GEOL 462: Principles of Sedimentology and Stratigraphy

Lecture 12: Tuesday, February 24, 2009

Topics
1. Processes and Sedimentary Facies of Clastic Shelves
2. Deep Marine Processes and Sediment Sources
3. Sedimentary Facies of Deep Marine Environments
4. Submarine Fans System
5. Identifying Features
6. Outline of the Project Report

Processes and Sedimentary Facies of Clastic Shelves
1. Topography and physiology of continental shelves:
    Passive margins;
    Active margins;
    Shoreface; Inner shelf; Middle shelf; outter shelf;
    Seaward shelf barriers;
2. Processes:
    Tides; organisms-bioturbation; storms reworking; density flows;
3. Facies:
    Background deposits: parallel laminated fine-grained sediments (shale, siltstone, very fine-grained sandstone...); bioturbation;
    Event deposits: HCS-bearing sandstone; turbidites; lag deposits

Deep Marine Processes and Sediment Sources
Processes:
1. Gravity: suspension particles setting down by gravity
2. Seismicity-driven turbidite currents, submarine fan system (slope)
3. Geostrophic currents (Thermo-haline currents: T and saline)
4. Organisms: hot springs, methane seeps, other autotrophs
5. Volcanic activities

Sediment Sources:
1. Calcareous ooze, siliceous ooze (Biogenic material: Pelagic);
2. wind-blown dust, volcanic ash, river-derived silt, mud (Terrigenous material: Hemipelagic)
3. Geostrophic currents: mud, silt, fine-grained sand reworked from turbidites

Sedimentary Facies of Deep Marine Environments
1. Background Facies:
a. Calcareous ooze -- Lime mudstone;
b. Siliceous ooze -- Siliceous (chert) laminae;
c. Wind-blown Silt, clay -- Siltstone, shale
d. Volcanic ash, pyroclastic -- Ash beds, volcanoclastic rocks;

2. Event beds:
a. Normal graded bedding;
b. Turbidite beds, occasionally turbidite current form small-scale cross lamination;
c. Submarine Fan: sandstone, conglomerate, siltstone, shale, turbidites, debris flows, ….;
d. Reworked turbidites by Geostrophic currents -- Contourites;

Submarine Fans System
1. A point-source, sand-rich submarine fan system: Similar to a distal alluvial fan system, but is characterized by sand and turbidites, slump blocks, and pinches out to deep marine deposits;
2. A point-source, mud-rich submarine fan system: Similar to alluvial fan system, but is characterized by mud and turbidites, slump blocks, and pinches out to deep marine deposits. Interbedded mudstone and sandstone;
3. A point-source, gravel-rich submarine fan system: Similar to gravel-rich alluvial fan system, but is characterized by turbidites, slump blocks, and pinches out to deep marine deposits. E.g., along active basin margins (fault control);

Submarine Fans System: Sequences
Upwards:
1. Normal deep marine deposits (basin plain)
2. Lower fan: coarsing upwards, with turbidites
3. Middle fan: sandy turbidites, muddy levees
4. Upper fan: coarse channel fills (like river channels), turbidites, debris flow deposits

Identifying Features of Deep Marine Environments
1. Hemipelagic and pelagic mud: very thinly laminated lime mudstone, shale, siltstone, and siliceous (chert) beds;
2. Fe/Mn nodules (anoxic);
3. Turbidites (normally graded beds, Bouma sequences);
4. Slump structures, debris flow deposits, Talus, Avalanche deposits;
5. Negative evidence: NO SHALLOW WATER FEATURES LIKE TIDAL AND WAVE ACTIVITIES