Laminated carbonates of the Rasthof Formation, deposited in the aftermath of the early Cryogenian low-latitude glaciation (Sturtian, 717–662 Ma), preserve abundant round tests of agglutinated microscopic eukaryotes. Previously, fossil tests were reported in two localities (Ongongo and Okaaru) from microbially laminated carbonates in the Rasthof Formation, which revealed a previous unexplored Cryogenian taphonomic window. In order to better understand the lateral variability in these microfossil assemblages, this work systematically examines fossil tests from two additional localities, South Ombepera and Ombepera, and compares their preservation in thinly and thickly laminated microbial laminites. Cap carbonates in South Ombepera and Ombepera contain abundant, hollow, spheroidal agglutinated tests (50 to 225 µm in diameter). Some of these tests exhibit slitlike or triangular apertures. In contrast, much larger, oval tests with a tapering end dominate the assemblages at Okaaru, whereas oval, laterally compressed and round structures with slits, visors, or central apertures are found at Ongongo. The thinly laminated microbial laminites from Ombepera, South Ombepera, and Okaaru also preserve rare agglutinated tubes attributed to fossils of early Foraminifera. At all four localities, the thinly laminated microbial laminites preserve more microfossils than thickly laminated microbial laminites although these two facies commonly interfinger and are interbedded. This difference shows that conditions present during formation of the thinly laminated microbial laminites favored the preservation of round agglutinators, perhaps during early burial, lithification, and fossilization of the test walls.

Paleoecological interactions among fossil microorganisms have garnered significant interest within the paleobotanical community; however, an understanding of the early diagenesis of associated plant material is of critical importance when assessing putative body fossils of fungi and bacteria. Structures preserved within permineralized petioles of the Carboniferous fern Botryopteris tridentata Felix (Scott) have been interpreted as the earliest remains of Actinobacteria found in association with vascular plants, but re-examination of the specimens indicates instead that these biomimetic structures (BMS) are authigenic carbonate minerals. Using spinning disk confocal microscopy, we generated monochromatic luminescence maps of BMS found within the phloem cells of Botryopteris. Luminescence was captured at wavelengths of 665 nm, consistent with an interpretation of these structures as disordered dolomites, an inference subsequently corroborated with energy-dispersive X-ray spectrometry (SEM-EDS). The presence of high-magnesium carbonates within Botryopteris is suggestive of an early anaerobic stage of plant tissue degradation characterized by metabolic activities of sulfate-reducing bacteria. Anaerobic biodegradation may also have been performed by chytridiomycetes, and we interpret larger (5–8 µm) unicells found within the specimens as fossils of chytrid zoosporangia. Understanding microbial contribution to the early diagenesis of plants preserved within calcium carbonate concretions (coal balls) is dependent upon both characterizing diversity of microbial communities within fossil plants, and elucidating the geomicrobiological parameters of mineralization. As such, this study underscores the necessity of integrating geomicrobiology with plant taphonomy in investigations of the microbial component of ancient ecosystems.

Chione elevata is a venerid bivalve common in modern molluscan assemblages and in the fossil record throughout the southeastern United States. Knowledge of its life span and growth rates can provide insights into paleoenvironmental and paleoecological conditions for a large number of fossil assemblages. We used isotope sclerochronology to decipher the accretionary record in modern shells of C. elevata. Sixty-three live specimens were collected from a soft-substrate intertidal flat near Wilmington, North Carolina. Aragonite samples drilled from the outer shell layer of three specimens were analyzed for oxygen isotope ratios (δ¹⁸O). Previous studies show that dark growth lines in other bivalve taxa from the same geographic area, such as Mercenaria mercenaria, correlated with summer growth cessation. A similar accretionary pattern does not exist in C. elevata. Dark growth lines in C. elevata shells appear randomly distributed. Their occurrence does not always correspond with maxima in δ¹⁸O values (winter growth cessation). Additionally, dark growth lines are not correlated with concentric ornaments on the surface of the shell. Instead, maxima in δ¹⁸O values correspond to indentations, or notches, on the surface of the shell. We characterize these concentric external notches as annual markers of winter growth cessation.

