Seeing beyond the outcrop: Integration of ground-penetrating radar with digital outcrop models of a paleokarst system

Kim Senger,Julian Janocha,Aleksandra Smyrak-Sikora,Thomas Birchall

doi:10.1016/j.marpetgeo.2020.104833

Abstract

Paleokarst breccias are a common feature of sedimentary rift basins. The Billefjorden Trough in the High Arctic archipelago of Svalbard is an example of such a rift. Here the Carboniferous stratigraphy exhibits intervals of paleokarst breccias formed by gypsum dissolution. In this study we integrate digital outcrop models (DOMs) with a 2D ground penetrating radar (GPR) survey to extrapolate external irregular paleokarst geometries beyond the 2D outcrops. DOMs are obtained through combining a series of overlapping photographs with structure-from-motion photogrammetry, to create mm- to dm-resolution georeferenced DOMs. GPR is typically used for surveying the shallow subsurface and relies on detecting the contrasts in electro-magnetic permittivity. We defined three geophysical facies based on their appearance in GPR. By integrating subsurface geophysical data with DOMs we were able to correlate reflection patterns in GPR with outcrop features. The chaotic nature of paleokarst breccias is seen both in outcrop and GPR. Key horizons in outcrop and the GPR profiles allow tying together observations between these methods. Furthermore, we show that this technique expands the two-dimensional outcrop surface into a three-dimensional domain, thus complementing, strengthening and extending outcrop interpretations.

Highlights

Analyzing outcrops is a fundamental technique in many contempo rary geological investigations
In addi tion, we propose a workflow for digital outcrop models (DOMs) and ground penetrating radar (GPR) processing, as well as the integration of outcrop data with DOMs and GPR
The different facies types described from outcrop and DOM obser vations are lithofacies A, B and C, in the GPR profiles GPR facies A, B and C are observed

Summary

Introduction

Analyzing outcrops is a fundamental technique in many contempo rary geological investigations. DOMs are becoming a popular tool in geosciences and their advancement over the past two decades has been significant (Buckley et al, 2008, 2019; Carrivick et al, 2016; Enge et al, 2007; Senger et al, 2020; Wilkinson et al, 2016). The rapid evolution of structure-from-motion (SfM) algorithms and their implementation in user-friendly software, has led to an explosion of digital models from a wide variety of sources (Bemis et al, 2014; Carrivick et al, 2016; James et al, 2019; Smith et al, 2016; Westoby et al, 2012). DOMs are becoming increasingly valuable for teaching and planning geological field campaigns (McCaf frey et al, 2010; Senger et al, 2020)

Methods

Results

Discussion

Conclusion