Early Cretaceous Magnetostratigraphy and Paleolatitudes from the Mid-Pacific Mountains: Preliminary Results Bearing on Guyot Formation and Pacific Plate Translation

Abstract

Detailed thermal demagnetization experiments applied to some weakly magnetized shallow-water carbonates recovered at Site 866 (991-1622 mbsf) yield a characteristic remanent magnetization having maximum unblocking temperatures of 500° to 580°C, after the removal of one or more overprints. Alternating field (AF) demagnetization yields a similar characteristic component. This magnetization shows both polarities, which form 10 polarity zones that we correlate to the upper Mesozoic "M-sequence" of the marine magnetic anomaly record. Using tie points derived from paleontologic and isotopic studies, we tentatively assign the polarity zones to CM1 through CM7. Such an assignment requires that basement at Site 866 be of M7 age (or older), broadly consistent with radiometric age data that suggest an age of 128 Ma. Using this interpretation, at least one major hiatus and several substantial changes in sedimentation rate are required in the carbonate sequence.Paleolatitude data from the Site 866 carbonates (14.6°S) are within error of an early Aptian data set from nearby Site 463 (13°S), suggesting little (or no) latitudinal transport during the later part of the Early Cretaceous. Comparisons with younger data sets also suggest that total latitudinal translation from the time of edifice formation to the mid-Cretaceous was minor (±5°). These data do not support drift toward extreme southerly latitudes as a cause of platform drowning. This near-stationary behavior of the Pacific Plate over an area of vigorous mantle convection may account for some patterns of subsidence that are implied by the magnetostratigraphic data.

Magnetic Mineralogical Approach for the Exploration of Gas Hydrates in the Bay of Bengal

“…Nearly 60% of the LT‐SIRM imparted at 5 K is lost during warming between 5 and 35 K (Figures e–f). This indicates the presence of superparamagnetic (SP) magnetic particles (Passier & Dekkers, ; Tarduno et al, ). It is highly likely that the SP magnetic particles are greigite because fine magnetite particles would dissolve in sulfidic settings, while the SP greigite nanoparticles would be thermodynamically more stable in contrast to SP magnetite nanoparticles (Roberts et al, ; Rowan et al, ).…”

Magnetic Mineral Diagenesis in a Newly Discovered Active Cold Seep Site in the Bay of Bengal

“…We noticed that nearly 65% of the LT-SIRM imparted at 5K is lost during warming between 5 and 30 K ( Figures 5C,D). This reflects the dominant presence of superparamagnetic (SP) magnetic particles in these samples (Tarduno et al, 1995;Passier and Dekkers, 2002). Kars and Kodama (2015) noticed a similar pattern of rapid decrease in LT-SIRM from 5 to ∼30 K and ∼50-60% loss of the imparted remanence in the sediment samples from Magesplay fault Zone of the Nankai Trough, offshore Japan.…”

Supplemental Material: Stable Ca and Sr isotopes support volcanically triggered biocalcification crisis during Oceanic Anoxic Event 1a

“…δ 13 C Segmentation and Stratigraphic Correlation Magnetostratigraphy (Tarduno et al, 1995), benthic foraminiferal biostratigraphy (Arnaud-Vanneau and Sliter, 1995), and chemostratigraphy ( 87 Sr/ 86 Sr and δ 13 C) have aided correlation of the section (Jenkyns, 1995;Jenkyns and Wilson, 1999). The Cretaceous stage boundaries are taken from Jenkyns and Wilson (1999).…”