靖远黄土剖面磁性地层的初步研究

曹岘黄土剖面位于甘肃省靖远县,系黄河中游六级阶地黄土堆积,厚约505m,含33层古土壤,系黄土-古土壤系列,是目前已知世界上最厚的黄土剖面。作者对该剖面进行了古地磁学研究,结果表明:曹岘黄土剖面含布容正极性时和松山反极性时,B/M 界线位于L₈中部,加拉米洛正极性亚时位于L₁₀—L₁₃,位置。曹岘黄土堆积始于1.40MaB.P.,该黄土剖面可以与兰州、洛川和蓝田等黄土剖面对比。     

黄河源区距今13万年来古气候演化

综合分析黄河源区-青海玛多地区斗格涌盆地钻孔剖面的孢粉及易溶盐等气候代用指标,揭示了该区130ka B P以来的古气候演变规律。即:130.0-110.0ka B P寒冷干旱;110.0-82.0ka B P寒温较湿;82.0-10.4ka B P寒冷干旱;10.4ka B P至现代(即全新世)温湿冷干交替。全新世古气候又可划分为3期:早全新世升温期(10.4-7.5ka B P)(Anathermal);中全新世大暖期(7.5-3.5ka B P)(Megathermal);晚全新世降温期(3.5ka B P至今)(Katathermal)。本区古气候总的规律是:冷期长且比全球其它地方提前,暖期短且开始时期滞后。全新世以来气候波动具有千年尺度的振荡规律,晚全新世至今,气温有逐渐降低,湿度逐渐变干的趋势。      

Buchia faunas and biostratigraphy of the Jurassic-Cretaceous boundary deposits in the Komsomolsk section (Russian Far East)

Abundant Buchiidae (Bivalvia) from the Upper Volgian-Lower Valanginian sediments of the Northern Sikhote-Alin (Russian Far East) were studied in the key section at right bank of the Amur River opposite to Komsomolsk-on Amur. The analysis of the Buchiidae stratigraphic distribution in the section allowed us to reveal the sequence of Buchia-bearing beds: this is well correlated with the Buchia zonal scales of many Arctic regions. Here, from the base upward, there have been recognized the following: beds with Buchia terebratuloides, beds with B. unschensis and B. terebratuloides, beds with B. volgensis, and beds with B. inflata and B. keyserlingi. The beds with B. unschensis and B. terebratuloides also yielded the Berriasian ammonite Pseudosubplanites? sp. of Tethyan affinity. The obtained paleontological data confirm the occurrence of a large syncline in the studied section. The data also permit one to refine the age spans of the local stratigraphic units.     

Late-glacial vegetational and climatic history of the Allegheny Plateau and the Till Plains of Ohio and Indiana, U.S.A.

Shane, Linda C. K. 1987 03 01: Late-glacial vegetational and climatic history of the Allegheny Plateau and the Till Plains of Ohio and Indiana, U.S.A. Boreas , Vol. 16, pp. 1–20. Oslo. ISSN 0300–9483.
Pollen evidence from the Allegheny Plateau and the Till Plains south of the Great Lakes shows marked post-glacial vegetation gradients. C. 15,500–11,000 B.P .: On the Plateau, spruce forest was rapidly established, persisted for 2,000 years, then began a gradual change to deciduous-conifer forest. On the Till Plains, open spruce forest tundra closed slowly over 1,000 years, declined rapidly c . 13,500 B.P., and a deciduous open woodland developed. C. 11,000–10,300 B.P .: On the Till Plains, a brief cooling is recorded by increases in the abundance of spruce and fir, contemporaneous with the European Younger Dryas. No clear change is seen on the Plateau. 10,300–4,000 B.P .: Warming and/or drying occurred in both areas, as hemlock and jack/red pine trees immigrated, followed by white pine. Conifers disappeared from the Till Plains by 9,800 B.P., but pine and hemlock trees may have persisted on the Plateau. After 10,000 B.P. mixed deciduous forest was established across the entire region. Between 8,000 and 4,000 B.P., further warming/drying is indicated on the Till Plains with development of open oak forest and lake shallowing, and on the Plateau by a minor increase in herbs, lake shallowing, and reduction in pine.     

