Sea-level changes and hydrothermal sedimentary mineralization of large-superlarge ore deposits among Sinian to Triassic in South China

Among the Sinian to Triassic strata in South China, the stratiform, quasi-stratiform and lenticular metallic deposits in association with hydrothermal sedimentation mainly occur in the four periods: (1) the Sinian Datangpo interglacial period, (2) the early period of Early Cambrian, (3) the late period of Middle Devonian to early period of Late Devonian,and (4) the late period of Early Permian. The four mineralization periods all happened around the maximum flooding period in the third-order seal-level cycle during the ascending stage in the first-order sea-level cycle. The deep seawater layer, starved and non-compensatory basin, low sedimentary rate, and low energy and anoxic environment during the maximum flooding period are very suitable for the formation and preservation of large to superlarge hydrothermal sedimentary deposits. The maximum flooding period also coincided with the intensified regional tectonism, extensive deep magmatism and hydrothermal sedimentation, which provide, for the formation of large to superlarge hydrothermal sedimentary deposits through the rapid accumulation of hydrothermal sediments, the needed dynamics, ore-forming materials and favorable passway for hydrothermal fluids to enter the basin.     

Bio-reef-chert suite and superlarge ore deposits

The bio-reef-chert suite is an important ore-bearing rock assemblage and one of the metallogenic rock suites of superlarge ore deposits. It is formed as a fixed and ordered suite in space and time, and composed of different rocks formed by different geological processes. It is the product of basin evolution at special stage in a special geological setting. It is also the comprehensive product of normal sedimentary process, biological process in basin, hydrothermal sedimentary process under basin base and magmatic process in the deep lithosphere.     

Geo-tectonic conditions of the formation of Proterozoic large and superlarge ore deposits along northwestern margin of North China Plate

Four large and superlarge copper-multimetal ore deposits hosted in the Mid-Proterozoic Zhartaishan Group along northwestern margin of North China Plate are stratabound hydrothermal sedimentary deposits, and these deposits formed in mid-late stage of the Mid-Proterozoic Langshan-Zhartaishan rifting system. Four necessary conditions are proposed for the formation of these large and superlarge ore deposits: (i) favorable geological background and tectonic environment; (ii) abundant sources of metallogenic material; (iii) favorable sedimentary lithofacies and paleogeographic conditions; (iv) sudden change events during metallogenic processes.     

Synchronous structure control of superlarge ore deposits

The control of synchronous structures on formation of superlarge stratabound ore deposits is immense. Based on studies of ore deposits in South Qiniing, northern Guangdong, Langshan and other areas, three new ideas in comparison with examples of ore control of synchronous structures both in China and abroad are proposed: (i) multiorder ore control of synchronous structures, which means that synchronous structures of different orders display different controls on ore deposits; (ii) synchronous structures in different stages of basin evolution display different controls on basin fluid system and ore-forming system; (iii) synchronous strurture accompanying hydrothermal mineralization as a preexisting weak surface in earth crust often reactivate in later tcctono-thermal event to be a channelway for magma or thermal fluids which superimposed on and reformed preexisting ore beds to form large or superlarge composite ore deposits.     

Comprehensive constraint on the tectono-sedimentary setting of Late Paleozoic turbidites of the Kamuste area, eastern Junggar, Xinjiang

Petrography and geochemistry, combined with sedimentation analyses allow for a thorough evaluation of the tectono-sedimentary setting of late Paleozoic turbidites of the Kamuste area, eastern Junggar. Sandstones of the Alabiye¹⁾ Formation are composed mostly of volcanic and sedimentary detritus with lesser amounts of plagioclase and quartz. They were derived from an undissected magmatic-arc provenance. The geochemistry of sandstone-mudrock suites indicates a fesic-intermediate igneous provenance, and constrains the Alabiye Formation to have derived from a differentiated oceanic-continental margin island-arc tectonic setting. Likewise, geochemistry and sandstone petrography of the Kamuste Formation reflect a mixed provenance signature dominated by magmatic arc, basement uplift, and subduction-complex sources of a differentiated continental-island arc. Sedimentation analysis indicates that the Alabiye and Kamuste formations are two sets of turbidite sequences deposited on a submarine slope and a submarine fan and basin plain respectively. In conclusion, submarine slope turbidite deposition of the Alabiye Formation records the main sedimentary response to the development of early Devonian back-arc basins of the northern Junggar tectonic belt. Submarine fan and basin plain turbidite and background hemipelagic deposition of the Kamuste Formation record the main sedimentary response to the late Early Carboniferous development of an inter-arc relict ocean basin of the eastern Junggar composite terrane.     

