( 0/24/Sil/NY-CXU) (Clinton fm) What are oolites formed by? Are they primary or secondary? Does anyone know?ħ. Do these grains look like ( 0/2/Hol/Bah) or ( 0/6/HOL/G.S.L,Ut)?Ħ. Sketch way oolites are undergoing solution pressure. ( 0/23/Carb/Aust-CIZ) (Glenbaun Dam, New South Wales) and ( 0/22/Carb/Aust-CJC) (Glenbaun Dam, New South Wales). Do you see an "alignment fabric" of ooids at low power? Can you explain it?ĥ. What are nuclei? Compare grains with 0/22. The concentric, somewhat scalloped coatings are either blue-green algae encrustations or caliche concretions make a sketch to show how their structure differs from ordinary oolites. ( Pis/1/Pm/NMx-BWP) (Yates formation, Guadalupe Mts.) These are pisolitic grains.
( 0/21/PaNMx-BRP) (Virgilian rocks of Sacremento Mts.) How would you define the allochems of this rock? What is their origin?Ĥ. ( 0/31)- Note micritization of ancient oolites.ģ. Are there any superficial oolites? Note presence of oolites and other grains cemented by micrite. ( 0/20-Jur/Eng).-CKK (Osmington Oolite, Jurassic England) Note prevalence of terriginous nuclei. What is average size of cement-express as mm. (Newman limestone) Some nuclei are crinoid fragments, which extinguish as one unit. For all the following slides, in addition to the complete rock name list the thickness of the oolite coating, the structure of the oolite (whether radial, or concentric or both).Ī. This is a typical "ancient" oolite of lower Paleozoic or lower Mesozoic age. O/1 has excellent oolites with combined concentric and radial structure, What nuclei are present? Note superficial oolites with one coating. What is happening to some oolite corteses?ġ. ( O/11/Plei/Bah) is a Pleistocene oolite rock from Bimini, the Bahamas. ( O/7/Hol/Bah-24941) is a cemented dune sediment from Joulters Cay. This fabric is common to many ancient oolites which suggest the radial fabric is primary.ĥ. The blotchy grains are cut where the thin section plane does not pass through the nucleus. These oolites are composed of concentric aragonite and radial crystals. ( O/6/Hol/GSL.Ut-EZD) is of oolites from the Great Salt Lake, Utah. These are superficial oolites, in that they have very thin cortices.Ĥ. ( O/5/Hol/Sh.B,-EGH) is from Shark Bay, Australia. Are these also ooids? Compare the two samples and interpret the differences.ģ.
This is from same shoal but closer to the edge. ( O/4/Hol/AbuD-EWK) was collected from the interior of an oolite shoal in Abu Dhabi. What causes dark blotches in layers? What are nuclei. Note concentric coats to these aragonite grains. ( O/2/Hol/Bah 25608) is a recent oolite from a shoal south east of Joulters Cay. Occasionally ooids are washed into areas of ooze deposition or grow in such areas - although these settings are unusual, they may be of considerable environmental significance.ġ. These rocks are commonly well-sorted and cross-bedded. Most oolitic rocks have a sparry matrix (are oosparites) because the formation of ooids seems to require abundant agitation associated with water movement which seems to remove the bulk of microcrystalline ooze. If a better understanding is required than is provided in this set of exercises you are referred to the more extensive descriptions provided on this site under the heading of carbonate petrology. This group of exercises links to the thin section catalog and investigates ooids and oolitic rocks.
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