It’s been a while since our last post, but we’ve been working hard!
Since the last post, the team made great progress with lab work. First, samples were sent off to the University of Kansas (Lawrence), where one of the team member, Marina Suarez, analyzed their carbon and oxygen stable isotope composition. A very small amount of powdered sample (150-250 µg) is reacted with acid in a sealed glass vial after the air is flushed and replaced with helium. Results will aid at correlating between sections while informing on postdepositional transformation of the sediment as it is lithified and becomes a rock (diagenesis). Second, Dianna and Justin processed samples in our x-ray fluorescence spectrometry lab on UTSA main campus, to derive their geochemical composition (major and trace elements) following the method described under Facilities.
To measure the amount of volatile using the the LOI method, Justin must wear a heat-resistant equipment (a). Long tongs are used to place samples in the furnace (b); note how the plate is slightly pulled out to prevent touching the hot door of the furnace with the muffles. The green light and needle pointing to a high temperature (c) indicate the interlock is engaged, then samples are left in the furnace for 90 minutes (d), after that time they are left in the turned off furnace to cool down until they are not red anymore (e) and can be moved onto the countertop until they totally cool down.
Third, crushed and powdered samples were sent off to Kansas State University, where Brice Lacroix analyzed the mineralogy of the whole-rock sample and of the < 2 µm insoluble fraction, respectively, using x-ray diffractometry. After analyses were completed, spectra were sent back for San Antonio to identify and quantify minerals presents. The movie below shows how this can be done using Profex freeware. Whereas whole-rock mineralogy informs on the overall lithology of a sample, the mineralogy of the < 2µm fraction permits to identify the type of clay present; most clay minerals are a byproduct of the weathering of preexisting rocks under the influence of a specific climate, their identification thus opens a window into past climate during time of formation of the dinosaur tracks.
Fourth and last, we used a conventional petrographic microscope to observe thin sections. We assessed at the relative proportion of mud, grains and cement to name samples using the classification of Dunham (1962) and to retrieve information about the hydrodynamics at time of deposition. Conversely, the identification of grains gave us insights about the environments of deposition.
Justin and Alex discuss what allochems are present in thin sections, using a Motic petrographic microscope.
All this work is in progress, stay tuned for more detailed results!