Calcareous nannofossils, palynomorphs and benthic foraminifera of section L´Arboudeysse

To better understand the linkage between climate and ocean circulation under greenhouse conditions we have studied calcareous nannofossils, palynomorphs and benthic foraminifera from the Early Albian Oceanic Anoxic Event 1b black shale (OAE 1b) in the Vocontian Basin (SE France). We propose that monsoonal activity resulting from precessional forcing and modulated by eccentricity-driven temperature changes represents the driving factor of OAE 1b formation in low latitudes. With the onset of OAE 1b, increasingly warm and humid conditions, stronger winds and enhanced terrestrial input led to higher surface water productivity. Therefore, increased productivity is an important factor for OAE 1b formation in the Vocontian Basin. However, monsoonally forced productivity changes are a regional climate signal only. The supraregional occurrence of the OAE 1b is probably due to a reduction of deep water formation in the low latitudes under extremely warm and humid conditions, leading to enhanced preservation of organic matter.为深入厘清温室气候背景下气候与海洋环流之间的关联，我们针对法国东南部沃康松盆地（Vocontian Basin）早阿尔布期大洋缺氧事件1b（OAE 1b）黑色页岩中的钙质超微化石（calcareous nannofossils）、孢粉型化石（palynomorphs）及底栖有孔虫（benthic foraminifera）展开了系统研究。本研究提出，由岁差驱动、并受偏心率调控的温度变化所调制的季风活动，是低纬度地区大洋缺氧事件1b形成的核心驱动因素。随着大洋缺氧事件1b的发育，区域内逐步呈现气候暖湿化、风力增强以及陆源输入提升的特征，进而推动表层水体生产力显著升高。因此，生产力提升是沃康松盆地内大洋缺氧事件1b形成的关键影响因素之一。不过，季风驱动的生产力变化仅为区域性气候信号，大洋缺氧事件1b的跨区域发育则可能源于极端暖湿条件下低纬度地区深水形成作用的减弱，进而使得有机质的保存效率大幅提升。