Exercise 2.4. Identifying Sedimentary Facies
What To Do
Click here to download Tables 2.4, 2.5, and 2.6 as a PDF file.
Tables 2.4-2.6 explore idealized sedimentary facies in both clastic and carbonate environments. These facies models have been compiled by many geoscientists examining sediments in modern depositional environments.
Use your new knowledge of modern depositional environments and the idealized sedimentary facies tables to determine the ancient depositional environment for each of the observed sedimentary facies descriptions below.
Your Lab 2 worksheets include a form to record your answers.
Note: Tables 2.4 to 2.6 can seem a little overwhelming at first. Don’t Panic. You are not expected to memorize these tables, but you do need to learn to navigate your way around them and become familiar with them. You will be able to refer to copies of these tables on both lab exams.
Sedimentary Facies Descriptions
1. Intermixed coarse gravel and boulders grading laterally (sideways) to sheets of gravel, sand, and clay with fine laminations; asymmetric current ripples.
2. Mature, tan coloured, 10 metre-scale cross-beds in sandstone; reptile skeletons.
3. Medium to large-scale cross-bedded dunes, abundant Cruziana trace fossils.
4. Halite, gypsum interbedded with micrite, nodular siltstone, mud cracks and algal laminations.
5. Erosional surfaces beneath sandstone and siltstones with cross-beds and lenses of ripple cross laminations in repeated fining up sequences; in turn overlain by siltstone with root traces.
6. Grey laminated siltstone, black shale, containing thin coal seams and Cruziana trace fossils.
7. Bioturbated shelf deposits overlain by gently dipping beds of cross-bedded sandstone and siltstone topped by sandstone, siltstone and coal. Note: Bioturbated means that sediment that has been burrowed by many organisms so that most sediment layering or structure is destroyed by the mixing action of the burrowing organisms.
8. Massive non-stratified carbonate mounds with skeletal coral; lime mud matrix.
9. Massive, red-brown debris flow cycles: these are unsorted, non-stratified, coarse grained grain-supported gravels showing a rapid lateral decrease to matrix-supported gravel and sand with minor deposits of laminated sand and rare tree root casts.
10. Thick carbonate pellet beds, hummocky units, biosparite and oosparite, abundant horizontal burrows.
11. Biomicrite, unbroken fragile shells, calcium carbonate mud, a small patch reef.
12. Tan to grey, muds and sands with asymmetric cross beds, mud cracks.
13. Pink-brown, immature, grain-supported conglomerate in trough-like beds; fining up to sandstone with conglomerate, mud and plant material.
14. Coarse sands at the base of an upward fining graded bed, laminated sand, laminated mud and deep sea mud.
15. Unsorted, unconsolidated mix of clay, silt, sand, gravel and boulders with some striations on surfaces.
16. Mud and sand, small scale cross laminae, and grey-coloured symmetric cross-bedded sandstones with an eroded surface.
17. Horizontally bedded silts and fine sands cut by occasional elongate deposits of coarser sand deposited perpendicular to the inferred shoreline, marine fossils.
18. Dark grey, finely laminated to massive micrite and the trace fossil Zoophycus.