塔里木柯坪塔格地区构造抬升的新证据——来自(U-Th)/He年龄的约束

柯坪塔格地区位于西南天山与塔里木盆地之间, 是塔里木地台的一部分, 其构造隆升与天山和塔里木盆地的演化密切相关. 本文首次将(U-Th)/He热定年技术应用于该地区构造抬升的研究, 对该区震旦系露头样品的磷灰石和锆石的(U-Th)/He进行了年龄测定和热史模拟, 结果表明柯坪塔格地区主要经历了4期构造抬升事件, 导致震旦系抬升至地表, 其中磷灰石(U-Th)/He年龄揭示了晚白垩世和中新世两期的构造抬升事件. 在早石炭世, 震旦系温度达到最大, 介于133~150°C之间, 结合沉积埋藏史得到当时的最大埋深是3400~3900 m. 在渐新世-中新世, 受印度-欧亚板块碰撞远程效应的影响, 柯坪塔格地区沿柯坪塔格-沙井子断裂向巴楚隆起上逆冲, 地层快速抬升遭受剥蚀. 在15~10 Ma时, 柯坪塔格地区震旦系已抬升至地表. 自早石炭世至今, 柯坪塔格地区总剥蚀量达6170 m. 柯坪塔格地区自中生代以来的构造-热演化史与塔里木盆地北缘是一致的, 但与天山及处于塔里木盆地内部的巴楚隆起的构造抬升过程存在差异. 中新世以后, 受喜山运动远程效应影响, 柯坪塔格和天山才同处于抬升状态; 而巴楚隆起在古近纪早期仍处于抬升剥蚀状态, 与柯坪塔格地区接受沉积相反. 本文利用(U-Th)/He热定年技术成功地揭示了柯坪塔格地区自震旦纪以来的构造-热演化史, 这些结果有利于人们对这一地区构造抬升的正确认识. 同时, 本研究对塔里木盆地的油气勘探及天山地区的构造研究具有指导意义.     

四川盆地东西陆块中下地壳结构存在差异

四川盆地是中上扬子克拉通的主要组成部分.作为我国三大稳定克拉通之一,扬子克拉通经历了自太古代以来的长期演化,直到新元古代晚期与华夏板块发生碰撞拼合前,一直被认为是一个稳定的统一陆块.基底包括了新太古宙-新元古代岩层,其上广泛被新元古代晚期至显生宙地层覆盖,仅有~2.9—2.95Ga基底岩石零星出露于四川盆地的西缘、西南缘和三峡地区,使得对于沉积盖层之下的中下地壳的性质和分布规模的认识十分有限.重力异常则能够宏观揭示区域结构特征.本文通过刨除沉积盖层和莫霍面起伏引起的重力异常而获得了中下地壳的重力异常,反映了四川盆地东西陆块中下地壳存在结构差异,结合深地震反射资料、航磁异常和地球化学资料,证实了该分界线位于重庆—华蓥一线,故而推测中上扬子克拉通在太古宙-古元古代可能存在东西两个陆核.     

Seismic-stratigraphic framework of the forearc basin off central Sumatra,Sunda Arc

New multichannel seismic reflection data provide information on the stratigraphic framework and geologic history of the forearc basin west of central Sumatra. We recognize six seismic-stratigraphic sequences that reflect the Cenozoic history and development of the outer continental shelf and forearc basin southeast of Nias Island. These sequences indicate several episodes of uplift of the subduction complex and filling of the forearc basin.Early in the development of this margin, Paleogene slope deposits prograded onto the adjacent basin floor. Onlapping this assemblage are two units interpreted as younger Paleogene(?) trough deposits. Uplift associated with rejuvenation of subduction in the late Oligocene led to erosion of the Sumatra shelf and formation of a regional unconformity.The early Miocene was a period of significant progradation. A Miocene limestone unit partly downlaps and partly onlaps the older Paleogene deposits. It is characterized by shallow shelf and oblique progradational facies passing into basin floor facies. A buried reef zone occurs near the shelf edge. The cutting of an erosional unconformity on the shelf and slope in late Miocene/early Pliocene time culminated this episode of deposition.In the late Pliocene, a large flexure developed at the western boundary of the basin, displacing the outer-arc ridge upward relative to the basin. Over 1 km of Pliocene to Recent sediment was deposited as a wedge in the deep western portion of the basin landward of the outer-arc ridge. These deposits are characterized by flat-lying, high-amplitude, continuous reflections that overstep the late Miocene unconformity. Up to 800 m of shallow-water limestone have been deposited on the shelf since mid-Pliocene time.     

