Precession‐scale cyclicity in the fluvial lower Eocene Willwood Formation of the Bighorn Basin,Wyoming (USA)

Little is known about controls on river avulsion at geological time scales longer than 10⁴ years, primarily because it is difficult to link observed changes in alluvial architecture to well‐defined allogenic mechanisms and to disentangle allogenic from autogenic processes. Recognition of Milankovitch‐sale orbital forcing in alluvial stratigraphy would provide unprecedented age control in terrestrial deposits, and also exploit models of allogenic forcing enabling more rigorous testing of allocyclic and autocyclic controls. The Willwood Formation of the Bighorn Basin is a lower Eocene fluvial unit distinctive for its thick sequence of laterally extensive lithological cycles on a scale of 4 to 10 m. Intervals of red palaeosols that formed on overbank mudstones are related to periods of relative channel stability when gradients between channel belts and floodplains were low. The intervening drab, heterolithic intervals with weak palaeosol development are attributed to episodes of channel avulsion that occurred when channels became super‐elevated above the floodplain. In the Deer Creek Amphitheater section in the McCullough Peaks area, these overbank and avulsion deposits alternate with a dominant cycle thickness of ca 7·1 m. Using integrated stratigraphic age constraints, this cyclicity has an estimated period of ca 21·6 kyr, which is in the range of the period of precession climate cycles in the early Eocene. Previous analyses of three older and younger sections in the Bighorn Basin showed a similar 7 to 8 m spacing of red palaeosol clusters with an estimated duration close to the precession period. Intervals of floodplain stability alternating with episodes of large‐scale reorganization of the fluvial system could be entirely autogenic; however, the remarkable regularity and the match in time scales documented here indicate that these alternations were probably paced by allogenic, astronomically forced climate change.     

广西百色盆地古近系始新统沉积相特征及演化

利用野外露头、地震、测井和分析化验等资料,对盆地古近系始新统那读组和百岗组进行层序地层和沉积相研究。那读组和百岗组可划分为3个Ⅲ级层序,9个体系域,那读组那三段构成层序Ⅰ,那读组那二段和那一段构成层序Ⅱ,百岗组构成层序Ⅲ。层序Ⅰ和层序Ⅱ是盆地断陷期沉积,发育冲积扇相、河流相、三角洲相、扇三角洲相、深湖亚相和滨-浅湖亚相。层序Ⅱ湖泊沉积范围广,厚度大,厚层的湖相暗色泥岩是盆地主要烃源岩和区域性盖层。层序Ⅲ是盆地坳陷期的沉积,发育冲积扇相、扇三角洲相、河流相、三角洲相和滨-浅湖亚相。盆地中古近系沉积经过了洪积或冲积扇、河流三角洲→湖泊（扇三角洲）→河流的发育过程,反映了盆地从初期形成→扩张→萎缩的完整的演化序列。在层序Ⅰ和层序Ⅱ的低水位体系域,田东凹陷的中央断凹、南部次凹和那笔凸起的北部断鼻等区带发育长轴分布的河流三角洲砂岩,这些砂岩处于烃源岩成熟区,油气成藏条件优越,是河道岩性油藏勘探的有利区。在层序Ⅱ湖侵体系域和高水位体系域,北部陡坡发育扇三角洲砂体,与烃源岩指状交叉接触,有利于油气运聚成藏,容易形成大量上倾尖灭岩性油藏。     

Facies,environments and sedimentary cycles in the Middle Eocene,Bracklesham Formation of the Hampshire Basin: evidence for global sea-level changes?

