Soft-Tissue, Rare Earth Element, and Molecular Analyses of Dreadnoughtus schrani, an Exceptionally Complete Titanosaur from Argentina.

Evidence that organic material preserves in deep time (>1 Ma) has been reported using a wide variety of analytical techniques. However, the comprehensive geochemical data that could aid in building robust hypotheses for how soft-tissues persist over millions of years are lacking from most paleomolecular reports. Here, we analyze the molecular preservation and taphonomic history of the Dreadnougtus schrani holotype (MPM-PV 1156) at both macroscopic and microscopic levels. We review the stratigraphy, depositional setting, and physical taphonomy of the D. schrani skeletal assemblage, and extensively characterize the preservation and taphonomic history of the humerus at a micro-scale via: (1) histological analysis (structural integrity) and X-ray diffraction (exogenous mineral content); (2) laser ablation-inductively coupled plasma mass spectrometry (analyses of rare earth element content throughout cortex); (3) demineralization and optical microscopy (soft-tissue microstructures); (4) in situ and in-solution immunological assays (presence of endogenous protein). Our data show the D. schrani holotype preserves soft-tissue microstructures and remnants of endogenous bone protein. Further, it was exposed to LREE-enriched groundwaters and weakly-oxidizing conditions after burial, but experienced negligible further chemical alteration after early-diagenetic fossilization. These findings support previous hypotheses that fossils that display low trace element uptake are favorable targets for paleomolecular analyses.

Cadmium isotopes in Bahamas platform carbonates: A base for reconstruction of past surface water bioproductivity and their link with chromium isotopes.

The distribution of cadmium (Cd) within the oceans strongly suggests that it is used as a nutrient by marine phytoplankton. Biologically induced removal of Cd from modern surface waters is accompanied by an isotopic fractionation leaving surface-waters enriched in isotopically heavy Cd. This first study focusses on tying the Cd isotopic record preserved in modern shallow platform carbonates of the Great Bahama Bank (GBB) to conditions in the upper water column, and provides a base for future studies aiming at reconstructing past bioproductivity levels in ancient ocean/basin surface waters. In addition, we compare δ114Cd values with previously published chromium (Cr) isotope values and link signals of bioproductivity with redox conditions in the surface waters. The GBB core samples yield [Cd] (21-188 µg/kg), which increases with depth alongside changes in carbonate mineralogy related to sediment supply and diagenesis. The δ114Cd values of these carbonates are mainly positively fractionated with an average of 0.11‰ ± 0.17 (2σ; n = 17) relative to the NIST 3108 reference standard. Unlike previously observed for Cr isotopes, there is no control of δ114Cd values by relative abundances of the carbonate polymorphs aragonite and calcite in the studied profile. Likewise, δ114Cd values are not correlated to major and trace element (e.g. Ca, Mg, Mn and Sr) contents. We postulate that the burial and diagenetic processes of carbonate cannot modify the Cd isotope signals. Using the experimental fractionation factor for Cd into calcite (-0.45‰), calculated seawater δ114Cd of +0.56 ± 0.17‰ is in agreement with values for modern North Atlantic Surface Seawater. This study's results suggest that δ114Cd values in carbonates are a reliable tool for reconstruction of bioproductivity levels in past surface seawaters, and open new possibilities in combination with Cr isotopes to link these with past ocean redox.

Distribution and fractionation of rare earth elements in sediments and mangrove soil profiles across an estuarine gradient.

