XVIII
13.5
The Chemical Composition of Hydrothermal Vent Fluids and Precipitates . . . 468
13.6
Characteristics of Cold Seep Fluids at Subduction Zones . . . . . . . . . . . . . . . . . 472
13.7
Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473
14
Gas Hydrates in Marine Sediments
GERHARD BOHRMANN AND MARTA E. TORRES
14.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482
14.2
Hydrate Crystal Chemistry and Stability of Gas Hydrates . . . . . . . . . . . . . . . . . 482
14.2.1
Cages and Three Crystal Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482
14.2.2
Guest Molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483
14.2.3
Stability and Phase Boundaries of Gas Hydrates . . . . . . . . . . . . . . . . . . . . . . . . . . 484
14.3
Hydrate Occurrence in The Oceanic Environment . . . . . . . . . . . . . . . . . . . . . . 485
14.3.1
Gas Hydrate Stability Zone in Marine Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . 485
14.3.2
Seismic Evidence for Gas Hydrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487
14.3.3
Generation of Gases for Hydrate Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
14.3.4
Methane Transport and Hydrate Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490
14.3.5
Gas Hydrate Accumulation in Sediments and Fabric of Natural Gas Hydrates . . . . . . 492
14.4
Pore Water Anomalies Associated with Gas Hydrate Formation and
Decomposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494
14.4.1
Gas Hydrate and Chloride Anomalies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495
14.4.2
Gas Hydrate and Water Isotope Anomalies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
14.5
Gas Hydrate Carbonate Formation and Anaerobic Oxidation of Methane . . . . . 503
14.5.1
Petrographic Characteristics of Clathrites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503
14.5.2
Carbonate Precipitation through Microbial Activity . . . . . . . . . . . . . . . . . . . . . . . . . . 504
14.6
Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506
14.7
Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
15
Conceptual Models and Computer Models
HORST D. SCHULZ
15.1
Geochemical Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513
15.1.1
Structure of Geochemical Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513
15.1.2
Application Examples of Geochemical Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . 517
15.2
Analytical Solutions for Diffusion and Early Diagenetic Reactions . . . . . . . . . . 523
15.3
Numerical Solutions for Diagenetic Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524
15.3.1
Simple Models with Spreadsheet Software (‘Press-F9-Method’) . . . . . . . . . . . . . . . . 525
15.3.2
Two-Step Models with Explicit Numerical Solution of Fick’s 2
nd Law. . . . . . . . . . . . . . 529
15.3.3
Two-Step Models for Combined Complex Transport/Reaction Processes. . . . . . . . . .
538
15.4
Bioturbation and Bioirrigation in Combined Models . . . . . . . . . . . . . . . . . . . . . 543
15.5
Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545
Answers to Problems
Index
13.5
The Chemical Composition of Hydrothermal Vent Fluids and Precipitates . . . 468
13.6
Characteristics of Cold Seep Fluids at Subduction Zones . . . . . . . . . . . . . . . . . 472
13.7
Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473
14
Gas Hydrates in Marine Sediments
GERHARD BOHRMANN AND MARTA E. TORRES
14.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482
14.2
Hydrate Crystal Chemistry and Stability of Gas Hydrates . . . . . . . . . . . . . . . . . 482
14.2.1
Cages and Three Crystal Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482
14.2.2
Guest Molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483
14.2.3
Stability and Phase Boundaries of Gas Hydrates . . . . . . . . . . . . . . . . . . . . . . . . . . 484
14.3
Hydrate Occurrence in The Oceanic Environment . . . . . . . . . . . . . . . . . . . . . . 485
14.3.1
Gas Hydrate Stability Zone in Marine Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . 485
14.3.2
Seismic Evidence for Gas Hydrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487
14.3.3
Generation of Gases for Hydrate Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
14.3.4
Methane Transport and Hydrate Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490
14.3.5
Gas Hydrate Accumulation in Sediments and Fabric of Natural Gas Hydrates . . . . . . 492
14.4
Pore Water Anomalies Associated with Gas Hydrate Formation and
Decomposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494
14.4.1
Gas Hydrate and Chloride Anomalies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495
14.4.2
Gas Hydrate and Water Isotope Anomalies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
14.5
Gas Hydrate Carbonate Formation and Anaerobic Oxidation of Methane . . . . . 503
14.5.1
Petrographic Characteristics of Clathrites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503
14.5.2
Carbonate Precipitation through Microbial Activity . . . . . . . . . . . . . . . . . . . . . . . . . . 504
14.6
Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506
14.7
Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
15
Conceptual Models and Computer Models
HORST D. SCHULZ
15.1
Geochemical Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513
15.1.1
Structure of Geochemical Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513
15.1.2
Application Examples of Geochemical Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . 517
15.2
Analytical Solutions for Diffusion and Early Diagenetic Reactions . . . . . . . . . . 523
15.3
Numerical Solutions for Diagenetic Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524
15.3.1
Simple Models with Spreadsheet Software (‘Press-F9-Method’) . . . . . . . . . . . . . . . . 525
15.3.2
Two-Step Models with Explicit Numerical Solution of Fick’s 2
nd Law. . . . . . . . . . . . . . 529
15.3.3
Two-Step Models for Combined Complex Transport/Reaction Processes. . . . . . . . . .
538
15.4
Bioturbation and Bioirrigation in Combined Models . . . . . . . . . . . . . . . . . . . . . 543
15.5
Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545
Answers to Problems
Index