In this study, the inversion of TEM sounding is investigated. I solved the over-determined and the under-determined inversion problems using the steepest descent and the conjugate gradients methods. The study depends on results from the inversion of synthetic responses generated by synthetic test models.

In the over-determined problem, the inversion of layer conductivities and thicknesses are solved separately for few-layer Earth models. Out of 468 inversion runs, the results showed that the conjugate gradients method demands less calculation than the steepest descent method. The final model error and misfit values are generally better for the conjugate gradients. Although the Inversion for layer conductivities proved to be impractical in the over-determined problem, the inversion for layer thicknesses proved to be very reliable. I suggested a strategy to use both inversion types in mapping horizontal layers.

The under-determined problem was solved by a regularized inversion. A total of 48 inversion runs of five synthetic responses and one real data set have been performed. The steepest descent and the conjugate gradients methods showed a comparable performance. The regularized under-determined inversion proved to be more satisfactory in constructing the original test models than the over-determined problem, in consistency with previous works. The inversion of real data from a geologically 1-D site in Central Texas resulted in final models consistent with prior geological information about the site.

---

In this model, we will show that the high-density quasi-plasma forms at the outer surface of the outer core and accounts for the geomagnetic field. The level of thermo-ionization at the outer surface of Earth’s outer core is investigated. The density and the frequency of the plasma formed by the thermion are obtained. The high-density plasma formed by ionization can block the electromagnetic field and prevent it from penetrating the outer core.

Thermion has been well researched by physicists. In general, most of metals have large thermionic emissions when their temperatures are above 1500K. The Emission Current Density of iron at this temperature is ~10-1 A/m2 and rise sharply with temperature increases.

The earth’s outer core is liquid and consists primarily of iron with temperatures in excess of 4000K. The core mantle boundary temperature might reach 4800K or even higher and the emission current density for iron at this temperature is over 108A /m2. Equilibrium between electron emission from the outer core and electron attracted to the outer core is reached when the surface positive charge density is around 10–3 to 10-5 C/m2 at the surface of the outer core. The electrons within the mantle may form high-density plasma around the outer surface of the outer core, diffuse into the mantle and the crust or return to the core.

The relative motion between the electrons and cations produces magnetic field. The magnitude of this magnetic field is direct ratio of their relative velocity. If the geomagnetic field is mainly produced by this way, the relative circular velocity between the ions and the electrons should be ~0.1 (rad/s).

---

Seismic velocities in young (e.g., < 1 Ma) upper oceanic crust increase with depth from ~2.0 km s-1 at the top of the basaltic crust to ~6.8 km s-1 at its base. Also, seismic velocities at the top of the upper oceanic crust increase with age, while the velocities at the base remain fairly constant. The increase in seismic velocities with depth and age in oceanic crust can be explained by the stiffening of cracks with increasing overburden pressure and infilling of pore space with alteration products, respectively. Both of these mechanisms increase the moduli of the igneous crust and thus raise its seismic velocities.

Using the spheroidal pore shapes model of Kuster-Toksöz, laboratory measurements of P- and S-wave velocities, densities, and porosities of basaltic mini-cores from Hole 990A on the Southeast Greenland Margin show that pores can be effectively sealed by alteration products, and that the distribution of pore shapes is independent of porosity. Analyses of sonobuoy data collected over 0–7 Ma oceanic crust near the East Pacific Rise using the hidden layer method estimates seismic velocities of the upper oceanic crust. Sonobuoy analyses results indicate that mean top-of-basement velocities and velocity gradients are 2.8±0.1 km s-1 and 2.7±0.1 s-1, respectively. Results also suggest that top-of-basement velocities increase at a rate of 0.12±0.05 km s-1 Ma-1. A pressure-dependent asperity-deformation model describes the increase in seismic velocities with depth observed from the sonobuoy data. The asperity-deformation model incorporates a velocity variation of the form V(z) = V0(1+z/z0)n, where z is depth, V0 is the velocity at the seafloor, and z0 and n are constants. The asperity-deformation model describes how seismic velocities can increase with pressure simply through the stiffening of cracks without a need for a change in mineral moduli. Results adequately model the observed traveltimes to within an average root-mean-square misfit of 3.5 ms (less than 0.8 percent).

