Implications of Hydrocarbon and Helium Gas Analyses of Springs from the Ouachita Mountains, Arkansas

One hundred and three ground water samples (predominantly springs) were analyzed for headspace light hydrocarbon gases and helium. Four of the formations (Arkansas Novaculite, Bigfork Chert, Stanley Shale, and Womble) having the highest mean methane values are the only Ouachita Mountain facies to produce petroleum or exhibit marginally commercial production. This observation suggests that the mean methane values are useful as an indication of the relative hydrocarbon content of these formations Anomalous helium values are generally associated with mapped faults

Comparison of Environmental Assessments of Two Proposed Harbor Expansions on the Mississippi River

The National Environmental Policy Act of 1969 requires federally funded projects to be evaluated for environmental impact to determine if a complete environmental impact statement must be prepared. Such an environmental assessment must also be included in any feasibility study for harbor enlargement and bank stabilization measures under the Water Resources Development Act. Population increases, coupled with economic growth from increased agricultural and industrial productivity, have resulted in increased Mississippi River barge transportation needs for Arkansas and Missouri. We report here two such environmental assessments of planned harbor expansions of the New Madrid County and Pemiscot County ports in the Missouri bootheel along the Mississippi River. We evaluated the environmental settings, presence of wetlands, and the presence of hazardous, toxic or radioactive wastes (HTRW) at the two sites. The results of these evaluations were used to determine the possible significant resources and impacts (including endangered species) associated with harbor expansion at the two sites. No significant HTRW were present or likely to be encountered during construction at either site. However, differences in 1) the environmental settings (open high banks vs. bottomland forest), 2) significant resources (historical accounts of least tern colonies at one site), and 3) presence of wetland habitat at one site may preclude or reduce the level of one or both harbor expansions. Careful consideration of possible environmental impacts may help guide the choice of sites for similar harbor expansions in Arkansas

On the statistical modeling of persistence in total ozone anomalies

Geophysical time series sometimes exhibit serial correlations that are stronger than can be captured by the commonly used first‐order autoregressive model. In this study we demonstrate that a power law statistical model serves as a useful upper bound for the persistence of total ozone anomalies on monthly to interannual timescales. Such a model is usually characterized by the Hurst exponent. We show that the estimation of the Hurst exponent in time series of total ozone is sensitive to various choices made in the statistical analysis, especially whether and how the deterministic (including periodic) signals are filtered from the time series, and the frequency range over which the estimation is made. In particular, care must be taken to ensure that the estimate of the Hurst exponent accurately represents the low‐frequency limit of the spectrum, which is the part that is relevant to long‐term correlations and the uncertainty of estimated trends. Otherwise, spurious results can be obtained. Based on this analysis, and using an updated equivalent effective stratospheric chlorine (EESC) function, we predict that an increase in total ozone attributable to EESC should be detectable at the 95% confidence level by 2015 at the latest in southern midlatitudes, and by 2020–2025 at the latest over 30°–45°N, with the time to detection increasing rapidly with latitude north of this range

Advancements in decadal climate predictability: the role of nonoceanic drivers

We review recent progress in understanding the role of sea ice, land surface, stratosphere, and aerosols in decadal-scale predictability and discuss the perspectives for improving the predictive capabilities of current Earth system models (ESMs). These constituents have received relatively little attention because their contribution to the slow climatic manifold is controversial in comparison to that of the large heat capacity of the oceans. Furthermore, their initialization as well as their representation in state-of-the-art climate models remains a challenge. Numerous extraoceanic processes that could be active over the decadal range are proposed. Potential predictability associated with the aforementioned, poorly represented, and scarcely observed constituents of the climate system has been primarily inspected through numerical simulations performed under idealized experimental settings. The impact, however, on practical decadal predictions, conducted with realistically initialized full-fledged climate models, is still largely unexploited. Enhancing initial-value predictability through an improved model initialization appears to be a viable option for land surface, sea ice, and, marginally, the stratosphere. Similarly, capturing future aerosol emission storylines might lead to an improved representation of both global and regional short-term climatic changes. In addition to these factors, a key role on the overall predictive ability of ESMs is expected to be played by an accurate representation of processes associated with specific components of the climate system. These act as “signal carriers,” transferring across the climatic phase space the information associated with the initial state and boundary forcings, and dynamically bridging different (otherwise unconnected) subsystems. Through this mechanism, Earth system components trigger low-frequency variability modes, thus extending the predictability beyond the seasonal scale

Possible relict meanders of the Pliocene Mississippi River and their implications

