LESSON-7-自翻.docx

LESSON 7 DEPOSITIONAL BASINS AND PLATE TECTONICSFrom analysis of stratigraphic data accumulated during the past 100 years, it is clear that preserved sedimentary rocks are dominantly marine. There are several reasons for the dominance of marine sediments: (分析过去100年的地层学数据，明显可知残留下来的沉积岩主要在海里。海洋沉积物占大部分主要有几个原因)The light sialic material that forms a large proportion of continental masses is limited in volume, with the result that continental areas constitute only about 30% of the earths surface. The marine areas are sediment traps that cover 70% of the earths surface.（构成大陆块一大部分的硅铝质物质体积有限，导致陆地区域只占地球表面约30%，海洋由沉积物构成，占地球表面的70%）Because of the movement and subduction of oceanic lithosphere at the edges of some continental blocks, topographically depressed areas (trenches) with adjacent easily eroded highland areas exist at active continental margins.（因为板块运动和一些大陆板块边缘发生的洋壳俯冲，临近的负地形（海沟）很容易侵蚀掉活动大陆边缘的高地）There has been a pronounced tendency through time for broad areas of the continental blocks to be invaded by shallow marine waters (epicontinental seas). The resulting shallow-water marine sediments are laterally extensive on the craton, although typically they are thin. Figure 11-2 shows the number and extent of the major global transgressions and regressions of these seas, as determined from seismic records; but many more minor transgressive-regressive sequences are known to be present. The tectonic explanation for at least the major cycles is the changing volume of the oceanic rift system. An increase in volume of the ridges results in a decrease in volume of the ocean basins and subsequent flooding of the low-lying parts of continents. It is clear that there have been two first-order transgressions, the first extending from Early Cambrian to Late Cambrian time and the second from Early Cretaceous to Late Cretaceous time. Extensive continental flooding also was prominent from Cambrian through Mississippian time. The causes of higher order cycles might be either the waxing and waning of ice sheets or regional tectonic movements. Phanerozoic continental glaciations are known to have occurred in every geologic period except Cambrian, Triassic, Jurassic, and Cretaceous.（随着时间推移，大陆板块的广大地区存在明显会被浅海侵蚀的趋势（陆缘海）。结果浅海沉积物在克拉通边缘广泛分布，尽管通常很薄。插图11-2展示了主要的全球性海侵和海退的次序和程度，这些都是从地震记录得来的；但是许多更小的一连串的海侵海退现在也被人们所知。主要的沉积旋回的构造学解释是其由大洋裂谷体积改变引起的。大洋体积扩张导致海洋盆地体积减少，随后导致大陆低洼部分被海水淹没。很明显全球有两期一级海侵，第一期从早寒武世到晚寒武世，第二期从早白垩世到晚白垩世。寒武世到密西西比世也主要以大陆广泛遭受海侵为主。次级海进海退的原因可能是冰席的消融和凝结或者是区域性的构造运动。显生宙大陆冰期已知发生在除了寒武纪、三叠纪、侏罗纪和白垩纪的每一个地质时期。）Continental deposits are, by definition, formed above sea level and hence are subject to removal should the rate of accumulation fall behind the erosion rate. It is no accident that stratigraphic sections on the continental blocks contain many more large unconformities than deeper marine or oceanic sections.（陆相沉积物，根据定义讲，形成于海平面之上，因此与消除作用有关，即沉积的速率应该小于剥蚀的速率。无疑大陆板块的地层相比深海或者海洋中有更多大型不整合界面。）It is clear from studies of sediment distribution in the oceans that the thickest accumulations of Cenozoic sediment occur adjacent to the continental margins; and paleogeographic reconstructions based on stratigraphy, paleontology, and facies analysis indicate that the same pattern has existed throughout geologic history. Figure 11-3 shows the extent of accretion onto the Precambrian nucleus of the United States during Phanerozoic time. Also shown is the position of the United States with respect to the equator during each geologic period; it is apparent that the area was located within 30 of the equator from Cambrian through Triassic time. This position implies a continual tropical to subtropical climate, and climate is an important control of the mineral composition of sediments (see Chapter 12).