The Bracklesham Formation is of Middle Eocene age and occurs throughout the Hampshire Basin of southern England. The basin is elongated east-west and filled with Lower Tertiary sediments. Its southern margin is marked by either large, northward-facing monoclines, or faults, both of which underwent differential movement, with uplift of the southern side throughout the Middle Eocene. The Bracklesham Formation, which is up to 240 m thick, shows pronounced lateral facies changes with dominantly marine sediments in the east passing to alluvial sediments in the west. Four principal sedimentary environments: marine, lagoonal, estuarine and alluvial are distinguished. Marine sediments comprise six facies including offshore silty clays and glauconitic silty sands, beach and aeolian dune sands, and flint conglomerates formed on pebble beaches. Offshore sediments predominate in the eastern part of the basin, as far west as Alum Bay, where they are replaced by nearshore sediments. Lagoonal sediments comprise four facies and formed in back-barrier lagoons, coastal marshes and, on occasions, were deposited over much of the basin during periods of low salinity and restricted tidal motion. Five estuarine facies represent tidal channels, channel mouth-bars and abandoned channels. These sediments suggest that much of the Bracklesham Formation was deposited under micro- to meso-tidal conditions. Alluvial sediments dominate the formation to the west of Alum Bay. They comprise coarse to fine sands deposited on the point-bars of meandering rivers, interbedded with thick sequences of laminated interchannel mudstones, deposited in marshes, swamps and lakes. Extensive layers of ball clay were periodically deposited in a lake occupying much of the alluvial basin. In alluvial areas, fault movement exposed Mesozoic rocks along the southern margin of the basin, the erosion of which generated fault-scarp alluvial fan gravels. Locally, pisolitic limestone formed in pools fed by springs emerging at the faulted Chalk-Tertiary contact. In marine areas, flint pebbles were eroded from coastal exposures of chalk and accumulated on pebble beaches and in estuaries. From other evidence it is suggested that older Tertiary sediments were also reworked. The Bracklesham Formation is strongly cyclic and was deposited during five marine transgressions, the effects of which can be recognized throughout the basin in both marine and alluvial areas. Each of the five transgressive cycles is a few tens of metres thick and contains little evidence of intervening major regression. The cycles are thought to represent small-scale eustatic sea-level rises (‘paracycles’) superimposed upon a major transgressive ‘cycle’ that began at the base of the Bracklesham Formation, following a major regression, and was terminated, at the top of the Barton Formation by another major regression. This major cycle can be recognized world-wide and may reflect a period of rapid northward extension of the mid-Atlantic ridge.     

First occurrence of the Salvador Formation in the Jatobá Basin (Pernambuco,Northeast Brazil): Facies characterization and depositional systems

Fan deltas, constituting proximal depositional systems adjacent to boundary faults, are common features associated with rift basins. The Cretaceous fan delta systems of the Salvador Formation, deposited during the rift phase of the Recôncavo-Tucano-Jatobá Basin, were first reported in the Recôncavo Basin and later discovered in the Tucano Basin. Because of the absence of any outcrops in the Jatobá Basin until now, these alluvial fans were interpreted solely through seismic analysis. We report the first revealed outcrops of the Salvador Formation in that basin and characterize their depositional systems as interlayered with the lacustrine Candeias Formation. Based on facies and architecture, the alluvial system can be subdivided into three associations: (1) proximal fan delta, characterized by meter-scale conglomerate bodies with a predominance of boulders and cobbles with thin sandstone layers; (2) distal fan delta, characterized by sheet-like pebble conglomerate and sandstone layers with flame and load structures; and (3) lacustrine, further subdivided into shallow lake facies reddish shales and mudstones with oolitic limestones and deep lake facies grey to green shales with pyrite. Paleocurrent measurements for the proximal fan association show paleoflow direction varying from SW to SE, which is expected for the rift phase alluvial system. The Recôncavo-Tucano-Jatobá rift system has two conglomeratic units, namely the Salvador and Marizal Formations, the former a syn-rift and the latter a post-rift unit. The absence of sedimentary clasts in the conglomerates, very low maturity, the presence of giant clasts, and a visible relationship between boundary faults in the outcrop, define the syn-rift Salvador Formation characteristics. Based on the facies and paleocurrent analyses, the Salvador Formation deposits in Jatobá Basin were interpreted as a deposition of a debris flow-dominated fan delta, indicating the lacustrine setting represented by the Candeias Formation.     

