Sharp------> gradational-------> amalgamated
– Bedding planes:
– Non-deposition, erosion, or change in depositional regime
• Note the time significance of ―non-deposited strata‖ • Sedimentary record is sparse; More time, with NO deposition, than record.
– May (in conjunction with other facies characteristics) be indicative of Sedimentary Depositional Environment.
• • • • Primary Current Induced structures. Biogenic Structures. Deformational Structures. Secondary Mineralization.
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– Biogenic structures nfluenced by:
Biogenic Structures; Mode of Living
• Discrete burrows:
• Form and shape
– – – – Vertical escape artists: Skolithos Horizontal grazers: Zoophycus/Nereites 3D miners: Cruziana Glossifungites » ―Hard-rock‖ miners: burrows into firm substrate
Primary Current-Induced Sedimentary Structures
Climbing ripples
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Planar-tabular x-beds
trough x-beds
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Deformational Sedimentary Structures
• Desiccation
• Ethological approach (environmental conditions determine organisms behavior –> sedimentary record). • Abundance of life. • Types of organisms (plants, animals; Single/ multicellular etc). • Mode of living.
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Sedimentary Structures
• Features preserved in sedimentary strata that indicate.
• Physical, • Biological, and. • Chemical processes and conditions during and after deposition.
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Primary Current-Induced Sedimentary Structures
• Types of bedding (mechanical aggradation)
• Horizontal stratification
– Suspension settling: vertical accretion – Graded bedding:
Mud cracks, clear indication of subaerial exposure
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Biogenic Sedimentary Structures
• Syndepositional modification of sediment by biological agents.
– Indicative of particular sedimentary depositional environments
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Primary Current-Induced Sedimentary Structures
• Accretionary and Erosional
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Sedimentary Depositional Environments
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Distinctive and Common Stratigraphic Successions
• Vertical successions principally identified by lithology, associations and vertical arrangement of sedimentary structures
Primary Current-Induced Sedimentary Structures
• Bedding:
• lithologic, textural, structural homogeneity indicating discrete time intervals of essentially constant (or constantly changing) deposition
• Regular variation in particle size in an individual bed (constantly changing hydrodynamic conditions)
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• Types of bedding (mechanical aggradation)
– Bedding:
• lithologic, textural, structural homogeneity indicating discrete time intervals of essentially constant (or constantly changing) deposition
Primary Current-Induced Sedimentary Structures
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• Types of bedding (mechanical aggradation)
– Traction: lateral accretion from bed load
• Cross stratification – Scale » Cross laminations; < 3cm amplitude, < 40 cm λ » Cross beds; > 10cm amplitude, > 10cm λ – Planar tabular cross Strat vs trough cross Strat
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Primary Current-Induced Sedimentary Structures
• Erosional (scour):
– Bedding contacts:
• Sediment removal by currents • Change in depositional regime
– Vertical accretion: parallel horizontal layers – Lateral accretion
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– Accretionary/Aggradational:
• Physical, chemical, biological accumulation
Mud cracks, clear indication of subaerial exposure
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Sedimentary Depositional Environments
• Siliciclastic
– Short – Long
• Carbonate
– Rimmed margins – Ramps – Patforms
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Biogenic Structures; Mode of Living
– Vertical accretion: parallel, horizontal layers
• Typically suspension settling/chemical aggradation
– Lateral accretion; Traction transport
• Beds > 1cm • Laminations < 1cm
Sedimentary Structures and Preliminary to Sedimentary Environments
Understanding what sedimentary structures mean in terms of physical, biological, and chemical processes that occurred during, shortly after, and subsequent to deposition is the starting point for the analysis of sedimentary rocks and the environments in which they were deposited. Knowing something about fluid dynamics, ecology, and chemical processes is useful!