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1.
The early Mesoproterozoic Rohtas Limestone in the Son valley area of central India represents an overall shallowing-upward
carbonate succession. Detailed facies analysis of the limestone reveals outer- to inner-shelf deposition in an open marine
setting. Wave-ripples, hummocky cross stratifications and edgewise conglomerates argue against a deep marine depositional
model for the Rohtas Limestone proposed earlier. Stable isotope analysis of the limestone shows that δ13C and δ18O values are compatible with the early Mesoproterozoic open seawater composition. The ribbon limestone facies in the Rohtas
Limestone is characterized by micritic beds, each decoupled in a lower band enriched and an upper band depleted in dissolution
seams. Band-wise isotopic analysis reveals systematic short-term variations. Comparative enrichment of the heavier isotopes
in the upper bands is attributed to early cementation from sea water and water derived from the lower band undergoing dissolution
because of lowering of pH at depth. The short-term positive shifts in isotopic compositions in almost every upward gradational
transition from a seamed band to a non-seamed band support the contention that dissolution seams here are of early diagenetic
origin, although their formation was accentuated under overburden pressure. 相似文献
2.
《International Geology Review》2012,54(15):1909-1921
This paper reports the carbon and oxygen isotope compositions of lacustrine carbonate sediments from the Palaeogene Shahejie Formation, Qikou depression, Bohaiwan Basin, with the aim of determining the palaeoenvironmental conditions in the region. Results from Es2, the second member of the Shahejie Formation, showed values of δ13C and δ18O from –1.2‰ to +2.4‰ (average +0.6‰) and from –6.8‰ to –4.7‰ (average –5.7‰), respectively, suggesting a relatively hot climate attending deposition. The slightly closed nature of the lake, which contains brackish water, resulted in higher carbonate δ13C and δ18O values than in a meteoric environment. The values of δ13C and δ18O preserved within the carbonates of the overlying lower Shahejie I (Es1) varied between +1.3‰ and +4.9‰ (average +3.2‰) and from ?4.4‰ to ?1.8‰ (average ?3.1‰), respectively, indicating that the climate became colder at that time. Subsequently, a marine transgression caused the salinity of the lake water to increase. The values of δ13C and δ18O were controlled by salinity. The high δ13C values were also influenced by the rapid burial of the lake organisms and by algal photosynthesis. Values of δ13C and δ18O from carbonates in upper Es1 ranged from ?8.0‰ to +11.0‰ (average +10.1‰) and from ?5.0‰ to ?1.5‰ (average ?3.4‰), respectively, indicating a slight increase in the temperature over time. In the closed and reducing environment, extremes in δ13C values resulted from biochemical fermentation. The positive δ13C excursion recorded in the carbonates of the Shahejie Formation in the Qikou depression indicates that the palaeoclimate underwent a significant transformation during the Eocene and the Oligocene. 相似文献
3.
Yann Rolland Sandra Billo Michel Corsini Marc Sosson Ghazar Galoyan 《International Journal of Earth Sciences》2009,98(3):533-550
The Amassia–Stepanavan blueschist-ophiolite complex of the Lesser Caucasus in NW Armenia is part of an Upper Cretaceous-Cenozoic
belt, which presents similar metamorphic features as other suture zones from Turkey to Iran. The blueschists include calcschists,
metaconglomerates, quartzites, gneisses and metabasites, suggesting a tectonic mélange within an accretionary prism. This
blueschist mélange is tectonically overlain by a low-metamorphic grade ophiolite sequence composed of serpentinites, gabbro-norite
pods, plagiogranites, basalts and radiolarites. The metabasites include high-P assemblages (glaucophane–aegirine–clinozoisite–phengite), which indicate maximal burial pressure of ∼1.2 GPa at ∼550°C. Most
blueschists show evidence of greenschist retrogression (chlorite—epidote, actinolite), but locally epidote-amphibolite conditions
were attained (garnet—epidote, Ca/Na amphibole) at a pressure of ∼0.6 GPa and a temperature of ∼500°C. This LP–MT retrogression
is coeval with exhumation and nappe-stacking of lower grade units over higher grade ones. 40Ar/39Ar phengite ages obtained on the high-P assemblages range between 95 and 90 Ma, while ages obtained for epidote-amphibolite retrogression assemblages range within
73.5–71 Ma. These two metamorphic phases are significant of (1) HP metamorphism during a phase of subduction in the Cenomanian–Turonian
times followed by (2) exhumation in the greenschist to epidote-amphibolite facies conditions during the Upper Campanian/Maastrichtian
due to the onset of continental subduction of the South Armenian block below Eurasia. 相似文献
4.
