Macro to micro aspects of the plant preservation in the Early Devonian Rhynie cherts, Aberdeenshire, Scotland

Abstract

Material excavated from a trench dug to expose the Rhynie Cherts Unit of the Dryden Flags Formation included blocks of Rhynie chert up to 50 cm thick and comprising the full thickness of plant-bearing chert beds. These blocks, and others collected as float, display a variety of macro-textures typical of silicification at the terrestrial surface and in shallow water. On sandy terrestrial surfaces, autochthonous and allochthonous plant debris and plant rhizomes are well preserved, but aerial axes generally decayed prior to silicification. In shallow water, clonal plants, particularly Rhynia, are preserved with aerial axes in growth position, supported by microbial mats and meshworks. Preservation of such delicate fabrics required the creation of a load-bearing framework early in the silicification process, to prevent crushing during early burial.On the microscale, plant taphonomy reveals characteristic features due to plant decay prior to silicification in both wet and dry conditions, and also during the silicification process. Silicification of plants was frequently very rapid, preserving delicate transient features such as spore germination and ejection of sperm cells from antheridia. In situations where plant tissue continued to decay during silicification, the process was slower.

Fungi and fungal interactions in the Rhynie chert: a review of the evidence, with the description ofPerexiflasca taylorianagen. et sp. nov.†

“…[134][135][136]). It is becoming increasingly clear that the Rhynie chert comprises different (micro-)facies characterized by communities of organisms that reflect once differing types of (micro-)habitats [30]. Drill core data suggest that there are greater than 50 fossiliferous chert layers [27,30,137], and the number of distinctive environments preserved in these layers is probably even larger.…”

A review of active hot-spring analogues of Rhynie: environments, habitats and ecosystems

“…At comparable accretion rates the 10-20 cm thick chert beds commonly recorded at Rhynie (e.g. [43][44][45]) would have been created on yearly to decadal timescales rather than days or weeks. [46].…”

“…This widespread cementation represents silica precipitation in the shallow subsurface as alkali-chloride geothermal fluid percolated laterally and vertically through porous sediments (e.g. [45]). Hence, the Rhynie deep subsurface, shallow subsurface and sinter depositional areas of the surface environment are dominated by indicators of alkali-chloride geothermal fluids.…”

Testate Amoebae in the 407-Million-Year-Old Rhynie Chert

“…Modern arcellinids occur in a range of terrestrial, freshwater, and brackish habitats. The Rhynie chert is known to host different microenvironments ranging from brackish and freshwater to fully terrestrial [43]. Our analysis of the associated biota (Figure 3), which includes cyanobacterial sheaths, the crustacean Lepidocaris, the charophycean alga Palaeonitella, and a recently described zoosporic fungal association [12], indicates a shallow aquatic environment, proximal to fully terrestrial conditions, as indicated by the vascular plant Asteroxylon.…”

“…Plants grew in thin soils on sandy substrates on a sinter apron crossed by streams. Silicification ensued from geothermal outwash of alkali-chloride hot springs at some distance from vents and probably at low temperature (< 40-50 C) [43]. Opinions on the salinity of the system vary, with arguments for both low ($<1 wt.% NaCl) [52] and high values [53].…”