Ichnology

Field and Experimental Ichnology

Collaborators:

Steve Hasiotis (University of Kansas), H. Allen Curran (Smith College), Daniel Hembree (Ohio University), Jon Smith (Kansas Geological Survey), Brian Platt (University of Mississippi)

LITHOLOGICAL ANOMALIES IN SANDS: IMPLICATIONS FOR VERTEBRATE ICHNOLOGY

Despite the dynamic nature and coarse texture of sandy substrates, many studies report abundant vertebrate and invertebrate tracks, from Paleozoic sandstones to Holocene depositional environments. Track preservation in sand typically requires moisture or clay laminae, but in mid-high latitudes freezing before burial may also increase substrate strength and resistance to erosion. Recognition of tracks in plan-view and cross-section remains a challenge, especially in unconsolidated sands. In many coastal and aeolian settings, lithological anomalies, such as heavy-mineral concentrations (HMCs), represent density lag formation during episodes of increased wave or wind activity. HMCs not only act as environmental indicators, but also accentuate vertebrate and large invertebrate tracks due to their darker color. Using examples from the U.S. East Coast and Eastern Europe (Baltic Sea coast), this project examines the occurrence of avian and mammalian footprints in beach and aeolian HMCs. During post-storm periods or intervals of non-deposition, surficial heavy-mineral concentrations may serve as distinct tracking surfaces. In cross-section, even thin HMCs (1-3 mm) accentuate the shapes of traces and associated structures, as exemplified by a possible cervid track preserved in 1,100-year-old dune slipfaces at the Baltic Sea site. Since many HMCs are enriched in magnetite, low-field magnetic susceptibility (MS) can be used for in situ analysis of track and undertrack laminae. With sub-centimeter sensitivity, a decrease in MS from magnetite-enriched surface laminae (>50×10-5 SI) to quartz-rich track fill (<5) helps constrain track parameters. Where HMC thickness is comparable to the resolution of a ground-penetrating radar (GPR) signal, they produce sharp subsurface reflections. This method is useful for detecting deformation features ranging from 20 cm to less than 2 cm using antenna frequencies between 400 MHz and 2.3 GHz, respectively. Some irregular laminations in shallow subsurface images may potentially represent trampled surfaces and caution must be taken in interpreting them as primary sedimentary structures. Future field and experimental research must combine MS and GPR imaging of vertebrate tracks to better understand how lithological anomalies reflect the final track architecture.

MODERN VERTEBRATE TRACKS FROM COASTAL LITHUANIA: REGIONAL DISTRIBUTION ANDTAPHONOMIC FACTORS

 

Donatas Pupienis (Vilnius University, Lithuania), Albertas Bitinas (Klaipeda University, Lithuania), Aldona Damušytė (Lithuanian Geological Survey)

The formation and preservation of vertebrate traces in modern settings provides a useful guide to locating and analyzing their counterparts in sand-dominated coastal and aeolian sequences. A diverse suite of vertebrate footprints along the Baltic Sea coast offers insights into the distribution and preservation potential of tracks in sandy substrates. At the mainland beach site of Butinge, northernmost Lithuania, artiodactyl (deer) and mustelid (?) tracks occur behind the foredune ridge, with canid (fox) tracks found in association with deep excavations in back dunes. At the southernmost Curonian Spit site, three types of avian footprints occur on the high-energy Baltic Sea beach, along the low-energy Curonian Lagoon shoreline, and on a 50-m-high slipface of the active Parnidis Dune. Mammal traces along the lagoon shoreline include numerous canid tracks (also found on nearby steep dune slopes), suid (wild boar) trackways and trampled surfaces, and a few mustelid footprints. Shore-perpendicular aquatic rodent trackways, drag traces, and gnaw marks suggest that beaver activity is more prominently displayed than that of a recently introduced muskrat. Cervid (elk and deer) trackways follow trails across high vegetated dunes. Based on the wide use of horses on the spit for at least 700-800 years, their hoofprints may be preserved in the shallow subsurface of dune and beach sequences. The habitat preferences result in a predictable distribution of track assemblages allowing differentiation between the open sea vs. lagoon shoreline, stable vs. active dunes, and coastal forest (palve). The medieval phase of dune reactivation contains deformation structures interpreted as tracks with marginal ridges. Although scientific names are not used for modern tracks, once preserved in plan view of cross-section, it is reasonable to apply Vialov’s (1966) ichnotaxonomy to those footprints which readily resemble their recent counterparts and have been used for some Cenozoic tracks (Canipeda, Cervipeda, Hippipeda, Mustelipeda, Suipeda, etc.). Surface moisture, occasional freezing, rapid aeolian burial, and lithological anomalies (heavy-mineral concentrations) increase the preservation potential of tracks. Once buried, the attitude of trackways with respect to bedding surfaces determines their ultimate context.