---

A trend of Wolfcampian-Leonardian carbonate buildups is located in the southwestern Midland Basin, Upton County, Texas. The buildup trend is located east of the eastern faulted margin of the Central Basin Platform and north of the Ozona Arch. Carbonate deposition began during lowstand times, within or just below wave base. In the Southwestern Midland Basin, the Wolfcampian-Leonardian carbonate interval is lithologically heterogeneous due to the presence of abundant lithoclastic debris that was shed from the uplifted Central Basin Platform. The lithologic heterogeneity makes it difficult to identify the buildups on seismic profiles. Several inferred buildups have been drilled in the past, but many boreholes only penetrated lithoclastic facies, not true buildup facies.

Analyses of various seismic attributes were conducted for the Wolfcampian-Leonardian interval in the SW Midland Basin in an attempt to improve the recognition and imaging of the carbonate buildups. The objective was to identify a set of attributes that directly indicate the buildup locations. After extensive trail of various attributes, the variance attribute was selected as the optimum seismic attribute. The resultant 3D variance volume was used to detect the buildup locations, and some aspects of their internal stratigraphy, and to establish the fault framework in the Amacker survey. The instantaneous frequency attribute, combined with the variance attribute was also marginally useful for imaging the buildups.

The variance attribute and instantaneous frequency were compared. Images generated from the variance attribute are better than those generated using the instantaneous frequency because on these images, it is possible to localize the buildups. The instantaneous frequency attribute combined with the variance attribute allows recognition of lithologic heterogeneities inside the buildup interval.

---

Offshore Togo, West Africa provides exciting potential for hydrocarbon exploration and potential. This area to date is virtually unexplored with prior exploration focused on shallow water pre-1986. This investigation focuses on a 625 km2 section of 3100 km2 of high quality 3D seismic data (acquired by PGS). The study area ranges from approximately 300 m – 2500 m water depth.

Research included seismic interpretation, and structural modeling of the major fault systems and unconformities within the study area. Proven source and reservoir formations from existing oil and gas fields in neighboring countries are analogous to formations identified on seismic for offshore Togo. Structures suitable for hydrocarbon accumulation were identified on seismic within potentially productive formations. Based on the correlations, seismic interpretation and modeling four possible exploration prospects were identified. The prospects were ranked according to exploration potential based on structural characteristics and a preliminary OOIP calculation. The existence of suitable structures for hydrocarbon accumulation in potentially productive formations makes offshore Togo highly prospective.

---

Experiments were conducted in flow-through reactors to investigate the creep compaction and quartz-water interactions under hydrostatic conditions at 150°C and 34.5MPa of effective pressure (pore pressure Pp=0, 0.14 MPa, and 11.7 MPa). The starting materials were St. Peter quartz sand (90-124mm, 124-180mm, and 250-350mm) and disaggregated novaculite (35mm). Theoretical models were developed to investigate 1) the relationships between grain convergence rate and pore-fluid flow, and 2) the evolution of porosity and fluid chemistry, during creep compaction of quartz sand by intergranular pressure solution.

Experiments indicate that the presence of water increases the rate of compaction. Creep compaction rates decay exponentially with strain most rapidly under dry conditions, less rapidly under vapor-dominated conditions, and slowest for water-dominated conditions. Strain rate varies inversely in power law with grain size raised to power 1.5-2.5 in water-dominated conditions.

Creep compaction rates in experiments also depend on fluid flow rate. Theoretical modeling shows that an increase in flow rate leads to higher removal rate of dissolved materials from the system, lower saturation state, and more rapid grain convergence. Grain convergence rate is nonlinearly related to flow velocity, and also varies with intergranular dissolution rate, strain, grain size and grain boundary properties.

Theoretical models indicate that porosity loss is nonlinearly related to strain. Porosity loss also depends on grain packing, stress state, and the saturation state of solution. At early stages of compaction porosity loss is dominated by intergranular pressure solution, but with increasing compaction, cementation becomes increasingly important. Isotropic compaction leads to more porosity loss by pressure solution, but less porosity loss by cementation, than uniaxial compaction.

Both experiments and numerical models indicate that pore fluids are supersaturated at early stages of creep compaction and gradually become saturated with increasing compaction. Accordingly, pressure solution should be rate-limited by precipitation kinetics at the early stages of compaction but switch to rate-limited by grain-boundary diffusion or dissolution at grain contacts with increasing compaction. The decrease in silica concentration probably results from the lessening in pressure solution and in creation and dissolution of ultrafines and high-energy surfaces.

