Longitudinal profiles and knickzones: the example of the rivers of the Cher basin in the northern French Massif Central

This work examines the longitudinal profiles of 27 rivers in the upper Cher basin, of various lengths, in order to characterize their shape and the knickzones (high gradient sections) that disrupt their longitudinal profiles. No smooth, concave-upwards long profile has been found in the study area, located at the contact between the Massif Central basement rocks and the Paris Basin sedimentary rocks, because of the heterogeneous geological structure and lithology. The analysis of the main knickzone parameters allows us to distinguish two knickzone assemblages: the 53 knickzones of the first have a lithological origin and are characterized by a gradient equal to or lower than that given by the power curve y = 63.306 × ^−0.4392; the 30 knickzones of the second assemblage, which have a higher gradient than that of the curve, and give clear outliers in the DS (distance-slope) plot, are due to active faulting. The locations of this second group of knickzones delimit the areas that have experienced important local vertical crustal motions, too rapid for fluvial incision to have reduced the effect of knickzones caused by active faulting. In these uplifted areas, headward erosion has been arrested by knickzones of the second type, allowing the preservation of shallow-dell valley heads without any incision.     

泥石流流域岩性的坚固系数与暴发频率的关系

坚硬岩性地区的泥石流暴发频率较低在定性上基本可以概括岩性与泥石流暴发频率的关系,但目前还没有定量地描述岩性与泥石流暴发频率的关系。以四川省17个泥石流流域作为研究对象,通过现场调查研究泥石流形成区和堆积区粗化层颗粒的岩性、硬度以及泥石流的暴发频率,得出：①泥石流堆积区岩性组成特征基本可以代表形成区的岩性组成特征;②用地...     

Crustal transect from the North Atlantic Knipovich Ridge to the Svalbard Margin west of Hornsund

The crustal structure along a 312 km transect, stretching from the axial mountains of the North Atlantic Knipovich Ridge to the continental shelf of Svalbard, has been obtained using seismic reflection data and wide angle OBS data. The resulting seismic V_p and V_s models are further constrained by a 2-D-gravity model. The principal objective of this study is to describe and resolve the physical and compositional properties of the crust in order to understand the processes and creation of oceanic crust in this extremely slow-spreading counterpart of the North Atlantic Ridge Systems. V_p is estimated to be 3.50–6.05 km/s for the upper oceanic crust (oceanic layer 2), with a marked increase away from the ridge. The measured V_p of 6.55–6.95 km/s for oceanic layer 3A and 7.10–7.25 km/s for layer 3B, both with a V_p/V_s ratio of 1.81, except for slightly higher values at the ridge axis, does not allow a clear distinction between gabbro and mantle-derived peridotite (10–40% serpentized). The thickness of the oceanic crust varies a lot along the transect from the minimum of 5.6 km to a maximum of 8.1 km. The mean thickness of 6.7 km for the oceanic crust is well above the average thickness for slow-spreading ridges (<10 mm/year half-spreading rate). The areas of increased thickness could be explained by large magma production-rates found in the zones of axial highs at the ridge axis, which also have generated the off-axial highs adjacent the ridge. We suggest that these axial and off-axial highs along the ridge control the lithological composition of the oceanic crust. This approach suggests normal gabbroic oceanic crust to be found in the areas bound by the active magma segments (the axial and off-axial highs) and mantle-derived peridotite outside these zone.     

裂缝性潜山油藏储集体岩性定量识别———以埕北30 太古界潜山储集体为例

由于油井取芯费用高昂加之油层保护的需要,不可能大量取芯,因此利用少量的岩芯资料,结合其它一些手段来预测未取芯井段的岩性,就成为有效识别和预测潜山储层分布的重要途径之一。该文针对埕北30 太古界潜山储集体,运用BP神经网络技术对测井资料进行了潜山储集体岩性的定量识别,经与岩芯观察、薄片分析、成像测井结果对比检验, 符合率达到了90%,从而为开展潜山油藏裂缝预测研究奠定了基础。      

Influence of sedimentary environments on mechanical properties of clastic rocks

The sedimentary environments are the intrinsic factor controlling the mechanical properties of clastic rocks. Examining the relationship between rock sedimentary environments and rock mechanical properties gives a better understanding of rock deformation and failure mechanisms. In this study, more than 55 samples in coal measures were taken from seven different lithologic formations in eastern China. Using the optical microscope the sedimentary characteristics, such as components of clastic rocks and sizes of clastic grains were quantitatively tested and analyzed. The corresponding mechanical parameters were tested using the servo-controlled testing system. Different lithologic attributes in the sedimentary rocks sampled different stress–strain behaviors and failure characteristics under different confining pressures, mainly due to different compositions and textures. Results demonstrate that clastic rocks have the linear best-fit for Mohr-Coulomb failure criterion. The elastic moduli in clastic rocks are highly dependent upon confining pressures, unlike hard rocks. The envelope lines of the mechanical properties versus the contents of quartz, detritus of the grain diameter of more than 0.03 mm, and grain size in clastic rocks are given. The compressive strength or elastic modulus and the grain diameter have a non-monotonic relation and demonstrate the “grain-diameter softening” effect.     

