Petrographic study of the Deicke and Millbrig K-benonite beds (altered volcanic ash) of Rocklandian age has revealed that they can be distinguished by their non-clay mineralogy. The Deicke phenocryst assemblage is primarily labradorite, Fe-Ti oxides, apatite, and zircon, while the Millbrig assemblage is primarily andesine, quartz, biotite, apatite, and zircon. The Deicke is altered dacitic ash, while the Millbrig is altered rhyodacitic ash.
Alkylammonium ion exchange, x-ray powder diffraction (XRD), x-ray fluorescence spectroscopy (XRF), and high resolution transmission electron microscopy (HRTEM) have been used to study the chemistry and the physical properties of illite/smectite (I/S) clays from Paleozoic K-bentonites. The data have been used to evaluate current models of I/S interstratification and the mechanism of formation of illite during bentonite diagenesis.
A 3rd order theory of folding of viscous multilayers indicates that forms of folds are controlled by the behavior of layer contacts or interbeds, the relative stiffnesses of the multilayer and confining media, and the scale of the folding. A 2nd order analysis shows that asymmetry of folds is determined largely by the behavior of layer contacts and the sense of layer-parallel shear during folding.
In east-central Utah, tide-, wind-, and wave-currents deposited the Middle Jurassic (Callovian) Curtis and Summerville Formations and the Moab Member of the Entrada Sandstone along the southern and eastern coastal plain of an interior seaway. Four facies of the Curtis were deposited during maximum transgression and incipient regression. Interbedded, heterogeneous litharenite and sublitharenite microsequences in the sandstone-mudstone facies record the initial transgression and development of sedimentation on a nearshore shelf. Sand and mud were intermittently transported by tidal- and wave-currents at near wavebase depths. The composite sandstone facies contains amalgamated, crossbedded and parallel-bedded subarkosic microsequences which were deposited during late transgression, stillstand and incipient regression in a tidal channel, sand-shoal, berm system. Sand, silt and mud were transported in the form of ripples, sand waves and dunes in tidal channels controlled by spring and neap tidal current. At shallower intertidal depths, interchannel sand shoals and berms were constructed by plane- and cross-laminated strata. Contemporary crosslaminated and locally crossbedded sublitharenites in the rippled silty facies and the redbed facies were deposited by spring-tide and wind- or storm-enhanced tidal currents in higher intertidal and supratidal zones respectively.
A stratigraphic and paleontological analysis of 303 samples of Paleocene sediments of the eastern Gulf Coastal Plain of Mississippi, Alabama, and Georgia provided the basis for a geochronologic, quantitative paleoecologic, and paleoceanographic model.
It is recognized that the ecology of planktonic foraminiferal assemblages provides information about the chemical and physical properties of the water in which they live. Their areal and vertical distributions in the water column and in deep-sea sediments may be used to derive oceanographic and climatic models of Recent and past oceans.
Metamorphism in the Ollo de Sapo Antiform, part of the Variscan Orogen in NW Spain, was controlled by local, complex interactions of deformation, granitoid intrusions, and regional low pressure metamorphic (LPM) gradient. Detailed analysis of mineral parageneses, in conjunction with geothermobarometry and one-dimensional thermal modeling, have been used to constrain pressure-temperature-deformation (P-T-D) paths for rocks in the antiform.