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Reexamination of Mohnian Type Section: ABSTRACT

1973; American Association of Petroleum Geologists; Volume: 57; Linguagem: Inglês

10.1306/819a42c4-16c5-11d7-8645000102c1865d

1558-9153

David Ford,

Geology and Paleoclimatology Research

Examination of 471 samples collected from the Modelo Formation exposed along Topanga Canyon Boulevard has shown that two of the foraminiferal zones of the Mohnian as published by Kleinpell are in need of revision. As a result of detailed sampling, many more foraminifer-bearing samples allowed the reevaluation of the faunal ranges through the Modelo lithologic units described by Hoots. The Bolivina modeloensis Zone contains a distinctive fauna represented by Pulvinulinella gyroidinaformis, Baggina californica, and Valvulineria subinaequalis. With the rare exception of a possibly reworked specimen, this faunal assemblage does not range any higher than Hoots' unit 5. Bulimina unvigerinaformis, formerly considered not to range above unit 6, has been found through unit 8 and rarely in unit 9. Bolivina sinuata alisoensis was not found above unit 6. The Bolivina hughesi Zone which included Hoots' units 7 through 16 is best represented in unit 9. Restricted to unit 9 are Bolivina hughesi and Buliminella semihispida. Above unit 9 foraminifers are very scarce. The faunal top of the Mohnian is in question because no foraminifers restricted to the Mohnian could be found higher than unit 13. End_of_Article - Last_Page 433------------