Research and Meetings

GATES, David J., James A. Clark, Stephen O. Moshier, Valerie Tewell, Daniel Master, Mario Martin, and John Sheffer

Tel Shimron is an archaeological site in the Lower Galilee region of northern Israel. The tel is located on the northern margin of the Jezreel Valley and was inhabited from the Early Bronze Age to Islamic Period. Summer 2017 marked the first season of excavation and the start of this research. This study’s purpose was to provide the archaeological team information on the local geology as it pertains to settlement patterns and ancient resources through both surficial mapping and geophysical prospection of the bedrock. The regional geology includes Eocene chalks of the Avedat Group with localized pedogenic alteration to calcrete (known regionally as nari) as well as Miocene basalt. The substantial exposure of basalt adjacent to the tel is of poor quality and was not used for tools, but rather extensively quarried for rampart construction and paving material. Hard nari was used for building stone and both chalk bedrock and nari are a local source of flint for tools.

Three geophysical methods were used to construct a partial subsurface model of the tel: electrical resistivity, seismic refraction and seismoelectric. Processed data revealed varying thickness of cultural “fill” over bedrock and suggested that the original topography beneath the tel may have influenced development patterns and rampart construction. Shallow buried structures, such as walls and broad floors were revealed in transects on the southwestern edge of the tel. This information will be used to influence archaeological decision-making and promote a multifaceted approach to site excavation in future seasons.

THIELMAN, Rebekah, MADSEN, Andrew and SMIDT, Samuel J.

Surface water-groundwater interactions are critical for overall stream health, but identifying the locations of these interactions often requires expensive or intensive field equipment. Moreover, field sampling is often site-specific and identification at multiple locations along a stream reach is limited. Streamlining the identification of surface water-groundwater interactions along a stream reach is a necessary step to large scale restoration projects, particularly in ungauged or unstudied areas. Here, we used a preliminary solute mass balance approach to efficiently estimate the magnitude of downstream surface water-groundwater interactions. We injected an in-stream saline tracer and simultaneously monitored for conductivity and dissolved oxygen adjacent to the stream channel using several groundwater monitoring wells. We then quantified the magnitude of surface water present in groundwater flow paths using a solute mass balance approach. Dissolved oxygen was then used as a proxy for  conductivity to identify the location of downstream surface water-groundwater interactions and to quantify the magnitude of surface water present in groundwater flow paths.

Results from this study can be used in watershed restoration projects or site assessments as a way to identify the locations of key flow paths that benefit overall stream function.

THIELMAN, Rebekah and SMIDT, Samuel J.

Constant rate tracer injections typically rely on a peristaltic pump, but few pumps are adapted to extreme field conditions. Pumps used by researchers generally fall into two categories:

• lab-based designs implemented in a field setting or
• do-it-yourself pump designs constructed by the researcher.

Lab-based designs are often expensive (>$1,000) and sensitive to damage and moisture common in a field setting, and both pump categories often require large and heavy batteries to drive long injections at high flow rates (>1 L/min). The purpose of this study was to develop a cost-effective, do-it-yourself alternative ideal for robust field conditions. We used a bipolar stepper motor (12V-36V, 1.5A) connected to a microstep driver (40V, 4A) to create a continuous peristaltic rotation. The pump is controlled by an Arduino Uno microchip processing board, allowing for variable pump rates to be defined by the user. Waterproof housing was constructed using a Pelican 1200 case (7.29” x 4.78” x 3.33”), which can support up to 2 motor systems per case, allowing for dual tracers or double flow rate. Each motor system only draws ~2A of current, allowing for extended battery life using only a small sealed lead acid 12V battery. Batteries can also be stored in an adjacent Pelican 1200 case for a complete weather-proof system. Our maximum flow rate was ~1 L/min per pump, or 2 L/min per housing case. Total cost of the design was $300 for a dual pump set-up.

HESS, Benjamin Levi, Adrian Fiege and Nicholas Tailby

The major and trace element composition of apatites from the Lachlan fold belt (LFB) S- and I-type granitoids (Australia) and the Central French Massif (CFM) S-type leucogranites (France) were analyzed to investigate their compositional and redox variation. Apatite is a common accessory mineral in magmatic systems that can incorporate a variety of trace elements, including the polyvalent elements sulfur (S), iron (Fe), and manganese (Mn). It was recently discovered that apatite can incorporate three oxidation states of S (S6+, S4+, S2-) into its structure as a function of oxygen fugacity.
However, the oxidation states of Mn and Fe in apatite are essentially unknown (2+ and/or 3+).
In this study, we collected many electron probe line transects across apatites in several different host phases from a variety of S- and I-type plutons. The F-H-Cl contents of the S- and I-type LFB samples were similar (~2.9 wt% F, ~0.4 wt% Cl, ~0.5 wt% OH).
The CFM S-types contained virtually no Cl and ranged from nearendmember OH-apatite to near-endmember F-apatite. The apatites of all studied the S- and I-type plutons are characterized by similar ranges of Fe content (<1.5 wt% Fe), while Mn reaches much higher concentrations in the S-type when compared to I-type apatites (<6.5 wt% Mn). The S content of the apatites varies significantly, from <50 ppm S in the LFB S-types, up to 2,000 ppm S in the LFB I-types, and reaching 1,650 ppm S in the CFM S-types.
The elevated S contents in the LFB I-type and CFM S-type apatites allowed us to measure the S oxidation states by using X-ray absorption near-edge structure (XANES) spectroscopy. The spectra show variability in S oxidation states ranging from mostly sulfate down to nearly equal S6+/S2- ratios, indicating redox variations during apatite formation. The S-type Mn + Fe content plots in a 1:1 ratio against calcium (Ca) in atoms per formula unit, while the I-type apatites have too low Mn and Fe to show a clear trend. Thus, divalent Mn and Fe probably replace Ca2+ in the S-types’ apatite structure, while the incorporation of trivalent Mn or Fe in apatite is rather unlikely. We suggest that Mn and Fe contents in apatite may become a useful tracer of melt evolution once the distributions coefficients are experimentally calibrated.

LEEBURN, J. M., B. W. Denevi, C. M. Ernst, and R. L. Klima

Understanding the origin and evolution of Mercury’s crust was a key goal of the MESSENGER mission. Prior to MESSENGER’s exploration of Mercury, a leading hypothesis for the formation of the planet’s crust was through crystal–liquid fractionation of a magma ocean, leading to a plagioclase flotation crust analogous to that of the Moon. However, reflectance observations and elemental abundance data make it clear that Mercury’s crust is very different from the Moon’s, and interpretations based on the planet’s geomorphology and crater size– frequency distributions imply widespread resurfacing occurred, likely through a combination of volcanism and impact cratering. This geologic activity complicates an examination of Mercury’s early crust. Here we investigate Mercury’s stratigraphy as exposed by impact craters >20 km in diameter in order to evaluate the mode(s) of formation of a key crustal unit, the low-reflectance material (LRM). LRM has been documented to be mainly exposed from depth, and proposed to be at the bottom of the stratigraphic column, either as a component of the lower crust or upper mantle.
The reflectance of LRM is up to ~30% below the global mean, and it has a shallower (bluer) spectral slope, with a broad absorptionband-like feature at ~600 nm. These properties together with thermal neutron measurements have led to the interpretation that LRM is rich in graphite (up to 5 wt.%). Geochemical modeling has also shown that graphite is the only mineral that would have been buoyant in a magma ocean, suggesting it may have been a component in the earliest-forming crust. We explore whether the global occurrences and regional variations of LRM are consistent with this scenario, and investigate the role of early volcanism in the formation of Mercury’s crust.