Chapter 5 - Palygorskite Clays in Marine Sediments: Records of Extreme Climate

Abstract

The distribution of palygorskite clay (comprising the fibrous clay minerals palygorskite and sepiolite) in marine sediments is extremely inhomogeneous, both stratigraphically and spatially. Palygorskite minerals are typically only present in trace amounts but sporadically can even make up the bulk of a sediment. Oceanic palygorskite clays commonly occur in oceanic deep-sea deposits off the palaeoslope break of low-latitude continents. They are particularly abundant and pure in some deep-sea sediments that accumulated slowly in a belt about 30° North, as well as South of the middle Cretaceous to lower Eocene equator, approximately 100 to 50 million years ago. In some deposits, palygorskite clay was formed on adjacent continents and was subsequently transported to the deposition site. However, microstructural and mineralogical evidences suggest that the purest deposits were formed in situ on the seafloor in the case of the middle Cretaceous to lower Eocene. Middle Cretaceous to early Eocene oceanic circulation patterns were remarkably different from today. Warm, saline waters were present on the seafloor during this long-lasting, extreme greenhouse period. The known abundance peaks of palygorskite clays correlate with the time intervals of such warm and saline deep-water circulation during the Cretaceous and Palaeogene. The physical and chemical conditions of these saline bottom waters stimulated the authigenic formation of palygorskite clay on the deep seafloor. Thus, the occurrence of palygorskite clay in the deep-sea realm may be used as a proxy of the presence of Warm Saline Bottom Water (WSBW) and help to reconstruct palaeoceanographic environments.