2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 247-10
Presentation Time: 4:00 PM


POWARS, David S., U.S. Geological Survey, National Center, Reston, VA 20192 and EDWARDS, Lucy E., U.S. Geological Survey, 926A National Center, 12201 Sunrise Valley Drive, Reston, VA 20192, dspowars@usgs.gov

The interbedded to massive kaolinite dominated clays and silts of the Marlboro Clay, which formed in response to global warming during the Paleocene-Eocene Thermal Maximum (PETM), record dramatic changes in sedimentation sources and rates across the mid-Atlantic Coastal Plain shelf. Analysis of thirty-one cores from Virginia and Maryland and span nearly 200 m of relief and provide information on facies, thickness, and relief of the Marlboro Clay from its thickest point at the Cambridge-Dorchester Airport, within the axis of Salisbury Embayment to its thinnest, near the Capital Beltway in Maryland. At Matawommen Creek Billingsley Road, one of our most updip locality, a cluster of five cores within a 10-m radius allows for recognition of hundreds of individual depositional packages. Many packages are uniform in color and thickness from core to core, others are uniform in color but not thickness and some packages can not be traced.

The updip facies is characterized by common intervals of stacked fining-upward packages of silt to clay. These packages consist of erosive bases that vary in depth of erosion and angle of contact and are overlain by basal lamina set of white to tan quartz silt and clay with curved ripple lamina (occasionally with very fine sand and/or organic-rich lamina). This in turn is overlain by a wavy parallel lamina set of graded slit and clay, overlain by clay which generally contains numerous very fine laminations (10-26/cm), some organic-rich. Some stacks include another graded clay-silt at the top. Although some up-dip sections are all gray, a typical pattern is gray in the lowest 0.3-1.2 m, pink-red-brown in the middle, and gray at the top 0.3-0.7 m. Further downdip, wisps of silt and faint lamina coupled with more massive intervals result in fewer recognizable fining-upward packages; however the basal 0.3 m is always graded. Colors in intermediate sections are similar to the updip sections except that some sections near the Port Royal fault zone show the middle pink-red-brown with numerous patches of gray throughout. Down-dip sections are all gray. Updip sections contain dinocysts, foraminiferal linings and calcareous microfossils throughout and interpreted as pro-delta front turbidites and/or wave enhanced sediment gravity flows.