Depositional environment and sedimentary of the basinal sediments in the Eibiswalder Bucht (Radl Formation and Lower Eibiswald Beds), Miocene Western Styrian Basin,Austria

The Eibiswald Bucht is a small subbasin of the Western Styrian Basin exposing sediments of Lower Miocene age. In the past the entire sequence exposed in the Eibiswalder Bucht has been interpreted as being of fluvial/lacustrine origin; here, results are presented of detailed sedimentological investigations that lead to a revision of this concept. The lowermost siliciclastic sedimentary unit of the Eibiswalder Bucht sequence is the Radl Formation. It is overlain by the Eibiswald Beds, which are subdivided into the Lower, Middle and Upper Eibiswald Beds. The Radl Formation and the Lower Eibiswald Beds are interpreted as a fan delta complex deposited along NNW-SSE striking faults. Based on the sedimentary facies this fan delta can be subdivided into a subaerial alluvial fan facies group, a proximal delta facies group and a distal delta/prodelta facies group. The Radl Formation comprises the alluvial fan and proximal delta facies groups, the Lower Eibiswald Beds the distal delta/prodelta facies group. The alluvial fan and the proximal delta consist of diverse deposits of gravelly flows. The distal delta/prodelta consists of wave-reworked, bioturbated, low density turbidites intercalated with minor gravelly mass flows. The prodelta can be regarded as as the basin facies of the small and shallow Eibiswalder Bucht, where marine conditions prevailed. The basin was probably in part connected with the Eastern Styrian Basin, the contemporary depositional environment of the Styrian Schlier (mainly turbiditic marine offshore sediments in the Eastern Styrian Basin). Analysis of the clast composition, in conjunction with the paleotransport direction of the coarse delta mass flows of the Radl Formation, shows that the source rocks were exclusively crystalline rocks ranging from greenschists to eclogites.     

塔里木盆地西南地区白垩系沉积相特征

塔西南白垩系发育,可分为上、下两统。下白垩统克孜勒苏群可分4段,多以陆相沉积为主,富含棕红色砂砾岩夹少许砂岩、粉砂岩、泥岩和砾岩。上白垩统英吉沙群为海陆相并存,库克拜组可分2段,常见泥岩、膏岩和海相化石;乌依塔格组多为红色泥岩、泥质粉砂岩夹砂岩;依格孜牙组多见灰岩、白云质灰岩,富含海相化石;吐依洛克组为棕红色泥岩、石膏和砂、砾岩,含海相化石。通过勾勒9个岩性单元的沉积相展布,分析昆仑山前白垩纪的沉积环境演化过程。克孜勒苏群西区多为陆相快速堆积,东区远离陆源为三角洲和滨岸沉积,具有宽泛的冲积扇—辫状河三角洲相分布。库克拜组总体显示为辫状河三角洲—潮坪相变的过程;乌依塔格组以潮坪为主;依格孜牙组表现为碳酸盐岩台地—台地边缘的演化;吐依洛克组为宽广潮坪。     

试论宁夏地区始新统寺口子组沉积的构造背景

做为新生代宁夏境内的第一套沉积,始新统寺口子组具有其特殊的意义,但一直没有得到满意的解释。从寺口子组的沉积规模以及较为剧烈的沉积相变化来看,寺口子组的沉积来的很突然。通过沉积相以及构造分析表明寺口子组是走廊南山前陆盆地中前隆位置靠前陆盆地一侧的沉积。该盆地是30～40Ma之间走廊南山逆冲隆起的前陆盆地,盆地的前隆沉积单元位于鄂尔多斯西缘及香山等地区,隆后沉积单元位于鄂尔多斯西缘以东,由于挠曲作用在该前隆上产生了许多倾向造山带的正断层,这些正断层控制了寺口子组的分布．基本上是一种近源的快速堆积,形成一系列围绕前隆的冲积扇或洪积扇沉积,物源为鄂尔多斯西缘隆起等地区。     

Palaeoenvironmental significance of Late Permian palaeosols in the South‐Eastern Iberian Ranges,Spain

The Late Permian (Wuchiapingian) Alcotas Formation in the SE Iberian Ranges consists of one red alluvial succession where abundant soil profiles developed. Detailed petrographical and sedimentological studies in seven sections of the Alcotas Formation allow six different types of palaeosols, with distinctive characteristics and different palaeogeographical distribution, to be distinguished throughout the South‐eastern Iberian Basin. These characteristics are, in turn, related to topographic, climatic and tectonic controls. The vertical distribution of the palaeosols is used to differentiate the formation in three parts from bottom to top showing both drastic and gradual vertical upwards palaeoenvironmental changes in the sections. Reconstruction of palaeoenvironmental conditions based on palaeosols provides evidence for understanding the events that occurred during the Late Permian, some few millions of years before the well‐known Permian‐Triassic global crisis.     