Many hypotheses have been raised about the controls of the distribution and fractionation of the rare earth elements (REE) in coastal ecosystems. Here, REE were measured in estuarine sediments and in six mangrove soil profiles along the estuarine salinity gradient of the Jaguaripe estuary, northeastern Brazil. The aim of this study was to evaluate the fractionation, distribution, remobilization, and possible sources of these elements. The ΣREE and Y in oxic estuarine sediments ranged from 202 to 220 mg kg-1 and from 12 to 15 mg kg-1, respectively. The normalized abundances to the Post Archean Australian Shale (PAAS) showed that light REE (LREE; La, Ce, Pr, and Nd) were consistently enriched over heavy REE (HREE; Er, Tm, Yb, and Lu). Among the REE, only LREE showed significant correlation with Al (r = 0.85) and Fe (r = 0.96) indicating that Al and Fe oxy-hydroxides are the main host phases of the LREE in estuarine sediments. The average ΣREE for mangrove soils throughout the salinity gradient ranged from 161 ± 18 mg kg-1 (lower estuary) to 183 ± 16 mg kg-1 (upper estuary). Al-normalized Mn and Fe concentrations showed small peaks down-core, indicating diagenetic remobilization. Vertical REE profiles have shown that post-deposition processes might contribute to the patterns in the abundances of the ΣREE and their fractionation at the surface and subsurface mangrove soils. Below the top 15 cm, diagenetic alteration after burial is not leading to substantial variation in the LREE/HREE profiles. The coincidence of peaks in individual REE/Al down core along with Fe and Mn peaks reflects the participation of the REE in early diagenesis. The REE abundances observed here corroborate to the characterization of the Jaguaripe estuary as a pristine system and can be used as a background for the region.

Diagenetic production, accumulation and sediment-water exchanges of methylmercury in contrasted sediment facies of Lake Titicaca (Bolivia).

Monomethylmercury (MMHg) concentrations in aquatic biota from Lake Titicaca are elevated although the mercury (Hg) contamination level of the lake is low. The contribution of sediments to the lake MMHg pool remained however unclear. In this work, seven cores representative of the contrasted sediments and aquatic ecotopes of Lake Titicaca were sliced and analyzed for Hg and redox-sensitive elements (Mn, Fe, N and S) speciation in pore-water (PW) and sediment to document early diagenetic processes responsible for MMHg production and accumulation in PW during organic matter (OM) oxidation. The highest MMHg concentrations (up to 12.2 ng L-1 and 90% of THg) were found in subsurface PWs of the carbonate-rich sediments which cover 75% of the small basin and 20% of the large one. In other sediment facies, the larger content of OM restricted MMHg production and accumulation in PW by sequestering Hg in the solid phase and potentially also by decreasing its bioavailability in the PW. Diagenetically reduced S and Fe played a dual role either favoring or restricting the availability of Hg for biomethylation. The calculation of theoretical diffusive fluxes suggests that Lake Titicaca bottom sediments are a net source of MMHg, accounting for more than one third of the daily MMHg accumulated in the water column of the Lago Menor. We suggest that in the context of rising anthropogenic pressure, the enhancement of eutrophication in high altitude Altiplano lakes may increase these MMHg effluxes into the water column and favor its accumulation in water and biota.

Formation and Preservation of Microbial Palisade Fabric in Silica Deposits from El Tatio, Chile.

Palisade fabric is a ubiquitous texture of silica sinter found in low temperature (<40°C) regimes of hot spring environments, and it is formed when populations of filamentous microorganisms act as templates for silica polymerization. Although it is known that postdepositional processes such as biological degradation and dewatering can strongly affect preservation of these fabrics, the impact of extreme aridity has so far not been studied in detail. Here, we report a detailed analysis of recently silicified palisade fabrics from a geyser in El Tatio, Chile, tracing the progressive degradation of microorganisms within the silica matrix. This is complemented by heating experiments of natural sinter samples to assess the role of diagenesis. Sheathed cyanobacteria, identified as Leptolyngbya sp., were found to be incorporated into silica sinter by irregular cycles of wetting, evaporation, and mineral precipitation. Transmission electron microscopy analyses revealed that nanometer-sized silica particles are filling the pore space within individual cyanobacterial sheaths, giving rise to their structural rigidity to sustain a palisade fabric framework. Diagenesis experiments further show that the sheaths of the filaments are preferentially preserved relative to the trichomes, and that the amount of water present within the sinter is an important factor for overall preservation during burial. This study confirms that palisade fabrics are efficiently generated in a highly evaporative geothermal field, and that these biosignatures can be most effectively preserved under dry diagenetic conditions.

The impact of burial period on compact bone microstructure: Histological analysis of matrix loss and cell integrity in human bones exhumed from tropical soil.