（通过对大洋中沉积物分布的研究，显然最厚的新生代沉积物在邻进大陆边缘出现。并且基于地层学，古生物学，沉积相分析对古地理进行重建表明相同的（沉积）模式在地质历史中一直存在。图11-3展示了美国前寒武纪结晶基地在显生宙时期增长的规模。同样也展示了在各个地质时期美国相对于赤道的位置。显然美国地区从寒武纪到三叠纪处于赤道三十度以内。这个位置意味着连续的热带亚热带气候，而且气候是沉积矿产的一个重要的控制因素（见12章）A universally accepted classification scheme for sedimentary basins has yet to appear, but those proposed so far are based on three factors: whether the basin is underlain by continental or oceanic crust; whether the basin was formed along a divergent, convergent, or strike-slip plate margin; and the position of the basin on the plate. The geologic history of each basin may then be subdivided into cycles on the basis of three parameters: basin-forming tectonics, depositional sequences, and basin-modifying tectonics. All types of complexities can be accommodated within this framework.（现在还没有一个被广泛接受的沉积盆地的分类方案，但是到目前为止那些提议主要是基于三个方面：盆地是否下伏在大陆或者洋壳之下；盆地是否沿着分离，聚合或者是走滑板块边缘产出；盆地在板块上的位置。每个盆地的地质历史可以细分至旋回，基于三个因素：形成盆地的大地构造，沉积旋回，和使盆地发生变化的大地构造。在分类框架中，各种复杂的因素都应该被考虑。）In the present discussion we group the major types of sedimentary basins into six categories, each of which has distinctive structural and sedimentary petrologic characteristics.（现有讨论中，我们将主要的沉积盆地分为六类，每一种都有各自的构造和沉积岩石学特征。）Oceanic basins are areas of deposition underlain by oceanic lithosphere, for example, the bulk of the Atlantic and Pacific Ocean basins. Mesozoic examples of oceanic deposits now accreted to the continental blocks are well known in the circum-Pacific region. Paleozoic examples occur in eastern Canada.（大洋盆地是海洋岩石圈上的沉积区域，比如大西洋盆地和太平洋盆地的大部分区域。现产出于大陆板块附近的中生代海洋沉积矿产的例子众所周知在环太平洋带。显生宙的例子在加拿大东部。）Arc-trench system basins, the most complex zone of basin development, form in convergent-margin areas and pose very difficult problems of interpretation because of the intense tectonism that accompanies subduction. Examples have been described from around the Pacific rim. (弧沟体系盆地，是盆地发展最复杂的区域，形成于聚合边界地区并且因为强烈的构造运动伴随着洋壳俯冲，导致有多问题难以解释。例子已经在环太平洋带提到。)Continental-collision basins develop along zones where continental plates collide and are different from the collision zone of an oceanic plate and a continental plate. Examples of such basins have been described from the Ouachita (Carboniferous) and Himalaya belts.（大陆碰撞型盆地形成在大陆碰撞区域，并且和陆块与洋块碰撞区不同。这种盆地的例子在沃希托河系（石炭系）和喜马拉雅造山带中提到）Basins in displaced terranes occur along continental margins. Geologists sometimes visualize the oceanic plate that is subducted during convergence as a relatively flat surface composed of biogenic oozes and abyssal clay. Commonly, however, the plate also contains old island arcs and other oceanic terranes; and as the plate is subducted, these arcs and their included basins are plastered onto the side of the continental plate. These oceanic plate fragments are termed exotic terranes and occur along the western margin of the United States from Alaska southward to southern California (Figure 11-4). They are recognized in many other regions as well. Such terranes are structurally, stratigraphically, and paleontologically discordant with the adjacent continental block and may contain oceanic sediment, forearc basins, intraarc basins, or backarc basins.（移置地体中的盆地出现在大陆边缘。地质学家有时把板块聚合过程中的洋壳看作由生物软泥和深海粘土组成的近乎平坦的界面。然而，一般来说，大洋板块也含有古老的岛弧和其他大洋地体；随着板块俯冲，这些岛弧和其内部的盆地一起伏到大陆板块下侧。这些大洋板块的碎片被称为外来地体，沿着美国西部边界从阿拉斯加南部到加利福尼亚州南部分布（图11-4）。在其他地区也可以见到。这些地体在构造，地层和古生物方面都与毗邻的大陆板块不协调，而且混含有大洋沉积物，弧前盆地，弧内盆地或者弧后盆地的成分。）