A micromorphological and mineralogical study of site formation processes at the late Pleistocene site of Obi‐Rakhmat,Uzbekistan

Site formation processes at the Late Pleistocene rockshelter deposit of Obi‐Rakhmat were reconstructed through soil micromorphology and Fourier transform infrared spectroscopy (FTIR). The entire sequence has undergone limited diagenesis and is well preserved. The base of the stratified sequence represents a karstic setting with intermittent, low‐energy deposition of autochthonous gravitational debris and anthropogenic material in a wet, muddy environment. These sediments were post‐depositionally affected by episodic waterlogging. The bulk of the sequence overlying the karstic layers comprises a continuous series of primary freshwater spring deposits containing reworked anthropogenic material that was buried penecontemporaneously with calcium carbonate deposition. The top of the sequence is weakly cryoturbated, indicating a periodically cold, wet environment. No alluvial elements that could suggest sediment inputs from the nearby river terraces were documented. A single exogenous layer was identified, representing an episode of colluviation from directly above the rockshelter preceding a major roofspall event. The basal part of the sequence contains slightly reworked anthropogenic remnants of intense activities, including combustion. The anthropogenic elements present in the spring deposits show higher degrees of reworking, suggesting within‐layer translocation. The development of spring activity at the site did not cause humans to abandon the rockshelter; they continued to carry out their activities throughout a changing local environment. © 2009 Wiley Periodicals, Inc.     

“Mind the gap”: Caves,radiocarbon sequences,and the Mesolithic–Neolithic transition in Europe—lessons from the Mala Triglavca rockshelter site

Radiocarbon sequences from some northern Mediterranean cave sites show a temporal gap between Mesolithic and Neolithic occupations. Some authors regard this as a regional phenomenon and have sought to explain it in terms of a general population decline in the late Mesolithic, which facilitated the replacement of indigenous foragers by immigrant farmers. New evidence from the rockshelter site of Mala Triglavca, in Slovenia, leads us to question this view. We describe the deposits in the rockshelter and discuss the results of AMS radiocarbon dating of bone samples recovered in excavations in the 1980s. New archaeological investigations and associated soil/sediment analyses show that in the central part of the rockshelter a well‐defined stratigraphic sequence can be established, despite post‐depositional modification by soil forming processes. There is also evidence of substantial post‐depositional disturbance of the cave sediments by human agency and geomorphological processes, which have created “temporal gaps” and “inversions” in the radiocarbon sequence. The relatively large series of radiocarbon dates obtained enables some of the post‐depositional processes to be identified. © 2008 Wiley Periodicals, Inc.     

Geoarchaeology and Paleoenvironmental Context of the Burntwood Creek Rockshelter,High Plains of Northwestern Kansas,U.S.A

The first systematic geoarchaeological study of a rockshelter in Kansas yielded information about rockshelter formation, Holocene paleoenvironments, archaeological site formation processes, and prehistoric human habitation and site use. The rockshelter was carved by groundwater sapping; colluvium, alluvium, and roof‐fall debris subsequently accumulated on its floor. An assemblage of Late Archaic (∼2000–4000 ¹⁴C years before present [yr B.P.]) cultural deposits (lithic material, bone, and charcoal) is preserved in a 2‐m thick package of colluvium and alluvium in front of the shelter. Chipped stone analysis indicates that Late Archaic occupants of the shelter were using mostly local materials and resharpening their stone tools at the shelter. Stable carbon isotope and phytolith analyses indicate that a mixed C₃ and C₄ plant community existed in the study area and that it changed in composition through the late Holocene. Based on the phytolith assemblage from an unlined fire pit at the front of the shelter, Late Archaic people used local hackberry trees for fuel and/or food.     

Effects of bears on rockshelter sediments at Tanay Sur‐les‐Creux,southwestern Switzerland

Sur‐les‐Creux rockshelter is located in the Prealps of southwestern Switzerland. The sequence of deposits in the rockshelter is 80 cm thick and consists of weathered gravels in a phosphate‐rich matrix. A few Middle Palaeolithic artifacts and the bones of cave bear (Ursus spelaeus) were recorded in the fill. We present the results of sedimentological, geochemical, and micromorphological analyses of the rockshelter sediment. All analyses suggest an endokarstic origin of the sediments. The alteration cortices of the gravels imply in situ weathering over a long period. The phosphates are essentially biogenic and have an apatitelike nature. Phosphatization and intense mixing of the sediment are attributed to cave bear (digging of lairs, input of excrements, and carcasses). Only rare carnivore coprolites (lynx) were preserved in the cave deposits. © 2004 Wiley Periodicals, Inc.     