Although the late Quaternary history of the Mississippi River, the largest North American river, has been intensely studied, its Pliocene history is largely unknown. We assert that large relict meander bends (oxbows) of the Pliocene Mississippi River are preserved as arcuate valleys of local streams in the northwest area of the state of Mississippi. These arcuate valleys are within the Pliocene Upland Complex stratigraphic unit that occurs as a high-level alluvial terrace along the lower Mississippi River Valley. Outside these arcuate valleys, the Upland Complex is a braidedriver gravel deposit that shows southward (downvalley) paleoflow directions. Interiors of the arcuate valleys are occupied by Upland Complex point bar deposits with large-scale cross-bedding showing a range of paleoflow directions, commonly upvalley flow indicative of a meandering regime. We used measurements of the radii of the putative relict meander bends and of their paleochannel widths to estimate paleodischarge of the Pliocene Mississippi River based on equations empirically derived from modern meandering rivers. These discharge estimates, the first for the Pliocene Mississippi River, show it may have had as much as six to eight times the discharge of the modern river. This result suggests that (1) the North American Pliocene climate was much wetter, and/or (2) the Pliocene Mississippi River’s drainage basin was much larger, extending into southern Canada. Better age constraints and a detrital zircon provenance study of the Upland Complex are needed to test these hypotheses

Quaternary uplift in the lower mississippi river valley

Discontinuous high-level terrace remnants of the ∼3.1 Ma ancestral Mississippi River floodplain, locally called the Upland Complex (UC), are mapped from Louisiana into Illinois. We interpret the UC to be the basal sand and gravel erosional remnant of a much thicker Pliocene floodplain. The Pliocene Mississippi River, at the latitude of Tennessee, has a base-of-terrace elevation 70 m higher than the base of the Holocene Mississippi River floodplain. This difference cannot be attributed solely to changes in sea level and suggests Quaternary uplift that may be ongoing. Borehole data reveal that the base of the UC and that of the Mississippi River alluvium have been tilted southeast. The geomorphology of the central Mississippi River Valley also supports regional Quaternary uplift. Mississippi and Ohio/Mississippi river terrace distribution reveals that these rivers shifted away from the down-valley axis during the Wisconsinan, and basin asymmetry analysis also indicates Quaternary tributary valley migrations away from this axis. Pliocene sea level is estimated to have been at +25 m, requiring that the UC has risen 45 (70-25) m within the past ∼2.4 My. We believe this 45-m uplift may be isostatic. However, 15 m of overlying Pleistocene loess deposition would result in 8 m of isostatic subsidence, suggesting an original isostatic uplift of 53 (45 + 8) m. A 53-m isostatic uplift response indicates that 141 m of the UC was eroded. Since the current average thickness of the UC is 10 m, its original thickness was 151 m. This proposed isostatic response to Pleistocene erosion of the Mississippi River Valley supports the denudation model for Quaternary reactivation of the underlying Reelfoot rift faults and its New Madrid seismic zone and suggests that uplift mechanisms should be considered in the denudation model

Petrology of pliocene Mississippi river alluvium: Provenance implications

Pliocene Mississippi River terrace gravels, the Upland Complex, crop out east and west of the present Mississippi River in the northern Mississippi Embayment. As the only sedimentary unit in the northern Mississippi Embayment deposited between the end of the Eocene and the onset of glaciation, its origin provides ground truth about conditions that existed in the heartland of North America within this 30-m.yr. interval. Recent studies concluded that the Pliocene Mississippi River originated in what is now southern Canada and that the Upland Complex is the remnant of a much larger deposit that once extended from Canada to the Gulf of Mexico. Is there some evidence in the petrology of the Upland Complex that can confirm this conclusion? To determine the provenance of the Upland Complex, we sampled 18 exposures, analyzed ∼50 thin sections, and obtained source terrane age data from its zircons. Upland Complex gravel came from proximal early Paleozoic carbonate rocks containing bedded and nodular chert north and northeast of the Mississippi Embayment with a possible distant contribution from as far away as southcentral Canada. Upland Complex sand came from multiple sources, including the Saint Francois Mountains of Missouri, the Grenville Terrane, and, possibly, southcentral Canada. We conclude that the Pliocene Mississippi River probably drained a much larger area than present Mississippi, an area that extended well north of the US-Canada border into Manitoba and Ontario

Paleoseismic evidence for multiple Mw ≥6 earthquakes in the eastern Tennessee seismic zone during the late quaternary

The eastern Tennessee seismic zone (ETSZ) is the second-most active seismic zone in the eastern United States, but it has not generated an earthquake larger than Mw 4.8 in historic time. Earthquakes are sourced deep in autochthonous basement, and there are no known faults originating at this depth that break the surface. As a result, until recently, there has been virtually no fieldwork to identify Quaternary paleoseismic features in the ETSZ. We present new results from paleoseismic investigations of coseismic features that indicate the ETSZ generated Mw ≥6 earthquakes during the late Quaternary. Detailed geologic mapping and trenching near Dandridge, Tennessee, record a northeast-trending zone of seismically generated features. Optically stimulated luminescence ages delimit timing for the formation of paleoseismic features crosscutting Quaternary alluvium and alluvium-filled fissures, including a thrust fault with ∼1 m displacement. Collectively, this zone of faults and fissures provides significant evidence that the ETSZ has produced at least three large earthquakes during the late Pleistocene and at least one that exceeded Mw 6