We describe the biostratigraphy and palaeoecology of the Dalichai Formation based on calcareous nannofossils from the Guydagh section in the western Alborz Mountains, north-west Iran. The nannofossils are moderately to well-preserved, and 25 species belonging to 8 genera have been distinguished, representing the Early Berriasian to Late Hauterivian ages according to the CC1–CC4b biozones of Sissingh (1977). The recorded nannofossils are generally Tethyan and cosmopolitan, while the record of Nannoconus inornatus, a Boreal species, at the top of the section reflects the water mass connection between the Boreal and Tethyan domains during the Late Hauterivian. The records of Nannoconus spp., Watznaueria spp., and Rhagodiscus asper show that the sedimentary basin of the Dalichai Formation was located at low latitudes of the Tethyan realm with warm surface waters. Palaeoecologically, the findings represent a marine transgression and increasing depth, and the palaeoenvironmental conditions change from low-high mesotrophic (shown by the dominance of W. britannica) to oligotrophic (from the dominance of nannoconids), r- to K-strategy of life (from the dominance of nannoconids), and became increasingly stable (shown by the reduction of W. britannica) towards the top of the section.

我们根据伊朗西北部厄尔布尔士山脉西部 Guydagh 剖面的钙质超微化石描述了 Dalichai 组的生物地层学和古生态学。根据 Sissingh（1977 年）的 CC1-CC4b 生物带，纳米化石保存完好，属于 8 属的 25 个物种已被区分，代表了早贝里亚世至晚 Hauterivian 时代。记录的纳米化石一般是特提斯和世界性的，而剖面顶部的北方物种Nannoconus inornatus的记录反映了晚Hauterivian期间北方和特提斯域之间的水体联系。的记录Nannoconus属，Watznaueria属，和Rhagodiscusasper 表明，大里柴组沉积盆地位于特提斯地区低纬度地区，地表水温暖。Palaeoecologically，调查结果表示海进和深度的增加，和古环境条件从低-高营养型（由的显性示出改变W.全书）到贫营养（从nannoconids的主导地位），R-对生命的K-策略（从 nanoconids 的主导地位），并变得越来越稳定（由 W. britannica 的减少显示）朝向该部分的顶部。