<Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr anomalies in Late Cretaceous-Early Tertiary strata of the Cauvery basin,south India: Constraints on nature and rate of environmental changes across K-T boundary

The Ariyalur-Pondicherry sub-basin of the Cauvery basin comprises a near complete stratigraphic record of Upper Cretaceous-Lower Tertiary periods. Earlier studies have documented variations of clay mineral assemblages, change in microtexture of siliciclasts and many geochemical and stable isotopic anomalies far below the Cretaceous-Tertiary boundary (KTB) in these strata. This paper documents the occurrences of two positive ⁸⁷Sr/⁸⁶Sr anomalies preceding K-T boundary in this basin and discusses plausible causes. Analysis of trace elemental and stable isotopic profiles, sedimentation history, petrography and mineralogy of the rocks reveal that while both the anomalies may be due to increased detrital influx caused by sea level and climatic changes, the second anomaly might have been influenced by Deccan volcanism which in turn predated KTB. Record of such anomalies preceding K-T boundary supports the view of multi-causal step-wise extinction of biota across KTB.     

Positive Eu anomaly development during diagenesis of the K/T boundary ejecta layer in the Agost section (SE Spain): implications for trace-element remobilization

K/T boundary geochemical anomalies have been used previously to support the impact event at the end of the Cretaceous. However, impact models and assessment of the extraterrestrial contribution to the boundary sediments should also consider the diagenetic alteration of the impact signatures. Mineralogical and geochemical studies centring on redox proxies reveal differences in trace-element concentrations at Agost and Caravaca (SE Spain), two of the most complete K/T boundary sections. These differences probably derive from variations in the diagenetic evolution of the ejecta layer. Several redox proxies, such as extensive pyrite formation, high authigenic uranium concentration and positive Eu anomalies, indicate very strong reducing conditions at Agost. Positive Eu anomalies are extremely unusual in sediments, and in this case are interpreted to indicate a highly reducing environment. In such conditions, certain trace elements such as Ir, may have been remobilized, thereby masking the original signature of the impact.     

High-resolution geochemical record of Cretaceous-Tertiary boundary sections in Mexico: New constraints on the K/T and Chicxulub events

The investigation of eight Cretaceous-Tertiary (K/T) sections in Mexico, based on major and trace element, platinum group element (PGE), stable isotope, and multivariate statistical analysis, reveals a complex depositional history across the Chicxulub and K/T boundary events. At the biostratigraphically determined K/T boundary, a minor but significant Ir-dominated PGE anomaly (0.2-0.8 ng/g) is present in most sections. This Ir anomaly originated from an impact event and is always stratigraphically and geochemically decoupled from the underlying spherule-rich ejecta deposit related to the Chicxulub event. In all sections examined, one to three glass spherule ejecta layers and one or two chondrite-dominated PGE anomalies are separated by a bioturbated siliciclastic deposit and/or hemipelagic marl, which indicates the occurrence of at least two impact events separated by a considerable amount of time. In addition, bentonite layers and Pt and Pd-dominated PGE anomalies below and above the K/T boundary indicate volcanic activity. Above the K/T boundary, reduced bioproductivity is documented by a decrease in the biogenically bound fraction of nutrients and fluctuating ratios of immobile elements (e.g., Ti/Zr). Variations in detrital elements reflect changes in the depositional environment. Carbon and oxygen isotope and trace element distribution patterns indicate a gradually changing climate during the latest Maastrichtian, an abrupt change at the K/T boundary, and a slight recovery during the lowermost Paleocene.     