---

We explored the colonization and destruction by wood-boring bivalves (teredinids and pholads) and wood-boring isopods (Limnoria) of conifer and angiosperm wood in a subtropical marine carbonate environment (Bahamas) and a marine siliciclastic and carbonate environments (Gulf of Mexico). Wood samples were kiln-dried lumber except for pieces of Quercus stellata Wang, which had decomposed in a terrestrial environment prior to deployment. Samples in weighted bags were deployed at a range of depths from 15 to 267 mbsl along two transects and retrieved them after one and two years in the Bahamas, and at 18 sites (60-571 mbsl) after two years in the Gulf of Mexico.

Limnoria (gribbles) attack the surface of the wood creating shallow tunnels (<2 mm diameter) initially parallel to wood grain that eventually become narrow grooves. Recovered Limnoridae include Limnoria platycaudata Menzies (15 to 73 mbsl) which produces narrow sinuous tunnels and L. pfefferi Calman (70 to 267 mbsl) which produces wider tunnels with a right-angle branching pattern. Burial of wood to a depth of more than 2 cm prohibits wood-boring isopod attack.

All of the recovered wood in the Bahamas contained Teredinid (shipworms) borings into wood creating calcite-lined tubes (5 mm diameter). Recovered Teredinidae include Teredothyra dominicensis Bartsch (15 to 88 mbsl), T. macototana Bartsch (183 to 267 mbsl) and Nodoteredo sp. (183 to 267 mbsl).

Teredinids, pholads (piddocks), and Limnoria are the dominant wood borers in the Gulf of Mexico. There was significantly more wood destruction at the shelf sites (60-183 mbsl) than the slope sites (360-570 mbsl) in the Gulf of Mexico. The amount of attack in the Gulf of Mexico was much greater than that in the Bahamas for sites of equivalent depths. At each Gulf shelf site at least one wood sample was completely destroyed; whereas we recovered all wood samples deployed in the Bahamas. Terrestrially-exposed Quercus stellata was the only wood type recovered at all sites in the Gulf of Mexico. Nonetheless, similar aspects of wood anatomy and biochemistry inhibited attack in both the Gulf of Mexico and Bahamas.

---

The Lake Maracaibo basin is a prolific basin. Its study is not straightforward due to complex tectonic history. At this time, most of the reservoirs have been found and our aim is to better understand the reservoirs and their characteristics to better anticipate production behavior and to explore new areas that are more complex.

Five reflectors were picked: the overlying unconformity, C4 reservoir layer, C5 reservoir layer, the Guasare Formation and the La Luna Formation (the source rock). Faults were picked according to the non-continuity of the seismic reflectors. The fault network is complex and consists of normal, reverse and strike-slip faults. Mapping these reflectors better defined the area of production. The main trap is a positive flower structure situated in the central area of the field. Associated faults create numerous compartments that trap hydrocarbon flow. My interpretation suggests that area west of the main fault could be interesting. This needs confirmation by a more-detailed study and more well control. Wells are mainly concentrated in the area of production; there was no well data available for the western part.

---

Experimentally deformed physical rock models are used to examine the effects of changing mechanical stratigraphy and initial fault angle on the development of fault-propagation folds over a flat-ramp-flat thrust geometry. This study also investigates the scaling properties of the models to that of natural structures and processes.

The model configurations used consist of a stratigraphic package that overlies a thrust fault that ramps upward from a basal detachment through a competent sandstone layer along a 20 or 30 degree precut ramp. Two different stratigraphic packages are used to show how the overlying stratigraphic sequence can affect the final geometry of the fault-propagation fold. One stratigraphic sequence contains a thick weak ductile layer that can undergo large thickness changes by shearing (lead is used to simulate a shale) and an overlying limestone layer that maintains constant thickness during deformation. The second stratigraphic sequence replaces the lead layer with a weak brittle layer that deforms by faulting and fracturing (dried pottery clay simulates an interbedded siliciclastic unit). The models were deformed in a triaxial deformation rig at confining pressure of 50 Mpa at room temperature.

Each model formed a fault-propagation fold with an associated footwall syncline in the footwall of the fault and hanging wall anticline. The layers within the footwall syncline exhibit steeply dipping to overturned beds. The hanging wall anticline has an asymmetric geometry with a steeply dipping forelimb and a gently dipping backlimb. Although the preceding description applies to both the lead and clay models, the mechanical responses and resulting fault-propagation fold geometries between the two stratigraphies are strikingly different. In the lead models, the thick ductile lead unit absorbs a large amount of fault displacement and promotes folding in the overlying competent unit. In the clay models, the clay absorbs limited amounts of fault displacement and has a tendency to localize strain, which results in macroscopic faulting within the clay layer. The clay transmits the associated stresses and faulting to the overlying limestone unit, which develops a forelimb thrust. The models are then compared and contrasted to natural examples.

