Barium anomaly preceding K/T boundary: possible causes and implications on end Cretaceous events of K/T sections in Cauvery basin (India), Israel, NE-Mexico and Guatemala

Maastrichtian–Danian strata of the Cauvery basin as well as selected sections of NE-Mexico, Guatemala and Israel record Ba anomalies, away from the Cretaceous/Tertiary boundary (KTB) in addition to common occurrences of geochemical and stable isotopic anomalies across the KTB. Ba anomalies were recorded in monotonous shallow marine sandstones of the Cauvery basin (south India) which contain minor amounts of Ba-orthoclase. Barium anomalies were observed also in shallow marine carbonates in sections of Israel, NE-Mexico and Guatemala. Calculation of excess Ba with reference to PAAS (Post-Archaen Average Australian Shale), comparison of coeval geochemical anomalies, depositional pattern and associated petrographic and mineralogical features of the Cauvery basin revealed that while a first Ba peak was related to detrital influx, the second Ba peak was coincident with sea level fall which in turn may have been influenced by emission of volatile hydrocarbons and resultant climatic changes. In view of intrinsic involvement of Ba in various geochemical processes and occurrence of Ba anomalies in K/T sites distributed around the world (NE-Mexico, Guatemala and Israel), it is suggested that probable causes of such widespread Ba-anomalies should be taken into consideration while analyzing end Cretaceous events. These observations support the views espoused by many workers who have stated that the K/T boundary was also accompanied by many non-catastrophic events that might have contributed to environmental stress on marine fauna, as a result of which selective multi-stage extinctions occurred.     

新疆塔西南区海相白垩系—第三系界线的地球化学异常

新疆塔里木盆地西南地区海相白垩系—第三系的界线粘土层发现于依格孜牙组和吐依洛克组之间。这一层具有相当复杂的元素组合 ,存在诸多元素异常。它不仅是一条生物界线 ,而且是一条地球化学界线。这一异常事件层代表了白垩纪与第三纪之交的突变事件 ,具有全球的一致性和等时性 ,因而具有自然界线性质。     

鞍山地区3．3Ga岩浆热事件——SHRIMP年代学和地球化学新证据

鞍山是世界上少有几个保留丰富的太古宙地质记录的地区之一。本文报道了该区东山古老岩石带古太古代闪长质片麻岩和细粒奥长花岗岩的SHRIMP测年结果和地球化学组成。闪长质片麻岩(A9317)稀土元素总量较高(ΣREE=145×10-6),轻重稀土元素分异不强,(La/Yb)n=2.8,207Pb/206Pb加权平均年龄为3321±6Ma。细粒奥长花岗岩(A0426)稀土元素总量相对较高(ΣREE=169×10-6),轻重稀土元素强烈分离,(La/Yb)n=49.9,207Pb/206Pb加权平均年龄为3321±5Ma。研究表明,古太古代晚期是鞍山地区重要的陆壳增生时期,存在来自亏损地幔源区和壳内再循环两种不同类型岩浆作用。     

Platinum-group elements (PGE) and rhenium in marine sediments across the Cretaceous-Tertiary boundary: constraints on Re-PGE transport in the marine environment