The Cretaceous–Tertiary transition in Guatemala: limestone breccia deposits from the South Petén basin

Limestone breccia deposits in southern Mexico, Guatemala and Belize have recently been interpreted as proximal to distal ballistic fallout deposits, generated by a bolide impact that struck Yucatan at K/T boundary time. We review the age, lithology and the depositional environment of five K/T boundary sections in the South Petén area of Guatemala (Caribe, Aserradero, Chisec, Actela, Chemal) in order to evaluate the nature and origin of K/T limestone breccia deposition. The sections are located 500?km south of the proposed impact site at Chicxulub and trend in an east–west direction from the Guatemala/Mexico border to southern Belize. In four of the five sections examined, a breccia unit up to 50?m thick overlies reef-bearing shallow-water limestones of late Cretaceous (Campanian-Maastrichtian) age. Rhythmically bedded limestones, marls and siltstones of early Danian age overlie the breccia and were deposited under middle-to outer-neritic conditions. The breccia consists of differently coloured layers of shallow-water limestones. Clast size generally decreases upsection to thin layers of predominantly rounded clasts, and these fine-grained rudstones grade into grainstones at the top. In at least one section (EI Caribe) diagenetically altered glass spherules are present in the uppermost layers of the grainstone. These glass spherules are of stratigraphic position and chemical composition similar to black and yellow glass from Beloc, Haiti and Mimbral, Mexico, which some workers have chemically linked to melt glass within the breccia of the Chicxulub cores. We suggest that breccia deposition in Guatemala may have been multi-event, over an extended time period, and related to the collision of the Yucatan and Chortis plates as well as related to a major impact or volcanic event at the end of the Cretaceous.     

The Cretaceous/Tertiary boundary: sedimentology and micropalaeontology at El Mulato section, NE Mexico

ABSTRACT In the El Mulato section (NE Mexico), the Upper Cretaceous marly Méndez and the Lower Palaeogene marly Velasco Formations are separated by a clastic unit. Benthic foraminifera from both marly formations indicate lower bathyal depths. The clastic unit, in contrast, contains platform sands, muddy pebbles and neritic (shallow) faunas mixed with microspherules, indicating that it was allochthonously deposited into the deep basin. The diversity and the variability in origin of the components in the clastic unit, and its sedimentological features, support a model of deposition by turbidity currents related to mass-wasting processes triggered by the Cretaceous/Tertiary (K/T) boundary impact. Planktic foraminifera were affected by a catastrophic extinction at the K/T boundary, whereas benthic foraminifera show reorganization of the community structure rather than significant extinction. The benthic faunal turnover may have resulted from the drop in primary productivity after the asteroid impact at the end of the Cretaceous.     

Biostratigraphy and depositional environments of subsurface sediments in well Arani-A,Palar basin,Tamil Nadu

The first exploratory well Arani–A was drilled in the Palar basin to a depth of 2400m and terminated within the granitic basement.This well offered the first ever opportunity to understand biostratigraphy, sedimentation history and depositional environment of the entire sedimentary column based on arenaceous foraminifera, spores, pollen and dinoflagellate cyst assemblages. Previous studies on few scattered outcrops around Sriperumbudur, Chengalpattu and Sathyavedu areas have documented palynofossil assemblage of Neocomian–Aptian age. The present study reveals the presence of middle Jurassic (Bajocian-Callovian) sediments (2360-1725 m) resting on the granitic basement. The sediments are interpreted to have deposited under lacustrine/estuarine conditions with high tides providing occasional marine influence. The middle Jurassic sediments are conformably overlain by late Jurassic (Oxfordian–Tithonian) sediments (1725 - 950 m). The late Jurassic sediments have been inferred to have got deposited under fluctuating near shoremarginal marine conditions. There is a 55m thick boulder bed (950 - 895 m) separating the overlying Valanginian sediments. Early Cretaceous (Valanginian-Early Albian) sediments are developed in the interval from 895-50m. The boulder bed possibly corresponds to the missing Berriasian stage of the earliest Cretaceous representing an unconformity of the order of ~5 Ma across Jurassic-Cretaceous boundary. These sediments are inferred to have deposited under shallow inner neritic conditions. The sediments from 50m to surface consist mainly of lateritic sandstone and alluvium. The sedimentary history of Palar basin began in Bajocian stage of middle Jurassic (170-168 Ma) and ended in early Albian stage of early Cretaceous (113-105 Ma). The late Albian marine transgression which facilitated huge sedimentation in Cauvery and Krishna-Godavari basins has bypassed the Palar basin thus adversely affecting the hydrocarbon potential.     

