scholarly journals TAPHONOMIC BIAS OF SELECTIVE SILICIFICATION REVEALED BY PAIRED PETROGRAPHIC AND INSOLUBLE RESIDUE ANALYSIS

Palaios ◽  
2015 ◽  
Vol 30 (8) ◽  
pp. 620-626 ◽  
Author(s):  
SARA B. PRUSS ◽  
JONATHAN L. PAYNE ◽  
SOPHIE WESTACOTT

Abstract Silicification is an important mode of fossil preservation but the extent to which silicified material represents an unbiased sampling of the total fossil assemblage within a given rock sample remains poorly quantified. Here, we use paired analyses of thin sections and acid-extracted silicified specimens from the same samples to examine the biases introduced during silicification of Lower Triassic Virgin Limestone carbonates preserved in the Muddy Mountains of southern Nevada. Bivalves dominate most thin sections in the point count data, but rarely silicify completely enough to be recognized in residue. Echinoderms and gastropods are less abundant in thin section but dominate the residues. The abundances of these groups in thin section and residue are only weakly correlated. These findings suggest that although silicification generally captures relative trends in proportional abundance of higher taxa among samples, the silicification process can be taxonomically biased. Given the biases that can occur during silicification, it should not be assumed that silicified collections present a pristine picture of taxonomic or paleoecologic composition. Petrographic analysis has the potential to illuminate the reliability of paleontological data based on silicified collections.

Geosciences ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 36
Author(s):  
Vayia Xanthopoulou ◽  
Ioannis Iliopoulos ◽  
Ioannis Liritzis

The present study deals with the characterization of a ceramic assemblage from the Late Mycenaean (Late Helladic III) settlement of Kastrouli, at Desfina near Delphi, Central Greece using various analytical techniques. Kastrouli is located in a strategic position supervising the Mesokampos plateau and the entire peninsula and is related to other nearby coeval settlements. In total 40 ceramic sherds and 8 clay raw materials were analyzed through mineralogical, petrographic and microstructural techniques. Experimental briquettes (DS) made from clayey raw materials collected in the vicinity of Kastrouli, were fired under temperatures (900 and 1050 °C) in oxidizing conditions for comparison with the ancient ceramics. The petrographic analysis performed on thin sections prepared from the sherds has permitted the identification of six main fabric groups and a couple of loners. The aplastic inclusions recognized in all fabric groups but one confirmed the local provenance since they are related to the local geology. Fresh fractures of representative sherds were further examined under a scanning electron microscope (SEM/EDS) helping us to classify them into calcareous (CaO > 6%) and non-calcareous (CaO < 6%) samples (low and high calcium was noted in earlier pXRF data). Here, the ceramic sherds with broad calcium separation are explored on a one-to-one comparison on the basis of detailed mineralogical microstructure. Moreover, their microstructure was studied, aiming to estimate their vitrification stage. The mineralogy of all studied samples was determined by means of X-ray powder diffraction (XRPD), permitting us to test the validity of the firing temperatures revealed by the SEM analysis. The results obtained through the various analytical techniques employed are jointly assessed in order to reveal potters’ technological choices.


