Late Permian (Lopingian) foraminifers from the Doi Chiang Dao Limestone in the Inthanon Zone of Northern Thailand

Late Permian foraminifers were found from six localities belonging to the Doi Chiang Dao Limestone, which is considered as having a Paleo-Tethyan seamount-capping carbonates origin, distributed in the Inthanon Zone of Northern Thailand. Among them, three age-diagnostic assemblages are recognized. They are represented by the occurrences of Codonofusiella kwangsiana, Palaeofusulina cf. minima, and P. prisca, and are referable to the Wuchiapingian, early Changhsingian, and late Changhsingian, respectively. In particular, the discovery of an assemblage characterized by advanced Palaeofusulina (P. prisca) is significant because it clearly indicates that the deposition of the Doi Chiang Dao Limestone had continued until the very end of the Permian. These three Late Permian assemblages can be compared with those recently reported from the Shifodong Formation of Pa-leo-Tethyan mid-oceanic carbonates in the Changning-Menglian Belt of West Yunnan, Southwest China.     

Paradise (and Herrin) lost: Marginal depositional settings of the Herrin and Paradise coals, Western Kentucky coalfield

This is the fourth installment in a series of papers on the Asturian (Westphalian D) disrupted mire margins, termed the “ragged edge” in previous papers, and limestone distributions in the Herrin–Baker coal interval in the Western Kentucky extension of the Illinois Basin. New data, indicating in-situ peat development and marine influence, collected from the first in-mine exposure of this interval are presented. Borehole data from the region are examined in the context of “ragged edge” exposures and a carbonate platform depositional model for this portion of the Illinois Basin is presented. This shows that deposition of the sequence was influenced both by the underlying sediments and by a marine transgression. The former influence is seen in variations in coal and limestone thickness over sandstone-filled channels versus over shale bayfill deposits. The latter is marked by the progressive upwards loss of coal benches (i.e., the bottom bench of both coals is the most extensive and the Herrin coal is more extensive than the overlying Paradise coal) and by marine partings in both coals. Further, the brecciated margins seen in both coal seams are similar to brecciated peats encountered along the Everglades margins of Southwest Florida. Overall coal distributions are similar to both those along the Everglades margins and those along a transect from the Belize coast to Ambergis Caye.     

Limestone assimilation by basaltic magmas: an experimental re-assessment and application to Italian volcanoes

The results of an experimental study of limestone assimilation by hydrated basaltic magmas in the range 1,050–1,150°C, 0.1–500 MPa are reported. Alkali basalts doped with up to 19 wt% of Ca, Mg-carbonates were equilibrated in internally heated pressure vessels and the resulting phase relationships are described. The major effects of carbonate incorporation are: (1) generation of CO₂-rich fluid phases; (2) change in liquidus phase equilibria; the crystallization of Ca-rich clinopyroxene is favored and the other phases (e.g. olivine, plagioclase), present in the absence of carbonate assimilation, are consumed. As a consequence of the massive clinopyroxene crystallization, the residual melt is strongly silica-depleted and becomes nepheline-normative. Compositional and mineralogical evolutions observed in Mt. Vesuvius eruptive products match those documented in our experiments with added carbonates, suggesting the possibility that carbonate assimilation increased during the last 25 ka of activity. In Central-Southern Italy, carbonate assimilation at shallow levels probably superimposes on deeper source heterogeneities.     

A note on the characteristics and possible origins of desert varnishes from southeast Morocco

Two substrate-controlled varnish types were identified from arid southeast Morocco: (1) patchy varnish interspersed with ‘silica glaze’ on silicified limestone and (2) a complete varnish cover on partially-silicified limestone. Electron probe microanalysis was used in conjunction with scanning electron microscopy to investigate their chemical composition. In both instances, varnishes are predominantly silica and iron-rich with localized concentrations of manganese. Inorganic fixation of iron and manganese is the preferred explanation, with manganese and iron derived predominantly from external sources—possibly wind-blown dust. Some iron and silica may also be derived by outward migration from within the substrate, particularly on partially silicified limestone.     

澳大利亚十二门徒中新世地层成因研究

澳大利亚维多利亚州南部海岸坎贝尔港（Port Campbell）附近的十二门徒（The Twelve Apostles）地层主要为石灰质地层,偶见海相生物贝壳,一直被认为是浅海大陆架石灰岩（limestone）沉积。野外考察发现,该地层不仅存在海相生物碎片,同时也存在根化石、钙结核层等地表古土壤特征。为了更好地分析其沉积环境,本文对十二门徒剖面样品的粒度、石英颗粒表面形态以及稀土元素进行了系统分析,并将其结果与第四纪西峰黄土古土壤和现代海滩砂进行比较。结果表明,整个剖面序列以细粉砂为主,与典型风积黄土古土壤具有相似的粒度分布与粒度象特征,Sahu判别分析结果表明绝大部分样品值都小于-2.7411,显示了剖面整体以风积成因为主。样品的石英颗粒呈现出不规则的棱角状、次棱角状,显示风成特征;此外,十二门徒剖面样品具有与黄土古土壤以及上地壳（UCC）相似的稀土元素分配模式。因此,我们认为该地层并非海相石灰岩沉积,而是一套在半干旱气候条件下发育的具有多层钙结核的风积序列地层。该地层记录了澳洲东南海岸16.0~5.3Ma以来的风积历史与气候变化,表明澳大利亚的干旱化至少是在16Ma前就开始了。由于这套风积地层靠近海岸,易受地质时期海平面变化的影响,以致在地层中的局部层位出现海相生物碎屑,但地层的物质来源可能来源于澳大利亚的艾尔湖（Lake Eyre）盆地。