The basinal facies of the Lopingian Zechstein Limestone in SW Poland consists of thin (often less than 1 m thick) limestones and/or dolomites, often containing the Kupferschiefer (few tens of centimetres thick) at their base, and local thick (up to 90 m) reefal carbonates. The δ13C curve of these basal Zechstein deposits strongly suggests that even when the Kupferschiefer is lacking, the thin (condensed) sequences record the entire interval of the Zechstein prior to the onset of evaporite deposition, in contrast to the thick reef sequences which lack the characteristic δ13C curve for the lowermost part of the Zechstein. The calcite samples show considerable ranges of δ18O values. If the maximum δ18O values are considered to be the closest to the pristine original ones and if δ18Owater value = 0 is assumed, then the calculated range of palaeotemperatures for the Kupferschiefer and Zechstein Limestone calcite ranges from 19 to 34 °C. The faunal restriction, common dwarf foraminifers and the predominance of lagenids in the foraminiferal assemblage indicate continual dysaerobic conditions and possibly elevated salinity of seawater during deposition of thin basinal Zechstein Limestone deposits. The mixing of shallow and deeper waters in the stratified Zechstein Basin caused by upwelling could result in prolific carbonate precipitation in reefs located at the slope of the marginal carbonate platform of the Zechstein Limestone and in isolated reefs related to palaeohighs within the basin; however, there is no isotopic record of eventual upwelling. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
5.
Devendra Lal William G. Large Stephan G. Walker 《Journal of Earth System Science》2007,116(3):171-177
This paper attempts at full characterization of the unique global 8.2 Kyr B.P. cooling event. Significant atmospheric cooling
started during 9.5–8.5 Kyr B.P. when the Sun was extremely quiet during three periods of ∼ 50–100 years. The flood of melt
water in the N. Atlantic from glacial lakes during the demise of the Laurentide ice sheet, starting at ∼ 8.5 Kyr B.P., adds
to the atmospheric cooling. Climatic forcing events occurred at 8.5 Kyr B.P., at 8.2 Kyr B.P. and finally at 8.06 Kyr B.P.,
leading to concurrent increases or decreases in the atmospheric Δ14C levels, completely consistent with the climatic forcing proposed here. 相似文献
6.
Amanda M. Oehlert Peter K. Swart Gregor P. Eberli Samantha Evans Tracy D. Frank 《Sedimentology》2019,66(1):241-261
This study investigates the covariation between carbonate and organic δ13C values in a proximal to distal transect of four outcrops in the Madison Limestone in the Western United States Rockies, combined with δ34S values of carbonate associated sulphate, the concentration of acid‐insoluble material and measurements of total organic carbon. These new geochemical datasets not only allow for an evaluation of carbon isotope covariance during one of the largest perturbations to the global carbon cycle over the past 550 Myr, but also constrain the cause of the excursion in carbonate δ13C values. The results support the hypothesis that a period of anoxia did not play a role in generating the positive carbonate δ13C values, but rather favour interpretations by previous workers that the proliferation of land plants destabilized the Carboniferous carbon cycle, setting the stage for a significant change in the carbonate δ13C values of contemporaneous marine carbonates. These results also demonstrate that one of the largest perturbations to the global carbon cycle did not produce synchronous variations in carbonate and organic δ13C values, emphasizing the importance of local depositional controls on carbon isotope covariance in the geological record in both modern and ancient environments. 相似文献
7.
