Abstract A suite of outcrop samples from the Cauvery Basin belonging to the mudrock-claystone dominated Karai Formation were analysed for nannofossil biostratigraphy in two newly measured sections at Karai and Garudamangalam. The age of the Karai Section is interpreted as early Albian to early Turonian, whereas the Garudamangalam Section is interpreted as late Albian to late Cenomanian. The Albian ‘BC’ zones of Bown et al. (1998) are applicable in both sections, whereas the Cenomanian and Turonian ‘UC’ zones of Burnett (1998), are only partially applicable, due to some problematic primary and secondary markers. The Albian-Cenomanian boundary appears to be continuous and is approximated in both sections using the FO of lower Cenomanian ammonites of the M. mantelli Zone. The Cenomanian-Turonian boundary interval is incomplete in the two sections, with a hiatus of ~0.66 myr, indicated by the absence of the upper Cenomanian Nannofossil Zone UC5. The nannoplankton assemblages are composed of broadly cosmopolitan taxa, despite the relatively high-latitude setting of SE India during the Albian (~45°S), which is reflected in the common occurrence of biogeographically bipolar taxa such as Repagulum parvidentatum and Seribiscutum primitivum. The palaeobiogeographic affinity of the nannoplankton, however, does not bear a distinct Austral stamp, as typical Austral taxa, such as Sollasites falklandensis and Zeugrhabdotus kerguelenensis are very rare in the studied sections. The early appearance of Crucibiscutum hayi in the lower Albian, and Gartnerago segmentatum in the upper Albian in the Cauvery Basin suggests that these two species may have originated in southern high latitudes before migrating to the northern Boreal regions. Four new calcareous nannofossil species, Calculites karaiensis, Loxolithus bicyclus, Manivitella fibrosa and Tranolithus simplex are described.

中文翻译：

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印度东南部陆上 Cauvery 盆地的白垩纪 (Albian-Turonian) 钙质纳米化石生物地层

摘要 在 Karai 和 Garudamangalam 的两个新测量剖面中，对 Cauvery 盆地的一套露头样品进行了纳米化石生物地层分析，这些样品属于以泥岩-粘土岩为主的 Karai 组。Karai 段的时代被解释为早阿尔比安到早图伦阶，而 Garudamangalam 段被解释为晚阿尔比安到晚 Cenomanian。鲍恩等人的阿尔比 'BC' 区。(1998) 在这两个部分都适用，而 Burnett (1998) 的 Cenomanian 和 Turonian 'UC' 区域仅部分适用，这是由于一些有问题的主要和次要标记。Albian-Cenomanian 边界似乎是连续的，并且在两个剖面中都使用 M. mantelli 区的下 Cenomanian 菊石的 FO 近似。两段的森诺曼阶-土伦阶边界区间不完整，有约 0.66 myr 的间断，表明没有上 Cenomanian 纳米化石区 UC5。尽管在阿尔比 (~ 45°S) 期间印度东南部的纬度相对较高，但纳米浮游生物组合由广泛的世界性分类群组成，这反映在生物地理双极分类群的常见发生中，例如 Repagulum parvidentatum 和 Seribiscutum primitivum。然而，纳米浮游生物的古生物地理亲和力并不具有明显的南方印记，因为典型的南方类群，如 Sollasites falklandensis 和 Zeugrhabdotus kerguelenensis 在研究的部分非常罕见。Crucibiscutum hayi 在下阿尔比安的早期出现，Cauvery 盆地上部阿尔比安的 Gartnerago segmentatum 表明这两个物种可能起源于南部高纬度地区，然后迁移到北方地区。描述了四种新的钙质纳米化石物种：Calculites karaiensis、Loxolithus bicyclus、Manivitella fibrosa 和 Tranolithus simplex。