Thomas T. Tieh

The role of carboxylic acids in albite and quartz dissolution: An experimental study under diagenetic conditions

Abstract Simple water soluble organic acids may promote secondary porosity development in sandstones during diagenesis by increasing feldspar solubility and dissolution rate. To test this hypothesis, Amelia albite and Brazilian hydrothermal quartz were reacted with 0.07 m acetate and 0.07 m acetate-0.005 m oxalate solutions at selected pH values, and distilled water. Pore fluid chemistry was monitored through time at various flow rates to obtain both solubility and dissolution rate data. The experiments were conducted in large volume, semi-static, flow-through systems at 100°C and 347 bars. These systems simulate subsurface flow rates, low mass water/rock, and high surface area/fluid mass. Acetate and acetate + oxalate solutions significantly increase albite solubility at temperatures, pressures, and pH values typical of diagenetic environments. Albite solubilities increased in acetate and acetate + oxalate solutions by factors of 2 and 3.4, respectively, compared to distilled water. In these same solutions, Al concentrations were ≈ 140 and ≈480 times higher than that calculated for kaolinite solubility at the same conditions without organic species. These enhanced solubilities occur at pH values (4.6–4.8) that may overlap with formation waters. In contrast to albite, quartz solubility was essentially identical in all solutions investigated. Dissolution rates in the acid region decreased with increasing pH in the acetate and acetate + oxalate solutions. Slopes of log rate vs. pH curves were ≈0.6 for acetate and ≈0.3 for acetate + oxalate. Although the effects of acetate on the dissolution rate are small, the effects of oxalate are significant. A rate law valid for albite dissolution at 100°C, oxalate concentrations to 0.01 m, and pH values ranging from 3.4 to 5.5 is given below (assuming activity coefficients = 1 and acetate rate ≈ the proton-promoted rate): R total = 5.88 × 10 −11 + 5.01 × 10 −8 m 0.56 H+ + 6.7 ×10 −10 2.3 × 10 −4 m O x /(1.0+2.3 × 10 −4 m O x ), where m O x and m H + are oxalate and H + molal concentrations, respectively. Reacted albite grains examined by SEM show extensive dissolution concentrated along cleavage planes and structural imperfections such as twin boundaries and fluid inclusions, consistent with surface-controlled reaction kinetics. No authigenic aluminosilicate minerals were observed. The lack of authigenic clays indicates the efficiency of oxalate and acetate in mobilizing and transporting Al. The combination of enhanced solubility and increased dissolution rates indicates that carboxylic acids may play major roles in feldspar dissolution and secondary-porosity development during diagenesis of feldspathic sandstones.

Release of uranium from granitic rocks during in situ weathering and initial erosion (central Texas)

Abstract The abundance, distribution and nature of occurrence of uranium in granitic rocks in central Texas, and that in soil profiles and local stream sediments derived from these rocks have been determined by fission-track mapping, delayed-neutron counting and gamma-ray spectrometry. Selected samples were also analyzed for Th and K. In the granites, U occurs primarily in weathering-resistant accessory minerals (here called resistate U) and along grain boundaries of major minerals, particularly biotite (here called intergranular U). During in situ weathering and initial erosion of the granite, changes in U concentration are controlled by the chemical mobility of intergranular U and dispersal of the resistate U. No distinct trend is detected in soil profiles except that, in general, a slight depletion of U is noted at the top of the profiles, which may be followed by a slightly enriched zone and another zone of depletion before approaching the original U content of the granite at depth. Neither organic matter nor clays (mostly kaolinite) appear to be effective fixing agents of U in this area. However, in briefly-transported granitic sediment, mostly sand and gravel, significant loss of both U and Th has occurred. In the 1-km distance studied, U abundance reflects almost entirely the concentration of resistate U. These results indicate that most, if not all, of the mobile, intergranular U is released from granites during in situ weathering and initial transport; in granitic sediments resistate U is likely the predominant form. The mineralogical occurrence of Th has not been determined, but the rate of Th loss in stream sediments is even greater than that of U. Th, leached from granite during weathering, may have become adsorbed on clays and dispersed with them.

Fission track study of uranium in two granites of central texas

The four primary modes of microscopic occurrence of uranium in the Katemcy and Streeter granites of central Texas as revealed by fission track “mapping” are: 1) in accessory minerals; 2) along grain boundaries; 3) in microfractures; and 4) in quartz and feldspars. Most of the uranium occuring in the first three modes, accounting for more than three-fourths of the total, appears to be readily mobilized during weathering.

The effects of wind transport on the shapes of quartz silt grains

ABSTRACT Wind-blown terrigenous silt is a common component in marine sediment, but it is often difficult to distinguish from fluvial silt. A field experiment was conducted in the Loess Plateau of China to determine the effect of eolian transport on the shapes of detrital quartz silt grains and to define grain-shape criteria for the recognition of eolian silt. The results show that eolian transport results in a rapid downwind increase in the roundness of quartz silt grains, and that this increase in roundness is apparently due to preferential transport, or shape-sorting, of more rounded grains. This capacity for shape-sorting distinguishes eolian from fluvial transport, which has no great effect upon the shapes of quartz silt grains, and provides a petrographic criteria for the distinction of t e eolian and fluvial silt components in marine sediments.