2021 ◽  
Author(s):  
Irfan Sh. Asaad ◽  

Lithostratigraphy and microfacies analysis of the Avanah Formation (Middle Eocene) were studied in the Gomaspan section in the Bina Bawi anticline, northeast of Erbil city, Kurdistan Region, Iraq. The field observations refer that the formation attains 56 m of medium to thick bedded yellow limestone, grey dolomitic limestone and blue marly dolomitic limestone interbedded with thin beds of blue marl and dark grey shale with an interval of sandy limestone in the middle part and thin to medium bedded limestone interbedded with red mudstone. The petrographic study of 29 thin sections of Avanah carbonates revealed that the majority of the matrix is carbonate mud (micrite) with few microspar. The skeletal grains include benthic foraminifera, dasycladacean green algae, ostracods, calcispheres, pelecypods, rare planktonic foraminifera and bryozoa in addition to bioclasts. Non-skeletal grains encompass peloids, oncoids, intraclasts and extraclasts with common monocrystalline quartz. Based on the field observation and petrographic analysis, three different lithostratigraphic units were identified. They are in ascending order: A-Thick bedded dolomitic marly limestone interbedded with shale. B- Bedded dolomitic limestone interbedded with shale and marl. C- Thin to medium bedded limestone interbedded with red mudstone. Depending on detailed microfacies analysis of carbonate rocks, three main microfacies and 12 submicrofacies are recognized. From the sum of all petrographic, facies, textural analyses, it is concluded that Avanah Formation in Gomaspan section, was deposited in shallow marine environment, semi restricted lagoon, in lower and upper parts and open lagoon environment in the middle part interval.


Author(s):  
Lucile-Morgane Hays ◽  
Adeline Kerner

Digitization and online publishing of museum specimen data are happening worldwide. Studies based solely on online data become increasingly accessible. The current events, for example, reducing our transport-related carbon footprint or the COVID-19 pandemic, provide key opportunities to highlight the full value of digitized collections and their related tools, which allow us to continue our research from home or at least without travelling. Are existing data resources and tools adequate for engaging in a research project from beginning to end? To address this issue, we propose to use the Mexican archaeocyaths digitized collection from the Museum National d’Histoire Naturelle, Paris, France (MNHN) and the freeware Annotate in order to describe and identify all the archaeocyaths from the Mexican Cambrian reef. Archaeocyaths are aspiculate sponges that lived during the Cambrian Period. They were the first animals to build reefs. In the MNHN collection, they are found as thin-sections with several archaeocyaths per thin-section (Fig. 1). Multiple individuals are grouped under a single collection number and a single species name. The list of species in the thin-section is only captured on the paper label, and cannot currently be found online. To study an archaeocyaths' reef, the archaeocyaths have to be described and identified one by one, and the location of each specimen has to be accuratly captured. Is it possible to do this with Annotate? Can a palaeontologist use only digitized specimens and Annotate to study a complete fauna of a given time and space? Annotate is an image annotation tool for the natural sciences. It allows users to measure, count, and tag all the morphological structures of an organism. Photos may be imported from the Recolnat database or users may import their own photos. Users can measure lengths, surfaces, and angles, count occurrences and add points of interest. Users can also tag the different individuals to identify them. Morphological terms may be imported as a standardized list from Xper2 or Xper3. Xper3 is a web platform that manages descriptive data and provides interactive identification keys. The results of the measurements and annotations can be exported into CSV format (comma-separated values) or into a structured descriptive data (SDD) format. To identify an archaeocyath to genus level, we need to identify morphological structures and count the occurrence of some of them, and for an identification to the species level, we need to measure different additional parts. The standardized list of morphological terms has been imported from the archaeocyaths genera knowledge base and the list of measurements has been created directly in Annotate. Lengths (e.g., pore size, cup diameter), counts (e.g., number of septae, number of pores) and points of interest (e.g., tumuli, canals, septa) are easy to use. What are the key lessons learnt to remember at the end of this study? The digitized archaeocyaths from Mexico have been identified as easily with Annotate as if a microscope and thin sections were used. The CSV export provided quick access to statistics calculations. The main difference between a microscope and Annotate is the working time. Some functionalities of Annotate are not optimized, their uses are time consuming. For instance, the importation of photos is not really appropriate for archaeocyaths studies. Two sections (transversal and longitudinal) per specimen are necessary to see all the morphological structures. These two parts of the same rock are packed together with one collection number. While users can easily switch from one section to another with a microscope, they can not with Annotate. Annotate allows only one photo per collection number from Recolnat, but not images of the two sections and their metadata. The main difference between a microscope and Annotate is the working time. Some functionalities of Annotate are not optimized, their uses are time consuming. For instance, the importation of photos is not really appropriate for archaeocyaths studies. Two sections (transversal and longitudinal) per specimen are necessary to see all the morphological structures. These two parts of the same rock are packed together with one collection number. While users can easily switch from one section to another with a microscope, they can not with Annotate. Annotate allows only one photo per collection number from Recolnat, but not images of the two sections and their metadata. Although Annotate is not an intuitive tool to use it is still very powerful however, some training is required to fully take advantage of it, and there is no documentation available. This freeware has great potential as it can assist researchers in their work and proposes an alternative to the need to travel around the world to study a fossil.


