Detection of mineralogically accentuated biogenic structures with high-resolution geophysics: implications for ichnology and geoecology

Ilya V Buynevich

doi:10.15421/112023

Abstract

Identification and mapping of small-scale physical and biogenic structures in sand has been a challenge to sedimentologists and ichnologists. Under natural conditions, biogenic activity (trampling tracks, burrows) alter primary sedimentary structures, but also serve as important paleoenvironmental indicators of geotechnical properties of sediments, omission surfaces, and ecosystem dynamics. Therefore, the ability to recognize such structures as anomalies in shallow subsurface, especially when using indirect non-invasive methods, such as geophysical imaging, is an important aspect of assessing their relative contribution to the overall erosional-depositional record. This study presents experimental evidence of the viability of two highresolution geophysical methods in detecting sediment deformation that mimics shallow animal traces. High-frequency (800 MHz) ground-penetrating radar (GPR) imaging aided in visualizing a buried depression produced by a deer hoofprint cast indenter, with high-amplitude reflection return enhanced by a heavy-mineral concentration (HMC). Bulk in situ low-frequency (930 Hz), low-field magnetic susceptibility (MS) experiment supported the theoretical pattern of a decrease in MS over the thickest cover sand (maximum indentation depth) to ~0 mSI and the highest values over raised HMC horizon (marginal ridge; >8 mSI). Because both methods are affected by the presence and relative abundance of heavy minerals, the present approach can be applied in most siliciclastic settings. This study demonstrates the promise of extending the 2D visualization of subsurface targets to 3D datasets, with potential implications for sedimentological, ichnological, archaeological, and geoecological research that involves animal-sediment interaction at different scales.

Highlights

A wide suite of vertebrate and invertebrate organisms is responsible for generating billions of biogenic structures in both modern and ancient depositional settings (Vialov, 1966; Frey and Pemberton, 1986; Loope 1986; Fornós et al 2002; Roberts 2003; Hasiotis et al, 2007; Lockley et al 2007; Milàn et al 2007a,b; Zonneveld, 2016)
New applications of high-resolution geophysical techniques, such as ground-penetrating radar (GPR or georadar), high-amplitude signal return in georadar images and can be detected using low-field magnetic susceptibility (MS) surveys (Buynevich, 2012). The latter is especially sensitive to ferrimagnetic content. These techniques are potentially applicable to detecting near-surface biogenic structures accentuated by heavy-mineral concentration (HMC)
This paper presents examples of laboratory experiments using an ungulate cast track indenter, with the aim of demonstrating the ability to detect the near-surface structure using high-resolution georadar imaging and magnetic susceptibility trends

Summary

Introduction

A wide suite of vertebrate and invertebrate organisms is responsible for generating billions of biogenic structures (surface traces and burrows) in both modern and ancient depositional settings (Vialov, 1966; Frey and Pemberton, 1986; Loope 1986; Fornós et al 2002; Roberts 2003; Hasiotis et al, 2007; Lockley et al 2007; Milàn et al 2007a,b; Zonneveld, 2016). Виявлення мінерально-акцентованих біогенних структур з використанням геофізичних методів високої роздільної здатності: наслідки для іхнології та геоекології New applications of high-resolution geophysical techniques, such as ground-penetrating radar (GPR or georadar), high-amplitude signal return in georadar images and can be detected using low-field magnetic susceptibility (MS) surveys (Buynevich, 2012).

Results

Conclusion