2/25/2009. Carbonate Diagenesis. Early Diagenesis. Cements are indicative of diagenetic environments

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1 Carbonate Diagenesis Early Diagenesis A Short Course VU March, 2009 Peter Swart University of Miami Cements are indicative of diagenetic environments 1

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3 Figure from Moore

4 Figure from Moore 2001 Meteoric Diagenesis Figure from Moore

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Allan And Matthews (1982) Five Distinctive Isotopic Zones Calcrete, caliche,

calcretes Vadose Freshwater- phreatic zone Mixing-zone Marine-zone (Melim et al

Caliche or Calcrete "A surface developed on carbonate rocks which are exposed

6 Allan And Matthews (1982) Five Distinctive Isotopic Zones Calcrete, caliche, sub-aerial exposure surfaces Penetrative calcretes (Rossinsky Surficial calcretes Vadose Freshwater- phreatic zone Mixing-zone Marine-zone (Melim et al 1988) Non-depositional surfaces (Swart and Melim, 2000) Figure from Moore 2001 Caliche or Calcrete "A surface developed on carbonate rocks which are exposed to the atmosphere or developed associated with roots. The surface is frequently laminated." 6

7 Picture Rossinsky Picture Rossinsky Picture Rossinsky Picture Rossinsky 7

Caliche or Calcrete Associated with a pronounced negative shift in the carbon isotopic composition and a slight enrichment in the oxygen isotopic ratio The negative carbon is derived from the

Isotopic Calcretes 1 1 0 Oxygen Isotopic Composition 0-1 -2-3 -4 Carbon Isotopic Composition -1-2 -3-4 -5-6 -7-8 -8-6 -4-2 0 2 100 Oxygen -5 CAICOS GUN KEY KEY LARGOSANSAL EXUMA BPK ANASTASIA

8 Caliche or Calcrete Associated with a pronounced negative shift in the carbon isotopic composition and a slight enrichment in the oxygen isotopic ratio The negative carbon is derived from the decomposition of organic material and the respiration plants The enrichment of oxygen arises from the evaporation near the surface. Isotopic Calcretes Oxygen Isotopic Composition Carbon Isotopic Composition Oxygen -5 CAICOS GUN KEY KEY LARGOSANSAL EXUMA BPK ANASTASIA Locality -9 CAICOS GUN LARGO SANSAL EXUMA BPK ANASTASIA Locality 105 Data from Rossinsky and Swart (1993) Carbon Picture Rossinsky Data from Clino Data from Clino Kievman and Swart (unpublished) Data from Rossinsky (1990) 8

Additional Caliche Signatures Shifts towards more negative carbon isotopic signatures occur within an overall isotopic regime which is already depleted.

with heavier values in more arid climates. Trace Elements Trace elements in isolated carbonate platforms are derived mainly from dust.

9 Additional Caliche Signatures Shifts towards more negative carbon isotopic signatures occur within an overall isotopic regime which is already depleted. Shifts in carbon appear to be independent of climate Oxygen isotopic values are not always enriched and the overall depletion is related to climate, with heavier values in more arid climates. Trace Elements Trace elements in isolated carbonate platforms are derived mainly from dust. Exposed surfaces tend to have higher concentrations of Fe and Mn Surfaces which are related to roots have lower concentrations (penetrative calcretes Rossinsky et al., 1993) 9

Fe (ppm) Thousands 0 2 4 6 8 50 E1 HostCavity E2 E3?(Pipe) PipePipe Pipe?

? Exposure Exposure 200 Exposure Exposure Exposure Picture Rossinsky 250 Vadose Zone Constant oxygen isotopic composition

isotopically light carbon dioxide and dissolution of carbonate 1 cc of seawater contains 1/16 moles of oxygen (0.

10 Fe (ppm) Thousands E1 HostCavity E2 E3?(Pipe) PipePipe Pipe?? Soil 100 Above Surface Host Host Surface Host Exposure Surface Depth (ft) 150?? Exposure Exposure 200 Exposure Exposure Exposure Picture Rossinsky 250 Vadose Zone Constant oxygen isotopic composition Large source of homogenous oxygen Variable carbon isotopic composition Variable amounts of mixing of organically derived isotopically light carbon dioxide and dissolution of carbonate 1 cc of seawater contains 1/16 moles of oxygen ( M), but only M of C. Therefore it is easier to alter O than C Figure from Moore 2001 Carbon Vadose Zone Alteration (ft) Depth 80 Variable C 100 Relatively constant O 120 Data from Clino Kievman and Swart (unpublished) 10

