海洋地质(英文)复习题.docVIP

1.andesite:an intermediate type of volcanic rock between basalt and rhyolite.2.back-arc basic:a seafloor spreading system of volcanoes caused extension behind an island arc that is above a subduction zone.3.barrier island:a low,elongated coastal island that parallels the shoreline and protects the beach from storms.4.basalt:a dark,volcanic rock rich in iron and magnesium and usually quite fluid in the molten state.5.carbonate:a mineral containing calcium carbonate such as limestone and dolostone.6.Cenozoic:an era of geologic time comprising the last 65 million years.7.Circum-Pacific belt:active seismic regions around the rim of the belt Pacific plate coinciding with the Ring of Fire.8.continental drift:the concept that the continents drift across the surface of Earth.9.continental shelf:the offshore area of a continent in shallow sea.10.continental slope:the transition from the continental shelf to the deep-sea basin.11.Convergent Plate margin:the boundary between crustal plates where the plates come together;generally corresponds to the deep-sea trenches where old crust is destroyed in subduction zones.12.delta:the wedge-shaped pile of sediments deposited at the mouth of a river.13.divergent plate margin:the boundary between lithospheric plates where they separate;it generally corresponds to midocean ridges where new crust is formed by the solidification of liquid rock rising from below.14.erosion:the wearing away of surface materials by natural agents such as wind and water.15.fossil:any remains,impressions,or traces in rock of a plant or animal of a previous geologic age.16.geologic column:the total thickness of geologic units in a region.17.granite:a coarse-grain,silica-rich rock consisting primarily of quartz and feldspars.18.guyot:undersea volcano that once existed above sea level and whose top was flattened by erosion;later,subsidence caused the volcano to sink below the ocean surface,preserving its flat-top appearance.19.hydrocarbon:a molecule consisting of carbon chains with attached hydrogen atoms.20.igneous rocks:all rocks solidified from a molten state.21.island arc:volcanoes landward of a subduction zone,parallel to a trench of a subducting plate and above the plates melting zone.22.lava:molten magma that flows out onto the surface.23.limestone:a sedimentary rock composed of calcium carbonate that is secreted from seawater by invertebrates and whose skeletons compose the bulk of deposits.24.lithospheric plate:a segment of the lithosphere,the upper-layer plate of the mantle,involved in the interaction of other plates in tectonic activity.25.magma:a molten rock material generated withn Earth and that is the constituent of igneous rocks.26.midocean ridge:a submarine ridge along a divergent plate boundary where a new ocean floor is created by the upwelling of mantle material.27.Ring of Fire:a belt of subduction zones around the Pacific plate related to volcanic activity.28.seafloor spreading:a theory that the ocean floor is created by the separation of lithospheric plates along midocean ridges,with new oceanic crust-formed from mantle material that rises from the mantle to fill the rift.29.seamount:a submarine volcano that never reaches the surface of the sea.30.sedimentation:the deposition of sediments.31.subduction zone:a region where an oceanic plate dives below a continental plate into