Holocene Pedogenesis in Fluvial Deposits of the Conejos River Valley, Southern Colorado

Relatively few geomorphic studies have examined Holocene-aged soils developed in alluvial deposits in the Rocky Mountains. Here, we present a soil morphological investigation from a suite of fluvial terraces in the glaciated portion of the Conejos River Valley, southern Colorado. The surficial geology of 25 km of the glacial valley was mapped in detail. Within three separate sub-reaches (Platoro, Lake Fork and South Fork) a total of thirteen soil pits and exposures were excavated and described on alluvial deposits. Soil samples were analyzed for particle size and extractable iron. Soil horizonation (A/C to A/B/2C), structure (fine sub angular to medium angular blocks), clay content of the B horizon (8.0% to 22.8%) and Feo/Fed (0.39 to 0.80) illustrate trends with relative terrace deposit age in individual sub-reaches. However, only Feo/Fed ratios displayed similar rates of development between all sub-reaches highlighting the usefulness of this metric for determining accurate rates of pedogenesis and relative age for Holocene-aged deposits in sub-alpine environments. Results indicate that clay content and structure developed in alluvial deposits of similar ages vary between sub-reaches. Clay contents were found to be lower in the Platoro sub-reach (e.g. 13.1% at Platoro and 20.0% at South Fork on Qt1 deposits). This variation is attributed to heterogeneity in the nature of the inherited parent material and potential variability in aeolian dust contributions throughout the Holocene

Depositional History of an Oxbow Lake: Duck Cove of the Catawba River, Charlotte, NC

There are relatively few high-resolution terrestrial records of Holocene climate change for the southeastern United States. We are investigating the feasibility of obtaining such a record from oxbow lakes found along major drainages of the mid-Atlantic coast. The Catawba River is a single channel, meandering, incised river that drains 8556 square km from its headwaters on the Blue Ridge escarpment, through the Piedmont physiographic province of North and South Carolina to the Coastal Plain. The river currently is controlled by a series of dams and reservoirs operated by Duke Energy. Immediately downstream of the Cowans Ford Dam near Charlotte, NC, there is a free-flowing stretch where the Catawba River and its adjacent valley are characterized by steep valley walls, 3-4 fluvial strath terraces and a potential oxbow lake known as Duck Cove. The sediments of Duck Cove are meters thick and largely composed of laminated and bioturbated silty muds interbedded with centimeter thick fine sands with 14C-datable leaves and twigs dispersed throughout. Cores are capped by a planar-bedded fine to coarse sand up to 30 cm thick immediately overlying an organic rich layer dated at 1808 +/- 96 AD (calibrated radiocarbon age). The 30 cm thick sand is interpreted as a deposit from the 1916 flood that affected much of the region. Age dates from lower in the cores are inconclusive. Pollen analyses document abundant pine, oak and ragweed as well as corn, cotton, hemlock, fungal debris and charcoal suggesting that this alluvial environment was dominated by input from both a weedy, fire-prone nearby upland and Piedmont sources. We conclude that Duck Cove and other oxbow lakes are promising candidates to contain a long term (Holocene) climate record for the southeastern United States

Pollen Evidence for the Age of the Lilesville Gravels: A Neogene Strath Terrace Deposit From the Fall Zone of North Carolina, USA

In the vicinity of Lilesville, NC, there are extensive, previously undated, quartz-rich, coarse-grained gravel deposits found capping interfluves in the dissected Piedmont landscape of the Fall Zone. These deposits unconformably overlie the Late Paleozoic Lilesville pluton and its saprolite. They are interpreted as the highest surviving strath terrace from the paleo-Pee Dee River which currently flows at an elevation about 100 m below the Lilesville gravels. The Lilesville gravels occur as channel fills, channel bars, pebble lags, trough cross-stratified sands, reworked mud clasts and low-flow deposits composed of fine sands. Paleoflow indicators suggest southerly transport, parallel to the modern Pee Dee River. The age of the gravels has been estimated at about 7–12 Ma based solely on the height of this terrace above current river level using the approach of Mills (2000). A recently discovered organic-rich mud layer below the gravels contains abundant, well-preserved plant macrofossils and microfossils. The organic-rich mud layer is sandwiched between dark gray to black clay layers which together are ~4 meters thick. The clay layers likely protected the plant material from oxidizing and thereby resulted in this unusually well-preserved deposit. Pollen from the black, organic-rich mud layer support a Neogene age for the gravels and show that the sediment was derived from an upland mixed hardwood/pine environment. Based on analysis of three samples, the most common pollen are (mean %): Taxodium (18.2), Pinus (17.1), Quercus (15.4), Carya (13.5), Tricolpites (5.7), and Alnus (5.3). Also noteworthy is the presence of the Tertiary taxon Nothofagidites (0.95) but the absence of grasses or composites. The macroflora has not yet been examined. It is likely that the organic-rich mud layer was deposited in an abandoned channel of the ancestral Pee Dee River when it was a steeper-gradient, coarser-bedload, higher-discharge, aggrading, braided stream as compared to the current incising, single-thread river. These observations are consistent with a wetter paleoclimate in the Neogene than at present, and/or topographic rejuvenation in the source area via either stream network reorganization or regional upwarping

