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Page 1: Fluvial Systems and River Dynamics

• Fluvial systems

  • Definition: River systems responsible for

    • Sediment transport across continents

    • Erosion and denudation

    • Formation of depositional environments

• Sinuosity of a river

  • Defined as the ratio of the river's length along its thalweg (deepest channel) to the straight-line distance between endpoints.

• Main types of rivers

  • Meandering, braided, anastomosing, and straight rivers.

• Oxbow lake

  • Definition: A crescent-shaped lake formed when a meandering river cuts off a bend, isolating it from the main flow.

• Floodplain deposits

  • Fine-grained sediments deposited when rivers flood and sediment settles on the adjacent plain.

• Crevasse splay

  • Definition: A small, delta-shaped body of sediments deposited when a river breaks through its levee.

• Braided rivers

  • Characteristics: Low sinuosity, multiple shallow channels, high bedload, and coarse deposits.

Page 2: Sedimentary Deposits and Structures

• Point bars

  • Depositional features on the inner bends of meandering rivers with upward fining sediment layers.

• Turbidites

  • Definition: Sedimentary deposits formed by turbidity currents, marked by graded bedding.

• Bouma sequence

  • A characteristic sequence of turbidite layers from coarse (Ta) at the base to fine (Te) at the top.

• Carbonate compensation depth (CCD)

  • The ocean depth below which carbonate dissolves faster than it accumulates.

• Stromatolite

  • Layered sedimentary structures created by cyanobacteria trapping and binding sediments.

• Hjulstrom diagram

  • Graph showing the relationship between particle size, fluid velocity, and thresholds for erosion, transport, and deposition.

• Sedimentary structures

  • Features indicating deposition or post-depositional processes, including ripples, cross-bedding, and mud cracks.

Page 3: Fossils and Flow Dynamics

• Trace fossils (ichnofossils)

  • Sedimentary structures formed by biological activity (e.g., burrows and footprints) providing clues to depositional environments.

• Reynolds number

  • Dimensionless number determining whether flow is laminar or turbulent; calculated as inertial forces divided by viscous forces.

• Froude number

  • Dimensionless number representing the ratio of flow velocity to the velocity of gravity waves, indicating tranquil or rapid flow.

• Stokes’ Law

  • Formula describing the settling velocity of particles in a fluid, dependent on particle size, fluid viscosity, and density differences.

• Saltation

  • Movement of sedimentary particles in a fluid flow where they bounce or jump intermittently along the bed.

• Delta

  • Landform created by sediment deposition where a river enters a standing body of water like a lake or ocean.

Page 4: Depositional Features and Layers

• Levees in a fluvial system

  • Elevated ridges along a river channel formed by sediment deposition during floods.

• Varves

  • Thin layers of sediment, typically in glacial lakes, representing annual deposition cycles.

• Sedimentary basin

  • Low area in the Earth's crust where sediments accumulate over time.

• Terminal splay

  • Fan-shaped sedimentary deposit formed when a river loses flow into the substrate or due to evaporation in arid climates.

• Chemostratigraphy

  • Study of chemical variations within sedimentary rocks to correlate and date strata.

• Bouma layers

  • Five distinct layers (Ta to Te) in a turbidite deposit, reflecting various sedimentation processes.

• Wackes vs Arenites

  • Wackes: Contain >15% matrix; Arenites: Less matrix and coarser.

Page 5: Rock Properties and Deposits

• Porosity

  • Percentage of void space in a rock, determining its ability to store fluids.

• Permeability

  • The ability of a rock to allow fluids to flow through its pore spaces, measured in Darcys.

• Dropstones

  • Large clasts deposited by icebergs in fine-grained sediment, indicative of glacial environments.

• Turbidite

  • Sedimentary deposit formed by turbidity currents, typically showing graded bedding.

• Glauconite

  • Green, iron-rich mineral commonly found in marine sedimentary rocks, indicating slow sedimentation.

• Hummocky cross-stratifications

  • Sedimentary structures formed by storm wave action in shallow marine environments.

• Lithostratigraphy

  • Study of rock layers based on lithology and stratigraphic relationships.

Page 6: Carbonate Deposits and Environmental Indicators

• Stromatolites

  • Laminated sedimentary structures formed by microbial activity, usually in shallow marine settings.

• Carbonate compensation depth (CCD)

  • Depth where carbonate dissolution exceeds deposition, inhibiting carbonate accumulation.

• Graded bed

  • Sedimentary layer exhibiting a vertical change in particle size, coarser at the bottom and finer at the top.

• Flaser, wavy, and lenticular bedding

  • Sedimentary structures formed from the interplay of sand and mud in tidal conditions.

• Trace fossils

  • Structures indicating biological activity, such as burrows, tracks, or feeding marks.

