Abstract

In the present paper we describe and discuss belemnite finds from the basal part of the middle Jurassic sequence at the southwest of the Republic of Tatarstan (Tetyushi district). The belemnites were collected from the outcrops located along a shoreline of the Kuybyshevskoye reservoir (Volga river) between the place Tarkhanovskaya pristan’ and the former village Dolinovka. These belemnites indicate that the basal part of the Jurassic sequence is Early Bathonian (Ishmae Zone) or, less probable, Middle Bathonian in age. Such dating triggers a critical review for the age of the middle Jurassic sequence in the region. In particular, poorly preserved ammonites previously collected from the same outcrops higher in the succession and interpreted as members of the Late Bajocian subfamily Garantianinae, are in fact Late Bathonian Gowericeratinae. Consequently, “Beds with Garantiana”—nominally the most ancient ammonite-based biostratigraphic unit within the whole Jurassic of European Russia, based on this assemblage,—is invalid.

中文翻译：

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tar斯坦西南部的前Callovian侏罗纪层序时代（俄罗斯中部，Tarkhanovskaya pristan'–Dolinovka参考部分）和上巴约期“ Garantiana-beds”的状态，先前在此处描述

摘要

在本文中，我们描述并讨论了Ta斯坦共和国西南部（特提西区）中侏罗纪层序底部的贝莱石发现。从位于Kuybyshevskoye水库（伏尔加河）海岸线附近的露头上收集贝利尼特犬，该水库位于塔尔哈诺夫斯卡娅·普里斯坦（Tarkhanovskaya pristan）与前村庄多利诺夫卡（Dolinovka）之间。这些贝勒尼人表示，侏罗纪层序的基础部分是早巴东期（以实玛地区），或者年龄不太可能是中巴东期。这种约会触发了对该地区中侏罗纪层序年龄的严格审查。特别是，以前从同一演替序列中较高的露头收集的保存不佳的铵矿，实际上被解释为晚巴乔期亚科Garantianinae的成员，实际上是晚巴东期Gowericeratinae。基于这种组合，“ Garantiana ”（名义上是整个欧洲俄罗斯侏罗纪中最古老的基于mon石的生物地层单元）是无效的。