Human bone histological analysis is a useful tool to assess post mortem diagenesis and to predict successful nuclear DNA typing of forensic material. This study is part of a series of studies developed by the authors intended to improve the understanding of post mortem diagenesis and to develop applications for DNA analysis of skeletal species from tropical soils, in order to optimize genetic and anthropological protocols. The aim of this study was to analyze the impact of burial period on the integrity of exhumed compact bone microstructure from tropical climate. In fragments of exhumed human femora from 39 individuals from the same cemetery (exhumed group) and 5 fresh femora from routine autopsies (control group), sections stained by hematoxylin-eosin were analyzed in order to measure bone microstructural integrity. We found that bone integrity index in exhumed group was negatively influenced by the period of burial (r = -0.37, p < 0.05) and highly significantly decreased (p < 0.0001) in comparison to control group. The period of burial and nitric acid decalcification time was positively correlated (r = 0.51; p < 0.01), leading to imply a bone petrification process during inhumation. Exhumed group showed higher level of matrix bone loss (p < 0.001), as expected, and 87% of cases analyzed were "tunneled" as described by Hackett. Bone integrity index and bone matrix tend to decrease in bones buried in tropical soil between 8-14 years of inhumation. This period is short if we consider cases in which there are preserved bones interred for longer periods in other environments. These data must be considered in cases where genetic identification of exhumed skeletons from tropical environment is required. The diagenesis in these bones and the variations of results found are discussed, clarifying some challenges for forensic laboratories, especially in DNA analysis.

Nutrient regeneration susceptibility under contrasting sedimentary conditions from the Rio de Janeiro coast, Brazil.

Dissolved silicate (DSi), NH4(+), NO3(-) and PO4(3-) susceptibility to be exchanged between sediment pore waters and overlying waters was evaluated in Jurujuba Sound (JS station) and Coroa Grande Sound (CGS station), southeastern Brazil. Sedimentary elemental (C, N and P) and isotopic (δ(13)C and δ(15)N) compositions evidenced stronger anthropogenic fertilization in JS station. Net NO3(-) influxes from overlying waters occurred, which was two orders of magnitude higher under the more fertilized condition. This condition resulted in 6-13-times higher net effluxes of NH4(+), DSi and PO4(3-) to overlying waters. Vertical alternation between production and consumption processes in pore waters contributed for a more limited regeneration in CGS station. This was associated with diagenetic responses to sedimentary grain size variability in deeper layers and biological disturbance in upper layers. Nearly continuous production of NH4(+), DSi and PO4(3-) in pore waters implied in intensified susceptibility to remobilization under the eutrophic condition of JS station.

Characteristics, distribution and diagenetic stages of chert in the La Silla Formation (Lower Ordovician), Argentine Precordillera

The late Cambrian - late Tremadocian La Silla Formation is a carbonate unit of the eastern Precordillera in Argentina whose facies indicate a shallow platform environment. Until this moment, there were no studies that referred to the diagenetic evolution of these rocks. The present study involves the characteristics and distribution of the silicification that affects this unit and determines its different diagenetic stages through petrographic (with cathodoluminescence support) and stratigraphic analyses. An early diagenetic chert, in a stage previous to the compactation, was observed. This chert is related to silica-rich seawater in contact with permeable and porous sediments. A later pulse of chert, associated with fracturing, also occurs. The knowledge provided by the characteristics and distribution of chert in these carbonates is significant, especially when considering that the La Silla Formation in San Juan province is the most quarried unit for the elaboration of lime.

A Formação La Silla (Neo Cambriano-Neo Tremadociano) é formada por depósitos carbonáticos da região da Pré-Cordilheira leste, Argentina. As faciologias encontradas em tais depósitos indicam um ambiente de deposição caracterizado por uma plataforma rasa. Até o momento, nenhum estudo tratou especificamente da evolução diagenética dessas rochas. O presente estudo envolve as características e distribuição da silicificação que afeta esta formação e apresenta os diferentes estágios diagenéticos ocorridos, através de análises petrográficas (auxiliadas por catodoluminescência) e estratigráficas. Foi identificado um pulso precoce de silicificação, anterior ao processo de compactação das rochas afetadas. Esta silicificação foi favorecida pela presença de água do mar rica em sílica em contato com sedimentos porosos e permeáveis. Também foi identificado um pulso de silicificação tardia, associado a eventos de fraturamento das rochas. O conhecimento adquirido sobre as características e a distribuição da silicificação nestes depósitos carbonáticos é importante, especialmente quando se considera que a Formação La Silla, na Província de San Juan, é a formação mais minerada para a produção de calcário.