) 2/25/2009 Freshwater Phreatic "A zone located below

mainly with water rather than air" Relatively

groundwater is still isotopically depleted, but is

constant O Large pool of homogenous oxygen Phreatic

constant C Depth (ft) 150 Phreatic Relatively

11 ) 2/25/2009 Freshwater Phreatic "A zone located below the water table in which the pore space is filled mainly with water rather than air" Relatively constant, but negative C The input of C into the groundwater is still isotopically depleted, but is better mixing than in the vadose zone Relatively constant O Large pool of homogenous oxygen Phreatic Zone Carbon Vadose Relatively constant C Depth (ft) 150 Phreatic Relatively constant O 200 Data from Clino Kievman and Swart (unpublished) McClain et al. (1992) 11

12 McClain et al. (1992) McClain et al. (1992) McClain et al. (1992) 12

13 18 O 13 C McClain et al. (1992) McClain et al. (1992) 13

14 Bottom Sediment Bahama Bank Algae Bahama Bank 4.00 Oxygen Corals Florida Altered Pleistocene San Salvador Carbon Inverted "J" The inverted "J" is a pattern of C and O isotopes which is defines the alteration of original material. Carbon Isotopic Composition MCL Lohmann, Oxygen Isotopic Composition Inverted "J" Part I The story starts with deposition of the original sediments which may have a carbon value of +2 to +3 and an oxygen of -1 to -1.5 per mille. Carbon Oxygen 14

Perverted "J" Part II As the original sediment becomes exposed to meteoric fluids it is recrystallized and starts to change its O isotopic composition while

n Carbon 5 0-5 -10-5 -3-1 1 Oxygen The recrystallization of the sediment causes the O isotopic composition of the calcite to approach a steady value which is

15 Perverted "J" Part II As the original sediment becomes exposed to meteoric fluids it is recrystallized and starts to change its O isotopic composition while maintaining its C value. This is because there is a lot of oxygen circulating through the sediment, but relatively little C. n Carbon Oxygen The recrystallization of the sediment causes the O isotopic composition of the calcite to approach a steady value which is characteristic of the water which is doing the work and the temperature. This line is called the Meteoric Calcite Line (MCL). Inverted "J" Part III on Carb MCL Oxygen 2 1 Figure from Moore

Mixing-zone "A zone located between the marine phreatic zone and the freshwater phreatic zone which is characterized by mixing betwen these two end members" Mixing-zone diagenesis produces covarying

16 Mixing-zone "A zone located between the marine phreatic zone and the freshwater phreatic zone which is characterized by mixing betwen these two end members" Mixing-zone diagenesis produces covarying trends between alteration by meteoric waters ( -ve C and O) and alteration by marine fluids (+ve C and O). Covarying trends Mixing-Zone Isotopic Composition Carbon Oxygen Depth (ft) Oxygen Carbon Data from Clino Kievman and Swart (unpublished) 16

17 Vadose, phreatic, mixing-zone 200 Isotopic Composition Surface Vadose 300 Freshwater Phreatic 400 Mixing-zone Depth (ft) Data from Clino Kievman and Melim and Swart 700 Marine-Phreatic "A zone in which the porespace is filled with marine dominated fluids" Isotopic Composition Heavy Carbon Heavy Oxygen 400 Carbon Depth (ft) 600 Oxygen Oxygen =red, carbon = blue 13 C & 18 O ( o / oo ) th (ft) Dep

18 Cements are indicative of diagenetic environments 18

19 Cementation is very fast! Occurs within months Rate decreases with depth 8 months original 20 months Example: Oolithic sand in 30 m water depth is a rock after 20 months 19

20 Figure from Moore

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27 Swart et al

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29 Late Diagenesis 29

Bahamian Dolomites. Occurrences in the Bahamas 2/25/2009. Platform Dolomites. Cretaceous Dolomite. San Salvador Little Bahama Bank.

Bahamian Dolomites. Occurrences in the Bahamas 2/25/2009. Platform Dolomites. Cretaceous Dolomite. San Salvador Little Bahama Bank. Bahamian Dolomites A Short Course VU March, 2009 Peter Swart University of Miami Occurrences in the Bahamas Platform Dolomites San Salvador Little Bahama Bank Bahamas Drilling Project Unda Clino Cretaceous