Paleomagnetic data of the Balzes Anticline

This dataset is built from data published in two different articles (Rodríguez-Pintó et al. 2012 and 2016). The main scientific goal described in the articles is the quantification of vertical axis rotations (VAR) around the bended axis of the Balzes anticline in the South Pyrenean frontal thrust (External Sierras). 74 sites and one short magnetostratigraphic section were sampled following standard paleomagnetic field procedures; in total 984 oriented cores were drilled in the field. Paleomagnetic sites are evenly distributed along strike changes of the fold and were drilled in Eozene rock of the Ypresian (Cuisian), Lutetian and Bartonian rocks. Lithologies and affinity may vary; some rocks are marine limestones and marls (Boltaña, Paules and Guara Formations), others (sandy limestones and marls) represent transitional environments (Belsué-Atarés Formation) while the remaining are continental siltstones and sandstones from the Campodarbe Formation. Every site contains an average out of 9.6 standard cores (stand. dev. 5.8) but varies between 3 and 35. For the small magnetostratigraphic section 65 cores were sampled. Thermal demagnetization was the main laboratory analysis performed searching for VAR values at the site scale. The analyses were performed in the laboratories of the Universities of Barcelona and Burgos. 2G magnetometer were used to measure the magnetization in both laboratories and MMTD80 (Magnetic Measurements) and TD-48 SC (ASC Scientific) furnaces, respectively.

1149 standard specimens were subjected to stepwise detailed demagnetization (increments of 20–30-50 were applied) up to magnetite maximum unblocking temperatures (575°C). PCA was the main method to fit the ChRM directions, although other approaches were also used as auxiliary tools (linearity spectrum analysis, stacking routine, virtual directions). The VPD software was used for the visualization and fitting of characteristic remanent directions (ChRM). ChRMs at the specimen level were fitted with an averaged out of 6.4 steps (stand. dev: 2.3) and associated MAD angles displayed a slightly high mean value (12.4 stand. dev: 8.0) because of the weak and partially unstable signal of the rocks (noise caused by sulphides). Fisherian means at the site level are based on 10/15 considered/measured specimens in averaged. Statistical parameters of the site means (a95 and k) yield slightly scattered results; an averaged out of 16° and 36.4 respectively (and 9.7 and 45.7 related standard deviations) but still allow building robust averages of VAR after the grouping of sites in five structural sectors (defined following the changes of the fold-axis trend). These five groups displayed mean values with a95 angles < 10.3° and k > 18.4 and honored standard reliability criteria for paleomagnetic data allowing for the fold axis curvature kinematics reconstruction. The data are povided in .csv and Microsoft Excel (.xlsx) formats. Additional data description including the explanation of variables in the data file is available in pdf (Data Description).