Lower and middle Jurassic woods of the Cleveland Basin (North Yorkshire), England

Abstract

Allochthonous Lower and Middle Jurassic (Pliensbachian–Bathonian) permineralized and charcoalified woods from the Cleveland Basin (North Yorkshire, England) are assigned to five genera of gymnospermous wood (Cupressinoxylon spp., Taxodioxylon spp., Cedroxylon spp., XenoxylonAraucarioxylon) and two species (Xenoxylon phyllocladoidesAraucarioxylon lindlei). Cell structure is commonly well preserved, particularly in calcified and charcoalified samples, and several features of the growth rings have palaeoclimatological significance. These include distinct growth rings, commonly narrow latewood, low to moderate annual sensitivity and mean sensitivity values, and presence of false rings. Overall, these characteristics reflect fairly consistent growth, both during the growing season and from year to year. Temporally, there is a transition towards narrower rings of more variable width, proportionally wider latewood, and more abundant false rings in Bathonian woods. Water supply is interpreted as the primary limiting control on growth and was probably more restricted in the Bathonian. This is suggested to be a consequence of relatively low sea‐level and, more importantly, a genuinely drier climate at this time, manifested as an accentuated annual dry season. In all, the increase in seasonality during the Early and Mid Jurassic in North Yorkshire is compatible with the effects of a developing Mediterranean‐type climate.