Rockshelter sedimentation in a dynamic tropical landscape: Late Pleistocene–Early Holocene archaeological deposits in Kitulgala Beli‐lena,southwestern Sri Lanka

Kitulgala Beli‐lena, a rockshelter in gneiss in humid tropical southwestern Sri Lanka, was inhabited by Late Pleistocene–Early Holocene (>31,000–7880 B.P.) hunter‐gatherers who made geometric microliths and exploited rainforest resources. Micromorphological analysis of a ca. 3‐m‐thick succession of diamictic loams, clays, and breccia with cultural content suggests that relative contribution of episodic colluviation and roof fall, water seepage through joints and diverse human activity varied through time. Facies changes across the profile reflect monsoon weakening ca. 20,000–16,000 cal B.P. and abrupt intensification ca. 15,700 cal B.P., on the wane of the global Last Glacial Maximum (LGM). Post‐depositional modification included clay, sesquioxide, and minor phosphate translocation; termite and other arthropod bioturbation; and clast weathering on the rockshelter floor. Human input (tools and tool‐making refuse, reworked charcoal and associated combustion by‐products) is markedly higher in sediments younger than ca. 15,700 cal B.P., suggesting intensification of site use immediately after the LGM. © 2009 Wiley Periodicals, Inc.     

The structure of the Miocene sediments in the Southeastern Escarp of the Fiolent Cape in Southwest Crimea

Structural and morphological analysis of the Miocene sediments that build up the Mekenzievi rock sequence at the Fiolent Cape made it possible to define the major characteristics of its inner structure. The largely homogeneous carbonate sediments are composed of clinoform complexes and bodies that fill in erosion paleochannels. The Mekenzievi rock sequence was formed under tectonic activity in the basin with intensive hydrodynamics. Most of the Mekenzievi rock sequence is dated as Early Chokrakian.     

Rock fall hazard along the railway corridor to Jerusalem,Israel, in the Soreq and Refaim valleys

We evaluate rock fall hazard along the railway corridor to Jerusalem, Israel, in the Soreq and Refaim valleys. For the purpose, we use a combination of historical information on past rock fall events, field surveys aided by the interpretation of aerial photographs, and numerical rock fall modeling. Historical information indicates that on July 11, 1927 an m _L 6.2 Dead-Sea transform earthquake caused rock falls in the studied area. The seismically induced rock falls damaged the railway tracks. Field observations revealed that the source area for the 1927 failures was located in the Aminadav formation, at the contact with the Moza formation. At the stratigraphic contact, rock blocks 10⁰–10¹ m³ in size are formed as a result of tensile stresses and associated fracturing in the dolomite of the Aminadav formation, combined with continuous creep of the blocks on the marl of the underlying Moza formation. We use topographical, geological, and geomorphological information to calibrate a three-dimensional numerical simulation of rock falls in the studied area. We use the results of the numerical modeling, and additional independent information, to assess rock fall hazard and the associated risk in the Soreq and Refaim valleys. Results indicate that in the studied area, rock fall risk to the railway line to Jerusalem is due primarily to Dead-Sea transform earthquakes, with m _L  > 6. We identify nine sections of the railway line where rock fall risk exists, for a total length of 2.5 km. We further note that seismically induced rock falls can produce damage to the road network in the studied area, make it difficult or impossible for earthquake casualties to reach hospitals in Jerusalem. We conclude offering recommendations on how to mitigate the risk posed by earthquake-induced rock falls in the studied area.     