Amelioration of calcareous sandy soil productivity via incorporation between biochar and some organic manures

Most arid and semi-arid soils, especially calcareous sandy soils, are widely distributed in the Middle East region; the deficiency in their content of many nutrients particularly phosphorus and organic matter limits crops production. This study aimed to assess the effects of adding biochar (B) with farmyard manure (FYM) and poultry manure (PM) on some soil properties, phosphorus (P) availability, and barley growth in calcareous sandy soil. The pot experiment includes the following treatments: Control, B, B?+?FYM (1:1), B?+?PM (1:1), B?+?FYM (2:1), B?+?PM (2:1), FYM?+?B (2:1), and PM?+?B (2:1). Biochar combined with FYM and PM enhanced the water holding capacity (WHC) and soil organic matter (SOM) content in calcareous sandy soil. Phosphorus availability was increased significantly by applying biochar mixed with farmyard manure and poultry manure at all treatments. Green biomass of barley improved because of adding biochar alone, poultry manure alone, and biochar co-applied with poultry manure at all mixing ratios. Biochar application caused significant increases in phosphorus use efficiency (PUE) by barley plants compared to all other treatments, except for the control. We recommend adding biochar either individually or mixed with poultry manure to improve the productivity of calcareous sandy soil.     

Geological characteristics and evolution of the eastern Qinghai-Tibetan plateau since the late Cenozoic

The eastern edge of the Qinghai-Tibetan plateau developed an integrated series of late Cenozoic lacustrine, loess, red and moraines deposits. Various genetic sediments recorded rich information of Quaternary palaeoenvironment changes. Xigeda Pliocene lacustrine deposits, formed during 4.2 Ma B.P.–2.6 Ma B.P., experienced nine periodic warm-cold stages. Eolian deposition in western Sichuan began at 1.15 Ma B.P., and the loess-soil sequences successively record fourteen palaeomonsoon change cycles. Red clay in the Chengdu plain record five stages of paleoclimatic change stages since 1.13 Ma B.P.. There was an old glacial period of 4.3 Ma B.P. in the eastern Qinghai-Tibetan plateau. During the Quaternary, there were five extreme paleoclimatic events corresponding to five glaciations. __________ Translated from Geological Bulletin of China, 2007, 26(12): 1620–1626 [译自: 地质通报]     

莱河矿的超结构和低温穆斯堡尔谱的对比研究

本文进行了莱河矿3C超结构和4.2K穆斯堡尔谱的对比研究。研究表明。莱河矿的非等效位置M2A+M2C,M2B,M1B,M1A和VB能够分别与Kan等(1985)测定的莱河矿穆斯堡尔谱的吸收双峰A,B,C,D和E对应,不仅解决了超结构位置和吸收双峰之间的对应,而且圆满解释了吸收双峰A:B和C:D的强度比为2:1的关系。另外,还利用莱河矿超结构的资料讨论了莱河矿的反铁磁性内部作用。     

Syros Metasomatic Tourmaline: Evidence for Very High-{delta}11B Fluids in Subduction Zones

High-pressure (HP) metamorphic blocks enclosed in a mafic toultramafic matrix from a mélange on the island of Syrosare rimmed by tourmaline-bearing reaction zones (blackwalls).The B isotopic composition of dravitic tourmaline within theseblackwalls was investigated in situ by secondary ion mass spectrometry.Boron in these tourmalines is unusually heavy, with ¹¹B valuesexceeding +18 in all investigated samples and reaching an extremevalue of +28·4 in one sample. Blackwalls formed duringexhumation of the HP mélange at a depth of 20–25km at temperatures of 400–430°C, by influx of externalhydrous fluids. The compositions of the fluids are estimatedto be in the range of 100–300 µg/g B with ¹¹B valuesof +18 to +28. The high ¹¹B values cannot be explained by tourmalineformation from unmodified slab-derived fluids. However, suchfluids could interact with the material in the exhumation channelon their way from the dehydrating slab to the site of tourmalineformation in the blackwalls. This could produce exceptionallyhigh ¹¹B values in the fluids, a case that is modelled in thisstudy. The model demonstrates that subduction fluids may beeffectively modified in both trace element and isotopic compositionduring their migration through the material overlying the subductingslab. Blackwall tourmaline from Syros has a large grain size(several centimetres), high abundance, and an exceptionallyhigh ¹¹B value. The formation of tourmaline at the contact betweenmafic or felsic HP blocks and their ultramafic matrix involvedfluids released during dehydration reactions in the subductingslab. It forms a heavy-boron reservoir in hybrid rocks overlyingthe subducting slab, and may, thus, have a significant impacton the geochemical cycle of B and its isotopes in subductionzones. KEY WORDS: boron isotopes; tourmaline; subduction zone; fluid, high pressure     

