ABSTRACT

During a detailed stratigraphic study in the area of Hunter Wash, near Bisti, a new leaf locality was discovered in a sequence of mudstones, carbonaceous shales, siltstones, and sandstones. In the Bisti area, the boundary between the Fruitland and Kirtland formations is taken at the top of the highest carbonaceous shale above the highest Fruitland coal and below the prominent brown sandstone. The leaf locality lies within a 59-ft (18 m) measured section, about 14 ft (4.5 m) above the highest carbonaceous shale, within a gray-green shaly siltstone protected by an overlying sideritic concretion. Poorly preserved bivalves and gastropods are present in the deposit, but leaves predominate.

Leaf collections contain the remains of ferns, conifers, and angiosperms; angiosperms dominate the assemblage. The most common angiospermous genera include Cercidiphyllum, Cissus, Ficus, Laurophyllum, Myrtophyllum, Platanus, Salix, and Rhamnus. Preliminary analysis of the collection has revealed that most of the angiospermous leaves are of medium size with entire, or nearly entire margins and drip points. These features indicate that during early Kirtland time, the climate of the area was warm-temperature to subtropical.

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