FINAL- Sed and Soil

Sedimentary Grains

particles of rock, mineral, or organic material that are transported and deposited by wind, water, or ice, and later compacted and cemented to form sedimentary rocks. They vary in size from clay to boulders and can include sand, silt, pebbles, or fossil fragments.

Clastic Grains

Fragments of pre-existing rocks or minerals that have been broken down by weathering and erosion, then transported and deposited to form clastic sedimentary rocks. (also called siliciclastic, terrigenous, or detrital sediments). Common minerals are quartz, feldspar, and and mica.

Types of Clastic Grains

Detrital grains (minerals eroded from pre-existing rocks (quartz, feldspar, micas))

Lithic fragments (sand sized pieces of rock, any rock type, requires petrographic analysis to identify)

Authigenic grains (minerals precipitated in place (carbonates, evaporites, glauconite) and need to be related to specific environments)

What is a clast and how are they produced?

Fragment or grain of pre-existing rock or mineral that has been broken off through weathering and erosion. Clasts are the building blocks of clastic sedimentary rocks.

Where do clastic grains originate (inside or outside the basin)?

Typically originate outside the basin. They form from the weathering and erosion of rocks in source areas (like mountains), then are transported into the sedimentary basin by rivers, wind, or glaciers.

What is compositional maturity in sandstones?

How stable and resistant the mineral grains in a sandstone are. A compositionally mature sandstone is rich in quartz and lacks unstable minerals like feldspar or lithic fragments.

What is textural maturity in sandstones?

Describes the grain size, sorting, and roundness in a sandstone. A texturally mature sandstone has well-rounded, well-sorted grains with little to no matrix.

Goldich stability series

Ranks minerals by their resistance to weathering. Minerals that crystallize first from magma (like olivine and pyroxene) weather fastest, while those that crystallize last (like quartz) are most stable at Earth's surface.

Non-clastic grains

Particles in sedimentary rocks that do not originate from the physical breakdown of other rocks. They include organic materials (like plant matter or shells) and chemically precipitated minerals (like salt or limestone crystals).

Types of Non-clastic grains

Skeletal: fragments of organisms or parts of organisms that have been preserved in sedimentary rocks.

Ooids and Pisoids: Small, spherical grains formed by the precipitation of minerals around a nucleus. Ooids are usually smaller, while pisoids are larger.

Peloids: Small, rounded grains of fine material, often composed of algae or microbial remains, typically found in carbonate-rich rocks.

Intraclasts:Fragments of previously formed sedimentary rock that have been broken and re-deposited within a new sedimentary rock, often found in limestones.

How are non-clastic grains produced?

Biologically: Organisms (like corals, mollusks, and algae) secrete or accumulate hard parts (such as shells or skeletons) that eventually become part of the sediment.

Chemically: Minerals precipitate directly from water due to evaporation or chemical reactions, forming grains like halite (salt) or gypsum.

Evaporatively: As water evaporates, dissolved minerals like calcium carbonate crystallize, forming grains such as ooids.

Where do non-clastic grains originate (inside or outside the basin)?

Typically originate inside the basin. They often form in situ within the sedimentary basin through biological processes (like the growth of marine organisms), chemical precipitation (such as the formation of evaporites), or by the accumulation of organic materials.

Transport Processes

Bedload Transport: movement of larger particles (like gravel or sand) along the riverbed by rolling, sliding, or hopping. These particles do not remain suspended in the water.

Suspension: transport of fine particles (such as silt and clay) that are lifted and carried by the flow of water, remaining suspended in the water column.

Entrainment – The process by which particles (sand, gravel, silt) are picked up from the bed and carried into the flow of water, typically by the force of the water current overcoming the particle’s weight.

Depositional Environments

Locations where sediment accumulates and forms sedimentary rocks, common environments are: Marine Environments, Fluvial Environments, Deltaic Environments, Aeolian Environments, Glacial Environments, Lacustrine Environments

How does shear stress change through time over a depositional event?

