Observations on the lithostratigraphy and ammonite succession of the Aptian (Lower Cretaceous) Lower Greensand of Chale Bay, Isle of Wight, UK
Observations on the lithostratigraphy and ammonite succession of the Aptian (Lower Cretaceous) Lower Greensand of Chale Bay, Isle of Wight, UK
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DOI：
10.1006/cres.1997.0105
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发表时间：
1998-06
影响因子：
2.1
通讯作者：
R. Casey;H. Bayliss;Martin I. Simpson
中科院分区：
文献类型：
--
作者：
R. Casey;H. Bayliss;Martin I. Simpson
对怀特岛查尔湾标准剖面的下格林砂群的部分阿瑟菲尔德粘土和含铁砂地层（下-上阿普第阶）进行了修订后的岩石地层学，本质上保留了菲顿的经典命名法。根据现场获得的新菊石收藏，提出了地带性和次地带性边界的变化。 Atherfield 粘土的上龙虾床部分与 Deshayesites callidiscus 亚区分离，并置于 D 区顶部的单独的 Deshayesites annelidus 亚区中。福贝西。巨角兽、龟角兽、拟星藻和辛佐维亚在这一层位的涌入具有古地理意义，表明与巴黎盆地的海洋联系已打开，并证实了上龙虾层是海侵地平线。铁质砂岩的 Scaphites 层的上部，以前包括在 thedeshayseiZone 中，由于其中出现了 Tropaeum 和 Dufrenoyia 物种，因此被转移到位于 Tropaeum(T.)bowerbanki 区域底部的 Dufrenoyia transoria 亚带。其原始的环状角鲨（钩状）形式，例如T。 (T.)hillsii 的生物年代学价值有限，与 Bowerbanki 区域的 criocone（螺旋）物种一起存在，并产生了 T.) 的局部地平线。 (T.)pseudophilllsia 位于上 Crioceras 层（基底上阿普第阶）的底部。对 Walpen 粘土和沙地与上 Crioceras 层进行了更精确的划界，并且铁质沙地这两个部分的交界处被重申为下/上 Aptian 边界，与 T 区的交界处重合。 (T.)bowerbankian 和 Epicheloniceras martinodes。跨越边界的逐层收集表明，表龟类不再被视为上阿普第阶底部的主要生物地层标志； Dufrenoyia的灭绝具有更大的意义。迄今为止，仅模糊地固定在柱中的 Vectisites 属以及 Ammonitoceras 和 Caspianites 的某些物种的来源被精确定位在 martinioides 区域。 Tropaeum(T.)drewiis 的地平线被证实位于 BowerbankiZone (meyendorffiSubzone) 的高处，而德国上阿普第阶 (=中阿普第阶基底，Kemper, 1995) 底部的“drewiZone”的有效性受到质疑。在对下/上阿普第阶边界的审查中，建议将德国地层称为 Cicatrites?tenuinodosus 地平线，并暂时放置在下阿普第阶顶部。菊石命名法的这些变化和其他变化在系统注释中进行了解释。
A revised lithostratigraphy is given for parts of the Atherfield Clay and Ferruginous Sands Formations (Lower-Upper Aptian) of the Lower Greensand Group of the standard section in Chale Bay, Isle of Wight, retaining in essence the classic nomenclature of Fitton. Changes in zonal and subzonal boundaries are proposed on the basis of new collections of ammonites obtainedin situ. The Upper Lobster Beds Member of the Atherfield Clay is detached from the Subzone ofDeshayesites callidiscusand placed in a separate Subzone ofDeshayesites annelidusat the top of the Zone ofD. forbesi. The influx ofMegatyloceras, Cheloniceras, PseudosaynellaandSinzoviaat this level has palaeogeographic implications, pointing to the opening of a marine link with the Paris Basin and confirming the Upper Lobster Beds as a transgressive horizon. The upper part of the Scaphites Beds Member of the Ferruginous Sands, previously included in thedeshayseiZone, is transferred to the Subzone ofDufrenoyia transitoria, at the base of the Zone ofTropaeum(T.)bowerbanki, on the strength of the occurrence therein of species ofTropaeumandDufrenoyia.Tropaeumis not present below thebowerbankiZone as now defined; its primitive ancyloceratoid (hooked) forms such asT. (T.)hillsiihave limited biochronological value, persisting alongside the criocone (spiral) species of thebowerbankiZone and giving rise to a local horizon ofT. (T.)pseudophillsiat the bottom of the Upper Crioceras Beds (basal Upper Aptian). A more precise delimitation of the Walpen Clay & Sands from the Upper Crioceras Beds is made and the junction of these two members of the Ferruginous Sands is reaffirmed as the Lower/Upper Aptian boundary, coinciding with the junction of the Zones ofT. (T.)bowerbankiandEpicheloniceras martiniodes. Bed-by-bed collecting across the boundary shows thatEpichelonicerascan no longer be taken as the prime biostratigraphical marker for the base of the Upper Aptian; greater significance is given to the extinction ofDufrenoyia. The sources of the genusVectisitesand some species ofAmmonitocerasandCaspianites, hitherto fixed only vaguely in the column, are pinpointed in themartinioidesZone. The horizon ofTropaeum(T.)drewiis confirmed as high in thebowerbankiZone (meyendorffiSubzone) and the validity of a ‘drewiZone’ at the base of the German Upper Aptian (=base of Middle Aptian, Kemper, 1995) is questioned. In a review of the Lower/Upper Aptian boundary, it is suggested that the German stratum be called the Horizon ofCicatrites?tenuinodosusand placed tentatively at the top of the Lower Aptian. These and other changes in ammonite nomenclature are explained in the systematic notes.