Mechanisms of Sedimentation Inferred from Quantitative Characteristics of Heavy and Light Minerals Sorting and Abundance
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Hydraulic behaviors of particles with contrasting sizes and densities and flow structure of hyperconcentrated suspensions were empirically studied in a thin vessel by using particle-image-velocimetry techniques. Particle volumetric concentration, C_(v), of the suspensions were mainly affected by the majority particle species, silica ballotini. The minority population was aluminum ballotini (hydraulically fine). At high C_(v), aluminum particles were less retarded and settled as if they were hydraulically coarser. This was because particles moved in a cluster-like motion. Terminal settling velocities of both particles converged at C_(v )≥ 25%, and particle sorting was diminished. Spatial and size distributions of mineral grains with contrasting densities in massive sandstones of turbidites from the Middle Permian Brushy Canyon Formation were used to estimate suspended sediment concentrations and interpret hydraulic evolution of the turbidity currents. Semi-quantitative elemental distributions were estimated by x-ray fluorescence analytical microscopy, μXRF. Within the structureless sandstone, zircon grains (hydraulically fine) fined upward while feldspar grain (hydraulically coarse) sizes did not change. Both grains had hydraulically equivalent settling velocities in overlying siltstone layers. These suggest that these sandstone divisions were deposited from hyperconcentrated suspensions where particle segregation was diminished and hydraulically fine grains were entrained with hydraulically coarse particles. While structureless sandstones were deposited, C_(v) increased through distance and time because hydraulically fine particles were fining upward. This evolution likely be resulted from volumetric collapse of the turbidity currents. Geochemical concentrations and properties of Zr- and Ti-rich particles were used to qualitatively estimate erosional event sizes of hemipelagic thinly laminated siltstone. Zircon and rutilated quartz particle sizes, Zr/Ti fluorescence ratio, and lamination thickness were determined by μXRF. Zircon grains were finer than rutilated quartz grains. Their grain sizes were systematically correlated but neither was correlated with Zr/Ti ratio. Instead, Zr/Ti ratio covaried with lamination thickness. Since zircon grains are smaller but heavier than rutilated quartz grains, zircon has lower susceptibility to erosion, particularly by wind. Thus, fluctuations of Zr/Ti fluorescence ratio in Brushy canyon Formation siltstones most likely result from variations in the intensity of erosional events at the particle source or sources, with high Zr/Ti ratios reflecting periods of intense erosion.
Motanated, Kannipa (2014). Mechanisms of Sedimentation Inferred from Quantitative Characteristics of Heavy and Light Minerals Sorting and Abundance. Doctoral dissertation, Texas A & M University. Available electronically from