西藏申扎地区德日昂玛-下拉剖面：冈瓦纳和特提斯晚石炭世-早二叠世地层和古生物对比的桥梁

西藏北部申扎县永珠地区德日昂玛-下拉剖面中石炭系和二叠系地层发育完整,出露良好,化石丰富。该剖面中查果罗玛组碳酸盐岩地层(泥盆纪—早石炭世)和下拉组(中二叠世)碳酸盐岩地层之间的碎屑岩夹灰岩地层,在沉积上表现为冰海相杂砾岩,在古生物化石面貌上表现为特提斯-冈瓦纳古生物群混生。古生物群混生的现象为石炭纪—二叠纪的特提斯生物区与冈瓦纳生物区之间的地层和古生物对比建立了一座桥梁。永珠组中上部地层中同时产有牙形石和腕足类,牙形石的研究表明其时代为晚石炭世莫斯科期,而腕足类的研究则表明其为早二叠世萨克马尔期。这一矛盾预示着在(亲)冈瓦纳相地区晚石炭世晚期地层缺失的意见需要重新审视。     

Till in the marine environment

Till is of common occurrence in the marine environment and can be both subglacial and proglacial in origin. Former glacial margins are often represented by till tongues, that are interbedded with stratified glaciomarine sediment, and the relationship is readily mappable using seismic reflection techniques. It is inferred that within individual till tongues, sediment-gravity flow deposits form transitional contacts with till of subglacial origin, but these contacts cannot be distinguished on seismic profiles. These unstratified, gravity-induced deposits formed in close proximity to the glacial source at the grounding line are considered to be secondary tills (flow-till complex) in terms of the INQUA classification of tills. Till-tongue successions and till deltas are large, ice-marginal depocentres associated with floating front ice-margins, and appear to be closely related in origin. Tabular and hummocky moraines of the mid-Norwegian Shelf also are considered to be products of floating-front margins and represent a large proportion of the retreat tills formed during ice recession. Seismostratigraphic evidence for channelisation in ice-marginal deposits appears to provide a means of distinguishing between former tidewater and floating-front margins.     

湖北省宜昌县震旦系南沱组成因的新认识

在峡东王丰岗南沱组剖面上有一些杂砾岩透镜体和一些水道砂岩透镜体。这些是冰水环境的产物。在南沱组与莲沱组的界线上,见到了几个骑线砾石。这是冰陆环境的有力证据。由此可见,早期主要是冰陆环境,冰川刨蚀和剥蚀作用占主导,沉积作用是次要的。随着气温的回升,冰盖逐渐后退。当冰盖前沿退到研究区内,或刚退出本区时,就形成了本区冰期的主要沉积。因此,可以认为,本区南沱组杂砾岩主要是近源冰海相沉积。     

A review of progress in identifying and characterizing biocrusts using proximal and remote sensing

Biocrusts are critical components of desert ecosystems, significantly modifying the surfaces they occupy. The mixture of biological components and soil particles that form the crust, in conjunction with moisture, determines the biocrusts’ spectral signatures. Proximal and remote sensing in complementary spectral regions, namely the reflective region, and the thermal region, have been used to study biocrusts in a non-destructive manner, in the laboratory, in the field, and from space. The objectives of this review paper are to present the spectral characteristics of biocrusts across the optical domain, and to discuss significant developments in the application of proximal and remote sensing for biocrust studies in the last few years. The motivation for using proximal and remote sensing in biocrust studies is discussed. Next, the application of reflectance spectroscopy to the study of biocrusts is presented followed by a review of the emergence of high spectral resolution thermal remote sensing, which facilitates the application of thermal spectroscopy for biocrust studies. Four specific topics at the forefront of proximal and remote sensing of biocrusts are discussed: (1) The use of remote sensing in determining the role of biocrusts in global biogeochemical cycles; (2) Monitoring the inceptive establishment of biocrusts; (3) Identifying and characterizing biocrusts using Longwave infrared spectroscopy; and (4) Diurnal emissivity dynamics of biocrusts in a sand dune environment. The paper concludes by identifying innovative technologies such as low altitude and high resolution imagery that are increasingly used in remote sensing science, and are expected to be used in future biocrusts studies.     

Late glacial and Holocene marine records from the Independence Fjord and Wandel Sea regions, North Greenland

The first marine sediment cores from the unexplored Independence Fjord system and the Wandel Sea, North Greenland, have been investigated to reveal the glacial marine history of the region. Two key sites in the Independence Fjord system, and an earlier analysed site from the Wandel Sea continental slope, off the mouth of Independence Fjord, are presented. The Independence Fjord sites reveal an early Holocene record (10.0–8.9 Kya) of fine-grained reddish muds with calcareous microfossils, dominated by the benthic foraminifera Cassidulina neoteretis . We suggest that a semi-permanent fast ice cover characterized the region in the early Holocene, and that the deeper troughs in the mouth region of the Independence Fjord system were intruded by subsurface Atlantic water. A stiff diamicton, at least 1.3 m thick, with coal and sandstone clasts of mainly local origin, and a 0.5-m-thick Holocene cover, are found in one of the sites. The diamicton is assumed to represent a subglacial till predating the early Holocene sediments (>10 Kya). Shallow seismic records off the mouth of Independence Fjord reveal kilometre-sized troughs with signs of glacial erosion, till deposition and a Holocene glaciomarine deposition. These features could indicate that glacial ice debouching from the Independence Fjord system at some time during the last glacial period extended to the mid-outer Wandel Sea shelf. Data from a high-resolution sediment core previously retrieved from the adjacent Wandel Sea slope indicate that the maximum ice sheet advance in this area culminated about 25–20 Kya.     

