scholarly journals Development characteristics of the third-order sequence of Upper Devonian–Lower Carboniferous shore-mixed shelf in Tarim Basin, NW China

2019 ◽  
Vol 46 (4) ◽  
pp. 701-710
Author(s):  
Qing MA ◽  
Tao MA ◽  
Haijun YANG ◽  
Xueqin ZHAO ◽  
Yiqing ZHU
Keyword(s):  
Tarim Basin ◽  
Upper Devonian ◽  
Third Order ◽  
Lower Carboniferous ◽  
Nw China ◽  
The Third ◽  
Order Sequence

Depositional Cycles in a Lower Cretaceous Limestone Reservoir, Onshore Abu Dhabi, U.A.E.

2018 ◽  
Vol 88 (7) ◽  
pp. 753-776 ◽  
Author(s):  
Stephen N. Ehrenberg ◽  
Stephen W. Lokier ◽  
Liu Yaxin ◽  
Rulin Chen
Keyword(s):  
Sea Level ◽  
Lower Cretaceous ◽  
Clay Content ◽  
Storm Events ◽  
Humid Climate ◽  
Third Order ◽  
Depositional Sequence ◽  
The Third ◽  
Depositional Cycles ◽  
Order Sequence

AbstractThe upper reservoir zone of the Lower Cretaceous Kharaib Formation (46–54 m thick in the studied wells) is regarded as the upper portion of a third-order depositional sequence comprising higher-order cycles. Whereas the third-order sequence interpretation is clearly supported by the upward-shoaling trend of the reservoir zone, relationships defining the component cycles have not previously been documented and are the focus of the present study. Core descriptions from four wells in a single oilfield reveal little evidence of facies changes or trends of facies patterns indicative of high-frequency depositional cycles. Cycle boundaries could possibly be represented by the repetitive pattern of coarse beds (rudstone and floatstone) 0.1–2 m thick, commonly having sharp basal contacts and gradational upper contacts with enclosing packstone to wackestone. Because the coarse beds do not appear correlative between wells, however, we prefer the alternative interpretation that they reflect episodic storm events which locally redistributed detritus, sourced from a patchwork of low-relief lithosomes, across the flat surface of the epeiric Kharaib platform–lagoon. Although the existence of high-order eustatic fluctuations during upper Kharaib deposition is well established, low-amplitude variations in water depth may not have touched down on the sea floor to significantly affect sediment textures in contrast with the dominant storm signal.Reservoir sub-zones used for production operations, but previously suggested to be fourth-order parasequence sets, are defined by dips in porosity-log profiles, reflecting thin (approximately 1 m) intervals of increased stylolite frequency. These boundaries are thus diagenetic in character, but their correlation over tens to hundreds of kilometers indicates an underlying depositional control. We suggest that the link between sea level and diagenesis is depositional-clay content, which facilitates stylolitic dissolution. Profiles of bulk-rock alumina analyses in the studied cores show subtle indications of higher clay content at the sub-zone tops. Much greater clay peaks mark the third-order sequence boundaries, resulting in the “dense” (very low porosity) zones above and below the studied reservoir zone and the increased stylolite frequency in the upper and lower several meters of the zone. Possible factors promoting clay influx across a carbonate shelf during falls in sea level include increased stream gradients and more humid climate.

Upper Devonian miospores from the Escuminac Formation, eastern Québec, Canada

1970 ◽  
Vol 7 (1) ◽  
pp. 29-45 ◽  
Author(s):  
Wayne W. Brideaux ◽  
Norman W. Radforth
Keyword(s):  
Middle Devonian ◽  
Russian Platform ◽  
Upper Devonian ◽  
New Combinations ◽  
Lower Carboniferous ◽  
The Third ◽  
Large Size ◽  
Assem Blages ◽  
Small Spore ◽  
Orcadian Basin

Miospores of early Frasnian age are described from the third unit of the Escuminac Formation in eastern Québec, Canada. The assemblage comprises 34 species, including 8 species proposed as new, 2 new combinations, and 12 sparsely represented forms not considered synonymous with previously described species.The assemblage is most closely comparable to a Middle Devonian assemblage from the Orcadian Basin, Scotland. Similarities are also noted with European and Russian assemblages, particularly from the Eifelian–Givetian of the Russian Platform. Except for five long-ranging species, elements of Lower Carboniferous assemblages are lacking. Evidence suggests a transitional nature for this Escuminac assemblage. Miospores of relatively large size, a feature of Middle Devonian assemblages, are present. Marked differentiation of large and small spore types, found in several other Upper Devonian assem blages is absent. Apiculate and anchor-spined species dominate the Escuminac assemblage.

Probe size and 5th-order aberration

1987 ◽  
Vol 45 ◽  
pp. 134-135 ◽  
Author(s):  
Zhifeng Shao
Keyword(s):  
Electron Probe ◽  
Spherical Aberration ◽  
Wave Length ◽  
Cylindrical Symmetry ◽  
Electron Wave ◽  
Third Order ◽  
The Third ◽  
Probe Radius ◽  
Small Probe ◽  
Probe Size

A small electron probe has many applications in many fields and in the case of the STEM, the probe size essentially determines the ultimate resolution. However, there are many difficulties in obtaining a very small probe.Spherical aberration is one of them and all existing probe forming systems have non-zero spherical aberration. The ultimate probe radius is given byδ = 0.43Csl/4ƛ3/4where ƛ is the electron wave length and it is apparent that δ decreases only slowly with decreasing Cs. Scherzer pointed out that the third order aberration coefficient always has the same sign regardless of the field distribution, provided only that the fields have cylindrical symmetry, are independent of time and no space charge is present. To overcome this problem, he proposed a corrector consisting of octupoles and quadrupoles.

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