Limestone outcrops

NaCl from the deep brine springs and CaC03 from limestone outcroppings in a simple reaction, which yielded two useful products. 

Figure 2.2. Bedding planes in a limestone outcrop (by courtesy of D.D. Brumhead)...

The core part of a larger subsidence observation network is shown in Fig. 1. It is height oriented on benchmark AO stabilized in limestone outcrops of the basement structure of the deposit. Its stability has been proved by long-term observations. The outer parts of the network are not shown. They but indirectly concern the problem discussed by increasing the total observation time to three weeks. During this time interval, benchmark subsidence velocities produced observation differences of systematic character, well above any acceptable limit. This is seen from Table 1 where all measured (single) height differences are listed. 

Surface drainage is usually sparse in areas of thick limestone. Dry valleys are common, although they may be occupied by streams during periods of intense rainfall. Underground streams may appear as vaclusian springs where the water table meets the surface. Occasionally, streams that rise on impervious strata may traverse a broad limestone outcrop without disappearing. 

The Toca do Serrote da Bastiana shelter is small, perhaps 3-4 meters wide, with an overhang of only a few meters. It is located at a limestone outcrop where local inhabitants were, until recently, actively dynamiting the rock to process it to lime by heating on-site. That activity has damaged - and had threatened to destroy completely - the rock paintings in the shelter. There are approximately a dozen images there. 

Tropical dry forests, called tropieal hardwood hammocks or hardwood hammocks in Horida, historically occurred on limestone outcrops in extreme southern Florida. Today, tropical dry forests occur on islands in the Keys, on elevated limestone along the Atlantic coast and as fragments within... 

Paleozoic limestone (Webb et al. 2004). These kimberlites all have similar groundmass mineralogies consisting mainly of carbonate, spinel, and serpentine with lesser monticellite, mica, apatite, and perovskite (Kong et al. 1999) and they are all of volcaniclastic facies near ground surface. Varying thicknesses of clay and fine marine sediments of the Tyrell Sea ( 4000 - 12000 years BP) and 1 to 4 m of peat overlie kimberlites (Fraser et al. 2005). Bioherms composed of coral and skeletal remains of other marine organisms sometimes outcrop. 

Not all mine drainage or natural runoff from rock outcrops are acidic, even when extensive sulfide oxidation is present. Synthetic cyanide solutions, which are often used to extract gold and other metals from ores, can greatly increase the alkalinity of mining wastes and neutralize sulfuric acid (Craw et al., 1999). In other cases, the sulfuric acid is effectively neutralized by alkaline soils, limestones, dolostones, marbles, shams, or other carbonate-rich rocks (Pfeifer et al., 2004, 219 Razo et al., 2004 Lee, Lee and Lee, 2001, 491 Mendoza et al., 2006). Reactions between calcium carbonate and sulfuric acid may precipitate gypsum (CaS04 2H20). 

Halley R.B. and Evans C.C. (1983) The Miami Limestone A guide to selected outcrops and their interpretation. Miami Geological Society, 67 pp. 

Fig. 11.16 Study area of the Judean Mountains, central Israel. Limestone and dolomite (Cenomanian-Turonian) outcrops serve as recharge areas into a phreatic aquifer, confined on the flanks by younger chalk (Senonian). (From Mazor and Kroitoru, 1987.)...

The outcrops of very old Archean rocks are few and thus may not be representative of the original sediment compositions deposited. Nevertheless, it appears that carbonate rocks are relatively rare in the Archean. Based on data from the limited outcrops, Veizer (1973) concluded that Archean carbonate rocks are predominantly limestones. During the early Proterozoic, the abundance of carbonates increases markedly, and for most of this Era the preserved carbonate rock mass is typified by the ubiquity of early diagenetic, and perhaps primary, dolostones (Veizer, 1973 Grotzinger and James, 2000). In the Phanerozoic, carbonates constitute 30% of the total sedimentary mass, with sandstones and shales accounting for the rest. The Phanerozoic record of carbonates will be elaborated upon in the subsequent text. 

Figure 4 Stromatolitic limestone, Cheshire Formation, Belingwe belt, Zimbabwe (2.6-2.7 Ga old) (a) outcrop surface—structures occur on a variety of scales, from microscopic to metre relief (b) detail of one outcrop (from Nisbet, 1987) and (c) shallow-water shale associated with Cheshire stromatolites.

The lower unit of the Ohio Shale which is present in the outcrop area of eastern Kentucky is the Huron Member. Primarily, the Huron consists of black to brownish-black to gray-black, laminated, siliceous, OM-rich shales. Calcareous laminae, cone-incone limestone, dolomitic gray shales, dolomite beds and biotur-bated greenish-gray shales occur as interbeds and laminae in the lower parts of the member. Pyrite occurs as framboids, nodules, and irregular forms. 

Figure 11.15 Changes in Eh, pH, dissolved oxygen and HS" in the direction of ground-water flow in the Lincolnshire Limestone aquifer, U.K. Distances are measured from the outcrop area, which is oxidizing, to deeper, confined portions of the formation downdip, where the groundwater becomes anaerobic. After D. R. Champ and J. Gulens, Oxidation-reduction sequences in groundwater flow systems. Can. J. Earth Sci. 16 12-23. Copyright 1979 by NRC Research Press. Used by permission.

Fig. 7. Schematic north—south cross-section through San Antonio and the Muil Field (see Fig. 1). Jurassic and Lower Cretaceous sediments (the aquifer ) are shown by the limestone Pattern since most are carbonates. They are overlain by Upper Cretaceous clay and chalk. The northern-most outcrops are associated with the Balcones Fault zone near San Antonio. The shallow part of the section is underlain by Paleozoic basement , or by Triassic rocks further south. Jurassic salt is shown by solid hatchures. Darkened areas at A, B and C depict the three producing zones, the Stuart City Reef Trend (the carbonate platform margin), the Karnes Trough and the Atascosa Trough, respectively. Note the faulting associated with them. The temperature axis is speculative below 5 km.

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