Geoarchaeological investigations of henson creek: A low-order tributary in Central Texas

A complex late Quaternary alluvial history was documented along Henson Creek, a low order tributary on the Fort Hood Military Reservation in central Texas. Three Quaternary alluvial landforms were recognized: terrace 2 (T2), terrace 1 (T1), and the modern floodplain (T0). The late Pleistocene T2 terrace may contain an array of sites spanning the entire known cultural record, while T1 may have sites spanning the last 5000 years only. Five fluvial units, three colluvial facies, two alluvial fan facies, and two buried paleosols were also recognized. Fluvial deposition was occurring approximately 15,000 yr B.P., 10,000-8000 yr B.P., 7000–4800 yr B.P., 1650-600 yr B.P., and during the last 400 years. Colluvial deposition was ongoing mainly in the early and middle Holocene, while alluvial fan aggradation was proceeding primarily in the middle Holocene. Because of erosional unconformities, there is minimal potential for recovering buried sites dating to intervals between depositional eposides for most of the drainage basin. Preservation potentials for buried sites are greatest in fine-grained fluvial deposits dating to the late Pleistocene, early Holocene, and parts of the late Holocene, and in fine-grained colluvial deposits dating to the early and middle Holocene. This investigation demonstrates that within the study area, and perhaps throughout much of central Texas, a greater continuum of sediments and preservation potentials exists in late Quaternary alluvial deposits of rivers than in low-order tributaries.     

A geoarchaeological approach to using surface sites for paleoenvironmental reconstructions

Archaeological sites that have only surface scatters are usually considered to be of little or no use in reconstructing paleoenvironmental conditions during episodes of human occupation. However, geoarchaeological research at the Skare site in south-central Wisconsin reveals that these sites can be used to provide information about the timing of paleoenvironmental changes and their affect on the location of human occupations. Geomorphic investigations revealed the presence of Alfisols formed in late Wisconsin loess on upland and low bench positions; morphologically younger Mollisols formed in alluvial and colluvial sediments on low alluvial plain positions; and beach sediments that represent the low-water stand of Glacial Lake Yahara. Semiquantitative age control for timing the formation of these soils and the lake level(s) of Glacial Lake Yahara is based on the location of diagnostic artifacts (Early Paleoindian to Late Woodland) recovered during ten separate surface collections. Early and Late Paleoindian artifacts all occur on Alfisols and are only found above the low-water stand of Glacial Lake Yahara, indicating that loess deposition and subsequent soil formation happened sometime between 12,000 and 11,000 yr B.P., and that Glacial Lake Yahara remained near the low-water stand at least until ∼9500 yr B.P. Early Archaic artifacts are present below the low-water stand and provide ages for lowering of the lake to be between 8000 and 9500 yr B.P. Middle Archaic artifacts are present on Mollisols and provide an age of soil formation to be between 5000 and 3000 yr B.P. A majority of Woodland artifacts occur on these Mollisols and are present along the floodplain of the Yahara River, possibly representing a change in subsistence strategy and settlement patterns relative to Paleoindian and Archaic occupations. The agreement of soil morphological and sedimentological data with semiquantitative age data of diagnostic artifacts provides evidence that archaeological surface scatters can be useful tools in dating soils and landforms associated with these sites. © 1998 John Wiley & Sons, Inc.     

美国中西部第四纪冰川与黄土研究的进展和问题

本文对美国中西部和中国黄土高原０．５Ｍａ以来的气候序列进行了对比。０．５—０．１ＭａＢ．Ｐ．，美国中西部间冰期以干暖为特征，１０００００—３５０００ａＢ．Ｐ．，气候从干暖向温湿转化。本次冰进阶段，冰盖达到最大后，风尘堆积占优势，气候湿凉为主。全新世先从温凉转为温湿，继而干暖，后又转向湿凉。总之，０．５Ｍａ以来除末次冰期外，美国中西部与中国黄土高原温度变化的总趋势是一致的，但两地的湿度变化是相反的。     