松辽盆地营城组火山岩储层成因及储集性能演化过程

在岩心观察基础上,通过应用全岩主量元素分析、显微镜下常规与铸体薄片观察鉴定和定量统计、图像孔喉分析、物性测试、X-射线衍射分析、包裹体荧光分析、均一温度与激光拉曼探针成分分析等多种手段,研究了松辽盆地营城组火山岩岩性和火山岩储层成因; 结合成岩作用与储集空间特征研究,分析了火山岩储层孔隙演化过程。结果表明,火山岩经历了冷却成岩作用、岩浆期后热液作用、风化淋滤剥蚀作用以及埋藏成岩作用等4个成岩作用阶段。火山岩储层的形成、孔隙演化和储集性能的改善主要与火山岩在浅埋A期后期-深埋成岩B期成岩过程中的断裂、不整合面及构造裂缝的发育以及热液流体沿断层、不整合面和构造裂缝流动的过程中对火山岩产生溶蚀作用密切相关,营城组火山岩属于构造-岩性火山岩气藏。     

树分类器在测井岩性评价中的应用

 利用测井资料进行岩性定量识别,分类方法的设计是决定分类结果好坏的关键。本文讨论了树分类器与产生式规则相结合的方法在岩性分类中的应用。利用数据完整的测井曲线参与树分类器的学习、判别工作,用树分类器进行岩性的“逐级识别”,不完整的特征交由定性规则处理,既实现了岩性的细分,且保证了分类的精度。     

Petrology and depositional evolution of the Paleozoic rocks of Iraq

The study integrates petrographical and lithological data from deep exploration wells and outcrops in northern Iraq to better understand the sedimentary environments present in the basin and to evaluate the depositional evolution of the Paleozoic rocks in Iraq. The studied Paleozoic successions are represented by five sedimentary cycles of intracratonic sequences. These are dominated mainly by siliciclastic and mixed sedimentary packages, and are separated by major and minor unconformity surfaces. These cycles are as follow: the Ordovician cycle, represented by the Khabour Formation; the Silurian cycle, represented by the Akkas Formation; the Middle-Late Devonian to Early Carboniferous cycle, represented by the Chalki, Pirispiki, Kaista, Ora and Harur formations; the Permian–Carboniferous cycle, represented by the Ga’ara Formation and late Permian cycle, represented by the Chia Zairi Formation. Generally, the cycles are characterized by siliciclastic and mixed carbonate–clastic facies with abrupt changes during Late Paleozoic reflecting the environmental and tectonic events during this period. The Ordovician Khabour Formation is suggested to be of shallow marine environment of deposition with stacked transgressive and regressive cycles that are eustatically controlled. The shale of Silurian Akkas Formation was deposited in open-marine environment. Depositional regimes in the Late Devonian to Early Carboniferous are considered as a continuation of deposition in the subsiding basin with a wide geographic distribution that reflect the epicontinental or epeiric seas in a homoclinic ramp setting. The Permo-Carboniferous Ga’ara Formation was deposited in continental to paralic environment while the Late Permian Chia Zairi Formation represents the carbonate platform deposition. The study revealed that potential source rocks may include some shale beds of the Khabour Formation, hot shales of Akkas Formation and the shales of Ora Formation. The sandstones of the Khabour, Akkas and Kaista formations have good reservoir potential. The Late Permian carbonates of Chia Zairi Formation may be self-sourcing and contain multiple reservoirs. The occurrence of shale as source rocks and limestone as reservoir rocks and some evaporates as sealing horizons make the formation as a reservoir in its own right.     

Sedimentation processes and new age constraints on rifting stages in Lake Baikal: results of deep-water drilling

 With this paper we present a first attempt to combine the direct results on lithology, composition and age dating in the boreholes BDP-93, BDP-96 and BDP-97 with geological and seismic data from the areas where those sections were drilled. The sedimentary environments represented by the BDP boreholes are markedly different and possess characteristic lithological features. The results of the deep drilling provide the essential means for testing numerous age models used in geological reconstructions of the Lake Baikal rifting dynamics. Neither the basin-wide unconformity interpreted from seismic data, nor the interpreted change from shallow-water to deep-water facies at the boundary of the seismic stratigraphic complexes were found in the BDP-96 boreholes on Academician Ridge. Also, lithology does not support the proposed reconstructions of intense lake level fluctuations and transgressions during the Pliocene at Academician Ridge. The continuous deep-water hemipelagic sedimentation at Academician Ridge has existed for the past 5 Ma. The beginning of an intense rifting phase of the Neobaikalian sub-stage and related drastic changes in sedimentation processes were interpreted on seismic sections as the basin-wide unconformity B10. Different age estimates for this boundary ranged from Late Pliocene (3.5 Ma) to Plio-Pleistocene boundary. As shown by BDP-96 borehole, B10 is associated with a lithological change from diatomaceous ooze to dense silty clay and not with an erosional contact. The new age for this boundary in BDP-96 is approximately 2.5 Ma. This new age constraint suggests that the upper sedimentary strata of Northern Baikal (1.5–1.7 km thick) have formed during the past 2.5 Ma with average sedimentation rates of 60–70 cm/ka. The BDP-93 boreholes at Buguldeika suggest that uplift in Primorsky Range took place prior to 1.07–1.31 Ma, a date which exceeds the age of previous geological models. Received: 12 March 1999 / Accepted: 10 February 2000