Zircon U–Pb ages of granitic and mafic dikes associated with granitoids and metamorphic rocks of the Ryoke Belt in the eastern Kii Peninsula,southwest Japan

Zircon U–Pb dates for felsic and intermediate to mafic dikes intruding into the Ryoke granitoids and metamorphic rocks at selected outcrops in the Takamiyama area of the eastern Kii Peninsula, southwest Japan, were determined along with their geology and petrography to reveal the history of Cretaceous magmatism. At each outcrop, the felsic and intermediate to mafic dikes exhibit specific structures that are indicative of magma intermingling and have coeval intrusion ages of ca. 81–77 Ma. Our zircon U–Pb data complement previously published data, suggesting that the mafic magmatism continued intermittently from 83 to 76 Ma in the Takamiyama area and that magmatism migrated eastward within the Ryoke Belt. A comparison of intrusion ages between a dike and a host Ryoke granitoid at one outcrop indicates that the host rock experienced ductile deformation at ~88 to ~83 Ma. Judging from the small number of zircons and the concordant date distributions, we didn't recognize the evidence suggesting the partial melting of the host rocks, as Nakajima et al. (Journal of the Geological Society of Japan, 2021, 127, 69–78) reported.     

Reworked marine pythonomorph (Reptilia,Squamata) remains in Late Pleistocene cave deposits in central Spain

Three sites at the Calvero de la Higuera complex (Camino Cave, Navalmaíllo Rock Shelter, and Buena Pinta Cave), near the village of Pinilla del Valle (Madrid, Spain), are known for their record of Neanderthals and other Late Pleistocene mammals. Occasionally, they also yield much more ancient reworked remains, which come from the Upper Cretaceous dolomites and carbonatic sandstones in which these caves and shelters are developed. These are mostly teeth of sharks and rays and vertebrae and teeth of bony fishes, but several reptile vertebrae and teeth have also been found. These reptile remains, which we describe here, likely belong to the pythonomorph incertae sedis Carentonosaurus cf. mineaui. This taxon is known from several outcrops in the southwest of France but is rare on the Iberian Peninsula; indeed, only a few remains possibly related to the genus have been found (in the Cabaña Formation, Asturias, Spain). The pythonomorph remains discussed here are the first fossils of marine reptiles from the Madrid region. Should the assignment to Carentonosaurus be confirmed, the teeth would provide novel data on the characteristics of this rather poorly known taxon, and might help clarify its phylogenetic relationship within Pythonomorpha.     

Record of Late Pleistocene Glaciation and Deglaciation in the Southern Cascade Range. I. Petrological Evidence from Lacustrine Sediment in Upper Klamath Lake, Southern Oregon

Petrological and textural properties of lacustrine sediments from Upper Klamath Lake, Oregon, reflect changing input volumes of glacial flour and thus reveal a detailed glacial history for the southern Cascade Range between about 37 and 15 ka. Magnetic properties vary as a result of mixing different amounts of the highly magnetic, glacially generated detritus with less magnetic, more weathered detritus derived from unglaciated parts of the large catchment. Evidence that the magnetic properties record glacial flour input is based mainly on the strong correlation between bulk sediment particle size and parameters that measure the magnetite content and magnetic mineral freshness. High magnetization corresponds to relatively fine particle size and lower magnetization to coarser particle size. This relation is not found in the Buck Lake core in a nearby, unglaciated catchment. Angular silt-sized volcanic rock fragments containing unaltered magnetite dominate the magnetic fraction in the late Pleistocene sediments but are absent in younger, low magnetization sediments. The finer grained, highly magnetic sediments contain high proportions of planktic diatoms indicative of cold, oligotrophic limnic conditions. Sediment with lower magnetite content contains populations of diatoms indicative of warmer, eutrophic limnic conditions. During the latter part of oxygen isotope stage 3 (about 37–25 ka), the magnetic properties record millennial-scale variations in glacial-flour content. The input of glacial flour was uniformly high during the Last Glacial Maximum, between about 21 and 16 ka. At about 16 ka, magnetite input, both absolute and relative to hematite, decreased abruptly, reflecting a rapid decline in glacially derived detritus. The decrease in magnetite transport into the lake preceded declines in pollen from both grass and sagebrush. A more gradual decrease in heavy mineral content over this interval records sediment starvation with the growth of marshes at the margins of the lake and dilution of detrital material by biogenic silica and other organic matter.     

