تعیین سن به روش کربن(14)-4

Variability in amount of carbon

 In addition to the variation in production and distribution of 14C over time and within portions of various carbon reservoirs, variations may result from situations where carbon not in equilibrium with the contemporary standard values is added or removed from any reservoir. Two instances are well documented since they occurred within the last century as a result of human intervention in the carbon cycle. The first, beginning in the middle of the nineteenth century, is known as the industrial or Suess effect. The combustion of fossil fuels added enough “dead” 14C to the atmosphere to result in the reduction by about 3% in biospheric 14C activity.

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تعیین سن به روش کربن(14)-3

Main trend

 Upon examination of the data in Fig. 4 and other similar plots, it becomes apparent that radiocarbon years and calendar years are not necessarily equivalent. If such had been the case, all of the data points plotted on Fig. 4 would lie along the horizontal 0 line. In fact, some of the points lie above the line, indicating that 14C values in these periods are too old. Conversely, those below the 0 line are too young when compared to the tree-ring data. This plot indicates that there are two major components to the deviations. The first is a general main-trend secular variation phenomenon (the curved line) exhibiting during the Holocene, a sine-wave function with an apparent period of about 8500–9000 years, with a maximum deviation of about 800 years, approximately 8000 years ago.

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تعیین سن به روش کربن(14)-2

Gas counters

In the early 1950s, both proportional (Fig. 2) and Geiger gas counters were employed in 14C work, using carbon dioxide, carbon disulfide, acetylene, methane, or ethane as counting gases. As in the case of the solid carbon system, the center counter containing the sample was surrounded by individual Geiger tubes or an annular or continuous ring guard, all housed within an iron or lead shield assembly. Efforts to reduce the background values in gas detectors have resulted in various types of experimental arrangements, including the location of counters in underground vaults. In such underground facilities, the contribution of the meson flux, the major contributor to the background rate, can be significantly reduced. Because of the 90–95% efficiency in most gas detector systems, the typical maximum age limits were extended to 40,000–60,000 years, depending on the experimental configuration, including the volume of the detectors and the level of the background count rates in specific detectors. Isotopic enrichment of sample gases permits the maximum age attainable to be extended several additional half-lives. In general, sample-size requirements with gas detectors were reduced from that required with the solid carbon method—special systems being designed to permit the measurement of a sample with as little as 0.1 g (3.5 × 10−3 oz) of carbon.  See also: Geiger-Müller counter; Ionization chamber; Meson

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تعیین سن به روش کربن(14)-1

تعیین سن به روش کربن(14)

Radiocarbon dating

A method of obtaining age estimates on organic materials which has been used to date samples as old as 75,000 years. The method was developed immediately following World War II by Willard F. Libby and coworkers, and has provided age determinations in archeology, geology, geophysics, and other branches of science.

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کانی های رسی2 - Clay minerals

Pyrophyllite-talc group

These 2:1 layer silicates possess a c dimension of slightly more than 0.9 nm and exist in several polytypes and chemical varieties. Talc generally shows a triclinic structure (lTc), but a disordered variety is called kerolite. Minnesotaite is an iron-rich variety of talc, and willemseite is a nickel-rich variety. Polytypes of pyrophyllite are monoclinic, triclinic, and disordered pyrophyllite. Generally, these 2:1 minerals possess a high thermal stability, have a low cation-exchange capacity, and do not swell in water or in intercalation agents. See also: Pyrophyllite; Talc

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کانی های رسی1 - Clay minerals

کانی های رسی - Clay minerals

Clay minerals

Fine-grained, hydrous, layer silicates that belong to the larger class of sheet silicates known as phyllosilicates. Their structure is composed of two basic units. (1) The tetrahedral sheet is composed of silicon-oxygen tetrahedra linked to neighboring tetrahedra by sharing three corners to form a hexagonal network (Fig. 1). The fourth corner of each tetrahedron (the apical oxygen) points into and forms a part of the adjacent octahedral sheet. (2) The octahedral sheet is usually composed of aluminum or magnesium in sixfold coordination with oxygen from the tetrahedral sheet and with hydroxyl. Individual octahedra are linked laterally by sharing edges (Fig. 2). Tetrahedral and octahedral sheets taken together form a layer, and individual layers may be joined to each other in a clay crystallite by interlayer cations, by van der Waals and electrostatic forces, or by hydrogen bonding

