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: (分析過去100年的地層學(xué)數(shù)據(jù)，明顯可知殘留下來的沉積巖主要在海里。海洋沉積物占大部分主要有幾個原因)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.（構(gòu)成大陸塊一大部分的硅鋁質(zhì)物質(zhì)體積有限，導(dǎo)致陸地區(qū)域只占地球表面約30%，海洋由沉積物構(gòu)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.（因為板塊運動和一些大陸板塊邊緣發(fā)生的洋殼俯沖，臨近的負(fù)地形（海溝）很容易侵蝕掉活動大陸邊緣的高地）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.（隨著時間推移，大陸板塊的廣大地區(qū)存在明顯會被淺海侵蝕的趨勢（陸緣海）。結(jié)果淺海沉積物在克拉通邊緣廣泛分布，盡管通常很薄。插圖11-2展示了主要的全球性海侵和海退的次序和程度，這些都是從地震記錄得來的；但是許多更小的一連串的海侵海退現(xiàn)在也被人們所知。主要的沉積旋回的構(gòu)造學(xué)解釋是其由大洋裂谷體積改變引起的。大洋體積擴(kuò)張導(dǎo)致海洋盆地體積減少，隨后導(dǎo)致大陸低洼部分被海水淹沒。很明顯全球有兩期一級海侵，第一期從早寒武世到晚寒武世，第二期從早白堊世到晚白堊世。寒武世到密西西比世也主要以大陸廣泛遭受海侵為主。次級海進(jìn)海退的原因可能是冰席的消融和凝結(jié)或者是區(qū)域性的構(gòu)造運動。顯生宙大陸冰期已知發(fā)生在除了寒武紀(jì)、三疊紀(jì)、侏羅紀(jì)和白堊紀(jì)的每一個地質(zhì)時期。）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.（陸相沉積物，根據(jù)定義講，形成于海平面之上，因此與消除作用有關(guān)，即沉積的速率應(yīng)該小于剝蝕的速率。無疑大陸板塊的地層相比深?；蛘吆Ｑ笾杏懈啻笮筒徽辖缑妗＃㊣t 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).（通過對大洋中沉積物分布的研究，顯然最厚的新生代沉積物在鄰進(jìn)大陸邊緣出現(xiàn)。并且基于地層學(xué)，古生物學(xué)，沉積相分析對古地理進(jìn)行重建表明相同的（沉積）模式在地質(zhì)歷史中一直存在。圖11-3展示了美國前寒武紀(jì)結(jié)晶基地在顯生宙時期增長的規(guī)模。同樣也展示了在各個地質(zhì)時期美國相對于赤道的位置。顯然美國地區(qū)從寒武紀(jì)到三疊紀(jì)處于赤道三十度以內(nèi)。這個位置意味著連續(xù)的熱帶亞熱帶氣候，而且氣候是沉積礦產(chǎn)的一個重要的控制因素（見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.（現(xiàn)在還沒有一個被廣泛接受的沉積盆地的分類方案，但是到目前為止那些提議主要是基于三個方面：盆地是否下伏在大陸或者洋殼之下；盆地是否沿著分離，聚合或者是走滑板塊邊緣產(chǎn)出；盆地在板塊上的位置。每個盆地的地質(zhì)歷史可以細(xì)分至旋回，基于三個因素：形成盆地的大地構(gòu)造，沉積旋回，和使盆地發(fā)生變化的大地構(gòu)造。在分類框架中，各種復(fù)雜的因素都應(yīng)該被考慮。）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.（現(xiàn)有討論中，我們將主要的沉積盆地分為六類，每一種都有各自的構(gòu)造和沉積巖石學(xué)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.（大洋盆地是海洋巖石圈上的沉積區(qū)域，比如大西洋盆地和太平洋盆地的大部分區(qū)域?，F(xiàn)產(chǎn)出于大陸板塊附近的中生代海洋沉積礦產(chǎn)的例子眾所周知在環(huán)太平洋帶。顯生宙的例子在加拿大東部。）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. (弧溝體系盆地，是盆地發(fā)展最復(fù)雜的區(qū)域，形成于聚合邊界地區(qū)并且因為強(qiáng)烈的構(gòu)造運動伴隨著洋殼俯沖，導(dǎo)致有多問題難以解釋。例子已經(jīng)在環(huán)太平洋帶提到。)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.（大陸碰撞型盆地形成在大陸碰撞區(qū)域，并且和陸塊與洋塊碰撞區(qū)不同。這種盆地的例子在沃希托河系（石炭系）和喜馬拉雅造山帶中提到）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.（移置地體中的盆地出現(xiàn)在大陸邊緣。