“Orca Basin”的意思、由来-开放百科全书

The Orca Basin is a mid-slope, silled, mini-basin in the northern Gulf of Mexico some 300 km southwest of the Mississippi River mouth on the Louisiana continental slope.^[1] It is unique amongst the mini-basins in this area, in containing a large brine pool of anoxic salt brine. The pool is approximately {{convert|123|km2|abbr=on}} in area and up to {{convert|220|m|abbr=on}} deep^[2] under {{convert|2400|m|abbr=on}} depth of Gulf water^[1] and is derived from dissolution of underlying Jurassic age Louann Salt. With a volume of {{convert|13.3|km3|abbr=on}} the pool results from the dissolution of about 3.62 billion tonnes of the Louann Salt bed into seawater.^[2] The basin owes its shape to ongoing salt tectonics and is surrounded by salt diapirs.^[1]

Based on light δ13C values, the origin of the hydrate gas is biogenic. Researchers also noted that some of the hydrates appeared to occur in the sandy layers of the cores. In contrast to other gas hydrate occurrences in the Gulf of Mexico, the gas hydrate was found within a mini-basin instead of on the fractured and faulted rim of the mini-basin.^[4] It was also noted that the depth of gas hydrate occurrence coincides with the presence of black organic and/or pyrite-rich mud.^[3]

Importance of Orca basin as a study site

The Orca Basin is important in understanding glacial and deglacial changes, including the history of meltwater flows from the Laurentide Ice Sheet, that have affected North America and the Gulf of Mexico.^[5] The sediments that fill the Orca Basin contain an important record of the paleoenvironment and paleo-oceanology of the Louisiana continental slope south of the Mississippi River Delta for at least the last 25,000 years.^[6]^[7] Because of location of this basin, paleoenvironmental proxies, e.g. planktonic foraminifers, stable isotope ratios, changes in sediment texture, and reworked calcareous nannofossils, preserved in its sediment also recorded the impact and chronology of meltwater floods that flowed down the Mississippi River on the Gulf of Mexico during the last deglaciation.^[8]^[9]

In addition, the only recorded recovery of gas hydrates in the Gulf of Mexico from depths greater than 66 fbsf (20 mbsf) occurred at DSDP Site 618 in Orca basin.^[10] The recovery of biogenic methane hydrate from Orca basin is also significant due to the high salinity values, which at the sediment/water interface were nearly 5 times as high as those found in the Red Sea (with salinity values of 240-260 PSU). The values decreased rapidly with depth to about 98 fbsf (30 mbsf) before becoming constant (48-56 PSU).^[3] The hydrate recovered from both sites in Orca Basin were in the range of 85-121 fbsf (26-37 mbsf) and are physical evidence of the decreased salinity levels.

References

1. ^¹²Meckler, A. N., et al., [https://web.archive.org/web/20160304042237/http://www.climategeology.ethz.ch/publications/2008_Meckler_et_al.pdf Glacial to Holocene terrigenous organic matter input to sediments from Orca Basin, Gulf of Mexico,] Earth and Planetary Science Letters 272 (2008) 251–263.
2. ^¹Pilcher, R.S. and Blumstein, R.D. 2007. Brine volume and salt dissolution rates in Orca Basin, northeast Gulf of Mexico. AAPG Bulletin; 91; no. 6; p. 823-833. Abstract
3. ^¹²DSDP Leg 96 Shipboard Science Party 1986. DSDP Leg 96 Shipboard Science Party. Site 618 Initial Report. DSDP Leg 96. Washington (U.S. Govt. Printing Office): DSDP, 1986, 399-407.
4. ^Milkov and Sassen 2000.Milkov, A., and R. Sassen. "Thickness of the natural gas hydrate stability zone, Gulf of Mexico continental slope." Marine and Petroleum Geology 17, no. 9 (2000): 981-991.
5. ^Poore, R.Z., Verardo, S., Caplan, J., Pavich, K. and Quinn, T., 2011. Planktic Foraminiferal Relative Abundance and Trends in Gulf of Mexico Holocene Sediments. in Tunnell, J.W., Felder, D.L., Earle, S.A., Buster, N.A., Holmes, C.W. and Camp, D.K. eds., p. 367-379. Gulf of Mexico Origin, Waters, and Biota: Volume 3, Geology (Vol. 3). College Station, Texas, Texas A&M University Press. {{ISBN|978-1-603-44290-9}}.
6. ^Flower, B.P., and Kennett, J.P., 1995, Biotic responses to temperature and salinity changes during the last deglaciation, Gulf of Mexico, in Stanley, S.M., ed., p. 209–220. Effects of past global change on life: Washington, D.C., National Academy Press, National Research Council Studies in Geophysics. {{ISBN|978-0-309-05127-9}}.
7. ^Kennett, J.P., Elmstrom, K. and Penrose, N., 1985. The last deglaciation in Orca Basin, Gulf of Mexico: high-resolution planktonic foraminiferal changes. Palaeogeography, Palaeoclimatology, Palaeoecology, 50(2-3), pp.189-216.
8. ^Brown, P., Kennett, J.P. and Ingram, B.L., 1999. Marine evidence for episodic Holocene megafloods in North America and the northern Gulf of Mexico. Paleoceanography, 14(4), pp.498-510.
9. ^Marchitto, T.M. and Wei, K.Y., 1995. History of Laurentide meltwater flow to the Gulf of Mexico during the last deglaciation, as revealed by reworked calcareous nannofossils. Geology, 23(9), pp.779-782.
10. ^Hutchinson, D.R., Ruppel, C.D., Roberts, H.H., Carney, R.S. and Smith, M., 2011. Gas hydrates in the Gulf of Mexico. in Tunnell, J.W., Felder, D.L., Earle, S.A., Buster, N.A., Holmes, C.W. and Camp, D.K. eds., p. 247-276. Gulf of Mexico Origin, Waters, and Biota: Volume 3, Geology (Vol. 3). College Station, Texas, Texas A&M University Press. {{ISBN|978-1-603-44290-9}}.

Importance of Orca basin as a study site

References

External links