大别山北缘早白垩世黑石渡组沉积体系研究

分布于大别山北缘晓天-磨子潭断裂以北和金寨-响洪甸-西汤池断裂以南呈东西向延伸的早白垩世黑石渡组,厚达千米,岩相主要有角砾岩、砾岩、砂岩、粉砂岩、泥岩等,包括冲积扇、河流、扇三角洲和湖泊沉积体系,其中河流沉积主要由洪泛平原和决口扇组成。黑石渡组属于向上变细层序,早期为冲积扇沉积,中期为洪泛平原、决口扇和扇三角洲沉积,晚期为深湖浊流沉积。冲积扇和湖相浊流沉积主要发育于盆地东段舒城晓天地区,洪泛平原和决口扇沉积主要发育于盆地西段霍山地区,扇三角洲在两地都比较发育。这是一个不对称的断陷盆地,晓天-磨子潭断裂可能对盆地的发育具有控制作用。     

四川攀枝花昔格达组下伏砾石层成因和时代探讨与古金沙江河谷发育

本文主要描述和讨论了四川省攀枝花市沿金沙江分布、并以炳草岗地龙箐剖面为代表的昔格达组湖相沉积下伏的砾石层的沉积特征及其河流相成因.根据前人对昔格达组湖相沉积的磁性地层学研究结果,为4.2/3.28～2.6/2.12/1.78 MaBP的上新世中、晚期或至早更新世早期,表明其下伏厚达50 m的砾石层的形成时代约为4.2～4.5/5 MaBP的上新世早期.早上新世金沙江河流相砾石层在接近金沙江谷底位置的发现,表明金沙江很早就已经从青藏高原主夷平面下切了2000 m以上、已在接近其现今谷底的位置上存在.这对于探讨古金沙江的河谷发育及其与青藏高原隆升的关系,具有重要的指示意义.     

Quaternary alluvial fans in the Gobi of southern Mongolia: evidence for neotectonics and climate change

Alluvial fans in southern Monglia occur along a group of narrow discontinuous mountain ranges which formed as transpressional uplifts along a series of strike-slip faults. They provide information on the nature of neotectonic activity in the eastern Gobi Altai range and on palaeoclimate change. Alluvial fan formation was dominated by various geomorphological processes largely controlled by climatic changes related to an increase in aridity throughout late Quaternary times. Their sedimentology shows that initially they experienced humid conditions, when the sedimentary environments were dominated by perennial streams, followed by a period of increasing aridity, during which coarse fanglomerates were deposited in alluvial fans by ephemerial streams and active-layer structures were produced by permafrost within the alluvial fan sediments. With climatic amelioration during early Holocene times, the permafrost degraded and fan incision and entrenchment dominated. Sedimentation was then confined to the upper reaches of the fans, adjacent to steep mountain slopes, and within the entrenched channels. The alluvial fans have been neotectonically deformed, faulted and their surface warped by small thrust faults that propagate from the mountain fronts into their forelands. Localised uplift rates are in the order of 0.1 to 1 m Ka⁻¹. © 1997 John Wiley & Sons, Ltd.     

Holocene alluvial stratigraphy in the upper Susquehanna River Basin, New York

Two alluvial terraces and the present flood plain were studied at two locations along the Susquehanna and Unadilla Rivers in south-central New York state. They have formed since deglaciation and incision of the stream channels into the valley train deposits. The higher terrace has noncumulative soil profiles with well-developed color B horizons predominantly of silt loam and very fine sandy loam. The terrace is weathered to a degree similar to nearby glacial outwash terraces that have caps of similarly textured sediments. Incision that produced the terrace occurred before 9705 ± 130 yr B.P. The lower terrace is characterized by relatively thick, vertical-accretion deposits of silt loam that contain sequences of thin, buried A, color B, and C horizons. They were formed between about 3240 ± 110 (¹⁴C data of soil humin) and 235 ± 80 yr B.P. Deposits above the 235 ± 80 yr B.P. stratum are unweathered. The soil stratigraphy and ¹⁴C dates of soil humin from buried A horizons are surprisingly well correlated between sites. Most sediments of the present flood plain have been deposited since 1120 ± 80 yr B.P. Incipient A horizons and oxidation of inherited organic matter in the subsoil are the only evidence of pedogenesis in the flood-plain deposits that are older than 275 ± 80 yr B.P. The most recent flood-plain fill deposited since then is unaltered. These youngest sediments of the flood plain along with the youngest veneer of vertical-accretion deposits on the lowest terrace are associated with an increased rate of deposition largely attributable to clearing of the forests by settlers, beginning in the late 1700s. Comparison of the alluvial stratigraphy with the radiocarbon-dated pollen stratigraphy of southwestern New York (Miller 1973) reveals some apparent time correlations between alluvial events and vegetation changes. This gives reason to speculate that climatic change or forest catastrophes such as disease or drought are causes of some of the alluvial events.     

