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Full-Text Articles in Physical Sciences and Mathematics
Exceptionally Well-Preserved Early Oligocene Diatoms From Glacial Sediments Of Prydz Bay, East Antarctica, John A. Barron, Albert D. Mahood
Exceptionally Well-Preserved Early Oligocene Diatoms From Glacial Sediments Of Prydz Bay, East Antarctica, John A. Barron, Albert D. Mahood
United States Geological Survey: Staff Publications
An exceptionally well-preserved early Oligocene diatom assemblage is documented and illustrated from the internal sediment of a gastropod shell, which was collected from glacial sediments recovered at Ocean Drilling Program Site 739 on the continental shelf in Prydx Bay, Antarctica. The diatoms were deposited between 35.9 and 34.8 Ma according to diatom and calcareous nannofossil stratigraphy, apparently soon after a period of major ice sheet advance across the Prydz Bay continental shelf. The diatom assemblage is neritic in character. but it can readily be correlated with open ocean assemblages from the Southern Ocean as well as with similar material recovered …
Short-Term Sediment Accumulation Rates Determined From Eocene Alluvial Paleosols, Mary J. Kraus, Thomas M. Bown
Short-Term Sediment Accumulation Rates Determined From Eocene Alluvial Paleosols, Mary J. Kraus, Thomas M. Bown
United States Geological Survey: Staff Publications
A new method uses alluvial paleosols to calculate sediment accumulation rates for thin (25 m) stratigraphic intervals and allows the reliable interpolation of ages for stratigraphic levels within a thick stratigraphic interval bounded by established dates. Sediment accumulation rates calculated for a 650 m composite section in the Eocene Willwood Formation of Wyoming span time intervals ranging from only 0.05 to 0.25 may. Important sedimentologic changes coincide with changes in accumulation rate and indicate close and direct relations between the history of basin subsidence and depositional patterns.
Seismotectonics Of The San Andreas Fault System Between Point Arena And Cape Mendocino In Northern California' Implications For The Development And Evolution Of A Young Transform, David A. Castillo, William L. Ellsworth
Seismotectonics Of The San Andreas Fault System Between Point Arena And Cape Mendocino In Northern California' Implications For The Development And Evolution Of A Young Transform, David A. Castillo, William L. Ellsworth
United States Geological Survey: Staff Publications
The northernmost and relatively youthful segment of the San Andreas fault system is situated within a 100+ km wide zone of northwest trending strike-slip faults that includes, from west to east, the San Andreas, Maacama, and Bartlett Springs faults. Although the San Andreas fault is the principal strike-slip fault in this system, it has been virtually aseismic since the 1906 earthquake. Moderate levels of seismicity locate to the east along the Maacama fault and, to a lesser extent, the Bartlett Springs fault at focal depths typical of other strike-slip faults within the San Andreas fault system in central California. North …
Time-Stratigraphic Reconstruction And Integration Of Paleopedologic, Sedimentologic, And Biotic Events (Willwood Formation, Lower Eocene, Northwest Wyoming, U.S.A.), Thomas M. Bown, Mary J. Kraus
Time-Stratigraphic Reconstruction And Integration Of Paleopedologic, Sedimentologic, And Biotic Events (Willwood Formation, Lower Eocene, Northwest Wyoming, U.S.A.), Thomas M. Bown, Mary J. Kraus
United States Geological Survey: Staff Publications
Relative paleosol maturities are inversely proportional to the accumulation rates of the sediment upon which they formed, and are therefore excellent relative indicators of how much geologic time elapsed between any two horizons. An empirically-based model is advanced using paleosol maturities to estimate the relative geologic time separating any stratigraphic levels within the lower Eocene Willwood Formation. The revised Willwood time stratigraphy from this analysis helps evaluate the nature, tempo, and possible causes of three major episodes of mammalian appearance and disappearance. These faunal events are directly correlated with certain aspects of paleosol evolution in the Willwood Formation. That evolution …
Systematics, Biostratigraphy, And Dental Evolution Of The Palaeothentidae, Later Oligocene To Early-Middle Miocene (Deseadan-Santacrucian) Caenolestoid Marsupials Of South America, Thomas M. Bown, John G. Fleagle
Systematics, Biostratigraphy, And Dental Evolution Of The Palaeothentidae, Later Oligocene To Early-Middle Miocene (Deseadan-Santacrucian) Caenolestoid Marsupials Of South America, Thomas M. Bown, John G. Fleagle
United States Geological Survey: Staff Publications
The family Palaeothentidae contains some of the dentally more specialized of the small-bodied marsupials of South America and was a clade almost equivalent with the Abderitidae in having been the most abundant caenolestoids. They were unquestionably the most diverse, containing two subfamilies, nine genera, and 19 species, with a distribution ranging from Colombia to Tierra del Fuego. The best and most continuous record of the Palaeothentidae is from Patagonian Argentina where eight genera and 17 species are recognized. There, the Palaeothentidae ranged in age from the Deseadan (later Oligocene) through the late Santacrucian (middle Miocene-the Santacrucian record lasting from about …