Papers by Allard, M.M.

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Allard, M.M. . 1988. Heavy Mineral Analysis of Inner Continental Shelf Sediments, Northeastern Gulf of Mexico. Geology. Tallahassee, Florida State University.
A heavy mineral analysis was conducted using samples from eleven vibrocores retrieved from the inner shelf of northeastern Gulf of Mexico. Heavy mineral weight percentages averaged 0.2% in the 2-3 phi fraction and 0.5% in the 3-4 phi size fraction. Mineral abundances ranged between 0.03% and 2.9%, with kyanite, sillimanite and zircon dominating the heavy mineral suite. Heavy mineral abundances generally increase westward in the 2-3 phi fraction from 0.11% to 0.24% in the top core intervals. An average increase in abundance of 0.15% occurs with depth in this size fraction in cores from Cape San Blas Shoal. Cores located on St. George Shoal contain the largest heavy mineral percentages, 1.6% and 1.8%, in the 3-4 phi fraction. The westward increase of heavy minerals found in the 2-3 phi fraction is not observed in the 3-4 phi fraction. Textural analysis indicates the study area sediment is medium to fine sand with virtually no gravel or mud. The eastern sediment suite includes cores from offshore middle St. George Island west to St. George Shoal. The sediment suite includes cores from Cape San Blas Shoal west to offshore Panama City. A slight increase in maturity as indicated by suite statistics occurs in the western sediment suite. The eastern sediment suite is less mature and appears to be more characteristic of a river- dominated environment. Quantitative analysis of the heavy mineral suite was accomplished on the x-ray diffractometer. This method was tested statistically and a comparison was made with the traditional point-counting technique. XRD standards consisting of heavy minerals found in the study area and a fluorite spike were used to calibrate standard curves for predicting heavy mineral weight percentages in sediment samples. Several samples of known composition comprised of eight heavy minerals were analyzed and plotted on the regression curves as a further check of the XRD method. Most samples fell within the second error envelope, the 95% confidence level, on the regression lines. The error envelopes serve as confidence levels for predicting a dependent variable based upon a known independent variable. Point-counting and x-ray diffractometry identified the same heavy mineral suite, with the exception of kyanite, which was not detected in a few of the XRD patterns.
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