STRATIGRAPHY AND SEDIMENTATION (SHALLOW MARINE) Flashcards
Weak grains of sediments composed of Feldspar and Lithic Fragments
Labile Minerals and Grains
An authigenic material considered to be a reliable indicator of Shallow Marine Conditions
Glauconite
Greensands are shallow marine deposits rich in glauconite that are particularly common in what strata and what area of the world?
Northern Hemisphere, Cretaceous Strata
This is most intense in Sandy Shallow Marine Enviroment
Bioturbation
How much of the modern shelves are storm dominated?
80% Majority
How much of the modern shelves are Tide Dominated
17%
Shelves that are generally narrow and lie adjacent to strong GEOSTROPHIC Currents in which SANDWAVES and SAND RIBBONS form on them which make them similar to tidal shelves but the driving origin is not tidal
Ocean Current Dominated (3%)
Sea Level Rise for the past 10000yrs
Holocene Trangression
Shallow marine sedimanetatio is domiated by what type of deposits?
Terrigenous clastics
Shallow seas that are not supplied by much terrigenous materials are said to be areas of
Carbonate Sedimentation
What about areas that are cold and are not supplied much by terrigenous materials?
They are STARVED
Textural and compositional characteristics of Shallow Marine Sands
Compositionally and Texturally mature except in polat areas
What are the other distinctive characteristics of Shallow Marine deposits?
Diverse shells and skeletons presered in mudrocks and bicolastic fragments in sands
What kind of organisms dominate shallow marine?
Benthic
Why are primary sed structures not always preserved in Shallow Marine?
Because of High rates of Bioturbation
Type of Shallow Marine Clastic Environments
Storm Dominated
Tide Dominated
Ocean Current Dominated
Facies or parts of a Storm Dominated shallow Clastic Seas
1) Shoreface
2) Offshore Transitio
3) Offshore
These are the SHALLOWER PARTS of the Shelf and epicontinental sea and within the DEPTH ZONE FOR WAVE ACTION
Shoreface
Characteristics of Sand Deposits in Shorface
Wave Ripple Cross lamination
Horizontal Lamination
Flaser Beds(MinS)
Another common feature in Shoreface zone formed by Glows generated by EDDY Currents related to storms and/or wave-driven long shore drift
Sandy Ridges
Zone located between the Fairweather wave base and storm wave base
Offshore transition zone
Sedimentary structure that is thought ot be characteristics of STORM CONDITIONS on a SHELF
Hummocky Cross Stratification
Convex upward (Crests) that dip in all direction at agles 10-20 deg
Hummocks
Areas in between hummocks
Swales
Where concave layers are preserved it is said to be
Swaley Cross Stratification
What Forms HCS and SCS?
Combined flow of Strong Storm Current and oscillatory motion of waves
What are the limiations of HCS and SCS?
Formed only on fine to meium grained sand deposited in offshore transition
Characteristics of a idealized tempestite?
(B-T) NORMALLY GRADED!!!
1. Sharp Erosive Base
2. Structureless Coarse Sand and/or gravel
(First two layers represent scouring and initial deposition)
3. Hummocky-Swaley Cross Stratification in finer sands (Waning of Storm)
4. Overlain by Fine sand and silts with horizontal wave ripple lamination (Decrease in oscillation)
5 Top mud laminations
Characteritiscs of Offshore Zone?
Predominantly mud deposits (w/ Sand only in case of extraordinary storms)
Grey colored because of anoxic environment which allows preservation of organic matter within mud
Charactersitics of a Storm dominated Shallow Marine Envronment?
- Foreshore Beach Deposit of Stratified Sands
- Shoreface
Sandy deposits with symmetric wave ripple lamination, horizontal stratification which may be destroyed by Bioturbation
2.Offshore Transition Zone
Tempestites (Scoured Base, Corase sand and gravel, HCS and SCS in finer sands, Fine sands and silts with wave ripple lamination) - Offshore
Mud with some bioturbation
These are deposited near shorelines thate experience STRONG TIDAL CURRENTS
Offshore Sand Ridges
Characteristcis by TIDAL OFFSHORE SAND RIDGES
Stacks of Cross-bedded and Cross laminated sandstone
Basal Lag Deposits (Lag is kapag naiwan ang coarse seds dahil nawinnow na ung fine particles can be alluvial, fluvial or tidal)
In a mixed storm-tidal shallow marine environment what is the characteristics of deposit
Shallow - Tidal
Offshore Transition - Storm
Forms when velocity of current is 50 cm/s
Low Relief Sand Sheets and Patches with ripple surface
Forms when velocity of current is 50-100 cm/s
Sandwaves (perpendiculat to the lfow with large-scale cross bedding)
Forms when velocty is >100 cm/s
Sand Ribbons (Parallel to the flow and have small scale cross bedding)
Huge sediment supply will cause sand ribbons to amalgamate and form
Sand Ridges
what is the distinctive characteristics of tide dominated clastic shallow seas
Shoreface is dominated by Cross bedded sands that contain fullt marin fauna and lack evidence for any subaerial exposure
The only force that can maintain large subaqueous dune or sandwae bedform
Tide
Reliable indicator of a Tidal Dominated Clastic Shallow Seas
Extensive Sheets and ridges of Cross Bedded Sand Deposit