Comprehensive Geology: Sediments, Environments, and Depositional Systems

What determines the origin and transport of sediments on continents?

Tectonics and climate

What are the two tectonic processes that affect sediment formation?

Uplift and subsidence

What processes generate sediments on continents?

Weathering and erosion

What are the main erosional and transport processes acting on sediments?

Gravity, water, air, and ice

How does sediment size affect transport by air?

Air cannot transport larger sediments like sand.

What is a bedform in an aeolian environment?

The shape that moves along the bed, such as ripples, dunes, and anti-dunes.

What characterizes an aeolian environment?

Regions shaped by wind, such as deserts, beaches, and tidal flats.

What is a Draa in aeolian environments?

A very large, slow, and complex dune controlled by long-term regional climate.

What is a Dune in aeolian environments?

A medium-sized dune (7 cm to hundreds of meters) shaped by local wind conditions.

What is a Ripple in aeolian environments?

The smallest bedform (<1 cm) that changes within hours, formed by sand grain interactions and wind speed.

What type of dune is formed with a prevailing wind direction and medium sand supply?

Barchan dune

What type of dune is formed with high sand supply and a prevailing wind direction?

Transverse dune

What type of dune is created by two wind directions at ~45 degrees?

Linear dune

What type of dune is formed by multiple prevailing wind directions creating a star shape?

Star dune

What is necessary for dune deposits to be preserved?

Water and subsidence for burial and cementation.

What are the sedimentary characteristics of aeolian deposits?

Well sorted, very well rounded, and mature sands.

What is winnowing in aeolian environments?

The process where wind removes finer sand, leaving gravel behind.

What are the facies associations found in aeolian environments?

Dunes (large scale cross bedding), interdune (horizontal lamination), sandsheets (horizontal lamination).

What defines an alluvial system?

A system formed by a river or stream that deposits sediment as it slows.

What are the main components that influence river processes?

Water speed, sediment size/origin, and energy.

What are the depositional features associated with rivers?

Braided rivers, meandering channels, alluvial fans, and floodplains.

What characterizes braided rivers?

High sediment supply, low vegetation, and bars & channels that easily migrate.

What are the facies associated with braided rivers?

Overbank muds, channel fill successions of cross-bedded sands, and imbrication.

How do meandering rivers differ from braided rivers?

Meandering rivers have lateral accretion surfaces and are characterized by winding, S-shaped patterns.

What are the facies associated with meandering rivers?

Similar to braided rivers, including overbank muds and channel fill successions.

What are alluvial fans?

Cone-shaped deposits formed from debris flow with episodic water transport.

What are the facies models for alluvial fans?

Poorly sorted gravels on the fan surface and matrix-supported conglomerate beds.

What processes form sedimentary deposits in braided rivers?

Constant erosion and deposition due to high sediment supply.

What processes form sedimentary deposits in meandering rivers?

Erosion on outer banks and deposition on inner banks.

What are paleosols?

Ancient soils preserved in the geologic record, useful for interpreting past climates.

What is avulsion in river systems?

A sudden shift in the river channel to a steeper gradient.

How does subsidence affect river systems?

It decreases gradient, flow velocity, and transport capacity.

What is the neritic zone?

The marine zone from sea level to the shelf edge break, typically 0-200m deep.

What is the abyssal zone?

The marine zone past 2000m depth, characterized by regular patterns of trace fossils.

How do waves, tides, and currents affect sediment?

They rework sediment from the shore to the abyssal plain, creating distinct sedimentary features.

What is progradation in delta systems?

The seaward growth of a shoreline, leading to a thick sequence of sediment.

What are the main parts of a delta?

Delta plain, delta front, and prodelta.

How does sediment size affect delta characteristics?

Fine-grained deltas have extensive muddy prodelta deposits, while coarse-grained deltas have gravelly mouth bars.

What distinguishes river-dominated deltas from wave-dominated deltas?

River-dominated deltas are elongate with high sediment input, while wave-dominated deltas are cuspate and shaped by wave action.

What is the significance of soft sediment deformation in delta deposits?

It occurs due to instability in mud-rich settings, leading to mass movement of sediment.

What is the difference between transgressive and regressive sequences?

Transgressive sequences occur during sea level rise, while regressive sequences occur during sea level fall.

What is the relationship between sedimentation rate and fossil accumulation?

Fossils accumulate when sedimentation rates are low, allowing for preservation.

What types of trace fossils are found in different marine environments?

Vertical burrows in littoral zones, surface traces in subtidal zones, and regular patterns in abyssal zones.

What are the sedimentary processes associated with delta mouth bars?

Mouth bars are typically composed of sandstones, often cross-bedded by wave reworking.

What is the role of tidal currents in sedimentary features?

Tidal currents can create distinct features such as herringbone cross-stratification and mud drapes.

What is the significance of the Hjulstrom diagram?

It illustrates the relationship between sediment size and the velocity required for erosion, transport, and deposition.

What is the impact of climate on paleosols?

Paleosols provide insights into past climate, landscape, and vegetation based on their characteristics.

What is the primary characteristic of delta top sediments?

Delta top sediments are a mix of channel sands and delta plain muds, often with crevasse splays.

How do sedimentary structures differ between fluvial and alluvial deposits?

Fluvial deposits may show crossbedding and ripple marks, while alluvial deposits may include conglomerates and mud cracks.

What is an aeolian environment?

A region shaped by wind, such as deserts, beaches, and tidal flats.

What are the three types of bedforms in aeolian environments?

Ripples, dunes, and anti-dunes.

What characterizes a Draa?

Very large, very slow, complex dunes controlled by long-term regional climate.

What is a Barchan dune?

A dune formed with a prevailing wind direction and medium sand supply.

How are aeolian deposits preserved?