2021 ◽  
Vol 15 ◽  
Author(s):  
Ronald S. Petralia ◽  
Ya-Xian Wang

The post-embedding immunogold (PI) technique for immunolabeling of neuronal tissues utilizing standard thin-section transmission electron microscopy (TEM) continues to be a prime method for understanding the functional localization of key proteins in neuronal function. Its main advantages over other immunolabeling methods for thin-section TEM are (1) fairly accurate and quantifiable localization of proteins in cells; (2) double-labeling of sections using two gold particle sizes; and (3) the ability to perform multiple labeling for different proteins by using adjacent sections. Here we first review in detail a common method for PI of neuronal tissues. This method has two major parts. First, we describe the freeze-substitution embedding method: cryoprotected tissue is frozen in liquid propane via plunge-freezing, and is placed in a freeze-substitution instrument in which the tissue is embedded in Lowicryl at low temperatures. We highlight important aspects of freeze-substitution embedding. Then we outline how thin sections of embedded tissue on grids are labeled with a primary antibody and a secondary gold particle-conjugated antibody, and the particular problems encountered in TEM of PI-labeled sections. In the Discussion, we compare our method both to earlier PI methods and to more recent PI methods used by other laboratories. We also compare TEM immunolabeling using PI vs. various pre-embedding immunolabeling methods, especially relating to neuronal tissue.


1998 ◽  
Vol 6 (7) ◽  
pp. 8-9
Author(s):  
Ian Chaplin

The optical examination of a rock sample in thin section is the quickest and most economical method for classifying rock type and determining which analytical route to follow.Thin sections for transmitted light are the most common, but there are also:Polished Thin Sections • Polished sections are used for classification and identification of minerals that cannot be determined in standard thin sections. They are also essential for microprobe analysis. Minute mineral grains are analyzed by bombarding them with a focused bean of electrons, which generate x-rays, characteristic of the elements within the grains. X-rays are identified and quantified to determine the chemical composition of minerals.


2021 ◽  
Author(s):  
Hesham Talaat Shebl ◽  
Mohamed Ali Al Tamimi ◽  
Douglas Alexander Boyd ◽  
Hani Abdulla Nehaid

Abstract Simulation Engineers and Geomodelers rely on reservoir rock geological descriptions to help identify baffles, barriers and pathways to fluid flow critical to accurate reservoir performance predictions. Part of the reservoir modelling process involves Petrographers laboriously describing rock thin sections to interpret the depositional environment and diagenetic processes controlling rock quality, which along with pressure differences, controls fluid movement and influences ultimate oil recovery. Supervised Machine Learning and a rock fabric labelled data set was used to train a neural net to recognize Modified Durham classification reservoir rock thin section images and their individual components (fossils and pore types) plus predict rock quality. The image recognition program's accuracy was tested on an unseen thin section image database.


