Shallow bias in Mediterranean paleomagnetic directions caused by inclination error

Abstract

A variety of paleomagnetic data from the Mediterranean region show a strong bias toward shallow inclinations. This pattern of shallow inclinations has been interpreted to be the result of (1) major northward terrane displacement, (2) large nondipole components in the Earth's magnetic field, and (3) systematic inclination flattening of the paleomagnetic directions. Here, we use the observation that, in addition to the well-known variation of magnetic inclination with latitude, the N -S elongation of directional dispersion also varies, being most elongate at the equator and nearly symmetric at the poles. Assuming that inclination shallowing follows the relationship long known from experiment, we invert the inclinations using a range of ''flattening factors'' to find the elongation/inclination pair consistent with a statistical model for the paleosecular variation. We apply the so-called ''elongation/inclination'' method to the extensive paleomagnetic data sets from the Miocene sediments of the Calatayud basin (Spain) and the island of Crete (Greece). After correction, the Spanish data are in good agreement with the expected middle Miocene latitude of the region. The data from Crete suggest that it occupied a position in the late Miocene about 275 km north of the predicted location. This is in agreement with the geological and geodynamical models for the east Mediterranean region, which indicate that slab rollback processes in combination with Anatolian push generated southward migration of Crete. The 7.5 million year average displacement rate of Crete estimated by the E/I method is 37 mm/yr to the south, which closely coincides with present-day rates based on global positioning system (GPS) and model measurements. We also show that inappropriate tilt corrections lead to a shallow inclination bias as well, explaining that observed in studies of lava flows of the region. We conclude that the east Mediterranean inclination anomaly is caused by sedimentary inclination error and not by a persistent octupolar contribution to the geomagnetic field, or northward transport. D

Influence of inclination error in sedimentary rocks on the Triassic and Jurassic apparent pole wander path for North America and implications for Cordilleran tectonics

“…I error has sometimes been dismissed as being not very important because of bioturbation or lack of appreciable compaction [e.g., Opdyke , 1961; Irving and Major , 1964; Irving , 1967; Kent , 1973; Van der Voo et al , 1995], as shown for many deep‐sea sediments [ Opdyke and Henry , 1969; Schneider and Kent , 1990]. Recently, however, especially in terrestrial sedimentary rocks, I error has been more widely recognized using the elongation/inclination ( E/I ) statistical method [ Tauxe and Kent , 2004] on the distribution of directions [ Krijgsman and Tauxe , 2004; Krijgsman and Tauxe , 2006] and by magnetic anisotropy measurements [ Garcés et al , 1996; Kodama , 1997; Tan and Kodama , 2002]; where they have been compared, these two methods yield consistent estimates of I error [ Kent and Tauxe , 2005; Tan et al , 2007; Tauxe et al , 2008]. Igneous rocks are not subject to I error, and where comparisons between coeval layered igneous and sedimentary rocks have been made the shallowing of sedimentary inclinations is often apparent.…”

“…E/I tests on Cretaceous sedimentary rocks of the Nanaimo Group of Vancouver Island indicated either essentially no significant shallowing ( f = 0.95) in terrestrial strata, or substantial flattening ( f = 0.68) in fine‐grained marine strata [ Krijgsman and Tauxe , 2006]. In contrast, terrestrial and marine marls of Miocene age in the Mediterranean region gave consistent values of f ∼ 0.7 [ Krijgsman and Tauxe , 2004]. Much more severe shallowing ( f ∼ 0.3) has been reported in Cretaceous red beds from the Tarim Basin from modeling of magnetic anisotropy [ Gilder et al , 2003].…”

“…Solid circles are data from experiments on reconstituted hematite‐bearing sediments characterized by a mean flattening factor of f = 0.55 (dashed curve [ Tauxe and Kent , 1984]). Inset shows estimates of flattening factor using the E/I method [ Tauxe and Kent , 2004] on a variety of sedimentary formations of Miocene to Triassic age [ Krijgsman and Tauxe , 2004; Tauxe and Kent , 2004; Kent and Tauxe , 2005; Krijgsman and Tauxe , 2006; Kent and Olsen , 2008]. …”

Oxygen and carbon isotope signatures in late Neogene horse teeth from Spain and application as temperature and seasonality proxies

“…According to paleomagnetic reconstructions the paleolatitude of the study region was situated~2-4°more south than today 10 million years ago, depending on the pole path chosen (Krijgsman and Tauxe, 2004;Torsvik et al, 2008;Langereis, pers. comm.).…”

Effect of magnetic anisotropy on the natural remanent magnetization in the MCU IVe' layer of the Bjerkreim Sokndal Layered Intrusion, Rogaland, Southern Norway

“…This effect may have severe consequences for paleomagnetic interpretations. For example, shallow paleomagnetic directions can lead to the interpretation that a rock was magnetized at lower latitudes; however, they can also be caused by anisotropy‐induced deflection of a steeper NRM, with major influence on apparent polar wander paths and paleogeographic reconstructions [ Bilardello and Kodama , ; Krijgsman and Tauxe , ; Muttoni et al ., ; Tan and Kodama , ; Vaughn et al ., ]. For this reason, some authors warn against using paleomagnetic data from anisotropic rocks [ Kirker and McClelland , ].…”