Shear stress changes over time in a depositional event based on factors like water velocity, sediment type, and flow conditions:

Initial Phase – shear stress is high due to stronger water currents or forces required to move larger particles (such as gravel).

Middle Phase – As sediment begins to accumulate, shear stress may decrease because the flow becomes less turbulent or the water velocity reduces.

Final Phase – Shear stress typically stabilizes or becomes minimal as deposition slows and finer particles (like silt or clay) settle out, reducing the flow's capacity to move sediment.

How are depositional events recorded in the rock record?

Recorded in the rock record through the formation of sedimentary layers (strata). These layers capture information about: Sediment Type,Stratification, Fossils, Cross-bedding, Ripple Marks, and Mud Cracks, Unconformities

Bedforms

distinct shapes or patterns that develop on the surface of sedimentary beds as a result of the movement of sediment. They provide important clues about the flow conditions and energy of the environment. Common types of bedforms include: ripples, dunes, cross bedding, mudcracks

Unidirectional flow and current bedforms

Water or air that moves in one constant direction, typically in rivers, streams, or wind-driven environments. The types of bedforms that develop in unidirectional flow environments are influenced by the speed and energy of the flow. Common current bedforms include: ripples, dunes, antidunes, linear cross bedding

Ripple Migration

Transport Process: Slow-moving water (or air) moves over fine-grained sediments. The flow causes the sediment to be pushed up into small, regular wave-like patterns.

Depositional Process: As the flow moves, the ripples migrate in the direction of flow. The sediment is deposited on the downstream side of the ripple crest, creating layers (strata) that record the direction of flow.

Dune Migration

Transport Process: Form in areas with faster flows, where the current can move larger particles. As the current moves, it transports sediment up the stoss side (upstream side) of the dune, where it is then deposited on the lee side (downstream side).

Depositional Process: Grow and migrate downstream as the material accumulates and is deposited at the dune's crest, leading to the formation of cross-bedded layers that indicate the flow direction.

What sedimentary structures are produced by current bedform migration?

Cross Bedding, Ripple Marks, Trough Cross-stratification, plane bed, antidunes

Orbital motion

Circular movement of water particles in waves, typically observed in shallow marine environments. As waves pass through the water, water particles move in orbits: they rise to the surface, move forward, then descend and move backward, completing a circular path. This motion influences the movement of sediment at the seafloor, particularly in environments with wave action, such as beaches or shallow marine settings.

oscillatory motion

back-and-forth movement of water particles driven by wave action, typical in shallow marine environments. As waves pass, water particles move in small, circular orbits (orbital motion), causing the sediment on the seafloor to be displaced. This motion is particularly important in shallow water environments, where wave energy is strong enough to move fine-grained sediment (like sand or mud), but not enough to cause significant transport in deeper water

wave base

Depth below the water's surface where the motion of surface waves no longer affects water particles. It is typically at a depth of about half the wavelength of the wave. Below this depth, the water particles move in a much smaller orbit and are not influenced by the passing waves.

Rolling-grain ripples

small, wave-like patterns that form when grains of sand roll along the bottom of a water body. This happens in places with moderate to strong currents, like in rivers or shallow oceans, where the grains are too big to float but can roll across the surface.

wave ripples

mall, regular, wave-like patterns formed on the surface of the sediment by the motion of waves. They typically form in shallow water where wave action is strong enough to move the sediment, like on beaches or shallow marine environments.

post-vortex ripples

bedforms that form after the flow of water or air has passed over a surface, leaving behind ripple-like patterns. These ripples are typically created by the movement of fluid over the sediment, where the vortexes (swirling currents) formed during flow break down, resulting in the creation of smaller, regular wave-like patterns. (form in environments where turbulent flow transitions to more steady, laminar flow, such as in shallow water after a wave has passed.)