Facies and Architecture of a Carboniferous Grounding-line System From the Guandacol Formation, Paganzo Basin, Northwestern Argentina

New outcrops of Middle Carboniferous glacigenic deposits found in the Guandacol Formation (western Paganzo Basin) are described in this paper. The study locality of Los Pozuelos Creek (northwestern Argentina) includes coarse-grained diamictites, rhythmites, laminated pebbly mudstones and shales that represent an expanded column of the Gondwanic glaciation in this region. Thirteen lithofacies recorded at the measured section have been grouped into three facies associations. Facies Association I is composed of coarse-grained massive and stratified diamictites (lithofacies Dmm, Dms, Dmg, Dcs), laminated siltstones with dropstones (Fld) and interstratified sandstones and mudstones (Fl, Sr). These rocks represent both tillites and resedimented diamictites closely associated to small water bodies where laminated siltstones with dropstones and stratified sandstones and mudstones were deposited. Facies Association II comprises couplets of matrix-supported thinly bedded diamictites (Dmld) and laminated mudstones with dropstones (Fld). This facies association results from the combination of three different processes, subaqueous cohesionless debris flows, coeval rainout of ice-rafted debris and settling of fine-grained particles from supension. Finally, Facies Association III is made up of laminated mudstones without dropstones, thin marl levels and scarce fine- to very fine-grained sandstones. This assemblage clearly suggests sedimentation in a deep marine environment below the wave base.The architecture of the glacigenic deposits has been investigated using photomosaic panels. The geometry of the depositional bodies and facies suggest that Los Pozuelos Creek outcrops exhibit a well preserved three-dimensional example of a grounding-line system. In particular, three different subenvironments of a morainal bank were interpreted: a bank-front, a bank-core and a bank-back. The bank-front assemblage is characterized by coarse-grained, mainly resedimented, diamictites grading laterally to prograding clinoforms composed of interbedded matrix-supported thinly bedded diamictite and mudstones. The bank-core assemblage is formed by a stacking of coarse-grained diamictites where at least five major erosional surfaces, bounding four multistory diamictite bodies, can be recognized. Finally, the bank-back assemblage corresponds to discontinuous intervals of striated lodgement till, and coarse-grained resedimented diamictites showing important post-depositional deformation. The retrogradational stacking of the morainal banks indicate an overall glacial retreat and a glacioeustatic sea-level rise. Erosional surfaces at the base of each morainal bank suggest intervening short term episodes of ice advance.The new data presented here confirm the existence of "true" tillites in western Paganzo Basin and suggest several (at least four) pulses of glacial advance and retreat during the Namurian glaciation in the region and permit a more refined interpretation of the glacial deposits in the Huaco area.     

层序地层格架下烃源岩地球化学研究:以尼日尔Termit盆地为例

如何利用有限的烃源岩样品的实验分析数据和地质资料尽可能地提高烃源岩评价和预测的精度,是当今烃源岩地球化学研究亟需解决的问题.采用层序地层学与油气地球化学相结合的方法,研究了非洲尼日尔Termit盆地基于层序地层格架下,上白垩统Yogou组烃源岩空间分布特征及有机质地球化学性质,初步展示了层序地层格架下烃源岩地球化学研究的方法、应用效果及优势.Termit盆地上白垩统Yogou组海相泥页岩是该盆地主要的烃源层,自下而上可划分为YSQ1、YSQ2和YSQ3共3个三级层序.根据层序/体系域发育特征、岩性录井和测井曲线响应特征,识别出外陆棚、内陆棚、三角洲、滨岸相泥岩及煤/炭质泥岩共5种不同沉积类型的烃源岩,不同层序与体系域具有不同的烃源岩纵向叠置关系和横向分布特征.不同类型的烃源岩有机质具有明显不同的地球化学性质:外陆棚和内陆棚泥岩有机质丰度中等-好,有机质生物来源中,低等水生生物贡献高,沉积于偏还原的沉积环境.滨岸和三角洲相泥岩有机质丰度高,具有低等水生生物和高等植物来源的双重贡献,沉积于偏氧化的沉积环境.三级层序或其体系域控制下的沉积相分布和演化导致不同类型烃源岩的发育和横向分布特征,同一沉积相类型的烃源岩具有相似的地球化学性质.与传统的以组、段为单元的烃源岩地球化学研究相比,层序地层格架下的烃源岩评价可以刻画不同层序、不同体系域和沉积相带烃源岩有机质地球化学性质的差异,提高资源评价和油-源对比的精度.      

