GEOL 340 Sedimentology and Stratigraphy
Lecture 8
1. Classification of Sedimentary Structures
2. Stratification and Sedimentary Structures
Classification of Sedimentary Structures
Descriptive Classification
stratification and bedforms
bedding and lamination
bedforms and stratal geometries
cross-lamination
irregular stratification
bedding-plane markings
other structures
Genetic Classification
sedimentary process (depositional) structures
erosional structures
soft-sediment (penecontemporaneous) structures
biogenic (trace fossil) structures
Stratification and Sedimentary Structures
Bedsets = groups of beds
Internal Stratification of Bedsets (Cross-Beds) (Fig. 4.13,
p. 100)
tabular cross-bedding = laterally broad with respect to thickness
(Fig. 5.13)
planar-bedding and planar-laminae = parallel to bounding bedding
planes
trough cross-bedding = bounding bedding planes or surfaces are
curved (Fig. 5.14)
inclined with respect to bounding bedding planes
Cross-Beds = mostly from ripple migration
Graded Bedding
normal = coarser grains at bottom = turbidity currents plus others
reversed = coarser grains at top = beaches, pyroclastics, others
Massive Bedding = homogeneous and lack internal structure
in many cases = 100% bioturbation
Ripple Marks = unidirectional or oscillatory
foresets (lee side) and bottomsets (stoss side) (Fig. 2.8, p.
38)
ripple cross-lamination (climbing ripples) = rapid sed rates
(Fig. 4.15, p. 101)
flaser bedding = mud/silt between sand laminae, fluctuating hydrology
laminae are laterally continuous (Fig. 4.19, p. 103)
lenticular bedding = interbedded mud and sand
laminae laterally discont., mud preservation favored (Fig. 4.20,
p. 104)
hummocky cross-bedding = concave-up and convex-up
formed by strong oscillatory surges?? (Fig. 4.21, p. 104)