The Depositional Environments Of The Six Facies Displayed

2414 Words10 Pages
1. The depositional environments of the six facies displayed in Figure 1 are as follows:
• Fore reef (dark blue)-The mudstones indicate a low energy environment and small amounts of skeletal fragments creating a wackestone, suggesting an infrequent presence of organisms. The conglomerates have formed due to gravity driven flows.
• Reef crest (orange) - Indicated by the presence of red algae and Schleractinian corals e.g. .Acropora (Oppen, at el, 2000), which suggests a low energy crest.
• Lagoon (light blue) - Ooids can precipitate in depths up to 15m (but usually within the top 5m) indicating a shallow water environment. Green algae and foraminifera represent a lagoon floor environment whilst the skeletal grainstones are more
…show more content…
2. The facies distribution in both layers indicate that this platform has a rimmed shelf geometry, most likely an accretionary rimmed shelf, however there is not enough distal data to determine how steep the fore reef slope is, see Figure 9 (Read, 1985). This platform follows a distal to proximal trend moving from East to West. Within layer A, the facies in well A are fore reef and reef crest. Moving westwards, the abundance of the fore reef decreases as water depth decreases, allowing the reef and lagoonal facies to become more abundant. The lagoonal facies in well B will have a higher concentration of skeletal grainstones than green algae as it will be closer to the lagoon barrier than well C. Well C is dominated by lagoonal facies with a small amount of a lower intertidal zone facies, indicating a more proximal environment. Wells D, E and F are dominated by lower intertidal zones with small deviations into lagoonal and upper intertidal zone facies. The abundance of anhydrite and gypsum facies increases moving westwards as the platform becomes more proximal and may be moving into a supratidal facies.
Within layer B, the platform begins with a fore reef slope and reef crest for the first 4km, followed by facies exhibiting a steady decrease in energy moving westwards (oolitic grain stones to mudstones and wackestones). These layers differ as layer A has a larger reef crest and a lagoon which extends more distally. The larger reef could lead to the larger
    Get Access