The biota and palaeoenvironments of the Windyfield chert, early Devonian, Rhynie, Scotland
The Windyfield chert is located 700 meters NE of the original Rhynie chert locality at Rhynie, Aberdeenshire, and similarly represents a fossil sinter containing an abundant, diverse, and remarkably well-preserved biota. Originally identified by concentrations of surface float material, a drilling and trenching programme of the area in 1997 revealed a chert ‘pod’ in situ interbedded with hydrothermally altered fluvio-lacustrine sediments. This material has allowed further insights into the nature of the palaeoenvironments and palaeoecology of the Rhynie area during the Early Devonian. Chert morphotypes identified from float blocks and trench material range from laterally discontinuous tabular beds to lenticular pods displaying massive, nodular, lenticular, laminated and brecciated textures. A suite of floral and faunal associations, when combined with distinctive macro and microscopic chert textures, have been used to interpret depositional conditions. These indicate a suite of palaeoenvironments related to deposition at the hotter and cooler ends of a thermal gradient. Palaeoenvironments ranged from terrestrial laminated, brecciated and vegetated sinter sheets to low temperature pools and marginal aquatic settings. The flora comprises six higher land plant species, nematophytes, charophytes, various fungi and probable cyanobacteria. Anthropods include branchiopods, euthycarcinoids, trigonotarbid arachnids, centipedes and enigmatic myriapods. Aquatic elements of the biota probably represent normal freshwater organisms. New faunal elements described here include two trigonotarbids, two centipedes, and the first eoarthropleurids known from the area. The first branchipod nauplii from the cherts are described. The arthropod Leverhulmia is here interpreted as a hexapod of uncertain affinities. Comparisons are made with the Windyfield biota and that of other near contemporary assemblages. Analogues in modern epithermal systems for cherts displaying aquatic textures and biota are examined.