They require water and subsistence for burial and cementation, with rising water tables protecting from erosion.

What sedimentary characteristics define aeolian deposits?

Well-sorted, very well-rounded sediments with fine to coarse sand, often exhibiting large-scale cross bedding.

What is an alluvial system?

A system formed by a river or stream that deposits sediment as it slows.

What are the main components of an alluvial system?

Sediment source, water source, and flow.

What distinguishes braided rivers?

They have high sediment supply, low vegetation, and easily migrating bars and channels.

What is a meandering river characterized by?

Lateral accretion surfaces that are perpendicular to cross-beds.

What is the morphology of braided rivers?

Multiple channels that split and rejoin around islands and sandbars.

What is the significance of sedimentation rates for fossil accumulation?

Fossils accumulate when sedimentation rates are low; they are rare in environments with high sedimentation.

What is progradation in the context of deltas?

The seaward growth of a shoreline, leading to a coarsening upwards sedimentary sequence.

What distinguishes river-dominated deltas?

They are elongate with high sediment input and stable distributary channels.

What is a wave-dominated delta characterized by?

Cuspate shapes with coastal sand plains, where waves rework sediment.

What processes control relative sea level change?

Ocean volume changes due to warming and ice sheet dynamics, as well as land elevation changes.

What are the sedimentary facies of a delta?

Delta slope mudstones, pro-delta siltstones, delta mouth bars, and delta top channel sandstones.

What is the role of waves in sediment reworking?

Waves create ripple marks and influence sediment distribution in the foreshore and shoreface.

What is the significance of trace fossils in sedimentary environments?

Trace fossils can indicate past biological activity and are often preserved better than body fossils.

What is the relationship between sedimentation rates and body fossils?

Body fossils are more likely to accumulate when sedimentation rates are low.

What is the impact of soft sediment deformation in delta deposits?

It can lead to mass movements like slumps and slides, preserved in the sediment.

What are the characteristics of alluvial fans?

Cone-shaped deposits formed from debris flow with episodic water transport.

How do tides affect sedimentary features?

Tidal currents can create distinct features like herringbone cross-stratification and mud drapes.

What is the significance of sediment sorting in fluvial deposits?

Sediment sorting indicates energy levels and transport processes within the river system.

What is the difference between the neritic, bathyal, and abyssal zones?

Neritic zone is shallow (0-200m), bathyal zone is intermediate (200-2000m), and abyssal zone is deep (2000m+).

What are the characteristics of sedimentary structures associated with fluvial deposits?

Crossbedding, ripple marks, mud drapes, and planar lamination.

What is the role of sedimentary processes in delta formation?

Sedimentary processes like deposition and erosion shape the morphology and facies of deltas.

How does the Hjulstrom diagram relate to sediment transport?

It illustrates the relationship between sediment size and the velocity required for transport.

What are the sedimentary characteristics of beach deposits?

Beach deposits exhibit low angle stratification and are subject to wave reworking.

Describe the sedimentary features of lagoon deposits.

Lagoon deposits may be laminated and wave rippled, often showing signs of bioturbation.

What sedimentary structures are found in tidal channel systems?

Tidal channel systems display cross bedding, cross lamination, and inclined heterolithic stratification.

What are the characteristics of tidal mudflats?

Tidal mudflats feature ripple cross lamination and flaser or lenticular bedding.

What are chenier ridges and how do they form?

Chenier ridges are sandy washover, beach, and dune deposits over muds formed in marshes and tidal flats, created by wave winnowing.

Define a tidal flat.

A tidal flat is a large, gently sloping area of soft sediment (mud/sand) that is submerged at high tide and exposed at low tide.

How does sediment grain size vary in tidal flats?

Sediment grain size coarsens upward, with fine sediments near the edges and coarser sands in deeper water due to stronger currents.

What are the depositional environments associated with estuaries?

Estuaries have mixed sediment sources, variable salinity, and can be wave or tide dominated, featuring deltas, beaches, and tidal flats.

What is the significance of relict sediments on continental shelves?

Relict sediments were deposited during lower sea levels and are often coarse sand or gravel, as the current environment is not strong enough to rework them.

Explain the concept of Holocene transgression.

Holocene transgression refers to the rise in sea level over the past 12,000 years due to glacial melting.

How do storm and wave processes shape sediment deposits on the continental shelf?

Wave-dominated environments feature sand ridges in offshore transition zones, while storm-dominated environments have sand ridges reworked by storm waves and currents.

What is the carbonate factory?

The carbonate factory is where organisms produce carbonate sediments, typically found in shallow, sunlit waters.

What determines whether calcium carbonate will dissolve or precipitate in ocean water?

The saturation of CaCO2 (calcium carbonate) in the water determines its dissolution or precipitation.

What are the basic depositional facies associated with shallow marine carbonate environments?

Shallow marine carbonate environments mainly consist of limestone, featuring crossbedding and oolite shoals, sometimes alongside evaporites.

Differentiate between carbonate platforms and carbonate ramps.

Carbonate platforms have vertical reefs and can be rimmed or unattached, while carbonate ramps are less steep with varying sediment types across their zones.

Where do mixed siliciclastic-carbonate depositional environments occur?

They occur where clastic material is transported into carbonate factory areas, often due to storms or mixing in basins.

Describe the depositional facies of arid carbonate environments.

Arid carbonate environments feature reefs with carbonate sands above fair weather wave base and deeper water with mud packstones and wackestones.

What is a sabkha?

A sabkha is a desert-like environment where hypersaline groundwater sources salts, often found in supratidal environments.

Explain the phrase 'the play remains the same, only the players change' in the context of sediment production.

This phrase indicates that while siliclastics follow a consistent weathering and deposition process, the carbonate factory evolves with different organisms over time.