Basalt from Louisiana continental shelf

A basalt outcrop was discovered on Alderdice Bank on the outer Louisiana continental shelf. The basalt shows an age of 76.8 ± 3.3 × 106 years. Textural, mineralogical, and chemical characteristics indicate that it is an alkali basalt of shallow intrusive origin. It was probably brought to the seafloor by salt tectonics and exposed due to salt dissolution.An accurate account of the Mesozoic geologic history of the Gulf of Mexico must consider the apparent consanguinity of all magmatic rocks of the region, including the Alderdice Bank basalt, and the apparent basinward decrease in age of magmatic activities.

Trapping capacity of faults in the Eocene Yegua Formation, East Sour Lake field, southeast Texas

The properties of a sheared zone in the Eocene Yegua Formation were investigated to evaluate the trapping capacity of faults. An 11-m core of Yegua sandstone at a depth of 3029 m shows highly sheared bedding and increasing dip from 10 to 30 with depth. Porosity and permeability of the sheared zone range from 10 to 12% and 1 to 5 md, respectively (about 10–16% of porosity reduction and 29–60 md of permeability reduction). Most pores in this sandstone are of secondary origin. Pores in the sheared zone were deformed and collapsed because of clay smears and shear. Physical characters of sheared zones were investigated by optical and scanning electron microscopy (SEM). A reduction of porosity and permeability with depth approaching the sheared zones created a capillary barrier that prevents hydrocarbon drainage and compartmentalized the reservoir. Initial oil/water, capillary displacement pressure of the sheared zone is 100 psi (6.89105 Pa), sufficient to trap an average oil column of 210 m and gas column of 70 m.

Effects of Laboratory Consolidation on Petrophysical Properties of Fine-Grained Marine Sediments: Electron Microscopic Observations

Abstract Pliocene-Recent marine sediments, recovered at site 1125 by ODP Leg 181 on the eastern New Zealand margin, were subjected to laboratory consolidation tests and analyzed by scanning electron microscopy (SEM) before and after consolidation test. The primary objective of this study is to document the effects of consolidation on microfabric and petrophysical properties. X-ray diffraction and grain-size distribution data indicate that the samples are mineralogically and texturally similar and thus are ideal for the present study on the role of consolidation solely on petrophysical properties. Porosity was measured before and after each consolidation test, and permeability was estimated indirectly based on the theoretical method. SEM photomicrographs show details of changes of pore geometry and distribution after the consolidation test that account for the porosity loss.

Chemical variations in sedimentary facies of an inner continental shelf environment, Northern Gulf of Mexico

Abstract Four major sedimentary provinces of the inner continental shelf off the Louisiana coast have been recognized by textural studies (Krawiec, 1966): deltaic, non-deltaic, and relict sediments; and deltadestructional sands. Samples from these provinces have been analyzed for Rb, Sr, Ni, Fe,Mn, Ti, and Zr; trend surface analysis has been used to discern regional trends of these elements. These trends substantiate the previous division of shelf provinces. Although deltaic and non-deltaic sediments cannot be distinguished by chemical criteria, they are distinctive from relict sediments, which are low in Mn, Fe, Ti, Zr, Rb, and Ni, and high in Sr. The delta-destructional sands are distinctive from the other three provinces by their low contents of Mn, Fe, Rb, and Ni, and high Ti, Zr, and Sr. In an energetic environment such as this, processes subsequent to deposition tend to disperse Rb, Fe, Ni, and Mn, as these elements are closely associated with the clays; these processes may give rise to enrichment of Zr due to the high stability and density of the mineral zircon, or the enrichment of Sr by accumulation of organic remains.

Carbonate-Rich Dikes in Ignimbrites of Southeastern Nevada

In southern Lincoln County, Nevada, carbonate-rich dikes ranging in width from a few inches to about 40 ft intrude rhyolitic ignimbrites of the late Tertiary Kane Wash Formation. In the cryptocrystalline calcite matrix that forms 40 to 55 percent of the rock are embedded xenoliths of rhyolitic tuff and abundant crystals and crystal fragments of quartz and sanidine. Minor constituents are iron-oxide granules, andradite crystals, basalt fragments, and small glass particles, many of which are tubular. This intrusive rock lacks the trace-element composition and petrologic associations of accepted carbonatites. Carbon, oxygen, and strontium isotope ratios are not diagnostic. The chemical composition, the texture of the calcite, the forms of the glass particles, and the occurrence in ignimbrites that contain primary calcite indicate that the intrusive melt was formed by mixing of a silicate magma and melted limestone.

Heavy mineral assemblages in some Tertiary sediments in San Mateo County, California

ABSTRACT Four heavy mineral assemblages, each characteristic of a stratigraphic horizon, have been found in Eocene and Miocene sediments disclosed along the Stanford Linear Accelerator excavation in central California; they are: Middle and Upper Eocene: zircon-tourmaline Upper Eocene: biotite-garnet-sphene Lower Middle Miocene: epidote-glaucophane-chromite-hornblende Upper Middle Miocene: sphene-garnet-zircon-tourmaline. The Middle and Upper Eocene assemblage was derived from the Sierra Nevada, and it appears that this assemblage has a widespread occurrence in central California. Paucity of heavy minerals, a distinctive characteristic of this assemblage, and abundance of authigenic minerals are attributed to intensive weathering of source rocks and diagenetic alterations. The Upper Eocene assemblage was derived largely from intrusive and metamorphic rocks of the Coast Range. Predominance of epidote and abundance of chromite, hornblende, and glaucophane in the lower Middle Miocene assemblage indicate that during that time the area was situated in an enclosed embayment bordered by rocks of the Franciscan group. The upper Middle Miocene assemblage shows a mixed character, minerals characteristic of both he Sierra Nevada province and the Franciscan rocks of the Diablo and Coast Ranges are persistent constituents.