Contemporary sedimentation rates and depositional structures in a montane lake basin,southern Coast Mountains,British Columbia,Canada

Spatial variability of recent lacustrine sedimentary structures and sedimentation rates are examined for Green Lake, a morphologically complex lake basin of the southern Coast Mountains, British Columbia. A dense, 100 m grid sampling scheme was used for sediment coring within the 2 km² lake basin. Deltaic, massive, weakly laminated, and varved sediment sequences are identified within the sediment record. Spatial patterns among these sedimentary deposits are related to within‐lake sediment transfer processes, morphometric controls, and the extent of post‐depositional mixing by bioturbation. Unconformities, turbidites, and cohesive slump failure deposits, observed within the contemporary varve sequences, could all be correlated with major flooding events in the catchment area and direct anthropogenic disturbances along the shoreline. There is an overall, non‐linear decrease in sedimentation rates with increasing distance from the lake inflows; however, this pattern is disrupted in deep water sites of intervening lake sub‐basins where locally higher accumulation rates are observed. Spatial sedimentation patterns are quantitatively described by an empirically‐derived model. Systematic variations in the model parameters are observed for different lake sub‐regions and are associated with changing sediment transfer dynamics between proximal and distal sub‐basin settings. Copyright © 2006 John Wiley & Sons, Ltd.     

Paleostructural geomorphology of the Paleozoic central uplift belt and its constraint on the development of depositional facies in the Tarim Basin

Inclined eastward and consisting of the Hetianhe, Hetianhedong, Tazhong paleouplifts and Bachu paleoslope, the central paleouplift belt in the Tarim Basin was a large composite paleouplift and paleoslope belt with complicated palaeogeomorphic features during the Middle to early Late Ordovician. A number of paleostructural geomorphic elements have been identified in the paleouplift belt and surrounding areas, such as the high uplift belts, the faulted uplift platforms, the marginal slopes and slope break zones flanking the paleouplift belt, the surrounding shelf slopes or low relief ramps, the shelf slope break zones and deep basin plains. They exerted great influence on the development of paleogeography of the basin. The marginal slopes and slope break zones flanking the uplift belt constrained the formation and deposition of the high-energy facies including reefal and shoal deposits during the Late Ordovician, which comprise the major reservoirs of the Lower Paleozoic in the basin. Toward the end of the Ordovician, the Tazhong paleouplift hinged westward and became a westward-dipped nose as the southeastern margin of the basin was strongly compressed and uplifted. The tectono-paleogeomorphic framework of the central northern basin during the Early Silurian and the Late Devonian to Early Carboniferous changed remarkably in topography from the initial low in east and high in west to high in northeast and low in southwest. The major paleogeomorphic elements developed in these periods included the strong eroded uplift high, the uplift marginal slope, the gentle ramp of the depression margin and the depression belt. The sandstones of the lowstand and the early transgressive systems tracts were deposited along the uplift marginal slopes and the gentle ramps of the depressions comprise the prolific reservoirs in the basin. The study indicates that the distribution patterns of the unconformities within the basin are closely related to the paleogeomorphic features and evolution of the paleouplift belt. From the high uplift belt to the depression, we found the composed unconformity belts at the high uplift, the truncated and onlap triangular unconformity belts along the uplift marginal slopes, the minor angular unconformity or discontinuity belts along the transitional zones from the uplift marginal slopes to depression and the conformity belt in the central depression. The truncated and the onlap triangular unconformity belts are the favorable zones for the formation of stratigraphic trap reservoirs. Supported by National Basic Research Program of China (Grant No. 2006CB202302), National Natural Science Foundation of China (Grant No. 40372056) and Frontier Research Project of Marine Facies     

Depositional model of Permian Luodianian volcanic island and its impact on the distribution of fusulinid assemblage in southern Qinghai, Northwest China

