On-fault earthquake energy density partitioning from shocked garnet in an exhumed seismic midcrustal fault

The energy released during an earthquake is mostly dissipated in the fault zone and subordinately as radiated seismic waves. The on-fault energy budget is partitioned into frictional heat, generation of new grain surface by microfracturing, and crystal-lattice distortion associated with dislocation defects. The relative contribution of these components is debated and difficult to assess, but this energy partitioning strongly influences earthquake mechanics. We use high-resolution scanning-electron-microscopy techniques, especially to analyze shocked garnet in a fault wall-rock, to provide the first estimate of all three energy components for a seismic fault patch exhumed from midcrustal conditions. Fault single-jerk seismicity is recorded by the presence of pristine quenched frictional melt. The estimated value of energy per unit fault surface is ~13 megajoules per square meter for heat, which is predominant with respect to both surface energy (up to 0.29 megajoules per square meter) and energy associated with crystal lattice distortion (0.02 megajoules per square meter).

The cono-dos and cono-dont's of phosphatic microfossil preparation and microanalysis

Scanning electron microscope (SEM) imaging of fossils allows unlocking ultrastructural information about their skeletal tissues, but sample preparation of biominerals forming their skeletons requires time, patience, and knowledge. SEM and associated analytical methods allow the observation of internal microstructure, shedding light on function, growth and chemistry. Sample preparation is the process by which material is fixed within a medium (e.g. epoxy resin), a transect created and surface defects removed. This step is arguably the most important in any SEM-based analysis, allowing for the acquisition of reliable, high quality data sets. When conducting any SEM-based technique, the presence of a flat surface is needed to collect consistent and reliable data. Surfaces with topography will both induce charging effects but will also compromise the reliability of data acquired. Techniques from material science are continuously adapted to palaeontological applications, in particular with respect to calcareous microfossils. However, similar studies have not been extensively conducted on bioapatite, owing in part to the difficulties faced in sample preparation alongside its susceptibility to electron beam damage. This case study focuses on conodonts, a marine vertebrate group ranging from the late Cambrian to the Late Triassic. They have been chosen as a model due to the abundance of material, complexity of internal tissues and previous work focused on histological features. With these phosphatic microfossils, we attempt to outline the process of sample preparation and provide information on how to avoid and overcome common pitfalls.

Wear, tear and systematic repair: testing models of growth dynamics in conodonts with high-resolution imaging

Conodont elements are the earliest mineralized vertebrate dental tools and the only ones capable of extensive repair. Two models of conodont growth, as well as the presence of a larval stage, have been hypothesized. We analysed normally and pathologically developed elements to test these hypotheses and identified three ontogenetic stages characterized by different anisometric growth and morphology. The distinction of these stages is independently corroborated by differences in tissue strontium (Sr) content. The onset of the last stage is marked by the appearance of wear resulting from mechanical food digestion. At least five episodes of damage and repair could be identified in the normally developed specimen. In the pathological element, function was compromised by the development of abnormal denticles. This development can be reconstructed as addition of new growth centres out of the main growth axis during an episode of renewed growth. Our findings support the model of periodic retraction of elements and addition of new growth centres. Changes in Sr content coincident with distinct morphology and lack of wear in the early life stage indicate that conodonts might have assumed their mature feeding habit of predators or scavengers after an initial larval stage characterized by a different feeding mode.

Influences of diet, short-chain fatty acids, lactate and chloride on bicarbonate movement across the reticulo-rumen wall of sheep

Influences of short-chain fatty acids (SCFA), chloride or lactate on net bicarbonate movement were determined in the temporarily isolated and washed reticulo-rumen of sheep used to 100% hay or 81% concentrate diets. Replacement of SCFA by gluconate and mannitol reversed net bicarbonate secretion into net absorption. The reversal of net bicarbonate movement could not be prevented by presence of D/L-lactate. Replacement of chloride in addition to replacement of SCFA enhanced net absorption of bicarbonate. Feeding concentrate diets resulted in an elevation of net bicarbonate secretion and of net SCFA absorption. It is concluded that under the conditions tested net bicarbonate secretion mainly depends on the luminal presence of SCFA. Furthermore, bicarbonate secretion into the reticulo-rumen may be an important factor for alkalizing the rumen contents, especially in sheep adapted to concentrate diets.