四川盆地奥陶系岩相古地理与勘探潜力

在前人研究基础上,依托露头和钻井资料,以沉积相分析为核心,结合四川盆地构造演化,采用单因素分析多因素综合法,以"组"为单元编制了奥陶纪岩相古地理图。奥陶纪四川盆地及邻区总体呈现西高东低的古地理格局,自西向东发育滨岸相、混积潮坪相、局限台地相、开阔台地相和斜坡相—盆地相。从岩相古地理视角对成藏条件的分析表明:奥陶系五峰组沉积期四川盆地主体属于局限海环境,发育了一套优质烃源岩,此外,与奥陶系临近的上覆志留系龙马溪组和下伏寒武系筇竹寺组烃源岩在有断层沟通的情况下可提供有效气源;奥陶系碳酸盐岩总体致密,白云石化、表生溶蚀和裂缝的存在是储层形成的关键因素,对应发育了桐梓组—红花园组颗粒滩白云岩储层、岩溶储层和宝塔组裂缝储层等三类储层;奥陶系发育下部(下生上储)和上部(上生下储)两套成藏组合,具有较好的勘探潜力。     

西藏昂仁县扯假错渐新统日贡拉组地层沉积相及沉积演化特征

沉积相是研究古环境、古气候及岩相古地理的基础与重要依据。本文报道西藏昂仁县扯假错剖面渐新统日贡拉组的岩性特征、基本层序、沉积相及垂向上沉积演化特征。该组为一套紫红色碎屑岩系,为砾岩、砂岩夹粉砂岩和泥质岩,具典型的河流环境沉积特征,为进一步研究该地区该时期的沉积环境提供了线索。     

齐姆根-桑株河地区侏罗纪沉积盆地及沉积相

齐姆根-桑株河地区侏罗纪形成昔力必里-库斯拉甫断陷盆地和达木斯-莫莫克-克里阳坳陷盆地,其间以琼阔若勒克背斜带相分割.下侏罗统莎里塔什组为冲积扇相沉积,康苏组属湖泊-三角洲相沉积,中侏罗统杨叶组至塔尔尕组以湖泊相沉积为主,上侏罗统库孜贡苏组为扇三角相沉积.沉积特征为侏罗纪早期快速充填,中期稳定沉降,晚期萎缩充填.康苏组、杨叶组湖泊相暗色碳质泥岩、粉砂质泥岩有机质含量高,厚度较大,为塔西南重要的生油岩.     

Exploration prospects of oil and gas in the Northwestern part of the Offshore Indus Basin,Pakistan

Oil and gas resources are short in Pakistan and no commercially viable oil and gas sources have been yet discovered in its offshore areas up to now. In this study, the onshore-offshore stratigraphic correlation and seismic data interpretation were conducted to determine the oil and gas resource potential in the Offshore Indus Basin, Pakistan. Based on the comprehensive analysis of the results and previous data, it is considered that the Cretaceous may widely exist and three sets of source rocks may be developed in the Offshore Indus Basin. The presence of Miocene mudstones has been proven by drilling to be high-quality source rocks, while the Cretaceous and Paleocene–Eocene mudstones are potential source rocks. Tectonic-lithologic traps are developed in the northwestern part of the basin affected by the strike-slip faults along Murray Ridge. Furthermore, the Cretaceous and Paleocene–Eocene source rocks are thick and are slightly affected by volcanic activities. Therefore, it can be inferred that the northwestern part of Offshore Indus Basin enjoys good prospects of oil and gas resources.     