Quaternary Evolution of an Incising Piedmont River: the Catawba River Near Charlotte, NC

The long-term evolution of down-cutting rivers in eastern North America is of widespread interest. We have examined Quaternary incision, lateral migration, oxbow sedimentation and a chronosquence of soils developing in terraces of the Catawba River in the vicinity of Charlotte, NC. The Catawba River is a single channel, meandering river that drains 8556 square km from its headwaters on the Blue Ridge escarpment, through the Piedmont of North and South Carolina to the Coastal Plain. The river currently is controlled by a series of dams and reservoirs. Downstream of Cowans Ford dam there is a free-flowing stretch where the Catawba River and its adjacent valley are characterized by steep valley walls, 5 fluvial terraces, and several oxbow lakes produced by channel straightening, the timing and cause of which remain uncertain. Coring, ground penetrating radar and air photo data indicate that during its most recent history, the Catawba River migrated laterally and produced a widespread basal erosion surface carved into bedrock, ~9 m thick point bars, and scroll bar and swale deposits. Once the channel was abandoned, the oxbow lakes filled with fine-grained sediments, became emergent and vegetated, and then cultivated. Backwater effects associated with the damming of the Catawba River have flooded the formerly emergent farmland. Pollen analyses from oxbow lake samples document abundant pine, oak and ragweed as well as corn, cotton, hemlock, fungal debris and charcoal suggesting that this alluvial environment was dominated by input from both a weedy, fire-prone nearby upland and Piedmont sources. The 5 terrace deposits each are characterized by distinctive morphology, soil development and basal quartz pebble conglomerates. Tentative ages are assigned to the terraces by comparison to regional terrace elevation/age curves. The elevations (and inferred ages) of the 5 terraces are: 3 m (4 kyr), 10 m (50 kyr), 14 m (128 kyr), 28 m (610 kyr) and 41 m (1,470 kyr) above the modern river yielding incision rates ranging from 0.02 to 0.61 mm/yr which increase progressively through time

Clinical Importance of Placental Testing among Suspected Cases of Congenital Zika Syndrome

Contemporaneous Zika virus (ZIKV) strains can cause congenital Zika syndrome (CZS). Current ZIKV clinical laboratory testing strategies are limited and include IgM serology (which may wane 12 weeks after initial exposure) and nucleic acid testing (NAT) of maternal serum, urine, and placenta for (+) strand ZIKV RNA (which is often transient). The objectives of this study were to determine if use of additional molecular tools, such as quantitative PCR and microscopy, would add to the diagnostic value of current standard placental ZIKV testing in cases with maternal endemic exposure and indeterminate testing. ZIKV RNA was quantified from dissected sections of placental villi, chorioamnion sections, and full cross-sections of umbilical cord in all cases examined. Quantitation with high-resolution automated electrophoresis determined relative amounts of precisely verified ZIKV (74-nt amplicons). In order to localize and visualize stable and actively replicating placental ZIKV in situ, labeling of flaviviridae glycoprotein, RNA ISH against both (+) and (−) ZIKV-specific ssRNA strands, and independent histologic examination for significant pathologic changes were employed. We demonstrate that the use of these molecular tools added to the diagnostic value of placental ZIKV testing among suspected cases of congenital Zika syndrome with poorly ascribed maternal endemic exposure