Using Soil Magnetic Properties to Determine the Onset of Pleistocene Human Settlement at Gledswood Shelter 1, Northern Australia

In regions that lack built structures or stratified open archaeological sites, such as precolonial Australia, rockshelters are a major source of detailed information for understanding the nature and timing of human occupation. A key concern is that the proposed ages for the earliest archaeological sites are based on luminescence dating of sediments, rather than directly of cultural materials, leaving the association between the sediments and evidence of human activity questionable. Here, we present evidence of magnetic enhancement associated with cultural horizons within the deposits of a Pleistocene rockshelter in interior northern Queensland. Soil magnetic studies combined with experimental burning show that magnetically enhanced sediments in Gledswood Shelter 1 are the result of anthropogenic burning of hearth fires, which burn hotter and for a longer time than natural wild fires. These techniques appear to work in this setting because of the nature of the local geology and the geological antiquity of the landscape. Susceptibility and frequency dependence of susceptibility signatures provide a critical tool to resolve that human occupation starts at 2.2 m depth within a stratigraphic section. In conjunction with luminescence dating, soil magnetic studies provide an opportunity for archaeologists to resolve the timing of human settlement in Australia and other intracratonic plate settings.     

Abiotic and Biotic Links Work Two Ways: Effects on the Deposit at the Cliff Foot Induced by Mechanical Action of Date Mussel Harvesting (<Emphasis Type="Italic">Lithophaga lithophaga</Emphasis>)

The existence of linkages between ecological and geomorphological processes and the influence of human activities both on the biota and on geomorphology is well known for terrestrial environments, while it has been seldom reported for submerged ones. A survey in the Noli-Bergeggi area (NW Mediterranean Sea) has been carried out to test the hypothesis that the harvesting of Lithophaga lithophaga has an impact not only on the hammered rock, but also on the sediments at the cliff foot. Size and roundness of pebbles have been measured at different stations and statistical analyses have been used to test the differences between impact and control situations. Results show a dependence of the roundness of pebbles on the date mussel harvesting, indicating a decrease both of the roundness index and of its variability at the cliff foot in impacted sites. Conclusions stress the biogeomorphological nature of this activity, not limited to the present location.     

Fragmentation during Rock Falls: Two Italian Case Studies of Hard and Soft Rocks

In recent years, rock fall phenomena in Italy have received considerable attention for risk mitigation through in situ observations and experimental data. This paper reports the study conducted at Camaldoli Hill, in the urban area of Naples, and at Monte Pellegrino, Palermo, Italy. The rocks involved are volcanic Neapolitan yellow tuff (NYT) in the former area and dolomitic limestone in the latter. Both rocks, even though with different strength characteristics, have shown a significant tendency towards rock fragmentation during run out. This behavior was first investigated by comparing the volumes of removable blocks on the cliff faces (V ₀) and fallen blocks on the slopes (V _f). It was assumed that the ratio V _f/V ₀ decreases with the distance (x _f) from the detachment area by an empirical law, which depends on a coefficient α, correlated with the geotechnical properties of the materials involved in the rock fall. Finally, this law was validated by observation of well-documented natural rock falls (Palermo) and by in situ full-scale tests (Naples). From the engineering perspective, consideration of fragmentation processes in rock fall modeling provides a means for designing low-cost mitigation measures.     

Genesis of siderite nodules from the lower carboniferous terrigenous sequence in the Subpolar Urals

The paper presents the lithological, mineralogical, and geochemical characteristics of the composition, structure, and organic matter of siderite nodules and host mudstones in the Lower Carboniferous (Tournaisian–Visean) siderite-bearing sequence exposed along the Kozhym River on the western slope of the Subpolar Urals. The obtained results revealed that organic matter in the mudstones is dominated by C₁₆ and C₁₈ n-alkanes, suggesting a significant microbial activity in the sedimentation environment. The formation of nodules was promoted by the activity of diverse bacterial communities, the abundance of which was related to processes of methanogenesis in bottom sediments owing to gaseous fluid seepages that promote the saturation of sediments with methane and the flourishment of bacterial colonies. Such processes in a marine basin led to the local freshening or some salinization of water and the development of euxinic setting and specific bacteria. Consequently, siderite nodules therein are marked by bacteriomorphic textures and specific authigenic mineralization (framboidal pyrite, sphalerite, galena, sulfoselenides, and tellurides). Bacteria utilized the substrate of the redeposited weathered crust, resulting in a large-scale formation of the nodular siderite.     

Vein arrays, hydraulic fractures and pressure-solution structures in a deformed flysch sequence S.W. England

Vein arrays and pressure-solution cleavages are common in the sandstone units of the deformed flysch. Both structures were established prior to the folding of the sediments, and they continued to evolve during this folding. Tensile fractures and conjugate sets of shear fractures (of wrench fault type) were formed. En-echelon arrays of veins are closely associated with the formation of these principal veins. The geometry and relations of the veins are described in detail and their relation to the principal stresses at the time of formation is discussed.