---

Models of gas hydrate stability for the northern Gulf of Mexico continental slope address basic problems of gas hydrate geology. The maximum thickness of the gas hydrate stability zone (GHSZ) at key gas hydrate study sites is estimated, and a generalized GHSZ profile across part of the central Gulf of Mexico slope is constructed. The thickness of the GHSZ increases with increasing water depth and may reach >1 km at deepest gas hydrate sites.

Resource estimation is based on assessment of the volume of the GHSZ and concentration in sediments. The total estimate of gas hydrate resource in the Gulf of Mexico (10-14_1012 m3) is two orders of magnitude less than previously estimated. However, structurally-controlled accumulations of gas hydrate on the rims of salt withdrawal basins could be economic in the future. Bacterial gas hydrates in salt withdrawal basins are unlikely to represent a significant energy resource because they are disseminated.

The modeled minimum water depths at which gas hydrates crystallize at present in the Gulf of Mexico is 330-615 m, depending on the source gas composition. Bottom water temperature variations from seasonal changes and warm Loop Current eddies could affect sea-floor gas hydrate stability only in the upper 1-2 m of sediments. A thin but extensive hydrate geohazard zone is hypothesized on the upper Gulf slope in 440-720 m water depth. Petroleum exploitation may be impacted in this zone by sediment deformation from repetitive cycles of gas hydrate formation and dissociation.

It has been suggested that release of methane from sudden decomposition of gas hydrates could cause geologically rapid global change. The potential effect of a 100 meter sea level drop on gas hydrate stability across the slope is not significant. Larger volumes of methane and other greenhouse gases could be released in response to an increase in seafloor water temperature of 4 0C. However, several processes keep the released gas in sediments. More complicated models are needed to estimate the amount of hydrate-released gas that escapes to the ocean and participates in global change.

---

The Nam Con Son (NCS) Basin, located offshore of SE Vietnam, is one of several Tertiary rift basins that formed during initial Eocene(?)-Oligocene rifting. Following cessation of rifting at the end of Oligocene time, these basins were subjected to spatially and temporally variable, complex inversion events during Miocene time.

Fault orientations on inversion structures in the West Natuna Basin and the Western NCSB closely parallel the western side of the Natuna Arch, which may have served as a regional "buttress" where stress was concentrated and strain was deflected from Early to Late Miocene time. Early to Middle Miocene basin inversion across the Western NCSB was coincident with the most intense phase of basin inversion in the West Natuna and Malay basins.

Contraction in the Western NCS, West Natuna, and Malay basins was accommodated through reactivation of major basin-bounding fault systems that resulted in asymmetric fault-bend folding of syn- and early post-rift strata. Inversion of western Sunda Shelf basins progressed from the West Natuna and Western Nam Con Son basins into the southern Malay Basin from Early to Middle Miocene time. The most intense inversion was recorded in the West Natuna Basin during Early Miocene time with regional uplift of the southern Malay and West Natuna basins during Middle Miocene time.

Whereas both the Eastern and Western NCS sub-basins experienced fault reactivation during Miocene time, the timing and styles of inversion are different. Unlike the Western NCSB, the Eastern NCSB experienced only mild positive reactivation of pre-existing synthetic and antithetic hanging-wall faults, causing simple amplification of pre-existing rollover in the hanging-wall fill during Middle Miocene time.

Basin inversion of the West Natuna, Western Nam Con Son, and Malay basins is attributed to collision-induced clockwise rotation of Borneo and the attached, rigid Natuna Arch and Natuna Basement Ridge, beginning during Early Miocene time. This accounts for: 1) the south to north progression of inversion from Early to Late Miocene time, 2) magnitudes of inversion documented within each basin, 3) the suggested NW-SE orientation of s1, 4) the approximately N-S azimuth of compression that caused observed styles of inversion to form.

---

Samples were collected from the Caussou peridotite in the French Pyrenees, and this peridotite represents a portion of the Earth's upper mantle. These samples contain the minerals olivine, clinopyroxene, orthopyroxene, and amphibole. Therefore, the H2O-buffering equilibria:

2Tremolite + 2Forsterite ÷ 4Diopside + 5Enstatite + 2H2O
2Ca2Mg5Si8O22(OH)2 + 2Mg2SiO4 ÷ 4CaMgSi2O6 + 5Mg2Si2O6 + 2H2O

can be applied to constrain values of aH2O in these mantle samples.

