Palaeoenvironmental changes during Pleistocene: An integrative approach of biotic and abiotic proxies
Creators: name: Dorador, Javier
name: Rodríguez-Tovar, Francisco J
name: Abrantes, Fátima
name: Rodrigues, Teresa
name: Cabrera-Ortiz, José F
name: Hodell, David A V
Publisher: name: Zenodo
Year: 2019

description: Pleistocene climate variations have been widely studied during the last decades due to their importance to understand how the orbital changes affected the ocean/atmosphere dynamic and the palaeoenvironmental conditions. Particularly, some time periods are of special interest, as the case of the Marine Isotope Stage (MIS) 19 as a potential analogue for the<br> Holocene. These palaeoenvironmental changes are usually studied from different disciplines, including biotic and abiotic proxies, as micropalaeontology, ichnology or geochemistry, among others. In the last years, ichnological approach has been proved as a very useful tool for sedimentary basin analysis, including palaeoenvironmental research,<br> providing information about variable environmental parameters (e.g., oxygenation, organic matter, sedimentation rate). The usefulness is even better when ichnological analysis is complemented with other independent proxy data in a multidisciplinary approach. Here we present the ichnological study of hemipelagic sediments deposited in the SW Iberian margin<br> from MIS 21 to MIS 18 (~ 850-750 ka), integrated with benthic foraminifera d18O and d13C, Total Organic Carbon (TOC) data and Alkenone concentration records. Seven ichnotaxa were identified (Chondrites, ?Nereites, Palaeophycus, Planolites, Thalassinoides, Thalassinoides-like and Zoophycos) and six ichnofabrics characterised (Mottled ichnofabric,<br> Planolites ichnofabric, Thalassinoides ichnofabric, Thalassinoides-like ichnofabric, Chondrites ichnofabric and Zoophycos ichnofabric). The ichnological features allow the differentiation of two different patterns: A) intervals characterized by dominant middle tier ichnofabrics (e.g., Thalassinoides ichnofabric and Thalassinoides-like ichnofabric) and an<br> intermediate degree of bioturbation and, B) intervals dominated by shallow tier ichnofabrics (i.e., Mottled ichnofabric and Planolites ichnofabric) showing a low degree of bioturbation with a local presence of high bioturbated parts characterised by deep tier ichnofabrics (i.e., Chondrites ichnofabric and Zoophycos ichnofabric). The distribution of both intervals concurs with the d18O and TOC variability, but also shows a higher correlation with those<br> proxies associated to primary production and CO content in bottom water. Ichnological features of pattern A are related with high or medium primary productivity periods and low bottom water CO content pointing high ventilated bottom water and allowing the development of complex ichnofabrics dominated by Thalassinoides or Thalassinoides-like.<br> On the other hand, sections where pattern B is identified are linked to intervals with relatively low primary productivity and O depleted bottom water, favouring the bioturbation by Chondrites or Zoophycos trace maker. These observations support the use of ichnology in multi proxy studies, refining interpretation of bottom ocean palaeoenvironmental conditions during Pleistocene in the SW Iberian margin.