Manganese carbonate stromatolites of the Ediacaran Doushantuo Formation in Chengkou, northern Yangtze Craton, China

The origin process of manganese ores remains unsolved worldwide. Exploring the origins of stromatolites that contain manganese may be a key to deciphering the sedimentary environments and metallogenic processes of these deposits. However, only a few manganese stromatolites have been discovered and described until now. Microbialites are well developed in the manganese deposits, located near the top of the Ediacaran Doushantuo Formation in Chengkou area of Chongqing, northern Yangtze Craton, but has not been explicitly studied; and whether they are true stromatolites or Epiphyton microbialites remains controversial. Based on field and core observations and thin section microscopy, the characteristics of five types of manganese stromatolites and their growth modes are described in detail in this study. The results show that these stromatolites grew in a biostrome in shoal and lagoon environments and were syngenetic with oncolites and oolites on a carbonate ramp behind the shoal. Manganese stromatolites can be categorized into three forms: (1) stratiform; (2) columnar, which includes branched and columnar types; and (3) stratiform-columnar, which is a transitional type. Based on a criterion that the diameter is less than or greater than 1 mm, columnar stromatolites are further divided into micro-columnar (< 1 mm) and columnar (> 1 mm) columns, which display synchronous growth and are similar to Pseudogymnosolenaceae. Their shapes are mainly controlled by water depths and hydrodynamic strengths. The greater the water depth, the more columnar the columns tend to be. Excessively strong hydrodynamic conditions decrease the growth rate of stromatolites, and they even stopped growth due to wave damage. Furthermore, pillared laminar textures (not Epiphyton), which consist of dendritic, micro-branched and micro-columnar stromatolites, are a common feature of the larger stratiform, stratiform-columnar and columnar stromatolites. The alternations of laminae with different internal textures record subtle fluctuations in water depths and hydrodynamic strengths, which indicate that stromatolite growth is controlled by tidal cycles at the lamina level. Therefore, it is possible that the vertical evolution of the stromatolites could reveal the changing characteristics of both local and regional sedimentary environments, i.e., stromatolite shape changes from columnar to stratiform can represent the onset of shallower environments with weak hydrodynamic conditions. In addition, as important reef builders in shallow carbonate ramps, microstromatolites accelerate the development from ramp to platform. Indicators of microbial control on stromatolite shapes and manganese sedimentation processes include the fabric of stromatolite laminae, organic rhodochrosite with a micritic texture that is usually clotted, spherical, tubular, fibrous or dendritic, which suggests that the laminae resulted from microbially induced in situ precipitation.

Radiocarbon Age Determinations of Mosaic Mortar Layers of Churches from North Jordan

This research is aimed at radiocarbon dating organic inclusions and lime-binder powders of mortar layers of mosaic pavements in four churches of arguable archaeological date located in northern Jordan. One mortar sample from each mosaic pavement of each church was collected, examined by thin section microscopy, and then physically pretreated by gentle crushing and dry sieving to collect lime-binder powders of different grain sizes. Charcoal samples uncovered from three samples and the CO2 gases, collected by hydrochloric acid (HCl) hydrolysis of the powders, were 14C dated using accelerator mass spectrometry (AMS). Four powders of 63–45 μm from the four samples and two powders of 45–38 μm from two samples were analyzed in order to get more precise dates and examine previous proposed models for the interpretation of the results. 14C determinations showed agreement between charcoal ages and archaeological data, while the fine lime-binder's powders, especially from the mosaic's bedding layer, produced more precise dates. Results suggest that 14C date profiles produced by HCl hydrolysis of the lime-binder powders can be clearly interpreted by the existing models.

3-D Reconstruction of Thick IVEM Samples Using Tuned Aperture Computed Tomography® (TACT®)

Most objects in our world are 3-dimensionai (3-D), and this is certainly true of cellular ultrastructure. The challenge in microscopy has always been how to analyze this 3-D information. Traditional thin-section microscopy has a minimal ability to view 3-D structure, because it is limited to viewing thin, almost twodimensional (2-D) planes taken from the specimen. The development of high and intermediate voltage electron microscopes (HVEM and IVEM) provides the ability to investigate the ultrastructure of thick biological samples—allowing a unique view of the 3-D interrelationships of cells and organelles.

A new fixative for the preservation of actin filaments: fixation of pure actin filament pellets.

Conventional fixation for thin-section microscopy is insufficient to preserve many elements of cells and tissues. Actin filaments, for example, are destroyed during post-fixation in OsO4. In our search for a better fixative, we chose pellets of pure actin filaments as a very sensitive model system. In the present study, the potential of amines for improving aldehyde fixation was explored, and the results were compared to those obtained with the use of tannic acid. Aldehyde and amine were used together as an initial fixative, followed by aldehyde alone with postfixation in 1% OsO4 in buffer at 4 degrees C for 15 min, uranyl acetate en bloc stain, acetone dehydration, and embedding in Epox 812. Some primary monoamines improved the preservation of filaments; filaments were not broken beyond recognition by OsO4, as occurs when glutaraldehyde alone is used. Excellent preservation was seen when certain primary diamines were used. The quality of this fixation was superior to that obtained with tannic acid and was without the large increase in filament diameter that is seen with concentrations of tannic acid sufficient to protect filaments against osmium damage. The effects on filaments of the amines lysine, putrescine, ammonium, and arginine have been documented in detail, as we systematically varied all the major parameters normally considered in formulating fixation protocols.