the mantle;ocean trenches are the surface expression of a subduction zone.32.tectonic activity:the formation of Earths crust by large-scale movements throughout geologic time.33.transform fault:a fracture in Earths crust along which lateral movement occurs;a common feature of the midocean ridges created in the line of seafloor spreading.34.trench:a depression on the ocean floor caused by plate subduction.35.turbidite:a slurry of mud that periodically slides down often gentle slopes toward the deep-sea floor.1. The plate tectonics model.New oceanic crust is generated at spreading ridges,and old oceanic crust is destroyed in subduction zones,which moves the continents around Earth.The discovery of many mysteries on the seabed,including spreading ridges and deep-sea trenches,led geologists to develop an entirely new way of looking at Earth,called the theory of plate tectonics(fig1).Tectonics is the geologic process responsible for features on Earths surface.The theory incorporated the process of sea-floor spreading and continental drift into a comprehensive model.The Atlantic Ocean is bisected by the Mid-Atlantic Ridge,which manufactures new oceanic crust as the continents surrounding the Atlantic basin spread apart.The Mid-Atlantic Ridge is the center of intense seismic and volcanic activity.It is the focus of high heat flow from Earths interior.Molten magma originating from the mantle rises through the lithosphere and erupts onto the ocean floor,adding new oceanic crust to both sides of the ridge crest.2. (The oceanic crust comprises a top layer of pillow basalts,a second layer of sheeted dikes,a third layer of gabbros,and an underlying layer of layered periditities above the mantle)Oceanic crust does not from as a single homogeneous mass.Instead,it comprises long,narrow ribbons laid side by side with fracture zones in between.The oceanic crust is comparable to a layer cake with four distinct strata.The upper layer is pillow basalts,formed when lava extruded undersea at great depths.The second layer is of a sheeted-dike complex,consisting of a tangled mass of feeders that brought magma to the surface.The third layer is of gabbros,which are coarse-grained rocks that crystallized slowly under high pressure in a deep magma chamber.The fourth layer is of peridotites segregated from the mantle below.Gabbros containing higher amounts of silica solidify out of the basaltic melt and accumulate in the lower layer of the oceanic crust.3. (A profile of the ocean floot)The sediments settle onto the continental shelf,which extends up to 100 miles or more and reaches a depth of roughly 600 feet.In most places,the continental shelf is nearly flat,with an average slope of only about 10 feet per mile.Beyond the continental shelf lies the continental slope,which extends to an average depth of more than 2 mile.It has a steep angle of several degrees,comparable to the slopes of many mountain ranges.Sediments reaching the edge of the continental shelf slide down the contiengtal slope under the pull of gravity.Often,huge masses of sediment cascade down the continental slope by gravity slides that can gouge out steep submarine canyons.They play an important role in building up the continental slope and the smooth ocean bottom below.4. (A stratigraphic cross section showing a sequence of sandstones,siltstones,and shales overlying a basement