Middle Campanian-lowermost Maastrichtian nannofossils and foraminifers of the northwestern Australian margin@en

The middle-late Campanian was marked by an increase in the bioprovinciality of calcareous microfossil assemblages into distinct Tethyan, Transitional, and Austral Provinces that persisted to the end of the Maastrichtian. The northwestern Australian margin belonged to the Transitional Province and the absence of key Tethyan marker species such as Radotruncana calcarata and Gansserina gansseri has led petroleum companies operating in the area to use the locally developed KCCM integrated calcareous microfossil zonation scheme. The KCCM zonation is a composite scheme comprising calcareous nannofossil (KCN), planktonic foraminiferal (KPF) and benthonic foraminiferal (KBF) zones. This paper presents the definitions and revisions of Zones KCCM8-19, from the highest occurrence (HO) of Aspidolithus parcus constrictus to the lowest occurrence (LO) of Ceratolithoides aculeus, and builds on our previous early-late Maastrichtian study. The presence of a middle-upper Campanian disconformity is confirmed by microfossil evidence from the Vulcan Sub-basin, Exmouth and Wombat plateaus, and the Southern Carnarvon Platform. In the Vulcan Sub-basin and on the Exmouth Plateau (ODP Hole 762C) the hiatus extends from slightly above the LO of common Rugoglobigerina rugosa to above the LO of Quadrum gothicum. On the Wombat Plateau (ODP Hole 761B) it spans from above the LO of Heterohelix semicostata to above the LO of Quadrum gothicum; and in the Southern Carnarvon Platform the disconformity has its longest duration from above the HO of Heterohelix semicostata to above the LO of Quadrum sissinghii. A significant revision of the events which define Zones KCCM18 and 19 was necessary owing to the observation that the LO of Ceratolithoides aculeus occurs below the HOs of Archaeoglobigerina cretacea and Stensioeina granulata incondita and the LO of common Rugoglobigerina rugosa. In the original zonation these events were considered to be coincident.中晚坎潘期以钙质微化石组合的生物地理分区性显著强化为标志，形成了清晰划分的特提斯（Tethyan）、过渡（Transitional）与澳大拉西亚（Austral）三省，该分区格局一直延续至马斯特里赫特阶末期。澳大利亚西北陆缘隶属于过渡省，区内缺失Radotruncana calcarata与Gansserina gansseri等特提斯域关键标志属种，这使得在该区域开展作业的石油公司采用了本土研发的KCCM综合钙质微化石分带方案（KCCM integrated calcareous microfossil zonation scheme）。该方案为复合分带体系，涵盖钙质超微化石（calcareous nannofossil, KCN）分带、浮游有孔虫（planktonic foraminiferal, KPF）分带与底栖有孔虫（benthonic foraminiferal, KBF）分带。本文阐述了KCCM8至KCCM19带的定义与修订内容，其时限范围从Aspidolithus parcus constrictus的最高产出层位（Highest Occurrence, HO）至Ceratolithoides aculeus的最低产出层位（Lowest Occurrence, LO），研究基于我们此前开展的早-晚马斯特里赫特期工作展开。瓦尔坎次盆（Vulcan Sub-basin）、埃克斯茅斯高原（Exmouth Plateau）、Wombat高原（Wombat Plateaus）与南卡那封台地（Southern Carnarvon Platform）的微化石证据证实了中晚坎潘期存在沉积间断。其中，瓦尔坎次盆与埃克斯茅斯高原（大洋钻探计划762C井，Ocean Drilling Program, ODP Hole 762C）的沉积间断时限为常见Rugoglobigerina rugosa最低产出层位之上至Quadrum gothicum最低产出层位之上；Wombat高原（ODP Hole 761B）的沉积间断时限为Heterohelix semicostata最低产出层位之上至Quadrum gothicum最低产出层位之上；而南卡那封台地的沉积间断持续时间最长，时限为Heterohelix semicostata最高产出层位之上至Quadrum sissinghii最低产出层位之上。鉴于观测到Ceratolithoides aculeus的最低产出层位出现于Archaeoglobigerina cretacea与Stensioeina granulata incondita的最高产出层位以及常见Rugoglobigerina rugosa最低产出层位之下，因此有必要对界定KCCM18与KCCM19带的相关事件进行重大修订。在原始分带方案中，这些事件曾被认为是同步发生的。