Pan-riftizational tectonic activity reached climax at Luodianian (Permian) in the East Tethyan Domain, Qinghai-Tibet Plateau. Because of eruptive volcanics and influence of terrigenous materials, a complex volcanic-sedimentary landform formed on the sea floor in southern Qinghai. Four sedimentary facies types were recognized based on detailed field mapping. Spatially, platform facies volcanic-limestone type was located at the center belt approximately trending NWW, surrounded by shallow water slope facies tuff/tuffite type at the two flanks and deep water slope facies breccia/calcirudite at the most outside. The depression facies sandstone-mudstone type, which comprised mainly mudstone, de-posited between volcanic islands (platform facies volcanic-limestone type). Based on the field map-ping and stratigraphic section data, seven rift-related sedimentary facies were recognized and a depo-sitional model for volcanic island was proposed. It is revealed that some volcanic island chain formed quickly and intermittently in the Qamdo Block during violent eruption, and small carbonate reef, shoal, platform occurred above or on edge of volcanic island, and some slope sedimentary facies surrounded volcano island chain during dormant period of volcanic activities. Three types of fusulinid assemblages were distinguished in the carbonate rocks, which deposited in varied positions of a palaeo-volcanic island: (1) Misellina-Schwagerina assemblage occurred above or on edge of volcanic island, (2) Para-fusulina assemblage was located at restricted depression facies among volcanic islands or carbonate platform, and (3) the reworked Pseudofusulina-Schwagerina assemblage occurred at slope facies near margin of volcanic island, which originally deposited in the shallow-water carbonate platform, then collapsed along the volcanic island margin with fusulinid-bearing grain-supported carbonate con-glomerate or calcirudite, and finally re-deposited on the deeper slope. The sedimentary sequence re-sulting from calm shallow water was deposited at the interior of the Qamdo Block from the Devonian to early Early Permian. At the beginning of the peak period of activity of pan-riftzation (Luodianian), al-ternate volcanic island and shallow marine environment within continent crust came into being. Uni-form and stable shallow-water carbonate platform was formed during the Xiangboan. This suggested that the activity of rift basin was evidently weakened. Subsequently the instability of the basin appre-ciably increased with the occurrence of basalt in late Kuhfengian. At last the whole Qamdo Block turned into the closure period of rift during the Late Permian.     

The scientific connotation of oil and gas formations under deep fluids and organic-inorganic interaction

As a relatively stable craton block in the earth system, the petroliferous basin is influenced by the evolution of the earth system from the early development environment of source rocks, hydrocarbon formation, and reservoir dissolution to hydrocarbon accumulation or destruction. As a link between the internal and external factors of the basin, deep fluids run through the whole process of hydrocarbon formation and accumulation through organic-inorganic interaction. The nutrients carried by deep fluids promote the bloom of hydrocarbon-generating organisms and extra addition of carbon and hydrogen source, which are beneficial to the development of high-quality source rock and enhancement of the hydrocarbon generation potential. The energy carried by the deep fluid promotes the early maturation of the source rock and facilitates the hydrocarbon generation by activation and hydrogenation in high-mature hydrocarbon sources. The dissolution alteration of carbonate rocks and clastic reservoirs by CO_2-rich deep fluids improves the deep reservoir space, thus extending the oil and gas reservoir space into greater depth. The extraction of deeply retained crude oil by deep supercritical CO_2 and the displacement of CH_4 in shale have both improved the hydrocarbon fluidity in deep and tight reservoirs. Simultaneously, the energy and material carried by deep fluids(C, H, and catalytic substances) not only induce inorganic CH_4 formation by Fischer-Tropsch(F-T) synthesis and "hydrothermal petroleum" generation from organic matter by thermal activity but also cause the hydrothermal alteration of crude oil from organic sources. Therefore, from the perspective of the interaction of the earth's sphere, deep fluids not only input a significant amount of exogenous C and H into sedimentary basins but also improve the reservoir space for oil and gas, as well as their enrichment and accumulation efficiencies.     

