MGS geologists presented research at the 2015 Geological Society of America Annual Meeting, November 1-4, 2015

PRESENTATIONS:

Buckboard to iPad: A Tribute to South Mountain Mappers and their Methods

Rebecca Kavage Adams

ABSTRACT

The geologists of Maryland have for over a century been gathering facts in regard to South Mountain. Interpretations have changed and been refined over time as mappers’ technology advances and they build on the work of their predecessors. Maryland Geological Survey’s current digital mapping efforts continue this tradition.

Keith’s 1894 Harpers Ferry folio, drawn on the first generation of USGS topographic maps at 1:125,000, was completed by horse and buckboard. His map established stratigraphic nomenclature and relations that are still in use today. He noted prominent sandstone outcrops on the ridge of South Mountain and drew them as the axis of a syncline thrust over younger rocks to the west.

Fifty years later, aided by cars and recent road cuts, Jonas and Stose’ (1939) and Cloos’ (1941) 1:62,500 maps differed from Keith’s and each other. Jonas and Stose retained Keith’s vision of a syncline and mapped thrust faults bordering both east and west sides. Cloos declared South Mountain the western limb of an overturned anticline, reversed upper and lower ledge forming quartzites described by Jonas and Stose and placed a normal fault west of the mountain.

One hundred years after Keith’s folio, Brezinski (1992) used aerial photography, Landsat imagery and traditional mapping to divide South Mountain’s ridge forming quartzite into three members. The new stratigraphic nomenclature formally captured Jonas and Stose’ two ledge formers and addressed cases of mistaken identity in the middle incompetent unit. Shortly thereafter Southworth and Brezinski (1996) released a map of the 1:24,000 Harpers Ferry quadrangle. Like Keith, they placed thrust faults to the west of South Mountain but had the benefit of structural analysis from a core drilled directly through the fault.

South Mountain is now the test site for Maryland Geological Survey's new digital mapping techniques. Utilizing an iPad, ESRI collector customized for geologic mapping and LIDAR at 1 meter resolution increases mapping accuracy, efficiency and insight.

Baseline Dissolved-Methane Concentrations in Water-Supply Wells in the Appalachian Plateau Physiographic Province of Maryland

David W. Bolton

ABSTRACT

The extensive development of the natural gas resources of the Marcellus Shale in the northeastern Appalachian basin has led to concerns that methane and other produced fluids may be contaminating shallow aquifers that are the primary water supplies in rural areas. However, because methane is not usually tested for in private water wells, there is relatively little data regarding methane concentrations prior to natural-gas-extraction activities. The Marcellus Shale is considered prospective for gas production in the Appalachian Plateau province of western Maryland, but it has not yet (2015) been developed due to a moratorium on drilling in Maryland.

In order to collect baseline data on methane in wellwater, Maryland Geological Survey personnel collected water samples from 87 water-supply wells (mostly private wells) throughout the Appalachian Plateau region of western Maryland in 2012-2014. The region is underlain by gently folded Paleozoic strata, and slightly more than half of the study area is underlain by Pennsylvanian-age rocks that include significant coal seams. Water samples were analyzed for dissolved methane, ethane, propane, ethene, and field-measured parameters (pH, specific conductance, dissolved oxygen, and chloride). Dissolved-methane concentrations ranged from less than 0.0015 milligrams per liter (mg/L) to 8.55 mg/L, and methane was detected in all nine geologic formations in which sampled wells were located. Samples from seven wells exceeded 1 mg/L, and more than half the wells had less than 0.0015 mg/L methane (the reporting level). Ethane was detected in six wells. Methane was detected in 63 percent of wells that were located in valleys, compared with 30 percent of wells located in upland settings. Methane was also detected in 54 percent of wells in areas underlain by coal, compared with 40 percent of wells in non-coal areas. Methane samples collected at monthly intervals from three wells showed a 20 to 30 percent average variation from the median monthly methane concentration in each well, although individual variations were frequently much larger. The data indicate that low-level concentrations of methane in wellwater are common throughout the region.

Origin of the Carnegie Quarry Sandstone, Morrison Formation (Jurassic), at Dinosaur National Monument, Utah (Poster)

David K. Brezinski and Albert D. Kollar

ABSTRACT

The Carnegie Museum dinosaur quarry at Dinosaur National Monument was developed in a sandstone unit locally referred to as the "Quarry Sandstone” bed of the Morrison Formation. The Quarry Sandstone is a localized, discontinuous, heterolithic unit that is present within the Brush Basin Member, a thick succession of greenish gray mudstone containing thin limestone beds and nodules. These fine-grained strata have been interpreted as being deposited in low-relief paludal and lacustrine environments. Some authors have attributed the genesis of the Quarry Sandstone to a variety of river channel deposits, including meandering and braided. Detailed study of numerous measured sections through, and along, the Quarry Sandstone's 1.8-km outcrop belt indicates that this sandstone is actually an assemblage of a number of separate sandstone bodies. The lowest part of the Quarry Sandstone is a laterally continuous, tabular unit composed of graded sandstone and conglomerate that overlies lacustrine mudstones of the Brushy Basin Member. This sandstone unit contains re-sedimented carbonate nodules from the surrounding Brushy Basin, and a sharp basal contact. Overlying the tabular basal unit are numerous, discontinuous sandstone bodies. Some of these units exhibit erosional bases and fine upsection, while others display flat bases and coarsen upsection. These discontinuous sandstone bodies interfinger with reddish-brown, rooted, mudstones containing calcic paleosols. The heterolithic character and rapid vertical and lateral facies variations exhibited by the Quarry Sandstone indicate that this unit was deposited as a local crevasse splay that formed during multiple channel avulsion events. The Carnegie Quarry was opened within one of the distributary channel sandstones of this splay complex.

FIELD TRIPS:

ACOUSTIC SEAFLOOR MAPPING OF THE BALTIMORE HARBOR

Stephen VanRyswick, Primary Leader

Elizabeth Sylvia, Leader

BUILDING STONES OF DOWNTOWN BALTIMORE

David W. Bolton, Primary Leader

Joseph T. Hannibal, Leader

CAMBRIAN-ORDOVICIAN OF THE CENTRAL APPALACHIANS: CORRELATIONS AND EVENT STRATIGRAPHY OF CARBONATE PLATFORM AND ADJACENT DEEP-WATER DEPOSITS

David K. Brezinski, Primary Leader

John F. Taylor, John E. Repetski and James D. Loch, Leaders

CRETACEOUS STRATIGRAPHY AND PALYNOLOGY OF THE MARYLAND COASTAL PLAIN

Heather Quinn, Leader

Peter P. McLaughlin Jr., Primary Leader

KARST OF THE MID-ATLANTIC REGION IN MARYLAND, WEST VIRGINIA, AND VIRGINIA

David J. Weary, David K. Brezinski, Randall C. Orndorff and Lawrence E. Spangler, Leaders

Daniel H. Doctor, Primary Leader

LATE DEVONIAN CLIMATE CHANGE AND GLACIGENIC FACIES IN THE CENTRAL APPALACHIANS

David K. Brezinski, Primary Leader

Blaine Cecil and William DiMichele, Leaders