Neogene calcareous nannofossils of ODP Leg 133 holes@en

Two major transects were drilled across the northeastern Australian margin during Leg 133. The southern transect, consisting of Sites 812 through 818 (and 826), extends from the northern edge of Marion Plateau north to the southern edge of Queensland Plateau. Hemipelagic and pelagic sediments were recovered at all sites from the Holocene back to the upper Miocene sections. Calcareous nannofossils are a major constituent of these sediments. Nearly all of the low-latitude nannofossil biohorizons can be identified in the Pliocene and Pleistocene, which makes it possible to construct a reasonably accurate biochronology for each site. Sites 813 and 814 are similar in sedimentation rate and succession of biohorizons, and both have a hiatus (nondeposition) that straddles the Miocene/Pliocene boundary; much of the lower Pliocene is missing. Site 812 is also similar to the last two, but its biostratigraphic resolution is reduced because of poorer preservation in critical intervals. Sites 815 and 816 are broadly similar in that both have excellent biostratigraphic resolution in the Pleistocene and uppermost Pliocene intervals, even though the sedimentation rate for the two is different. Both sites have an expanded mid-Pliocene section. At Site 815 the expanded Pliocene section has been identified as a contourite; however, there is no evidence in the nannofossils for significant redeposition. Site 815 also has exceptionally good biostratigraphic resolution into the upper Miocene section. The ranges of Amaurolithus tricorniculatus and Amaurolithus amplificus were clearly identified at this site, although the lack of a magnetostratigraphy prevents assigning precise ages to them. Sites 817 and 818 also are similar, although Site 818 is more expanded. Both sites have a hiatus at the Pliocene/Pleistocene boundary.在大洋钻探第133航次（Leg 133）期间，科研人员于澳大利亚东北缘钻取了两条主要钻探断面。南部断面涵盖812至818号站位（含826号站位），其展布范围起自马里恩高原（Marion Plateau）北缘，向北延伸至昆士兰高原（Queensland Plateau）南缘。所有站位均采获了全新统至上中新统的半远洋（hemipelagic）与远洋（pelagic）沉积物。钙质超微化石（calcareous nannofossils）是此类沉积物的主要组成部分。几乎所有低纬度超微化石生物标志层（biohorizons）均可在更新统与上新统中被识别，这为建立各站位精度较高的生物年代地层格架（biochronology）提供了可行基础。813与814号站位的沉积速率及生物标志层序列均较为相似，二者均存在横跨中新统/上新统分界的沉积间断（hiatus，无沉积阶段），缺失了大部分下上新统地层。812号站位与上述两个站位特征相近，但由于关键层位的化石保存效果欠佳，其生物地层分辨率有所降低。815与816号站位具有相似特征：尽管二者沉积速率存在差异，但两者的更新统与最上部上新统层位均具备极佳的生物地层分辨率，且均发育增厚的中上新统剖面。在815号站位，这套增厚的上新统剖面被判定为等深积岩（contourite），但超微化石证据并未显示存在显著的再沉积作用。该站位的上中新统层位同样具备极高的生物地层分辨率。科研人员在此站位清晰识别出三刺美星石（Amaurolithus tricorniculatus）与扩张美星石（Amaurolithus amplificus）的产出范围，但因缺乏磁地层学（magnetostratigraphy）数据，无法为其赋予精确的年代归属。817与818号站位特征亦较为相似，不过818号站位的剖面更为增厚。两个站位均在更新统/上新统分界处存在沉积间断。