广西西湾煤系首次发现牙形刺及其地层意义

西湾煤系是广西重要含煤层位之一,以碳酸盐岩夹煤层为特征,自下而上分天堂组和大岭组,主要煤层赋存于大岭组中。煤系时代有晚三叠世与早侏罗世之争。1988年笔者之一冯少南,曾报道了天堂组产植物化石Danaeopsis fecunda Halle,为煤系时代归属提供了重要古生物依据。今年笔者在大岭组的灰岩中分析出牙形刺,认为大岭组的时代应属晚三叠世,并进一步说明大岭组为潮坪泻湖→滨海沼泽相沉积。     

Indosinian Tectonic Transition in Yunkai Massif: Petrological and Geochemical Constraints from Two-mica Granite in Yangchun Area,South China

The tectonic background of the Indosinian granites in South China Block remains highly debated. The Yunkai massif, connecting the Paleo-Tethys and Paleo-Pacific tectonic domains, is a key site for studying the tectonic background of the Indosinian granitoids in South China. In this paper, we select a two-mica granitic pluton from the Yangchun area of the Yunkai Massif to conduct comprehensive researches including petrology, geochronology, and geochemistry. Zircon U-Pb dating yield two concordant 206Pb/238U ages of 426.4±1.7 Ma (MSWD=2.4, n=8) and 239.1±1.7 Ma (MSWD=1.2, n=4), respectively. A further monazite U-Pb dating gives only one concordant 206Pb/238U age at 239.0±0.3 Ma (MSWD=1.2, n=31), consistent with the younger zircon U-Pb age. We therefore conclude that the Yangchun two-mica granite was formed during Triassic (ca. 239 Ma). The granite rocks belong to S-type granite with a peraluminous affinity. They also show enrichment in large ion lithophile elements and depletion in high field strength elements and relatively flat chondrite-normalized rare earth element patterns with negative Eu anomalies, and have low zircon saturation temperature of 725–747 ℃ as well. The bulk-rock and monazite Nd and zircon Hf isotope analyses yield whole-rock εNd(t) values from –10.8 to –9.4, monazite εNd(t) values from –10.9 to –8.4, and zircon εHf(t) values from –13.2 to –7.8, with depleted model age ranges of 1.8–1.9 Ga for whole rock tDM2(Nd), 1.7–1.9 Ga for monazite tDM2(Nd) and 1.8–2.1 Ga for zircon tDM2(Hf). The consistent Nd and Hf isotope data among the bulk rock, monazite and zircon in the Yangchun two mica granite indicate that the granite was derived from ancient recycled crustal components. The parent magma experienced a dominated fractionation of plagioclase and monazite which resulted in the negative Sr and Eu anomalies and low LREE concentrations. Considering the regional geological background, we propose that the two-mica granite in the Yangchun area formed during the tectonic transition between the oceanic slab subduction and orogenic collapse: The late Permian shallow-marine sedimentary sequences and I-type granitic magmatism indicate the subduction of Paleo- Tethys Ocean; the early-middle Triassic crustal shortening and thickening triggered the crustal anatexis to form the S-type granitic magmas such as the Yangchun two-mica granitic pluton; the late Triassic terrestrial red deposits and the occurrence of A2-type granite suggest a stage of orogenic collapse and the resultant lithospheric extension. © 2023 Science Press. All rights reserved.     

新疆西昆仑盼水河地区晚三叠世花岗闪长斑岩LA-ICP-MS锆石U-Pb年龄和岩石地球化学特征

为进一步丰富西昆仑地区黑石北湖-三道河子一带侵入岩数据,为盼水河锑矿的形成时代提供年代学制约,对盼水河花岗闪长斑岩进行了地质学、岩石学、地球化学及年代学研究。LA-ICP-MS锆石U-Pb测年结果显示,盼水河花岗闪长斑岩年龄为210.9±2.8 Ma,形成于晚三叠世。岩石地球化学特征显示,盼水河花岗闪长斑岩SiO2含量为66.1%~72.03%,全碱（Na2O+K2O）含量为5.95%~8.29%,平均值为7.10%,K2O>Na2O,岩石富钾,显示为高钾（钙碱性）岩;岩石稀土元素总量较低,且强富集轻稀土元素,Eu具弱负异常（δEu=0.66~0.90）,相对富集Rb、Th、Ta、Ce、Hf,贫化Ba、K、P、Ti。构造环境判别图解显示,盼水河花岗闪长斑岩形成于同碰撞的构造环境,揭示区内松潘-甘孜陆块西北缘在华力西晚期-印支期发生了同碰撞造山作用,区内黑石北湖-三道河子岩浆岩带正是该造山作用及洋陆转换的产物。     