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رس - Clay

رس - Clay

Clay

A term used to refer to the finest-grain particles in a sediment, soil, or rock. According to the Wentworth scale (see table), clay is finer than silt, characterized by a grain size of less than approximately 4 micrometers. However, the term clay can also refer to a rock or a deposit containing a large component of clay-size material. Thus clay can be composed of any inorganic materials, such as clay minerals, allophane, quartz, feldspar, zeolites, and iron hydroxides, that possess a sufficiently fine grain size. Most clays, however, are composed primarily of clay minerals. See also: Clay minerals; Feldspar; Quartz; Zeolite

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تعيين ضخامت حقيقى طبقات حفارى شده

تعيين ضخامت حقيقى طبقات حفارى شده

تعيين ضخامت حقيقى طبقات حفارى شده

يک از متداولترين روشهاى تعيين ذخيره مخازن نفتى سطح آزمائى از نقشه هاى ميزان منحنى تحت الارضى مى باشد که در دو نوبت صورت مى گيرد. يکبار براساس سطح فوقانى يک سازند و بار ديگر بر اساس سطح تحتانى همان سازند. از آنجايى که سطوح تحتانى سازندهايى مانند آسمارى و بنگستان با وجود سطوح منعکس کننده هاى REFLECTOR موثر همراه نيست

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مطالعه مرجان هاى ممبر A سازند گچا ل (كوه راهدار،) غرب طبس

متن فارسى: 

مقطع چينه شناسى مورد مطالعه در منطقه کلمرد از حوضه هاى اقليم زمين ساختى بلوک طبس (از بلوکهاى ايران مرکزى) مى باشدکه مرجانهاى (روگوزا و تابولاتا) ممبرA سازند گچال واقع د ر70 کيلومترى غرب طبس مورد بررسى قرار گرفته است. حاصل اين بررسى شناسايى 11 جنس، 17 گونه و3 زيرگونه است که در مجموع نشاندهنده سن تورنزين است.

سنگواره هاى مرجانى مورد مطالعه شاخص حوضه مديترانه اى هستند و شباهت زيادى با سنگواره هاى مرجانى کربونيفر پيشين البرز مرکزى نشان ميدهند. اين مجموعه با مرجانهاى کربونيفر پشين ساير نواحى دنيا قابل مقايسه اند.. براکيوپودها فراوان ترين گروه فسيلى همراه مرجان ها مى باشند..به علاوه سنگواره هايى از بريوزوئرها، کرى نوئيدها، گاستروپودها و تريلوبيت ها نيز مشاهده مى شوند. از ميکرو فسيل ها نيز فرامينيفرها وکنودونت ها وجود دارند. با توجه به گسترش و وضعيت قرار گيرى مرجان ها، 2 زون اکولوژيکى براى مقطع مورد بررسى مشخص گرديد. زون شماره 1 حاوى مرجانهاى كوچك و بدون دبس اپيمنت است كه در منطقه عميق پلاتفرم باز مى زيسته اند و زون شماره 2 حاوى مرجانهاى روگوزاى بزرگ ديس اپيمنت دار و كلنى هاى تابولاتا است كه در منطقه كم عمق پلاتفرم باز توسعه يافته اند

متن انگليسى: 

Abstract:

Corals (Rugosa and Tabulata) of Member A of Gachal Formation (Carboniferous) have been examined.The studied stratigraphical section is located in Kalmard province,Tabas region, as a block in Central Iran.The best section for coral study selected in Rahdar Mountain about 70 km west of Tabas , east Iran.

In this study, 11 genera,17 species and 3 subspecies were distinguished.This fauna represent a Tournaisian age.The studied corals represent Mediterranean province.They can be compared with corals of Central Alborz and other regions in the world.

The associated fossils are:brachiopods,bryozoans,crinoids,gastropods and trilobites,which the brachiopods is the dominant one .Microfossils such as foraminifera and conodonts also have been founded .Based on the spreading and arrangement of corals, two ecological zones for member A of the Gachal Formation were distinguished  .Zone number1 contains small corals without dissepiment and lived in deep open marin. Zone number2 distinguished by large rugosa corals with dissepiment and tabulate colonies.These corals have expanded in shallow open marine.

 منبع:http://www.geology.ir/news/news_detail.asp?id=50