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

No abstract

No abstract

No abstract

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.

No abstract

Quantitative estimates of increased heat transfer by atmospheric H 2 O vapor during the Albian greenhouse warming suggest that the intensified hydrologic cycle played a greater role in warming high latitudes than at present and thus represents a viable alternative to oceanic heat transport. Sphaerosiderite ␦ 18 O values in paleosols of the North American Cretaceous Western Interior Basin are a proxy for meteoric ␦ 18 O values, and massbalance modeling results suggest that Albian precipitation rates exceeded modern rates at both mid and high latitudes. Comparison of modeled Albian and modern precipitation minus evaporation values suggests amplification of the Albian moisture deficit in the tropics and moisture surplus in the mid to high latitudes. The tropical moisture deficit represents an average heat loss of ϳ75 W/m 2 at 10؇N paleolatitude (at present, 21 W/m 2). The increased precipitation at higher latitudes implies an average heat gain of ϳ83 W/ m 2 at 45؇N (at present, 23 W/m 2) and of 19 W/m 2 at 75؇N (at present, 4 W/m 2). These estimates of increased poleward heat transfer by H 2 O vapor during the Albian may help to explain the reduced equator-to-pole temperature gradients.

No abstract