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Examination: Sedimentary Petrography/Diagenesis & Carbonates and Evaporites WS 12/13

Last name: First name: Matr.-Nr. You can reach a maximum score of 40 points; a minimum score of 20 points is required to pass the test. Good luck! Please, answer the following questions:

01. Interpret the depositional environment (e.g.: relative water depth and water energy) and give a paragenetic sequence (relative timing of diagenetic events) for the thin-section shown below. In which diagenetic zone was the rock cemented? On which thin-section observation did you base your interpretation? (6)

Remark: The photograph was taken under plane polarized light (ppl). There is no open porosity in this thin-section.

~1.0 mm

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02. Which cement type is present in the thin-section shown below? In which diagenetic zone was the rock likely cemented, if the mineralogy of the cement is low-magnesium calcite with a d18O value of -3 permil? Please give reasons for your interpretation (2)

Remark: ppl, blue epoxy-resin was used to highlight open porosity.

03. Name the dominant porosity type (open and/or closed) for each of the two thin-sections shown below using the Choquette & Pray (1970) porosity classification. (2)

PPL, porosity is cemented PPL, blue epoxy-resin 04. What are the problems of the facies model of Wilson (1975)? Name and explain three points where the facies model might differ from real world examples (3)?

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05. The diagram below shows the relationship between p-wave velocity and porosity for carbonate rocks with various pore types. An exponential best fit curve (black line) through the data is shown for reference. Different pore types cluster in the porosity velocity field, indicating that scattering at equal porosity is caused by the specific pore type and their resultant elastic property. Rocks with moldic pores show on average higher velocities compared to rocks with e.g. interparticle pores (for a given porosity). Explain why (4).

. 06. Define the terms heterotrophy and autotrophy. Give one example for a heterotrophic and one example for an autotrophic carbonate-producing organism. (4) 07. Which environmental parameters favour the growths of modern, tropical coral-reef systems, with respect to: temperature range (in °C), nutrients (l ow or high), salinity (low/normal/high), suspended sediments (low/high). (4) 08. Draw a table showing the Dunham classification (Dunham, 1962) of carbonates (for which the depositional texture is recognizable). The table should indicate the criteria which are used to distinguish between the Dunham classes. (5):

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09. Describe the given thin-section petrographically: Please list the dominant components (> 10%; such as bioclasts, intra- and extraclasts, ooids, oncoids, …). Describe important diagenetic events (e.g. Compaction, cement and porosity types, including closed porosity). Classify your sample according to the Folk scheme and to the Dunham scheme. Use the diagrams on the following pages to derive the most likely Wilson Zone for your sample. Discuss your interpretation based on additional petrographic evidence (10). Remark: The photograph was taken under plane polarized light (ppl). There is no open porosity in this thin-section.

0.4 mm

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