Computed reconstruction of spatial ammonoid-shell orientation captured from digitized grinding and landmark data

Abstract

The internal orientation of fossil mass occurrences can be exploited as useful source of information about their primary depositional conditions. A series of studies, using different kinds of fossils, especially those with elongated shape (e.g., elongated gastropods), deal with their orientation and the subsequent reconstruction of the depositional conditions (e.g., paleocurrents and transport mechanisms). However, disk-shaped fossils like planispiral cephalopods or gastropods were used, up to now, with caution for interpreting paleocurrents. Moreover, most studies just deal with the topmost surface of such mass occurrences, due to the easier accessibility. Within this study, a new method for three-dimensional reconstruction of the internal structure of a fossil mass occurrence and the subsequent calculation of its spatial shell orientation is established. A 234 million-years-old (Carnian, Triassic) monospecific mass occurrence of the ammonoid Kasimlarceltites krystyni from the Taurus Mountains in Turkey, embedded in limestone, is used for this pilot study. Therefore, a 150×45×140 mm3 block of the ammonoid bearing limestone bed has been grinded to 70 slices, with a distance of 2 mm between each slice. By using a semi-automatic region growing algorithm of the 3D-visualization software Amira, ammonoids of a part of this mass occurrence were segmented and a 3D-model reconstructed. Landmarks, trigonometric and vector-based calculations were used to compute the diameters and the spatial orientation of each ammonoid. The spatial shell orientation was characterized by dip and dip-direction and aperture direction of the longitudinal axis, as well as by dip and azimuth of an imaginary sagittal-plane through each ammonoid. The exact spatial shell orientation was determined for a sample of 675 ammonoids, and their statistical orientation analyzed (i.e., NW/SE). The study combines classical orientation analysis with modern 3D-visualization techniques, and establishes a novel spatial orientation analyzing method, which can be adapted to any kind of abundant solid matter.

Taphonomy and palaeoecology of Late Triassic (Carnian) ammonoid concentrations from the Taurus Mountains, Turkey

“…The 3D‐visualization‐method described by Lukeneder et al . () was used to analyse a possible spatial orientation of the ammonoids within the shell bed AS 6. The whole ammonoids, but also the gastropods (Fig.…”

“…Following Lukeneder et al . () we used only those ammonoids for orientation analyses that were reconstructed from at least six slices when analysing the lineation A:B. At least three slices were required when analysing the imaginary sagittal‐plane (Fig.…”

“…We adopted a new study‐approach on such planispirally coiled ammonoids, already tested by Lukeneder et al . ().…”

“…The main aim of this study was to solve the following research questions: Are these ammonoids orientated in the same way as already tested within the smaller reference block (done by Lukeneder et al . ), and what does this result mean for the depositional conditions? Does the orientation of the ammonoids fit with the taphonomic interpretation of this shell bed?…”

Automatic determination of 3D orientations of fossilized oyster shells from a densely packed Miocene shell bed

“…The advantage of 3D data is spatial positioning of objects, parallel or tilted to the bedding plane, which might reveal imbrication or can support finding object movements due currents, transport mechanisms, local fault lines, or encrustations. Lukeneder et al (2014) and Mayrhofer et al (2016) developed a 3D approach to capture the orientations of ammonite shells in a sediment block by virtual shell reconstructions, derived from serial grinding techniques. The resulting 3D visualizations allowed measuring the azimuth angle and two more angles.…”