Depth of post-depositional remanence acquisition in deep-sea sediments: a case study of the Brunhes-Matuyama reversal and oxygen isotopic Stage 19.1

Although post-depositional remanent magnetization (PDRM) in deep-sea sediments appears to be acquired during the earliest stages of sediment compaction, the natural variability of the PDRM lock-in depth in deep-sea sediments is poorly understood and as yet unquantified. Here we consider variations in the relative stratigraphic positions of oxygen isotopic interglacial Stage 19.1 and the Brunhes-Matuyama (B/M) Chronozone reversal for eight deep-sea sediment cores. Results from a similar study of the displacement between a widespread microtektite layer and the B/M boundary are also included [1]. The PDRM lock-in depth and the temporal relationships between the B/M and Stage 19.1 datums can be determined from the offsets between the paleomagnetic and the isotopic (and microtektite) stratigraphies. For cores with sedimentation rates greater than 1 cm kyr−1, the depth offset between the paleomagnetic and isotopic datums is a linear function of sedimentation rate. A simple model (r2 = 0.77) demonstrates that (1) PDRM acquisition occurs ∼ 16 cm below the sediment surface, and (2) the B/M reversal occurs 6 kyr (±2 kyr) after the Stage 19.1 datum, and the Stage 19.1 datum occurs 9 kyr (±3 kyr) after the deposition of the Australasian microtektite strewnfield. This example argues against simple geophysical models linking geomagnetic field reversals to climate change or impact events. The B/M boundary is anomalously deep (30–50 cm) in very low accumulation rate sediments ( < 1 cm kyr−1) and this may reflect the unusual physical properties of these sediments. A review of the geotechnical literature suggests that very low accumulation rate sediments have sufficient time to develop enhanced interparticle rigidity (structural strength) which inhibits early compaction and, hence, PDRM acquisition

The geology and stratigraphy of the lower Nanaimo group, Nanaimo, British Columbia

The western part of the Late Cretaceous Nanaimo Basin is exposed on Vancouver Island at Nanaimo, British Columbia. The five lowest members of the Nanaimo Group are present and represent a complete sedimentary cycle. The two lowest formations, the Comox and Haslam, represent the marine part of the cycle. The Comox rests with angular unconformity on the underlying Triassic Karmutsen volcanics, and is composed of shallow marine deposits of sandstones, conglomerates and limestones, one of the limestones being an algal type not previously reported for the Nanaimo Basin. The Haslam represents a quiet marine environment, possibly lagoonal, which grades upward into a swampy environment represented within the lower Extension Formation. The Extension Formation represents the first of the terrestrial part of the cycle. Above the Wellington Coal Member, deposited in a swampy environment, lie channel conglomerates and sandstones indicative of a braided stream environment. The Newcastle Formation onlaps the Extension Formation and is composed of sandstones, siltstones, conglomerates, and the Newcastle and Douglas Coal Seams. The environments of deposition of the Newcastle Formation are postulated to be the upper floodplain of a short headed stream. Paleocurrent data and composition of the rocks indicate sources to the west. The Protection Formation is the uppermost of the formations in the area, and is composed of thick- and thin-bedded sandstones. The sandstones indicate a barrier-beach complex, probably deposited as the paleo-shoreline migrated west during a transgression. Subsequent faulting, and fluvial and glacial erosion produced the present topography of the area

A practical solution: the Anthropocene is a geological event, not a formal epoch

The Anthropocene has yet to be defined in a way that is functional both to the international geological community and to the broader fields of environmental and social sciences. Formally defining the Anthropocene as a chronostratigraphical series and geochronological epoch with a precise global start date would drastically reduce the Anthropocene’s utility across disciplines. Instead, we propose the Anthropocene be defined as a geological event, thereby facilitating a robust geological definition linked with a scholarly framework more useful to and congruent with the many disciplines engaging with human-environment interactions. Unlike formal epochal definitions, geological events can recognize the spatial and temporal heterogeneity and diverse social and environmental processes that interact to produce anthropogenic global environmental changes. Consequently, an Anthropocene Event would incorporate a far broader range of transformative human cultural practices and would be more readily applicable across academic fields than an Anthropocene Epoch, while still enabling a robust stratigraphic characterization

Atlantic Ocean circulation during the Younger Dryas : insights from a new Cd/Ca record from the western subtropical South Atlantic

Author Posting. © American Geophysical Union, 2003. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 18 (2003): 1086, doi:10.1029/2003PA000888.Benthic foraminiferal Cd/Ca from an intermediate depth, western South Atlantic core documents the history of southward penetration of North Atlantic Intermediate Water (NAIW). Cd seawater estimates (CdW) for the last glacial are consistent with the production of NAIW and its export into the South Atlantic. At ∼14.5 ka concurrently with the onset of the Bølling-Allerød to Younger Dryas cooling, the NAIW contribution to the South Atlantic began to decrease, marking the transition from a glacial circulation pattern to a Younger Dryas circulation. High CdW in both the deep North Atlantic and the intermediate South Atlantic imply reduced export of deep and intermediate water during the Younger Dryas and a significant decrease in northward oceanic heat transport. A modern circulation was achieved at ∼9 ka, concurrently with the establishment of Holocene warmth in the North Atlantic region, further supporting a close linkage between deepwater variability and North Atlantic climate.This work was supported by an MIT John Lyons Fellowship, a WHOI Ocean and Climate Change Institute Fellowship, and NSF grant OCE96-33499

Living on a flammable planet: interdisciplinary, cross-scalar and varied cultural lessons, prospects and challenges: Table 1.

Living with fire is a challenge for human communities because they are influenced by socio-economic, political, ecological and climatic processes at various spatial and temporal scales. Over the course of 2 days, the authors discussed how communities could live with fire challenges at local, national and transnational scales. Exploiting our diverse, international and interdisciplinary expertise, we outline generalizable properties of fire-adaptive communities in varied settings where cultural knowledge of fire is rich and diverse. At the national scale, we discussed policy and management challenges for countries that have diminishing fire knowledge, but for whom global climate change will bring new fire problems. Finally, we assessed major fire challenges that transcend national political boundaries, including the health burden of smoke plumes and the climate consequences of wildfires. It is clear that to best address the broad range of fire problems, a holistic wildfire scholarship must develop common agreement in working terms and build across disciplines. We must also communicate our understanding of fire and its importance to the media, politicians and the general public. This article is part of the themed issue ‘The interaction of fire and mankind’