The stable carbon isotope (δ13C) and elemental C/N ratios in Total Organic Carbon (TOC) extracted from radiometrically dated cores from two Midwestern USA
lakes were determined to investigate the factors that control these values in temperate lakes. The range of δ13C values (-26 to -32%) and C/N ratios (mean value ∼10.8) are typical of values reported for other temperate lake organic matter
in this region. In the core from Lake Winnebago, Wisconsin, a negative correlation was seen between the TOC and δ13C, which can be interpreted in terms of a re-mixing and consumption of sedimented organic carbon along with rapid equilibration
throughout the water column. No correlation was seen between the TOC and δ13C in the record from Ladd Lake, Ohio, implying that in this latter lake productivity alone was not a singular process controlling
the isotope ratio. Here, it is suggested that equilibrium conditions are maintained such that the DIC of the water is never
depleted of aqueous CO2 during high organic production and the resulting δ13C of the organic carbon lacks correlation with the TOC. Further, in this lake a fine resolution analysis was carried out which
indicated a possible anthropogenic influence on the isotope ratio around times when human settlement (∼300 yrs ago) and enhanced
agricultural practices (∼80 yrs ago) were significant. The study shows that carbon isotope studies are useful in paleolimnologic
investigations. 相似文献
8.
A. B. Kuznetsov M. A. Semikhatov A. V. Maslov I. M. Gorokhov E. M. Prasolov M. T. Krupenin I. V. Kislova 《Stratigraphy and Geological Correlation》2006,14(6):602-628
New data on Sr-and C-isotopic systematics of carbonate rocks from the Upper Riphean stratotype (Karatau Group of the southern Urals) are obtained for several southwestern sections of the Bashkirian meganticlinorium, which have not been studied before. The results obtained supplement the Sr-and C-isotopic information for the group upper horizons thus detailing chemostratigraphic characterization of the entire succession. Limestone and dolostone samples used to analyze the Sr isotope composition satisfy strict geochemical criteria of the isotopic system retentivity and have been subjected to preliminary treatment in ammonium acetate to remove secondary carbonate phases. Data on 255 samples of carbonate rocks (171 studied for the first time) show that δ13C value varies in the Karatau Group succession from ?2.8 to +5.9 ‰ V-PDB with several in-phase excursions from the general trend in all the sections studied in the area 90 × 130 km. The δ13C variation trend demarcates several levels in the carbonate succession of the Karatau Group suitable for objectives of regional stratigraphy and for C-isotope chemostratigraphic subdivision of the Upper Riphean. The results of Sr isotopic analysis of 121 samples (51 unstudied before) from the Karatau Group imply that rocks in its lower part (the Katav Formation and basal horizon of the Inzer Formation) experienced considerable secondary alterations, while limestones and dolostones of the overlying interval of the group are frequently unaltered. In the “best” samples satisfying geochemical criteria of the isotopic system retentivity, the 87Sr/86Sr initial ratio increases from 0.70521–0.70532 in the lower Inzer deposits to 0.70611 in the upper Min’yar carbonates, decreasing to <0.70600 near the top of the latter. Above the regional hiatus separating the Min’yar and Uk formation, this ratio grows from 0.70533 to 0.70605–0.70609 in the limestone succession of the last formation. 相似文献
9.