Complex pedostratigraphy of a terrace fragipan at the Memorial Park site,central Pennsylvania

A fragipan (Bxb horizon) encountered during the excavation of a multicomponent archaeological site buried on an alluvial terrace in central Pennsylvania was evaluated to determine the degree of development, pedostratigraphy, and age. Based on the horizon thickness, and the degree of development of adjacent horizons, we believe that the fragipan was weakly developed. Two to three buried A horizons (Ab) occurred within the Bxb, thus, the fragipan formed in a cumulative, or fluvent, type alluvial landscape and postdates the Ab horizons overprinted by it. The buried soils were associated with stratified cultural remains. Artifact and radiocarbon ages indicate that the fragipan formed in the last 4500 years. Fragipan-containing soils on alluvial terraces should be investigated for buried soils and associated stratified cultural remains overprinted by subsequent pedogenesis. © 1998 John Wiley & Sons, Inc.     

Geochronology of paleoenvironmental change,clovis type site,Blackwater draw,New Mexico

Geoarchaeological investigations at the Clovis type site, Blackwater Locality No. 1, in 1983 and 1984 included core drilling, archaeological test excavations, stratigraphic profiling, sedimentary analyses, and radiocarbon dating. Six lines of core holes transverse to the outlet channel clearly defined the subsurface configuration and stratigraphy of the prehistoric spring run. Pieces of large animal bone from units B, C, D, and E that elsewhere in the site contain Paleoindian artifacts suggest occurrences of additional buried sites along the ancient spring run. Four Paleoindian projectile points recovered during archaeological testing confirm these prospects. The Clovis type site, located in an abandoned gravel pit, is in a natural depression initially occupied by a late Pleistocene lake. After breaching of the depression by overflow or sapping, it became a springhead and was enlarged by slumping and slopewash. Detailed stratigraphic profiling of the south wall of the abandoned gravel pit provided precise stratigraphic control for sediment sampling and radiocarbon dating, and revealed more complex microstratigraphy and facies relationships than heretofore known for the site. The interfingering of dune facies around the depression with lacustrine and spring-laid facies within it aid paleoclimatic interpretation. Deflational contacts within the depression appear to correlate with adjacent wedges of dune sand reflecting relatively arid intervals. Between these arid episodes occur intervals of increased ground water level attended initially by deposition of spring-laid sands of unit B during the late Pleistocene (13,000–11,500 yr B.P.). As the water table rose following a period of severe deflation, slumping and gravity flow deposited clayey sand, Unit C, on the floor of the blowout between 11,500 and 11,000 yr B.P. During this time Clovis people first appeared at the site. After another brief period of deflation, a lake rose causing sand of Unit D₀ to be washed in from shore followed by deposition of diatomities, units D₁ and D₂. These were separated by a brief influx of eolian sand, unit D_2z. Between 10,800 and 10,000 yr B.P. outflow from the lake was reduced by accumulation of eolian sand in the outlet while Folsom people and later Agate Basin people arrived to hunt bison during this time. Cody complex people appeared during and after a brief erosional episode that preceded deposition of eolian silt and sand of units E and F from 10,000 to 8000 yr B.P. Eolian deposition during post-Folsom time converted the pond to a wet meadow and eventually, during Cody time, to a grassy swale. Some of these deposits were blown out during the Altithermal arid period (ca. 8000-5000 yr B.P.), a time when prehistoric Archaic peoples excavated wells in the floor of the depression. Subsequent eolian activity has resulted in deflation and dune migration during the late Holocene. The best prospects for Paleoindian finds are along the buried outlet south of the south wall and in early Holocene dune sands on the uplands around the depression. © 1995 John Wiley & Sons, Inc.     