     

Surface sediment characteristics and tower karst dissolution, Guilin, southern China

Dissolution of extensive outcrops of limestone and dolostone in humid tropical and subtropical southern China produced numerous caves and residual hills that are referred as tower karst. This study identifies and relates the physical and chemical characteristics of the surface sediment with the limestone bedrock in Guilin to assess the influence of the limestone dissolution process on sediment composition.The results of this study indicated that (i) both limestone and dolostone of the region are very pure (99.5% and 98.5% of CaCO₃ and MgCO₃, respectively); (ii) the material composition of limestone and dolostone is different from that of soil and sediment of the region: constituents of surface sediments are highly related with the clastic sedimentary rocks, such as the mudstone, but show negative correlation with limestone and dolostone; (iii) the limestone formations are highly resistant to physical weathering and disintegration; their durability versus physical weathering and their high susceptibility to chemical dissolution account for why residual towers can form and persist; (iv) a dual-zone environmental structure exists vertically downward from the surface in Guilin: the zone of unconsolidated clastic sediments that is predominantly acidic, and the zone of karstified limestone that is predominantly basic. The evidence suggests that the environment and processes differ in these two zones. The chemical dissolution of limestone that formed tower karst of the region is not mainly responsible for the accumulation of clastic sediment on the surface.     

粤北稀土微肥资源及其开发应用

本文根据稀土微肥在各类农作物大面积喷施所取得高产优质效益的试验资料，分析了粤北丰富的花岗岩风化壳型稀土矿床易被开发利用的实际情况，认为粤北稀土微肥资源具有开发前景，特别是在土地生产潜力低下的石灰岩农业类型地区推广应用，具有使山区脱盆贫致富的现实意义，笔者建议组织有关部门，开创稀土微肥化学工业，为大农业的丰收做出了更大的贡献。     

广西永福某石灰岩矿山地质环境问题及恢复治理探讨

桂林是广西石灰岩矿的主要产地之一,开采石灰岩的矿山达250个。桂林地区石灰岩矿山的地质环境问题基本类似,发育的地质灾害主要有崩塌、滑坡、岩溶地面塌陷。该文以广西永福某石灰岩矿山为例,在收集矿山地质资料的基础上,通过详细的野外调查,发现该矿山地质环境问题主要为采场的高陡岩质边坡,基岩裸露,破坏和影响了地貌景观,容易引发岩质崩塌灾害;矿山功能区和废渣、表土的堆放占用和破坏了土地资源,可能引发小型的滑坡;灰岩石料加工等人类工程活动致使粉尘污染和噪音污染较为严重,对附近居民的生活环境造成了影响。针对矿山的地质环境问题划分了恢复治理分区,提出了相应的工程措施,恢复治理工程的实施可从根本上改变矿山采场的地貌景观,恢复破坏和压占的土地资源,消除地质灾害隐患,创造绿色矿山,为桂林地区石灰岩矿山的地质环境问题恢复治理提供参考。     

‘frost and salt’ weathering: Further experimental results

A laboratory experiment has been conducted to examine the effects of ‘frost and salt’ weathering (i.e. physical breakdown by the freezing of salt solutions) on a limestone. Results show that the presence of certain salts in solution can inhibit frost damage. These findings are in direct conflict with those presented by Goudie (1974) and, more recently, Williams and Robinson (1981). Comparison of the experimental methods used in each of these three studies suggests that opposing results can be explained in terms of the different experimental procedures which were employed. If salt supply is frequent and plentiful then it seems likely that rock breakdown will be enhanced-this is the case represented by the experiment of Williams and Robinson. Conversely if the salt supply is limited and the amounts of salt remain more or less constant then rock breakdown will be inhibited-the case of the present experimental study. Caution is therefore advocated when attempting to extrapolate laboratory-derived results to infer on the behaviour of rocks under natural conditions. Several environmental situations in which ‘frost and salt’ weathering may be a possibility are dsiscussed, but it is concluded that further field data, especially concerning temperature regimes and salt availability at and below rock surfaces in cold regions, would be necessary before more definite statements could be made about the efficacy of this process.     

Cosmogenic isotope (Cl) surface exposure dating of the Norber erratics, Yorkshire Dales: Further constraints on the timing of the LGM deglaciation in Britain

Cosmogenic isotope (³⁶Cl) surface exposure dating of four of the erratic boulders at Norber in the Yorkshire Dales National Park, northwest England, yielded mean ages of ∼22.2 ± 2.0 ka BP and ∼18.0 ± 1.6 ka BP for their emplacement. These two mean values derive from different ³⁶Cl production rates used for exposure age calculation. The ages are uncorrected for temporal variations in production rates and may underestimate the true ages by 5-7%. The former age, although implying early deglaciation for this area of the British ice sheet, is not incompatible with minimum deglaciation ages from other contexts and locations in northwest England. However, the latter age is more consistent with the same minimum deglaciation ages and geochronological evidence for ice-free conditions in parts of the northern sector of the Irish Sea. Within uncertainties, the younger of the mean ages from Norber may indicate that boulder emplacement was associated with North Atlantic Heinrich event 1. The limited spatial (downvalley) extent of the Norber boulders implies that at the time of their deposition the ice margin was coincident with the distal margin of the erratic train. Loss of ice cover at Norber was followed by persistent stadial conditions until the abrupt opening of the Lateglacial Interstadial when large carnivorous mammals colonised the area. The ³⁶Cl ages are between ∼3.0 ka and ∼13.0 ka older than previous estimates based on rates of limestone dissolution derived from the heights of pedestals beneath the erratics.