Immunological studies on microbial mats from Solar Lake (Sinai)— A contribution to the organic geochemistry of sediments

Immunological and biochemical techniques were used to investigate organic matter in microbial mats from Solar Lake (Sinai, Egypt). Antibodies, elicited in rabbits against samples taken at different depths from a core of these mats, were used for the detection of immunological determinants preserved in these samples. Special attention was given to an antiserum directed against a top mat fraction (3–10 mm depth) and an antiserum against a fraction from a lower section of the core (380–390 mm depth). Both antisera, tested in a dot-blot immunobinding assay, were found to give positive reactions with organic matter from different depths of the sediment. An immunohistochemical experiment with the antisera points to antigenic determinants on Recent and subfossil sheaths of Microcoleus. In addition, extracts of sediment samples were submitted to electrophoresis in polyacrylamide gels in order to characterize the separated macromolecules by immunological means. The results showed a rapid decrease in the number of antigenic determinants from Recent to subfossil samples. However, even in the deepest layers of the sediment (690–700 mm depth) intact biopolymers were detected.     

Weathering and biokarst development on marine terraces,northwest Morocco

Weathering features are described from an arid coastal area in northern Morocco which are indicative of invasive chasmolithic and endolithic microbial communities. Active weathering of marine terraces and karst development is associated with endolithic and epilithic algae responsible for boring, disintegration of matrix and mineral fabrics, solution and biomineralization that undermines the marine carbonate platform. Evidence of a range of biological weathering agents remains preserved, speci?cally calci?ed ?laments and sporangial material. An abundance of ?laments and spores representative of a consortium of algae, fungi, cyanobacteria and lichens is associated with the most denuded outcrops. The array of microbes contributes to the formation of the stromatolites to depths of 0·5 m within the limestone substrate. The preservation of stromatolites is supported by calci?cation of spores and ?laments, with trapping and binding of carbonate held in suspension by vadose waters. The pervasive weathering on this sector of coastline has important practical implications for coastal planning and development authorities in Morocco. Copyright © 2003 John Wiley & Sons, Ltd.     

Mathematical and Image Analysis of Stromatolite Morphogenesis

Stromatolites are internally laminated organosedimentary structures that result from the environmental interactions of Benthic Microbial Communities. They have been traditionally described and classified either by quasi-Linnean taxonomic systems or by morphometric schemes. Neither of these approaches has proved entirely satisfactory. The application of the mathematics of evolving surfaces provides a promising alternative for the modelling and classification of stromatolites in terms of their morphogenesis. The suggestion of Grotzinger and Rothman that stromatolite-growth in general could be attributed to a combination of four processes that constitute the variables of the Kardar–Parisi–Zhang (KPZ) equation has been analyzed and found to be an oversimplification. While some stromatolites can be characterized in this way, because of local growth effects, the majority of stromatolite forms exhibit nonlocal growth characteristic of Laplacian growth. Work is being undertaken to model such growth.     

铁岭组中风化柱状叠层石灰岩强度确定概率方法

研究区大量分布中风化柱状叠层石灰岩, 岩石强度具有很强的变异性和区域性, 而岩石强度是影响边坡稳定的重要因素。要进行边坡稳定性评价, 就需要对研究区现场试验数据作为随机变量进行概率统计分析, 获取可靠的岩石强度指标。本文通过对研究区内中风化柱状叠层石灰岩( t23 ) 现场点荷载实验数据进行统计分析, 利用x2 检验进行拟和, 得到岩石强度的概率密度函数和概率分布形式, 抗压强度和抗拉强度均服从对数正态分布。在此基础上, 结合相近岩性岩石强度的拟和结果, 建立区内中风化柱状叠层石灰岩点荷载试验强度概率分布函数。运用Bayes估计推断区域内中风化柱状叠层石灰岩岩石点荷载强度, 得到岩石抗压强度预测值为72. 42 MPa, 抗拉强度预测值为2. 29 MPa, 相对误差较小, 样本信任度达到70%以上。该方法对于岩石强度估计是有效的, 由该方法所得到的估计值对研究区边坡稳定性评价以及后期边坡治理都具有重要的实践意义。     

