Export 2 results:
Sort by: Author Title Type [ Year  (Desc)]
Bowles, J, Tauxe L, Gee J, McMillan D, Cande S.  2003.  Source of tiny wiggles in Chron C5: A comparison of sedimentary relative intensity and marine magnetic anomalies. Geochemistry Geophysics Geosystems. 4   10.1029/2002gc000489   AbstractWebsite

[1] In addition to the well-established pattern of polarity reversals, short-wavelength fluctuations are often present in both sea-surface data ("tiny wiggles'') and near-bottom anomaly data. While a high degree of correlation between different geographical regions suggests a geomagnetic origin for some of these wiggles, anomaly data alone cannot uniquely determine whether they represent short reversals or paleointensity variations. Independent evidence from another geomagnetic recording medium such as deep-sea sediments is required to determine the true nature of the tiny wiggles. We present such independent evidence in the form of sedimentary relative paleointensity from Chron C5. We make the first comparison between a sedimentary relative paleointensity record (ODP Site 887 at 54degreesN, 148degreesW) and deep-tow marine magnetic anomaly data (43degreesN, 131degreesW) [ Bowers et al., 2001] for Chron C5. The sediment cores are densely sampled at similar to2.5 kyr resolution. The inclination record shows no evidence for reverse intervals within the similar to1 myr-long normal Chron C5n.2n. Rock magnetic measurements suggest that the primary magnetic carrier is pseudo-single domain magnetite. We choose a partial anhysteretic magnetization (pARM) as our preferred normalizer, and the resulting relative paleointensity record is used as input to a forward model of crustal magnetization. We then compare the results of this model with the stacked deep-tow anomaly records. The two records show a significant degree of correlation, suggesting that the tiny wiggles in the marine magnetic anomalies are likely produced by paleointensity variations. An analysis of our sampling density suggests that if any reverse intervals exist at this site, they are likely to be <5 kyr in duration. Furthermore, we suggest that reverse intervals during Chron C5n.2n documented in other locations are unlikely to be global.

Friedman, R, Gee J, Tauxe L, Downing K, Lindsay E.  1992.  The Magnetostratigraphy of the Chitarwata and Lower Vihowa Formations of the Dera-Ghazi-Khan Area, Pakistan. Sedimentary Geology. 81:253-268.   10.1016/0037-0738(92)90074-2   AbstractWebsite

Three sections of the Chitarwata and lower Vihowa formations were sampled along the Dalana River on the southeastern flank of the Zinda Pir Dome in the southern Sulaiman Range near Dera Ghazi Khan, Pakistan. Together they provide nearly 800 m of a continuous sedimentary record of the Miocene derived from the uplifted Himalayan highlands. Previous studies have examined the Middle and Upper Miocene sediments, the Siwalik Group, of the Potwar Plateau to the north. However, detailed investigations of earlier periods are impossible in that area due to the absence of Oligocene and Lower Miocene sediments caused by continued overthrusting associated with the Himalayan orogeny. Fortunately, the Sulaiman basin to the south, which was further removed from the tectonic activity, provides a record of the Early Miocene in the form of the Chitarwata Formation. The Dalana A, B, and C sections (DGA, DGB, and DGC) were examined and sampled for this study. A magnetostratigraphic analysis was carried out to correlate and date the Chitarwata and Vihowa formations exposed in this area. The samples were subjected to step-wise demagnetization to resolve the primary and secondary remanent magnetization components. Thermal demagnetization trajectories indicate that the majority of samples have sufficient internal consistency that their calculated polarities are reliable. Likewise, the majority of the 126 measured sites showed statistically significant agreement between the three measured samples per site. However, the bimodal data set does not pass the reversal test and so is deemed unsuitable for tectonic interpretations. The individual sections were initially correlated using lithologic and stratigraphic methods, and the relationship was reinforced by the magnetostratigraphy. The composite DG section was tentatively correlated with the standard magnetic polarity time scale placing the disconformable base of the Chitarwata in the DGA section at just older than 22 Ma, the Chitarwata/Vihowa contact at 18.6 Ma, and the top of the Vihowa in the DGC section at about 16 Ma. The assignment of these dates to the Chitarwata will aid in future biostratigraphic and lithostratigraphic correlation of Early Miocene sediments, effectively extending the well-established Siwalik faunal sequence back by four million years.