Magnetostratigraphy of the Toarcian Ammonitico Rosso limestone at Iznalloz, Spain

Abstract

The Iznalloz section (Betic cordillera, Spain) provides a continuous outcrop (20 m thick) of Toarcian ammonitico rosso limestones with all the ammonite zones defined in the Betic realm. The characteristic magnetization direction for each sample was obtained by detailed thermal demagnetization and was stable from about 450 to 560°C. The magnetic polarity sequence extends from the Polymorphum to the Aalensis ammonite zone, and covers the whole Toarcian stage. Thus this section presents a good pattern of the reversal succession during Toarcian times. Considering hiatuses of sampling and excluding single‐sample magnetozones, there does not seem to be any important change in the reversal rate during this period.

Base of the Toarcian Stage of the Lower Jurassic defined by the Global Boundary Stratotype Section and Point (GSSP) at the Peniche section (Portugal)

“…Level 15c of Peniche is the equivalent of levels 23-28 of The Almonacid de la Cuba magnetostratigraphy (Fig. 12) shows the N3 magnetozone also observed in the Iznalloz section (Betic Cordillera, southern Spain; Galbrun et al, 1990) and in the Sierra Palomera and Ariño sections (Iberian Range, Central Spain; Osete et al, 2007). The R2 magnetozone corresponds to the reversed polarity observed in the lower part of the Iznalloz section.…”

Magnetostratigraphy of the Hettangian Langmoos section (Adnet, Austria): evidence for time-delayed phases of magnetization

“…Recently, considerable effort has been made to expand the reference polarity time scale to the period of time for which there is no sea-floor magnetic anomaly record. Results for the Late-Middle Jurassic (Steiner et al 1986;Steiner, Ogg & Sardoval 1987); Channell et al 1990b), Lower Jurassic (Marton, Marton & Heller, 1980;Horner & Heller 1983;Channell et al 1984;Galbrun, Gabilly & Rasplus 1988;Galbrun et al 1990), Late Triassic (Witte, Kent & O l d n 1991;Molina-Garza et al 1991 ;Galbrun, Crasquin-Soleau & Jaugey 1992;Gallet et al 1992Gallet et al , 1993 Lower Triassic (Steiner et al 1989;Ogg & Steiner 1991) and for the Late Permian (Steiner et al 1989;Haag & Heller 1991) have been obtained. These studies, which provide only a discontinuous magnetic sequence back to the Late Permian, could constrain the changes in the magnetic reversal frequency for these periods (see Gallet et al 1992 for a review).…”

The Neuquén composite section: magnetostratigraphy and biostratigraphy of the marine lower Jurassic from the Neuquén basin (Argentina)

“…In the Toarcian, Ogg [2] notes that correlations of polarity Zones between the Toarcian sections at Breggia Gorge [5] and Iznalloz [8] were di¤cult to establish, because of stratigraphical discontinuities and regional di¡erences among the sections. Thus, in Breggia Gorge, the Tenuicostatum Zone plus the base of the following Falciferum Zone depict only reversed polarity, whereas in Iznalloz the same interval includes a normal polarity interval as well (Fig.…”

“…The lower part of the Upper Sinemurian, in part controlled by ammonites, depicts a dominant normal polarity, while the uppermost Sinemurian and lowermost Pliensbachian lack magnetostratigraphic data [2,3]. In most of the Pliensbachian^Toarcian interval, polarity ages are assigned on the basis of studies carried out in Breggia Gorge (Switzerland), Alpi Turati (Italy) [5], Thouars^Airvault (France) [7], Iznalloz (Spain) [8] and Bakonycsernye (Hungary) [12]. In Bakonycsernye, a 9 m thick section comprises Ammonitico Rosso facies, in which most of the Pliensbachian (Ibex to Spinatum Standard Zones) was recognized [13].…”

“…In Breggia Gorge, a ca 100 m thick section comprises Ammonitico Rosso facies with Pliensbachian (Jamesoni to Spinatum Standard Zones) and Toarcian (Tenuicostatum to Pleydellia aalensis Standard Zones) ammonites [14,15]. In Iznalloz, a 20 m thick section of Ammonitico Rosso limestones covers the entire Toarcian [8].…”