Microbial primary dolomite from a Norian carbonate platform: northern Calabria, southern Italy

The origin of fine‐grained dolomite in peritidal rocks has been the subject of much debate recently and evidence is presented here for a microbial origin of this dolomite type in the Norian Dolomia Principale of northern Calabria (southern Italy). Microbial carbonates there consist of stromatolites, thrombolites, and aphanitic dolomites. High‐relief thrombolites and stromatolites characterize sub‐tidal facies, and low‐relief and planar stromatolites, with local oncoids, typify the inter‐supratidal facies. Skeletal remains are very rare in the latter, whereas a relatively rich biota of skeletal cyanophycea, red algae and foraminifera is present in the sub‐tidal facies. Some 75% of the succession consists of fabric‐preserving dolomite, especially within the microbial facies, whereas the rest is composed of coarse dolomite with little fabric preservation. Three end‐members of dolomite replacement fabric are distinguished: type 1 and type 2, fabric retentive, with crystal size <5 and 5–60 μm, respectively; and type 3, fabric destructive, with larger crystals, from 60 to several hundred microns. In addition, there are dolomite cements, precipitated in the central parts of primary cavities during later diagenesis. Microbialite textures in stromatolites are generally composed of thin, dark micritic laminae of type 1 dolomite, alternating with thicker lighter‐coloured laminae of the coarser type 2 dolomite. Thrombolites are composed of dark, micritic clotted fabrics with peloids, composed of type 1 dolomite, surrounded by coarser type 2 dolomite. Marine fibrous cement crusts are also present, now composed of type 2 dolomite. Scanning electron microscope observations of the organic‐rich micritic laminae and clots of the inter‐supratidal microbialites reveal the presence of spherical structures which are interpreted as mineralized bacterial remains. These probably derived from the fossilization of micron‐sized coccoid bacteria and spheroidal–ovoidal nanometre‐scale dwarf‐type bacterial forms. Furthermore, there are traces of degraded organic matter, probably also of bacterial origin. The microbial dolomites were precipitated in a hypersaline environment, most likely through evaporative dolomitization, as suggested by the excess Ca in the dolomites, the small crystal size, and the positive δ¹⁸O values. The occurrence of fossilized bacteria and organic matter in the fabric‐preserving dolomite of the microbialites could indicate an involvement of bacteria and organic matter degradation in the precipitation of syn‐sedimentary dolomite.     

自然电场法勘探火山岩地区地下水的研究

多个火山岩地区找水的勘探实例表明,地表观测到的自然电位异常（简称SP）与地下非饱和区厚度相关。本文认为这种自然电位异常是由于雨水垂直向下流经非饱和区（渗流区）到达地下不透水界面引起,并提出产生自然电位异常的地下极化模型,进而根据静电场理论建立了水文地质模型与自电异常之间的理论关系。这一理论能够实现把一种波数域反演技术引进自然电位异常的反演,以便计算地下水的位置和深度。模型算例和勘探实例表明这一方法可以用于勘探火山岩地区地下水。     

夜天光近紅外区光譜的光电研究

作者叙述了一种旋轉光柵的单色器,用以观測夜天光近紅外区的光譜（0.7至1.1μ）。我们所用的光电接收器是一种拉耳茫（Lallemand）的Cs-Ag-O式、19級放大的光电倍加管。記录的时間是10或45分鐘。在描迹記录上,我們观測到OH的振动-轉动光带,它們的位置一般是和由理論所推得的波长相重合的,此外还有强度很有变化的大气里的氧的光带（0-1）。因为仪器的分辨率相当高,可以部分地观測到OH光带的結构。这些光带的相对强度,經我們加以測量。