The samples collected from the Caussou peridotite contain grains with different sizes. Included are large grains, porphyroclasts, that range in size from 2 to 4 mm; an intermediate grain size, medium-sized grains, that range in size from 0.6 to 1.0 mm; and finally a very small grain size, neoblasts, that range in size from 0.01 to 0.10 mm.

Amphibole grains are texturally associated with the medium-sized and neoblast grains, and this indicates that the amphibole grains are in equilibrium with these grain sizes. Consequently, the calculation of aH2O using the above equilibria has been based upon the compositions of grains with these sizes. Use of the above equilibria requires independent determination of temperature values. Thus, geothermometry was used to determine temperature estimates. This geothermometry suggests temperatures ranging from 720 to 810 °C for the medium-sized grains, and 640 to 740 °C for the neoblast grains. Pressure estimates of 8 to 10 kilobars are based upon previous work in this peridotite. These values of temperature and pressure, in conjunction with the above equilibria, yield values for aH2O that are&Mac178; 0.10.

---

This work explores cephalopod life history traits and the evolutionary consequences of those strategies. In a systematic note based on re-analysis of both morphological and genetic data generated by previous research of various authors, I propose a taxonomic revision of extant nautiloids wherein only one genus, Nautilus, and two species, N. pompilius and N. scrobiculatus, are given formal recognition.

Reproductive strategies, sexual maturity, sexual dimorphism, and heterochrony are investigated in the context of a case study of the Middle Carboniferous ammonoid Arkanites relictus from northern Arkansas. Analyses indicate that, depending on what trait is examined and what shell character is used as the proxy for age of individuals, the sexual dimorphism in A. relictus was produced by acceleration, neoteny, or hypermorphosis plus neoteny..

Analysis of intra- and inter-specific variation of embryonic morphology in Middle Carboniferous ammonoids from northern Arkansas reveals there is little variation in protoconch and ammonitella size within populations and species. In addition, data from four Carboniferous ammonoid lineages demonstrate that embryonic shell size within species is relatively stable through time. These results suggest that some embryonic features may be useful in phylogenetic analyses.

To explain the disparity in taxonomic durations and species richness between major cephalopod groups, I develop the hypothesis that species in clades characterized by short stratigraphic ranges and high total diversity had a semelparous reproductive strategy (parental mortality follows mass spawning event), whereas species in clades with long stratigraphic ranges and low total diversity had an iteroparous reproductive strategy (repeated, isolated breeding events). The relationship between reproductive strategy and embryonic shell size is discussed, and original data collected from the Carboniferous of the southern mid-continent as well as data compiled from the literature are analyzed. Compared to ammonoids, nautiloid embryonic shells are roughly an order of magnitude larger on average, and nautiloid taxonomic longevities are about three to four times greater. Differences between the groups are statistically significant across all taxonomic levels, and these results support the hypothesis that reproductive strategy has played a major role in shaping the evolutionary history of the Cephalopoda.

---

Marine vertical cable acquisition is an emerging technology. It represents an alternative to surface seismic in areas congested by platforms or other obstacles. The vertical cable acquisition consists in recording pressure at several fixed vertical receiver arrays just like for VSP. A small vessel carries only the source and is very flexible. The vertical cable receivers are in a quiet environment that can explain the data quality.

One main concern with vertical cable data is to remove the multiples, which are mainly the free-surface multiples and the receiver ghosts of multiples, preserving the primaries. Furthermore the emerging imaging algorithms tend to use the receiver ghosts of primaries instead of the primaries themselves.

The classical approach to remove multiples in vertical cable data is to consider the primaries as up-going waves and the multiples as down-going waves. The current multiple attenuation methods used in E&P industry are actually up/down wavefield separation. Different techniques can be used to achieve the wavefield separation. The common technique is the F-K dip filtering. But this method suffers from the space sampling with the aliasing problem that controls the efficiency of the filtering. An interpolation method can be used to construct the needed traces to satisfy the sampling theorem and to remove the aliases. A wave equation based up/down separation can also be used for vertical cable surveys. This method has the advantage of being less influenced by the sampling problem but it is dependent on the availability of vertical particle velocity data. This particle velocity data can be calculated from the pressure gradient and a good cable design is required for using this method.

The up/down separation based multiple attenuation methods give only a partial answer to the multiple attenuation process. This technique ignores all the remaining free-surface multiples still contained in the up-going waves. So it fails in removing all the multiples.