河北省头泉叠层石与古地理探讨

元古代叠层石是研究古地理变化的重要材料。井陉县头泉村叠层石显示了原始的群落状态,经鉴定其时代为元古代高于庄组,代表性分子为拟灌木藻板锥叠层石、多角紊乱锥叠层石、圆筒锥叠层石、杨沙候锥叠层石和高于庄叠层石。叠层石形态分异多样,与滨海、浅海相白云岩伴生,个体有较强的铁染现象,在纵向剖面上多期生长;它反映了当时古海洋的温度、盐度条件基本稳定,水动力、水深、光照条件有一定变化,古地理演化可划分为6个阶段。     

The Upper Riphean of the Yenisei Range

The Yenisei Range and the adjacent territories in the east are subdivided into (1) the Mid-Angara intracratonic depression; (2) the Yenisei pericratonic trough; and 3) a marginal oceanic block, the Isakovka-Predivinsk area. The lower part of the Riphean succession is subdivided into two principally different sedimentary complexes — the Lower Sukhoi Pit Subgroup and the Upper Sukhoi Pit Subgroup (the Pogoryui-Alad'in interval of the succession). The fundamental nature of the events that separate these two complexes and the characteristic, rhythmically bedded structure of the Upper Sukhoi Pit Subgroup allow the latter to be ranked a separate straton, the Bol'shoi Pit Group. Its lower boundary is associated with the Grenvillian events commencing with the emplacement of the Teya granite-gneiss domes and other intrusive complexes dated at 1100–1000 Ma. In the sedimentation record these events are manifested as a sudden change from the slate complex, for which we keep the name Sukhoi Pit Group, to the rhythmically bedded succession of the Bol'shoi Pit Group. The latter is interpreted as a product of uproofing of an elevated hinterland to the west. Insofar as the amplitude of this elevated area decreases progressively toward the Mid-Angara trough, the Bol'shoi Pit erosional unconformity and the associated interval of nondeposition are absent from the area. In the west of the Yenisei Range, in contrast, there is a major stratigraphic gap in the sequence, which is associated with the aforementioned events. The hypothesis on intensive events separating the deposition of the Bol'shoi Pit Group of the Kerpylian Horizon and the Tungusik Group of the Lakhandinian Horizon is not supported by the new data. The change from carbonate facies into siliciclastics in the west was misinterpreted as an erosional unconformity, with basal deposits corresponding to the lower boundary of the Tungusik Group. The occurrence of the Upper Tungusik deposits overlying much older rocks is a result of the pre-Bol'shoi Pit erosion and the gradual expansion of the Tungusik transgression. Thus, there are no grounds to argue for significant pre-Lakhandinian events in the region. Hence, the Kerpylian and Lakhandinian in the Yenisei Range, as well as in other parts of the Siberian Craton, constitute two parts of a larger supraregional straton, which corresponds to the lower half of the Upper Riphean and is designated here the Mayanian. The fundamentally different nature of the events associated with the next, Baikalian stage of the development allows its tripartite subdivision in the region. Deposition of the Lower Baikalian (the Oslyanka Group) was preceded by the crustal extension at the junction between the continental and oceanic blocks and, possibly, the formation of one of the Yenisei Range ophiolite complexes, followed by the emplacement of the Tatarka-Ayakhta batholiths at around 850 Ma. Fragments of both complexes are found as clasts in the basal conglomerates of the Middle Baikalian Chingasan Horizon. The specific character of the pre-Baikalian events determines their apparently poor expression in the sedimentation (weaker metamorphism of the Oslyanka deposits compared with the Tungusik Group). Even the activity leading to the formation of the Tatarka-Ayakhta granites cannot be regarded as a full-scale orogenic process. Collisional events separating the Lower and Middle Baikalian are manifested as the erosional unconformity at the base of the Chingasan Group and the emplacement of the Glushikha granites (760–730 Ma). The Middle Baikalian age of the Chingasan deposits is constrained by the data from paleontology, historical geology, and geochronology. Furthermore, the presence of glacial deposits renders this straton as a global stratigraphic marker. Further expansion of transgression in the Upper Baikalian is linked to another important event, but additional paleontological and geochronological information is needed to date the Upper Baikalian (Chapa Group) more accurately. The Baikalian events synchronously manifested themselves in all structural-facies zones of the Yenisei Range and are coeval to structural complexes from adjacent areas of the Siberian Craton. The tripartite Baikalian, therefore, has a potential for being included into the General Scale of the upper Upper Riphean.     