Grabens along continental margins are depocenters formed by rifting along the margins of stable continental crust in association with the formation of an oceanic basin. Most such grabens are oriented parallel to the sides of the oceanic basin, but others can be oriented at a large angle to the coastline, in a reentrant (an aulacogen).（大陆边缘地堑是形成于隆升的稳定陆壳边缘的沉积中心，与大洋盆地的形成有关。大部分这样的地堑走向与大洋盆地的边缘平行，但是有些可能走向与海岸线大角度斜交，在凹陷地方产出（坳拉槽）Intracratonic basins are depocenters formed independently of tectonic activity at plate margins and at unpredictable locations within the continents. Their locations are thought to reflect buried ancient rift zones. Sediment thicknesses in the basins are typically 1000 to 5000 m greater than those in the geographic surroundings; examples include the Illinois, Michigan, and Williston Basins. The sedimentary fill in these basins is dominated by carbonates, shales, evaporites, and some quartz-rich sandstones. Rocks such as conglomerates, lithic or feldspathic sandstones, turbidites, and bedded cherts are uncommon to rare 句法错误。不定式后直接加形容词 because the tectonic setting surrounding intracratonic basins is nonorogenic and the depositional environments are invariably located in shallow waters. （内克拉通盆地是构造活动中独立形成于板块边缘的沉积中心和陆地无法预测的位置上。这些盆地的位置被认为反映了埋藏的古老抬升区域。盆地的沉积厚度一般1KM-5KM，比那些周围地理环境中形成的盆地要厚。例如，伊利诺斯盆地、密西根盆地和威利斯顿盆地。这些盆地中的沉积物主要是碳酸盐岩，页岩，蒸发岩和一些富含石英的砂岩。像砾岩、岩屑砂岩或者是长石砂岩，浊流岩，层内的燧石岩这些岩石很少见因为内克拉通盆地周围的构造背景是非造山带地区并且沉积环境是不太动荡的浅水沉积环境。）Oceanic BasinsThe principal settings of oceanic facies controlled by tectonic relations are shown in Figure 11-5. They are (1) bathymetric highs of ridge crests at divergent plate junctions, where igneous rocks are formed along the trends of the spreading centers; (2) the zone where the oceanic substratum gradually subsides as it cools in moving away from spreading centers; and (3) deep basins beneath which the thermal contraction of the lithosphere is essentially complete.（表11-5展示了相关构造控制的海相沉积的主要形成背景。它们包括(1)洋中脊等深的分离板块结合点，在结合点，火成岩沿着扩张中心的走向产出(2)洋底逐渐向两边退去的区域，在该区域，洋底逐渐冷却并远离扩张中心(3)深海盆地，在其之下岩石圈的热收缩几乎完成。）The pelagic sediment that covers the basaltic ocean crust has a stratigraphy and a facies relationship that reflect changing water depths. Near the upper part of the ridge, the water depth is commonly less than about 4000 m; here pelagic shells of calcium carbonate can accumulate. Below this depth-called the carbonate-compensation depth (CCD)-the degree of undersaturation of the water with respect to calcite or aragonite is so great that shell accumulation is not possible (see Chapter 16). Lower on the rise flanks, in the deep basins and in cold waters, brown clay or siliceous shells accumulate. If the depositional site is sufficiently near a land-mass, then continental sediment is carried into the deep oceanic basin by turbidity currents (see Chapter 13) and is interbedded with the calcareous and siliceous oceanic deposits.（覆盖在玄武质洋壳的远洋沉积物，它的地层学和沉积相关系能反映水深变化。接近洋中脊上部，水深一般小于4KM；由钙质碳酸盐构成的远洋沉积层在这里沉积。在这个深度下称作碳酸盐补偿深度（CCD）-水中对方解石类或文石类极度不饱和使（钙质）沉积不可能发生（见16节）。向下在洋脊的翼部，深海盆地和冷水中，棕色的粘土或者硅质层沉积下来。如果沉积地点足够接近大陆，而后陆源沉积物被浊流带入深海（见13节）和钙质硅质的海洋沉积物互层。）Arc-Trench System BasinsArc-trench systems occur along convergent plate margins and include a variety of morphotectonic elements (Figure 11-6), each of which can accumulate a distinctive sedimentary assemblage: （弧沟系统发育在聚合板块边缘，包括一系列地貌构造单元（表11-6），每一个单元中都有不同的沉积物。）The trench, a bathymetric deep, floored by oceanic crust（海沟-以洋壳为底的，等深的深沟）The subduction zone（俯冲带）The arc-trench gap, a belt within which a forearc basin may occur between the trench and the magmatic arc (弧沟间隙-在岩浆弧和海沟之间可能产生弧前盆地的带状区域)The magmatic arc, within which intraarc basins may occur.