Abstract The latest Jurassic was a crucial time for calcareous nannoplankton as a major speciation episode took place with the appearance and rapid evolution of several new genera and species, particularly of highly calcified nannoliths at low latitudes: this origination pulse provides the opportunity to achieve high-resolution biostratigraphic data amplifying the possibility of dating and correlating. A thorough revision of published as well as newly updated nannofossil biostratigraphies across the Tithonian-lowermost Berriasian interval was achieved to quantitatively evaluate the reliability of individual nannofossil events. Our database comprises 95 land and oceanic sites from different paleogeographic settings and latitudes (Europe, Atlantic Ocean, America, South Asia). We excluded sections with hiatuses or characterized by uncertain calcareous nannofossil biostratigraphy due to scarcity of data and/or poor preservation, as well as taxonomic incongruities. For each stratigraphic section, the critical assessment took into account sampling rates, nannofossil preservation, abundance and taxonomy: biohorizons based on single samples, questionably determined, or based on ambiguous/mismatching taxonomic concepts were excluded. We first performed calibration of nannofossil events against magnetostratigraphy to highlight reproducibility and time variability through the CM22–CM17 interval. The time uncertainties of individual nannofossil events were calculated, considering sampling and sedimentation rates derived from magnetostratigraphy. The reproducibility and variability of nannofossil events were also estimated relative to calpionellid biostratigraphy, as the latter is the primary tool selected by the Berriasian Working Group (ICS) for the definition of the Cretaceous base. We distinguished highly reliable events characterized by maximum reproducibility, shorter time variability, common and continuous occurrence; moderately reliable events are distinguished by intermediate reproducibility and time variability; unreliable events have minimum reproducibility and longest time variability. The quantitative evaluation of 37 events against magnetostratigraphy in the CM22–CM17 interval allowed to discriminate among 9 highly reliable first occurrences, 4 reliable first occurrences, 10 moderately reliable events (7 first occurrences, 2 last occurrences and 1 last common occurrence), 6 poorly reliable events (5 first occurrences and 1 last occurrence) and 8 unreliable first occurrences. The evaluation of 18 events against the calpionellid zonation resulted in 4 highly reliable first occurrences. The revisited taxonomy and reliability assessment of calcareous nannofossil events were used to revise the calcareous nannofossil zonation of the Tithonian–early Berriasian time interval: one zone (NC 0 Zone) and four subzones (NC 0a, NC 0b, NJT 14a, NJT 14b Subzones) are newly defined here. Moreover, one zonal definition is emended (NJT 17 Zone) and the age of top/bases of four zones (NJT 14, NJT 15; NJT 16, NC 1 Zones) are revised. The first appearance datum of Nannoconus wintereri, showing the highest reproducibility and lowest time variability, correlates with magnetochron 19n-2n and results to be the calcareous nannofossil event best approximating the base of the Calpionella alpina Zone equated to the Jurassic/Cretaceous boundary.

中文翻译：

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Tithonian-Berriasian 时间间隔内钙质纳米化石事件的可靠性：对修订后的高分辨率分带的影响

摘要 侏罗纪末期是钙质纳米浮游生物的关键时期，随着几个新属和新种的出现和快速进化，特别是低纬度高度钙化的纳米石的出现和快速进化，这是一个主要的物种形成时期：这种起源脉冲提供了实现高分辨率生物地层数据放大了测年和关联的可能性。对已发表和最新更新的纳米化石生物地层进行了全面修订，以定量评估单个纳米化石事件的可靠性。我们的数据库包含来自不同古地理环境和纬度（欧洲、大西洋、美洲、南亚）的 95 个陆地和海洋站点。由于数据稀缺和/或保存不良以及分类学上的不协调，我们排除了具有间断或以不确定的钙质纳米化石生物地层为特征的部分。对于每个地层剖面，关键评估都考虑了采样率、纳米化石保存、丰度和分类学：排除了基于单个样本、可疑确定或基于模棱两可/不匹配的分类学概念的生物地平线。我们首先根据磁地层学对纳米化石事件进行校准，以突出 CM22-CM17 间隔的可重复性和时间可变性。考虑到来自磁地层学的采样和沉积速率，计算了单个纳米化石事件的时间不确定性。纳米化石事件的可重复性和可变性也相对于 calpionellid 生物地层学进行了估计，因为后者是 Berriasian 工作组 (ICS) 选择的用于定义白垩纪基底的主要工具。我们区分了高度可靠的事件，这些事件具有最大的可重复性、更短的时间可变性、常见和连续发生；中等可靠性事件的特点是中等重现性和时间可变性；不可靠的事件具有最小的可重复性和最长的时间可变性。CM22-CM17 区间内 37 个事件与磁地层学的定量评估允许区分 9 个高度可靠的首次出现、4 个可靠的首次出现、10 个中等可靠的事件（7 个首次出现、2 个最后一次出现和 1 个最后一次常见事件），6 个不太可靠的事件（5 次首次发生和 1 次最后一次发生）和 8 次不可靠的首次发生。针对 calpionellid 分区对 18 次事件的评估导致 4 次高度可靠的首次发生。重新审视的钙质纳米化石事件的分类和可靠性评估被用来修正提通阶 - 贝里亚斯早期时间间隔的钙质纳米化石区带：一个区（NC 0 区）和四个亚区（NC 0a、NC 0b、NJT 14a、NJT 14b） ) 是在这里新定义的。此外，修改了1个地带性定​​义（NJT 17 Zones），修订了4个地带（NJT 14、NJT 15；NJT 16、NC 1 Zones）的顶底年龄。Nannoconus Wintereri的首次出现数据，表现出最高的再现性和最低的时间变异性，