Inoceramid sclerochronology - Advancing Late Cretaceous climate reconstructions

白垩纪是温室世界的典型例子，属于地球历史上研究最多的时间段之一。然而，仍然不确定不同纬度和水深的实际温度是什么，当时温带外海洋的季节和年际环境变化几乎一无所知。这些信息对于限制经向温度梯度、验证极地冰的存在或不存在、检验关于大气和海洋环流模式的假设以及进一步完善数值气候模型至关重要。它还可以用来更详细地研究沉积作用和轨道强迫之间的联系，因为后者改变了季节性温度模式。此外，高分辨率的温度(和其他环境)数据可以帮助更好地了解物种分布模式、生物的古生物学和生活史特征以及类群兴衰的潜在原因。白垩纪温带海洋的季节性到年际气候动态的破译档案--其全部潜力到目前为止还没有被发掘--包含在双壳类贝壳中。这个特殊的物种群出现在二叠纪，由于未知的原因，在白垩纪/古近纪界线之前数百万年灭绝。尽管经过了几十年的研究，人们对诺卡氏虫的生物学、生态学和生活史特征知之甚少，但它们在中生代晚期的温室气候中茁壮成长。在晚白垩世，它们显然主导了温带大型动物。巨大的贝壳大小可达3米(！)，诺维拉虫属于有史以来最大的双壳类。几乎任何深度的水中都有神经节细胞存在，甚至在恶劣、缺氧的环境中大量出现。通过应用最先进的成岩年代学技术和广泛的成岩作用筛选试验，拟议的研究将为在高分辨率古气候学中常规使用接种剂双壳类铺平道路。为了展示这一档案的潜力，我们将示范地研究(1)在白垩纪温室期间，即在OAE2(塞诺马尼亚/图罗尼亚阶段界线；明斯特兰盆地)之前、期间和之后的季节温度变化；(2)在坎帕尼亚阶段(北海道)。(3)分析由不同岩石类型(明斯特兰盆地)的壳体重建的季节环境变量是否存在差异。如果沉积是轨道强迫的，那么石灰岩和泥灰岩沉积的季节温度、初级生产力等应该是不同的。(4)此外，还将确定选定的接种者的生活史特征，包括个体发育年龄以及季节性壳长的时间和速度。

The Cretaceous serves a classic example of a greenhouse world and belongs to one of the best studied time intervals of Earth history. However, it still remains uncertain which actual temperatures prevailed at different latitudes and water depths, and almost nothing is known about the seasonal and inter-annual environmental variability in extratropical oceans at that time. Such information is essential to constrain meridional temperature gradients, verify the presence or absence of polar ice, test hypotheses on atmospheric and oceanic circulation patterns and further refine numerical climate models. It may also be used to study the link between sedimentation and orbital forcing in more detail, because the latter modifies seasonal temperature patterns. Furthermore, high-resolution temperature (and other environmental) data can help to better understand species distribution patterns, the paleobiology and life history traits of organisms as well as potential causes for the rise and demise of taxa. A promising archive for deciphering seasonal to inter-annual climate dynamics in extratropical Cretaceous oceans - whose full potential has by far not been explored - is contained in shells of inoceramid bivalves. This peculiar species-group appeared in the Permian and, for yet unknown reasons, became extinct several million years prior to the Cretaceous/Paleogene boundary. Despite decades of research, not particularly much is known about the biology, ecology and life-history traits of the inoceramids, but they thrived in the greenhouse climate of the late Mesozoic. During the Late Cretaceous, they clearly dominated the extratropical megafauna. With enormous shell sizes of up to 3m (!), inoceramids belong to the largest bivalves that ever lived. Inoceramids inhabited nearly any water depth and even occurred abundantly in hostile, dysoxic environments. By applying state-of-the-art sclerochronological techniques combined with a broad spectrum of diagenesis screening tests, the proposed study will pave the way toward a routine use of inoceramid bivalves in high-resolution paleoclimatology. To demonstrate the potential of this archive, we will exemplarily study how seasonal temperatures changed (1) during the Cretaceous hothouse, i.e. before, during and after OAE2 (Cenomanian/Turonian stage boundary; Münsterland Basin) and (2) during the Campanian stage (Hokkaido). (3) In addition, it will be analyzed if a difference exists between seasonal environmental variables reconstructed from shells of different rock types (Münsterland Basin). If sedimentation was orbitally forced, seasonal temperatures, primary productivity etc. should have differed between times of limestone and marl deposition. (4) Furthermore, the life history traits of selected inoceramid taxa will be determined including ontogenetic ages as well as the timing and rate of seasonal shell growth.