The Valanginian "cold snap" and its impact on terrestrial environments - insights from plant biomarkers, stable isotopes and spore-pollen assemblages

为了更好地了解早白垩纪气候变化对大陆环境和生态系统的影响，对陆地代用记录进行批判性评估至关重要。该项目利用来自两个不同研究地点的陆地植物生物标志物和孢子花粉记录，涵盖Valanginian碳同位素偏移（CIE），允许(1)解决响应气候冷却和相关湿度变化的植被模式发展；(2)获取低纬度和中纬度湿度分布变化对植物13C辨别的影响。从法国东南部Vocontian盆地连续150米的剖面将允许以高时间分辨率研究中纬度陆地气候演变和相关植被响应，并将与来自低纬度地点（摩洛哥Agadir-Essaouira盆地）的类似数据集进行详细比较。包括高分辨率化学地层学在内的综合地层学格架的建立将有助于将陆地记录与现有的海洋温度演化代用数据相结合。基于植物源生物标志物的δ13C特征，建立了与瓦兰吉尼期CIE相关的湿度变化定量模型。期望通过有机地球化学和孢粉学调查以及生物地球化学模拟等综合方法来实现这些目标。

A critical assessment of terrestrial proxy records is essential to better understand the impact of early Cretaceous climatic variability on continental environments and ecosystems. The proposed project uses land plant biomarkers and spore-pollen records from two different study sites covering the Valanginian carbon isotope excursion (CIE) that allow (1) to address the development of vegetation patterns in response to climatic cooling and associated humidity changes and (2) to access the effects of changes in low- and mid-latitude moisture distribution on plant 13C discrimination. A continuous 150 m section from the Vocontian Basin, SE France will allow to study mid-latitude terrestrial climate evolution and the associated vegetation response at a high time resolution and will be compared in detail with a similar data-set from a low-latitude site (Agadir-Essaouira Basin, Morocco). The establishment of an integrated stratigraphic framework including high-resolution chemostratigraphy will facilitate the integration of the terrestrial records with existing marinederived proxy data on temperature evolution. Based on the δ13C signature of plant-derived biomarkers, a quantitative model of the humidity changes associated with the Valanginian CIE will be established. The achievement of these goals is expected from a combined approach including organic geochemical and palynological investigations as well as biogeochemical modelling.