Portable X-ray fluorescence identification of the Cretaceous–Paleogene boundary: Application to the Agost and Caravaca sections,SE Spain

It is shown that portable X-ray fluorescence (pXRF) is a powerful tool for the identification and geochemical characterization of prospective Cretaceous–Paleogene (K–Pg) boundary sites. Field measurements in two well-known K–Pg boundary sequences, located at Agost and Caravaca, SE Spain, have been performed. A sizable enrichment around the K–Pg horizon of several elements such as K, Ti, Fe, Ni, Cr, Cu, Zn, As or Pb, together with a strong reduction in the Ca content, is found with the pXRF instrument. These observations represent a primary geochemical signature of the K–Pg boundary in distal marine sections such as those of Agost and Caravaca. Also, the intensities of the pXRF peaks correlate well with elemental composition data obtained by inductively coupled plasma-mass spectrometry (ICP-MS) on collected samples. Hence, the pXRF field measurements are shown to provide fast and useful quantitative information about K–Pg boundary sequences.     

The biostratigraphy of the uppermost calcareous nannofossils of Cretaceous deposit in both Shahdar and Namazgah sections (NE Iran)

A moderately various calcareous nannofossil assemblage of 44 species assigned to 24 genera is identified in samples collected from the Shahdar section and 18 genera and 43 species in Namazgah section. Testing of calcareous nannofossil has permitted recognition of few important coccolith events in stratigraphic interval occupied by the uppermost layers of Cretaceous in the Shahdar and Namazgah sections. These events are correlated to the CC24–CC26 of Sissingh (Geol Minjbouw 56: 37–65, 1977) in two sections. According to these biozones, the age of the studied sections in Shahdar and Namazgah is Early Maastrichtian–Late Maastrichtian. On the basis of paleoecological interpretation, the last layers related to the Cretaceous deposits in two sections were deposited in shallow marine environment in relatively low latitude, and the depth of the basin from the Cretaceous deposits toward Fajan Formation is minimized.     

西藏仲巴地区白垩纪末期—始新世早期海相地层

西藏仲巴县北部地区出露有晚白垩世至古近纪的海相地层 ,本次工作新测制了卓勒剖面 ,并对原错江顶剖面上部地层做了再次研究。地层中化石丰富 ,据有孔虫化石研究结果重新厘定曲下组时代为古新世早期、加拉孜组上段属始新世早期 ,认为该区白垩 /古近纪界线位于曲贝亚组与曲下组之间。在这一界面上 ,古新世磨拉石直接覆于晚白垩世的陆棚碳酸盐台地沉积之上 ,其间存在沉积间断 ,为弧前盆地演化后期的重大沉积转变。古新世早期曲下组为近海相磨拉石沉积 ,古新世晚期至始新世早期加拉孜组为残留海盆沉积。加拉孜组顶部为该区最高海相地层 ,其上为冈底斯群的磨拉石不整合覆盖。冈底斯群的时代应晚于始新世中期。     

Physils and organic matter-base palaeoenvironmental records of the K/Pg boundary transition from the late Cretaceous-early Palaeogene succession of the Um-Sohryngkew River section of Meghalaya,India

