Interaction Between Animal Burrowing and Loess Cave Formation in the Chinese Loess Plateau

Although the interactions between biotic and geomorphic processes usually occur on small spatial and short temporal scales, many of the mechanisms remain to be investigated. This study provides the first direct evidence of the interaction between biotic burrowing and loess cave formation in the Chinese Loess Plateau (CLP). The study area is the Qingshui Valley in the western CLP, near Lanzhou. We surveyed the target site (with an area of ∼13,367 m2) four times from Jul 2019 to Dec 2020, using an unmanned aerial vehicle (UAV). High resolution UAV images enabled us to determine the temporal and spatial dynamics of biotic burrowing and loess caves. The results show that loess caves tended to develop down valley below collapses, while animal burrows were preferentially located upslope away from collapses. Despite the distinct “topographic niches” for both biotic and abiotic processes, we observed an interaction between the two processes in space when tracking their temporal dynamics. Three out of seven new loess caves were in the process of formation at typical “topographic niches” of animal burrows and there was a significantly high animal burrow density around these three caves before their initiation. These results indicate that the three caves were directly initiated from animal burrows and/or developed under the influence of biotic activities. Therefore, biotic burrowing promotes the spatial heterogeneity of loess cave distribution. We also found significant decreases in animal burrow density surrounding the newly-formed loess caves after their initiation. This may reflect a risk avoidance strategy of animal burrowing, which causes animals to avoid areas of recent mass movement (i.e., collapses and new caves). The formation and expansion of loess caves can dictate the distribution of active areas of biotic disturbance. Our results demonstrate a clear interaction between biotic burrowing and loess cave formation, and they emphasize the role of biological agents as a mechanism for the formation of loess caves, which enrich the understanding of searching fingerprints of life during landscape evolution.

High-resolution geophysical imaging of reptile burrows (San Salvador rock iguana, The Bahamas): implications for ichnology and conservation ecology

Neoichnological research of terrestrial tracemakers in coastal settings provides important palaeoenvironmental information about their context within the subaerial facies. Here we present the first geophysical dataset of reptile burrows in a carbonate substrate and use it to help visualize parts of the burrows of the Bahamian (San Salvador) rock iguana (Cyclura rileyi). High-resolution 800 MHz ground-penetrating radar (GPR) images within an enclosure on San Salvador Island were employed to discriminate between the electromagnetic signal response from subsurface anomalies related to air-dominated voids or live animals within burrows. The dielectric contrast between the carbonate substrate and open burrows was sufficient to identify the majority of 15-20-cm-wide subsurface extensions of the inclined tunnels in the upper 30-40 cm. Whereas limestone clasts induced some interference, it is possible to differentiate their high-amplitude diffractions from those produced by the iguana burrows. Our research indicates that GPR imaging is a viable, rapid, non-invasive method of visualizing animal burrows, with implications to neoichnology, paleoichnology, and conservation ecology of semi-fossorial species. Furthermore, the critically endangered status of Bahamian land iguanas, as well as ongoing threats from natural and introduced pressures, highlights the need for research into their ichnological record.

Exceptional sulfur and iron isotope enrichment in millimetre-sized, early Palaeozoic animal burrows

Pyrite-δ34S and -δ56Fe isotopes represent highly sensitive diagnostic paleoenvironmental proxies that express high variability at the bed (< 10 mm) scale that has so far defied explanation by a single formative process. This study reveals for the first time the paleoenvironmental context of exceptionally enriched pyrite-δ34S and -δ56Fe in bioturbated, storm-reworked mudstones of an early Ordovician storm-dominated delta (Tremadocian Beach Formation, Bell Island Group, Newfoundland). Very few studies provide insight into the low-temperature sulfur and iron cycling from bioturbated muddy settings for time periods prior to the evolution of deep soil horizons on land. Secondary ion mass spectroscopy (SIMS) analyses performed on Beach Formation muddy storm event beds reveal spatially distinct δ34S and δ56Fe values in: (a) tubular biogenic structures and trails (δ34S ~ +40‰; δ56Fe ~ −0.5‰), (b) silt-filled Planolites burrows (δ34S ~ +40‰; δ56Fe ~ +0.5 to + 2.1‰), and (c) non-bioturbated mudstone (δ34S ~ +35‰; δ56Fe ~ +0.5‰). δ34S values of well above + 40.0‰ indicate at least some pyrite precipitation in the presence of a 34S-depleted pore water sulfide reservoir, via closed system (Raleigh-type) fractionation. The preferential enrichment of 56Fe in Planolites burrows is best explained via microbially-driven liberation of Fe(II) from solid iron parent phases and precipitation from a depleted 54Fe dissolved Fe(II) reservoir. Rigorous sedimentological analysis represents a gateway to critically test the paleoenvironmental models describing the formation of a wide range of mudstones and elucidates the origins of variability in the global stable S and Fe isotope record.

Three-gene phylogeny of the genus Arthroderma: Basis for future taxonomic studies

Arthroderma is the most diverse genus among dermatophytes encompassing species occurring in soil, caves, animal burrows, clinical material and other environments. In this study, we collected ex-type, reference and authentic strains of all currently accepted Arthroderma species and generated sequences of three highly variable loci (ITS rDNA, β-tubulin, and translation elongation factor 1-α). The number of accepted species was expanded to 27. One novel species, A. melbournense (ex-type strain CCF 6162T = CBS 145858T), is described. This species was isolated from toenail dust collected by a podiatrist in Melbourne, during an epidemiological study of four geographical regions of Eastern Australia. Trichophyton terrestre, Chrysosporium magnisporum, and Chrysosporium oceanitis are transferred to Arthroderma. Typification is provided for T. terrestre that is not conspecific with any of the supposed biological species from the former T. terrestre complex, that is, A. insingulare, A. lenticulare and A. quadrifidum. A multi-gene phylogeny and reference sequences provided in this study should serve as a basis for future phylogenetic studies and facilitate species identification in practice. Lay abstract The genus Arthroderma encompasses geophilic dermatophyte species that infrequently cause human and animal superficial infections. Reference sequences from three genetic loci were generated for all currently accepted Arthroderma species and phylogeny was constructed. Several taxonomic novelties are introduced. The newly provided data will facilitate species identification and future taxonomic studies.

Plant Root Systems Preserved in the Permian Cedar Mesa Sandstone at Moki Dugway, Southeastern Utah

Rooted green plants represent the base of the food chain for most terrestrial ecosystems, but, compared to animal burrows, root systems are relatively rarely recognized in ancient sedimentary rocks. Plant roots that penetrate unconsolidated sand dunes, especially those containing not only quartz grains, but also abundant grains of calcite (CaCO) are commonly replaced by fine crystals of calcite (Klappa, 1980). These structures (known by geologists as rhizoliths from the Greek for “root rock”) are one form of calcite cemented soil and sediment called caliche. Caliche crystallizes well above the water table and its calcite crystals are tiny because of rapid evaporation of soil water. One source of the calcium (Ca) and carbonate (CO) ions necessary for making the calcite of caliche is falling dust, and another source is the dissolution of calcite grains already in the soil.