The nature of Re-platinum-group element (PGE; Pt, Pd, Ir, Os, Ru) transport in the marine environment was investigated by means of marine sediments at and across the Cretaceous-Tertiary boundary (KTB) at two hemipelagic sites in Europe and two pelagic sites in the North and South Pacific. A traverse across the KTB in the South Pacific pelagic clay core found elevated levels of Re, Pt, Ir, Os, and Ru, each of which is approximately symmetrically distributed over a distance of ∼1.8 m across the KTB. The Re-PGE abundance patterns are fractionated from chondritic relative abundances: Ru, Pt, Pd, and Re contents are slightly subchondritic relative to Ir, and Os is depleted by ∼95% relative to chondritic Ir proportions. A similar depletion in Os (∼90%) was found in a sample of the pelagic KTB in the North Pacific, but it is enriched in Ru, Pt, Pd, and Re relative to Ir. The two hemipelagic KTB clays have near-chondritic abundance patterns. The ∼1.8-m-wide Re-PGE peak in the pelagic South Pacific section cannot be reconciled with the fallout of a single impactor, indicating that postdepositional redistribution has occurred. The elemental profiles appear to fit diffusion profiles, although bioturbation could have also played a role. If diffusion had occurred over ∼65 Ma, the effective diffusivities are ∼10⁻¹³ cm²/s, much smaller than that of soluble cations in pore waters (∼10⁻⁶ cm²/s). The coupling of Re and the PGEs during redistribution indicates that postdepositional processes did not significantly fractionate their relative abundances. If redistribution was caused by diffusion, then the effective diffusivities are the same. Fractionation of Os from Ir during the KTB interval must therefore have occurred during aqueous transport in the marine environment. Distinctly subchondritic Os/Ir ratios throughout the Cenozoic in the South Pacific core further suggest that fractionation of Os from Ir in the marine environment is a general process throughout geologic time because most of the inputs of Os and Ir into the ocean have Os/Ir ratios ≥1. Mass balance calculations show that Os and Re burial fluxes in pelagic sediments account for only a small fraction of the riverine Os (<10%) and Re (<0.1%) inputs into the oceans. In contrast, burial of Ir in pelagic sediments is similar to the riverine Ir input, indicating that pelagic sediments are a much larger repository for Ir than for Os and Re. If all of the missing Os and Re is assumed to reside in anoxic sediments in oceanic margins, the calculated burial fluxes in anoxic sediments are similar to observed burial fluxes. However, putting all of the missing Os and Re into estuarine sediments would require high concentrations to balance the riverine input and would also fail to explain the depletion of Os at pelagic KTB sites, where at most ∼25% of the K-T impactor’s Os could have passed through estuaries. If Os is preferentially sequestered in anoxic marine environments, it follows that the Os/Ir ratio of pelagic sediments should be sensitive to changes in the rates of anoxic sediment deposition. There is thus a clear fractionation of Os and Re from Ir in precipitation out of sea water in pelagic sections. Accordingly, it is inferred here that Re and Os are removed from sea water in anoxic marine depositional regimes.     

Proximal impact deposits at the Cretaceous-Tertiary boundary in the Gulf of Mexico: a restudy of DSDP Leg 77 Sites 536 and 540

Restudy of Deep Sea Drilling Project Sites 536 and 540 in the southeast Gulf of Mexico gives evidence for a giant wave at Cretaceous-Tertiary boundary time. Five units are recognized: (1) Cenomanian limestone underlies a hiatus in which the five highest Cretaceous stages are missing, possibly because of catastrophic K-T erosion. (2) Pebbly mudstone, 45 m thick, represents a submarine landslide possibly of K-T age. (3) Current-bedded sandstone, more than 2.5 m thick, contains anomalous iridium, tektite glass, and shocked quartz; it is interpreted as ejecta from a nearby impact crater, reworked on the deep-sea floor by the resulting tsunami. (4) A 50-cm interval of calcareous mudstone containing small Cretaceous planktic foraminifera and the Ir peak is interpreted as the silt-size fraction of the Cretaceous material suspended by the impact-generated wave. (5) Calcareous mudstone with basal Tertiary forams and the uppermost tail of the Ir anomaly overlies the disturbed interval, dating the impact and wave event as K-T boundary age. Like Beloc in Haiti and Mimbral in Mexico, Sites 536 and 540 are consistent with a large K-T age impact at the nearby Chicxulub crater.     

Oil exploration in the Southern Gulf of Mexico and the Chicxulub impact

Discovery of the Chicxulub multi-ring impact crater came as a result of oil exploration surveys in the southern Gulf of Mexico. Subsequent studies on the Chicxulub impact and the Cretaceous/Palaeogene (K/Pg) boundary have revealed links between the impact and hydrocarbons, with implications for the K/Pg global environmental and climatic effects, as well as for oil exploration in the Gulf.     

