Learn about sedimentary structures, such as laminations, cross bedding (planar vs trough cross bedding, herringbone cross stratification, & hummocky and swaley cross stratification), ripples, graded bedding, growth bedding, and mud cracks!
In this video, we start with defining beds, strata, and laminations, and the geometry of bedding. Then we discuss planar laminations, such as varves or tidal rhythmites and the depositional environments where laminations form (calm waters such as lower shorface, pelagic marine, glacial lakes or glaciomarine, or low energy tidal environments). Then we move on to planar and trough cross stratification & the depositional environments where cross bedding is common, such as eolian (desert), middle to upper shoreface (or lower shoreface during storms), high energy tidal, and fluvial (river) environments. Then we discus hummocky and swaley cross bedding and then herringbone cross bedding. Since cross bedding is the result of dune or ripple migration, we also go over the difference between dunes and ripples (which is just scale). However, ripples can also appear on the tops of bottoms of preserved beds in which they can further narrow the possible depositional environment. There are symmetrical and asymmetrical ripples. Asymmetrical ripples form due to unidirectional flow, such as a river, and symmetrical ripples form in bidirectional flow regimes, like some tidal systems or mid-upper shoreface environments because waves are symmetrical orbitals that only become directional when their base hits the sediment near the beach/foreshore. Then we touch on climbing ripples which indicate waning flow such as upper sections of turbidite sequences (Bouma sequences) or when fluvial environments flood and flow velocity decreases and deposition occurs. Then we go over heterolithic bedding like flaser, wavy, and lenticular bedding and how it may form in tidal, fluvial, or glacial environments. More mud (lenticular bedding) indicates calmer waters (low energy systems). Graded bedding is typical of the base of Bouma sequences caused by turbidity currents. Growth bedding is typically of chemical precipitation (chemical sedimentary rocks) such as evaporites. And lastly, mud cracks form due to dessication of mud in dry environments.
References: Sedimentary Rocks by Pettijohn: https://amzn.to/3tnWuVu
Sedimentology and Stratigraphy by Boggs: https://amzn.to/31VIG9x
GEO GIRL Website: https://www.geogirlscience.com/ (visit my website to see all my courses, shop merch, learn more about me, and donate to support the channel if you'd like!)
0:00 beds vs. strata vs. laminations
2:12 bedding geometry & lateral continuity
3:36 planar lamination depositional environments
5:45 seasonal laminations (varves)
6:55 tidal rhythmite laminations
7:43 lamination preservation requires low O2
8:44 planar vs. trough cross bedding
11:05 hummocky & swaley cross bedding
12:17 herringbone cross bedding
14:44 dunes vs. ripples
16:12 symmetrical vs. asymmetrical ripples
18:01 climbing ripples
20:09 flaser vs. wavy vs. lenticular bedding
21:51 graded bedding & turbidites
25:29 growth bedding
26:55 mud cracks
28:17 related videos & references
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