Ronner Bendezú Laurence Page Richard Spikings Zoltan Pecskay Lluís Fontboté 《Mineralium Deposita》2008,43(7):777-789
We present 40Ar/39Ar data acquired by infra-red (CO2) laser step-heating of alunite crystals from the large Miocene Colquijirca district in central Peru. Combined with previously
published data, our results show that a long (at least 1.3 My) and complex period of magmatic-hydrothermal activity associated
with epithermal Au–(Ag) mineralization and base metal, Cordilleran ores took place at Colquijirca. The new data indicate that
incursion of magmatic SO2-bearing vapor into the Colquijirca epithermal system began at least as early as ∼11.9 Ma and lasted until ∼10.6 Ma. Four
alunite samples associated with high-sulfidation epithermal Au–(Ag) ore gave 40Ar/39Ar plateau ages between ∼11.9 and ∼11.1 Ma (compared to the previously documented ∼11.6 to ∼11.3 Ma). By combining individually
these new ages with crosscutting relationships, the duration of the Au–(Ag) deposition period can be estimated to at least
0.4 My. Three new 40Ar/39Ar plateau ages on alunite associated with the base-metal Cordilleran ores are consistent with previously obtained ages, all
of them between 10.83 ± 0.06 and 10.56 ± 0.06 Ma, suggesting that most of the sulfide-rich polymetallic deposits of Smelter
and Colquijirca formed during this short period. The recognition of consecutive alunite-bearing and alunite-free mineral assemblages
within both the Au–(Ag) and the base-metal Cordilleran ores may suggest that SO2-bearing magmatic vapor entered the epithermal environment as multiple discontinuous pulses, a number of which was not necessarily
associated in time with ore fluids. It is likely that a period of SO2-bearing vapor degassing longer than 11.9 to 10.6 Ma may be recognized with further more detailed work.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
10.
Haidi J. L. Hancock Gerald R. Dickens Ellen Thomas Kevin L. Blake 《International Journal of Earth Sciences》2007,96(5):925-946
Bulk carbonate content, planktic and benthic foraminiferal assemblages, stable isotope compositions of bulk carbonate and
Nuttallides truempyi (benthic foraminifera), and non-carbonate mineralogy were examined across ∼30 m of carbonate-rich Paleogene sediment at Deep
Sea Drilling Project (DSDP) Site 259, on Perth Abyssal Plain off Western Australia. Carbonate content, mostly reflecting nannofossil
abundance, ranges from 3 to 80% and generally exceeds 50% between 35 and 57 mbsf. A clay-rich horizon with a carbonate content
of about 37% occurs between 55.17 and 55.37 mbsf. The carbonate-rich interval spans planktic foraminiferal zones P4c to P6b
(∼57–52 Ma), with the clay-rich horizon near the base of our Zone P5 (upper)—P6b. Throughout the studied interval, benthic
species dominate foraminiferal assemblages, with scarce planktic foraminifera usually of poor preservation and limited species
diversity. A prominent Benthic Foraminiferal Extinction Event (BFEE) occurs across the clay-rich horizon, with an influx of
large Acarinina immediately above. The δ13C records of bulk carbonate and N. truempyi exhibit trends similar to those observed in upper Paleocene–lower Eocene (∼57–52 Ma) sediment from other locations. Two successive
decreases in bulk carbonate and N. truempyi δ13C of 0.5 and 1.0‰ characterize the interval at and immediately above the BFEE. Despite major changes in carbonate content,
foraminiferal assemblages and carbon isotopes, the mineralogy of the non-carbonate fraction consistently comprises expanding
clay, heulandite (zeolite), quartz, feldspar (sodic or calcic), minor mica, and pyrolusite (MnO2). The uniformity of this mineral assemblage suggests that Site 259 received similar non-carbonate sediment before, during
and after pelagic carbonate deposition. The carbonate plug at Site 259 probably represents a drop in the CCD from ∼57 to 52–51 Ma,
as also recognized at other locations. 相似文献
11.
J. N. Pattan Toshiyuki Masuzawa D. V. Borole G. Parthiban Pratima Jauhari Mineko Yamamoto 《Journal of Earth System Science》2005,114(1):63-74
A 2m-long sediment core from the siliceous ooze domain in the Central Indian Ocean Basin (CIOB; 13‡03′S: 74‡44′E; water depth
5099m) is studied for calcium carbonate, total organic carbon, total nitrogen, biogenic opal, major and few trace elements
(Al, Ti, Fe, K, Mg, Zr, Sc,V, Mn, Cu, Ni, Zn, Co, and Ba) to understand the productivity and intensity of terrigenous supply.
