Middle Triassic paleosols and paleoclimate of Antarctica

The Lashly Formation in the Allan Hills of southern Victoria Land, Antarctica, is now at a latitude of 768S and during the Middle Triassic was at least 708S. The combined evidence of fossil roots and soils indicates a paleoclimate unusual for such a high latitude. Temperate paleotemperature is indicated by roots, logs, and leaves of woody plants and the degree of chemical weathering and clay formation within the paleosols. Paleosols of the Lashly Formation are more like soils of southern Sweden than those of either Finland or southern Europe. Silt infiltration structures around root traces and in cracks within the paleosols are evidence for a seasonally snowy climate, but there is no evidence of ice wedges or other permafrost features in the paleosols. Other evidence of climatic seasonality includes well-defined growth rings in fossil wood, and abscission scars at the base of fossil leaves. Diverse broadleaf plants, and noncalcareous paleosols, indicate a humid climate with mean annual precipitation of about 1200 mm. Such a wet climate is anomalous for the interior of the supercontinent of Pangea, and such a warm and mildly seasonal climate is anomalous for such high latitudes. This paleoclimatic anomaly may be a lingering effect of global greenhouse initiated at the Permian–Triassic boundary. Paleoclimatic variables calculated here may be useful for recalibrating global paleoclimatic models for the middle Triassi

Regional Paleoprecipitation Records from the Late Eocene and Oligocene of North America

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/148635/1/Sheldon_and_Retallack_2004_JGeol-EOT_climate_spatial_gradients.pd

Early Miocene Cape Blanco Flora of Oregon

60 pagesDeposition of the shallow marine sandstone of Floras Lake was interrupted by a transient del-taic progradation of redeposited volcanic tuff, which contains the Cape Blanco flora. Dating by 40Ar/39Ar on fresh plagioclase constrains the age of the plant-bearing tuff to 18.24 ± 0.86 Ma, because we interpret this age of eruption and landscape loading with ash, as within only a few years of redeposition. Several plausible sources of the tuff can be identified from caldera eruptions in the Cascade Volcanic Arc. The relation between the early Miocene Cascade volcanic arc and the Klamath Terrane has been fixed since the early Miocene, and the high Cr2O3 in the sandstones is an indication that the source area for the sandstone of Floras Lake was the Klamath Terrane. Fossil leaves and other plant organs of 33 species of the Cape Blanco flora represent floral diversity and paleoclimate of coastal Oregon during the early Miocene. The flora includes a variety of thermo-philic elements from California, including coast redwood (Sequoia affinis), and avocado (Persea pseudocarolinensis), and is numerically dominated by live oak (Quercus hannibalii), and chinqua-pin (Chrysolepis sonomensis). The size and proportion of serrate margins of the fossil leaves are evidence of mean annual temperature of ~14 º C and a mean annual precipitation of ~223 cm/yr for the Cape Blanco flora. Comparison of the Cape Blanco flora with the Temblor flora of Cali-fornia and the Seldovia flora of Alaska reveals a latitudinal gradient of ~ 0.6 º C/degree latitude, compared with a gradient of ~0.3 º C/degree latitude from isotopic composition of marine foramin-ifera of the northeast Pacific Ocean. Both results confirm that the late early Miocene mean annual temperature at 45º north latitude was 4-5 º C warmer than today

Geochemical climofunctions from North America soils and application to paleosols across the Eocene-Oligocene boundary in Oregon

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/148640/1/Sheldon_et_al_2002_JGeol-new_paleoclimate_proxies_and_applications_to_the_EOT.pd

Oregon 2100: Projected Climatic and Ecological Changes

28 pagesGreenhouse climatic warming is underway and exacerbated by human activities. Future outcomes of these processes can be projected using computer models checked against climatic changes during comparable past atmospheric compositions. This study gives concise quantitative predictions for future climate, landscapes, soils, vegetation, and marine and terrestrial animals of Oregon. Fossil fuel burning and other human activities by the year 2100 are projected to yield atmospheric CO2 levels of about 600-850 ppm (SRES A1B and B1), well above current levels of 400 ppm and preindustrial levels of 280 ppm. Such a greenhouse climate was last recorded in Oregon during the middle Miocene, some 16 million years ago. Oregon’s future may be guided by fossil records of the middle Miocene, as well as ongoing studies on the environmental tolerances of Oregon plants and animals, and experiments on the biological effects of global warming. As carbon dioxide levels increase, Oregon’s climate will move toward warm temperate, humid in the west and semiarid to subhumid to the east, with increased summer and winter drought in the west. Western Oregon lowlands will become less suitable for temperate fruits and nuts and Pinot Noir grapes, but its hills will remain a productive softwood forest resource. Improved pasture and winter wheat crops will become more widespread in eastern Oregon. Tsunamis and stronger storms will exacerbate marine erosion along the Oregon Coast, with significant damage to coastal properties and cultural resource

The ‘mosaic habitat’ concept in human evolution: past and present

The habitats preferred by hominins and other species are an important theme in palaeoanthropology, and the ‘mosaic habitat’ (also referred to as habitat heterogeneity) has been a central concept in this regard for the last four decades. Here we explore the development of this concept – loosely defined as a range of different habitat types, such as woodlands, riverine forest and savannah within a limited spatial area– in studies of human evolution in the last sixty years or so. We outline the key developments that took place before and around the time when the term ‘mosaic’ came to wider palaeoanthropological attention. To achieve this we used an analysis of the published literature, a study of illustrations of hominin evolution from 1925 onwards and an email survey of senior researchers in palaeoanthropology and related fields. We found that the term mosaic starts to be applied in palaeoanthropological thinking during the 1970’s due to the work of a number of researchers, including Karl Butzer and Glynn Isaac , with the earliest usage we have found of ‘mosaic’ in specific reference to hominin habitats being by Adriaan Kortlandt (1972). While we observe a steady increase in the numbers of publications reporting mosaic palaeohabitats, in keeping with the growing interest and specialisation in various methods of palaeoenvironmental reconstruction, we also note that there is a lack of critical studies that define this habitat, or examine the temporal and spatial scales associated with it. The general consensus within the field is that the concept now requires more detailed definition and study to evaluate its role in human evolution

Low oxygen levels in earliest Triassic soils

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/148641/1/Sheldon_and_Retallack_2002_Geology-low_O2_in_PTr_soils.pd

Reply to Huggett and Hesselbo Comment on, Low oxygen levels in earliest Triassic soils

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/148638/1/Sheldon_and_Retallack_2003_Geology-reply_to_comment_on_Sheldon_and_Retallack_2002.pd