Timing and distribution of alluvial fan sedimentation in response to strengthening of late Holocene ENSO variability in the Sonoran Desert,southwestern Arizona,USA

The integration of geomorphic mapping, soil stratigraphy, and radiocarbon dating of alluvial deposits offers insight to the timing, magnitude, and paleoclimatic context of Holocene fan sedimentation near Yuma, Arizona. Mapping of 3400 km² indicates about 10% of the area aggraded in the late Holocene and formed regionally extensive alluvial fan and alluvial plain cut-and-fill terraces. Fan deposits have weakly developed gravelly soils and yielded a date of 3200–2950 cal yr BP from carbonized wood. Alluvial plain deposits have weakly developed buried sandy soils and provided a date of 2460–2300 cal yr BP from a terrestrial snail shell. Precipitation records were analyzed to form historical analogues to the late Holocene aggradation and to consider the role of climatic variability and extreme hydrologic events as drivers of the sedimentation. The historical precipitation record indicates numerous above-average events correlated to the Southern Oscillation Index (SOI) in the region, but lacks any significant reactivation of alluvial fan surfaces. The timing of aggradation from 3200 to 2300 cal yr BP correlates well with other paleoclimatic proxy records in the southwestern U.S. and eastern Pacific region, which indicate an intensification of the El Niño-Southern Oscillation (ENSO) climatic pattern and rapid climate change during this period.     

Paleoindian environmental change and landscape response in Barger Gulch,Middle Park,Colorado

Middle Park, a high‐altitude basin in the Southern Rocky Mountains of north‐central Colorado, contains at least 59 known Paleoindian localities. At Barger Gulch Locality B, an extensive Folsom assemblage (˜10,500 ¹⁴C yr B.P.) occurs within a buried soil. Radiocarbon ages of charcoal and soil organic matter, as well as stratigraphic positions of artifacts, indicate the soil is a composite of a truncated, latest‐Pleistocene soil and a younger mollic epipedon formed between ˜6000 and 5200 ¹⁴C yr B.P. and partially welded onto the older soil following erosion and truncation. Radiocarbon ages from an alluvial terrace adjacent to the excavation area indicate that erosion followed by aggradation occurred between ˜10,200 and 9700 ¹⁴C yr B.P., and that the erosion is likely related to truncation of the latest‐Pleistocene soil. Erosion along the main axis of Barger Gulch occurring between ˜10,000 and 9700 ¹⁴C yr B.P. was followed by rapid aggradation between ˜9700 and 9550 ¹⁴C yr B.P., which, along with the erosion at Locality B, coincides with the abrupt onset of monsoonal precipitation following cooling in the region ˜11,000–10,000 ¹⁴C yr B.P. during the Younger Dryas oscillation. Buried soils dated between ˜9500 and 8000 ¹⁴C yr B.P. indicate relative landscape stability and soil formation throughout Middle Park. Morphological characteristics displayed by early Holocene soils suggest pedogenesis under parkland vegetation in areas currently characterized by sagebrush steppe. The expansion of forest cover into lower elevations during the early Holocene may have resulted in lower productivity in regards to mammalian fauna, and may partly explain the abundance of early Paleoindian sites (˜11,000–10,000 ¹⁴C yr B.P., 76%) relative to late Paleoindian sites (˜10,000–8000 ¹⁴C yr B.P., 24%) documented in Middle Park. © 2005 Wiley Periodicals, Inc.     

New data on the stratigraphy and pedology of the Clovis and Plainview sites, Southern High Plains