Forking at vein terminations, branch fractures and offset structures in veins are described. The analogies between these and structures produced in rock deformation experiments and found in magmatic dykes are discussed. The branch fracture provides a record of the orientation of the maximum principal stress at the time of its formation.

The veins are infilled with quartz and siderite displaying drusy growth fabrics, indicating that crystal growth occurred into a fluid-filled cavity. It is suggested that the veins originated as hydraulic fractures in a flysch sequence that had developed high pore-fluid pressures during sedimentation. The material in the veins was derived by pressure-solution activity in the sandstone units, which produced a spaced pressure-solution cleavage throughout the region. The relations between veins and pressure-solution cleavages are described. Both small- and large-scale solution transfer of material was involved.     

Late Quaternary environmental and human events at En Gedi, reflected by the geology and archaeology of the Moringa Cave (Dead Sea area, Israel)

The Moringa Cave within Pleistocene sediments in the En Gedi area of the Dead Sea Fault Escarpment contains a sequence of various Pleistocene lacustrine deposits associated with higher-than-today lake levels at the Dead Sea basin. In addition it contains Chalcolithic remains and 5th century BC burials attributed to the Persian period, cemented and covered by Late Holocene travertine flowstone. These deposits represent a chain of Late Pleistocene and Holocene interconnected environmental and human events, echoing broader scale regional and global climate events. A major shift between depositional environments is associated with the rapid fall of Lake Lisan level during the latest Pleistocene. This exposed the sediments, providing for cave formation processes sometime between the latest Pleistocene (ca. 15 ka) and the Middle Holocene (ca. 4500 BC), eventually leading to human use of the cave. The Chalcolithic use of the cave can be related to a relatively moist desert environment, probably related to a shift in the location of the northern boundary of the Saharo-Arabian desert belt. The travertine layer was U-Th dated 2.46 ± 0.10 to 2.10 ± 0.04 ka, in agreement with the archaeological finds from the Persian period. Together with the inner consistency of the dating results, this strongly supports the reliability of the radiometric ages. The 2.46-2.10 ka travertine deposition within the presently dry cave suggests a higher recharge of the Judean Desert aquifer, correlative to a rising Dead Sea towards the end of the 1st millennium BC. This suggests a relatively moist local and regional climate facilitating human habitation of the desert.     

Origin and diagenesis of lacustrine algal bioherms at the margin of the Ries crater, Upper Miocene, southern Germany

The marginal carbonate facies of the Miocene Ries meteorite crater lake in southern Germany contain bioherms up to 7 m high and 15 m across built by the green alga Cladophorites. The algae were externally encrusted during life by micrite, probably precipitated in response to photosynthetic uptake of CO₂, which produced tufts of fine (100 μm diameter), calcareous tubes. Coalescence of tufts, together with incorporation of peloidal and skeletal sand, created nodules and cones of algal tufa which in turn formed larger masses some of which are in the form of compound cones up to 2 m high. The bioherms are constructed by beds and groups of these cones and masses, and are surrounded by poorly cemented peloid, ostracod and gastropod sands. Five depositional and diagenetic stages of development can be distinguished: (1) growth and calcification (probably calcitic) of Cladophorites in shallow fresh- or slightly brackish water; (2) emergence due to a temporary fall in lake level and veneering of the algal tufa and adjacent sediments by laminated sinter; (3) resubmergence and deposition of peloidal and skeletal sands; (4) burial and partial phreatic dolomitization, together with dissolution of aragonite and penecontemporaneous deposition of thin isopachous rims of dolomite rhombs; (5) local vadose cementation by rhombs, spar and spikes of low-magnesian calcite. Stages 1–3 probably occurred several times. Most of the biohermal and surrounding sediments were produced by biological processes in the lake; subaerial sinter deposition and meteoric cementation have contributed relatively minor amounts of material and the majority of the sediments retain porosities of 10–30%.     

