A change from warm/humid to cold/dry climate conditions recorded in lower Barremian clay-dominated continental successions from the SE Iberian Chain (NE Spain)

Abstract

A combined facies and clay mineralogy analysis of the continental succession recorded in the lower part of the Blesa Formation (early Barremian, Oliete subbasin, NE Spain) allowed us to specify the palaeoclimatic and palaeoenvironmental conditions under which this sedimentary record originated. Six outcrops including clays, clays/marls and dm-thick interbedded palustrine-lacustrine limestone levels were logged and sampled for X-ray diffraction and optical and electron microscopy analysis. The lower levels consist of red clays with abundant ferruginous pisoids (1–5 mm in size) and macropisoids (>5 mm), whereas the intermediate and upper levels are ochre and violet clays/marls with few or no pisoids. The pisoids normally consist of a nucleus and a cortex made up of several layers. Some pisoids have a fragment of a previous pisoid acting as a nucleus, indicating local re-working processes. Both the nucleus and the cortex are formed by hematite, goethite, variable contents of kaolinite, and minor proportions of ilmenite. Their texture and mineralogy show an in-situ growth. Interbedded limestone beds within the clay- and clay/marl-dominated levels are formed by micrite, microsparite and sparite. These limestones are cemented by kaolinite and they also have pisoids, indicating the occurrence of edaphic processes. The red clays have the lowest calcite content and the highest hematite, anatase, diaspore, goethite and kaolinite content. By contrast, the ochre and violet clays/marls have higher illite content. Smectite is only detected in the ochre clays/marls. This mineral association is characteristic of lateritic palaeosols, formed under warm and humid conditions. Kaolinite and smectite textures indicate that they are authigenic, whereas illite may be of detrital origin. The upward decrease in kaolinite, hematite, anatase, diaspore and goethite content, along with the increase in quartz content and the presence of smectite and illite, reflect a change from warm and humid conditions to drier and colder conditions during the early Barremian in the studied area.