The well known Clovis and Plainview archaeological sites of New Mexico and Texas have yielded new data on regional late Quaternary geologic, paleoclimatic, and pedologic histories. Eolian sedimentation at the Clovis site from about 10,000 to less than 8500 yr B.P. was followed by the formation of a cumulic soil between 8500 and 5000 yr B.P. Episodic eolian and slope wash deposition then culminated in massive eolian sedimentation about 5000 yr B.P. after which a Haplustalf formed then was subsequently buried by part of a dune system within the last 1000 yr. At the Plainview site, a basal stream gravel contains Plainview cultural material (ca. 10,000 yr B.P.), which is followed by a localized early Holocene lacustrine deposit, two eolian deposits (the younger dating to about 5000 yr B.P.), and a marsh deposit which slowly accreted as an Argiustoll formed in the younger eolian unit. The data indicate that on the Southern High Plains (1) between 12,000 and 8500 yr B.P. sedimentation varied from site to site, (2) there was a regional climate change toward warming and drying in the early Holocene, (3) two episodes of severe drought apparently occurred in the middle Holocene (6500 to 4500 yr B.P.), (4) between 4500 yr B.P. and the present an essentially modern climate existed, but with several shifts toward aridity within the last 1000 yr, (5) argillic horizons have developed in late Holocene soils, (6) clay illuviation can occur in calcareous soils, and (7) long-distance correlation of Holocene stratigraphy in the region is possible, particularly with the aid of soil morphology.     

柴北缘牦牛山地区牦牛山组沉积相组合特征

柴达木盆地北缘牦牛山地区出露的牦牛山组是一套由冲积扇和扇三角洲相共同构成的陆相沉积组合,冲积扇相砾岩-粗砂岩组合主要分布于研究区SE侧,扇三角洲相砂岩-泥岩组合主要分布于研究区NW侧。古水流分析表明牦牛山组沉积物主要来自其SE侧古隆起,但后期扇三角洲相包含少量来自NW和NE向的沉积物。该套沉积组合序列特征与区域上分布在牦牛山西侧同时期形成的湖泊相、滨浅海相沉积共同表明,柴达木盆地北缘在晚志留-早泥盆世时期存在一NW向倾斜的古斜坡,且晚期北侧发生抬升。砾岩和砂岩碎屑组成与区域岩石组合类型对比表明,牦牛山组沉积碎屑物主要来自于滩间山群。沉积组合序列特征、碎屑组成和区域构造背景综合研究表明,牦牛山组可能为柴达木板块向北俯冲过程中形成的局部断陷盆地的充填物。     

Soil genesis and clay mineralogy on Aliabbas River Alluvial Fan, Kerman Province

Alluvial fan is among the important geomorphic positions in arid and semi-arid environments, and the history of settlement in central parts of Iran plateau has significantly been related to this landform. Soil properties are also related to the stability and the position of geomorphic surfaces. To study and compare clay mineralogy and soil physicochemical responses to geomorphic positions, 11 representative pedons on stable and unstable alluvial fan surfaces and plain geomorphic position in a transect from Sarcheshmeh Mountains toward Rafsanjan Plain were studied. Soil moisture and temperature regimes of the area were aridic and mesic, respectively. Smectite, kaolinite, chlorite, illite, and palygorskite clay minerals were found in almost all the studied soils. More salinity was investigated in stable alluvial fan surfaces than unstable positions. Evidence of a more humid paleoclimate shown by buried Bt horizons in plain surface was observed. Transformation of palygorskite to smectite in surface horizon of unstable alluvial fan position and preservation of palygorskite associated by gypsum crystals in By horizon of stable fan surfaces were among the important findings of the research. There was a significant and mutual relationship between geomorphology and physicochemical and mineralogical properties of soils under study.     

Sedimentary Response of Different Fan Types to the Paleogene–Neogene Basin Transformation in the Kuqa Depression, Tarim Basin, Xinjiang Province

A group of alluvial fans formed in the early Paleogene represent marginal sedimentary facies at the foot of the South Tianshan Mountain, Kuqa Depression, Tarim Basin, Xinjiang province. Two types of fans occurred in the middle–late Paleogene Kumugeliemu and Suweiyi formations: one alluvial, and the other fan delta deposited in a lacustrine setting. Within the early Neogene Jidike Formation, coastal subaqueous fans developed, probably in a deeper water lacustrine setting. The three types of fans are stacked vertically in outcrop with the sequence in ascending order: bottom alluvial, middle fan-delta, and top subaqueous. The subaqueous is a typical coarse-fan deposit occurring in the glutinite member of the Jidike Formation in some wells. Laterally, from the foreland to the lacustrine settings, the distribution pattern of sedimentary facies represents the same three fan types sequentially. The spatial distribution of these fans was controlled by the Paleogene–Neogene Basin transformation, and evolution with different types of fans developed in the Kuqa Depression in response. In the Paleogene, the Kuqa Depression was a rift basin where an alluvial fan was deposited in the foreland setting, which, by early Neogene, became a foreland basin when the lake level changed. With any rise in lake level, fan-deltas migrated from lacustrine to foreland settings, whereas when the lake level fell, fan migration was reversed. In the early Neogene, with increasing slope and rising lake level, fans progressed and covered the previous fan-delta and lacustrine mudstone. Eventually, subaqueous fans developed, forming the present spatial configuration of these three fan types.     