Utilization of boron as a critical parameter in water quality evaluation: implications for thermal and mineral water resources in SW Germany and N Switzerland

 In order to investigate the application of the elemental abundance of boron and its stable isotopes, ¹⁰B and ¹¹B, for tracing anthropogenic contamination of variably mineralized thermal and mineral waters, B concentrations and isotopic compositions (δ¹¹B) were determined for sample pairs collected during surveys in 1984–1986 and 1995 from representative wells discharging water from deep crustal reservoirs within the central European crystalline basement and sedimentary cover (SW Germany and N Switzerland). The data presented show that natural temporal variations in the total B contents of thermal and mineral waters are a common feature, which makes it difficult to recognize admixture of extraneous (anthropogenic) components from B concentrations alone. Delineation of the natural versus anthropogenic origin of solutes and quantification of the relative mixing proportions may thus benefit considerably from the utilization of boron isotopes as an additional parameter. Hypothetical mixing scenarios involving various thermal waters and municipal wastewater effluents from the study area, with the latter being characterized by conspicuously light boron isotopic compositions, reveal that, in certain cases, δ¹¹B values provide a superior diagnostic tool for detection of objectionable substances derived from the discharge of man-made boron products. Received: 14 September 1999 · Accepted: 8 March 2000     

Lacustrine strata sedimentology and lake-level history in ancient Zhuyeze Lake since the Last Deglaciation

The ancient Zhuyeze Lake lies in the east Hexi corridor of Northwest China and it is the interacting belt of the East Asian summer monsoon and the westerly line. The research on paleoclimate of the lake facilitates the understanding of the processes and mechanism of climate change in Northwest China since the Last Deglaciation. Related researches of this area started in the 1960s, and the research on environment changes has become the “hotspot” during the last 10 years. This paper focuses on four sections (Qingtuhu Section, Xiqu Section, Shakengjing Section, Jiutuoliang Section) in ancient Zhuyeze Lake. Much work was done in spot investigation, section strata comparison, geophysical analyses, geochemical analyses and dependable ¹⁴C dating in order to retrieve the dry-wet history of climate changes in ancient Zhuyeze Lake since the Last Deglaciation. The main conclusions are as follows: (1) the highest terminal lake level was 1313–1315 m. In Holocene, the highest lake level was 1308–1309 m occurring between 6700–5800 a B.P.. (2) After geophysical and geochemical analyses, high-resolution records of the climate change since the Last Deglaciation were revealed as follows: cold and dry during 15800–13000 a B.P.; cool and wet during 13000–9500 a B.P.; warm and dry during 9500–6700 a B.P.; warm and wet during 6700–4300 a B.P.; cool and wet during 4300–2700 a B.P.; and at last dry during 2700-0 a B.P.. __________ Translated from Journal of Arid Land Resources and Environment, 2007, 21(12): 161–169 [译自: 干旱区资源与环境]     

Boron recycling in the continental crust of the central Andes from the Palaeozoic to Mesozoic, NW Argentina

Whole-rock chemical composition and ¹¹B/¹⁰B isotope ratios in tourmaline was investigated to study the geochemical recycling of boron during the evolution of the Andean basement from the Palaeozoic to Mesozoic. In the basement (Cambrian to Ordovician high-grade paragneisses, migmatites and orthogneisses, the Eocambrian Puncoviscana Formation, and Paleozoic-Mesozoic granitoid igneous rocks) whole-rock B contents are generally below 100 ppm, but B contents of ˜1 wt% are found in cogenetic aplite and pegmatite dikes and in tourmaline–quartz rocks. In the metasedimentary rocks, no systematic variation in B content because of metamorphic grade and no correlation of B with other incompatible elements are apparent. Tourmalines from the high-grade metamorphic basement yield δ¹¹B values ranging from −11.2 to −6.8‰ and isotope fractionation during migmatisation was small. Metamorphic tourmalines from the Puncoviscana Formation have δ¹¹B values between −6.3 and −5.8‰. The calculated (corrected for fractionation) δ¹¹B values of −6 to −2‰ for the sedimentary protolith of the metamorphic basement indicate a continental B source with subordinate marine input. Tourmalines from Palaeozoic and Mesozoic granitoids display an identical range of δ¹¹B values from −12 to −5.3‰ and indicate a similarly homogeneous B source throughout time. Tourmalines from pegmatites and tourmaline–quartz rocks record the average δ¹¹B values of the parental granitic magma. We assume that B in the Palaeozoic and Mesozoic granitoids is derived from the local metamorphic basement supporting the hypothesis that recycling of the lower Palaeozoic crust is the dominant process in granitic magma formation from Palaeozoic to Mesozoic. Received: 15 December 1999 / Accepted: 11 July 2000     

