Departamento de Estratigrafía y Paleontología, Universidad de Granada, Avd. Fuentenueva s/n, 18002, Granada, Spain.
Department of Earth Sciences, Royal Holloway University of London, Egham, TW20 0EX, Surrey, UK.
Sci Rep. 2021 Feb 18;11(1):4198. doi: 10.1038/s41598-021-83820-x.
Oceanic gateways have modulated ocean circulation and have influenced climatic variations throughout the Earth´s history. During the late Miocene (7.8-7.35 Ma), the Atlantic Ocean and the Mediterranean Sea were connected through the Rifian Corridor (Morocco). This gateway is one of the few examples of deep ancient seaways with a semi-continuous sedimentary record. Deposits comprise turbidites intercalated between deep-sea mudstone (i.e., hemipelagites and drift deposits), channelized sandstone contourite facies, and shallow marine sandstone. Herein an ichnological analysis was conducted in these upper Miocene sediments to improve characterisation of palaeoenvironmental conditions. In addition, ichnofacies were analysed to elucidate how bottom currents control ichnofacies distribution and can modify their attributes. Turbidite deposits are typified by vertical trace fossils (i.e., Ophiomorpha), conforming the Ophiomorpha rudis ichnosubfacies. Contouritic sandstone exhibits high density and low diversity trace-fossil assemblage, with predominant Macaronichnus and Scolicia, resembling a proximal expression of the Cruziana ichnofacies. Shallow marine environments are dominated by vertical trace fossils (e.g., Conichnus, Ophiomorpha, Skolithos), allowing an assignation to the Skolithos ichnofacies. This study reveals for the first time a variability in ichnofacies attributes and distribution at the Rifian Corridor, associated with turbidites, contourite and shallow marine sediments. Hydrodynamic energy reveals as the major factor controlling trace maker communities in the studied seaway. Highly energetic conditions typical of shallower settings are present in deeper-water environments (i.e., slope), contributing to ichnodiversity impoverishment in ichnofacies.
大洋门户调节了海洋环流，并影响了地球历史上的气候变化。在中新世晚期（780-735 万年前），大西洋和地中海通过里菲安海峡（摩洛哥）相连。这个门户是少数几个具有半连续沉积记录的深海古代海道之一。沉积物包括深海泥岩（即半深海泥和漂移沉积物）之间的浊积岩，以及水道砂岩等浅海砂岩。本文对这些上新世沉积物进行了生物地层学分析，以改善古环境条件的特征。此外，还对生物地层相进行了分析，以阐明底流如何控制生物地层相的分布，并能改变其属性。浊积岩沉积物的特征是垂直痕迹化石（如 Ophiomorpha），符合 Ophiomorpha rudis 遗迹亚相。等深积砂岩表现出高密度和低多样性的痕迹化石组合，以 Macaronichnus 和 Scolicia 为主，类似于 Cruziana 遗迹相的近源表达。浅海环境以垂直痕迹化石（如 Conichnus、Ophiomorpha、Skolithos）为主，可归入 Skolithos 遗迹相。本研究首次揭示了里菲安海峡生物地层相属性和分布的变化，与浊积岩、等深积砂岩和浅海沉积物有关。水动力能量是控制研究海域迹动物群落的主要因素。在较深的水域（如斜坡）存在的较浅环境的高能量条件，导致生物地层相中的生物多样性贫化。
