Carbonate depositional environments JUNAID FOUAD KAREEMDOÇ.DR.ARIF DELİKAN

JEOLOJİ MÜHENDİSLİĞİ ANA BİLİM DALI FEN BİLİMLERİ ENSTİTÜSELCUK ÜNİVERSİTESİ

J_F_KAREEM@yahoo.com 2015/4/28

Microfacies analysis of carbonate rocks requires knowledge of modern carbonates and an understanding of biological and geological changes during earth history. (Schlager 1992).Today only around 10% of marine carbonate production takes place in shallow seas. 90% of the modren carbonate production is related to the deposition of calcitic plankton in the deep sea.Carbonates are originate as skeletal grains or precipitates within the depositional environment. terrigenous clastic sediments are formed primarily by the disintegration of parent rocks and are transported to the depositional environment. . E. Flügel (1934).  

ABSTRACT

LIST OF CONTENT Introduction1- Carbonate depositional environments and facies.1-1 Major variables Controls on Carbonates deposition.2- Marine Depositional Systems.2-1 Boundary Levels.2-1-1 Vertical Zonation.2-1-2 Horizontal zonation.2-2 carbonate platforms.3-Non-Marine carbonates sediments.4-Transitional Marginal-Marine Environments: Shorelines and Peritidal Sediments.

INTRODUCTIONCarbonate sediments originate on land and in the sea. They are formed in three major settings: On the continents, within the transitional area between land and sea, and in the shallow and deep sea. E. Flügel (1934). Shallow-marine carbonate depositional systems differ from siliciclastic depositional systems, these differences are of central importance in the application of sequence stratigraphy to carbonates (Schlager 1992). Non-marine carbonates originate in terrestrial and aquatic environments without marine influence. These carbonates, formed by abiotic or biotic processes differ in many aspects from marine carbonates.

1-Carbonate depositional environments and faciesCarbonates accumulate in a variety of depositional settings that have become better known largely through the exploration for more hydrocarbon reserves.Carbonate sediments originate on land and in the sea. They are formed in three major settings FIG (1):-James (1948).1-marine>ocean, sea.2-terrestrial>land.3-transitional>part land, part ocean. 

FIG(1) setting of carbonate depositional system

1-1 Major variables controls on carbonate deposition • Bathymetry – Sunlight, temperature & sea floor slope.• Eustatic sea level – Function of climate & tectonics.• Turbulence of water – Oxygen, CO2 & Clarity.• Ocean circulation – Dissolution or precipitation.• Nutrients – Clastic influx & ocean circulation.• Climate belt – Tropical, temperate or polar.• World atmosphere – Aragonite or calcite ocean.• Tectonic setting – Ocean width & plate position.•Biologic community. Boggs (2006)

2-Marine depositional systemsover 90% or more of the carbonates found in modern marine environments are biological in origin. the sediments are biotically induced or biotically controlled, Some of the 'abiotic' carbonate precipitation is also effected by organics or the activity of organisms. The dominant role of organisms in the formation of limestones was recognized as early as 1879 by Henry Clifton, Studying Paleozoic, Mesozoic and Tertiary carbonate rocks in thin sections; he recognized the overwhelming abundance of fossils and their importance in the composition of carbonate sands and muds. The distribution and frequency of carbonate-producing organisms depend strongly on environmental factors, such as light, water, temperature and sedimentary influx. E. Flügel (1934). Marine environments are classified into the benthic, for the sea bottom, and the pelagic, FIG (2).

Marine Depositional Systems are subdivided, Hedgpeth (1957) and Edwards (1979) into:-•wave-dominated coasts•tide-dominated coasts•fluvial-dominated coasts (deltas)•carbonate reefs•clastic shelves & platforms•carbonate shelves & platforms•deep water fans•pelagic abyssal plains

FIG (2) Marine depositional environments. Modified from Kennett (1982)

2-1 Boundary LevelsSeveral levels at the sea bottom and within the water column are commonly used in a vertical subdivision of marginal marine and marine environments. Microfacies analysis provides the basic data for recognizing these levels in ancient carbonate rocks.Essential critical interfaces that control sedimentary patterns and the distribution of organisms are:(1) The lower and the upper boundaries of the tides (control the

distribution of organisms. (2) The base of the photic zone (controls the distribution of light-

dependent phototrophic organisms).(3) The base of the zone of wave abrasion (above which bottom

currents and wave action may lead to erosion and cementation).

(4) The base of the action of storms on the sea bottom.(5) The 02 minimum zone (strongly limiting life on and in the sea bottom). (6) The thermocline (the layer of water that is too cold for most carbonate producing organisms).(7) The pycnocline (the layer of water where salinity is too high for most organisms).

$Pycnocline?? (A layer in an ocean or other body of water in which water density increases rapidly with depth.

2-1-1 Vertical zonationBenthic depth zones: The depth of the sea bottom and critical levels controlling the sedimentation subdivide the benthic environments into six zone FIG (2):-(1) coastal sublittoral zone (above high tide, corresponding to the supratidal zone).(2) littoral (between high and low tide, identical with the intertidal zone).(3) Sublittoral (below low tide, corresponding to the major part of the continental shelf).(4) Bathyal (approximately equal to the continental slope).(5) abyssal (corresponding to Subdivisions of marine environments). (6) the hadal zone (deep-sea and horizontal: trenches).And Modem carbonate sedimentation takes place within the range of zone 1 to parts of zone 5.

