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Year 2 of our continued research on the depositional and diagenetic history of the Navajo Sandstone in the Mollies Nipple (MN) area within Grand Staircase-Escalante National Monument in southern Utah has been very successful.  Our work in this area has continued to explore the distribution, geochemistry, origin, and implications of an isolated region of anomalous jarosite cement within the Navajo Sandstone.  In the last year this research has continued in multiple directions and has been focused on: 1) additional field-based characterization, mapping and sampling of depositional and diagenetic facies; 2) mapping of structural deformation and lineaments; 3) detailed analyses and mineralogical mapping from airborne reflectance spectroscopy datasets; 4) ground-truthing of mineralogical classifications and structural interpretations from airborne reflectance spectroscopy; 5)  laboratory experiments to better understand the controls on mineralogical spectral signatures; 6) quantification of sandstone characteristics from petrographic analysis; 7) integration of multiple datasets, including XRD, major oxide data, and trace element geochemistry to understand paleo-fluid chemistry; and 8) investigation into the potential for isotopic analysis of the jarosite that could yield important information about the age and origin of these cements.  Details of these research focuses are discussed below.     

A second field season with additional field support to allow for more extensive coverage and access to remote and difficult terrain revealed many important aspects of the depositional and diagenetic history of this region.  For example, significant sedimentary features such as very large scale soft sediment deformation and in situ interdune bedding with abundant trace fossils were discovered which suggest more complexity in both the depositional and early burial environment than was previously recognized.  The field work was also key in confirming the orientations of multiple fault and joint zones which are critical in helping to constrain the relative timing of specific diagenetic cements (for example, a population of iron oxide cements is offset by major E-W faulting, but the jarosite cements seem to follow that fault zone suggesting that the iron oxides were precipitated before the faulting and that the faulting provided a conduit for the acid sulfate fluids that precipitated the jarosite).  

In order to more fully capitalize on the value of the existing airborne hyperspectral datasets over this area, one PhD candidate (Juli Bell, who is focusing on this area for her dissertation research) and Dr.Bowen attended a spectral analysis workshop in late 2008 that proved to be an extremely beneficial step in furthering the level and depth of mineralogical and spatial complexity that could be derived from these datasets.  New spectral analyses have included quantification of relative abundance and the statistical significance and likelihood of mineral identifications from the airborne data.  The analysis has included detailed mapping of jarosite concentrations, and has also focused on mapping of other accessory minerals and spatial associations with the jarosite.  These analyses are tied to field-based observations (i.e., structural lineaments, spot sampling) in a GIS format.  Analyses of the spectral data have also spurred laboratory experiments to simulate some of the observed spectral features with known mineral combinations.  This work has helped to establish the correlations between percent abundance and depth of specific absorption features, and the complexities of how having multiple mineralogical components can cause overlap in certain wavelengths and influence the spectral signature in parts of the spectrum that may not typically be expected.  These analyses of the airborne spectroscopy are the basis for a manuscript that is in the final stages of preparation and will be submitted before the end of 2009. 

We have continued to analyze the thin sections that have been made from samples from this area and have worked on quantifying sedimentological, textural, and mineralogical properties.  Select samples with high concentrations of jarosite were sent to a lab that specializes in isotopic geochemistry and geochronology analysis of jarosites.  Since jarosite is a potassium iron sulfate, it contains K, SO4, and OH and can be dated using K/Ar or Ar/Ar methods.  In addition, we aim is to potentially measure the stable isotopic composition of S, H, and O from the jarosite.  Our work in this area has taken longer than expected; hence we have applied for a 1 year no-cost extension so that we may continue this work to its fruition.