2018 ◽  
Vol 6 (3) ◽  
pp. T723-T737
Author(s):  
Tao Nian ◽  
Zaixing Jiang ◽  
Hongyu Song

Electrical borehole image logs have the potential for direct interpretation of lithofacies characteristics. The challenge is to establish a set of reliable diagnostic criteria with which electrical images can be correlated to lithofacies features such as lithology, sedimentary structures, and bedding sequences. We used the “behind-outcrop” logging procedure that can link borehole images to actual rocks and also reduce errors that are associated with core-shift process. To better reveal the correlation between borehole images and carbonate lithofacies for subsurface reservoir applications, and also make a comparative petrographic analysis with the aim of establishing diagnostic criteria for borehole images, a 200 m well was drilled in the Tarim Ordovician outcrop. A full set of borehole image data and cores with approximately 100% coring recovery rate was acquired at the same depth interval, and more than 100 stained thin sections were prepared. Electrical borehole images in wells adjacent to the outcrop were further interpreted to validate the proposed criteria. Borehole image electrofacies were established according to the image elements, such as stacked mode, bed thickness, conglomerate diameter, rim characteristics, and internal structure of bed/conglomerate, to interpret depositional/diagenetic textures and platform-slope associations. Nine image electrofacies types, corresponding to mud/wacke/pack/grain/bindstone texture, were identified and interpreted in detail. Our method reveals a set of diagnostic criteria for borehole image interpretation in carbonate platform slope, and it finally provides a powerful tool for direct interpretation of electrical images in similar reservoir environment.


Author(s):  
P. W. Jayawickrama ◽  
R. Prasanna ◽  
S. P. Senadheera

A nationwide survey on design methods for achieving adequate skid resistance on hot-mix asphalt concrete pavements was conducted. Information was collected on the design practices used by 48 state departments of transportation (DOTs) in the contiguous United States. Survey findings show that the emphasis placed on the skid resistance aspects in various state DOT design procedures vary considerably. Based on the data collected, 21 out of 48 state highway agencies either do not have any design guidelines specifically addressing pavement skid behavior or assume that adequate skid resistance may be ensured through proper mix design. The general approach used by these agencies involves frequent monitoring of pavements to identify pavements with skid-related problems so that appropriate action may be taken. Survey findings indicated that state DOTs that consider skid resistance in their design procedures emphasize controlling the quality of coarse aggregates used in pavement surface course construction. The procedures used for aggregate qualification, however, vary significantly from one state agency to another. Some state DOTs rely on simple aggregate classification methods based on aggregate type, whereas others perform detailed laboratory evaluation. The laboratory test procedures that are most commonly used in evaluating aggregate frictional properties are the polish value test, acid insoluble residue test, and petrographic analysis. In addition to laboratory testing, Florida, Kentucky, Pennsylvania, and Texas use alternative procedures to qualify aggregates based on their field skid performance.


1978 ◽  
Vol 79 (3) ◽  
pp. 774-787 ◽  
Author(s):  
N S McNutt

Choroid plexus and intestinal microvilli in thin sections have microfilaments in the cytoplasm adjacent to the membranes, and in replicas have broken strands of filaments in both cytoplasm and on E faces of plasm membranes. The microfilaments contain actin as indicated by their binding of heavy meromyosin (HMM). In sections of choroid plexus, the microfilaments are 7-8 nm in diameter and form a loose meshwork which lies parallel to the membrane and which is connected to the membranes both by short, connecting filaments (8 times 30 nm) and dense globules (approximately 15-20 nm). The filamentous strands seen in replicas are approximately 8 nm in diameter. Because they are similar in diameter and are connected to the membrane, these filamentous strands seen in replicas apparently represent the connecting structures, portions of the microfilaments, or both. The filamentous strands attached to the membrane are usually associated with the E face and appear to be pulled through the P half-membrane. In replicas of intestinal brush border microvilli, the connecting strands attaching core microfilaments to the membrane are readily visualized. In contrast, regions of attachment of core microfilaments to dense material at the tips of microvilli are associated with few particles on P faces and with few filamentous strands on the E faces of the membranes. Freeze-fracture replicas suggest a morphologically similar type of connecting strand attachment for microfilament-membrane binding in both choroid plexus and intestinal microvilli, despite the lack of a prominent core bundle of microfilaments in choroid plexus microvilli.


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