Surface modification study of borate materials from B K-edge X-ray absorption spectroscopy

The B K-edge X-ray absorption near-edge structure (XANES) spectra of two borates with tetrahedrally-coordinated B [^[4]B; natural danburite (CaB₂Si₂O₈) and synthetic boron phosphate (BPO₄)] have been recorded in total electron yield (TEY) and fluorescence yield (FY) modes to investigate the surface and bulk structure of these materials. The TEY XANES measurement shows that danburite is susceptible to surface damage involving conversion of ^[4]B sites to ^[3]B sites by reaction with moisture and/or mechanical abrasion (grinding, polishing, etc.). The bulk of the mineral is essentially unaffected. Commercial boron phosphate powder exhibits more extensive surface and bulk damage, which increases with air exposure but is recovered on heating at 650°C. In contrast to ELNES, the XANES technique is not affected by beam damage and when collected in the FY mode is capable of yielding meaningful information on the coordination and intermediate-range structure of B in borate and borosilicate materials. Received: 7 April 1997 / Accepted: 30 July 1997     

Book Review

Books Review in This Article:
Carbonate Rocks—Physical and Chemical Aspects—Developments in Sedimentology . 9B. G. V. C hilingar , H. J. B issell and R. W. F afrbridge (Editors)     

Sedimentology,sequence stratigraphy and syn-rift model of younger part of Washtawa Formation and early part of Kanthkot Formation,Wagad, Kachchh basin,Gujarat

The 600 m thick prograding sedimentary succession of Wagad ranging in age from Callovian to Early Kimmeridgian has been divided into three formations namely, Washtawa, Kanthkot and Gamdau. Present study is confined to younger part of the Washtawa Formation and early part of the Kanthkot Formation exposed around Kanthkot, Washtawa, Chitrod and Rapar. The depositional architecture and sedimentation processes of these deposits have been studied applying sequence stratigraphic context. Facies studies have led to identification of five upward stacking facies associations (A, B, C, D, and E) which reflect that deposition was controlled by one single transgressive — regressive cycle. The transgressive deposit is characterized by fining and thinning upward succession of facies consisting of two facies associations: (1) Association A: medium — to coarse-grained calcareous sandstone — mudrocks alternations (2) Association B: fine-grained calcareous sandstone — mudrocks alternations. The top of this association marks maximum flooding surface as identified by bioturbational fabrics and abundance of deep marine fauna (ammonites). Association A is interpreted as high energy transgressive deposit deposited during relative sea level rise. Whereas, facies association B indicates its deposition in low energy marine environment deposited during stand-still period with low supply of sediments. Regressive sedimentary package has been divided into three facies associations consisting of: (1) Association C: gypsiferous mudstone-siltstone/fine sandstone (2) Association D: laminated, medium-grained sandstone — siltstone (3) Association E: well laminated (coarse and fine mode) sandstone interbedded with coarse grained sandstone with trough cross stratification. Regressive succession of facies association C, D and E is interpreted as wave dominated shoreface, foreshore to backshore and dune environment respectively. Sequence stratigraphic concepts have been applied to subdivide these deposits into two genetic sequences: (i) the lower carbonate dominated (25 m) transgressive deposits (TST) include facies association A and B and the upper thick (75m) regressive deposits (HST) include facies association C, D and E. The two sequences are separated by maximum flooding surface (MFS) identified by sudden shift in facies association from B to C. The transgressive facies association A and B represent the sediments deposited during the syn-rift climax followed by regressive sediments comprising association C, D and E deposited during late syn-rift stage.     