A continuous, shallow marine succession of the Um-Sohryngkew River section is distinct as it contains late Maastrichtian-early Danian planktonic foraminiferal zones and the K/Pg boundary, although K/Pg transition events remain inconclusive. Physils divide entire succession in to lower, middle and upper sub-divisions and represent anomalous values of redox-sensitive elements (δCe, La/Yb and Gd/Yb) in biozone CF3. Organic matter when analyzed show TOC and C spikes in biozone CF3. Illite thermometry also revealed sudden increase in the palaeo-temperature (>140 °C) for yellowish brown 1–2 mm thick organic rich clay layer in biozone CF3. Interestingly, conspicuous increase in the short chain n-alkanes and fatty acids is observed in the biozone CF3, although, long chain n-alkanes (C₂₇–C₃₃) derived from terrestrial plants show low abundance throughout the succession.High amount of combustion derived fluoranthene, pyrene, chrysene, benzo(a) anthracene PAH compounds found in the biozone CF3 are analogous to those reported from the K/T boundary sections of Stevns Klint, Gubbio, Woodside Creek and Arroyo el Mimbral. The pyrolitic signatures of these organic macro-molecules reflect global fire, caused distress to biota (during the deposition of biozone CF3 layer) which is coincidental with the well documented Ce anomaly layer, but, preceded by planktonic foraminiferal change in biozone P0 and PGE anomaly bearing layer in the biozone CF2. These organic macro-molecules reflect global fire, induced by the heat supplied by the late Cretaceous Abor and/or Deccan extrusions perhaps linked with the K/T transition events as later initiated prior to the K/Pg boundary, however, the main episode of Deccan volcanic activity occurred ∼300 ky earlier or at the K/Pg boundary itself. The deposition of 1–2 mm thick, yellowish brown, smooth (with conchoidal fracture) pyrite nodules and micro-spherules bearing organic rich clay layer marked with the decrease in the carbonate content (2.43%) that lies at the contact between the silty mudstone and grey calcareous shale located in the biozone CF3 of this succession coincides with the first appearance of Pseudoguembelina hariaensis representing age of 66.83–65.45 Ma is also related to the India’s collision with the Eurasia and Burma andextrusion of Abor volcanic.These events also endorse succeeding events such as anomalous concentration of platinum group of elements and concentration of spherules during biozone CF2, which are other end Cretaceous events before the advent of the K/Pg boundary.     

扬子地区典型剖面二叠系不同沉积相地球化学特征

对扬子地区2个典型剖面即四川广元上寺剖面和贵州罗甸纳水剖面二叠系系统采样,在沉积相研究的基础上,对华南二叠系碳酸盐岩地层不同沉积相地球化学特征进行了分析。研究表明:Co、Ba、V、Rb等具有指相意义的元素,在越靠近深水环境,Co、Ba、V、Rb平均丰度越高,而w(Sr)/w(Ba)值从开阔台地相到盆地相整体有降低趋势。贵州罗甸纳水剖面为斜坡沉积背景的典型剖面,从台地前斜坡相→陆棚相→斜坡相→盆地相,w(ΣREE)值逐渐增大,且各相带稀土元素配分模式存在明显的Ce异常。四川广元上寺剖面二叠系浅海陆棚相下部和盆地相地层中平均残余有机碳丰度大于1.5%,说明这2个沉积相带可能为该地区优质烃源岩发育相带,该剖面二叠系显示从开阔台地相到盆地相具有有机质逐渐富集的特点。     

The Cretaceous/Palaeogene (K/P) boundary at Aïn Settara, Tunisia: restructuring of benthic foraminiferal assemblages

Benthic foraminiferal assemblages, in contrast to planktic foraminifera, generally did not suffer mass extinctions at the Cretaceous/Palaeogene (K/P) boundary; extinctions were fewer in deeper water. However, the outer shelf, upper bathyal section at Aïn Settara, Tunisia, records a dramatic change in the structure of benthic foraminiferal assemblages across the K/P boundary. At the level of extinction of planktic assemblages and enrichment in Ir and other geochemical anomalies, highly diversified, low-dominance Upper Maastrichtian assemblages with infaunal and epifaunal morphogroups were suddenly replaced by taxonomically impoverished assemblages, strongly dominated by epifaunal morphogroups. This extinction or temporary emigration of most infaunal morphogroups is interpreted to be the result of a sudden breakdown in food supply. This, in turn, is the consequence of a sudden collapse in primary productivity, probably resulting from the impact of the K/P asteroid.     