南秦岭古生代热水沉积盆地与热水沉积成矿

扬子地块北部被动边缘的南秦岭古生代沉积盆地中,发育一套自早古生代—中生代以来的碳酸盐岩夹细碎屑岩沉积建造,形成规模巨大独具特色的以铅锌金为主的多金属成矿带。伸展构造体制下形成的裂陷或断陷型盆地中,正常水成沉积与热水沉积同盆共存。正常水成沉积中叠加的热水沉积是一个"突发事件或灾变事件",具有特殊的物质组成和产态。通过对区内沉积成矿盆地的识别、分级,二级沉积盆地中边缘部位常发育多个三级构造热水沉积成矿盆地,它受控于沉积盆地中的同生断裂,具有沉积岩相、热水沉积岩组合、显著成矿作用及物化探异常广布的特点。三级构造热水沉积成矿盆地是矿床定位的构造空间,四级热水沉积洼地为矿体(矿层)的容纳空间。区内热水沉积岩主要为重晶石(毒重石)岩、硅质岩、钠长石岩和铁碳酸盐岩类,铅锌重晶石等矿产多产于热水沉积岩中或上盘。热水沉积形成一般由早期的热水喷发交代→主期热水喷流→晚期热水喷气演变。早期的热水喷发交代往往沿矿液喷发通道,形成网脉状、角砾状矿化;主期热水喷流主要形成多金属及热水喷流相,形成块状、条带状、层纹状矿石或热水沉积岩;晚期热水喷气主要形成浸染状矿石和热水喷气岩石。     

潮水盆地侏罗系沉积特征及找煤潜力

潮水盆地侏罗系为完整的断陷湖泊充填沉积序列,沉积环境属多种沉积体系,具有低位体系域—湖侵体系域—高位体系域的多层序旋回的特点。下侏罗统为断陷初始形成期的湖泊沉积,具有断陷盆地形成初期“填平补齐”的沉积特点。地层厚度变化大,沉积相变快。在层序中可识别出低位体系域与湖侵早期体系域。低位体系域主要发育了冲积扇、辫状河道、滨浅湖砂砾、洪积物等;中侏罗统为裂陷发展期湖泊沉积,为盆地内主要含煤岩组。层序中粒度旋回较发育,通常在每一旋回的上部含煤层或炭质泥岩,层序底部常发育砾岩。在该层序中可识别出局部低位体系域与高位体系域。低位体系域发育河流砂砾沉积和滨浅湖砂砾,常表现出垂向加积或退积序列。而湖侵体系域则以较深水的湖相沉积为特征,常表现出向上泥岩厚度加大的退积式准层序组;同时,亦发育诸多三角洲相沉积;上侏罗统为断陷消亡期沉积,形成低位体系域浅湖、扇三角洲和冲积扇沉积体系。潮水盆地下侏罗统芨芨沟群上岩组和中侏罗统青土井群下岩组均具有成煤的构造、成煤的环境和成煤的物质来源,而找煤的关键是寻找目前技术、经济水平可以达到的赋煤构造。     

河北西北部熔积岩特征及其他质意义

熔积岩是火山碎屑岩的一种特殊类型,由熔浆和未固结的湿沉积物两种组分掺杂混合而成.熔积岩的形成主要受炽热熔浆与未固结的湿沉积物接触时引起的淬碎或蒸汽爆炸作用以及寄主沉积物流体化作用控制,通常分布于熔岩流底部或前缘,也可分布于超浅成侵入体周围.据熔浆碎屑物的结构特征,冀西北熔积岩可分为流状和块状两种类型.流状熔积岩多是熔浆与细粒沉积物混合的结果,块状熔积岩大多与粗粒沉积物相关.正确鉴别熔积岩对确定沉积作用与岩浆作用的时序、研究盆地发展演化历史具有重要意义.     