NEOICHNOLOGY AND ZOOGEOMORPHOGY OF LARGE DECAPODS IN COASTAL CARBONATES: THE BAHAMIAN LAND CRABS

H. Allen Curran (Smith College)

High-resolution geophysical imaging methods, such as ground-penetrating radar (GPR), are increasingly being employed in neoichnological research. In one of the first applications to carbonate coastal ichnocoenoses, >50 images of crustacean bioturbation structures were collected using 800 MHz georadar along tropical shorelines of Eleuthera and Exuma islands, Bahamas. Across the berm and adjacent dune sites, numerous active and partially filled burrows of ghost crabs (Ocypode quadrata) generate characteristic ground-wave gap (tunnel opening) and hyperbolic diffraction patterns. In unconsolidated aeolian sand (foredune ridges and backdune swales), dwelling tunnels of blackback land crabs (Gecarcinus lateralis) produce gently dipping reflection or en-echelon diffraction patterns, with their 2D geometry dependent on burrow spacing and orientation relative to survey lines. At Rock Sound, Eleuthera, a dense network of burrows (3-6/m2) by blue land crabs(Cardisoma guanhumi) dominates the landward margin of a recent overwash fan. Openings for inclined tunnels range from 4 to >20 cm in diameter and terminate at the saline groundwater table (depth: 40-60 cm). Intense bioturbation occasionally transports pre-historic (Lucayan) artifacts to the surface, thereby constraining their spatial distribution and depth range. Survey grids with closely spaced GPR profiles allowed pseudo-3D reconstruction of subsurface burrow segments, with 4-5 cm vertical resolution achievable in unsaturated carbonate substrates (better in saturated media). Lateral continuity and bottom “pull up” (hollow segments) are emerging as diagnostic features that distinguish bioturbation structures at different taphonomic stages from point-source diffraction patterns induced by buried clasts and tree roots. Future burrow casting will allow direct comparison to radargram patterns, with the ultimate goal of employing non-invasive geophysical methods at sensitive sites, for targeted excavation, and for recognizing large crustacean burrows in the rock record. Our research builds on previous findings that bioturbation structures in ancient tropical beach and aeolianite sequences may serve as sea-level indicators (e.g., ghost crab trace Psilonichnus upsilon) and act as megaroporosity anomalies in carbonate reservoirs.

NEOICHNOLOGY WITH ROVs: DEEP-SEA FISH TRACES AND SEDIMENT RE-SUSPENSION IN THE EASTERN MEDITERRANEAN

 

Collaborators:

Rami Tsadok, Max Rubin, Zvi Ben Avraham (Leon H. Charney School of Marine Sciences, University of Haifa, Israel), Dwight Coleman, Robert Ballard (URI/IFE), James A. Austin Jr. (University of Texas-Austin), Jake Benner (Tufts University). 

Observations by two remotely-operated vehicles (ROVs) at
four sites along the bathyal region (500-2,000 m) offshore Israel revealed
multiple traces produced by benthic and bentho-pelagic fish that reflect
near-bottom activity in one of the most biologically impoverished regions of
the World Ocean. High-resolution video and screen captures from the main
tethered ROV Hercules were complemented by Argus photography
from 15 m above the seafloor to provide a broad view of medium-scale (10-20 cm) biogenic structures.

Piscine traces made in soft or partially compacted muddy sediments include grooves, circular and semi-circular depressions, swimming and lateral sliding trails, as well as “resting” traces reflecting sheltering, nesting, and camouflaging/ambush behavior by scorpionfish, rays, eels, flounder, blennoid species, and others.

In most cases, the tracemakers were observed in the process of producing the
biogenic structures or using burrows and depressions made by other fish and
invertebrates. Several types of the imaged traces and seafloor disturbances are
known from the rock record (Undichna and Piscichnus ichnogenera). Their
preservation depends on sedimentation rates and overprint by subsequent
bioturbation. Near-bottom video also captured various behaviors leading to
sediment re-suspension by fish, both through near-bottom contact by pectoral,
pelvic, anal, and caudal fins, and by rapid collision with the seafloor. The
latter may have been due to ROV approach, but the behavior could be considered
analogous to predator avoidance or search for epifaunal or infaunal prey. A similar behavioral response was observed in several species of deep-water squid. Large (1-2 m long) grooves of deep-diving cetaceans (e.g., Cuvier’s beaked whales) were absent from all sites, but were observed in the vicinity of underwater volcanoes in the northern Mediterranean during other legs of this expedition and by earlier researchers.

The present study demonstrates that abundant fish traces and sediment re-suspension events represent important processes in the bathyal eastern Mediterranean, shedding new light on benthic species abundance and diversity, constraining the residence time of sediments and nutrients, and offering analogs for biogenic structures and trace fossil assemblages in deep-water shales.

 

Post a Comment

You must be logged in to post a comment.