High-resolution profile of stable isotopes and iridium across a K/T boundary section from Koshak Hill, Mangyshlak, Kazakhstan

Oxygen and carbon isotopes were measured to a high depth resolution in a nannoplankton carbonate sequence spanning the Cretaceous-Tertiary boundary at Koshak Hill, Mangyshlak Peninsula, Kazakhstan. The boundary is characterized by the presence of a ∼ 1 cm thick clay layer having a sharp peak in iridium concentration with a maximum value of 3.7 ng g^-1. The δ¹⁸O data reveal rapid (∼10³ years) excursion of sea-surface temperature at the boundary where an initial cold pulse is followed by a persistent warm period. The δ¹³C data, in contrast, indicate only a gradual change in productivity across the boundary. The observations suggest a biogeochemical scenario for the boundary event pertaining to shallow epicontinental seas.     

Palynological and bulk geochemical constraints on the paleoceanographic conditions across the Frasnian–Famennian boundary,New Albany Shale,Indiana

A down-core record of stable isotope and geochemical results is integrated with palynofacies (kerogen) data from the New Albany Shale (Indiana) to reconstruct environmental changes that occurred across the Frasnian–Famennian boundary. Preliminary interpretations are focused on developing several multiproxy linkages that will potentially lead toward a more robust understanding of the occurrence and significance of phytoplankton assemblage variations during the Late Devonian, a time of widespread black shale formation. Development of such linkages will potentially provide a more comprehensive assessment of the various controls on 1) primary production, and 2) carbon sequestration in a large, low-paleolatitude intracratonic basin.An abrupt change in the geochemical and biotic proxies for particulate organic matter across the Frasnian–Famennian boundary coincides with a distinct lithological change, characterized by laminated, brownish-black Famennian mudstones unconformably overlying alternating bioturbated, greenish-gray and non-bioturbated, dark-gray Frasnian mudstones. Elemental and isotopic profiles reflect different patterns of production, degradation, and removal of organic carbon in the two shale facies. A shift from acritarch- to prasinophyte-dominated waters across the boundary indicates the overall importance of bathymetric fluctuations, chemico-physical conditions, and nutrient availability related to eustatic sea-level change. A positive δ¹³C_V-PDB shift of 1.1‰ across the boundary is interpreted to be correlative with the global Upper Kellwasser Event. A preliminary model is proposed to explain the sustainable primary production during times of maximum flooding, thereby enhancing organic preservation during black shale formation.     

Microstructural constraints on the timing of Proterozoic deformation in Central New Mexico

The nature and extent of deformation associated with 1.4 Ga tectonism in the south-western USA are poorly understood. Two models have been proposed. Both agree that Proterozoic crustal accretion occurred at 1.65 Ga and that the rocks remained at mid-crustal conditions ( c . 12 km depth) until 1.4 Ga. However, one model suggests that 1.4 Ga deformation was regionally extensive, the other that it was localized around 1.4 Ga plutons. Following 1.4 Ga tectonism, the crust cooled below 300 °C. Detailed studies of quartz mylonite microfabrics in samples both adjacent to and removed from 1.4 Ga plutons in the Manzano Mountains, central New Mexico, are used to discriminate between these models of mid-Proterozoic thermotectonic history. In this area, as in much of northern New Mexico, the metamorphic conditions prior to emplacement of 1.4 Ga plutons were 500 °C and 4 kbar. The quartz mylonite microfabrics include ribbon grains, recrystallized grains with serrated boundaries, and strong c-axis crystallographic preferred orientations, which indicate no post-deformational modification. All of these microfabrics are consistent with deformation at upper greenschist/lower amphibolite facies conditions, and could have formed during either 1.65 or 1.4 Ga tectonism. Microfabrics formed during 1.65 Ga tectonism, however, should have been substantially modified by annealing recrystallization during residency in the middle crust and/or thermal/mechanical effects associated with 1.4 Ga tectonism. The observed microstructures are consistent with regional deformation associated with metamorphism at 1.4 Ga. The effects of deformation at 1.4 Ga in New Mexico are therefore more widespread than previously thought.     