鄂尔多斯盆地中-新生代岩石圈厚度演化——来自地热学的证据

盆地热历史可以为揭示深部动力学过程提供时间和空间上的连续信息. 本文利用镜质体反射率古温标模拟了鄂尔多斯盆地从东到西7口典型井的热历史, 并在此基础上计算了盆地中生代晚期、古近纪初期以及现今的"热"岩石圈厚度. 结果显示, 鄂尔多斯盆地在早白垩世末期经历了一次热流高峰, 热流值为73~78 mW/m², 此后的热流值一直降低至今,现今的平均值61.8 mW/m²; 早白垩世末期盆地"热"岩石圈厚度也经历了一次减薄高峰, 平均"热"岩石圈厚度为65 km左右, 此后逐渐增厚至现今的125 km左右. 鄂尔多斯盆地现今"热"岩石圈厚度中等, 早古生代200 km的厚岩石圈已不存在; 早白垩世末期是其地质发展历史的一个重大变革期, 此时"热"岩石圈厚度发生减薄, 深部构造活动强烈导致浅部盆地抬升剥蚀剧烈, 周缘岩浆活动强烈, 多种能源矿产形成, 这与华北克拉通东部构造转折的时间以及华北克拉通破坏的高峰时限具有一致性.     

Mesozoic basin-fill records in south foot of the Dabie Mountains: Implication for Dabie Orogenic attributes

For the Triassic continental collision, subduction and orogenesis in the Dabie-Sulu belt, a lot of data on petrology, geochemistry and chronology have been published[1]. However, so far no depositional records on the Triassic syn-collisional orogenesis of…     

Late Carboniferous – Middle Permian arc/forearc‐related basin in Central Asian Orogenic Belt: Insights from the petrology and geochemistry of the Shuangjing Schist in Inner Mongolia,China

The Solonker Suture Zone is thought to record the terminal evolution of the Central Asian Orogenic Belt (CAOB) in Inner Mongolia. However, two contrasting interpretations of the timing of suturing of the Solonker Suture Zone exist: (i) Permian to Early Triassic; and (ii) Middle Devonian or Late Devonian to Carboniferous. The Shuangjing Schist is exposed in the Linxi area along the Xar Moron Fault Zone, which marks the southern boundary of the Solonker Suture Zone in the eastern section of the CAOB, and thus provides insight into the timing of suturing of the Solonker Suture Zone. Detailed and systematic analysis of the petrology and geochemistry of the Shuangjing Schist shows that the Shuangjing Schist developed by greenschist facies prograde metamorphism of a volcanisedimentary rock series protolith. The volcanic parts of the Shuangjing Schist are a calc‐alkaline series with large volumes of intermediate members and subordinate acidic members. Volcanism occurred in a magmatic arc on the continental margin and was induced by subduction‐related magmatism resulting from mantle metasomatism. The sedimentary parts of the Shuangjing Schist reflect a transition from continental shelf to abyssal plain sedimentation. The formation of the Shuangjing Schist is suggested to be related to closure of an arc/forearc‐related ocean basin. The timing is constrained by a laser ablation inductively coupled plasma–mass spectrometry (LA‐ICP–MS) U–Pb magmatic zircon age of 298 ± 2 Ma from a carbonaceous biotite–plagioclase schist that was intruded by granite at 272 ± 2 Ma. In the Linxi area, southward subduction of the arc/forearc basin led to uplift, thickening, collapse, and erosion of the overriding continental crust. Collapse induced extension and widespread magmatism along the volcanic arc at the northern margin of the North China Craton. The closure of the arc/forearc‐related oceanic basin led to the formation of Late Permian to Middle Triassic collisional granites and the subsequent end of the collision of the Solonker Suture Zone.     

Sedimentation in Lake Biel,an eutrophic,hard-water lake in northwestern Switzerland

A 2-year study of sedimentation in Lake Biel reveals that three major factors can account for the spatial and temporal patterns of tripton sedimentation. Allochthonous inputs of particulate matter mostly derived from the Aare river during spring snowmelt and other high-water periods, provide about 50% of the carbonate and 50% of the siliceous matter collected in sediment traps. Phytoplankton activity in this eutrophic, hard-water lake accounts for the rest of the carbonate and siliceous matter, the latter being mostly diatom frustules. Sedimentation rates are thus highest during periods of maximum river flooding, maximum phytoplankton activity and following the breakdown of the thermocline, at which time trapped particles settle out. Resuspension of sediment is important in at least one basin. Resolution of carbonate appears to be minor.     

