--> Abstract: Preliminary Petrologic and Sedimentologic Comparisons Between Paleocene Conglomerates of Point Reyes and Point Lobos, California, by K. Burnham and T. B. Anderson; #90958 (1995).

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Abstract: Preliminary Petrologic and Sedimentologic Comparisons Between Paleocene Conglomerates of Point Reyes and Point Lobos, California

Kathleen Burnham, Thomas B. Anderson

Preliminary studies reveal many similarities between the Point Reyes Conglomerate at Point Reyes and the Carmelo Formation at Point Lobos. Both conglomerates rest nonconformably upon and in fault contact with granitic basement of the Salinian Block. Both are clast supported, poorly sorted, and occur in lensoidal beds up to several meters thick. Both include beds of conglomerate grading upward into sandstone, with sharp basal contacts and scour channels. Matrices are angular and poorly sorted subarkose to arkosic arenite, and are very coarse in conglomerate layers and finer in sandstone layers. Flame structures, shale rip-up clasts, and fine laminae are locally abundant. The most abundant and largest (up to 2.5 m) clasts are granitic, and match the basement rock. Second in abundance and size are well-rounded distinctive purple K-spar porphyry clasts. All other clasts are smaller, and most are well-rounded, fine-grained, and extremely hard. Both conglomerates are interpreted as submarine canyon deposits. Several identical fossil species and genera occur in both units. Both matrix and purple porphyry clasts of the two sites appear virtually identical at microscopic scale.

These results indicate the Point Reyes Conglomerate could be a part of the Carmelo Formation, separated by 180 km of lateral movement on the San Gregorio Fault since Paleocene time.

AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California