(Table 1) Distribution of Lower Cretaceous calcareous nannofossils at DSDP Hole 93-603B

Upper Berriasian to lower Aptian calcareous nannofossil assemblages have been studied from a siliciclastic deep-sea fan complex and a subjacent limestone sequence drilled beneath the lower continental rise in the western North American Basin, 270 miles (435 km) off Cape Hatteras, North Carolina (USA). Sharp lithologic facies changes and reworking by turbidites complicate the biostratigraphic interpretation, but provide an excellent opportunity to better distinguish "nearshore" from open-ocean nannofossil species, and to investigate the introduction of neritic taxa into the deep-see environment, a phenomenon that appears to have been widespread within the circum-North Atlantic during Neocomian times. Well-preserved assemblages in dark, carbonaceous claystones were probably displaced from the oxygen minimum zone along the upper slope or outer shelf. Neritic, continental margin species prevalent in this facies include the holococcolith Zebrashapka vanhintei n. gen., n. sp., Lithraphidites alatus magnus n. spp., Pickelhaube furtiva n. gen., and a host of nannoconids and micrantholiths. A qualitative evaluation of widely used guide fossils suggests that the triad of proposed markers for the base of Roth's Zone NC3 make their first appearances in the following (ascending) order: Diadorhombus rectus, TUbodiscus verenae, Calcicalathina oblongata. Of these, we chose the nominative species for the zone, T. verenae, to mark its base and to approximate the Berriasian/Valangian boundary. Cyclagelosphaera deflandrei is strongly affected by diagenesis and is therefore not a reliable index species for the base of Zone NC4 near the Valanginian/Hauterivian boundary (the last occurrence of T. verenae is also not suitable there). In addition, Lithraphidites bollii, a form apparently confined to the low latitudes of the Tethyan region, was absent at the more temperate Site 603 and not available as a subzonal marker for the upper Hautervian-lower Barremian (mid-NC4 and mid-NC5, respectively). Cruciellipsis cuvillieri, however, provides a reliable datum just below the Hauterivian/Barremian boundary (base of NC5), despite the potential for reworking in this section. Nannoconids tend to be reworked in this section, and do not provide trustworthy forms to mark the Barremian/Aptian boundary (base of NC6). Hayesites irregularis n. comb, probably does provide a useful first appearance datum within the lower Aptian, if it is not confused with a more birefringent and globular form, Rucinolithus terebrodentarius n. sp. Rhagodiscus angustus is mimicked by a similar form (Zeughrabdotusl pseudoangustus n. sp.), which apparently ranges down to the Hauterivian, thus Lithastrinus floralis provides a more useful first appearance datum for the base of the middle-upper Aptian Rhagodiscus angustus Zone (NC7). Aside from the new taxa mentioned above, the following are also described: Cretarhabdusl delicatus n. sp. and Cyclagelosphaera jiangii n. sp.对采自美国北卡罗来纳州哈特拉斯角以西270英里（435公里）的北美西部盆地下大陆坡之下钻取的硅质碎屑深海扇复合体（siliciclastic deep-sea fan complex）及下伏石灰岩序列（subjacent limestone sequence）中的贝里阿斯阶上部至阿普第阶下部的钙质超微化石（calcareous nannofossil）组合展开了研究。浊积岩（turbidites）引发的显著岩相变化与再沉积作用使得生物地层解释（biostratigraphic interpretation）趋于复杂，但也为更好地区分近岸与远洋钙质超微化石物种，以及探究浅海类群（neritic taxa）侵入深海环境这一现象提供了绝佳契机——该现象在尼欧克姆期（Neocomian times）的北大西洋周边（circum-North Atlantic）区域曾广泛存在。暗色炭质黏土岩中保存完好的化石组合大概率是从陆坡上部或外陆架（upper slope or outer shelf）的氧最低带（oxygen minimum zone）搬运而来的。该岩相中的优势浅海、陆缘类群包括全颗石（holococcolith）类的*Zebrashapka vanhintei*新属（n. gen.）、新种，翼石枝颗石（*Lithraphidites alatus*）大型新亚种（n. spp.），*Pickelhaube furtiva*新属，以及大量钙质超微球石（nannoconids）和微盾石类（micrantholiths）。 对广泛使用的标准化石（guide fossils）进行定性评估后发现，罗斯NC3带（Roth's Zone NC3）底界的三个候选标志种实际按上行地层顺序依次首现：直双角石（*Diadorhombus rectus*）、维氏管盘石（*Tubodiscus verenae*，原文笔误为TUbodiscus）、长形钙杯石（*Calcicalathina oblongata*）。其中我们选取该带的模式种*T. verenae*来界定其底界，并近似对应贝里阿斯阶/凡兰吟阶（Berriasian/Valangian）界线。德氏环球石（*Cyclagelosphaera deflandrei*）受成岩作用（diagenesis）影响显著，因此并不适合作为凡兰吟阶/豪特里维阶（Valanginian/Hauterivian）界线附近NC4带底界的可靠标志种；*T. verenae*的末现（last occurrence）在此界线处也并不适用。此外，博氏石枝颗石（*Lithraphidites bollii*）这一似乎仅局限于特提斯区（Tethyan region）低纬度区域的类群，在温带性更强的603站位（Site 603）中并未出现，因此无法作为豪特里维阶上部-巴列姆阶下部（分别对应NC4带中部和NC5带中部）的亚带标志种。不过，库氏十字椭球石（*Cruciellipsis cuvillieri*）虽在该剖面存在再沉积（reworking）风险，却能为豪特里维阶/巴列姆阶（Hauterivian/Barremian）界线之下（即NC5带底界）提供可靠的基准点。钙质超微球石（nannoconids）在该剖面中多发生再沉积，无法提供可信赖的标志种来界定巴列姆阶/阿普第阶（Barremian/Aptian）界线（即NC6带底界）。不规则海斯颗石新组合（*Hayesites irregularis* n. comb.）若未与更具双折射性（birefringent）的球状类群齿针皱球石新种（*Rucinolithus terebrodentarius* n. sp.）混淆，或可在阿普第阶下部提供有用的首现基准点。狭形皱盘石（*Rhagodiscus angustus*）会被类似种假狭形带杆颗石新种（*Zeughrabdotus pseudoangustus* n. sp.）所模拟，该类似种的延限可至豪特里维阶，因此花状石星颗石（*Lithastrinus floralis*）可为阿普第阶中上部狭形皱盘石带（NC7带）的底界提供更可靠的首现基准点。 除上述提及的新类群外，本次还描述了以下类群：纤细克里特颗石新种（*Cretarhabdus delicatus* n. sp.）及蒋氏环球石新种（*Cyclagelosphaera jiangii* n. sp.）。