（岩浆弧-在其中可能发育弧内盆地）The backarc area, within which may lie either an interarc basin floored by oceanic crust and separated from the rear of the arc by a normal fault system or a retroarc (or backarc) basin floored by continental basement and separated from the rear of the arc by a thrust fault system. (A retroarc basin is retro with respect to the arc. The basin can also be called a foreland basin because of its position with respect to the continent.)（弧后区-其中可能发育以洋壳为底的弧内盆地并且受到正断层作用，脱离弧后区，或者发育以大陆基质为底的弧后盆地并且受到逆断层作用，脱离弧后区。）In each of these morphotectonic settings, sedimentation, volcanism, and plutonic intrusions occur contemporaneously, although not necessarily at the same site.（每个地貌构造背景中，同时期都可能有沉积作用，火山作用，深成侵入作用发生，不过并不一定都发生在同一地点）TRENCH SEDIMENT. On the trench floor, variable thicknesses of turbidites are deposited above the oceanic sediment layers. Transport by turbidity currents within a trench is mainly longitudinal along the trench axis, although the initial entry of sediment into the trench can occur along the inner wall as well as from the ends of the trench. The volume of sediment within the trench at any given time reflects the balance between the rate of supply and the rate of plate consumption into the subduction zone. The trench is one of the possible sites of formation of melanges, which are chaotic mixtures of very large fragments of older sedimentary and crystalline rocks in a pelitic matrix. Melanges are known from every continent except Antarctica.（海沟沉积。在海沟表面，不同厚度的浊积岩沉积在海洋沉积沉积层上。海沟内浊流运动方向主要是沿着海沟的长轴，尽管沉积物进入海沟的初始位置可以是沿着内壁或者海沟的末端。任何时间海沟内沉积物的体积反映出供给速率和板块俯冲消耗速率的平衡。海沟是可能有混杂堆积层的地点之一，其内混合有非常大的古老沉积物的碎片和泥质母岩中的结晶岩石。除南极洲，混杂堆积层在各个大陆都有发现。）FOREARC BASINS. Immediately landward of the top of the trench lie forearc basins, which overlie older, deformed orogenic belts or perhaps oceanic or transitional crustal material. Forearc basins receive sediment mainly from the extensive nearby arc structures, where not only volcanic rocks but also plutonic and metamorphic rocks exposed by uplift and erosion serve as sources. Sources can also include local uplands along the trench-slope break or within the arc-trench gap itself. The sandstones are characteristically rich in volcanic rock fragments and calcic plagioclase grains. There may be little transfer of sediment into the subduction zone from the forearc basins; frequently, the forearc basins seem to completely override the subduction zone. The Great Valley sequence of California is an example of a forearc basin deposit.（弧前盆地。弧前盆地位于海沟朝向大陆方向的顶部，上边覆盖着古老变形的造山带物质或者是洋壳或者过度壳物质。弧前盆地主要从附近巨大的岛弧构造中接受沉积，物质来源不仅有火山岩，而且有由于抬升和剥蚀暴露在地表的深成侵入岩和变质岩。物质来源还可以包括沟坡折带的局部高地和弧沟间隙本身。砂岩富含火山岩碎屑和钙长石晶体。从弧前盆地到俯冲带，沉积物可以有些许变化；弧前盆地完全在俯冲带之上时，这种现象更加常见。加利福尼亚大峡谷的沉积序列就是弧前盆地沉积物的例证。）By inference from the bathymetry of modern forearc basins and from the sedimentology of older sequences assumed to have been deposited in similar settings, a forearc basin can contain a variety of facies. Shelf and deltaic or terrestrial sediments, as well as turbidites, occur in different examples. The local bathymetry is controlled by the elevation of the trench-slope break, the rate of sediment delivery to the forearc basin, and the rate of basin subsidence. Different facies patterns occur in various basins.（通过对现代弧前盆地地形和对在相似环境形成的古老沉积序列的沉积学研究，弧前盆地可以有各种沉积相。大陆架、三角洲或者陆相，还有浊积岩相在不同的标本中都可以看到。地区地形是由沟坡折带的抬升，沉积物沉积在弧前盆地的速率，和盆地下陷的速率决定的。不同的沉积相模式出现在不同的盆地中）INTRAARC BASINS. The sedimentary strata in modern intraarc basins include turbidite aprons of volcanic debris shed backward from magmatio arcs. These turbidite wedges rest almost directly on the basaltic oceanic crust with few or no intervening pelagic deposits. Landward from the intraarc spreading centers, sedimentation varies markedly（弧内盆地。