Carbonate reaction and condition for carbonate precipitation or dissolution o

Carbonate reaction and condition for carbonate

This preview shows page 2 - 4 out of 6 pages.

Carbonate reaction and condition for carbonate precipitation or dissolution o The solubility of CO2 in water is greatest at low temperatures and high pressures Surface water is less acid than deeper water, because the deeper the water, the lower T and higher P What is dolomitization and conditions that favor it o The process by which limestone is altered into dolomite This process creates secondary porosity o Conditions: High Mg2+/Ca2+ ratio in fluid High temperature Lack of sulfate (SO42-) Three forms of carbonate o Carbonate grains Silt to sand-sized grains, but larger particles of fossil shells Either skeleton or non-skeleton grains 5 types: Skeletal particles o Skeletal grains Skeletons differ widely in size and shape Skeletal materials are subject to mechanical abrasion & destruction by waves and currents; and bioerosion by boring organisms such as sponges, bivavles, algae Most common kind of grain in carbonate rocks Carbonate clasts o Non-skeleton grains o Carbonate rock fragments Derived by erosion of ancient limestone exposed on land (‘extraclasts’) or derived by erosion of carbonate
Image of page 2

Subscribe to view the full document.

sediments within the same depositional basin (‘intraclasts’) Range in size from very fine sand to gravel, show some degree of rounding, indicative of transport Ooids o Non-skeleton grains o Round grains, have a concentric internal structure: layers of carbonate around a nucleus o Formed through chemical or biological precipitation by the rolling action of waves on beaches o Require agitated or constantly moving water o Sediment consisting of ooids are called oolites—excellent reservoirs Peloids o Non-skeleton grains o Small (<2mm) spheroidal or oval particles of fine grained carbonate with no internal structure Various origins Most originate: fecal pellets or microbial breakdown of other particles o Fecal pellets- organic excrements generally produced by mud- eating grazing animals (crustaceans, worms, mollusks) Most 0.1-0.4 mm in diameter Round to oval shape Dark brown color Aggregates o Microcrystalline calcite Fine grains (<0.03mm) Carbonate mud (or lime mud) may contain small amounts of fine-grained detrital minerals such as clay minerals, quartz, feldspar, and organic matters Micrite as matrix among carbonate grains or form most of limestone Breakdown of calcareous algae Chemically precipitated Modern Ca-mud origin organic processes, mainly aragonite Deposition under quiet-water conditions o Sparry calcite Crystals in pore-spaces Large crystals (0.02~0.1mm) formed during diagenesis Distinguished from micrite by their larger size and clarity and from carbonate grains by their crystal shapes and lack of internal texture Indicates that grain framework voids were empty Deposition under high-energy flow condition Can also form by recrystallization of primary depositional grains and micrite during diagenesis Depositional environments: Dr. Wilson’s lecture
Image of page 3
Image of page 4
  • Fall '14
  • YanxiaMa
  • Geology, Dolomite

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Ask Expert Tutors You can ask 0 bonus questions You can ask 0 questions (0 expire soon) You can ask 0 questions (will expire )
Answers in as fast as 15 minutes