Seasonal temperatures from δ18O in recent Spanish tufa stromatolites: Equilibrium redux!

This study focuses on recent debate over the value of stable isotope‐based environmental proxies recorded in riverine tufa stromatolites. A twelve‐year record (1999 to 2012) of river‐bed tufa stromatolites in the River Piedra (north‐east Spain) was recovered in this study, along with a partly overlapping fifteen‐year record (1994 to 2009) of accumulations in a drainage pipe: both deposits formed in water with near identical physico/chemical parameters. Measured water temperature data and near‐constant δ ¹⁸O_water composition allowed selection of an ‘equilibrium’ palaeotemperature equation that best replicated actual temperatures. This study, as in some previous studies, found that just two published formulas for water temperature calculation from equilibrium calcite δ ¹⁸O compositions were appropriate for the River Piedra, where tufa deposition rates are high, with means between 5·6 mm and 10·8 mm in six months. The δ ¹⁸O_calcite in both the river and the pipe deposits essentially records the full actual seasonal water temperature range. Only the coldest times (water temperature <10°C), when calcite precipitation mass decreased to minimum, are likely to be unrepresented, an effect most noticeable in the pipe where depositional masses are smaller and below sample resolution. While kinetic effects on δ ¹⁸O_calcite‐based calculated water temperature cannot be ruled out, the good fit between measured water temperature and δ ¹⁸O_calcite‐calculated water temperature indicates that temperature is the principal control. Textural and deposition rate variability between the river and pipe settings are caused by differences in flow velocity and illumination. In the river, calcification of growing cyanobacterial mat occurred throughout the year, producing composite dense and porous laminae, whereas in the pipe, discontinuous cyanobacterial growth in winter promoted more abiogenic calcification. High‐resolution δ ¹⁸O_calcite data from synchronous pipe and river laminae show that reversals in water temperature occur within laminae, not at lamina boundaries, a pattern consistent with progressive increase in calcite precipitation rate as cyanobacterial growth re‐established in spring.     

The ca 2.74 Ga Mopoke Member,Kylena Formation: a marine incursion into the northern Fortescue Group?