地質(zhì)學(xué)家有時把板塊聚合過程中的洋殼看作由生物軟泥和深海粘土組成的近乎平坦的界面。然而，一般來說，大洋板塊也含有古老的島弧和其他大洋地體；隨著板塊俯沖，這些島弧和其內(nèi)部的盆地一起伏到大陸板塊下側(cè)。這些大洋板塊的碎片被稱為外來地體，沿著美國西部邊界從阿拉斯加南部到加利福尼亞州南部分布（圖11-4）。在其他地區(qū)也可以見到。這些地體在構(gòu)造，地層和古生物方面都與毗鄰的大陸板塊不協(xié)調(diào)，而且混含有大洋沉積物，弧前盆地，弧內(nèi)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).（大陸邊緣地塹是形成于隆升的穩(wěn)定陸殼邊緣的沉積中心，與大洋盆地的形成有關(guān)。大部分這樣的地塹走向與大洋盆地的邊緣平行，但是有些可能走向與海岸線大角度斜交，在凹陷地方產(chǎn)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 句法錯誤。不定式后直接加形容詞 because the tectonic setting surrounding intracratonic basins is nonorogenic and the depositional environments are invariably located in shallow waters. （內(nèi)克拉通盆地是構(gòu)造活動中獨立形成于板塊邊緣的沉積中心和陸地?zé)o法預(yù)測的位置上。這些盆地的位置被認(rèn)為反映了埋藏的古老抬升區(qū)域。盆地的沉積厚度一般1KM-5KM，比那些周圍地理環(huán)境中形成的盆地要厚。例如，伊利諾斯盆地、密西根盆地和威利斯頓盆地。這些盆地中的沉積物主要是碳酸鹽巖，頁巖，蒸發(fā)巖和一些富含石英的砂巖。像礫巖、巖屑砂巖或者是長石砂巖，濁流巖，層內(nèi)的燧石巖這些巖石很少見因為內(nèi)克拉通盆地周圍的構(gòu)造背景是非造山帶地區(qū)并且沉積環(huán)境是不太動蕩的淺水沉積環(huán)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展示了相關(guān)構(gòu)造控制的海相沉積的主要形成背景。它們包括(1)洋中脊等深的分離板塊結(jié)合點，在結(jié)合點，火成巖沿著擴(kuò)張中心的走向產(chǎn)出(2)洋底逐漸向兩邊退去的區(qū)域，在該區(qū)域，洋底逐漸冷卻并遠(yuǎn)離擴(kuò)張中心(3)深海盆地，在其之下巖石圈的熱收縮幾乎完成。）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.（覆蓋在玄武質(zhì)洋殼的遠(yuǎn)洋沉積物，它的地層學(xué)和沉積相關(guān)系能反映水深變化。接近洋中脊上部，水深一般小于4KM；由鈣質(zhì)碳酸鹽構(gòu)成的遠(yuǎn)洋沉積層在這里沉積。在這個深度下稱作碳酸鹽補(bǔ)償深度（CCD）-水中對方解石類或文石類極度不飽和使（鈣質(zhì)）沉積不可能發(fā)生（見16節(jié)）。向下在洋脊的翼部，深海盆地和冷水中，棕色的粘土或者硅質(zhì)層沉積下來。如果沉積地點足夠接近大陸，而后陸源沉積物被濁流帶入深海（見13節(jié)）和鈣質(zhì)硅質(zhì)的海洋沉積物互層。）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: （弧溝系統(tǒng)發(fā)育在聚合板塊邊緣，包括一系列地貌構(gòu)造單元（表11-6），每一個單元中都有不同的沉積物。）The trench, a bathymetric deep, floored by oceanic crust（海溝-以洋殼為底的，等深的深溝）The subduction zone（俯沖帶）The arc-trench gap, a belt within which a forearc basin may occur between the trench and the magmatic arc (弧溝間隙-在巖漿弧和海溝之間可能產(chǎn)生弧前盆地的帶狀區(qū)域)The magmatic arc, within which intraarc basins may occur.（巖漿弧-在其中可能發(fā)育弧內(nèi)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.)（弧后區(qū)-其中可能發(fā)育以洋殼為底的弧內(nèi)盆地并且受到正斷層作用，脫離弧后區(qū)，或者發(fā)育以大陸基質(zhì)為底的弧后盆地并且受到逆斷層作用，脫離弧后區(qū)。）In each of these morphotectonic settings, sedimentation, volcanism, and plutonic intrusions occur contemporaneously, although not necessarily at the same site.