What sedimentary structures are produced by wave ripples?

ripple marks, lamination, mudcracks

Foresets, set boundaries, sets, and co-sets

Foresets – Layers of sediment that are tilted, forming on the sloped side of dunes or ripples.

Set Boundaries – The lines that separate different groups of layers (sets).

Sets – Groups of layers that were deposited in the same conditions.

Co-sets – Groups of sets that share similar features or were formed in similar conditions.

Erosional Structures

features formed by the removal or erosion of sediment by natural forces like water, wind, or ice.

Scour Marks v. Tool Marks

Scour Marks: Grooves in the sediment made by flowing water that moves and erodes the surface.

Tool Marks: Small scratches or dents left on the surface by objects (like rocks or shells) scraping along it.

Deformational Structures

Formed by the deformation (bending, folding, or fracturing) of sedimentary layers due to tectonic forces, pressure, or other forces after deposition. Formed by tension, cementation, burial and lithification, thermal and chemicals

Biogenic structures

sedimentary features formed by the activities of organisms

Stromatolites

layered, dome-shaped structures formed by the activity of microorganisms, primarily cyanobacteria, in shallow water. These microorganisms trap and bind sediments, creating distinct, layered formations over time. Stromatolites are significant in the geological record because they are one of the oldest known forms of life on Earth, dating back over 3.5 billion years

Trace Fossils

indirect evidence of past life, created by the activities of organisms rather than their physical remains. These fossils provide insights into the behavior, movement, and interaction of ancient organisms with their environment.

Diagenesis

set of physical, chemical, and biological changes that occur in sediments after deposition and before metamorphism. These changes turn loose sediment into solid sedimentary rock.

Compaction and cement formation

Compaction: Sediment grains are squeezed together by the weight of layers above, reducing spaces between them.

Cementation: Minerals fill the gaps between grains and stick them together to form solid rock.

Nodules and concretions

Nodules: Hard lumps of minerals (like silica or phosphate) that form in sediment, often replacing the original material.

Concretions: Rounded, solid masses that form when minerals (like calcite or iron) build up around a center (like a fossil) in sediment before it hardens.

Facies

A body of rock with specific characteristics (like grain size, composition, or fossils) that tell you about the environment it was formed in—such as a river, beach, or deep sea.

Walther’s Law

environments that are next to each other in space will be stacked on top of each other in a rock sequence if there are no gaps in deposition.

How are sedimentary processes related to sedimentary structures?

Sedimentary processes (like water flow, wind, or wave action) create sedimentary structures by moving and depositing sediments in different ways.

Exp. Ripples form from gentle water or wind flow.

Cross-bedding forms from migrating dunes or ripples.

Mud cracks form when wet mud dries and shrinks.

Help us understand how and where sediments were deposited.

Fluvial Systems

A fluvial system is a river or stream system that moves water and transports, erodes, and deposits sediment. It includes channels, floodplains, levees, and deltas.

Lateral accretion

A river shifts side-to-side, depositing sediment along its banks. The river moves and deposits sediment on the inside of bends (point bars). Erosion happens on the outer bank as the river shifts. Deposited on Point bars: Sand and gravel deposited on the inside bend of the river. Cross-bedding: Layers of sediment formed at angles from changing water flow.

Vertical accretion

Sediment builds up vertically over time, typically in low-energy environments like river floodplains or lakes. Processes are: Flooding: When a river or lake floods, it deposits sediment (sand, silt, clay) on the surface. Slow deposition: Over time, finer sediments build up, creating layers on top of older ones.

Channel migration processes

Form when water in a river flows in a winding, curving path, often due to variations in water velocity.

Outer bank (cut bank): Water flows faster, eroding the bank.

Inner bank (point bar): Water slows down and deposits sediment, building up the bank.

Chute cut off, neck cut off, avulsion

Chute:river carves a new path through a meander, creating a more direct route results in abandonment of the old, meandering channel and a shortened course.