Deglaciation and postglacial timberline in the San Juan Mountains,Colorado

Lake Emma, which no longer exists because of a mining accident, was a tarn in a south-facing cirque near the headwaters of the Animas River in the San Juan Mountains of southwestern Colorado. During the Pinedale glaciation, this area was covered by a large transection glacier centered over the Lake Emma region. Three radiocarbon dates on basal organic sediment from Lake Emma indicate that by ca. 15,000 yr B.P. this glacier, one of the largest in the southern Rocky Mountains, no longer existed. Twenty-two radiocarbon dates on Picea and Abies krummholz fragments in the Lake Emma deposits indicate that from ca. 9600 to 7800 yr B.P., from 6700 to 5600 yr B.P., and at 3100 yr B.P. the krummholz limit was at least 70 m higher than present. These data, in conjunction with Picea:Pinus pollen ratios from both the Lake Emma site and the Hurricane Basin site of J. T. Andrews, P. E. Carrara, F. B. King, and R. Struckenrath (1975, Quaternary Research 5, 173–197) suggest than from ca. 9600 to 3000 yr B.P. timberline in the San Juan Mountains was higher than present. Cooling apparently began ca. 3000 yr B.P. as indicated by decreases in both the percentage of Picea pollen and Picea:Pinus pollen ratios at the Hurricane Basin site (Andrews et al., 1975). Cooling is also suggested by the lack of Picea or Abies fragments younger than 3000 yr B.P. at either the Lake Emma or the Hurricane Basin site.     

Holocene Relative Sea Level Changes along the Seattle Fault at Restoration Point, Washington

At a marsh on the hanging wall of the Seattle fault, fossil brackish water diatom and plant seed assemblages show that the marsh lay near sea level between 7500 and 1000 cal yr B.P. This marsh is uniquely situated for recording environmental changes associated with past earthquakes on the Seattle fault. Since 7500 cal yr B.P., changes in fossil diatoms and seeds record several rapid environmental changes. In the earliest of these, brackish conditions changed to freshwater 6900 cal yr B.P., possibly because of coseismic uplift or beach berm accretion. If coseismic uplift produced the freshening 6900 cal yr B.P., that uplift probably did not exceed 2 m. During another event about 1700 cal yr B.P., brackish plant and diatom assemblages changed rapidly to a tidal flat assemblage because of either tectonic subsidence or berm erosion. The site then remained a tideflat until the most recent event, when an abrupt shift from tideflat diatoms to freshwater taxa resulted from 7 m of uplift during an earthquake on the Seattle fault 1000 cal yr B.P. Regardless of the earlier events, no Seattle fault earthquake similar to the one 1000 cal yr B.P. occurred at any other time in the past 7500 years.     

Boric acid adsorption on humic acids: Ab initio calculation of structures, stabilities, B NMR and B,B isotopic fractionations of surface complexes

Boric acid, B(OH)₃, forms complexes in aqueous solution with a number of bidentate O-containing ligands, HL⁻, where H₂L is C₂O₄H₂ (oxalic acid), C₃O₄H₄ (malonic acid), C₂H₆O₂ (ethylene glycol), C₆H₆O₂ (catechol), C₁₀H₈O₂ (dioxynaphthalene) and C₂O₃H₄ (glycolic acid). McElligott and Byrne [McElligott, S., Byrne, R.H., 1998. Interaction of and in seawater: Formation of . Aquat. Geochem.3, 345-356.] have also found B(OH)₃ to form an aqueous complex with . Recently Lemarchand et al. [Lemarchand, E., Schott, J., Gaillardeet, J., 2005. Boron isotopic fractionation related to boron sorption on humic acid and the structure of surface complexes formed. Geochim. Cosmochim. Acta69, 3519-3533] have studied the formation of surface complexes of B(OH)₃ on humic acid, determining ¹¹B NMR shifts and fitted values of formation constants, and ¹¹B, ¹⁰B isotope fractionations for a number of surface complexation models. Their work helps to clarify both the nature of the interaction of boric acid with the functional groups in humic acid and the nature of some of these coordinating sites on the humic acid. The determination of isotope fractionations may be seen as a form of vibrational spectroscopy, using the fractionating element as a local probe of the vibrational spectrum. We have calculated quantum mechanically the structures, stabilities, vibrational spectra, ¹¹B NMR spectra and ¹¹B,¹⁰B isotope fractionations of a number of complexes B(OH)₂L⁻ formed by reactions of the type:

     

河南南襄盆地泌阳凹陷东南部古近系核桃园组物源分析*

在层序地层格架的基础上,结合区域地质概况和前人研究成果,充分运用重矿物的组合特征、岩心观察描述的岩性序列特征、岩性及电性的横向变化特征、地震反射特征,结合砂岩厚度、砂地比的平面展布规律,对南襄盆地泌阳凹陷东南部古近系渐新统核桃园组的物源方向进行了研究。结果表明,泌阳凹陷东南部主要发育5个物源,其中主要物源有1个,为泌150—泌285井区的平氏物源,该物源对研究目的层各个层序的西南部沉积砂体均有控制;次要物源有4个,即泌102—泌239井区的杨桥物源、正南方向的泌151—泌251井区的魏庄物源、东南方向泌129井区的栗园物源、以及东北方向的泌319井区的栗园东北物源,这些次要物源仅对部分层序的沉积砂体有控制作用。     

