflagellate content revealed 35 mainly long-ranging taxa. The associations and characteristic wall types (pithonelloid, oblique, radial, tangential) fluctuate quantitatively and qualitatively in distinct stratigraphic patterns. Significant shifts, primarily at the K/T boundary and the Paleocene/Eocene boundary, reflect changes in environmental conditions. Certain dinoflagellates forming calcareous cysts, such as Operculodinella operculata, were well adapted to the relatively rapid change of environmental conditions at the K/T boundary, thus blooming to dominate the carbonate flux to the ocean floor. In contrast to the stable Paleocene associations, Eocene calcareous dinoflagellates show fluctuations in relative abundances. These fluctuations can possibly be attributed to redeposition related to increased seaward transport of specimens, due to strengthened western boundary currents. The flora includes two new genera, one new species, and two new forms: Retesphaera diadema Hildebrand-Habel, Willems et Versteegh, gen. et. sp. nov., Cervisiella saxea (Stradner, 1961) Hildebrand-Habel, Willems et Versteegh, gen. et comb. nov., Sphaerodinella? tuberosa forma elongata Hildebrand-Habel, Willems et Versteegh, comb. et forma nov., Sphaerodinella? tuberosa forma variospinosa Hildebrand-Habel, Willems et Versteegh, comb. et forma nov. Three new combinations are proposed: Cervisiella saxea (Stradner, 1961) Hildebrand-Habel, Willems et Versteegh, gen. et comb. nov., Operculodinella operculata (Bramlette et Martini, 1964) Hildebrand-Habel, Willems et Versteegh, comb. nov., and Sphaerodinella? tuberosa (Kamptner, 1963) Hildebrand-Habel, Willems et Versteegh, comb. nov. The genus Operculodinella Kienel, 1994 is emended.

钙甲藻（calcareous dinoflagellates）通常为白垩纪至现代海洋沉积物中沟鞭藻囊孢组合的优势类群。但目前针对古近纪沉积物中钙甲藻的分布研究仍较为匮乏。对深海钻探计划（DSDP）356站位的样品进行钙甲藻组分分析，共检出35个主要为广布型的分类单元。其囊孢组合与特征性壁结构类型（皮通状、倾斜状、放射状、切向）在不同地层序列中呈现出定量与定性的双重波动。显著的群落更替主要发生在K/T边界与古新世-始新世边界，这一现象反映了当时的环境条件变化。部分形成钙质囊孢的沟鞭藻，如盖藻（Operculodinella operculata），可很好地适应K/T边界处相对快速的环境变化，因此大量繁殖，成为洋底碳酸盐通量的主导组分。与古新世稳定的囊孢群落不同，始新世钙甲藻的相对丰度呈现出明显波动。这类波动或可归因于再沉积作用：受西边界流增强影响，藻囊孢标本的向海搬运量增加，进而引发群落丰度变化。本研究报道的钙甲藻区系包含2个新属、1个新种与2个新变型：冠网球藻（Retesphaera diadema Hildebrand-Habel, Willems et Versteegh, gen. et sp. nov.）、坚硬颈囊藻（Cervisiella saxea (Stradner, 1961) Hildebrand-Habel, Willems et Versteegh, gen. et comb. nov.）、球甲藻属？ tuberosa的伸长变型（Sphaerodinella? tuberosa forma elongata Hildebrand-Habel, Willems et Versteegh, comb. et forma nov.）、球甲藻属？ tuberosa的多刺变型（Sphaerodinella? tuberosa forma variospinosa Hildebrand-Habel, Willems et Versteegh, comb. et forma nov.）。本次研究还提出了3个新组合：坚硬颈囊藻（Cervisiella saxea (Stradner, 1961) Hildebrand-Habel, Willems et Versteegh, gen. et comb. nov.）、盖藻（Operculodinella operculata (Bramlette et Martini, 1964) Hildebrand-Habel, Willems et Versteegh, comb. nov.）、球甲藻属？ tuberosa（Sphaerodinella? tuberosa (Kamptner, 1963) Hildebrand-Habel, Willems et Versteegh, comb. nov.）。同时对盖藻属（Operculodinella Kienel, 1994）进行了分类修订。