Neck: neck of a meander (the narrow land between two parts of the river) is eroded enough to form a new, straighter channel. Cutoff create ox-bow lake

Avulsion: A sudden shift in the river’s course, usually caused by high water or flooding, where the river abandons its old channel and forms a new one. Creates new channels

deltas

Depositional landforms that develop at river mouths where sediment is deposited as the river slows upon entering a standing body of water, and their structure typically includes topset, foreset, and bottomset beds, shaped by dominant river, wave, or tidal processes.

Delta top

The delta top includes distributary channels (fluvial flow, coarse sands), interdistributary bays (suspension settling, fine muds), natural levees (overbank flooding, sand and silt), and deltaic marshes/swamps (organic accumulation, peat and mud), each shaped by different depositional and hydrological processes.

Delta front

Lies seaward of the delta top and is dominated by sediment gravity flows and wave or tidal reworking, with foreset beds composed of sandy to silty sediments, cross-bedding, graded bedding, and ripple marks indicating moderate energy conditions.

Delta Slope

Lies between the delta top and prodelta, forming the inclined portion of the delta front; it is shaped by gravity-driven sediment transport, including turbidity currents and slumping, and is characterized by foreset beds with cross-bedding, graded bedding, and sand-to-silt-sized sediment.

Prodelta

Deepest and most distal part of the delta system, where fine sediments like clay and silt settle from suspension in quiet water, forming laminated or massive mudstones with low bioturbation and minimal current influence.

Marine Environments Relative to Normal and Storm Wave Base

Marine environments are defined by their depth relative to the normal wave base and the storm wave base. Environments above the normal wave base are more energetic, while those below the storm wave base experience calm, deep-water conditions.

Fore Shore

lies between high and low tide, experiencing tidal action. (water is shallow, energy is high, and sediments are well-sorted sands).

shoreface

extends from low tide to below the normal wave base and is dominated by wave action. (moderate water depth, high energy, and cross-bedded sands).

offshore transition

occurs between the normal and storm wave base, where sediment is influenced by both waves and storms. (deeper with moderate energy and interbedded sands and mud).

offshore

Zone is deeper than the storm wave base, with minimal wave energy. (zone is the deepest, low in energy, and primarily consists of fine mud or shale).

Estuaries

Estuaries are coastal areas where freshwater from rivers meets saltwater from the ocean. They have three main zones:

• Outer zone: Dominated by marine processes, high salinity, and tidal influence.

• Central zone: A mix of marine and fluvial processes, with varying salinity and water levels.

• Inner zone: Dominated by fluvial processes, low salinity, and weaker tidal effects.

Estuaries are influenced by the tidal regime, with tides causing water level fluctuations and salinity gradients, affecting mixing, sediment transport, and biological productivity.

Wave Processes – Orbital and Oscillatory Motion

Orbital motion: Water particles move in circular orbits in the open ocean due to wave energy.

Oscillatory motion: Water particles move back-and-forth near the surface, influenced by wave energy, decreasing with depth.

Wave Processes – Longshore Currents and Longshore Drift

Longshore currents: Coastal currents moving parallel to the shore, driven by angled waves.

Longshore drift: The movement of sediment along the shore, caused by waves and longshore currents.

Sediment Transport by Waves and Longshore Currents

Sediment is transported laterally along the shore by longshore currents and longshore drift, moving sand and gravel from shallow waters to beaches and forming features like spits and bars.Sediment Transport by Waves and Longshore Currents

Beach Zones – Foreshore, Berm, Backshore, Dunes, Strand Plains

Foreshore: Area between high tide and low tide marks, exposed during low tide. (erosion)

Berm: Flat area above the high tide mark, formed by sand deposition. (deposition)

Backshore: Dry, upper part of the beach, not typically affected by tides. (deposition)

Beach Dunes: Sand dunes formed by wind behind the backshore. (deposition)

Strand Plains: Low-lying sand areas near the shore.