A 10,700 years' paleotemperature record from Gotland and Pleistocene/Holocene boundary events in Sweden.

Lacustrine carbonate (Chara lime) from the Island of Gotland provides an excellent paleotemperature record for the last 10,700 years. From arctic conditions during the Younger Dryas Stadial, the temperature rapidly rose to the present level, which was reached at about 9000–9250 B.P. A Holocene climatic optimum is clearly recorded. It ended with a drastic deterioration at about 2500 B.P. at the Subboreal/Subatlantic transition. The Subatlantic temperatures are significantly lower than those of the climatic optimum. The Holocene of Sweden seems to have started with a tremendous earthquake linked to extensive faulting (explaining the inconsistencies in the sea level records and the 'drainage of the Baltic Ice Lake'), a distinct peak in the non-dipole geomagnetic field (explaining the intensity peak at this level in cores from different environments) and regional disturbancies of the sedimentation (explaining the 'drainage varve' character of varve - 1073 in the Swedish Time Scale).     

Deccan volcanism linked to the Cretaceous-Tertiary boundary mass extinction: New evidence from ONGC wells in the Krishna-Godavari Basin

A scientific challenge is to assess the role of Deccan volcanism in the Cretaceous-Tertiary boundary (KTB) mass extinction. Here we report on the stratigraphy and biologic effects of Deccan volcanism in eleven deep wells from the Krishna-Godavari (K-G) Basin, Andhra Pradesh, India. In these wells, two phases of Deccan volcanism record the world’s largest and longest lava mega-flows interbedded in marine sediments in the K-G Basin about 1500 km from the main Deccan volcanic province. The main phase-2 eruptions (∼80% of total Deccan Traps) began in C29r and ended at or near the KTB, an interval that spans planktic foraminiferal zones CF1–CF2 and most of the nannofossil Micula prinsii zone, and is correlative with the rapid global warming and subsequent cooling near the end of the Maastrichtian. The mass extinction began in phase-2 preceding the first of four mega-flows. Planktic foraminifera suffered a 50% drop in species richness. Survivors suffered another 50% drop after the first mega-flow, leaving just 7 to 8 survivor species. No recovery occurred between the next three mega-flows and the mass extinction was complete with the last phase-2 mega-flow at the KTB. The mass extinction was likely the consequence of rapid and massive volcanic CO₂ and SO₂ gas emissions, leading to high continental weathering rates, global warming, cooling, acid rains, ocean acidification and a carbon crisis in the marine environment.     

淡色花岗岩的岩石学和地球化学特征及其成因

淡色花岗岩(leucogranite)是一类高铝高硅碱的酸性侵入岩,主要地球化学特征是:SiO2≥72%,Al2O3≥14%,Na2O+K2O~8.5%,富Rb,亏损Th、Ba、Sr,稀土总量较一般花岗岩低(∑REE=(40~120)×10-6),且表现为中等分异的轻稀土弱富集型,一般具有Eu负异常;Sr-Nd-Pb-O同位素指示其岩浆明显的陆壳来源。淡色花岗岩主要发育于陆壳(俯冲)碰撞加厚带,由逆冲折返的俯冲板片变沉积岩部分经过脱水熔融产生。淡色花岗岩可划分为三种不同的岩石类型:(1)二云母型淡色花岗岩,由变泥质岩(或变硬砂岩)在中地壳水平经黑云母(和/或白云母)脱水熔融产生;(2)电气石型淡色花岗岩,由变泥质岩在较低温度下经白云母脱水熔融产生;(3)石榴子石型淡色花岗岩,由长英质下地壳经黑云母脱水熔融产生。源区残留独居石、磷灰石等富REE矿物是淡色花岗岩亏损REE、Th等元素的原因。源岩为变泥质岩及源区残留钾长石是淡色花岗岩亏损Sr、Ba的主要原因。     

