Cenozoic vegetation change in Western Siberia and northeastern Russia is quantified based on the analysis of diversity of plant functional types (PFTs). Carpofloras (148 total) compiled from published sources are assigned to a total of nine time slices spanning the period from the middle Eocene to the late Pliocene. Comparisons among four defined key regions allow study of spatial diversity gradients and their evolution. Our novel PFT classification scheme, designed for use in biome modeling, comprises 26 herbaceous to arboreal PFTs based on physiognomic characters and bioclimatic tolerances of plants, completed by an aquatic PFT. Using multivariate statistics, localities with similar PFT spectra are grouped and interpreted in terms of biomes. The results are visualized on paleovegetation maps and in PFT diversity records documenting vegetation evolution by key region. In northeastern Russia, mixed and conifer forest biomes existed during the Neogene. Diversity spectra indicate that even in the late Neogene, warm and humid conditions prevailed in this region, probably related to coeval intensification of the East Asian monsoon system. In Western Siberia, mesophytic forests with higher proportions of broadleaved evergreens dominated during the earlier Paleogene. Subsequent vegetation change is mainly expressed by a steadily increasing diversity of herbaceous PFTs. In the southern part of Western Siberia, distinct opening of the vegetation occurred in the late Miocene, connected to drying. The coeval declining trend of thermophilous PFTs in the north coincides with intensified cooling of the high latitudes.

Conodonts and scolecodonts are common Paleozoic microfossils that are often used to determine the geothermometry of Paleozoic sequences. The two fossils, which can be difficult morphologically to distinguish one from the other, undergo a different thermal alteration pathway. In this study, Fourier transform infrared (FTIR) spectroscopy of scolecodont and conodont microfossils from the Woodford Shale of southern Oklahoma, United States, confirmed they have different chemical compositions. Infrared (IR) spectra acquired from conodonts show a predominance of an inorganic carbonated hydroxylapatite (CO₃OHAp) with a minor organic composition of aliphatic hydrocarbon, containing carbonyl substituent functional groups. In contrast, IR spectra acquired from scolecodonts show no inorganic mineralogy but instead confirm that these microfossils are composed of organic material consisting of an aliphatic and aromatic hydrocarbon network with ether linkages and carbonyl substituent functional groups. These data reveal that scolecodont elements can easily be distinguished from conodont elements with FTIR microspectroscopy due to their different chemical compositions. This study provides future fossil workers with a viable method to independently identify enigmatic toothlike microfossils that cannot confidently be assigned to either scolecodont or conodont groups by morphology alone.

Modern to Pleistocene Amiantis purpurata shells collected in Bahía San Antonio (Patagonia, Argentina) were studied by X-ray diffraction (XRD), optical and electron microscopy, electron microprobe analyses, and microindentation, in order to characterize early diagenetic changes and mechanical resistance. The sole crystalline phase is twinned aragonite showing pseudohexagonal symmetry. The regularity of the crystallographic texture decreases in older samples, but average crystallite size does not increase. The microstructure, which is dominantly crossed lamellar, is progressively replaced by a more randomly oriented grain aggregate. Compositional profiles across the shell show gradients in Sr, Na, S, and Cl, whereas Mg and P are more evenly distributed. Each shell layer has a distinct chemical signature. A marked decrease in the concentration of all of these elements, along with flattening of profiles, is evident as age increases. Vickers microhardness is lowest in modern specimens, showing at the same time the least chipped regions; older shells become harder and more fragile. All of these changes are attributed to postdepositional modifications by dissolution-recrystallization processes mediated by a thin film of water in a vadose environment. Microstructural adjustments are more sluggish than chemical modifications produced by diagenetic processes, whereas microhardness rapidly reaches high values, probably due to the early degradation of organic compounds from the shell. Our study shows that aragonitic shells that retain their primary mineralogical composition have undergone subtle chemical and microstructural changes. A very small amount of calcite was produced during grinding for XRD. Care should therefore be taken when seeking calcite as evidence of diagenetic changes.

Early diagenetic chert nodules and beds in the upper Mesoproterozoic Angmaat (formerly Society Cliffs) Formation, Baffin and Bylot islands, preserve microfossils and primary petrofabrics that record microbial mat deposition and lithification across a range of peritidal carbonate environments. Five distinct microfossil assemblages document the distribution of mat-building and mat-dwelling populations across a gradient from restricted, frequently exposed flats to more persistently subaqueous environments. Mats built primarily by thin filamentous or coccoidal cyanobacteria give way to a series of more robust forms that show increasing assemblage diversity with decreasing evidence of subaerial exposure. Distinct fabric elements are associated with each microbial assemblage, and aspects of these petrofabrics are recognizably preserved within unsilicified carbonate in the same beds. These include some features that are distinctly geologic in nature (e.g., seafloor cements) and others that reflect microbial growth and decomposition (e.g., tufted microbialites). A particularly distinctive, micronodular fabric is here interpreted as carbonate infilling of primary voids within microbial mat structures. Such structures mark the co-occurrence of cyanobacterial photosynthesis that produced oxygen gas, filamentous mat builders that imparted the coherence necessary to trap gas bubbles, elevated carbonate saturation required to preserve void fabrics via penecontemporaneous cementation, and a relative paucity of detrital sediment that would have inhibited mat growth. Petrofabrics preserved in Angmaat samples are widespread in upper Paleoproterozoic and Mesoproterozoic carbonate successions but are rare thereafter, perhaps recording, at least in part, the declining carbonate saturation state of seawater. Covariation of microfossil assemblages with petrofabrics in both silicified and unsilicified portions of carbonate beds supports hypotheses that link stromatolite microstructure to the composition and diversity of mat communities.

The Upper Triassic Sonsela Member of the Chinle Formation is an alluvial succession containing interbedded sandstone and pedogenically modified mudstone. Despite preservation of silicified logs within channel sandstone beds, the Sonsela plant ecosystem is less understood than other intervals due to decreased preservation of nonconifer plant taxa. Sonsela paleosols and rhizoliths are evaluated using macromorphology, micromorphology, and geochemistry to determine the spatial distribution of paleosol characteristics and plant sizes and densities across the study area. Three pedotypes identified within the Sonsela are classified as Inceptisols and Vertisols that exhibit fining of matrix textures (from clayey siltstone to claystone) and reduced drainage with distance from the paleochannel. Overall, Sonsela paleosols are immature, suggesting that the Sonsela fluvial system experienced high rates of lateral migration and cannibalization of overbank sediments in a low-subsidence regime. Rhizohalos within the Sonsela Member are likely diagenetic and commonly include silicified roots (silica root petrifactions). Silicified roots provide information on root size and density that is not commonly afforded by other rhizolith types. Diagenetic rhizohalo diameters may be controlled by paleosol matrix textures within the Sonsela Member. Rhizolith characteristics suggest that channel-proximal paleosols contained only small-stature plants while distal floodplain paleosols may have hosted both small-stature and arborescent plants. Paleosols within the Sonsela Member do not contain rhizoliths whose size or abundance are reflective of a dense coniferous forest. Floodplain plants were commonly small of stature and immature, unable to evolve into more mature communities due to high rates of floodplain cannibalization during fluvial migration.