The age model of the sediment core is based on U-Th dating, occurrence of Youngest Toba Tuff of ∼ 74 ka and Australasian microtektites
of ∼ 770 ka.
Low carbonate content (< 1%) of sediment core indicates deposition below the carbonate compensation depth. Organic carbon
content is also very low, almost uniform (mean 0.2 wt%) and is of marine origin. This suggests a well-oxygenated bottom water
environment during the past ∼ 1100ka. Our data suggest that during ∼ 1100 ka and ∼ 400 ka siliceous productivity was lower,
complimented by higher supply of terrigenous material mostly derived from the metasedimentary rocks of High Himalayan crystalline.
However, during the last ∼ 400 ka, siliceous productivity increased with substantial reduction in the terrigenous sediment
supply. The results suggest that intensity of Himalayan weathering, erosion associated with monsoons was comparatively higher
prior to 400 ka. Manganese, Ba, Cu, Ni, Zn, and Co have around 90% of their supply from noncrustal (excess) source and their
burial to seafloor remained unaffected throughout the past ∼ 1100 ka. 相似文献
12.
V. N. Nijampurkar D. K. Rao H. B. Clausen M. K. Kaul A. Chaturvedi 《Journal of Earth System Science》2002,111(1):39-49
The depth profiles of electrical conductance, δ18O,210Pb and cosmogenic radio isotopes10Be and36Cl have been measured in a 30 m ice core from east Antarctica near the Indian station, Dakshin Gangotri. Using210Pb and δ18O, the mean annual accumulation rates have been calculated to be 20 and 21 cm of ice equivalent per year during the past ∼
150 years. Using these acumulation rates, the volcanic event that occurred in 1815 AD, has been identified based on electrical
conductance measurements. Based on δ18O measurements, the mean annual surface air temperatures (MASAT) data observed during the last 150 years indicates that the
beginning of the 19th century was cooler by about 2‡ C than the recent past and the middle of 18th century. The fallout of
cosmogenic radio isotope10Be compares reasonably well with those obtained on other stations (73‡ S to 90‡ S) from Antarctica and higher latitudes beyond
77‡N. The fallout of36Cl calculated based on the present work agrees well with the mean global production rate estimated earlier by Lal and Peters
(1967). The bomb pulse of36Cl observed in Greenland is not observed in the present studies – a result which is puzzling and needs to be studied on neighbouring
ice cores from the same region. 相似文献
13.
N. P. Sukumaran 《Journal of Earth System Science》1994,103(4):489-497
Examined in this paper is the tentative history of the depositional flux of230Thxs (the unsupported fraction of230Th scavenged from the overlying water column), for the Late Quaternary period from a sediment core of the Central Indian Basin
(CIB). The measured depositional flux of230Thxs is found substantially higher than that of the possible theoretical flux from the overlying water column. Historical records,
reconstructed from the230Thxs chronology suggests that the depositional flux has varied considerably with time, reflecting an enhanced scavenging during
the Holocene and the preceding interglacial periods whereas, comparatively lower flux than the predicted one occurred during
the Last Glacial Maximum (LGM) period. The average ratio of the measured depositional flux to that of the predicted flux from
the overlying water column, indicates that the core site acts as a sink for230Thxs and based on the existence of bottom current activity; the230Thxs could be the result of focusing of younger sediments. The depositional index (Di) has also been calculated to quantify the
extent of lateral supply throughout the core with time. The estimated (Di) suggests that bottom focusing and feeble deposition
and/or winnowing processes had occurred and that the former was most prevalent during the Holocene and the preceding interglacials,
whereas the latter was observed at the LGM period. 相似文献
14.