Impacts of explosive volcanism on distal alluvial sedimentation: Examples from the Pliocene–Holocene volcaniclastic successions of Japan

Volcanic activities can create cataclysmic hazards to surrounding environments and human life not only during the eruption but also by hydrologic remobilisation (lahar) processes after the cessation of eruptive activity. Although there are many studies dealing with the assessment and mitigation of volcanic hazards, these are mostly concentrated on primary eruptive processes in areas proximal to active volcanoes. However, the influence of volcaniclastic resedimentation may surpass the impacts of primary eruptive activity in terms of both extent and persistence, and can ultimately result in severe hazards in downstream areas.Examination of the volcaniclastic successions of non-marine Pliocene–Holocene sedimentary basins in Japan has revealed hydrological volcaniclastic sedimentation in fluvial and lacustrine environments hundreds of kilometres from the inferred source volcano. Impacts on these distal and often spatially separated basins included drastic changes in depositional systems caused by sudden massive influxes of remobilised pyroclastic material. Typical volcaniclastic beds comprise centimetre- to decimetre-thick primary pyroclastic fall deposits overlain by metre- to 10s of metres-thick resedimented volcaniclastic deposits, intercalated in sedimentary successions of non-volcanic provenance. The relatively low component of primary pyroclastic fall deposits in the volcaniclastic beds suggests that: 1) potential volcanic hazards would be underestimated on the basis of primary pyroclastic fall events alone; and 2) the majority of resedimented material was likely derived from erosion of non-welded pyroclastic flow deposits in catchment areas rather than remobilisation of local fallout deposits from surrounding hillslopes.The nature, distribution and sequence of facies developed by distal volcaniclastic sediments reflect the influence of: 1) proximity to ignimbrite, but not directly with the distance to the eruptive centre; 2) ignimbrite nature (non-welded or welded) and volume; 3) temporal changes in sediment flux from the source area; 4) the physiography and drainage patterns of the source area and the receiving basin, and any intervening areas; and 5) the formation of ephemeral dam-lakes and intra-caldera lakes whose potential catastrophic failure can impact distal areas. Models of the styles and timing of distal volcaniclastic resedimentation are thus more complicated than those developed for proximal settings of stratovolcanoes and their volcaniclastic aprons and hence present different challenges for hazard assessment and mitigation.     

安徽枞县拨茅山-牛头山铜矿床地质特征及找矿方向

拨茅山—牛头山铜矿床的的赋矿岩石为中生代的火成岩系。侵入岩一潜火山岩一火山岩构成完整的侵入—喷发系列。该矿床可分为火山气液—沉积铜矿床和斑岩型铜矿床两种类型。在成矿前期，陆相火山岩在湖底发生火山喷气、火山热泉以及火山热水沉积。潜火山岩的侵入，伴有长期热液循环活动，在张性断裂为主的赋矿空间生成与斑岩有关的各类型矿床。     

On the history of the Late Devensian Lake Sparks in southern Fenland,Cambridgeshire, England

A section in a gravel quarry at Somersham, Cambridgeshire, has revealed evidence for a lake, named Lake Sparks, in Fenland during the Late Devensian substage of the Pleistocene. Varved sediments were deposited in this lake over a minimum period of ca. 65 yr. The varved clays contain red diamicton clasts, interpreted as dump, delivered to the area by icebergs or floes from the ice-front in the Wash that deposited the Hunstanton Till. The lake is therefore considered a result of impounding by the Late Devensian ice advance on the east coast. A small number of pale varves have a characteristic structure indicating increased calcite deposition in the summer. They are interpreted as a result of cooler summers with reduced gelifluction from the surrounding Jurassic (Ampthill) Clay. Such gelifluction introduced a mudflow into the varved sequence at the southern end of the section. Pollen analysis confirms the derivation of the clays from the surrounding Ampthill Clay. The varved clays are succeeded by fluviatile sediments related to a delta building into the lake from the north. The delta sediments show periodic influx of sand into the lake interrupted by quiet periods with the development of Chara meadows. A thin spread of fluviatile gravels succeed the delta sediments, indicating the development of a braided river plain as the lake drained on the melting of the Late Devensian ice. This was followed by permafrost development, with the formation of thin thermal contraction cracks and coversand deposition. Later, degradation of the permafrost was associated with the formation of diapirs and a solifluction mantle, and incision of the fluviatile and lacustrine sediments took place. Flandrian peat and marl later filled the valley so formed. A radiocarbon date of 18310 yr BP from Salix leaves in a drift mud at the top of channel sands preceding lake sediment, in a neighbouring section, confirms the relation of the lake to the Late Devensian ice advance. The significance of the Late Devensian sediments at Somersham lies in the information they give on the timing and variety of processes related to drainage and ice movement in the period before, during and after the ice advance to the Wash. A period of low deposition rate in the lake was followed by rapid delta sedimentation and lake drainage, with implications for climatic change.