Vertical and horizontal datums used in the Lower Mississippi Valley for US Army Corps of Engineers projects

Six geodetic datums have been used by the US Army Corps of Engineers (USACE), Mississippi River Commission (MRC), for river surveys in the Lower Mississippi Valley (LMV). These legacy elevation datums are the Cairo datum, the Memphis datum, the Mean Gulf Level (MGL), the Mean Sea Level (MSL), the National Geodetic Vertical Datum (NGVD) 1929, and the North American Vertical Datum 1988 (NAVD88). The official geodetic datum currently prescribed by the USACE is NAVD88 (USACE 2010). In addition to these different geodetic datums, hydraulic datums are in use by the USACE for rivers, lakes, and reservoir systems. Hydrographic surveys from the Mississippi River are typically based on a low water pool or discharge reference, such as a low water reference plane (LWRP), an average low water plane (ALWP), or a low water (LW) plane. The following technical note is intended to provide background information about legacy datums used in the LMV to permit comparison of historic maps, charts, and surveys pertaining to the Mississippi River in the LMV. The purpose of this report is to provide background information and history of different published horizontal and vertical datums used for presentation of hydrographic survey data from the Mississippi River. The goal is to facilitate understanding of differences with comparison to other historic surveys for change-detection studies along the river. Conversion values are identified herein for the earlier surveys where appropriate, and methods are presented here to evaluate the differences between earlier and later charts and maps. This report is solely intended to address the LMV area and historic surveys made there. This note is not applicable to areas outside of the LMV. Throughout this technical note, historic hydrographic surveys and data from the Memphis, TN, to Rosedale, MS, reach will be used as examples of features of interest for discussion purposes. Selected historic hydrographic survey sheets at Helena, AR, are included as Plates 1 to 3 (Appendix C) of this document and will be used as examples for discussion purposes.

Well-Constrained Mineralization Ages by Integrated 40Ar/39Ar and U-Pb Dating Techniques for the Xitian W-Sn Polymetallic Deposit, South China

Mineralization ages of many mineral deposit types (such as orogenic Au, stratabound Cu, and Mississippi Valley-type Pb-Zn deposits) are still difficult to date by the traditional isotopic chronometry because of the lack of suitable minerals. We have made efforts to establish a widely suitable dating technique to determine ore formation ages using a high-precision 40Ar/39Ar method on ubiquitously present fluid inclusions in quartz, sphalerite, and other nonpotassium minerals from hydrothermal deposits. The Xitian W-Sn polymetallic deposit in central South China contains several minerals suitable for isotopic dating for interchronometer comparison. 40Ar/39Ar laser step heating of 16 micas from ore veins, greisen, and metallogenic granites yields flat age spectra and thus well-defined ore formation ages ranging from 152.4 ± 1.5 (2σ) to 148.1 ± 1.4 Ma with an average of 150.2 ± 0.6 Ma. 40Ar/39Ar progressive crushing of nine quartz samples produces well-defined isochron lines for their primary fluid inclusions corresponding to isochron ages of 153.7–149.9 Ma with an average of 151.6 ± 0.6 Ma. Cassiterites from three hand specimens have weighted mean 206Pb/238U ages of 151.5 ± 1.7 (2σ), 149.7 ± 2.1, and 151.7 ± 2.1 Ma. All these new geochronological dates and previous molybdenite Re-Os ages yield well-constrained mineralization ages of 153–148 Ma for the Xitian W-Sn polymetallic deposit, which also confirms conclusively that the quartz 40Ar/39Ar progressive crushing technique is a feasible, valid dating technique. Furthermore, significant age information on the secondary fluid inclusions is potentially obtained simultaneously by this technique. We expect that this novel dating technique will be widely applied to determine the geologic fluids trapped in minerals during hydrothermal mineralization, hydrocarbon accumulation, metamorphism, tectonic activities, and other geologic processes.

Personal Empires: Mapping, Local Networks, and the Control of Land in the Lower Mississippi Valley

The Louisiana and Florida territories sat at the intersection of empires in the late eighteenth century. Between 1750 and 1820 the area was controlled by the French and Spanish empires, the emerging United States of America, as well as the Choctaw, Creek, and Seminole nations. While political surveys produced images of the moving borders between sovereign powers, cadastral surveys show the constancy of local landowners. Landowners superseded national distinction and were a constant in an area in the midst of great change. As control of the region shifted, landowning families continued their way of life. The continued circulation of Spanish cadastral surveys after the transfer of the region to the United States of America shows how Spanish spatial representations of property ownership shaped the image of the Lower Mississippi Valley.