Beach Facies Features

Cross-bedding, ripple marks, and fine to medium sand.

Foreshore has well-sorted fine sand.

Berm may have coarser sand or pebbles.

Barrier Features – Spits and Barrier Islands

Spits: Elongated sand ridges extending into water from the shore, formed by longshore drift.

Barrier Islands: Narrow islands parallel to the coast, formed by sediment accumulation, protecting the mainland.

How Spits and Barrier Islands Form and Dissipate Energy

Spits form from sediment deposited by longshore drift.

Barrier islands form from the accumulation of sand and sediments, shielding the mainland.

Both features dissipate wave energy, reducing its impact on the coast.

Lagoons and Inlets – Dominant Processes in Lagoons

In lagoons, sedimentation occurs due to low-energy conditions, with shallow waters leading to the formation of saltwater marshes or mudflats.

Lagoons vs. Estuaries

Lagoons: Shallow coastal water bodies separated by barriers like islands, with minimal freshwater input.

Estuaries: Areas where freshwater meets saltwater, creating a brackish environment with strong river influence.

Tidal Processes – Causes of Tides

Tides are caused by the gravitational pull of the moon and sun on Earth's oceans, combined with Earth's rotation. Tides occur twice daily (a semi-diurnal cycle) in most places, though some areas experience a diurnal cycle (one tide per day).

Spring Tides vs. Neap Tides

Spring tides: Occur when the moon and sun are aligned (during new and full moons), causing higher high tides and lower low tides.

Neap tides: Occur when the moon and sun are at right angles (during the first and third quarters), resulting in lower high tides and higher low tides.

Ebb–Flood Tidal Cycle

The ebb tide is when water flows out of the coastline (low tide).

The flood tide is when water flows in toward the coastline (high tide).
This cycle typically occurs twice a day, in sync with the lunar cycle.

Tidal Range and Tidal Regimes – Microtidal, Mesotidal, Macrotidal

Microtidal: Tidal range less than 2 meters.

Mesotidal: Tidal range between 2 to 4 meters.

Macrotidal: Tidal range greater than 4 meters.

Tidal Regimes and Their Influence on Coastal Systems

The tidal regime (micro, meso, or macrotidal) influences:

Coastal morphology: Larger tidal ranges create broader tidal flats and more distinct channels.

Sediment transport: Larger tidal ranges result in more extensive reworking of sediments, creating larger mudflats and more dynamic tidal channels.

Tidal Zones – Subtidal, Intertidal, Supratidal

Subtidal: Area below low tide, always submerged.

Intertidal: Area between high and low tide, regularly exposed and submerged.

Supratidal: Area above high tide, rarely submerged (e.g., salt marshes).

Tidal Features – Tidal Channel, Tidal Flat, Salt Marsh

• Tidal channel: A narrow, flowing body of water within tidal flats, often formed by tidal currents.

• Tidal flat: Flat, low-lying areas covered at high tide and exposed at low tide; can be:

  • Sand flat: Dominated by sand.

  • Mixed flat: Mixture of sand, silt, and mud.

  • Mud flat: Dominated by mud.

• Salt marsh: Coastal wetlands with saline water, characterized by salt-tolerant vegetation and formed in low-energy areas.

How Do Tidal Environments Form in Relation to Tidal Zones?

Tidal channels form in the subtidal zone and are shaped by tidal currents.

Tidal flats form in the intertidal zone, accumulating sediments carried by ebb and flood tides.

Salt marshes develop in the supratidal zone, where sediment deposition is high and vegetation can grow.

Tidal Deposits – Tidal Bundles, Herringbone Cross-Stratification, Reactivation Surfaces, Mud Drapes

Tidal bundles: Alternating layers of sand and mud, representing tidal cycles.

Herringbone cross-stratification: Cross-bedding in two opposing directions, indicating bidirectional flow (caused by tidal currents).

