Palaeosecular variation in Java and Bawean Islands (Indonesia) during the Brunhes chron

Abstract

S U M M A R YA palaeomagnetic study has been conducted from Indonesian lava flows and dykes. Sampling was concentrated to the Merapi and Merbabu volcanoes (central Java), the Bromo-Tengger volcanic complex, the Lurus volcano (both east of Java), and the Bawean Island. Numerical dating indicates that the rock units sampled have ages that are well distributed within the Brunhes chron. Only a few reverse polarity flows were probably emplaced during the late Matuyama chron. Alternating field (AF) and thermal demagnetization treatments were routinely used for all sites. Results from both methods were generally in good agreement, demonstrating the reliability and the reproducibility of the palaeomagnetic determinations obtained from 36 independent sites. The large dispersion of the directions and the age distribution indicate that a large spectrum of the secular variation has been sampled. Our best estimate of the mean Brunhes field direction in Java is characterized by a zero declination and an inclination anomaly of −4.7 • (with a 95 per cent confidence angle of 5.3 • ). This value agrees with an axial dipolar field model, or a model to which a persisting zonal quadrupolar term of a few per cent of the geocentric axial dipole is added. This study adds new constraints to recent results which suggested that a large zone of negative inclination anomalies may have persisted in the southwestern Pacific ocean over the past 500 Kyr, and possibly extended toward the eastern Indian ocean. The present results do not support such an extension. They also suggest that the inclination anomaly may have varied over 100 Kyr, and that it was more pronounced in recent times.

Systematics of Eutropis rugifera (Stoliczka, 1870) (Squamata: Scincidae) including the redescription of the holotype

“…However, the species identity of these samples (NHM.OU.REP.3-2009, CES09/976, and CES09/943) is uncertain (Amarasinghe et al 2016a, b). The 4.3% genetic difference between the Bawean population and the other E. rugifera specimens may indicate that the populations on Bawean have been isolated for a substantial amount of time, bearing significance to the substantially wide sea passages between East Java, Bawean and Kalimantan (Borneo) and paleogeographic evidence (Elmaleh et al, 2004;Metcalf, 2011).…”

Equatorial paleosecular variation of the geomagnetic field from 0 to 3 Ma lavas from the Galapagos Islands

“…Binned entries were averaged in latitudinal bands from both hemispheres and are from Opdyke et al, 2006) is several degrees higher than these estimates; we suspect this is because of jitter from undetected tilting of lavas in that active Andean tectonic setting. According to a compilation by Opdyke et al (2010), the only other datasets within 15 • of the equator that meet modern reliability standards are from Java at 7.4 • S (S b = 12.9 • , confidence interval 11.0-15.4 • ; Elmaleh et al, 2004), Costa Rica at 10 • N (S b = 17.2 • , confidence interval 14.9-21.0 • ; Johnson et al, 2008), and the Afar region of Ethiopia at 12 • N (S b = 12.6 • , confidence interval 11.5-13.9 • ; Kidane et al, 2003). The Costa Rica dispersion estimate seems anomalously high, which as suspected for Equador might also reflect a contribution from undetected tectonic tilts of the lava flows.…”

Isolating climatic and paleomagnetic imbricated signals in two marine cores using principal component analysis

“…However, we see here some circular reasoning since the model predictions are not validated by enough data. Interestingly, no anomaly has been reported from the paleomagnetic study conducted in a large collection of volcanic lava flows from Java [ Elmaleh et al , 2004].…”

“…However, we see here some circular reasoning since the model predictions are not validated by enough data. Interestingly, no anomaly has been reported from the paleomagnetic study conducted in a large collection of volcanic lava flows from Java [Elmaleh et al, 2004]. [19] As noticed above, a striking feature of the MD98-2182 record is the large amplitude of the oscillations in the upper 8-10 m which has mainly been caused by oversampling of the water-rich…”