The sedimentary record reveals first-order changes in the locus of carbonate precipitation through time, documented in the decreasing abundance of carbonate precipitation on the seafloor. This pattern is most clearly recorded by the occurrence of seafloor carbonate crystal fans (bladed aragonite pseudomorphs neomorphosed to calcite or dolomite), which have a distinct temporal distribution, ubiquitous in Archean carbonate platforms, but declining through Proterozoic time and extremely rare in Phanerozoic basins. To understand better the potential influences on this pattern, we built a mathematical framework detailing the effects of organic matter delivery and microbial respiratory metabolisms on the carbonate chemistry of shallow sediments. Two nonunique end-member solutions emerge in which seafloor precipitation is favorable: enhanced anaerobic respiration of organic matter, and low organic matter delivery to the sediment-water interface. This analysis suggests that not all crystal fans reflect a unique set of circumstances; rather there may have been several different geobiological and sedimentary mechanisms that led to their deposition. We then applied this logical framework to better understand the petrogenesis of two distinct crystal fan occurrences—the Paleoproterozoic Beechey Formation, Northwest Territories, Canada, and the middle Ediacaran Rainstorm Member of the Johnnie Formation, Basin and Range, United States—using a combination of high-resolution petrography, micro X-ray fluorescence and wavelength dispersive spectroscopy, C isotopes, and sedimentary context to provide information on geobiological processes occurring at the sediment-water interface. Interestingly, both of these Proterozoic examples are associated with iron-rich secondary mineral assemblages, have elevated trace metal signatures, and sit within maximum flooding intervals, highlighting key commonalities in synsedimentary geobiological processes that led to seafloor carbonate precipitation.

Neoichnological experiments with vinegaroons (Arachnida: Thelyphonida: Thelyphonidae) were conducted to describe the trackway patterns, evaluate the preservation quality and potential of its trackways in different sediment textures and moisture conditions, and compare them to trackways found in the fossil record. Trackways were produced in nine experimentally controlled variations of sediment size (fine-, medium-, or coarse-grained sand) and moisture added to the sediment surface (0 mL, 5 mL, or 10 mL). Trackways were photographed and video recorded during trackway production, and cast in plaster. Individual tracks were oblong to linear, with the first and third foot on each side producing a track parallel to the direction of motion, and the second foot producing a track perpendicular to the direction of motion. Video evidence indicates that track associations form a triangular pattern with the track of the second foot furthest from the midline of the trackway, rather than a linear pattern as described for most other arthropod trackways. The morphology of vinegaroon trackways is indicative of hexapedal motion. Though similar to some fossil trackways attributed to eurypterids, vinegaroons are not good locomotion analogs for eurpyterids. No fossil trackway has been attributed to vinegaroons, so these trackways can serve as a model for assessment of fossil trackways. Trackway expression decreased as a function of increasing moisture content and grain size, with tracks becoming less oblong and more circular before ultimately becoming unexpressed on the surface. These trackways are more similar to the ichnogenus Hexapodichnus than to Lithographus. We propose a system to distinguish arthropod trackways based on the orientation of the triangular track series.

It is critical that the taphonomic processes by which taxa enter the fossil record be well documented and understood. This study focuses on the precision and accuracy of the fossil record of Ostracoda on San Salvador Island, Bahamas. This fauna has already been used to reconstruct climate change and sea-level fluctuations on San Salvador, but its taphonomy was not clearly understood. We test the accuracy of the record by examining correlations between rank abundance and taxonomic composition of sixteen living communities and death assemblages in seven lakes on the island. Additionally, we test the precision of this record by comparing the taxonomic composition and species abundances of sixteen death assemblages from each of the same seven lakes. In six out of seven of these lakes, the accuracy by which death assemblages record the taxonomic composition and rank-abundance distributions of living communities is high. In these same six lakes, the within-lake precision of the record is also high since death assemblages recovered from individual lakes are more similar to assemblages from the same lake than to any other lake. In the remaining water body tested, the accuracy and precision of the record exhibited wide variation at individual sampling sites that are related to its past use as a water resource for a nearby plantation, a steep depth gradient, and tidal fluctuations. This study demonstrates the high fidelity of the ostracode fossil record, but highlights the importance of site-specific taphonomic studies to understand physical and biological processes that may obscure this record.