Geology topics
Publications and source records attributed to E.T. Degens.
Lake Kivu, an African rift lake, contains about 50 cubic kilometers of methane (at standard temperature and pressure) in its deep water. Data resulting from two recent expeditions to the lake and a reevaluation of earlier data suggest that most of the methane was formed by bacteria from abiogenetic carbon dioxide and hydrogen, rather than being of volcanic origin or having formed from decomposing organic matter.
The origin and chemical nature of micron-sized spheres found as suspended particles in Lake Kivu are examined. It can be shown that the hollow spheres, with a wall thickness of 500 Å, consist of a complex polymeric resinous material which has little functionality, except for hydroxyl groups. The spheres arise in the process of degassing of water samples at depth. Tiny gas bubbles, about 1 micron in size, act as scavengers of dissolved resinous material. The newly created resinous membrane promotes the selective coordination of zinc dissolved in the water column. In the prevailing H 2 S regime, formation of sphalerite crystals in induced. The size range of the crystals, 5 to 50 Å, corresponds to 1 to 10 unit cells and suggests that the resinous membrane also acts as a template in sphalerite growth processes. The sources of the zinc and dissolved gases (CO 2 , CH 4 , H 2 S) are hydrothermal springs seeping from the lake bottom into the basin. Water discharge is substantial; about 100 years are required to fill the lake to its present level (ca. 550 km 3 water). The average Kivu water contains 2 ppm zinc. Thus, 1 million tons of zinc are contained in Lake Kivu in the form of sphalerite.
In some calcium carbonate-bearing sandstones from the edge of the continental shelf off the northeast United States, the δC 13 range is from -30 and -60 per mil for both aragonite and high-magnesium calcite. The δC 13 of co-existing shells of Modiolus sp. is normal (+ 1.7 to -2.7 per mil). The δO 18 values of around + 3.5 per mil in all samples suggest deposition at temperatures around 0°C. Quaternary methane oxidized either chemically or microbiologically to carbon dioxide is the probable source of carbon in these carbonates.
Sedimentary iron and heavy-metal deposits of undetermined size have been found in the middle of the Red Sea some 2000 meters below the surface of the sea (Fig. 1). This discovery has been made from the Research Vessel Atlantis II , which is still at sea engaged in a series of oceanographic investigations which ultimately will end in November 1965, after the ship has circumnavigated the globe. The discovery is significant because the environment and the processes controlling deposition of heavy metals are observable and appear to be still active.
Sedimentary iron and heavy-metal deposits of undetermined size have been found in the middle of the Red Sea some 2000 meters below the surface of the sea. This discovery has been made from the Research Vessel Atlantis II , which is still at sea engaged in a series of oceanographic investigations which ultimately will end in November 1965, after the ship has circumnavigated the globe. The discovery is significant because the environment and the processes controlling deposition of heavy metals are observable and appear to be still active. The environment of the deposits can be breiefly described as an isolated sub-marine pool of brine having a pH as low as 5.3, a temperature of 56° c. and a salt content of about 310 grams per liter (at 20° c). Shipboard oxygen determinations and the indicated presence of H 2 S, divalent iron and divalent manganese in the water suggest that the environment is anaerobic. This hot, dense brine is trapped in a local depression of the Red Sea median valley. (Atlantis II Deep). The iron deposits, consisting largely of hydrous iron oxides, are found in the same depression. Brines from the Discovery Deep (21° 17 1 N, 38° 02'E) (1), a few miles southwest of the Atlantis II Deep (21°21 1 N, 38 ° 04'E), have a pH of 6.2 and a temperature of 44.7° c, and are also associated with iron-bearing sedirnents. The Discovery and Atlantis II brine pools both extend about 150 meters above the bottom. A few miles south of the: Discovery Deep another depression of greater depth has been reported (2) containing essentially normal Red Sea water. Deeps several hundred miles to the north (Sta. 540) and south (Sta. 545) were investigated and contained no brine. One of these (Sta. 545) is known to contain normal sediments.