Non‐marine carbonate: wherefore art thou?

ABSTRACT Diatoms are common in terrestrial freshwater carbonate environments, but their influence on the resulting carbonate texture and porosity remains unquantified. This study investigates the effect of diatoms on the textural variability and syndepositional porosity of spring-associated carbonate coated grains from a freshwater spring in Henry Cowell State Park, northern California, USA. Carbonate coated grains (n = 60) were collected from the distal-most pool of the spring (∼ 300 m from the spring source) and the porosity of the 1 cm diameter fraction (n = 20) was determined using the ImageJ software by adjusting the threshold size for pores > 1000 μm2. Results reveal a strong positive correlation between the number of pores and the number of diatoms examined in each coated grain (r = 0.77). There is a moderate positive relationship between the length of the largest diatom and the minor-axis diameter of a best-fit ellipse of its corresponding pore (r = 0.60). The total pore area for pores associated with at least one diatom was significantly greater than the total pore area of pores that did not enclose diatom frustules (t = 1.80, p < 0.05). Textural observations show that fine-grained laminated textures contain fewer diatoms than the porous textures, suggesting that diatoms disrupt lamination continuity by introducing pore space. These findings have implications for the influence of diatoms on the syndepositional porosity of carbonate rocks from the Cretaceous to Recent and may help explain textural differences between modern marine carbonate microbialites and their Precambrian counterparts.

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The great Bahama Bank; studies in marine carbonate sediments

American Journal of Science ◽

10.2475/ajs.s5-16.93.239 ◽

1928 ◽

Vol s5-16 (93) ◽

pp. 239-246 ◽

Cited By ~ 2

Author(s):

R. M. Field

Keyword(s):

Carbonate Sediments ◽

Great Bahama Bank ◽

Marine Carbonate

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Origin of Boron and Brine Evolution in Saline Springs in the Nangqen Basin, Southern Tibetan Plateau

Geofluids ◽

10.1155/2018/1985784 ◽

2018 ◽

Vol 2018 ◽

pp. 1-12 ◽

Cited By ~ 1

Author(s):

Ji-long Han ◽

Feng-qing Han ◽

Syed-Asim Hussain ◽

Wen-yu Liu ◽

Xiu-qing Nian ◽

...

Keyword(s):

Tibetan Plateau ◽

Volcanic Rocks ◽

The Tibetan Plateau ◽

Molar Ratios ◽

Marine Carbonate ◽

O Isotopes ◽

Saline Springs ◽

Crustal Origin ◽

D Values ◽

Saline Spring

The Nangqen Basin is a typical shearing-extensional basin situated in the hinterland of the Tibetan Plateau. It contains abundant saline spring resources and abnormal trace element enrichments. The hydrochemical molar ratios (Na/Cl, B/Cl, and Br/Cl), H-O isotopes, and B isotopes of the saline spring were systematically measured to describe the evolution of brines and the origin of the boron. The sodium chloride coefficient of the water samples in this area is around 1.0 or slightly greater, which is characteristic of leached brines; the highest B/Cl value is 4.25 (greater than that of seawater). The Na/Cl, B/Cl, and Br/Cl values of the springs are clear indicators of a crustal origin. Theδ18O values of the spring waters range from −12.88‰to −16.05‰, and theδD values range from −100.91‰to −132.98‰. Meanwhile the B content and B isotopes in the saline springs are in the ranges of 1.00 to 575.56 ppm and +3.55‰to +29.59‰, respectively. It has been proven that the saline springs in the Nangqen Basin are a type of leached brine, suggesting that the saline springs have a terrestrial origin. Theδ11B-B characteristics of the springs are similar to those observed in the Tibetan geothermal area, indicating that these two places have the same B source. Moreover, they have a crustal origin (marine carbonate rocks and volcanic rocks) instead of a deep mantle source.

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