CALCAREOUS NANNOFOSSIL TAXONOMY AND BIOSTRATIGRAPHY OF THE TOARCIAN-LOWER BAJOCIAN COLLE DI SOGNO SECTION (LOMBARDY BASIN, SOUTHERN ALPS, ITALY)

IF 1.6 3区 地球科学 Q2 GEOLOGY
S. Visentin, G. Faucher, E. Erba
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引用次数: 1

Abstract

Calcareous nannofossil biostratigraphy was conducted in the Toarcian-lower Bajocian interval at Colle di Sogno (Lombardy Basin, Southern Alps, Northern Italy) where the type-section of the Sogno Formation consisting of pelagic marly limestone, marlstone and marly claystone was established. Semiquantitative analyses of calcareous nannofossil assemblages allowed to achieve a high-resolution biostratigraphy based on several biohorizons, including zonal/subzonal markers and additional events. The NJT5 to NJT9 Zones of the standard nannofossil zonation established for the Mediterranean Province were identified. The biostratigraphy obtained at Colle di Sogno was compared to published nannofossil events calibrated with ammonite zones in sections from SE Spain, S France, Portugal and N Algeria. This assessment evidenced some discrepancies in the succession of events of the standard zonation and, furthermore, resulted in the revision of the age of a few datums. Moreover, some new/additional nannofossil biohorizons are proposed as subzonal markers. A morphometric analysis of the genus Watznaueria was conducted to identify diagnostic features for unambiguous species identification. The species W. colacicchii and W. contracta are distinguished on the basis of the coccolith width/central area width ratio, whereas W. britannica britannica is discriminated by the size - as in the original definition of the species - relative to the new subspecies W. britannica minor. The new species W. gaetanii differs from all other Watznaueria taxa by the bridge ultrastructure. In the Toarcian-Aalenian interval a progressive increase in size of Watznaueria specimens is paralleled by the progressive closure of the central area and the modification of the central area structure passing from a cross (W. colacicchii and W. contracta) to a double-button bridge (W. gaetanii) to a single-button bridge (W. britannica). These intrageneric evolutionary innovations accelerated in the Aalenian under stable paleoceanographic conditions and an oligotrophic regime.
意大利南阿尔卑斯伦巴第盆地toarcian - bajocian colle di sogno剖面钙质纳米化石分类与生物地层学
在意大利北部伦巴第盆地Colle di Sogno的toarcian - Bajocian下段进行了钙质纳米化石生物地层学研究,建立了Sogno组由海相泥灰岩、泥灰岩和泥灰岩组成的类型剖面。对钙质纳米化石组合的半定量分析可以实现基于几个生物层的高分辨率生物地层学,包括地带性/次地带性标记物和其他事件。确定了地中海省标准纳米化石分带的NJT5 ~ NJT9带。在Colle di Sogno获得的生物地层学与已发表的纳米化石事件进行了比较,这些事件与西班牙东南部、法国南部、葡萄牙和阿尔及利亚北部剖面的鹦鹉螺带进行了校准。这一评估证明了标准分区事件的先后顺序存在一些差异,此外,还对一些基准的年龄进行了修订。此外,还提出了一些新的/额外的纳米化石生物层作为亚地带性标志。对水蛭属进行了形态计量学分析,以确定诊断特征,明确物种鉴定。物种colacicchii和W. contracta是根据球核宽度/中心区宽度比值来区分的,而W. britannica britannica则是根据其相对于新亚种W. britannica minor的大小来区分的。该新种的桥状超微结构不同于其他所有水蛭属植物。在Toarcian-Aalenian区间,Watznaueria标本大小的逐渐增加与中心区域的逐渐闭合和中心区域结构的改变相平行,从十字(W. colacicchii和W. contracta)到双扣桥(W. gaetanii)到单扣桥(W. britannica)。在稳定的古海洋学条件和少营养状态下,这些属内进化创新在阿勒期加速。
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来源期刊
CiteScore
3.60
自引率
4.30%
发文量
28
审稿时长
>12 weeks
期刊介绍: The Rivista Italiana di Paleontologia e Stratigrafia was founded in 1895. It publishes original papers dealing with all fields of paleontology and of stratigraphy, from Italy and the Mediterranean to the Tethys, as well across the globe from China to North America.
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