Abstract Colloid concentration is an important parameter in models of colloid-facilitated transport. The purpose of the present study is to characterize colloid concentrations and colloid stability in natural groundwater from the Horonobe Underground Research Laboratory (URL) in Hokkaido, Japan. The particle sizes of colloids in groundwaters from the Horonobe URL range from several nanometres to c . 500 nm, with a mode particle size of c . 120 nm. Evaluation of colloid stability by DLVO theory suggests that larger colloids (i.e. >100 nm in diameter) would be more stable than smaller colloids in some groundwaters. The estimated colloid particle concentrations when considering the results of DLVO calculations ranged from 2.33 × 10 6 to 1.12 × 10 8 particles/ml, and mass concentrations were estimated to range from 45 to 1540 µg l −1 for diameters greater than 100 nm. Colloids in Horonobe groundwaters appear to be less stable, with a moderate potential for transport, than colloids investigated in similar international studies. This reduced stability may be due to relatively higher ionic strengths and moderate dissolved organic concentrations in Horonobe groundwaters compared to their international counterparts.

ABSTRACT Lithologies, depositional environments, stratigraphic architecture, and conodont biostratigraphy of Lower to Middle Mississippian rocks in the western Ozarks comprise five depositional sequences in ramps on the southern Burlington shelf. Aggradational ramps in the Kinderhookian to early Osagean St. Joe group were relatively strongly overprinted by Ouachita-related tectonism involving inferred recurrent passage of fore-bulge highs and associated basins across central and southern parts of the outcrop area. Significant effects of tectonism are southward facies shallowing onto the broad Kanoka ridge paleotopographic high associated with locally extensive marine and lesser subaerial erosion, sediment thickening and deposition of generally northward down-lapping, resedimented wedges with dislodged reef blocks and conglomerates into relatively rapidly subsiding basins, and formation of a regionally extensive paleosol at the top of the group. Back-stepping subsidence due to middle Osagean foundering of the Kanoka ridge was followed by rapid, long-distance progradation of middle- and outer-ramp facies in the Bentonville and Reeds Spring limestones. Tectonism at this time resulted variously in local folding, uplift, marine and subaerial erosion, and reversal of shelf bathymetry. Southward erosion of the Reeds Spring and Bentonville occurred at least in Oklahoma on rejuvenated segments of the Kanoka ridge. Overlying lower Meramecian limestones are shallow-water deposits truncated by a major unconformity.

ABSTRACT Mississippian carbonates of northern Oklahoma were deposited on the Anadarko shelf (ramp) as several shallowing-upward sequences. In Woods County, Oklahoma, the Mississippian ranges in thickness from 350 ft (105 m) to the south to as little as 100 ft (30 m) to the north due to uplift and erosion. Lithologies observed in core are chert conglomerate, tripolitic chert (tripolite), dense chert, chert-rich limestone, dense limestone, and shale-rich limestone. To evaluate the spatial distribution of Mississippian lithologies and petrophysical properties, and to explore the controls on production, this study integrates 3-D seismic with core and well-log data. As a constraint for 3-D lithology modeling, lithology logs were estimated using a neural-network approach with core and log data resulting in 65.1% accuracy. A P-impedance volume from seismic inversion was used to constrain the spatial distribution of tripolite in the model, the main reservoir lithology. Lithology-constrained 3-D porosity and water saturation models show that tripolite is the most porous and heterogeneous lithology. Comparing lithology, porosity, and water saturation models to production data illustrates that production from vertical wells is primarily controlled by porous tripolite distribution, whereas horizontal wells produce from both tripolite and chert-rich limestones and are most sensitive to water saturation variations.

The Neogene Boca basin, located 15 km northeast of Truckee, California, records the depositional and deformational history for the late Miocene–Pliocene period in this part of the northern Sierra Nevada. This study consists of fine-scale analysis of the well-exposed Neogene sedimentary rocks in an otherwise poorly exposed area of the northern Sierra Nevada. The Neogene Boca basin sedimentary section is >500 m thick and dips generally west to southwest. Four distinct lithologic intervals are deposited unconformably over lahars and intermediate lavas of the Miocene Kate Peak Formation. An ~180-m-thick section of conglomerate and conglomeratic litharenite represents a generally southwest directed fluvial system that existed from at least 4.4 Ma (interval I). This is overlain by and locally interfingered with a ca. 4.38 Ma basalt flow of Boca Hill. Above this basalt, an ~107-m-thick section of quartz wacke and siltstone deposits represents a deltaic system controlled by local volcanic topography from ca. 4.4 to 4.1 Ma (interval II). Conformably above interval II, an ~122-m-thick section of silty diatomite deposits with interbedded tephra and litharenite represents a lacustrine environment from ca. 4.1 to 2.7 Ma (interval III). Overlying the diatomite along a disrupted surface, a >91-m-thick section of medium- to coarse-grained litharenite and cobble conglomerate represents an abrupt change in depositional environment, to a west directed fluvial system (interval IV). Pliocene westward tilting and change in base level began during deposition of interval IV (ca. 2.7 Ma) and prior to eruption of the Boca Ridge Formation (ca. 2.61 Ma). Four orientations of large faults (>0.1 m displacement) are distributed evenly across the basin: (1) northeast to north-northeast striking sinistral faults; (2) northwest to north-northwest striking dextral faults; (3) west to west-northwest striking oblique-reverse faults; and (4) other fault orientations that have apparent motions not included in these categories. Strike-slip faulting is thought to have occurred during tilting of the Neogene section. The distributed conjugate strike-slip faults in the rocks of Boca basin accommodated east-southeast directed extension and south-southwest directed contraction. These new stratigraphic and structural data provide information on late Miocene–Pliocene deformation at the eastern edge of the Sierra Nevada. The Boca basin appears to have been an isolated basin controlled by volcanic topography. A late Miocene deformation event is not recorded in Boca basin; however, a Pliocene event is recorded in the termination of deposition and deformation of the section through tilting, incision, and distributed faulting. Pliocene deformational style is consistent with generally east-west extension associated with westward encroachment of the Basin and Range or northward migration of normal faults at Lake Tahoe. The structural data cannot disprove migration of Walker Lane deformation into the Sierra Nevada but merely show that this did not occur in the area occupied by the Neogene Boca basin. The Pliocene deformation event coincided with local eruption of high-potassium lavas and a regional base-level change, and it may represent rollback of the Juan de Fuca plate after ca. 3 Ma.