Tracking the last sea-level cycle: seafloor morphology and shallow stratigraphy of the latest Quaternary New Jersey middle continental shelf

Seafloor geomorphology and surficial stratigraphy of the New Jersey middle continental shelf provide a detailed record of sea-level change during the last advance and retreat of the Laurentide ice sheet (120 kyr B.P. to Present). A NW–SE-oriented corridor on the middle shelf between water depths of 40 m (the mid-shelf “paleo-shore”) and 100 m (the Franklin “paleo-shore”) encompasses 500 line-km of 2D Huntec boomer profiles (500–3500 Hz), an embedded 4.6 km² 3D volume, and a 490 km² swath bathymetry map. We use these data to develop a relative stratigraphy. Core samples from published studies also provide some chronological and sedimentological constraints on the upper <5 m of the stratigraphic succession.The following stratigraphic units and surfaces occur (from bottom to top): (1) “R”, a high-amplitude reflection that separates sediment >46.5 kyr old (by AMS ¹⁴C dating) from overlying sediment wedges; (2) the outer shelf wedge, a marine unit up to 50 m thick that onlaps “R”; (3) “Channels”, a reflection sub-parallel to the seafloor that incises “R”, and appears as a dendritic system of channels in map view; (4) “Channels” fill, the upper portion of which is sampled and known to represent deepening-upward marine sediments 12.3 kyr in age; (5) the “T” horizon, a seismically discontinuous surface that caps “Channels” fill; (6) oblique ridge deposits, coarse-grained shelly units comprised of km-scale, shallow shelf bedforms; and (7) ribbon-floored swales, bathymetric depressions parallel to modern shelf currents that truncate the oblique ridges and cut into surficial deposits.We interpret this succession of features in light of a global eustatic sea-level curve and the consequent migration of the coastline across the middle shelf during the last 120 kyr. The morphology of the New Jersey middle shelf shows a discrete sequence of stratigraphic elements, and reflects the pulsed episodicity of the last sea-level cycle. “R” is a complicated marine/non-marine erosional surface formed during the last regression, while the outer shelf wedge represents a shelf wedge emplaced during a minor glacial retreat before maximum Wisconsin lowstand (i.e., marine oxygen isotope stage 3.1). “Channels” is a widespread fluvial subarial erosion surface formed at the late Wisconsin glacial maximum 22 kyr B.P. The shoreline migrated back across the mid-shelf corridor non-uniformly during the period represented by “Channels” fill. Oblique ridges are relict features on the New Jersey middle shelf, while the ribbon-floored swales represent modern shelf erosion. There is no systematic relationship between modern seafloor morphology and the very shallowly buried stratigraphic succession.     

一种用于海底类型聚类的新方法

By using sonar imaging, this paper presents a new algorithm for the clustering of seabed types based on the self-organizing feature maps （SOFM） neural network. The theory as well as data processing is studied in detail. Some valuable conclusions and suggestions are given     

海底冷泉在旁扫声纳图像上的识别

海底冷泉是指来自海底沉积地层(或更深)的气体以喷涌或渗漏的方式注入海洋中的一种海洋地质现象,它普遍发育于主动大陆边缘和被动大陆边缘。海底冷泉研究在天然气水合物、全球气候变化、极端生物群落等研究方面都具有重要意义。利用实测的海上资料,通过分析水体声学剖面上的冷泉气柱、旁扫声纳图像上的亮斑异常以及柱状沉积物样品中天然气水合物等的对应关系,指出旁扫声纳图像上出现的亮斑异常是海底冷泉喷逸的指示。海底冷泉逸出的大量气泡遮蔽海底,从而形成一个强波阻抗界面,这个强波阻抗界面在旁扫声纳图像上形成亮斑异常。通过亮斑异常,可以判定海底冷泉的存在。旁扫声纳可以成为海底冷泉探测的有力方法。     

Transition from wavelets to ripples in a laboratory flume with a diverging channel

