Relative abundances of benthic foraminifera at the Cretaceous/Paleogene boundary in DSDP Hole 62-465A, Southern Hess Rise in the central North Pacific (Appendix A)

Uppermost Maastrichtian benthic foraminiferal assemblages (>63 µm) are diverse, indicating mesotrophic conditions in lower bathyal DSDP Hole 465A (Hess Rise, central North Pacific), in 4 lower bathyal land sections in central-East and Northeastern Mexico, and in the upper to middle bathyal Agost section (Tethys area, Southeastern Spain). They indicate more eutrophic conditions in lower bathyal ODP Hole 1049C (Blake Nose, Northwestern Atlantic). Benthic foraminifers did not suffer significant extinction at the K/Pg boundary, but diversity and heterogeneity of the assemblages and the percentage of infaunal morphogroups decreased drastically in all sections, with the exception of DSDP Hole 465A where the percentage of infaunal taxa increased. These faunal changes probably reflect the effect on the benthic faunas of a widespread decrease in the food supply to the sea floor, as a result of the collapse of primary productivity at the K/Pg boundary. The decrease in food supply apparently affected the benthic faunas least at more eutrophic NW Atlantic ODP Site 1049 and at Pacific DSDP Site 465, which is distal from the impact site of the K/Pg bolide on the Yucatan Peninsula. At these sites the faunas recovered within the Parvulorugoglobigerina eugubina Biozone (~100 ky), although diversity and heterogeneity remained low through the early Danian, possibly indicating environmental stress. This stress might be related to a high or fluctuating food supply by primary producers that could not easily be used by the benthos, such as various bloom species of dinoflagellates. Benthic assemblages recovered more slowly (~300 ky) in the Mexican and Spanish sections. Low oxygen conditions after the K/Pg boundary could be inferred from the benthic assemblages at Agost (Southeastern Spain) only. A short episode of hypoxia, however, may be obscured at Pacific DSDP Hole 465A by drilling disturbance, and in the Mexican sections and Hole 1049C by incomplete sections due to downslope transport. Benthic foraminiferal assemblages thus appear to have been affected by the collapse of primary productivity at the K/Pg boundary to a different extent in different regions, and took different lengths of time for their recovery after the boundary.

马斯特里赫特阶最顶部（Uppermost Maastrichtian）的>63μm粒级底栖有孔虫（benthic foraminifera）组合分异度较高，指示北太平洋中部赫斯海岭（Hess Rise）的深海钻探计划（Deep Sea Drilling Project, DSDP）465A孔所处的下半深海带环境为中营养（mesotrophic）条件；该组合同时见于墨西哥中东部与东北部的4个下半深海带陆上剖面，以及西班牙东南部特提斯区域的阿戈斯特（Agost）中上半深海带剖面。大西洋西北部布莱克海岭（Blake Nose）的大洋钻探计划（Ocean Drilling Program, ODP）1049C孔的底栖有孔虫组合则指示了更为富营养（eutrophic）的下半深海带环境。在白垩纪-古近纪（K/Pg）界线处，底栖有孔虫并未发生显著灭绝，但所有剖面的底栖有孔虫组合分异度、异质性以及内生形态类群（infaunal morphogroups）占比均出现骤降；唯有DSDP 465A孔例外，其内生类群占比反而有所上升。这类群落变化可能反映了K/Pg界线处初级生产力崩溃后，海底表层食物供给普遍减少对底栖生物群落造成的影响。食物供给的减少对富营养程度更高的西北大西洋ODP 1049孔，以及距离尤卡坦半岛（Yucatan Peninsula）K/Pg陨击体（bolide）撞击点较远的太平洋DSDP 465孔的底栖生物群落影响相对最小。在这两个位点，底栖群落于小褶球虫优古巴（Parvulorugoglobigerina eugubina）生物带（约10万年）内完成恢复，尽管丹尼阶（Danian）早期的分异度与异质性仍处于较低水平，这可能指示当时仍存在环境压力。这类压力可能与初级生产者（如各类甲藻（dinoflagellates）水华物种）的高供给或波动供给有关，而这类食物资源难以被底栖生物有效利用。墨西哥与西班牙剖面的底栖群落恢复速度则更为缓慢（约30万年）。仅在西班牙东南部的阿戈斯特剖面，可通过底栖有孔虫组合推断K/Pg界线后存在低氧环境。不过，太平洋DSDP 465A孔的低氧短暂事件可能因钻探扰动而被掩盖，而墨西哥剖面与1049C孔则因斜坡搬运作用导致地层不完整，该信号可能被遮蔽。综上，底栖有孔虫组合在K/Pg界线处受到的初级生产力崩溃影响存在区域差异，且不同区域的群落恢复时长也各不相同。