Alluvial fan and lacustrine sediments from the Stephanian A and B (La Magdalena, Ciñera—Matallana and Sabero) coalfields, northern Spain

Vertical sequence analysis within 1500-2500 m thick coarse-grained coalfield successions allows six sedimentary associations to be distinguished. These are interpreted in terms of depositional environments on, or related to alluvial fans which fringed a fault bounded source region. (i) Topographic valley and fanhead canyon fills: occurring at the bases of the coalfield successions and comprising sporadically reddened, scree, conglomeratic thinning and fining upward sequences, and fine-grained coal-bearing sediments. (ii) Alluvial fan channels: conglomerate and sandstone filled. (iii) Mid-fan conglomeratic and sandstone lobes: laterally extensive, thickly bedded (1-25 m) and varying from structureless coarse conglomerates and pebbly sandstones, to stratified fine conglomerates and cross-bedded sandstones. (iv) Interlobe and interchannel: siltstones, fine-grained sheet sandstones, abundant floras, thin coals and upright trees. (v) Distal fan: 10 cm-1.5 m thick sheet sandstones which preserve numerous upright trees, separated by silt-stones and mudstones with abundant floras, and coal seams. The sheet sandstones and normally arranged in sequences of beds which become thicker and coarser or thinner and finer upwards. These trends also occur in combination. (vi) Lacustrine: coals, limestones, and fine-grained, low-energy, regressive, coarsening upward sequences. Proximal fan sediments are only preserved in certain basal deposits of these coalfields. The majority of the successions comprise mid and distal alluvial fan and lacustrine sediments. Mid-fan depositional processes consisted of debris flows and turbulent streamflows, whilst sheetfloods dominated active distal areas. A tropical and seasonal climate allowed vegetation to colonize abandoned fan surfaces and perhaps resulted in localized diagenetic reddening. Worked coals, from 10s cm-20 m thick, occur in the distal fan and lacustrine environments. These alluvial fan deposits infill‘California-like’basins developed and preserved along major structural zones. In many of their characteristics, in particular the occurrence of thinning and fining, and thickening and coarsening upward sequences and megasequences, these sediments have similarities to documented ancient submarine fan deposits.     

川西坳陷上侏罗统遂宁组洪水-漫湖沉积特征

利用岩芯、薄片鉴定、粒度分析、录井及测井解释等资料和手段,对四川盆地川西坳陷上侏罗统遂宁组沉积特征进行研究。结果表明,川西坳陷在遂宁组沉积时期处于稳定坳陷阶段,沉积作用明显受周期性洪水注入影响,形成“洪水-漫湖”沉积体系。“洪水-漫湖”沉积主要发育冲积扇、曲流河、曲流河三角洲和湖泊4个沉积相和若干个沉积微相,其沉积具有以下特征:①频繁的湖平面升降,形成砂泥互层的地层叠加样式;②缺乏大面积分布的半深湖-深湖沉积;③河流相为主要的沉积类型;④湖盆具有多物源、多期漫湖、满盆含砂的沉积特点。“洪水-漫湖”是川西坳陷遂宁组一种沉积充填新模式,对指导油气勘探具有重要的理论和实践意义。     