rock composed of limestone)Cementing agents such as silica or cdcium and the tremendous weigh of the overlying sedimentary layers pressing down onto the lower strata lithifies the sediments into solid rock.This provides a geologic column of alternating beds of lime-stone ,shales,siltstones,and sandstone.Abrasion eventually grinds down all rocks to clay-sized particles.Because clay particle are so small and sink so slowly,they normally settle out in calm,deep waters far from shore.Compaction from the weight of the overlying strata squeezes out water between sediment grains,lithifying the clay into mudstone or shale.5. (A cutaway view of intrusive magma bodies that invade Earths crust and erupt on the surface as volcanoes)The oceanic crust,composed of basalts originating at spreading ridges and sediments washed off continents and islands,gradually increases density and finally subducts into the mantle.On its way deep into Earths interior,the lithosphere and overlying sediments melt.The molten magma rises toward the surface in huge bubblelike structures called diapirs,from the Greek word diapeirein,meaning”to pierce.”When the magma reachers the base of the crust,it provides new molten rock for magma chambers beneath volcanoes and granitic bodies called plutons such as batholiths,which often form mountains.In this manner,plate tectonics is continuously changing and rear-ranging the face of Earth.油气储层的形成需要一系列特定的地质条件，包括生成石油的烃源岩、作为储层的孔隙性岩石和圈闭油气的构造。石油的生成需要数千万年到数亿年的时间，主要取决于沉积盆地的温度和压力条件。烃源岩是有机碳保存在细粒、富碳的沉积物中。例如砂岩和石灰岩这些孔隙性、渗透性的沉积岩可以形成储层。沉积岩层的褶皱作用和断裂作用形成的地质构造可以圈闭并储存油气。石油常与厚层的盐有关，因为盐岩比上覆沉积层的重量轻，所以盐能够上升到地表形成盐丘构造，有利于圈闭油气。生成石油的有机质来源于微生物，这些微生物主要生活在海水表层，并聚集在海底的细粒物质中。有机质向石油的转化要求高堆积速率或在底水中低氧环境，使有机质埋在沉积层之下以前免遭氧化，氧化作用会使有机质腐烂。因此，富含有机质的高沉积速率地区是最有利于烃源岩形成的地方。在沉积盆地中，深埋藏使处于高温、高压之下的有机质的温度进一步升高并使其发生化学变化。结果在地球内部热能作用下，有机质裂解为碳氢化合物。如果碳氢化合物过于成熟，那么则会形成天然气。在沉积物中储存的碳氢化合物的挥发性组分与海水一起通过渗透性岩层向上运移，聚集在沉积构造形成的圈闭中，这些圈闭阻碍了流体的进一步运移。在缺失盖层的情况下，挥发性组分会继续向地表运移并通过自然渗漏运移到海洋中，估计每年大约有150万桶石油自然渗漏到海洋中。然而，该数量与每年由于事故泄漏到海洋中大约2500桶的石油相比是微不足道的。实际上一些油气井可能有助于清除从海底泄漏的天然污染物。由于石油的年龄，它转化为像焦油一样的物质被冲到海岸。海上开采石油使自然泄漏到海底的石油减少了一半，尤其是最靠近生产平台的位置减少得更多。经过数年的油气开采，降低了海底油层的压力，因而减少了泄漏到海底石油的数量。但是，当流体和气体被注入岩石中使压力上升增加产量时，自然渗漏也会增加。海底地质学决定了是否存在圈闭油气的条件，这些有助于石油公司的勘探活动。石油勘探是从寻找连通含油圈闭的沉积构造开始的，通过利用空气枪爆炸激发类似于声波的地震波，利用拖在船尾的检波器接收这些反射信号，地震勘探可以描述这些构造。从各种沉积层反射和折射的地震波能够提供一张洋壳的抵制扫描图。选择好合适的井位后，石油公司运来钻井平台，把钻进平台竖在浅海海底或在深海底部采用自动浮标装置。当钻穿底部沉积层时，工人们开始下套管避免井壁崩塌，并起到输油管道的作用。预防井喷装置放在油层的顶部避免一旦钻头钻穿盖层，在巨大的压力作用下发生的井喷。如果幽径成功，那么就可以钻其余的井来完成油气开发任务。本章讨论形成海岸的作用。地表沉积物的不断搬运和海底沉积物的不断堆积使得地表处于不断变化之中。在强力的风暴潮期间，海水不断拍打海岸造成了海岸侵蚀，伴随风暴而来的巨浪强烈地侵蚀沙丘和海蚀崖。海浪的不断冲击也毁坏了许多防止海面上升的人工防波堤。美国过去的一个沙滩正在沉没于海面之下。沿美国东海岸和得克萨斯州沿岸的障壁岛和沙坝正在以惊人的速度消失。在加利福尼亚，海蚀崖正被侵蚀而伸入内陆，这种作用经常毁坏美丽的家园。大多数防护措施（如为阻止海岸侵蚀而修建的防波堤）常因海浪的不断拍打而被毁坏。地球是不断进化的行星，具有复杂的活动，例如流水和波浪运动。河流把大量的陆地冲刷物带入海洋，不断堆积在海岸地区。海岸在地形、气候和植被方面发生巨大变化，海岸带是大陆和海洋作用交互的地带，形成的地形总在发生快速的变化。海岸沙漠是独特的地形，在此海水沉积了沙漠沙。 在海底发生的大多数沉积是非常缓慢的。大陆是侵蚀作用的主要场所，而海洋是主要的沉积作用场所，海洋沉积物由从大陆侵蚀的一些物质组成，大多数沉积岩沿大陆边缘或在内陆海盆地中形成。例如，在中生代。这些海水侵入到了北美洲、南美洲、欧洲和亚洲内部，高沉积速率形成了数千英尺的沉积物，这些沉积物暴露于地表，单一沉积层可以徐延数百英里。 当侵蚀作用侵蚀山脉，河水把剥蚀碎屑物搬运到海洋时，沉积岩层即开始形成了。沉积物源于表层岩石的风化作用，风化产物包括许多物质，从细粒沉积物到巨大的砾石。暴露于地表的岩石，有的被化学作用分解成黏土和碳酸盐，有的被机械作用破碎为粉砂、砂和砾石。 雨、风或冰的侵蚀作用形成的沉积物被带入河流，河流把松散的沉积颗粒搬运到大海中。棱角状的沉积物颗粒表明搬运时间短，而浑圆的沉积物说明它在长时间搬运中受到严重磨损，或者经历了急流的改造作用，或者是由于岸边波浪的不断冲刷作用所造成的，确实，很多砂岩层曾经是海滩沉积物。 每年约250亿t沉积物经河流搬运到海洋并在大陆架上沉积。高耸的喜马拉雅山脉是最大的沉积源区。流经该区的主要河流包括著名的恒河和雅鲁藏布江，它们把占约全球40%的沉积物搬运到孟加拉湾，形成了3mile的沉积层。 当河流携带的沉积物到达海洋时