柴达木盆地碱山深钻的硼同位素地球化学特征

沉积物硼(B)同位素组成可以反映其地质成因及经历的地质过程,因此在许多领域的研究中都有较为广泛的应用。通过对位于柴达木盆地碱山背斜顶部的SG-1b钻孔沉积物(7.3～1.6 Ma)水溶组分的B同位素研究,发现钻孔沉积物B含量在38.55～172.3μg/g之间,平均含量为87.6μg/g;δ~(11)B值的变化范围在3.61‰～16.26‰之间,平均值为10.65‰,B含量与δ~(11)B值具有一定的正相关关系。进一步分析表明,受到碱山背斜构造隆升以及晚新生代以来气候干旱化的影响,柴西古湖逐渐咸化萎缩,沉积环境以及碳酸盐含量、粘土矿物含量及其矿物组合等也在发生变化,B含量和δ~(11)B值自钻孔底部向上的逐步增加以及后期的急剧增加,与水溶离子含量以及矿物和粒度等的变化一致,这说明柴达木盆地晚中新世以来湖泊沉积物的B含量和δ~(11)B值可以很好地反映研究区气候和湖水的演化过程,共同指示了研究区自7.3 Ma以来气候的持续干旱化和湖水盐度的逐步增加,以及3.3Ma以来干旱化和湖水浓缩过程的加剧。     

张家口-蓬莱断裂带渤海段晚第四纪活动特征

张家口-蓬莱断裂带是华北地区一条显著的地震带.利用最新获得的高分辨率浅层地震资料研究了渤海海域内该断裂带晚第四纪以来的活动特征.研究表明:在渤海,张家口-蓬莱断裂带主要由沙西断裂、埕北断裂、沙南断裂、沙东北断裂、柏各庄断裂、石臼坨3号断裂、渤中2号断裂和BZ29断裂等一系列NW走向断裂组成,走向在290°～310°之间;在浅层沉积物中各断裂由多条次级小断裂组成;晚第四纪以来主要表现出强烈的垂向运动特征,具有正断性质;海域各断裂的最新活动时代为晚更新世(Q3)末期-全新世(Q4)初期,并具有相同的活动趋势,在20 ka B.P.和60 ka B.P.左右活动强烈,统计计算显示平均垂向活动速率分别为0.15 mm/a和0.1 mm/a,近20 000 a以来的垂向活动速率超过0.06 mm/a.     

Regional variations in cleavage and fold development in North Wales

The arcuate pattern of the main Caledonian cleavage and associated fold axial plane traces in North Wales is due partly to NW-SE compression with tectonic transport to the southeast against the concealed crop of the Tan y grisiau Microgranite. Low-angle cleavage close to the microgranite is shown to be a local variant of the regional cleavage formed during the main deformation and not an earlier phase as previously supposed. Transcurrent movements along several major fault systems are also related to compression around the microgranite and the Harlech Dome block.     

A highstand oolitic sequence and associated facies from a Late Triassic lake basin, south-west England

High energy, lake‐shoreline carbonate sequences are rarely documented in the geological record. However, one example occurs in the Upper Triassic Mercia Mudstone Group (MMG) of southern Britain. The MMG is one of a number of thick, non‐fossiliferous mudstone deposits associated with North Atlantic Mesozoic rift basins. The origin of the MMG mudstones is the subject of current debate, with marine, playa‐lacustrine and alluvial–aeolian models having been proposed. Shoreline features have been documented from the northern margin of the basin, but the rarity of such features elsewhere in the MMG has led many workers to doubt a lacustrine origin for the mudstones. Wave‐dominated, lake‐shoreline deposits have been recognized in several sections from the southern basin margin in the Clevedon area of the Bristol Channel in south‐west England. These deposits provide evidence for the development of a sizeable perennial to semi‐perennial hypersaline lake in which the MMG mudstones accumulated. Shoreline sediments overlie alluvial stream and sheet‐flood deposits, and pass from transgressive gravel–conglomerate beach units with bioclasts, influenced by shore‐normal waves (deposited under semi‐humid conditions), to lower gradient, highstand oolitic sands affected by more varied wave approach (deposited under progressively more arid conditions), which culminated in lowstand, oolitic strand‐plain deposits overlain by a playa‐mudflat unit. Shoreline deposits record a simple shallowing‐upward transgressive–highstand–lowstand sequence. However, a change from a reflective (transgressive) to dissipative (highstand) shoreline is believed to represent a climatically induced change in prevailing wind direction. Shoreline features recognized in the MMG are similar to those of recent playa‐lacustrine basins of the western United States. Ooids display a variety of size, fracture and dissolution features in addition to beachrock fabrics, suggesting that they were originally composed of radial aragonite, similar to modern ooids from the Great Salt Lake, Utah.