Valley is a large, elongate northwest- 

 trending structural trough filled with a 

 thick sequence of sediments that range 

 in age from Jurassic to present. 



Heavy minerals. Detrital minerals that 

 have a specific gravity higher than a 

 standard, usually 2.85. 



Highstand. Generally referring to the high- 

 est eustatic sea levels during any period 

 of geologic time. 



Ice Age. A time of extensive glacial activ- 

 ity; most recently the Pleistocene, which 

 began about 1 .6 million years ago and 

 lasted until about 10,000 years ago. 



Igneous. Said of rocks or minerals that 

 solidified from molten or partly molten 

 material. 



Intervalometer. A timing device on a 

 submarine camera that automatically 

 operates the shutter at predetermined 

 intervals. 



Intrusion. The process of emplacement 

 of magma in preexisting rock, leading 

 to the formation of igneous rocks in 

 the form of dikes, plutons, and batho- 

 liths. 



Lava. Molten material erupted (extruded) 

 at the surface of the Earth; also, the rock 

 that solidifies from such material. 



Limestone. A sedimentary rock com- 

 posed chiefly of calcium carbonate 

 (CaCO 3 ), often from the shells of 

 marine organisms. 



Lithosphere. The solid outer portion of the 

 Earth; it includes the crust and upper- 

 most mantle, above the asthenosphere. 



Lithostratigraphic unit. A layer of rock 

 defined on the basis of lithologic char- 

 acteristics and stratigraphic position. 



Loran-C. A high-precision navigation 

 system. 



Lowstand. Generally referring to the 

 lowest eustatic sea levels during any 

 period of geologic time. 



Magma. Molten rock below the Earth's 

 surface. 



Magnitude (M). A measure of the strength 

 (energy released) of an earthquake. 



Mantle [Earth's]. The zone of the Earth 

 below the crust and above the core. 



Megalopa (megalops). An advanced larval 

 stage of crabs, just preceding the adult 

 stage. 



Mesozoic. An era of geologic time from 

 about 225 to about 65 million years ago, 

 best known as the time of the dinosaurs. 



Metamorphic. Pertaining to rocks and 

 minerals that have been changed by heat 

 and pressure. 



Oceanic plate. A tectonic plate of the 

 Earth's lithosphere that is characterized 

 by thin basaltic crust; moves horizon- 

 tally and adjoins other plates along seis- 

 mically active zones. 



Pelagic. Said of marine organisms whose 

 environment is the open ocean, rather 

 than the bottom or shore areas. 



Photic (euphotic) zone. The upper zone 

 of ocean waters in which sunlight pen- 

 etrates sufficiently to support photosyn- 

 thesis; generally the upper 150 to 450 

 feet of the water column. 



Photosynthesis. The process by which 

 plants make organic compounds from 

 carbon dioxide and water using the 

 energy of sunlight, a byproduct of 

 which is the production of free oxygen; 

 photosynthesis is the primary basis for 

 food production on Earth. 



Phytoplankton. Aquatic plants, mostly micro- 

 scopic, that have a planktonic lifestyle. 



Pillow basalt. A type of basalt that is char- 

 acterized by pillow-shaped structures, 

 generally interpreted to indicate that it 

 was erupted under water. 



Plankton. Aquatic plants and animals, 

 chiefly microscopic, that drift or float 

 in the water and are the main basis of 

 marine food webs. 



Plate tectonics. A theory of global tecton- 

 ics in which the lithosphere is divided 

 into a series of plates that move hori- 

 zontally relative to one another. 



Primary producers. Green plants, includ- 

 ing most phytoplankton; so called 

 because they produce, through photo- 

 synthesis, the organic compounds that 

 form the beginning link in food webs. 



Radiolarian chert. A layered (well 

 bedded) microcrystalline rock consist- 



ing of the remains of one-celled marine 

 animals called radiolarians. 



Ranging navigation system [Del Norte/ 

 Benthos]. A system used relatively 

 close to shore to determine a precise 

 position at sea. 



Red tide. A reddish discoloration of seawa- 

 ter caused by a bloom of toxic dinofla- 

 gellates. 



Salinian terrane/block (Salinia). A 

 300-mile-long slice of rock that forms 

 most of the basement in the central 

 coastal part of California, west of the 

 San Andreas Fault; this terrane has 

 been interpreted to be displaced north- 

 ward from a southward extension of the 

 Sierra Nevada or possibly from even 

 farther south. 



Sea-floor spreading. The process in which 

 new ocean crust is created by upwelling 

 of magma at midoceanic-ridge spread- 

 ing centers; as new crust is created, 

 it moves horizontally away from the 

 ridge. 



Seismic-reflection profile. A profile pro- 

 duced from the return of acoustic 

 energy reflected off the sea floor and off 

 density discontinuities at layers below 

 the sea floor. 



Seismometer. An instrument that detects 

 Earth motions. 



Serpentine. A group of common minerals, 

 commonly a mottled shade of green, 

 that form by alteration of olivine and 

 other magnesium-rich minerals found in 

 igneous and metamorphic rocks. 



Serpentinite. A characteristically green 

 rock consisting almost wholly of ser- 

 pentine-group minerals; it is a common 

 rock type in coastal central California. 



Shelf break. An abrupt change in slope 

 that marks the boundary between the 

 Continental Shelf and Slope. 



Sidescan sonar. An acoustic device that 

 emits sound signals to the side of a 

 ship's track; these signals are reflected 

 back from the sea floor, revealing its 

 character. 



Souter Van Veen grab sampler/corer. A 

 jawed or clam-like device that grabs or 



scoops up samples of sediment from the 

 sea floor. 



Stream valley. An elongate depression in 

 the Earth's surface carved by a stream. 



Structural fold. A fold in rock or strata 

 produced by deformation. 



Subaerial. Processes or conditions, such as 

 erosion, that exist or operate in the open 

 air at the Earth's surface. 



Subduction. The process of one litho- 

 spheric plate descending beneath 

 another along a convergent boundary. 



Subduction zone. A zone along which sub- 

 duction occurs. 



Tectonic plate. One of the large plates of 

 lithosphere constituting the surface of 

 the Earth that move horizontally relative 

 to one another. 



Terrane. A fault-bounded body of rock of 

 regional extent, characterized by a geo- 

 logic history different from that of adja- 

 cent terranes. 



Terrestrial lowland. An area or place 

 of low-lying land, especially near the 

 coast. 



Towfish. A device towed on a cable behind 

 a ship; commonly applied to a sidescan- 

 sonar transceiver. 



Transform boundary. In plate tectonics, a 

 plate boundary that ideally shows pure 

 strike-slip displacement (two plates slid- 

 ing horizontally past each other). 



Transmissometer. A device that measures 

 levels of light in the water, providing 

 an estimate of the amount of suspended 

 paniculate matter. 



Tsunami. A gravitational seawave initiated 

 by a short-duration, large-scale distur- 

 bance of the sea floor, usually by strong 

 earthquake. 



Unconformity. A substantial break or gap 

 in the geologic record where a rock unit 

 is overlain by another that is not next in 

 stratigraphic succession. 



Water column. A vertical section of water 

 from the surface to the bottom of a body 

 of water. 



Zooplankton. Aquatic animals, mostly 

 microscopic, that have a planktonic life- 

 style. 



78 Glossary 



ft U.S. GOVERNMENT PRINTING OFFICE: 2002 773-049 / 30070 Region No. 8 



