Dennis O. Terry

Large temperature drop across the Eocene–Oligocene transition in central North America

The Eocene–Oligocene transition towards a cool climate (∼33.5 million years ago) was one of the most pronounced climate events during the Cenozoic era. The marine record of this transition has been extensively studied. However, significantly less research has focused on continental climate change at the time, yielding partly inconsistent results on the magnitude and timing of the changes. Here we use a combination of in vivo stable isotope compositions of fossil tooth enamel with diagenetic stable isotope compositions of fossil bone to derive a high-resolution (about 40,000 years) continental temperature record for the Eocene–Oligocene transition. We find a large drop in mean annual temperature of 8.2 ± 3.1 °C over about 400,000 years, the possibility of a small increase in temperature seasonality, and no resolvable change in aridity across the transition. The large change in mean annual temperature, exceeding changes in sea surface temperatures at comparable latitudes and possibly delayed in time with respect to marine changes by up to 400,000 years, explains the faunal turnover for gastropods, amphibians and reptiles, whereas most mammals in the region were unaffected. Our results are in agreement with modelling studies that attribute the climate cooling at the Eocene–Oligocene transition to a significant drop in atmospheric carbon dioxide concentrations.

Effect of paleosol formation on rare earth element signatures in fossil bone

The rare earth element (REE) content of fossil bones was analyzed and compared with the degree of ancient pedogenic development and depositional environments from several locations in the Orellan Scenic Member of the Oligocene Brule Formation in Badlands National Park, South Dakota. Paleosols ranged from weakly developed Entisols to more strongly developed Inceptisols, all typical of fluvial environments and possible paleocatena variation. Paleosols were alkaline and well drained. Sediments with sparse soil features from an oxbow lake system suggest that conditions were too waterlogged and sedimentation rates too rapid for significant pedogenesis. The variance of REE signatures in fossil bones from the paleosol sites was significantly greater than that of fossils from minimally altered sediments of the former oxbow lake. Positive Ce anomalies were associated with low U concentrations and indicate paleoredox conditions. Greater degrees of pedogenesis, regardless of the horizon in which the bone was found, systematically correlated with increased heavy REE enrichment in fossil bones. The fossil-bone REE signatures from the different paleosols and depositional environments were significantly different and distinguishable.

Marine Cretaceous-Tertiary boundary section in southwestern South Dakota

A distinctive zone of disrupted strata, which we interpret as a distal manifestation of the end-Cretaceous Chicxulub impact event, occurs over 300 km 2 in southwestern South Dakota. This disrupted zone is within the Fox Hills Formation, ranges from 0.5 to 5 m in thickness, and contains large-scale slump-roll structures, clastic dikes, flame structures, and massive, homogenized beds. The zone is ∼0.5 m above a belemnite fauna Sr dated as 67.6 ± 0.5 Ma, contains scaphitid ammonites characteristic of the Jeletzkytes nebrascensis ammonite zone of the Fox Hills Formation, and is capped by a 0.5–4-cm-thick brownish-black mudstone that contains spherules. Pollen of the late Maastrichtian Wodehouseia spinata palynostratigraphic zone occurs immediately above and below the disrupted zone. The disrupted zone is overlain by an additional 25 m of marine Fox Hills Formation. These stratigraphic relationships suggest that the upper part of the Fox Hills Formation in this part of South Dakota is Paleocene; that the Western Interior Seaway was locally present well into the Paleocene; and that scaphitid ammonites may range the Cretaceous-Tertiary (K-T) boundary.

Reading Virginia's Paleoclimate From The Geochemistry And Sedimentology Of Clastic Cave Sediments

Clastic sediments in Bathers Cave, Virginia, are divided into distinct packages that reflect changes in water velocity, sediment source, surficial weathering conditions, and the cave depositional setting that are a function of Quaternary climate change. These packages are found in the same stratigraphic order at various levels on ledges within passages of elliptical cross section in the upper part of the cave system. Sediment extractions performed on separate fractions from each layer indicate changes in oxide mineralogy and clay mineralogy through the sedimentary sequence. Additional samples from a nearby flood plain, a terrace soil, and a sinkhole pond also show mineralogical and geochemical changes. Goethite is abundant in the lower layers of the cave sequence, while the upper layers have mostly ferrihydrite and abundant kaolinite.

Investigations into the origin of magnetic soils on the Oak Ridge Reservation, Oak Ridge, TN

In 1993-4, researchers at Oak Ridge National Laboratory collected high-resolution airborne geophysical data on the Oak Ridge Reservation, Tennessee (Doll et al., 2000). The data were collected in part to address concerns about possible undocumented hazardous waste sites. Interpretation of the aeromagnetic data was complicated, however, by the discovery of numerous small magnetic anomalies of natural origin. Magnetic susceptibility measurements made on core showed that the underlying Copper Ridge Dolomite is non-magnetic. Apparently, the magnetic anomalies were created by colluvial infilling of dolines with soil rich in maghemite. We discuss explanations offered in the literature for the formation of magnetic soils, and present evidence based on soil analysis, thin sections, x-ray diffraction, and scanning electron microscopy, that in this case maghemite formed either by anaerobic microbial iron reduction followed by the formation of single-domain maghemite, or by abiological weathering and reduction of an iron-bearing mineral followed by oxidation.