Deep time biogeomorphology: the coevolution of life and sediments

Amongst all the disciplines in Earth Sciences, paleontology and sedimentary geology share a particularly striking and complicated frontier. On the one hand, some of the topics that they encompass are apparently separated by huge gulfs in methods and expertise: multiple degrees of separation need to be counted to get from, say, molecular phylogeny to sediment diagenesis, or paleophysiology to sequence stratigraphy. Yet there are arguably further areas where the boundary between the subjects is far more porous, consisting of sub-disciplines that refuse to be pigeon-holed and instead demand consensus between paleontologists and sedimentary geologists. This hazy border zone is the natural territory of PALAIOS, the remit of which is to emphasize ‘‘the impact of life on Earth’s history as recorded in the paleontological and sedimentological records’’, and which has previously published seminal advances in topics such as ichnology, taphonomy, and carbonate sedimentology. Recognizing this, this first of two thematic sets in the journal, which seek to explore how the sedimentary rock record has chronicled ancient life and sediment interactions, might seem unnecessary. Yet what makes these collected papers distinct is that they defy classification within any particular subdiscipline: rather these are either ‘paleontological’ papers that pay additional attention to sedimentological context or ‘sedimentological’ papers that emphasize the importance of life in sedimentary environments. In each instance they demonstrate the potential to understand much more about ancient Earth when the procedures of the two disciplines are undertaken in unison, and hopefully showcase avenues of exploration to inspire further research in this vein. The collected papers demonstrate the intrinsic links between fossils and the strata that host them, with a particular emphasis on siliciclastic strata where such linkages have traditionally and oftentimes been overlooked. Together they show how investigation of these connections can reveal high-definition records of feedback between organisms and their physical environments at the time of deposition and illustrate case studies of sedimentary-stratigraphic characteristics that developed in synchronicity with the evolving biosphere at Earth’s surface (see Davies et al. 2020). The papers are necessarily selective and cannot encompass the entirety of the diverse life-sediment interactions that have existed throughout geologic history, but they serve to highlight the types of observations that can be employed and the detailed interpretations that can be made from them. This first thematic set has a loose running theme of ‘plants’, documenting examples of vegetation-environment interactions recorded in the rock record from the Mississippian to the Pliocene, and the forthcoming thematic set will follow a similar path for ‘animals’. These two kingdoms dominate the macroscopic biosphere that defines the Phanerozoic and have stamped their mark on the rock record over the last half a billion years (though this is not to understate the importance of microbiota, which have had such a clear impact on the sedimentary record (e.g., Riding 2000) that they may warrant a similar thematic set in the future).