A New Discovery of the Cretaceous/Tertiary Boundary from the Tethyan Belt,Hekimhan Basin,Turkey: Mineralogical and Geochemical Evidence

A Cretaceous/Tertiary (K/T) boundary location within the Tethyan region (present Mediterranean area) has been discovered in the Hekimhan basin, Malatya, Turkey. The K/T transition in a 1.65-m-thick marine evaporitic facies (gypsum and celestite) consists of laminated carbonate rocks (limestone, dolomitic limestone, dolomite) and marl in the upper part, and laminated limestone and marl in the lower part. The K/T boundary is marked by a 6-mm-thick clay layer that is entirely greenish pink in color. The stratum is characterized by a decrease in calcite content, and by an increase in the proportion of smectites and K-feldspar. Palygorskite and rarely serpentine are associated with smectite. A minimum in CaO + MgO content exists at the K/T boundary. The amounts of some transition metals, miscellaneous, low- and high-field-strength, platinum-group, and rare-earth elements reveal a substantial anomaly at the K/T boundary that supports both terrestrial (volcanic) and extraterrestrial (bolide) hypotheses.     

Syn-sedimentary tectonics and facies analysis in a rift setting: Cretaceous Dalmiapuram Formation,Cauvery Basin,SE India

The Cretaceous(Albian-Cenomanian) Dalmiapuram Formation is one of the economically significant constituents in the hydrocarbon-producing Cauvery rift basin, SE India that opened up during the Late Jurassic e Early Cretaceous Gondwanaland fragmentation. The fossil-rich Dalmiapuram Formation,exposed at Ariyalur within the Pondicherry sub-basin of Cauvery Basin, rests in most places directly on the Archean basement and locally on the Lower Cretaceous(Barremian-Aptian) Basal Siliciclastic Formation. In the Dalmiapuram Formation, a facies association of tectonically-disturbed phase is sandwiched between two drastically quieter phases. The early syn-rift facies association(FA 1), records the first carbonate marine transgression within the basin, comprising a bar-lagoon system with occasionally storms affecting along the shore and a sheet-like non-recurrent biomicritic limestone bed on the shallow shelf that laterally grades into pyrite e glauconite-bearing dark-colored shale in the deeper shelf. Spectacular breccias together with varied kinds of mass-flow products comprise the syn-rift facies association(FA 2). While the breccias occur at the basin margin area, the latter extend in the deeper inland sea. Clast composition of the coarse clastics includes large, even block-sized limestone fragments and small fragments of granite and sandstone from the basement.Marl beds of quieter intervals between tectonic pulses occur in alternation with them. Faulted basal contact of the formation, and small grabens filled by multiple mass-flow packages bear the clear signature of the syntectonic activity localized contortions, slump folds, and pillow beds associated with mega slump/slide planes and joints, which corroborates this contention further. This phase of tectonic intervention is followed by another relatively quieter phase and accommodates the late syn-rift facies association(FA 3). A tidal bar-interbar shelf depositional system allowed a transgressive systems tract motif to grow eventually passing upwards into the Karai Shale Formation, whose contact with the Dalmiapuram Formation is gradational.     