Coastal sedimentation associated with the December 12th, 1992 tsunami in Flores,Indonesia

This paper presents the result of a detailed granulometric investigation of sediments deposited by a modern tsunami, the 1992 tsunami in Flores, Indonesia. Eyewitness accounts indicate that sediments were deposited upon coastal lowlands over wide areas as a result of the tsunami inundation. Distinctive vertical and lateral variations in particle size composition are characteristic features of the tsunami deposits and these are intimately related to sedimentary processes associated with flood inundation. The geomorphological and sedimentary evidence is used here to establish a preliminary model of tsunami sedimentation. This information is believed to be of great value in understanding sedimentary processes associated with tsunami flooding and in the interpretation of palaeo-tsunami deposits.     

Anoxic environment and formation of superlarge ore deposits

The formation of many metallic and non-metallic ore deposits is a result of coupling of mineralization, related to anoxic environment and regional, or global background. Inter act~on, concordance and continual development of the mineralization and environmental background control the large to superlarge scale of ore deposits. Three kinds of ore-forming models related to anoxic environment and three important background patterns are suggested. The turning period of geological history is favorable to the formation of large to superlarge ore deposits.     

Evolution of the Taebaeksan Basin,Korea: II,late Paleozoic sedimentation in a retroarc foreland basin and assembly of the proto‐Korean Peninsula

The Taebaeksan Basin comprises the lower Paleozoic Joseon Supergroup and the upper Paleozoic Pyeongan Supergroup, which are separated by a disconformity representing a 140 myr‐long hiatus. This paper deals mainly with the late Paleozoic paleogeographical and tectonic evolution of the Taebaeksan Basin on the basis of updated stratigraphy, sedimentation, and geochronology of the Pyeongan Supergroup. Late Paleozoic sedimentation in the Taebaeksan Basin recommenced at ~ 320 Ma and formed a thick siliciclastic succession of marginal marine and non‐marine alluvial deposits, the Pyeongan Supergroup. The Pyeongan Supergroup was deposited in a retroarc foreland basin formed by build‐up of a magmatic arc along the northern margin of the Sino‐Korean Craton. The formation of sedimentary deposits ceased at ~ 250 Ma due to the collision of the Sino‐Korean Craton and South China Craton that generated the Triassic Songnim orogeny in Korea. Diverse tectonic models have been proposed for assembly of the proto‐Korean Peninsula, but the indented wedge model is considered to best explain the geological features of the peninsula. The indented wedge model entails northward subduction of the central block of the Korean Peninsula (part of the South China Craton) beneath the northern block of the Korean Peninsula (part of the Sino‐Korean Craton) along the Sulu‐Imjingang Belt.     

Climate change triggered sedimentation and progressive tectonic uplift in a coupled piedmont–axial system: Cuyama Valley,California, USA

Channels on the north‐facing piedmont of the Sierra Madre range in Cuyama Valley, California have alternated between three process regimes during the late Quaternary: (1) vertical incision into piedmont alluvium and older sedimentary deposits; (2) lateral erosion; and (3) sediment accumulation. The state of the piedmont system at a given time has been controlled by upstream sediment flux, regional tectonic uplift and incision of the axial Cuyama River. To better understand the timing and to attempt to interpret causes of past geomorphological processes on the Sierra Madre piedmont, we mapped the surficial geology and dated alluvial deposits using radiocarbon, cosmogenic and optical dating methods. Four primary episodes of sedimentation have occurred since ca. 100 ka, culminating in the most recent period of extensive piedmont sedimentation between 30 and 20 ka. Fill terraces in Cuyama Valley formed by piedmont sediment accumulation followed by vertical incision and lateral erosion are fairly planar and often mantle strath bedrock surfaces. Their vertical spatial arrangement is a record of progressive regional tectonic uplift and concomitant axial Cuyama River channel incision migrating up tributary piedmont channels. Subparallel longitudinal terrace profiles which have a linear age–elevation relationship indicate that multiple episodes of climatically controlled sedimentation overprints ～1 m kyr^?1 of regional uplift affecting the Cuyama River and its tributaries. Sedimentation was probably a result of increased precipitation that caused saturation landsliding in steep catchments. It is possible that increased precipitation during the Last Glacial Maximum was caused by both continental‐scale circulation pattern reorganization and increased Pacific storm frequency and intensity caused by ‘early warming’ of nearby Pacific Ocean surface waters. Older episodes of piedmont sedimentation are difficult to correlate with specific climate regimes, but may correlate with previous periods of increased precipitation. Copyright © 2007 John Wiley & Sons, Ltd.