Multiphase Late Devonian to Carboniferous volcanic events in the west of Oyu Tolgoi,southeastern Mongolia: New geochronological,geochemical, and isotopic constraints on tectonic history

The Late Paleozoic volcanic rocks distributed in southeastern Mongolia are key to reconstructing the tectonic processes along the south margin of the Central Asian Orogenic Belt during this period. In this study, representative volcanic samples were collected in the west of Oyu Tolgoi near the eastern border of the South Gobi and Trans-Altai Zones. The geochronological results reveal intermittent Late Devonian to Early Carboniferous volcanic belts with zircon UPb ages of 360, 320, and 340 Ma for the south, center, and north belts, respectively. Geochemical and isotopic results imply comparable petrogenesis for the samples from different belts. The basic samples are primarily derived from the different degrees of partial melting of a mantle source, and their compositions are slightly affected by the assimilation of crustal materials with different maturities. The intermediate to acidic samples were more likely produced by partial melting of a crust-derived source triggered by underplating of the mantle magma. The low Mg^# and apparent Eu anomalies of the extremely high-Si rhyolites sampled from a bimodal-like volcanic sequence in the south belt indicate strong fractional crystallization after derivation from the partial melting of the juvenile crust. In conjunction with the spatiotemporal distribution pattern of magma and the observations recorded in previous studies, we propose that the Late Devonian to Early Carboniferous volcanic rocks from the south and north belts are a continental arc formed from the northward subduction of the Tsagaan Uul terrane under the Mongolian microcontinent and that the Late Carboniferous volcanism in the center belt was produced under a post-collision extensional setting. The subsequent increasingly intense extension was also responsible for the local Late Carboniferous to Early Permian calc-alkaline to alkaline granitic plutons.     

The buried southern continuation of the Oaxaca-Juarez terrane boundary and Oaxaca Fault,southern Mexico: Magnetotelluric constraints

Thirty magnetotelluric soundings were made along two NW–SE profiles to the north and south of Oaxaca City in southern Mexico. The profiles crossed the N–S Oaxaca Fault and the Oaxaca-Juarez terrane boundary defined by the Juarez mylonitic complex. Dimensionality analysis of the MT data showed that the subsurface resistivity structure is 2D or 3D. The Oaxaca and correlative Guichicovi terranes consist of ca. 1–1.4 Ga granulitic continental crust overlain by Phanerozoic sedimentary rocks, characterized by high and low resistivities, respectively. The Juarez terrane consists of oceanic Mesozoic metavolcanic and metasedimentary rocks, characterized by a low to medium resistivity layer, that is approximately 10 km thick. The Oaxaca Fault is a Cenozoic aged, normal fault that reactivated the dextral and thrust Juarez mylonitic complex north of Oaxaca City: its location south of Oaxaca City is uncertain. In the southern profile, the MT data show a ca. 20–50 km wide, west-dipping, relatively low resistivity zone material that extends through the entire crust. This is inferred to be the Juarez terrane bounded on either side by the ca. 1–1.4 Ga granulites. The Oaxaca Fault is imaged only by a major electrical resistivity discontinuity (low to the west, high to the east) along both the western border of the Juarez mylonitic complex (northern profile) and the San Miguel de la Cal mountains (southern profile) suggesting continuity.     

A Comparison of the Geochemical Features of Some Loess Sections in New Zealand and China

A comparison of the geochemical features of loesses of New Zealand and China indicates that the distributions of the elements and their variations reflect the fluctuations of climate which can be compared with the oxygen isotope stages and glacial periods.New Zialand loess is different in source from Chinese loess.Therefore ,some differences are also noticed in their chemical compositions .Loess accumulation in New Zealand is later than that in China.Because of more rainfall in New Zealand and different distributions of loess the elements in loess have suffered stronger leaching than in China.     