松辽盆地白垩纪湖侵沉积层序与湖海沟通事件的地球化学记录

松辽白垩纪近海陆相盆地最大湖侵期的泉头组－嫩江组时期，可能发生了三次较大规模的海水入侵事件，时间分别为泉三、四段一青一段（阿尔布期），青二、三段顶部（土仑期）和嫩一、二段（晚桑托－早坎佩尼期）。海水注入使湖盆的水文地球化学和环境地球化学条件均发生改变，并在层序中留下沉积记录。海进期主要表现为：①重同位素组份增加，直至与同期海相层序的同位素组成相同；②介质的盐度指标（Ｓｒ／Ｂａ）、碱度指标（Ｃａ＋Ｍｇ）／（Ｓｉ＋Ａｌ）、还原性指标（Ｚｎ＋Ｎｉ）／Ｇａ和硫通量指标（Ｓ归一化含量）均系统增加。相反，海退期则上述指标显著降低。根据沉积层序的同位素组成、同期海水的同位素组成和同位素分馏的质量平衡关系，可求出研究层段内同位素的海水来源与淡水来源的比例（混合度）为０－５。并由此恢复出海平面升降曲线。     

广域电磁法在洞庭盆地北部生物气勘探中应用及远景靶区预测

洞庭盆地地处湘西古生界边缘,经历了中生代晚白垩世盆地基本成型和新生代断块运动为主的两期构造旋回,为终成于燕山(中生代)延续于喜马拉雅(新生代)的断陷盆地。盆内局部凹陷白垩系之上存在着持续砂泥岩沉积及第四纪河流湖泊相现代沉积,具备了形成一定规模生物气藏的地质条件。2013-2015年笔者通过洞庭盆地浅层沉积物系统地球化学勘探,基本搞清了盆地内渗漏甲烷气体异常的分布状况。根据各指标地球化学异常特征,发现洞庭盆地北部沅江凹陷北部斜坡、青树嘴-河坝镇一带是洞庭盆地内生物气资源最有可能突破的远景区。为了追索渗漏甲烷气体来源,深化地球化学异常解释评价以及浅层生物气系统研究,2015-2016年在发现的生物气远景区,部署完成5条广域电磁测深和两条汞气测量剖面。本研究旨在通过实测地球物理和地球化学综合剖面的对比研究,揭示本区第四系构造分布和地球化学异常机制,为洞庭盆地生物气资源远景和气藏靶区的预测划分提供科学依据,也为勘探第四系生物气资源方法技术的选择提供了建议。勘探成果表明：(1)本区第四系能够满足生物气系统“生储盖”条件,具有生物气资源潜力;(2)沉积物游离烃甲烷地球化学异常是下伏第四系内气体聚集沿断裂带或沉积层向表层渗漏运移所致。酸解烃指标是识别有利于生物气体生储环境的敏感因子之一;(3)洞庭盆地工区西北部,P2剖面南段和P2线北部与P3、P4剖面交汇区域,具有良好的“自生自储”型生物气藏资源远景,是本区勘探生物资源天然气最有希望的靶区;(4)洞庭湖北部工区东部,P6测线南部接近沅江凹陷中心的四季红一带,是本区寻找 “自生自储”和“下生上储”型气藏的有利地带和资源远景区;(5)浅层沉积物地球化学勘探,有利于发现与生物气有关的气体渗漏、评价下伏沉积体系特性、缩小地球物理勘探靶区。地球化学与广域电磁剖面测量的结合是勘探生物成因天然气经济快速的方法技术。     

新疆库车坳陷晚白垩世沉积的地球化学特征及意义

库车坳陷广泛发育的晚白垩世巴什基奇克组是新疆塔里木盆地北部地区克拉苏大型气田的主要储层,其沉积环境一直存在争议。本文依据塔里木盆地北部地区库车坳陷巴什基奇克组地球化学资料,对塔北地区晚白垩世时期发育海侵沉积进行了分析。结合野外露头剖面和钻井剖面巴什基奇克组上段新发现的大量海相钙质超微化石和沉积相特点,认为塔北地区晚白垩世时期曾发生明显的海侵作用,海水分布范围向东可达库车河地区,但沉积环境比较闭塞,古盐度指数反映水介质为咸水,古气候以干旱高温为特点。这一研究为塔西南地区和塔北地区晚白垩世地层对比奠定了基础,对本区的油气勘探和远景分析具有重要意义。     

