G342 Sedimentation and Stratigraphy Name:________________________Laboratory 7Assoc. Prof. A Jay Kaufman27 March 2006Carbonate environments and sedimentsMost carbonate sediment is produced from chemical or biochemical processes occurring in anenvironment of warm, generally shallow, clear marine water. Organisms contribute to detrital deposits ofvarying grain size size and also form large masses of precipitated limestone.Because most carbonate is organically produced, it is basically autochthonous, i.e., it is producedwithin a given basin and has not been transported from a distant source area by rivers and streams. Thisresults in a fundamental difference in the textural interpretation of detrital carbonates and terrigenousclastics. Because of the local origin of carbonate particles, variations in shape, dimension, mineralogy, andinternal structure may control the ultimate shape and size of particles much more than physical agents ofabrasion through transportation and deposition.Modern carbonate classifications are based primarily on the presence or absence of originalcarbonate mud and on types of grains. The amount of mud matrix is considered a better guide to currentenergy and transport mechanisms than grain size or shape.Carbonate facies patterns are controlled by basin configuration and water energy. Depth controlswater energy and also light, which enhances abundant biological activity in the photic zone. These factorsinteract to produce basic carbonate facies patterns on or bordering shallow water platforms or shelves intectonically stable areas.The following samples are examples of loose grains and calcareous algae from Florida Bay. Look at thesamples under the binocular microscope and for each sketch (with scale) identify the major allochems andindicate the carbonate mineralogy (see table provided in class). 1. Shell fragments in lag depositWhat composes the majority of the allochems? On what do these animals mostly feed? What might youexpect to flourish in the absence of these animals? In other words, what structures common to thePrecambrian might be present in modern environments?2. Halimeda algaeBased on the book Marine Plants of the Caribbean what species of Halimeda are present in the twospecimen trays? In what range in water depths are these commonly found?3. Penicillus algaeWhat species of Penicillus are present in these specimen trays? At what depths do they thrive? What typeof allochems do you think would be made by the breakdown of Penicillus fragments? Are these more orless durable than Halimeda fragments?4. Udotea or Avrainvillia algaeWhat family and species do you think these specimens represent? What range of water depths is common for these calcareous algae?5. Loose Halimeda and other shell and algal fragmentsWhat percentage of each allochem type is recognizable in the loose specimen? Is there any evidence ofboring (endoliths) in any of the shelly materials?6. Gelatinous mudFrom fragments of what calcareous algae would you suggest this mud was formed? What are some otherpossible sources of the mud?General question of specimen set from Florida Bay:What allochem type is conspicuously absent in these samples? Give a reason for the lack of theseallochems based on the depositional environment of Florida Bay.Petrographic analysis (include scale in all drawings)7. Oolitic limestoneMake a sketch of the center grain and surrounding matrix. Define and label the core, cortex, andmatrix cement. What is the grain size of the matrix? Why might you call this coated grain agrapestone?8. Siliceous ooliteSketch the field of view and focus on the crystal orientation. How many generations of cement canyou identify? In your drawing label cores, cortices, and cements. How do the cores and cortices differfrom the oolitic limestone sample?9. TufaEstimate the percentage of pore space (fenestrae) to mineral in this thin section. Is it allocthonous orautochtonous? What environment of deposition do you suspect for this rock? For a good view of asimilar rock go to the Physics lobby and sketch a portion of the facing stone on the walls.10. LimestoneMake a sketch of the stylolite and define the term. What is concentrated in the stylolite seam, and howmight it have formed? Illustrate the rhombs, stylolite, and clay minerals. How might the clays beenformed or transported into the depositional environment?11. DolomiteWhat is the characteristic shape of the dolomite crystals in the field of view? Do you think these wereprimary precipitates or diagenetic artifacts? How might these euhedral crystals have formed? Whatchemical or other conditions are necessary for dolomite