Another multiple attenuation method based on inverse scattering theory has been proposed by Ikelle (Geophysics, May-June issue, 2001) to preserve the primaries or the receiver ghosts of primaries for vertical cable data. It is efficient, but is dependent on the availability of surface seismic data. The method consists in combining the streamer data with the vertical cable data to predict the multiples and then to subtract them from the original vertical cable data after applying a scaling factor. The application of this technique on a synthetic model with the combining streamer and vertical cable data gives promising results, but in some cases the streamer data is not commonly available. It is then necessary to construct it from the vertical cable data with an extrapolation technique.

---

Over the past three decades, marine exploration has been essentially limited to water depths within the 200-500 m range. With most reservoirs in this range depleting, exploration is moving towards very shallow water, less than 100 m, as well as deeper water, greater than a kilometer in depth. These two frontiers pose new challenges for seismic acquisition and processing. Our interest in this thesis focuses on the challenges associated with acquisition and processing in shallow water regions, in particular the attenuation of free-surface multiples.

Free-surface multiple elimination in shallow-water must address removal of the direct wave, interpolation of missing near-offsets, and the presence of guided waves and strong refracted wave energy. In order to study these challenges associated with acquisition and processing of shallow-water data, synthetic seismic data for 150, 75 and 25 m water depths were generated using a fully elastic, finite difference algorithm. The direct wave was removed with a "model then subtract" method due to the interference with the sea-floor primary event. The synthetic data contained offsets from 0-2000 m, requiring no interpolation of missing near-offsets. The guided wave energy was removed with an f-k filter, and the refracted energy was muted after the data was corrected for normal moveout.

Predictive deconvolution (Preddcon) and Inverse Scattering Multiple Attenuation (ISMA) were two algorithms compared for their effectiveness in eliminating free-surface multiple energy from the data. For the 150 m case, Preddcon removed most of the multiple energy in the very near-offsets, where theoretical assumptions remained valid. Preddcon removed multiple energy over a larger offset range for the 75 m case, within the design window. For larger offsets, where the assumptions cannot be satisfied, multiples were not attenuated and primaries were altered. For both water depths, the two-pass approach adopted for ISMA performed far superior across all offsets for removing free-surface multiples, while preserving primary amplitudes, because the primaries and multiples were well-separated. However, for the 25 m case, where there is no separation between primaries and multiples and moveout difference is almost negligible, Preddcon had superior results because the multiple reverberation pattern remained similar across offsets.

---

The molecular mechanisms and major geochemical factors controlling the sorption of nonionic organic chemicals (NOCs) to hydrated mineral surfaces in low-organic-carbon environments are not yet fully understood. Although various models have been advanced to describe NOC sorption to mineral surfaces, none of them have been verified by spectroscopic data. The major hypothesis of this research was that the cation-p interactions form the predominant mechanism controlling polycyclic aromatic hydrocarbons (PAHs) sorption to hydrated mineral surfaces. Macroscopic sorption studies were conducted in conjunction with deuterium nuclear magnetic resonance (2H NMR) spectroscopy to examine the influence of mineral surface chemistry and the nature of exchangeable cations on the formation of cation-p bonds. The sorption of naphthalene and pyrene, as representative PAHs, was quantified to specific cation-saturated minerals, including porous silica gels, kaolinite, and vermiculite. Spin-lattice relaxation time (T1) and spin-spin relaxation time (T2) of deuterated benzene in aqueous solutions and clay suspensions were measured, providing spectroscopic evidence for the first time that cation-p interactions exist between PAHs and cations in aqueous solutions. The binding energy of the aqueous metal-benzene complex varied with the hardness/softness of the metal cation. An overall binding energy sequence of Ag+ >> Cs+ > K+ > Na+, Li+ in the aqueous phase was derived based on the T1 measurements of deuterated benzene. Saturating mineral surfaces with softer transition metals or base cations generally increased PAH sorption relative to harder cations. These results suggest that softer metal cations present on hydrated mineral surfaces can directly enhance the sorption of PAHs through cation-p interactions. Quadrupolar splitting of deuterated benzene in Na-montmorillonite suspensions indicated the ordering of benzene molecules with respect to the clay surface, which likely resulted from the cation-p interaction between benzene and exchangeable cations. Further T2 measurements of deuterated benzene in clay suspensions indicated that pH and ionic strength also affects PAH sorption through varying structures of adsorbed water and hence cation-p interactions at mineral surfaces.

---