The presence of natural gas hydrates (ice-bound methane) in submarine sediments of the landlocked South Caspian Sea (SCS) of Central Eurasia (Fig. 1) provides a unique natural laboratory to study the relationship of sea level changes and gas hydrate stability, with major implications for global climate change. Two USC owned 2-D seismic profiles (each ~70 km long) from the offshore Azerbaijan (named Absheron after a geographic location) document for the first time the occurrence of gas hydrates concealed beneath the seafloor (~300 m; Diaconescu and Knapp, 2000; Diaconescu et al., 2001). These are considerably shallower (~150 m) and thicker (~1500 m) hydrate deposits than other known hydrate provinces globally, and appear to control a large region (>200 km²) of overlying shallow deformation (the Absheron Allochton).

With this project, funds have been provided to establish a collaboration with Azeri scientists in order to secure a recently acquired 3-D seismic survey from the study area. This dataset is required for a proposal resubmission to the National Science Foundation (NSF) - Ocean Sciences in August 2003 for ~$200,000. Through extramural funds, this dataset will be processed and analyzed at USC to provide three-dimensional evidence for large-scale marine slumps produced by the catastrophic failure of the SCS continental slope as a result of dissociation of underlying buried gas hydrates. Climate-induced changes in the Caspian Sea level, with a long history of much larger fluctuations than the world’s ocean, may be responsible for large scale slope failure and seabed deformation through massive dissociation of buried gas hydrates during rapid sea level fall. Through these funds and subsequent extramural support, this project will have a major societal relevance with respect to understanding past global climate change patterns, with potential for predicting such phenomena in the future.

…

Figure 1. (top) Regional 2-D seismic reflection profiles (in red) and a 3-D seismic grid (orange rectangle) were acquired as part of ChevronTexaco’s exploration program in the deep water (300-720 m) of SCS. Central is the bathymetry of the seafloor highlighting the transition from the shelf edge to deep water. Star labeled C indicates location of coring. Inset shows the geographic setting of the Caspian Sea within Central Eurasia. SF stands for shallow faulting. SCS meets the pressure and temperature conditions required for gas hydrate formation as it has deep water (< 1100 m), low seafloor temperature (5.8-6.2°C), natural gas, and very low geothermal gradients (11-17°C/km) (Bagirov and Lerche, 1997); (bottom) Seismic section of ABSHERON 1 line showing a high velocity anomaly that is bound by high-amplitude reflectors at the top and bottom, named Top/Bottom Absheron Hydrate; TAH/BAH). Both TAH and BAH approximately parallel the sea floor, suggesting a thermobaric (of equal temperature and pressure), and not stratigraphic origin (Diaconescu et al., 2001), in support of a gas hydrate origin.

Personnel
Camelia C. Knapp
Christopher Mitchell
James H. Knapp

Return to GEL Home Page