Geology Reference
In-Depth Information
Peritidal
Shelf Shelf Slope Basin
margin
Stratification
Planar lamination
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Wavy lamination
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Crinkled lamination
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Planar thin bedding
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Wavy thin bedding
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Crinkled thin bedding
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Planar thick bedding
o
o
o
o
o
Wavycrinkled thick bedding
o
o
Hummocky crossbedding
o
o
Largescale crossbedding
o
o
o
o
o
Waveripple crossbedding
o
o
o
o
o
o
o
o
o
Heterolithic crossbedding
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Smallscale crossbedding
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Graded bedding
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Cracks
Mud cracks
o
o
o
Prism cracks
o
o
o
o
Sheet cracks
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Fenestrae
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Breccias - Conglomerates
Stormlag lithoclast gravels
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Channellag gravels
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Edgewise gravels
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Imbricate gravels
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Limestone breccias
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Submarine hardgrounds
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Neptunian dykes
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Deformation structures
o
o
o
o
Nodular structures
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Biogenic structures
Microbial laminites
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Stromatolites
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Thrombolites
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Bioturbation
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Diagenetic structures
Caliche
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Tepee
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Solution pores
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Evaporite minerals
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Chickenwire sulfates
o
o
Deformed sulfate layers
o
Fig. 3.4.
Common field criteria of carbonate rocks
include stratification types as well as sedimentary and diagenetic structures.
The processes causing many of these structures are highlighted by microfacies data (black dots). The figure considers the
scheme developed by Demicco and Hardie (1994) for shallow-marine carbonates.
fication and interpretation of layering without cross-
stratification, and can be applied both to field and thin-
section observations (see Fig. 3.3 and Pl. 18).
Bed thickness analysis of limestones can be used in
recognizing breaks in sedimentation, cyclic sedimen-
tation patterns and gradual environmental changes.
These investigations are based on the hypothesis that
the thicknesses of stratigraphic units follows a lognor-
mal distribution (Lumsden 1979).
Many beds are internally differentiated into lami-
nae and a number of informal units. Laminae result from
short changes in the depositional conditions causing
variations in grain size, composition and texture, fossil
content as well as the content of non-carbonate and or-
ganic material. Small-scale laminations of fine-grained
limestones assist in recognizing of yearly varves, dis-
tal turbidites or tidal rhythmites (Brown et al. 1990;
Archer and Feldman 1994). Fine-scale biogenic lami-
nation is particularly common in lagoonal and lacus-
trine sediments; stratification types of lake sediments
were classified by Cole and Picard (1975) and Bull-
winkel and Riegel (2001).
Internal layers and laminae that are essentially par-
allel to the bedding planes constitute a planar stratifi-
cation or planar lamination (Fig. 3.3). A practical key
(3)
Composition and internal structure
: Beds ap-
pearing internally homogeneous (massive, structure-
less) in the field, may exhibit textural and structural
inhomogenities when studied using staining and etch-
ing methods, ultra-thin sections, X-ray or tomography
(Larsen and Theide 1971; Kenter 1989).