Bioturbation in supratidal carbonate substrates has only recently received attention from ichnologists, relying primarily on traditional ground-based techniques. This study is the first high-resolution geophysical investigation of three decapod species inhabiting adjacent coastal biotopes on San Salvador Island. Extensive (>2 km) 800 MHz georadar surveys captured a diverse suite of >120 burrows of ghost (Ocypode quadrata), blackback (Gecarcinus lateralis) and blue (Cardisoma guanhumi) land crabs. Site-specific post-processing protocols were used to establish characteristic attributes that distinguish unfilled burrows from other discordant anomalies based on signal polarity structure. Variably oriented 2D and quasi-3D (~0.75-1.25 wavelength line separation) images allow the diagnostic signature of G. lateralis burrows to be distinguished from those of O. quadrata based on: 1) higher density of point-source diffractions (0.9-1.9/m vs. 0.01-0.06/m) and 2) shallower inclination angle (21-46° vs. >60°). C. guanhumi burrows are differentiated by: 1) larger diameter; 2) presence of an end chamber (where the radar signal is not attenuated by saline groundwater); 3) low electromagnetic signal velocity (~9 cm/ns vs. ~11 cm/ns) in organic-rich muddy substrate and 4) rapid signal decay. The migrated inclination angle (a) and the effective range (t0; time window of strongest reflectors) offer the best combination that differentiates between the three end-member structures and matrix properties. This study establishes GPR as a viable non-invasive subsurface imaging technique, with potential implications for: 1) identification of shifting ichnocoenoses, as exemplified by intense hurricane impacts (2015/2016); 2) recognition and mapping of similar biogenic structures in buried or lithified carbonates and, 3) quantification of a near-surface ichnofabric index and the dual porosity/permeability structure of prospective hydrocarbon reservoirs. Furthermore, the basic attributes of subsurface visualization can be readily extended to other mesoscale biogenic structures in evaporite and siliciclastic media. / Geology
| Identifer | oai:union.ndltd.org:TEMPLE/oai:scholarshare.temple.edu:20.500.12613/1656 |
| Date | January 2017 |
| Creators | Kopcznski, Karen A. |
| Contributors | Buynevich, Ilya V. (Ilya Val), Nyquist, Jonathan, Ravi, Sujith |
| Publisher | Temple University. Libraries |
| Source Sets | Temple University |
| Language | English |
| Detected Language | English |
| Type | Thesis/Dissertation, Text |
| Format | 347 pages |
| Rights | IN COPYRIGHT- This Rights Statement can be used for an Item that is in copyright. Using this statement implies that the organization making this Item available has determined that the Item is in copyright and either is the rights-holder, has obtained permission from the rights-holder(s) to make their Work(s) available, or makes the Item available under an exception or limitation to copyright (including Fair Use) that entitles it to make the Item available., http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | http://dx.doi.org/10.34944/dspace/1638, Theses and Dissertations |
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