Abstract
The Upper Cretaceous Pictured Cliffs Sandstone in the Bisti-Burnham area in southwestern San Juan basin, New Mexico, contains distributary-channel, delta-front, and beach-bar deposits. The distributary-channel deposit is a basally erosional, festooned, convoluted, and rippled sandstone. The delta-front deposits include distributary-mouth-bar sandstone, distal-bar sandstone, siltstone, shale, and intervening contorted sandstone. The distributary-mouth-bar sandstone is subparallel laminated, rippled, and festooned. The distal-bar sandstone is subparallel laminated and rippled. The intermediate contorted sandstone contains fold and ball-and-pillow structures. The distributary-channel and delta-front sandstones are very fine to fine grained, quartz poor (39%), and sparsely bu rowed by Ophiomorpha. The beach-bar deposits include shoreface-beach sandstone, siltstone, and shale, and tidal-channel and washover sandstones. Lower-shoreface deposits include parallel-laminated, rippled sandstone and bioturbated shale and siltstone. Middle-shoreface sandstone consists of a subparallel-laminated, rippled, and locally burrowed lower part, and a planar-cross-bedded and commonly burrowed upper part. Upper-shoreface-beach deposits consist of planar-cross-bedded, sparsely burrowed sandstone and lenticular, festooned, rippled, burrowed sandstone grading upward into subparallel-laminated, festooned, burrowed sandstone. The shoreface-beach deposits are dissected by bidirectionally End_Page 451------------------------------ festooned and planar-cross-bedded tidal-channel sandstone and festooned, burrowed washover sandstone. The beach-bar sandstones are very fine to medium grained, quartz rich (54%), and commonly burrowed by Ophiomorpha. Differentiation of Pictured Cliffs Sandstone depositional environments led to recognition of deltaic and back-barrier coal deposits of the overlying Fruitland Formation. End_of_Article - Last_Page 452------------
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