• Arkose

  • Sandstone with more than 25% feldspar, usually from granitic sources.

• Imbrication in sediments

  • Arrangement of flat clasts in a consistent orientation due to flow in fluvial deposits.

Page 7: Sediment Transport and Depositional Features

• Mass transport complex (MTC)

  • Large-scale sedimentary unit formed by slumps, slides, and debris flows on continental slopes.

• Cross-bedding

  • Sedimentary structures with inclined layers, indicating flow direction.

• Plane bedding

  • Horizontal sediment layers formed by settling from suspension or sheet flow.

• Sedimentary facies

  • Body of rock with characteristics reflecting its depositional environment.

• Paleosol

  • Fossilized soil horizon, suggesting previous surface conditions.

• Rip-up clast

  • Pieces of mud or clay ripped from a substrate and integrated into overlying sediment layers.

• Unconformity

  • Surface showing a gap in the geologic record, often due to erosion or non-deposition.

Page 8: Ichnofacies and Isotopic Analysis

• Ichnofacies

  • A set of trace fossils reflective of specific depositional environments.

• Delta notation (δ)

  • Expression of isotopic ratios in a sample compared to a standard, measured in parts per thousand (‰).

• Seismic sequence

  • Stratigraphic unit bounded by unconformities, interpreted from seismic reflections.

• Bouma Sequence

  • Sequence of sedimentary structures in turbidites: massive (Ta), planar (Tb), rippled (Tc), laminated (Td), and fine-grained fallout (Te).

• Orthoconglomerates vs Paraconglomerates

  • Orthoconglomerates: framework-supported; Paraconglomerates: matrix-supported.

• Hummocky cross-stratification

  • Structure formed by storm waves in shallow marine environments.

Page 9: Lithic Arenites and Diagenesis

• Lithic arenites

  • Sandstones with over 25% lithic fragments, associated with tectonically active regions.

• Diagenesis

  • Processes altering sediments post-deposition (physical, chemical, biological).

• Bioturbation

  • The reworking of sediments by organisms, disrupting sedimentary structures like laminations.

• Slumps and slides in sedimentary deposits

  • Mass wasting events on slopes preserving original bedding, typically on continental margins.

• Turbidity current

  • Gravity-driven flow of sediment-laden water depositing turbidites.

• Tool marks

  • Impressions left on sedimentary surfaces by objects transported by currents.

• Crystal cast

  • Sedimentary structure formed by crystal growth, typically in evaporative environments.

Page 10: Paleocurrent and Depositional Load Types

• Paleocurrent

  • Direction of ancient flow, determined by sedimentary structures like cross-bedding and ripple marks.

• Antidunes

  • Bedforms migrating upstream, formed in high-energy flows.

• Varve

  • Pair of sedimentary layers (one light, one dark) representing a single year of deposition.

• Three main types of sediment load

  • Bedload, suspended load, and dissolved load.

• Fluvial terraces

  • Step-like landforms along river valleys from changes in river level due to tectonics or climate.

• Debris flow

  • Dense, gravity-driven flow of sediments, water, and debris, leading to poorly sorted deposits.

• Evaporites

  • Minerals formed from evaporated water, like halite, gypsum, and anhydrite.

Page 11: Structures and Depositional Features

• Cross-lamination

  • Fine-scale cross-bedding formed by smaller bedforms (e.g., ripples).

• Terminal moraine

  • Ridge of sediment deposited at the glacier's maximum advance edge.

• Till

  • Unsorted glacial sediment deposited directly by ice.

• Dropstones

  • Large clasts dropped from melting icebergs into finer sediments.

• Cap carbonates

  • Carbonate layers above glacial deposits, associated with post-glacial transgressions.

• Transgression

  • The landward movement of the shoreline during rising sea levels.

• Regression

  • Seaward movement of the shoreline during falling sea levels.

Page 12: Tidal Structures and Depositional Processes

• Eolian deposits

  • Sediments moved and deposited by wind, typically forming dunes.

• Lenticular beds

  • Sedimentary structures with alternating sand and mud layers in tidal settings.

• Flaser bedding

  • Bedding with sand layers interspersed with mud from tidal influences.

• Ripple marks

  • Small-scale sedimentary structures formed by currents or waves.

• Lag deposit

  • Coarse sediments remaining after finer particles are eroded away.

• Soft-sediment deformation structures

  • Features like convolute bedding formed in water-saturated sediments.

• Biogenic structures

  • Sedimentary features stemming from biological activity, such as burrows or stromatolites.

Page 13: Carbonates and Sea Level Changes

• Micrite

  • Fine-grained carbonate mud, a common component of limestones.

• Ooid

  • Small, spherical grain made of concentric calcium carbonate layers.

• Diagenesis

  • Physical, chemical, and biological alterations in sediments after deposition.