Pelagic depth zones: Five zones are defined by the vertical distribution of floating and swimming life. These are, in descending order FIG (2):-1-epipelagic zone (the upper region of the oceans, extending to a depth of about 200 m).2- mesopelagic 800-1000m (intermediate).3-bathypelagic (deep).4-abyssopelagic (corresponding to oceanic environments below about 4 000 m).5- hadopelagic zone (bottom).

2-1-2 Horizontal zonationThe lateral distribution of pelagic organisms with respect to their distance from the coast characterizes two major zones of the ocean: The neritic zone is the water that overlies the continental shelf, today generally with water depth less than 200 m and covering about 8% of the ocean floor. The term oceanic zone refers to the water column beyond the shelf break, overlying the slope and the deep-sea bottoms, generally with water depths greater than 200 m and down to more than 10 000 m. E. Flügel (1934). Fig(2) 

2-2 carbonates platformCarbonate platform is a general term widely used for mostly shallow-marine carbonate that develops along passive continental margins. Five major types of carbonate platforms having particular pattern of facies and facies succession are recognized FIG (3):- (Ginsburg and James 1974)1. Ramp.Is a gently sloping surface with a generally high-energy, inner-ramp, affected periodically by storms10-100km. 2. Rimmed shelf.Is a shallow-water platform with a distinct break-of-slope into deeper water10-100km.3. Epeiric platform.Epeiric platform is a shallow epicontinental sea covering a large area (100-10 000km across).

4. Isolated platform.Isolated or detached platforms are surrounded by deep water and so are very much affected by prevailing few kilometers to a few hundred kilometers across. 5. Drowned platform.Is one that has suffered a relatively rapid sea-level rise so that deeper-water facies are deposited over shallow-water facies.

The type of carbonate platform developed is determined largely by:1. Tectonics.2. Relative sea-level change.

FIG (3) Carbonate Platforms

3- non-marine carbonates sedimentsNon-marine carbonates originate in terrestrial and aquatic environments without marine influence. These carbonates, formed by abiotic and/or biotic processes differ in many aspects from marine carbonates, These carbonates are formed in terrestrial subaerially exposed settings and in submerged aquatic settings FIG (4). They are of three types:A. inorganic precipitates, producing carbonate mud, mostly takes place through evaporation, as a result of plant photosynthesis or pressure-temperature change, and mixing of fresh stream or spring water with saline lake water, also causes carbonate precipitation. Precipitation in shallow agitated zones may produce ooids, as in the Great Salt Lake Utah. The mineralogy of the carbonate mud and ooids precipitated depends on the Mg/Ca ratio of the water.

B. carbonate muds also may be produced through the activities of algae, cyanobacteria and microbes, and from phytoplankton blooms.C. Skeletal sands that contains fragments of calcareous algae, such as Chara, as well as bivalves and gastropods. Edwards, A.R. (1 979).

FIG (4) Non-marine carbonate depositional environments

Non-marine carbonates formed in terrestrial subaerially exposed settings comprise pedogenic carbonates, palustrine carbonates, cave carbonates, eolian carbonates and glacial carbonates.Pedogenic carbonates: paleosols, calicheicalcrete, Formed by the accumulation of calcium carbonate within unconsolidated carbonate-rich soils.Palustrine carbonates: Carbonates formed in lacustrine and transitional non-marine/marine environments originating by short-term oscillations of the water levels and characterized by a mixture of subaerial and freshwater facies criteria.Cave carbonates, karst: Formed by the precipitation of calcium carbonate within caves.Eolian carbonates: Sedimentation of fine-grained, wind-born sand-sized carbonate material.Glacial carbonates: Dissolution and recrystallization of glacially transported carbonate debris, occurs in glacial-marine deposits.

Non-marine carbonates formed in aquatic settings comprise freshwater carbonates, lacustrine carbonates and fluvial carbonates.Freshwater carbonates: Travertine, calcareous tufa, calcareous sinter.Lacustrine carbonates: Deposition and precipitation of calcium carbonate in lakes of different salinity (freshwater lakes, salt lakes, playa lakes) and different settings.Fluvial carbonates: Carbonate deposits formed in rivers, creeks and waterfalls, originating from the combined activity of biotic and abiotic processes.

4-Transitional Marginal-Marine Environments: Shorelines and Peritidal Sediments

Marginal-marine environments (deltas, beaches and barrier-islands, estuaries, coastal lagoons and tidal flats) occur in a narrow near shore zone along the boundary between continental and marine depositional realms FIG(2). The shoreline is marked by great environmental instability resulting from intensive interaction between high energy forces related to waves, tides, wind, and currents and constantly changing sea levels. Carbonate deposition takes place in the coastal shoreline zone at the beach, in coastal lagoons behind bamers, and within the peritidal zone FIG(4).

References1-Flügel, E. (1982): Microfacies analysis of limestones.

2-James, N.P., Kendall, A.C. (1992): Introduction to carbonate and evaporate facies models.

3-Edwards, A.R. (1 979): Classification of marine paleoenvironments.

4-Hedgpeth, J. (1957): Classification of marine environments.

5-Ginsburg, R.N. (ed., 1975): Tidal deposits, a case book of Recent examples and fossil counterparts.

6-Schlager, W. (1992): Sedimentology and sequence stratigraphy of reefs and carbonate platforms.