川西前陆盆地上三叠统沉积特征

应用层序地层学方法将川西前陆盆地上三叠统划分为4个三级层序和12个体系域。在层序格架内,研究了不同时期的古地理背景、物源、沉积类型和沉积相展布,明确了上三叠统存在龙门山古陆、米仓山-大巴山古陆、康滇古陆、江南古陆4个物源,识别出上三叠统海湾、冲积扇、曲流河、辫状河、扇三角洲、辫状河三角洲、曲流河三角洲和湖泊8种沉积相类型。层序Ⅰ沉积时期,盆地处于海陆交互相向陆相转变的时期,整体具有填平补齐的沉积特征,发育海湾等沉积;层序Ⅱ沉积时期,川西前陆盆地成为统一的内陆湖盆,其湖侵期为须家河期最大的湖侵期,主要发育三角洲沉积和湖相沉积;层序Ⅲ沉积时期,米仓山-大巴山古陆提供充足的物源,在米仓山-大巴山两逆冲推覆带前缘广泛发育大型冲积扇、辫状河、辫状河三角洲沉积体系;层序Ⅳ沉积时期,主要受江南古陆的影响,发育三角洲沉积和湖泊沉积。整体上,川西前陆盆地沉积相带的展布格局受构造控制,具有平行构造带展布的特点。盆地西北部陡坡带发育粗粒的冲积扇、扇三角洲-湖底扇,西南部陡坡带发育辫状河三角洲、北部-东北部陡坡带发育辫状河三角洲,而在东南部缓坡带则发育远源的曲流河、曲流河三角洲。     

The Bolton spring site,Connecticut; Early holocene human occupation and environmental changes in southern New England

The recent discovery and excavation of the Bolton Spring Site, located in the glaciated uplands of eastern Connecticut, presents an enigma to archaeologists and geologists interested in dating and interpreting prehistoric human habitation sites. A single discrete charcoal-bearing occupation level at the site was characterized by artifacts of the Middle Archaic Period (8000-6000 B.P.) and contained an abundance of small-mammal remains typical of the Holocene woodland fauna. Although the site seemed to present a clearcut opportunity for radiocarbon-dating, C13-corrected radiocarbon dates from the cultural horizon span nearly three thousand years. Our interpretation is that occupation occurred near the end of a depositional hiatus during which noncultural charcoal accumulated. Subsequent burial of the cultural layer by eolian sediments may have resulted from deflation of pre-existing eolian sediments in the Connecticut River Valley during drier, mid-Holocene conditions. Substantial rockfall activity and rubble movement on adjacent slopes may have been restricted to late Holocene time.     

鄂尔多斯盆地及周缘地区下二叠统沉积特征

通过大量的野外剖面观察和盆地内钻井岩心的详细描述,综合测井资料,从岩石类型、结构、沉积构造、古生物化石及测井曲线响应特征等方面对鄂尔多斯盆地及周缘地区下二叠统太原组和山西组沉积相特征进行了全面分析研究。结果表明,太原组主要发育陆棚、海岸、冲积扇和三角洲等沉积相,海岸沉积相包括障壁岛、潟湖和潮坪沉积,三角洲沉积相可划分为三角洲平原、三角洲前缘和前三角洲沉积。山西组主要发育冲积扇、河流、曲流河三角洲、湖泊和海岸沉积相,其中河流沉积相包括辫状河和曲流河沉积,曲流河三角洲沉积相可划分为曲流河三角洲平原、曲流河三角洲前缘和前三角洲沉积,而湖泊沉积相以浅湖沉积为主,海岸沉积主要为潟湖沉积。太原期,海相沉积占主导,主要分布于银川-榆林北部一线以南广大地区,并且从东西两侧至中部地区由浅海陆棚沉积和滨浅海过渡为潟湖沉积和潮坪沉积,其间发育障壁岛。盆地西北缘发育冲积扇和扇三角洲沉积,北部广大地区以三角洲沉积为主,自北向南依次为三角洲平原和三角洲前缘沉积。山西期,海水从盆地东南部退却,整体演变为海陆过渡相沉积,盆地北部乌达-杭锦旗-鄂尔多斯一线发育冲积扇沉积,向南至靖边一带依次发育辫状河和曲流河沉积,靖边以南至延安以北地区以三角洲平原沉积为主,向南至同心-庆阳一线发育三角洲前缘沉积,盆地南部彭阳-泾阳地区主要为浅湖沉积,再向南发育物源来自南部的三角洲沉积,在东南部武乡-义马一带为潟湖沉积。