An experimental investigation on the initiation and development of bed forms on a bed of fine silica sand was conducted under alluvial flow conditions in a laboratory flume with a diverging channel. The main aims of the study were to assess： i） the steepness of bed forms in the transition stage of development; and ii） the threshold height of wavelets （ηt） that triggered the start of ripple development. Detailed bed profile measurements were carried out using an acoustic Doppler probe, traversed longitudinally over the sediment bed at various experimentation times. The bed form dimensions were extracted from such bed profile records and analysed for the wavelet, transition and equilibrium stages. It was found that the steepness of ripples in the transition and equilibrium stages were similar, confirming predictions of previous mathematical model simulations. A lognormal distribution fitted the wavelet length data. The wavelet threshold height was estimated as ηt ≈ 7 mm, or ηt≈ 80 in wall units. Such a height magnitude suggested that ripple development could be triggered by the wavelets reaching the outer flow zone of a turbulent boundary layer. The ηt value obtained corresponded generally to the intersection point between two predictive equations for bed form dimensions. A formulation was developed to predict ηt as a function of the sediment grain size, which was confirmed for the fine sand used in this study.     

一种针对侧扫声纳图像的数字镶嵌技术方法

以南海某海域实测侧扫声纳数据为例,研究侧扫声纳图像的数字镶嵌技术方法,对关键步骤进行详细的阐述。通过对原始侧扫声纳数据进行导航数据校正、海底线跟踪、斜距改正、TVG校正、船速校正、地理编码与重采样、拼接与镶嵌等处理,生成大区域、大范围、高分辨率、无缝拼接的侧扫声纳图像。实验结果证明声纳图像数字镶嵌技术的有效性,并取得理想的效果。     

Flow processes and sediment deformation in the Canary Debris Flow on the NW African Continental Rise

The Canary Debris Flow formed an extensive deposit on the NW African Continental Margin west of the Canary Islands. Sidescan sonar images and 3.5-kHz profiles show that the middle part of the debris flow deposit consists of complex channel systems separated by banks and ridges of debris. Channels are typically up to 10 km wide and 10 to 20 m deep, and have little or no debris fill. They appear to feed a more laterally continuous debris flow sheet which is seen further downslope. Interchannel banks and ridges are composed of 5 to 20 m thick debris deposits. This morphology is remarkably similar to that seen in subaerial debris flows, and we therefore infer that the observed submarine debris flow morphology is a primary flow fabric, rather than the result of the debris flow interacting with or exploiting pre-existing channels. High-resolution Sidescan sonar images show that the debris flow surface is covered by sediment blocks up to 300 m in diameter. A single core collected from the flow shows that most of the 4.6-m flow thickness at the core site is composed of a single clast. The clast has been folded, with its upper part consisting of an inverted minor image of the lower part. The same sequence occurs again, in situ, beneath the debris flow, suggesting that the clast may have a local source, rather than having been derived from the debris flow source area, some 200 km upslope. This indicates that the debris flow was capable of substantial seabed erosion in the middle part of its course. In these middle reaches, erosion within the channelled areas probably occurred simultaneously with deposition in the interchannel areas. Interchannel deposits may contain both locally derived and original source area material.     

侧扫声呐图像分割的中性集合与量子粒子群算法

针对现有的侧扫声呐图像分割方法存在分割准确率不高和效率偏低的问题,提出了一种基于中性集合和量子粒子群算法的侧扫声呐图像阈值分割方法。通过基于中性集合计算图像灰度共生矩阵,实现了侧扫声呐图像精细纹理的表达,提高了分割精度;基于二维最大熵理论,采用量子粒子群算法计算二维最优分割阈值向量,实现了分割阈值向量的快速准确获取,提高了分割效率和精度。最终实现了高噪声侧扫声呐图像目标的准确、高效分割。通过对含有不同目标的侧扫声呐图像的分割试验,验证了该算法的有效性。