Iron-bearing heavy minerals in the Sespe Formation (California)

Flemal, Ronald C.

doi:10.1306/74d71ebf-2b21-11d7-8648000102c1865d

Cited by 4 publications

(6 citation statements)

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Section: Discussionmentioning

confidence: 83%

“… Flemal [1969] found no magnetite in the polished grain mounts. As discussed here in section 4, microscopic examination of polished thin sections shows that the Piuma Member red beds are dominated by authigenic hematite and that the sediments contain only minor amounts of magnetite, in general agreement with Flemal 's [1969] observations. The discrepancy about the abundance of magnetite can be explained by the different objectives and sampling strategies of the studies by Prothero et al [1996] and Calvano et al [2008].…”

Section: Discussionmentioning

confidence: 90%

“…The discrepancy about the abundance of magnetite can be explained by the different objectives and sampling strategies of the studies by Prothero et al [1996] and Calvano et al [2008]. They focused on magnetostratigraphy, which included red beds and less oxidized pale beds, while Flemal [1969] and the current study utilized red beds exclusively. [38] The characteristic remanent magnetization of red beds in my study of the Piuma Member of the Sespe Formation is carried by hematite, as indicated by the thermal demagnetization results.…”

Section: Origin Of Magnetic Remanence In the Sespe Formationmentioning

confidence: 88%

“…Prothero et al [1996] added that chemical remanent magnetization (CRM) resided in authigenic hematite and related iron hydroxides within the reddened strata of the Sespe Formation. Flemal 's [1969] petrographic study of Sespe red beds in the Ventura Basin found wholesale authigenic replacement of iron‐bearing minerals to specular hematite, pseudomorphic hematite after titanomagnetite, and leucoxene after ilmenite. Flemal [1969] found no magnetite in the polished grain mounts.…”

Section: Discussionmentioning

confidence: 99%

“… Flemal 's [1969] petrographic study of Sespe red beds in the Ventura Basin found wholesale authigenic replacement of iron‐bearing minerals to specular hematite, pseudomorphic hematite after titanomagnetite, and leucoxene after ilmenite. Flemal [1969] found no magnetite in the polished grain mounts. As discussed here in section 4, microscopic examination of polished thin sections shows that the Piuma Member red beds are dominated by authigenic hematite and that the sediments contain only minor amounts of magnetite, in general agreement with Flemal 's [1969] observations.…”

Section: Discussionmentioning

confidence: 99%

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Clockwise rotation and implications for northward drift of the western Transverse Ranges from paleomagnetism of the Piuma Member, Sespe Formation, near Malibu, California

Hillhouse

2010

Geochem Geophys Geosyst

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New paleomagnetic results from mid‐Tertiary sedimentary beds in the Santa Monica Mountains reinforce the evidence for large‐scale rotation of the western Transverse Ranges, and anisotropy measurements indicate that compaction‐induced inclination flattening may resolve a long‐standing controversy regarding the original paleolatitude of the rotated block. Previously published paleomagnetic data indicate that post‐Oligocene rotation amounts to 70°–110° clockwise, affecting the Channel Islands, Santa Monica Mountains, and Santa Ynez Mountains. The Sespe Formation near Malibu consists of a lower member dominated by nonmarine sandstone and conglomerate and an upper section, the Piuma Member, which consists of gray‐red sandstone and mudstone interbedded with minor tuff and limestone beds. The Piuma Member has a paleomagnetic pole at 36.6°N, 326.7°E (A95min = 5.0°, A95max = 9.6°), obtained by thermal demagnetization of 34 oriented cores from Oligocene and early Miocene beds. After correcting for plunge of the geologic structure, the data are consistent with significant clockwise rotation (77° ± 7°) of the region relative to stable North America. Rotation of the western Transverse Ranges is generally viewed as a consequence of Pacific–North American plate interactions after 28 Ma, when east–west subduction gave way to northwest transform motion in southern California. Inclinations from the Piuma study indicate a paleolatitude anomaly of 11° ± 7° and are consistent with a mean northward drift that exceeds generally accepted San Andreas fault displacement by a factor of 3. However, sedimentary inclination error may accentuate the anomaly. Anisotropy of isothermal remanent magnetization indicates inclination flattening of approximately 8°, and correction for the effect reduces the paleolatitude anomaly to 5.3° ± 5.8°. Compaction may explain the inclination flattening in these sedimentary rocks, but the process does not adequately explain lower‐than‐expected inclinations found in previous studies of Miocene volcanic rocks of the western Transverse Ranges.

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Section: Discussionmentioning

confidence: 83%

Section: Discussionmentioning

confidence: 90%