PRELIMINARY RESULTS: COMPARING SILICICLASTIC CONTENT OF RAMP TO RIMMED CARBONATE SLOPE DEPOSITS DURING RELATIVE SEA LEVEL HIGHSTANDS
Samples were treated with formic acid and hydrogen peroxide to remove carbonate and organics, respectively. The remaining-residue fractions from the Bell Canyon Formation average 6.5% and range from 3-13% of the original rock weight. The Bone Springs Limestone’s remaining-residue fractions average 2.8% and range from 2-3% of the original rock weight. Furthermore, grain-size analysis of the remaining-residue demonstrates that the median grain size (D50) in each interval of the two sections is relatively consistent and ranges from 6-12 microns (very fine to fine silt), with each sample dominantly composed of grains 20 microns or smaller in diameter. Most coarse silt and sand-sized grains from all samples are diagenetic products, such as silicified paleomicrobe skeletons, amorphous silica precipitate, iron oxides, or glauconite, as determined by binocular microscopic analysis. Some samples did contain significant sand-sized detrital quartz grains, most notably those of the Bone Springs Limestone. Note, the remaining-residue weight fraction includes not only detrital silicate-mineral fraction, but also these diagenetic products.
Preliminary results indicate that most of the indissolvable silicate-mineral fraction is dominated by silt. Sand-sized particles from the Bell Canyon Formation are almost exclusively diagenetic products. Sand-sized detritus is more common in the Bone Springs Limestone than the Bell Canyon Formation, implying that a rimmed shelf limits sand grains bypassing the carbonate platform during relative highstand sea level.