18-Geol-A3 Sedimentation and Stratigraphy · December 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Geological Engineering, 04-Geol-A3, Sedimentation & Stratigraphy, 2017-Dec. Closed book, 3 hours, no calculator permitted.
Reference texts: Nichols, Sedimentology and Stratigraphy, 2nd ed. (depositional environments, facies models, flow regime and bedforms, carbonate platforms, stratigraphic principles, correlation, sequence stratigraphy); Boggs, Petrology of Sedimentary Rocks, 2nd ed. (weathering, sandstone and carbonate classification, diagenesis); Allen & Allen, Basin Analysis, 3rd ed. (basin classification, subsurface mapping); Tearpock & Bischke, Applied Subsurface Geological Mapping, 2nd ed. (structure-contour, isopach and lithofacies mapping, syndepositional structures).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
| Term | Applies? | Reason |
|---|---|---|
| a) Calcareous planktonic organisms | Yes | Foraminifera and coccolithophores settle from the water column to form calcareous ooze, the classic pelagic sediment above the CCD |
| b) Siliceous-walled planktonic organisms | Yes | Diatoms and radiolarians settle to form siliceous ooze, particularly in high-productivity or below-CCD settings where carbonate dissolves |
| c) Clay minerals | Yes | Wind-blown and current-transported terrigenous clay is the classic hemipelagic (background terrigenous) fraction reaching the open ocean |
| d) Fine-grained quartz | Yes | Wind-blown (eolian dust) quartz silt is a common hemipelagic terrigenous component even far from land |
| e) Fine-grained feldspars | No | Feldspar is chemically unstable and is destroyed by hydrolysis during weathering/transport well before reaching an open-ocean depositional site, so it is not a characteristic pelagic/hemipelagic constituent |
| f) Soil | No | Soil is a subaerial, terrestrial pedogenic product formed in place on land, not a marine depositional facies at all |
| g) Radiolarians & diatoms | Yes | The organisms that build siliceous ooze (same as b, restated as a specific taxon pair) |
| h) Biogenic oozes | Yes | Calcareous and siliceous oozes are themselves the dominant pelagic sediment type by volume across most of the deep ocean floor |
| i) Coral reefs | No | Reef frameworks are shallow, high-energy, photic-zone buildups — the opposite depositional setting from deep, quiet pelagic/hemipelagic sedimentation |
| j) Ooids | No | Ooids require sustained, shallow, agitated-water precipitation (Question 6/9 conditions) that does not exist in the deep pelagic realm |
The applicable terms are therefore a, b, c, d, g and h.