The soils on the calcareous sand dunes southeast of South Australia

 The properties of soils on previously dated sand dunes from Robe to Naracoorte in South Australia were examined. In these areas younger sand dunes are composed of fresh sand, but older sand dunes are composed of calcarenited sand. The soils on the sand dunes developed successionally by the age of sand dunes. The soil properties of these sand dunes differ depending on the ages of the sand dunes. The properties of sand particles in soils are as follows: (1) On the sand dunes of 4300 years B.P., A/C profile developed (Rendzina). On the sand dunes older than 125 000 years B.P. and on the plateau of Tertiary limestone, soil profiles of A₁/AB/B/C on the sand dunes of 83 000 years B.P. and A₁/A₃/B₁/B₂/C (Terra rossa) are well developed. (2) Within the sand of A/C horizons of the sand dunes with the age of 4300 year B.P., the calcite grain content is about 64%, and the quartz content is about 35%. Within the B horizons of soils on the dunes from 83 000 years B.P. to 347 000 years B.P., the calcite grain content is only 1–2%; however, the quartz grain content is about 92%. In the B₂ horizons of soils on the dune of 690 000 years B.P. and on the Tertiary plateau, there are some calcite grains but the quartz grain content is about 96%. (3) The average size of quartz grains in the soils on the sand dunes from 4300 B.P. to 347 000 years B.P. is generally smaller, but the average size of quartz on the sand dunes of 690 000 year B.P. becomes larger and the grains are well rounded. On the Tertiary limestone plateau, the average quartz size becomes again smaller, and the grains are more rounded. (4) Fe_t in B₂ horizon of the soil profiles increases clearly corresponding to the age. Iron activity expressed by Fe_o/Fe_d also shows a close relation to the chronological sequence. The B horizon of the soil profiles shows a drastic decrease of Fe_o/Fe_d according to the age. Iron crystalinity, (Fe_d-Fe_o)/Fe_t, has a tendency for a positive relation with increasing age. Received: 1 June 1995 · Accepted: 4 December 1995     

Trace element and petrologic clues to the formation of forsterite-bearing Ca-Al-rich inclusions in the Allende meteorite

This work presents new trace element and petrographic data for three forsterite-bearing, Ca-Alrich inclusions from the Allende meteorite: TE, 818a, and 110-A. Such inclusions form a continuum with Type B1 and B2 Ca-Al-rich inclusions (CAIs), and we refer to them as “Type B3” CAIs. Textures, mineral chemistries, crystal-chemically fractionated REE patterns, and other properties suggest that Type B3 crystallized from partly molten evaporative residues. The concentrations of refractory lithophile elements are lower than in Type B1 and Type B2, in approximately inverse proportion to the higher concentrations of Mg and Si in the Type B3's. The refractory trace element abundances of the forsterite-bearing, isotopically anomalous FUN CAIs TE and CG14 suggest that they formed at higher temperatures and under more oxidizing conditions than other Type B CAIs, thus strengthening the previously observed link between relatively oxidized CAI compositions and FUN properties.We also present evidence that 818a was strongly re-heated and modified in the nebula after its initial crystallization: it consists of a core of coarse-grained Ti-Al-pyroxene (Tpx), forsterite, spinel and metal grains and a thick, surrounding mantle of melilite that has been almost totally converted to fine-grained alteration products. In the core, the mean concentrations of refractory lithophiles and siderophiles are similar (both ~ 14 × CI), but in the mantle, the refractory siderophiles are a factor of 2 lower (~ 9 × CI) than the refractory lithophiles (~18 × CI). Because the core and mantle display similar, mineralogically-fractionated REE patterns (both sloping up from La to Lu), the pre-alteration mantle could not have formed during fractional crystallization of the primary CAI nor as a later condensate over the core. A 3-stage formation process is required for 818a: (1) crystallization of the primary CAI rich in Tpx throughout; (2) re-heating and partial volatilization of Mg and Si from the outer portion of the CAI, causing an increase in the concentration of refractory lithophiles, a loss of siderophiles, and converting Tpx to melilite; (3) metasomatic alteration of the melilite-rich mantle.