New constraints on the provenance of hopanoids in the marine geologic record: Bacteriohopanepolyols in marine suboxic and anoxic environments

The abundance and structural diversity of bacteriohopanepolyols (BHPs) was examined in three marine pelagic environments that are characterized by strong vertical redox gradients and water column suboxia or anoxia. The abundance and, in most instances, structural diversity of BHPs was highest at depths where conditions were suboxic or anoxic. However, the majority of the BHP structures that were identified are environmentally cosmopolitan and their biological sources are presently not well constrained. An isomer of bacteriohopanetetrol (denoted BHT II) was observed at all three study sites in association with anoxic and suboxic conditions within the water column. Based on the absence of BHT II from terrigenous and oxic marine environments studied to date, and its strong association with suboxic and anoxic marine pelagic environments, we propose that BHT II is a promising candidate biomarker for water column suboxia and anoxia in the marine geologic record. The molecular fingerprint of BHPs in suspended and sinking particles and core-top sediments indicates that hopanoids produced within the water column are exported to marine sediments and that their biological source is most likely associated with settling particles and not the free-water phase. Based on our observations, BHPs likely represent an important input to the sedimentary hopanoid inventory, particularly in upwelling environments characterized by pelagic oxygen minimum zones (OMZ) and anoxic marine basins.     

Tsunami backwash deposits with Chicxulub impact ejecta and dinosaur remains from the Cretaceous–Palaeogene boundary in the La Popa Basin,Mexico

The La Popa Basin in north‐eastern Mexico features outstanding, continuous three‐dimensional exposures of the Cretaceous–Palaeogene boundary event deposit in shallow shelf environments pierced by salt stocks. In the area to the south‐east of the El Papalote diapir, the Cretaceous–Palaeogene deposit consists of two superimposed sedimentary units and erosively overlies upper Maastrichtian sand‐siltstones with soft‐sediment deformation and liquefaction structures. The basal unit 1 is an up to 8 m thick chaotic, carbonate‐rich bed that discontinuously fills incised gutters and channels. Besides abundant silicic and carbonate ejecta spherules from the Chicxulub impact, unit 1 includes large sandstone boulders and abundant shallow‐water debris (for example, mud clasts, algae, bivalve shells, gastropod shells and vertebrate remains). Unit 1 is conformably overlain by unit 2. Distal to the diapir, unit 2 consists of a centimetre to decimetre‐thick conglomeratic, coarse bioclast and spherule‐bearing sandstone bed. Closer to the diapir, unit 2 becomes a metre‐thick series of four to eight conglomeratic to fine‐grained graded sandstone beds rich in shell debris and ejecta spherules. Unit 2 is conformably overlain by structureless to parallel laminated sandstone beds that may mark the return to the pre‐event depositional regime. The sedimentary characteristics of the Cretaceous–Palaeogene deposit, including its erosive base, its sheet‐like geometry, the presence of multiple, graded beds, evidence for upper flow regime conditions and the absence of bioturbation, support an origin by a short‐term multiphase depositional event. The occurrence of soft‐sediment deformation structures (for example, liquefaction) below the Cretaceous–Palaeogene deposit suggests that earthquakes were the first to occur at La Popa. Then, shelf collapse and strong backflow from the first tsunami waves may have triggered erosion and deposition by violent ejecta‐rich hyperconcentrated density flows (unit 1). Subsequently, a series of concentrated density flows resulting from tsunami backwash surges may have deposited the multiple‐graded bedding structures of unit 2. The specific depositional sequence and the Fe‐Mg‐rich as well as Si‐K‐rich composition of the ejecta spherules both provide a critical link to the well‐known deep marine Cretaceous–Palaeogene boundary sites in the adjacent Burgos basin in north‐eastern Mexico. Moreover, the pulse‐like input of Chicxulub ejecta material at the base of the event deposit allows for correlation with other Cretaceous–Palaeogene boundary sites in the Gulf of Mexico and the Atlantic, as well as in Central and Northern America. The presence of diverse dinosaur and mosasur bones and teeth in the event deposit is the first observation of such remains together with Chicxulub ejecta material. These findings indicate that dinosaurs lived in the area during the latest Maastrichtian and suggest that the tsunami waves not only eroded deltas and estuaries but the coastal plain as well.