Calcareous nannofossils are described from 4 sections of the Lower Cretaceous Dalichai Formation from the Eastern (Tepal, Talu and Lavan sections) and central Alborz Mountains (Yonjezar section), Iran. Forty-two species belonging to 18 genera have been identified from the 4 sections studied, including 13 species belonging to 8 genera of ascidian didemnids only from the Tepal section. These taxa indicate the CC1–CC5 biozones of Sissingh’s (1977) biozonation and an age of Berriasian to Early Barremian. The nannofossils recorded from the Dalichai Formation are generally Tethyan and cosmopolitan, while the presence of some Boreal taxa (Nannoconus abundans and N. borealis) may reflect connection between the Boreal and Tethyan realms in the Early Barremian. The sedimentary basin of the Dalichai Formation of the Tepal, Talu, and Yonjezar sections was located at low latitudes of the Tethyan realm with warm surface water. Also, trends of increasing depth and productivity, of a shift from r-selected to k-selected strategies and of a change from low-to-high mesotrophic to oligotrophic conditions, were deduced. A change from unstable to stable conditions towards the tops of sections is inferred for these localities. Laterally in the Dalichai Basin from the eastern to central Alborz, there was an increase in depth and productivity, and also a trend towards oligotrophic conditions and a dominance of low-stress conditions.

中文翻译：

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基于钙质纳米化石的阿尔伯兹山脉东部和中部（伊朗北部）大理柴组（下白垩统）的生物地层学和古环境解释

钙质纳米化石来自伊朗东部（Tepal、Talu 和 Lavan 部分）和 Alborz 山脉中部（Yonjezar 部分）的下白垩统 Dalichai 组的 4 个部分。研究的4个剖面共鉴定出18属42种，其中仅Tepal剖面的海鞘8属13种。这些分类群表明 Sissingh (1977) 生物区的 CC1-CC5 生物区和 Berriasian 到早 Barremian 时代。大理柴组记录的纳米化石一般是特提斯和世界性的，而一些北方类群（Nannoconus abundans 和 N.borealis）的存在可能反映了早巴雷米亚北方和特提斯界之间的联系。Tepal、塔鲁、大理柴组沉积盆地 和 Yonjezar 部分位于特提斯王国的低纬度地区，地表水温暖。此外，还推断出深度和生产力增加的趋势，从 r 选择到 k 选择策略的转变以及从低到高中营养条件到贫营养条件的变化。推断出这些位置从不稳定到稳定条件向截面顶部的变化。大理柴盆地从阿尔伯兹东部到中部，深度和生产力有增加的趋势，也有向贫营养条件和低应力条件占优势的趋势。推断出这些位置从不稳定到稳定条件向截面顶部的变化。大理柴盆地从阿尔伯兹东部到中部，深度和生产力有增加的趋势，也有向贫营养条件和低应力条件占优势的趋势。推断出这些位置从不稳定到稳定条件向截面顶部的变化。大理柴盆地从阿尔伯兹东部到中部，深度和生产力不断增加，也有向贫营养条件和低应力条件占优势的趋势。