Reactivation surfaces: Erosion surfaces formed by strong tides or waves that interrupt sediment deposition.

Mud drapes: Thin layers of mud deposited by calm tidal conditions.

Flaser, Wavy, and Lenticular Bedding in Tidal Environments

Flaser bedding: Predominantly sand with thin layers of mud, formed in strong tidal currents.

Wavy bedding: Equal proportions of sand and mud, created by tidal oscillations.

Lenticular bedding: Predominantly mud with sand lenses, formed in low-energy tidal environments.

Tidal Facies Models

Tidal facies models describe sedimentary structures and depositional environments found in tidal settings, including:

• Facies associated with tidal flats (sand and mud layers).

• Facies associated with tidal channels (coarse-grained, cross-bedded sands).

• Facies in salt marshes (mud-dominated with vegetation).

What is bioturbation?

The disturbance and reworking of sediments by organisms, such as through burrowing, feeding, or moving.

How does bioturbation affect sedimentary layers?

It destroys sedimentary structures, mixes layers, changes porosity and permeability, and indicates biologically active environments.

What is an ichnofossil?

A trace fossil recording the behavior of an organism, such as burrows, trails, feeding marks, or resting impressions.

What behaviors do ichnofossils record?

Feeding, dwelling, movement, and resting behaviors of ancient organisms.

What is an ichnofacies?

A characteristic assemblage of trace fossils reflecting a specific depositional environment and set of environmental conditions.

What factors control ichnofacies?

Substrate type, current strength/energy, sedimentation rate, oxygen levels, salinity, and nutrient availability.

How does trace fossil assemblage change with water depth/environment?

Deeper environments typically show fewer, simpler traces due to lower energy and oxygen; shallow environments have more diverse, active trace assemblages.

What is the Principle of Superposition?

In an undeformed sequence of sedimentary rocks, the oldest layers are at the bottom, and the youngest are at the top.

What is the Principle of Original Horizontality?

Sediments are originally deposited in horizontal or nearly horizontal layers.

What is the Principle of Lateral Continuity?

Sedimentary layers extend laterally in all directions until they thin out or encounter a barrier.

What is the Principle of Cross-Cutting Relationships?

A geologic feature that cuts through another is younger than the feature it cuts.

What is the Principle of Inclusions?

Fragments included in a rock are older than the rock that contains them.

What is an unconformity?

A surface representing a gap in the geologic record due to erosion or non-deposition.

How are stratigraphic principles used to determine relative ages?

By applying these principles, geologists can establish the chronological order of rock layers and events without knowing exact ages.

What is a geological formation and how is it used in geology?

A formation is a mappable, distinctive body of rock with consistent characteristics. It serves as a basic unit in lithostratigraphy, helping geologists correlate rock layers across regions and interpret geologic history.

What is a fossil range?

The span of geologic time between a fossil's first appearance and last appearance in the rock record.

What is a biozone?

A stratigraphic interval defined by the presence and range of particular fossil species, used to correlate layers across regions.

What are the characteristics of a good index fossil?

Short geologic time range, wide geographic distribution, easily recognizable, and abundant in the fossil record.

What are the main geochronologic units?

Eons, Eras, Periods, and Epochs

What are the age bounds of the Paleozoic, Mesozoic, and Cenozoic eras?

Paleozoic Era: 541 million years ago to 252 million years ago. (permian-triassic)

Mesozoic Era: 252 million years ago to 66 million years ago. (K-Pg)

Cenozoic Era: 66 million years ago to the present.

What is radiometric dating?

Radiometric dating is a technique used to determine the age of materials by measuring the amount of a specific radioactive isotope and its decay products.

What is paleomagnetism?

Paleomagnetism is the study of the Earth's ancient magnetic field as recorded in rocks, sediments, and archaeological materials.

What is chemostratigraphy?

Chemostratigraphy is the use of variations in the chemical composition of rock layers to date and correlate strata.