Stratigraphic sections, bedding sequences, and random processes

Both dependent and independent random processes can be used to study and synthesize stratigraphic sections and bedding sequences. Synthetic stratigraphic sections can be modeled to fit any geologic problem with a good correspondence between the synthetic and actual stratigraphic sections. To synthesize a sedimentary sequence, one needs only a transition procedure to go from one lithology or bedding type to another, and frequency distributions of thickness for the various lithologies. A sedimentation process with a "memory" is termed Markovian; if the past has no influence on either present or future sedimentation, it is called an independent trials process.     

Quantitative formulation of reliability in stratigraphic correlation

The probability that two stratigraphic events are in a particular order in a section in which they occur in sequence is p. Because of finite sampling, statistical techniques are used to calculate the parameters p' and p(l), which express the uncertainty of our knowledge of p; p' is the measured value of the maximum likelihood estimator of p and p(l) is the lower end point of the confidence interval on which p must lie. The most reliable sequence for stratigraphic correlation is obtained by maximizing the parameter p' (1-p(l)) between pairs of events.     

贵州六盘水地区马铃薯种植地质环境分析

为了探索贵州省六盘水地区马铃薯种植的有利种植区带,为该地区规模化种植马铃薯选区提供科学依据,采用现场调查、区域地质环境分析等方法,对贵州省六盘水地区马铃薯种植区域进行调查研究。结果表明:贵州省六盘水地区马铃薯主要种植区分布在海拔1 700m以上的高寒山区的山坡和谷地,地质环境为石炭系白云岩、二叠系茅口灰岩、二叠系玄武岩、三叠系泥质白云岩分布区域。在调查的基础上,结合区域地层分布和海拔等条件分析指出,六盘水地区优质马铃薯种植区域为二叠系玄武岩分布区域,其次是高海拔的二叠系茅口灰岩分布区域以及石炭系白云岩分布区域。     

Discovery of a large-magnitude, late pleistocene volcanic eruption in alaska

An extensive blanket of dacitic tephra was deposited across Alaska and the western Yukon Territory by a plinian eruption about 80,000 years ago. The volume of tephra erupted probably exceeded 50 cubic kilometers and the source was probably in the Wrangell Mountains. This widespread layer of tephra serves as an excellent late Pleistocene stratigraphic marker.     

Devonian brachiopods from the sillimanite zone, mount moosilauke, new hampshire

Devonian brachiopods, identifiable at the generic level, have been recovered from calc-silicate rocks more intensely metamorphosed and metasomatized than any other known fossil occurrence. The fossils are a key stratigraphic link between granulite facies rocks of central New Hampshire and fossiliferous rocks of western New Hampshire and Maine.     

Geograpehic variation and episodic evolution in an ordovician trilobite

A single lineage of the trilobite Flexicalymene shows two evolutionary "punctuated equilibria" within a 2-million-year, 1000-square-kilometer stratigraphic interval. The 2 x 10(5)-year-long "punctuation" may represent parapatric speciation. Commonness of depth-related clines before, during and after this event suggests that short-term adjustment to local conditions was important in long-term evolution.     

垂直铺塑和水泥土薄墙防渗技术在浑河防洪应急工程中的应用

根据浑河岸滩的地层特点，堤防工程的基础防渗成功地应用了垂直铺塑防渗和水泥土薄墙截渗新技术。工程取得了造价低、工效高、施工操作简便的效果。     

Nebraskan and kansan stades: complexit and importance

Several Early Pleistocene stadial tills and related soils in Kansas and Nebraska indicate a complex history of ice-sheet fluctuations. It is impossible to assign ages to individual till sheets solely on the basis of position in a stratigraphic column; all Early Pleistocene correlations must be reevaluated.     

Pleistocene Sea Levels, Southeastern Virginia

Detailed study of post-Miocene stratigraphy in southeastern Virginia reveals at least 13 formations which show six Pliocene (?) and Pleistocene cycles of emergence and submergence, with maximum submergent sea levels near +45, +45, +20, +25, +15, and 0 feet, respectively. The newly established stratigraphic framework disproves earlier interpretations of "terrace-stratigraphy" and sea level chronologies.     

An iridium abundance anomaly at the palynological cretaceous-tertiary boundary in northern new Mexico

An iridium abundance anomaly, with concentrations up to 5000 parts per trillion over a background level of 4 to 20 parts per trillion, has been located in sedimentary rocks laid down under freshwater swamp conditions in the Raton Basin of northeastern New Mexico. The anomaly occurs at the base of a coal bed, at the same stratigraphic position at which several well-known species of Cretaceous-age pollen became extinct.     