兰州-民和盆地早白垩世的沉积环境分析

兰州－民和盆地早白垩世充填了巨厚的陆源碎屑物,笔者通过对碎屑物组合方式的研究,陆盆内为冲积扇相→湖泊相→湖控三角洲相序的充填序列;通过对陆盆的基底特征,古流向、物源区和陆盆演化的分析,揭示了盆地的沉积特征。     

汾河裂谷晋中盆地内第四纪沉积序列与沉积环境恢复

晋中盆地是位于汾渭地堑系中部的新生代陆内断陷沉积盆地,研究晋中盆地第四纪的沉积序列对于进一步认识该盆地区域构造和区域气候环境变化具有重要意义。为查明晋中盆地第四纪沉积序列结构、研究揭示晋中盆地第四纪沉积环境及演化,通过构造岩相学方法,对晋中盆地地表和钻孔内第四纪沉积物和沉积环境进行了研究。结果表明:晋中盆地清徐地区地表第四纪沉积序列结构为盆地内部沱阳组河床相和河漫滩相-盆地边缘汾河组河流相—盆山过渡带峙峪组河流相、汾河组冲积扇相及马兰组风积相-基岩山地（盆地外围）二叠系浅海相。钻孔岩芯内第四纪沉积序列结构为下更新统浅湖相和滨湖相—中更新统浅湖相和河流相—上更新统河流相和冲积扇相—全新统冲积扇相。研究认为晋中新生代陆内断陷盆地内沉积序列和演化结构为早更新世陆相湖盆沉积环境—中更新世萎缩湖泊环境—晚更新世强烈萎缩的湖泊和河流环境—全新世再度沉降的陆相湖盆;陆相湖盆从中心向山地沉积环境分带为湖泊沉积环境—河流和湖泊沉积环境—冲积扇沉积环境（盆地边缘出山口区）。盆山过渡带地区上更新世沉积物错位现象与同沉积活动断裂有关,断裂活动性揭示了晋中盆地阶梯式断陷成盆的动力学机制。这些研究成果为区域气候环境变化和晋中盆地区域构造研究提供了新证据,也为太原市城市群建设中工程场址的选择提了供参考。      

Anatomy of an Upper Triassic continental to marginal‐marine system: the mixed siliciclastic–carbonate Travenanzes Formation (Dolomites,Northern Italy)

The Travenanzes Formation is a terrestrial to shallow‐marine, siliciclastic–carbonate succession (200 m thick) that was deposited in the eastern Southern Alps during the Late Triassic. Sedimentary environments and depositional architecture have been reconstructed in the Dolomites, along a 60 km south–north transect. Facies alternations in the field suggest interfingering between alluvial‐plain, flood‐basin and shallow‐lagoon deposits, with a transition from terrestrial to marine facies belts from south to north. The terrestrial portion of the Travenanzes Formation consists of a dryland river system, characterized by multicoloured floodplain mudstones with scattered conglomeratic fluvial channels, merging downslope into small ephemeral streams and sheet‐flood sandstones, and losing their entire discharge subaerially before the shoreline. Calcic and vertic palaeosols indicate an arid/semi‐arid climate with strong seasonality and intermittent discharge. The terrestrial/marine transition shows a coastal mudflat, the flood basin, which is usually exposed, but at times is inundated by both major river floods and sea‐water storm surges. Locally coastal sabkha deposits occur. The marine portion of the Travenanzes Formation comprises carbonate tidal‐flat and shallow‐lagoon deposits, characterized by metre‐scale shallowing‐upward peritidal cycles and subordinate intercalations of dark clays from the continent. The depositional architecture of the Travenanzes Formation suggests an overall transgressive pattern organized in three carbonate–siliciclastic cycles, corresponding to transgressive–regressive sequences with internal higher‐frequency sedimentary cycles. The metre‐scale sedimentary cyclicity of the Travenanzes Formation continues without a break in sedimentation into the overlying Dolomia Principale. The onset of the Dolomia Principale epicontinental platform is marked by the exhaustion of continental sediment supply.     

鄂尔多斯盆地延长组长1段烃源岩有机地球化学特征

鄂尔多斯盆地三叠系延长组长1段发育一套深湖相浊积岩及数层暗色泥岩。根据实测的有机碳含量、可溶有机质及族组分含量、有机元素和同位素等数据可知,该泥岩为一套较好—好的烃源岩。镜质体反射率及生物标志化合物成熟度指标显示,该段烃源岩有机质处于低成熟到成熟阶段。该套烃源岩的发现为陕北地区寻找新的油气勘探目标提供了依据。