Geomagnetic polarity event recorded at 1.1 m.y. B.P. on Cobb Mountain, Clear Lake volcanic field, California

Mankinen, Edward A.; Donnelly, Julie M.; Grommé, C. Sherman

doi:10.1130/0091-7613(1978)6<653:gperam>2.0.co;2

Cited by 105 publications

(61 citation statements)

References 0 publications

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“…Mountain "event" (Mankinen et al, 1978;Clement and Robinson, 1987). The horizon of the Matuyama/Gauss boundary (C2r/C2A) at 80 mbsf seems to be confirmed by the shorebased results.…”

Section: Site 721supporting

confidence: 67%

Magnetostratigraphy of Leg 117 Sediments from the Owen Ridge and the Oman Margin, Western Arabian Sea

Hayashida¹,

Bloemendal²

1991

Proceedings of the Ocean Drilling Program

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Magnetic measurements were made on discrete samples from the Neogene pelagic and hemipelagic sediments recovered during ODP Leg 117. Polarity zones, usually identified for uppermost 200 m, were correlated to the geomagnetic polarity time scale referring to biostratigraphic datums. Quality and resolution of the magnetostratigraphy was partly limited by the weak and relatively soft magnetic character of almost all intervals, and core disturbance by gas expansion at some Oman Margin sites. Clear polarity records of the Brunhes and Matuyama chrons (Cl to C2r) were observed at Sites 724 and 727 on the Oman continental margin. Extended reversal records of the Pliocene were found at Site 722 on the Owen Ridge and Site 728 on the Oman Margin, and correlated to the Gauss to Gilbert chrons (C2A to C3).

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“…Mountain "event" (Mankinen et al, 1978;Clement and Robinson, 1987). The horizon of the Matuyama/Gauss boundary (C2r/C2A) at 80 mbsf seems to be confirmed by the shorebased results.…”

Section: Site 721supporting

confidence: 67%

Magnetostratigraphy of Leg 117 Sediments from the Owen Ridge and the Oman Margin, Western Arabian Sea

Hayashida¹,

Bloemendal²

1991

Proceedings of the Ocean Drilling Program

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“…This magnetozone is correlated with the 1.1 Ma Cobb Mt. Subchron reported by Mankinen et al (1978). Where recovered, the sediment sequence form 22.5 to 61.7 m has dominantly reversed polarity and probably represents the Matuyama Chron.…”

Section: Hole 558amentioning

confidence: 62%

Magnetostratigraphy of Oligocene to Pleistocene Sediments, Sites 558 and 563

Khan¹,

Kent²,

Miller³

1985

Initial Reports of the Deep Sea Drilling Project

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Integrated magnetostratigraphic and biostratigraphic studies of DSDP Sites 563 and 558 (western North Atlantic) show that, except for a short (~2 Ma) early Miocene hiatus, deposition was continuous from time of seafloor formation (Site 563, between Anomalies 12 and 13; Site 558, between Anomalies 13 and 15) through the Miocene at both sites. Several biostratigraphic datum levels, which have been correlated firmly with magnetic polarity chrons elsewhere, allow correlation of the magnetostratigraphy with the geomagnetic polarity time scale. Based upon that calibration, sediment accumulation rates were low to moderate (< 10 m/Ma) in the Oligocene-early Miocene and higher (> 10 m/ Ma) in the middle-late Miocene after a short hiatus (Chron C5E is missing at both sites).The established magnetochronology is used to make direct magnetobiostratigraphic correlations. For the Oligocenelower Miocene samples, these correlations agree well with previously published first-order correlations. However, our correlations differ from the earlier indirect middle to upper Miocene correlations. In particular, indirect methods were previously used to correlate magnetostratigraphic Chron 11 (= Zone NN9) with marine Anomaly 5A (Chron C5AN). However, Zone NN9 ( = Chron 11) and associated Zone N16 occur in a long normal interval at Sites 563 and 558 that best correlates with marine magnetic Anomaly 5. This reassignment (Chron 11 = Anomaly 5 = Chron C5N) requires an approximately 1.5-2 Ma upward shift in nannofossil zonal boundaries NN7/NN8 through NN10/NN11. The stratotype lower upper Miocene (Tortonian) is biostratigraphically linked with Zones NN9-NN11. Because Zone NN9 occurs in magnetic Anomaly 5 correlative (Chron C5N), the middle-upper Miocene boundary (basal Tortonian) is probably near the base of Chron C5N, with an estimated magnetochronologic age of 10.4 Ma.

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“…The more recent one, the Cobb Mountain Subchron, was first recognized by paleomagnetic study of oceanic sediments (e.g., Watkins, 1968). It has also been observed from basalt flows (Mankinen et al, 1978;Mankinen and Grommé, 1982;Chauvin et al, 1990). K/Ar radiometric analyses (Mankinen et al, 1978;Duffield et al, 1980;Chauvin et al, 1990) give an age of about 1.12 m.y.…”

Section: Introductionmentioning

confidence: 99%

Paleomagnetic Analyses of Short Normal Polarity Magnetic Anomalies in the Matuyama Chron

Gallet¹,

Gee²,

Tauxe³

et al. 1993

Proceedings of the Ocean Drilling Program

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We document three short normal intervals in the natural remanent magnetization of sediments within the Matuyama Chron. These three anomalous zones of magnetization between the Jaramillo and Olduvai subchrons were identified from continuous measurements of archive halves from Hole 803 A using the pass-through 2G cryogenic magnetometer at Scripps. The U-channel samples were taken from the three intervals, analyzed using the pass-through system, and then cut into discrete 1 -cm-thick samples. Measurements on discrete samples confirmed the presence of the upper normal polarity zone. Based on sedimentation rate calculations, this zone is confidently correlated with the Cobb Mountain Subchron. For the two other anomalous zones, complete thermal demagnetization revealed a high-stability component (250°-575°C) of reversed polarity. The intensity of the low-stability normal polarity component, normalized by susceptibility, remains roughly constant throughout the entire interval sampled, whereas the intensity of the high-stability reversed component is much lower within the normal zone than outside. We interpret these two normal zones, then, as periods of low (reversed polarity) geomagnetic field intensity resulting in low magnetization of the sediments; the periods of these low magnetization reversed polarity zones are completely masked by the component acquired viscously in a normal polarity field.

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Geomagnetic polarity event recorded at 1.1 m.y. B.P. on Cobb Mountain, Clear Lake volcanic field, California

Cited by 105 publications

References 0 publications

Magnetostratigraphy of Leg 117 Sediments from the Owen Ridge and the Oman Margin, Western Arabian Sea

Magnetostratigraphy of Leg 117 Sediments from the Owen Ridge and the Oman Margin, Western Arabian Sea

Magnetostratigraphy of Oligocene to Pleistocene Sediments, Sites 558 and 563

Paleomagnetic Analyses of Short Normal Polarity Magnetic Anomalies in the Matuyama Chron

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