现代弧内盆地中的沉积地层包括浊积岩沉积堆，即来源于火山弧背侧的火山碎屑。这些浊积岩几乎直接楔入玄武质的洋壳当中，没有或很少产生混杂沉积岩。从弧内扩散中心到朝向大陆的一侧，沉积物变化相当剧烈。）.RETROARC BASINS. The sedimentary record of retroarc basins includes fluvial, deltaic, and marine strata as much as 5 km thick deposited in terrestrial lowlands and epicontinental seas along elongate, cratonic belts between continental margin arcs and cratons. Sediment dispersal into and across retroarc basins is from highlands on the side toward the magmatic arc and from the craton toward the continental side. The Sea of Japan is a modern example of an extensional retroarc basin. Ancient examples of compressional (thrust-faulted) retroarc basins are the Upper Cretaceous basins of the Western Interior and Rocky Mountain region of North America.（弧后盆地。弧后盆地的沉积记录包括河流相、三角洲相和海相地层，厚度可达5KM，沉积在大陆低地和沿着位于大陆边缘弧和克拉通之间的狭长克拉通带。分布在弧后盆地内外的沉积物来源于高地上朝向火山弧的一侧和克拉通朝向大陆的一侧。日本海是现代扩张性弧后盆地的典型。古老的压性（逆冲断层）弧后盆地的案例是上白垩世，北美西部内陆和落基山脉的盆地。）Continental-Collision BasinsContinental collision occurs when two plates carrying continental crust, and possibly associated island arcs, converge either by subduction or by strike-slip motion that has a component of convergence. Examples include the Late Paleozoic convergence of the northeastern part of the South American plate with the southeastern part of the North American plate, and the convergence of the Indian plate with the Asian plate during Tertiary time. Because convergence is seldom orthogonal, remnant ocean basins occur within the collision belt, and enormous quantities of sediment are available to fill basins formed during convergence. The collision of India with Asia has resulted in the accumulation of as much as 17 km of detrital sediment in Tertiary subduction-related troughsTrench 海沟 Trough 海槽 in Burma. The collision is also responsible for the formation of major molasse basins parallel to the Himalaya belt (Figure 11-7) and their filling with a fluviodeltaic facies of Late Tertiary age, one well-studied part of which is termed the Siwalik Series.（大陆碰撞盆地当两个板块裹挟陆壳，而且可能和岛弧一起，通过俯冲或者有汇聚性质的走滑运动汇聚在一起时，大陆碰撞盆地就会产生。例如，晚古生代南美板块的东北部与北美板块的东南部汇聚，三叠世印度板块和亚洲板块汇聚。因为汇聚很少是垂直碰撞，所以残留的大洋盆地会在碰撞带内产生，并且大量的沉积物可以充填在汇聚过程中形成的盆地。印度板块和亚洲板块的碰撞导致多达17km的碎屑沉积物沉积在缅甸地区第三系俯冲形成的海槽内。碰撞也与平行于喜马拉雅造山带的大型磨砾相盆地的形成及其晚第三系河流-三角洲相的沉积物有关，这是一个广泛研究的部分，术语称西瓦里克岩系）Basins in Displaced TerranesBasins within tectonically displaced terranes are now recognized in many parts of the world. More than 100 highly diverse fragments of exotic terranes have been identified along the eastern margin of the North Pacific Ocean. Although some are similar in geologic aspect, most record a geologic history significantly different from that of their neighbors. In most cases the differences are so pronounced that it is inconceivable for the rocks of neighboring terranes to have formed in close proximity.（移置地体中的盆地构造移置地体中的盆地现在在世界许多地方都可以看到。沿着北太平洋的东部边界，超过100种千差异别的外来地体碎屑被发现。尽管一些地体碎屑在地质学方面相似，但是大部分记录的地质历史与它们附近地体记录的地质历史迥然不同。大部分情况下碎屑之间的差异如此之大以至于附近地体的岩石根本不可能是一起形成的）Grabens Along Continental Margins (沿着大陆边缘分布的地堑)Prominent along the eastern coast of the United States are grabens created during Triassic-Jurassic整句倒装，定状语提前 time as an early stage of failed rifting as the North American plate separated from a larger plate (Pangaea) that included South America, Africa, and Europe. The axis along which separation occurred between North America-South America and Africa-Europe was the site of domal uplift and intense tensional forces that produced a large