藏南贡扎剖面赛诺曼阶/土伦阶与三冬阶/坎潘阶界线 附近地层的岩石磁学对比研究

为了研究白垩纪中期大洋缺氧事件及其后古海洋环境的变化,对藏南贡扎剖面白垩纪赛诺曼阶/土伦阶和三冬阶/坎 潘阶界线附近的浅海相沉积地层开展了详细的岩石磁学对比研究。 结果显示,这两个时间段的沉积物中磁性矿物含量和粒 度无显著区别,但赛诺曼阶/土伦阶地层中含有高矫顽力磁性矿物,如赤铁矿和针铁矿,而三冬阶/坎潘阶地层中则主要为 低矫顽力磁性矿物,如磁铁矿。 由于海平面位置在这两个时间段相近,海面变化对沉积物的磁学特征的影响很小。 磁性矿 物种类的变化可能主要是由于海洋沉积环境的变化所引起的。 高矫顽力磁性矿物在赛诺曼阶/土伦阶的出现及其在三冬阶/ 坎潘阶的缺失,表明赛诺曼阶/土伦阶氧化程度可能比三冬阶/坎潘阶更高。 这与深海沉积所记录的赛诺曼阶/土伦阶为缺氧 以及三冬阶/坎潘阶为富氧的特征明显不同。 这说明以江孜地区为代表的深海-半深海环境和以岗巴定日地区为代表的浅海 环境对白垩纪中期气候变化有着不同的响应。 深水和浅水环境的演化在这两个时间段的显著差异表明相应时期的大洋环流 也可能比以往所认识的更复杂。     

酒西盆地南缘旱峡早白垩世火山岩地球化学特征及其构造意义

酒西盆地旱峡和红柳峡等地有基性火山岩产出,它们曾一度被认为是新生代构造运动的产物。旱峡火山岩作为夹层产于早白垩世新民堡群下沟组地层中,火山岩气孔、杏仁构造发育。局部发育枕状构造,具明显的水下喷发特征。旱峡火山岩SiO2相对较低,K2O+Na2O不高,但钾相对较高。稀土总量为(211．875～237．454)×10^-6,轻稀土富集,(La/Yb)N为12．47—13．79;稀土配分曲线右倾、平滑,Ce为弱的负有异常,无Eu异常。在原始地幔标准化的微量元素蛛网图上,各元素均表现为相对富集,大离子亲石元素富集程度最高．有Nb,Ta槽,但相对于原始地幔不亏损;曲线表现为整体上隆的特征,表明其源区为富集地幔。旱峡火山岩与红柳峡粗玄质熔岩的稀土和微量元素的配分模式几乎完全相同,表明它们同源同期：运用多个玄武岩大地构造环境判别图解,最终确定洒西盆地早白垩世火山岩形成于大陆拉张环境。这与酒西盆地及其周围地区(酒泉盆地群)下白垩统构造特征和盆地群热演化特征一致。对酒西盆地火山岩形成构造背景的研究,对于深化酒西盆地构造演化特征有较为重要的意义。     

Near-K/T age of clastic deposits from Texas to Brazil: impact,volcanism and/or sea-level lowstand?

Near-K/T boundary clastic deposits from Texas, Mexico, Haiti, Guatemala and Brazil, often described as impact-generated tsunami deposits, are stratigraphically below well-defined K/T boundary horizons and appear not to be causally related to the K/T boundary event. Stratigraphic evidence indicates that their deposition began during the last 170–200 kyr of the Maastrichtian, coincident with a major eustatic sea-level lowstand that lowered sea level by as much as 70–100 m. Clastic deposition ended a few tens of thousands of years before the K/T boundary during a rapidly rising sea level. The presence of glass in clastic deposits in Haiti, northeastern Mexico and Yucatan suggests that the sea-level lowstand coincided with a time of major volcanism or pre-K/T boundary bolide impact.