Sand dunes as a major proximal dust source for late Pleistocene loess in the Negev Desert, Israel

Grain size analyses of three hilltop, primary eolian loess sequences in the Negev desert, southern Israel, show a bimodal grain-size distribution at 50-60 μm and 3-8 μm. Using analyses of mineralogy and OSL ages we demonstrate that the coarse mode is composed mostly of quartz grains and its relative magnitude increases regionally with time, suggesting an enhancement of a time-transgressive proximal dust source compared to a distal, Saharan fine-grain dust. The only proximal dust source for large amount of coarse silt quartz grains is the sands that advanced into Sinai and the Negev concurrently with the loess accretion during the late Pleistocene as a result of the exposure of the Mediterranean shelf. We therefore propose that the coarse silt quartz grains were formed through eolian abrasion within the margins of an advancing sand sea. This relationship between desert sand seas as a source for proximal coarse dust and desert margin loess deposits can be applicable to other worldwide deserts such as Northern Africa, China and Australia.     

Depositional origin of an adverse delta surface slope at Altermarka,northern Norway

Based on grain-size analysis of sediment samples from a delta at Altermarka, it has previously been suggested that two tills were deposited on the delta surface as a glacier planed off the delta topsets and created its adverse surface slope. In this reinvestigation of the delta, there was no evidence that a glacier overrode the surface: the topset beds remain intact and no appreciable till was found. Sediments resembling the ‘till’ samples were located, but soil processes and other sedimentary processes easily account for the wide grain-size distributions of these sediments. As a result, this study cautions against using grain-size analysis, on its own, to interpret the genesis of sediments. Other processes potentially responsible for the adverse surface slope include differential isostatic rebound, recent differential slip along ancient thrust faults, and failure of the delta surface to reach sea level. Based on the sedimentology of the topset beds and the local relative sea level history (indicating the delta (9495±70 ¹⁴C yr BP) formed about the time of the local marine limit (9560–9375 ¹⁴C yr BP) 17 m higher than the delta surface), the feature is determined to have built up below sea level with an adverse surface slope.     

A Weichselian deglaciation model applied to the Early Permian glaciation in the northeast Karoo Basin,South Africa

It generally is assumed that the Early Permian Gondwana deglaciation in South Africa started with a collapse of the marine ice‐sheet. The northeast part of the Karoo Basin became ice‐free as a result of this collapse. The deglaciation here probably took place under temperate glacial conditions. Three glacial phases have been identified. Phase 1: the marine ice retreat of 400 km over the northeast Karoo Basin, which may have been completed over a few thousand years. The glaciers grounded in the shallower areas around the shore of the basin. Phase 2: the smaller, now mainly continental ice‐sheet here re‐stabilised and remained more or less stationary for several tens of thousand years. During this phase, between 50 and 200 m of massive glaciomarine mud with dropstones accumulated in the open, marine basin that became ice‐free during Phase 1. Isostatic uplift, as a response to the first rapid deglaciation phase, can be traced in the inland part of the region. Phase 3: the final deglaciation may have taken 10 to 20 kyr. After this time no new ice sheet was built up over southern Africa. The entire Early Permian deglaciation of the northeast Karoo Basin was completed within thousands rather than millions of years. Phases 1 and 3 had lengths similar to typical Quaternary deglaciations, whereas Phase 2 was a long, stable phase, more similar to a full Quaternary glaciation. Copyright © 2001 John Wiley & Sons, Ltd.     

A critical review of the glaciomarine model for Irish sea deglaciation: evidence from southern Britain,the Celtic shelf and adjacent continental slope

In support of their ‘glaciomarine’ model for the deglaciation of the Irish Sea basin, Eyles and McCabe cited the occurrence of distal glaciomarine mud drapes onshore in the Isles of Scilly and North Devon, and of arctic beach‐face gravels and sands around the shores of the Celtic Sea. Glacial and sea‐level data from the southern part of the Irish Sea in the terminal zone of the ice stream and the adjacent continental slope are reviewed here to test this aspect of the model. The suggestion that the glacial sequences of both the Isles of Scilly and Fremington in North Devon are glaciomarine mud drapes is rejected. An actively calving tidewater margin only occurred early in the deglacial sequence close to the terminal zone in the south‐central Celtic Sea. Relative sea‐levels were lower, and therefore glacio‐isostatic depression less, than envisaged in the glaciomarine model. Geochronological, sedimentological and biostratigraphical data indicate that the raised beach sequences around the shores of the Celtic Sea and English Channel were deposited at, or during regression soon after, interglacial eustatic highstands. Evidence for ice‐rafting at a time of high relative sea‐levels is restricted to a phase(s) earlier than the Late Devensian. These data indicate that the raised beach sequences have no bearing on the style of Irish Sea deglaciation. Copyright © 2001 John Wiley & Sons, Ltd.