Evidence of strong earthquake shaking in the lower wabash valley from prehistoric liquefaction features

Earthquake-induced liquefaction features in Holocene sediments provide evidence of strong prehistoric shaking, magnitude m(b) 6.2 to 6.7, in the Wabash Valley bordering Indiana and Illinois. The source of the one or more earthquakes responsible was almost certainly in or near the Wabash Valley. The largest event is interpreted to have occurred between 7500 and 1500 years ago on the basis of archeological, pedological, and stratigraphic relations.     

Mazama ash in the northeastern pacific

Volcanic glass in marine sediments off Oregon and Washington correlates with continental deposits of Mount Mazama ash by stratigraphic position, refractive index, and radiocarbon dating. Ash deposited in the abyssal regions by turbidity currents is used for tracing of the dispersal routes of postglacial sediments and for evaluation of marine sedimentary processes.     

Status of the Pleistocene Wisconsin Stage in Central North America

A brief review of the history of the Wisconsin Stage in Pleistocene stratigraphy and of research since 1950 shows that post-Sangoman glacial drift older than the Wisconsin drift reported in the older literature is present in central North America. Known and possible stratigraphic positions of the relevant units are shown.     

Erratum

As published, figure 2 in the report "Disruption of the terrestrial plant ecosystem at the Cretaceous-Tertiary boundary, western interior" by R. H. Tschudy et al. (7 Sept., p. 1030) contained two errors. The break in the stratigraphic column should have been 3 m, and the iridium concentration should have been in parts per trillion. The correct figure is reproduced below. [see figure in source PDF].     

四川剑门关农业地质背景及农业旅游开发研究

通过对四川剑门关景区的调查研究,总结分析了剑门关景区的农业地质背景。对其地层特征、区域水文地质、地质构造、地球化学进行分析,最后提出相应的农业生态旅游开发策略。     

New evidence on the size and possible effects of a late pliocene oceanic asteroid impact

Debris from a late Pliocene asteroid impact is spread across at least 600 kilometers of the ocean floor in the southeast Pacific. On the basis of iridium concentrations in sediments from six deep-sea cores, the asteroid diameter was at least 0.5 kilometer; the impacting projectile may have been one of the largest in the last few million years. The stratigraphic age of this impact is the same as that inferred for the onset of Northern Hemisphere glaciation.     

Sudden productivity collapse associated with the Triassic-Jurassic boundary mass extinction

The end-Triassic mass extinction is one of the five most catastrophic in Phanerozoic Earth history. Here we report carbon isotope evidence of a pronounced productivity collapse at the boundary, coincident with a sudden extinction among marine plankton, from stratigraphic sections on the Queen Charlotte Islands, British Columbia, Canada. This signal is similar to (though smaller than) the carbon isotope excursions associated with the Permian-Triassic and Cretaceous-Tertiary events.     

辽河盆地西部凹陷曙光油田曙二区S~3_3油层储层建模研究

在辽河盆地西部凹陷曙光油田曙二区S33储层地质建模研究中,综合应用地质、地震和测井资料建立构造模型,以构造模型提供的地层格架,采用随机建模中序贯指示模拟的方法建立沉积微相模型。在此基础上,按相控建模的思路,选择地质统计学克里金方法中的球形变差函数模型对研究区储层参数进行模拟,建立了储层参数模型,为油藏数值模拟提供了精确的三维数据体。     

Comment on "Redefining the age of Clovis: implications for the peopling of the Americas"

Waters and Stafford (Reports, 23 February 2007, p. 1122) provided useful information about the age of some Clovis sites but have not definitively established the temporal span of this cultural complex in the Americas. Only a continuing program of radiometric dating and careful stratigraphic correlations can address the lingering ambiguity about the emergence and spread of Clovis culture.     

Historical dates for neolithic sites of southeast europe

Direct comparison of the radiocarbon contents of charcoal samples with those of bristlecone pine wood samples dated by tree rings shows that a full-fledged Neolithic with pottery and all the domesticated animals, except the horse, was present in southeast Europe as early as the 65th century B.C. The chronologies for the stratigraphic sequences of the settlements of Achilleion and Anza, based on a total of 37 La Jolla radiocarbon measurements, cover almost 1000 years.