Vicksburg and Port Hudson

Two sieges of Confederate bastions on the Mississippi River resulted in the Union conquest of the Mississippi Valley in July 1863. The fall of Vicksburg deeply wounded Confederate Mississippi, fractured White support for the Southern cause, and cracked open slavery in the west central part of the state. Tens of thousands of Black refugees fled plantations for the Union Army, many joining newly created Black regiments that would occupy Union posts in the valley. The fall of Vicksburg eliminated the most powerful Confederate blockade to Northern commercial use of the Mississippi River and played a pivotal role in boosting Northern and depressing Southern war morale. Problems associated with Confederate repatriation of thirty thousand paroled soldiers contributed to the breakdown of the prisoner exchange system. The fall of Port Hudson, overshadowed by Vicksburg, nevertheless completed Union conquest of the valley and allowed Northern merchant vessels to steam to New Orleans once again. The emotional benefit of these twin victories was worth the physical effort in reducing both strongholds, emboldening the North and dispiriting the South.

Mississippi Valley, 1862

Union victories at Island No. 10 and Forts Jackson and St. Philip in April 1862 allowed the United States to quickly capture New Orleans, Baton Rouge, Natchez, and Memphis. Their advances prompted the U.S. government to initiate Reconstruction policies that included the enlistment of White, Unionist Southerners. The government also worked with free Blacks, freedmen, and military commanders to start enlisting African American volunteers drawn from throughout the Mississippi Valley by passing the Second Confiscation Act. The Confederate government was badly shaken by its military defeats, especially because its troops suffered from widespread apathy, desertions, and mutinies throughout the Mississippi Valley in 1862. A Confederate conscription law was necessary to bolster its sagging army. The Confederate offensive at Baton Rouge in August was fueled in part by the conscription law and was aimed to interrupt Black enlistments and shore up slavery.

The Carolinas Campaign

This chapter examines the destructive Carolinas Campaign of 1864–1865 as a strategic culmination of the war by means of the transferal to the eastern theater of hard-war tactics that had long characterized the American Civil War’s western theaters. Infliction of property damage and psychological warfare expanded to wholesale destruction of towns and cities, widespread targeting of White civilians, male and female, summary punishment for irregular warfare, and the liberation of slaves in South Carolina as retribution for that state’s overwhelming and initial decision to secede. Federal commanders and soldiers alike, most from the West, were eager to implement this harder form of warfare in a theater known for a more traditional, limited mode of war making. The use of Black troops was most fully employed in the eastern theater in the Carolinas, much as it had been in the West in the Lower Mississippi Valley. As the war neared its end, the desperate Confederate commander in North Carolina, Gen. Joseph E. Johnston, unsuccessfully sought to prevent Maj. Gen. William T. Sherman’s troops from accomplishing destructive warfare, and thus victory, there. Sherman’s conciliatory surrender terms for Johnston’s army, which occurred days after Pres. Abraham Lincoln’s assassination, were rebuffed by angry Republicans in the cabinet, the War Department, and Congress, for whom leniency was now furthest from their minds.

Multiscale aspects of the 26–27 April 2011 tornado outbreak. Part I: Outbreak chronology and environmental evolution

One of the most prolific tornado outbreaks ever documented occurred on 26–27 April 2011 and comprised three successive episodes of tornadic convection that primarily impacted the southeastern U.S., including two quasi-linear convective systems (hereafter QLCS1 and QLCS2) that preceded the notorious outbreak of long-track, violent tornadoes spawned by numerous supercells on the afternoon of 27 April. The ~36-h period encompassing these three episodes was part of a longer multiday outbreak that occurred ahead of a slowly moving upper-level trough over the Rocky Mountains. In this Part I, we detail how the environment evolved to support this extended outbreak, with particular attention given to the three successive systems that each exhibited a different morphology and severity.The amplifying upper-level trough and attendant jet streak resulted from a Rossby wave breaking event that yielded a complex tropopause structure and supported three prominent shortwave troughs that sequentially moved into the south-central U.S. QLCS1 formed ahead of the second shortwave and was accompanied by rapid flow modifications, including considerable low-level jet (LLJ) intensification. The third shortwave moved into the lee of the Rockies early on 27 April to yield destabilization behind QLCS1 and support the formation of QLCS2, which was followed by further LLJ intensification and helped to establish favorable deep-layer shear profiles over the warm sector. The afternoon supercell outbreak commenced following the movement of this shortwave into the Mississippi Valley, which was attended by a deep tropopause fold, cold front aloft, and dryline that promoted two prominent bands of tornadic supercells over the Southeast.