Glossary 



Acoustic release package. A device 

 that upon command releases current 

 meters or other instruments from the 

 weight that holds them to the sea 

 floor. 



Acoustic system. Pertaining to a package 

 of devices that puts sound energy 

 into the water column, receives signals 

 reflected from the sea floor and layers of 

 rock and sediment below the sea floor, 

 and displays and records the reflected 

 signals. 



Advection [oceanography]. The horizon- 

 tal or vertical flow of water as an ocean 

 current. 



Amphipod. Any small crustacean of the 

 order Amphipoda with vertically thin 

 bodies and sets of legs used for both 

 swimming and hopping; one common 

 variety is the "sand flea." 



Arc volcanism. The processes associated 

 with the extrusion of lava on and adja- 

 cent to a chain of islands (for example, 

 the Aleutians) rising from the deep 

 sea floor. 



Asthenosphere. The zone of the Earth's 

 upper mantle, below the lithosphere, 

 where rock is weak and capable of 

 flowing. 



Basalt. A dark, fine-grained extrusive igne- 

 ous rock. 



Bathymetric contour. A line on a map 

 showing equal depth below sea level on 

 the sea floor. 



Bathymetry. The measurement of ocean 

 depths and the charting of the topogra- 

 phy of the sea floor. 



Bioturbated. Said of sediments disturbed 

 by organisms. 



Blueschist. A metamorphic rock with a 

 blue color due to the presence of certain 

 minerals produced at high pressures in 

 the Earth. 



Camera transect. A track across the sea 

 floor along which a camera takes a 

 series of photographs. 



Chert. An extremely fine-grained (micro- 

 crystalline) sedimentary rock composed 



of silica (SiO 2 ), often from the tiny skel- 

 etons of aquatic microorganisms. 



Continental margin. The ocean floor that 

 is between the shoreline and the deep 

 (abyssal) ocean floor. 



Continental shelf. That part of the conti- 

 nental margin from the shoreline to the 

 continental slope or, where there is no 

 noticeable break in slope, to a depth of 

 about 660 feet (200 meters). 



Continental slope. That part of the conti- 

 nental margin that is between the con- 

 tinental shelf and the deep (abyssal) 

 ocean floor. 



Convergent boundary [currents]. An area 

 or zone where ocean currents come 

 together. 



Convergent boundary [plate tectonics]. 

 A boundary between two tectonic plates 

 that are moving toward each other. 



Coring device. An apparatus used to take 

 vertical, cylindrical or rectangular sec- 

 tions of sediment from the sea floor. 



Core sample. A vertical, cylindrical or 

 rectangular sample of sediment from 

 which the nature or stratification of 

 the sea-floor deposits may be deter- 

 mined. 



Crust [Earth's]. The outermost layer or 

 shell of the Earth. 



Current meter. A device that measures the 

 speed and direction of ocean currents. 



Deep submergence vehicle. A submarine 

 that is capable of submerging to very 

 great depths, usually used for research. 



Diabase. An dark intrusive igneous rock. 



Diatom. A microscopic single-celled plant 

 that secretes a silica (SiO 2 ) skeleton; 

 diatoms are abundant in both marine 

 and fresh water. 



Dike. A tabular igneous intrusion that cuts 

 across the bedding or foliation of the 

 host rock. 



Dinoflagellate. A single-celled micro- 

 scopic organism with resemblances to 

 both plants and animals: most species 

 are marine, and some are the cause of 

 toxic "red tides." 



Divergent boundary [currents]. The area 

 or zone where different currents or 



water bodies move apart from each 

 other. 



Divergent boundary [plate tectonics]. A 

 boundary between two plates that are 

 moving apart from each other. 



Eclogite. A granular rock composed essen- 

 tially of garnet and sodic pyroxene. 



Ekman transport. The current generated 

 from wind blowing over the surface 

 of the water, where the surface current 

 moves at 45 degrees to the right of the 

 wind direction (northern hemisphere) 

 and successively deeper layers of water 

 move increasingly to the right until at 

 some depth the water is moving oppo- 

 site the wind direction; the net transport 

 is 90 degrees to the right of the wind 

 direction. 



El Nino. An anomalous wanning of the 

 surface waters of the eastern tropical 

 Pacific Ocean, which can have world- 

 wide and significant effects on weather, 

 ocean currents, and sea life and can 

 cause droughts, floods, and other natural 

 disasters. 



Entrenched valley. A deepened, incised 

 valley that suggests rapid vertical uplift 

 or lowering of base level. 



Epicenter. The point on the Earth's surface 

 that is directly above the focus of an 

 earthquake. 



Euphausiid. A group of small planktonic 

 marine shrimp, commonly called krill, 

 that are an important food source for 

 many marine animals, including some 

 whales. 



Eustatic [sea level]. Said of worldwide 

 changes in sea level that affect all the 

 world's oceans. 



Exotic terrane. A geologic terrane that has 

 moved far from its place of origin and is 

 unrelated to those adjacent to it. 



Factor analysis. A mathematical technique 

 used to discover simple patterns in rela- 

 tions among variables. 



Farallon Escarpment. The steep subma- 

 rine slope in the region of the Farallon 

 Islands; part of the Continental Slope. 



Farallon Shelf. The gently sloping part of 

 the sea floor in the vicinity of the Faral- 



lon Islands from the shore to the Faral- 

 lon Escarpment; part of the Continental 

 Shelf. 



Fault. A fracture or zone of fractures in 

 the Earth along which there has been 

 displacement of the sides relative to one 

 another. 



Flagellates. Microorganisms possessing 

 whip-like flagella, which they use for 

 propulsion. 



Franciscan Complex/Assemblage. A dis- 

 orderly assemblage of rocks of various 

 characteristics in the Coast Ranges of 

 California that have undergone unsys- 

 tematic disturbance; typical rocks of 

 this assemblage crop out in the vicinity 

 of San Francisco. 



Franciscan melange. A variation of Fran- 

 ciscan Assemblage; a melange is char- 

 acterized by fragments and blocks of 

 various rock types of all sizes. 



Gabbro. A dark, granular intrusive rock; 

 the intrusive equivalent of basalt. 



Geomorphological. Pertaining to the gen- 

 eral configuration of the Earth's surface; 

 the nature and origin of landforms. 



Geophysics. The study of the Earth by 

 quantitative physical means. 



Glacier. A large mass of ice formed by the 

 accumulation, compaction, and recrys- 

 tallization of snow. 



Global Positioning System (GPS). A net- 

 work of satellites used for navigation. 



Granite. A light-colored plutonic rock rich 

 in quartz and feldspar. 



Granitic. Of or pertaining to granite. 



Gravity corer. A device with a long cylin- 

 drical pipe topped by a heavy weight 

 used to take samples of sea-floor sedi- 

 ments. 



Graywacke. A dark-gray, hard, coarse- 

 grained sandstone that consists of 

 poorly sorted, angular to subangular 

 mineral grains embedded in a clay 

 matrix. 



Great Valley of California. Also called 

 the Central Valley, it is a nearly flat allu- 

 vial plain in the central part of Califor- 

 nia about 450 miles long and on average 

 50 miles wide. Geologically, the Great 



Glossary 77 



