RESEARCH METHODS Samples from the Dakota Formation were obtained from cores at Sergeant Bluff, Iowa (Witzke and Ludvigson, 1994). Samples from the Swan River Formation of Manitoba were obtained from unit 1 of outcrop section 57 of McNeil and Caldwell (1981, p. 349-350). Samples were impregnated with epoxy, and thin slabs and thin sections were cut perpendicular to bedding. Powdered
Core Ideas
Studying the critical zone requires targeted research on water, energy, gas, solutes, and sediments.
The SSHCZO targets a 165‐km2 watershed on sedimentary rocks in the northeastern United States.
One SSHCZO subcatchment, Shale Hills, provides extraordinary data describing a shale CZ.
The Susquehanna Shale Hills Critical Zone Observatory (SSHCZO) was established to investigate the form, function, and dynamics of the critical zone developed on sedimentary rocks in the Appalachian Mountains in central Pennsylvania. When first established, the SSHCZO encompassed only the Shale Hills catchment, a 0.08‐km2 subcatchment within Shaver's Creek watershed. The SSHCZO has now grown to include 120 km2 of the Shaver's Creek watershed. With that growth, the science team designed a strategy to measure a parsimonious set of data to characterize the critical zone in such a large watershed. This parsimonious design includes three targeted subcatchments (including the original Shale Hills), observations along the main stem of Shaver's Creek, and broad topographic and geophysical observations. Here we describe the goals, the implementation of measurements, and the major findings of the SSHCZO by emphasizing measurements of the main stem of Shaver's Creek as well as the original Shale Hills subcatchment.
We present a paleolatitudinal precipitation reconstruction for the greenhouse setting of mid-latitude North America based on the oxygen isotopic composition of sphaerosiderites found in middle Cretaceous wetland paleosols. Our reconstructed middle Cretaceous ␦ 18 O values of precipitation are ϳ4‰ less than values from comparable modern low-elevation coastal settings free of monsoons. The data fit a conceptual model in which the precipitation source for the eastern margin of the Cretaceous Western Interior Seaway of North America is an 18 O-enriched oceanic coastal jet. In this subtropical-tropical setting, mid-Cretaceous precipitation rates are interpreted to range from ϳ2500 to ϳ4100 mm/yr.
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