（每個地貌構(gòu)造背景中，同時期都可能有沉積作用，火山作用，深成侵入作用發(fā)生，不過并不一定都發(fā)生在同一地點）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.（海溝沉積。在海溝表面，不同厚度的濁積巖沉積在海洋沉積沉積層上。海溝內(nèi)濁流運動方向主要是沿著海溝的長軸，盡管沉積物進(jìn)入海溝的初始位置可以是沿著內(nèi)壁或者海溝的末端。任何時間海溝內(nèi)沉積物的體積反映出供給速率和板塊俯沖消耗速率的平衡。海溝是可能有混雜堆積層的地點之一，其內(nèi)混合有非常大的古老沉積物的碎片和泥質(zhì)母巖中的結(jié)晶巖石。除南極洲，混雜堆積層在各個大陸都有發(fā)現(xiàn)。）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?；∏芭璧匚挥诤铣虼箨懛较虻捻敳浚线吀采w著古老變形的造山帶物質(zhì)或者是洋殼或者過度殼物質(zhì)。弧前盆地主要從附近巨大的島弧構(gòu)造中接受沉積，物質(zhì)來源不僅有火山巖，而且有由于抬升和剝蝕暴露在地表的深成侵入巖和變質(zhì)巖。物質(zhì)來源還可以包括溝坡折帶的局部高地和弧溝間隙本身。砂巖富含火山巖碎屑和鈣長石晶體。從弧前盆地到俯沖帶，沉積物可以有些許變化；弧前盆地完全在俯沖帶之上時，這種現(xiàn)象更加常見。加利福尼亞大峽谷的沉積序列就是弧前盆地沉積物的例證。）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.（通過對現(xiàn)代弧前盆地地形和對在相似環(huán)境形成的古老沉積序列的沉積學(xué)研究，弧前盆地可以有各種沉積相。大陸架、三角洲或者陸相，還有濁積巖相在不同的標(biāo)本中都可以看到。地區(qū)地形是由溝坡折帶的抬升，沉積物沉積在弧前盆地的速率，和盆地下陷的速率決定的。不同的沉積相模式出現(xiàn)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（弧內(nèi)盆地?，F(xiàn)代弧內(nèi)盆地中的沉積地層包括濁積巖沉積堆，即來源于火山弧背側(cè)的火山碎屑。這些濁積巖幾乎直接楔入玄武質(zhì)的洋殼當(dāng)中，沒有或很少產(chǎn)生混雜沉積巖。從弧內(nèi)擴(kuò)散中心到朝向大陸的一側(cè)，沉積物變化相當(dāng)劇烈。）.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?；『笈璧氐某练e記錄包括河流相、三角洲相和海相地層，厚度可達(dá)5KM，沉積在大陸低地和沿著位于大陸邊緣弧和克拉通之間的狹長克拉通帶。分布在弧后盆地內(nèi)外的沉積物來源于高地上朝向火山弧的一側(cè)和克拉通朝向大陸的一側(cè)。日本海是現(xiàn)代擴(kuò)張性弧后盆地的典型。古老的壓性（逆沖斷層）弧后盆地的案例是上白堊世，北美西部內(nèi)陸和落基山脈的盆地。）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 海溝 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.（大陸碰撞盆地當(dāng)兩個板塊裹挾陸殼，而且可能和島弧一起，通過俯沖或者有匯聚性質(zhì)的走滑運動匯聚在一起時，大陸碰撞盆地就會產(chǎn)生。例如，晚古生代南美板塊的東北部與北美板塊的東南部匯聚，三疊世印度板塊和亞洲板塊匯聚。因為匯聚很少是垂直碰撞，所以殘留的大洋盆地會在碰撞帶內(nèi)產(chǎn)生，并且大量的沉積物可以充填在匯聚過程中形成的盆地。印度板塊和亞洲板塊的碰撞導(dǎo)致多達(dá)17km的碎屑沉積物沉積在緬甸地區(qū)第三系俯沖形成的海槽內(nèi)。碰撞也與平行于喜馬拉雅造山帶的大型磨礫相盆地的形成及其晚第三系河流-三角洲相的沉積物有關(guān)，這是一個廣泛研究的部分，術(shù)語稱西瓦里克巖系）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.（移置地體中的盆地構(gòu)造移置地體中的盆地現(xiàn)在在世界許多地方都可以看到。沿著北太平洋的東部邊界，超過100種千差異別的外來地體碎屑被發(fā)現(xiàn)。盡管一些地體碎屑在地質(zhì)學(xué)方面相似，但是大部分記錄的地質(zhì)歷史與它們附近地體記錄的地質(zhì)歷史迥然不同。大部分情況下碎屑之間的差異如此之大以至于附近地體的巖石根本不可能是一起形成的）Grabens Along Continental Margins (沿著大陸邊緣分布的地塹)Prominent along the eastern coast of the United States are grabens created during Triassic-Jurassic整句倒裝，定狀語提前 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