• Karst

  • Landscape shaped by dissolution of soluble rocks (e.g., limestone).

• Eustatic sea level changes

  • Global variations in sea level due to shifts in ocean water volume or basin size.

• Wackestone

  • Limestone with more than 10% grains and a muddy matrix.

• Grainstone

  • Limestone made entirely of grains without a muddy component.

Page 14: Features of Sedimentary Rocks

• Chert

  • Fine-grained siliceous rock, often from silica recrystallization of biogenic sources.

• Microbial mats

  • Layers of microorganisms that trap sediments, forming structures like stromatolites.

• Turbidite fan

  • Fan-shaped deposit at the base of a continental slope formed by turbidity currents.

• Marl

  • Sedimentary rock that combines clay and calcium carbonate.

• Trace fossil assemblage

  • A collection of trace fossils indicating a specific depositional environment.

• Alluvial fan

  • A fan-shaped sediment deposit at the base of a mountain where a stream loses energy.

• Reefal limestone

  • Limestone deposited from the accumulation of reef-building organisms.

Page 15: Reef Types and Builders

• Main types of reefs

  • Fringing reefs, barrier reefs, and atolls.

• Fringing reef

  • Reef forming along the shoreline with minimal lagoon between the reef and the land.

• Barrier reef

  • Reef that is separated from the shore by a lagoon, typically located offshore.

• Atoll

  • Circular or horseshoe-shaped reef surrounding a lagoon, forming around sinking volcanic islands.

• Patch reef

  • Small, isolated reef found in lagoons or shallow seas.

• Bioherms vs Biostromes

  • Bioherms: mound-like reefal structures; Biostromes: bedded, extensive reef deposits.

Page 16: Ooids and Carbonate Formation

• Common reef builders

  • Corals, sponges, bryozoans, and algae.

• Ooids

  • Spherical grains of calcium carbonate formed through chemical precipitation in warm, shallow environments.

• Oolite

  • Rock predominantly composed of ooids.

• Environmental conditions favoring ooid formation

  • Warm, shallow, agitated waters with high carbonate saturation.

• Peloids

  • Micritic grains lacking internal structure often produced biologically.

• Grapestones

  • Clusters of ooids or peloids cemented together in marine settings.

Page 17: Stratigraphic Studies

• Lithostratigraphy

  • Study of rock layers by lithology and stratigraphic relationships.

• Biostratigraphy

  • Study of rock layers by fossil content, utilizing index fossils for correlation.

• Chronostratigraphy

  • Study of rock layers focused on their age and temporal formation.

• Chemostratigraphy

  • Study of chemical variations in sedimentary rocks for correlation and interpretation.

• Sequence stratigraphy

  • Study of depositional sequences and boundaries correlating with sea level changes.

• Seismic reflections in stratigraphy

  • Used to identify subsurface sequences and unconformities.

• Transgressive systems tract (TST)

  • Sequence of sediments from rising sea levels.

• Highstand systems tract (HST)

  • Sequence of sediment during stable or gradually falling sea levels.

Page 18: Types of Sedimentary Structures

• Primary sedimentary structures

  • Structures formed during or shortly after deposition (e.g., cross-bedding).

• Secondary sedimentary structures

  • Structures formed post-deposition, including concretions and stylolites.

• Graded bedding

  • Structure where grain size decreases upward from a waning current.

• Trough cross-bedding

  • Curved surfaces indicating sediment migration by dunes or ripples.

• Interference ripples

  • Ripples formed from interactions of two currents or waves.

• Herringbone cross-bedding

  • Alternating cross-beds from bidirectional tidal currents.

• Mud cracks

  • Polygonal fractures resulting from drying and shrinking of muddy sediments.

Page 19: Continuing Sedimentary Features

• Flaser bedding

  • Thin streaks of mud among cross-laminated sand in tidal conditions.

• Ball and pillow structure

  • Bulbous structures from denser material sinking into less dense sediment.

• Flute casts

  • Elongated impressions formed by turbulent current flows.

• Geopetal structure

  • Feature indicating the original orientation of a sedimentary bed.

• Tool marks

  • Impressions made by objects carried in water on sediment surfaces.

• Load casts

  • Bulbous depressions from sinking denser sediments into softer layers.

• Convolute bedding

  • Sedimentary layers distorted by soft-sediment deformation.

Page 20: Advanced Sedimentary Concepts

• Dish structures

  • Circular features formed by fluid escape in fine sediments.

• Hummocky cross-stratification

  • Structure from storm wave activity in shallow marine areas, low-angle and curved.

• Clast imbrication

  • Alignment of elongated clasts indicating flow direction in sedimentary deposits.

• Sole marks

  • Erosional features on sedimentary beds showing flow direction.

• Turbidite

  • Sedimentary deposit created by turbidity currents, showing graded bedding and Bouma sequences.