WorldWide Drilling Resource

Frequently-Used Geological Terms Part 43 Glossary Adapted from the Dictionary of Geological Terms L - Continued Loran - Refers to various long-range radio position-fixing systems by which hyper- bolic lines of position are determined by measuring the difference in arrival times of synchronized pulse signals from two or more fixed transmitting radio stations of known geographic position. Lost Circulation - The condition during rotary drilling when the drilling mud es- capes into porous, fractured, or cavernous rocks penetrated by the borehole, and does not return to the surface. Louderback - A remnant of a lava flow appearing in a tilted fault block and bounded by a dip slope. It is named for American geologist G.D. Louderback who used it as evidence of block faulting in a basin-and- range topography Low-Angle Fault - A fault dipping less than 45 degrees. Low-Energy Environment - An aqueous sedimentary environment characterized by a low energy level and by standing water, or a general lack of wave or current action, permitting very fine-grain sediments to settle and accumulate. Lower - Refers to strata located below those of later formations of the same subdivision of rocks. The adjective is ap- plied to the name of a system, series, or stage to indicate position in the geologic column, and corresponds to early as ap- plied to the name of the equivalent geo- logic time unit. For example, rocks of the Lower Jurassic System were formed during the Early Jurassic Period. Lower Core - This term includes the earth’s inner core and the transitional zone of the outer core. The equivalent of the F and G layers. Lower Mantle - The part of the mantle located below a depth of about 620 miles. Also refers to the D layer. Low Grade - Ore with relatively low ore /mineral content. Low-Rank Graywacke - A graywacke (a conglomerate composed of firmly ce- mented fragments) in which feldspar is almost absent. Low-Rank Metamorphism - Metamor- phism accomplished under conditions of low to moderate temperature and pres- sure. Ancient 200-million-year-old Graywacke outcrop at the Omana Regional Park in Auckland, New Zealand. More terms to come next month! " ; # 511-,(2 0) 20'5&43 %9 4+(3( ,/( $/5)$&452(23 ; 08 029'0/ # ! : : $8 $,- 3$-(3 *,6(/3,/4(2/$4,0/$- &0. "(% ,4( 777 *,6(/3,/4(2/$4,0/$- &0. 49 WorldWide Drilling Resource ® OCTOBER 2015