Marine DepositionalEnvironmentsPresented by: Waqas Javaid

Table of Contents:• Introduction to Sedimentary Depositional Environment

• Marine Depositional Environment

• Shallow Marine environment

• Deep Marine Environment

• Diagnostic characteristics

Introduction to Depositional Environments:

Sedimentary depositional environment describes the combination of physical, chemical and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be formed after lithification.

• A depositional environment • is anywhere sediment accumulates• especially a particular area • where a distinctive kind of deposit originates • from physical, chemical, and biological processes

Introduction to Depositional Environments:

Three broad areas of deposition include• Continental Alluvial, Aeolian, Fluvial, Lacustrine• Transitional Deltaic, Tidal, Lagoon, Beach• Marine Shallow marine, Deep Marine

• Some other depositional Environments include:• Glacial• Evaporite• Volcanic

Introduction to Depositional Environments:

Marine depositional Environment:

Importance of Marine Depositional environment:• Sedimentary rocks cover 75% of the Earth's surface.• Most of these sedimentary rocks are deposited in marine environment.• Oceans and seas are the largest basins available for accumulation of

sediments.• Marine sediments are economically important due to hydrocarbons,

manganese nodules etc.

Source of sediments in marine depositional environment:• Rivers and streams (most important)• Wind action, dust blows• Volcanism• Organic contribution

Marine depositional Environment:

• Marine environments include:• Shallow Marine Environment i.e. shelf, slope, rise.• Deep Marine Environment

• Much of the sediments eroded from continents • are eventually deposited in marine environments

• but sediments derived from chemical • and organic activity are found here as well, such as

• limestone• evaporites• both deposited in shallow marine environments

Shallow Marine Environment:• It is the depositional environment which is present at continental

margin

• A continental margin is a zone of transition between continental crust and oceanic crust.

• It includes:• continental shelf (littoral + Sub-littoral zone)• continental slope (bathyal zone)• continental rise (bathyal zone)

Shallow Marine Environment:

Shallow Marine Environment:

Shallow Marine Environment

Shallow Marine Environment:• The main source of sediments in shallow marine environment are

streams and rivers carrying the sediment load from continents. • Large number of species also live in shallow marine environment.• After death, their skeletons also deposit as sediments.

General trend of sediments at Shallow Marine Environment:

Continental Shelf:• The gently sloping area adjacent to a continent

• is a continental shelf

• It consists of a high-energy inner part that is • periodically stirred up by waves and tidal currents

• Its sediment is mostly sand, • shaped into large cross-bedded dunes

• Bedding planes are commonly marked • by wave-formed ripple marks

• Marine fossils and bioturbation are typical

Continental Shelf:• Gentle, < 1o (1:500) slope

• 30m -1300km wide (passive vs active margins)

• Shelf break at ~ 130m depth

• 9% of total ocean area (6% Earth’s surface)

• 2.5 km sediment thickness

• 15% of marine sediment volume

• abundance of sand on the continental shelf

Continental Slope:• The low-energy part of the shelf

• Typically fine-grained sediments• has mostly mud/clay with marine fossils• Low temperature

• Much sediment derived from the continents • crosses the continental shelf • and is funneled into deeper water • through submarine canyons

• It eventually comes to rest • on the continental slope and continental rise • as a series of overlapping submarine fans

Continental Slope:• 2-6o slope

• 140m to 300-800m depth

• 6% of ocean area (4% Earth’s area)

• Cut by submarine canyons

• 9 km sediment thickness

• 41 % of marine sediment volume

Continental Rise:• Sediments - muds, channel sands (fans),turbidities, slump and slide

deposits

• Associated environments - deep marine, abyssal plain

• Fossils - rare, some broken shells from continental shelf, some forams

- 800 - 4,000 m depth - 6% of ocean area (4% Earth’s area) - Cut by submarine canyons - 8 km sediment thickness - 31 % of marine sediment volume - Submarine fan systems may contain coarse sediments - Extremely important hydrocarbon reserves

Turbidity Currents:• Once sediment passes the outer margin

• of the shelf, the shelf-slope break, • turbidity currents transport it

• So sand with graded bedding is common

• Also common is mud that settled from seawater

Shallow Marine Environment:

Sand with graded bedding and mud settled from seawater

Turbidity currents carry sediment to the submarine fans

Comparison of Marine Environments:

MARINE SEDIMENTARY ENVIRONMENT 

CONTINENTAL SHELFCONTINENTAL SLOPE AND

RISEDeep Marine

Rock TypeSandstone, shale, siltstone, fossiliferous

limestone, oolitic limestoneLitharenite, siltstone, and

shale (or limestone)Shale, chert, micrite,

chalk, diatomite

Composition Terrigenous or carbonate Terrigenous or carbonate Terrigenous or carbonate

Color Gray to brown Gray, green, brown Black, white red

Grain Size Clay to sand Clay to sand Clay

Grain Shape --- --- ---

Sorting Poor to good Poor Good

Inorganic Sedimentary Structures

Lamination, cross-beddingGraded bedding, cross-

bedding, lamination, flute marks, tool marks (turbidites)

Lamination

Organic or Biogenic Sedimentary Structures

Trails, burrows Trails, burrows Trails, burrows

Fossils Marine shells Marine shells, rare plant

fragmentsMarine shells (mostly

microscopic)