The northern part of the Fortescue Group consists of interbedded flood basalts and sedimentary rocks that were deposited on the southern margin of the Pilbara Craton, Western Australia, during one or more periods of continental rifting between ca 2.78 and ca 2.63 Ga. Well-preserved sedimentary intervals within the group have yielded stable carbon and sulfur isotope data that have been used to infer changes in geobiological processes in the Neoarchean. However, the Fortescue Group is notable for being a predominantly subaerial succession, and it remains unclear whether data obtained from these intervals should be interpreted in the context of deposition in marine environments, possibly recording changes in the global ocean/atmosphere system, or in local and restricted lacustrine settings. Here, we describe the sedimentology, stratigraphy, stromatolites and stable carbon isotope geochemistry of the ca 2.74 Ga Mopoke Member, Kylena Formation, the oldest stromatolitic horizon in the Fortescue Group. This unit differs in terms of internal stratigraphic relationships, sedimentology, carbonate mineralogy and stable isotope geochemistry when compared with intervals of probable lacustrine origin in the overlying Tumbiana and Maddina formations. In contrast, we suggest that parts of the Mopoke Member may have been deposited under open marine conditions, or alternatively, in a lacustrine environment characterised by differing water chemistry and basement topography. Stromatolitic microfabrics of the Mopoke Member are dominated by spar, dolospar and vertically aligned calcitic crusts, rather than the micritic microfabrics described from other Fortescue Group stromatolites. Mud-draped ripples are common sedimentary features in the Mopoke Member, suggesting a tidal influence. Mopoke Member δ¹³C_carb values are generally slightly positive, but also include some significantly depleted values, which may relate to the reoxidation of ¹³C-depleted organic matter. δ¹³C_org values average –36.7‰, consistent with Neoarchean marine units reported from elsewhere, but significantly less ¹³C-depleted than values reported from overlying lacustrine intervals in the Fortescue Group. We conclude that some features of Fortescue Group datasets relevant to the field of geobiology may be facies dependent, and that more work focusing on the overall depositional environments of the Fortescue Group is needed in order to appropriately interpret geobiological data reported from that group.     

Phosphatic series under Plio-Quaternary cover of Tadla Plain,Morocco: Gravity and seismic data

The Ouled Abdoun sedimentary basin in Morocco contains the largest phosphate reserves in the world. To the Northwest of the basin, the phosphate layers crop out or are at a shallow depth and are exploited in open pit mines. By contrast, towards the central and southwestern parts of the basin, the phosphate layers lay below the Plio-Quaternary sediments of the Tadla Plain. This study aims to characterize the distribution and structure of the phosphatic series at depth under this cover, in particular to guide the future exploration and exploitation of the phosphate deposits. The work is based on gravimetric and seismic data acquired in a previous oil exploration study, calibrated by borehole data. The analysis of the gravity data controlled by boreholes first reveals the existence of large regional faults in the basin, forming pronounced gradients in the gravity data. The faults are also seen in the seismic profiles. In the Southeast of the basin, the phosphatic series exhibit a stairway structure controlled by some of these regional faults.The drilling data and the isochron maps established from the seismic profiles show that the base of the phosphatic series is more than 500 m deep in the southeastern area of the basin. As the phosphatic layers get buried deeper, they also become thicker. The phosphate reserves thus increase towards the southeast, and our analysis identifies the areas where this reserve is larger. Our results eventually suggest that the mining methods currently adopted in the Khouribga mining district will need to be modified and adapted to the more complex situation of the phosphatic series deeply buried in the basin.     

扬子克拉通北缘中元古界神农架群乱石沟组叠层石类型及其沉积学意义*

扬子克拉通北缘神农架地区中元古界神农架群叠层石十分发育。该群下部乱石沟组中叠层石类型丰富,根据形态可分为柱状、穹状、层状叠层石以及锥状、层柱状、包心菜状、墙状叠层石和叠层石丘等。研究区叠层石以中小型为主,少数为大型和巨型;多数无壁,部分具单层壁;对称性和继承性由好到一般,部分较差。研究表明,叠层石的形态和规模,与水动力条件、水体深度及陆源组分含量关系密切,其中层状叠层石主要发育于潮间带上部,柱状叠层石产于潮间带下部和浅潮下带,穹状叠层石出现在潮间带和潮下带,锥状叠层石多见于潮间带下部和潮下带,层柱状、锥柱状叠层石则集中于潮间带,叠层石丘位于潮间带和潮下带。依据各类型叠层石宏观和微观特征、垂向组合类型、沉积构造及沉积岩相相互关系,并结合碳、氧同位素测试结果,综合研究认为: 虽然叠层石的形成受生物和环境等多重因素影响,但生物因素主要影响叠层石的微观组构,水动力条件则控制叠层石的宏观形态类型,水体深度影响叠层石的规模;另外,生物繁盛、陆源物质供给少的环境更有利于叠层石发育。