Post-mortem enamel surface texture alteration during taphonomic processes—do experimental approaches reflect natural phenomena?

Experimental approaches are often used to better understand the mechanisms behind and consequences of post-mortem alteration on proxies for diet reconstruction. Dental microwear texture analysis (DMTA) is such a dietary proxy, using dental wear features in extant and extinct taxa to reconstruct feeding behaviour and mechanical food properties. In fossil specimens especially, DMTA can be biased by post-mortem alteration caused by mechanical or chemical alteration of the enamel surface. Here we performed three different dental surface alteration experiments to assess the effect of common taphonomic processes by simplifying them: (1) tumbling in sediment suspension to simulate fluvial transport, (2) sandblasting to simulate mechanical erosion due to aeolian sediment transport, (3) acid etching to simulate chemical dissolution by stomach acid. For tumbling (1) we found alteration to be mainly dependent on sediment grain size fraction and that on specimens tumbled with sand fractions mainly post-mortem scratches formed on the dental surface, while specimens tumbled with a fine-gravel fraction showed post-mortem formed dales. Sandblasting (2) with loess caused only negligible alteration, however blasting with fine sand quartz particles resulted in significant destruction of enamel surfaces and formation of large post-mortem dales. Acid etching (3) using diluted hydrochloric acid solutions in concentrations similar to that of predator stomachs led to a complete etching of the whole dental surface, which did not resemble those of teeth recovered from owl pellets. The experiments resulted in post-mortem alteration comparable, but not identical to naturally occurring post-mortem alteration features. Nevertheless, this study serves as a first assessment and step towards further, more refined taphonomic experiments evaluating post-mortem alteration of dental microwear texture (DMT).

The effect of debris-flow sediment grain size distribution on fan forming processes

Knowledge of the processes driving debris-flow fan evolution are critical in the support of efforts to mitigate related hazards, reduce risk to populations and infrastructure, and reconstruct the history of sediment dynamics in mountainous areas. Research on debris-flow fan development has focused on topographic controls, debris-flow volume and rheology, and the sequence of occurrence of debris flows. While these items have explained a great deal about fan formation and specifically avulsion and runout mechanisms, there is a need to further investigate other properties as they relate to debris-flow fan formative process. Here, we examined the role of debris-flow grain-size distribution on fan formation. Flume experiments were employed to examine the morphology of debris-flow fans that resulted from flows with mono- or multi-granular sediment composition with the same average grain size. All other flow characteristics were held constant. The mono-granular flows formed a symmetric-like fan morphology because there was little avulsion during the formation process. The multi-granular flows produced fans with an asymmetric morphology. Avulsions occurred on both lateral extents of the fan during the early stages of fan development and caused the runout direction to shift produce the fan asymmetry. Grain-size distribution was closely related to spatial diversity in fan morphology and stratigraphy.

A Conversion for Average Grain Size Based on Gamma Ray Well Log: Application in the Second Member of Xujiahe Formation of Anyue Area, Sichuan Basin

The grain sizes of clastic rock sediments serve as important depositional indicators that are significant in sedimentology and petroleum geology studies. Generally, gamma ray, spontaneous-potential and resistivity well logs are utilized to qualitatively characterize variations in sediment grain size and determine the lithology in clastic reservoirs. However, grain size analysis of modern sedimentary samples collected from active rivers and deltas indicates that the percentage of fine depositional component has a logarithmic relationship with the average grain size in delta and river systems. Using the linear relationship to process the lithology interpretation, siltstones or mudstone is likely to be interpreted as sandstone. Therefore, a logarithmic conversion formula was built up between the gamma ray logs and measured grain size for the second member of the Xujiahe Formation of Anyue Area in the Sichuan Basin. Using the formula, the average grain size and lithology of the exploration wells were determined for the interest intervals. Furthermore, the calculated grain size gives a better understanding of the controlling factors of hydrocarbon-bearing reservoirs in the study area.

Measurement and Analysis of Acoustic Backscatter Value for Bottom Classification of waters Tidung Island

Sediment in a water has an important role for organisms, namely as a habitat, a place for foraging for food, and a place for spawning. These sediment can affect the composition of organisms in the water. The purpose of this study is to calculate the value of acoustic backscatter for the classification of the bottom of the water and to see the effect of sediment grain size on the backscatter value obtained from a single beam acoustic instrument. Data collection was carried out from 10 to 12 June 2021 in the water of Tidung Island, Seribu Islands, using the SIMRAD EK-15 single beam, single frequency 200 kHz instrument. Sediment sampling was carried out at 13 stations. The results showed that the waters of Tidung Island were dominated by muddy substrate which was classified based on the Surface Backscattering Strength (SS) value. Meanwhile, the grain size of the sediment affects the SVb value, where the large the grain size of the bottom sediment, the SVb value will be higher. The higher SVb value the SS value will be higher. Keywords: Bottom Classification, Acoustic Backscatter, Tidung Island

Identify the physical characteristics of bedload transport using accelerometer

Real-time sediment transport discharge monitoring in rivers is a challenge. One of the difficulties is the existence of the transport sediment on the bottom of the river bed, the water flow making it invisible to the naked eye, and the flow of velocity itself creates a barrier to measure and install devices in the river. Vibration-based sediment transport measuring instruments have been developed in developed countries. Only a few people in Indonesia have created a technique for quantifying transport sediment. The experiment was carried out in a flume with sediment of a specified diameter flowing through it. An accelerometer was installed at the bottom to measure the vibration induced by the sediment movement at the channel’s bottom. Impact energy is created when sediment grains collide with the channel’s bottom. The amount and size of the sediment determine how much energy is released. The accelerometer measures the amplitude of the vibration signal that is produced by the energy. The statistical parameters can be used with alternating quantities of data. The findings of the experiments reveal that the larger the parameters value linearly with the sediment grain size.

Impacts of Anthropogenic Stressors on Hydrochemistry, Benthic Macroinvertebrates and Sediment Characteristics of the Lagos Lagoon, Nigeria

The anthropogenic impact on the water, benthic macroinvertebrates and sediment grain size of Lagos lagoon was investigated between July and October, 2019. Ten sampling stations were selected based on their importance as likely sources of different forms of anthropogenic stressor to the lagoon. Water temperatures, pH and salinity were measured in situ. Water and benthic samples were collected monthly and analysed using standard methods. Nutrient levels were determined using a spectrophotometer. The hydrochemistry of the stations differed significantly (p<0.05) with the exception of temperature and pH. The sediment grains across the study stations consists basically of sand and mud, with sand dominating the grain type. A total of 502 individuals comprising 3 phyla, 4 classes, 10 families and 11 species was recorded. The phylum mollusca which contributed 92% to the total number of individuals was represented by two Classes; Gastropoda and Bivalvia, with the gastropod Tympanotonus fuscatus having the highest number of individuals (321). Thephylum Annelida represented by one Class, Polychaeta and two Species Nereis sp. and Capitella capitata contributed 6% to the total number of individuals. The class Crustacea, representing the Phylum Arthropoda was the least sampled (7 individuals) constituting about 1.4% of the total population Result showed that different pollution sources have negatively impacted the water chemistry of the lagoon and reduced the diversity and abundance of its benthic macroinvertebrates community. The sedentary nature of this group of benthic fauna could be the major reason why they are most impacted.