The Raipur Group of the Chattisgarh Basin preserves two major Late Mesoproterozoic carbonate platforms. The lower platform is about 490-m thick, separated from the upper platform (~ 670 m thick) by a 500-m thick calcareous shale. Carbonate strata cover almost 40% of the Chattisgarh Basin outcrop and represent two major platform types: a) a non-stromatolitic ramp (the Charmuria/Sarangarh Limestone) and b) a platform developed chiefly in the intertidal to shallow subtidal environment with prolific growth of stromatolites (the Chandi/Saradih Limestone). The first platform consists primarily of the black Timarlaga limestone that is locally replaced by early diagenetic dolomite. This carbonate platform experienced strong storm waves and was subsequently drowned by a major transgression, during which extensive black limestone–marl rhythmite was deposited, followed by deposition of the Gunderdehi Shale. The carbonate factory was later re-established with development of an extensive stromatolite-dominated Charmuria/Sarangarh platform that ranged from restricted embayment to open-marine conditions. Sea-level change played a major role in controlling the broad facies pattern and platform evolution. The δ13C signatures of the Chattisgarh limestones, falling within a relatively narrow range (0 to + 4‰) are typical for Upper Mesoproterozoic carbonate rocks. δ18O values, however, have a greater range (− 5.7 to − 13.3‰) indicating significant diagenetic alteration of some samples. Likely dysoxic or anoxic conditions prevailed during deposition of the black Timarlaga limestone and well-oxygenated conditions during deposition of the Gunderdehi Shale and Saradih/Chandi stromatolite. The lack of 17β,21α (moretanes) and high Tmax values suggest mature organic matter in the non-stromatolitic ramp. A paucity of diagnostic eukaryotic steroids indicates that algae were rare in the Chattisgarh Basin. A high content of hopanes supports a generally bacterially-dominated Proterozoic ocean in which various stromatolites flourished. 相似文献
15.
Evidence for Holocene environmental changes in the northern Fertile Crescent provided by pedogenic carbonate coatings 总被引:1,自引:0,他引:1
Holocene environmental changes in the northern Fertile Crescent remain poorly understood because of the scarcity of local proxy records in the region. In this study we investigated pedogenic (soil-formed) carbonate coatings on stones at the Pre-Pottery Neolithic site Göbekli Tepe as an indicator of local early-mid Holocene environmental changes. The 14C ages and stable isotopic composition of carbon and oxygen in thin (0.2–0.3 mm thick) pedogenic carbonate lamina indicate two main periods of coating formation: the early-Holocene (ca. 10000–6000 cal yr BP) and the mid-Holocene (ca. 6000–4000 cal yr BP). During the first period, there was an inverse relationship between δ13C and δ18O curves: a decrease in δ13C values coincide with an increase in δ18O values. For this period a trend towards higher temperatures is suggested. In the mid-Holocene, the mean rate of coating growth was 2–3 times higher than in the early Holocene. Both δ13C and δ18O reached their maximum values during this time and the direction of changes of the δ13C and δ18O curves became similar. The combination of data suggests that this period was the most humid in the Holocene and on average warmer than the early Holocene. At ca. 4000 cal yr BP secondary accumulation of carbonate ceased, presumably reflecting a shift to a more arid climate. 相似文献
16.
The variations of stable-carbon isotope ratios in Qilian juniper in northwestern China 总被引:1,自引:0,他引:1
This is the first study of δ13C values that considers elevational influences of the Qilian mountains of China. The δ13C values of different parts of the Qilian juniper (Sabina przewalskii Kom.) at different elevations of the Qilian mountains, China, were measured. Relatively constant differences in δ13C values existed between the tree leaves and the trunk wood. No strong dependency of δ13C values on elevation was found. The temporal changes of wood δ13C values with directions, elevations and height in the tree showed general similarity. These results suggest that the isotopic
effects of environmental factors expressed initially at the site of photosynthesis, i.e., the leaves could be contained in
the trunks of a tree. Regardless of elevation, direction or height in the tree, wood δ13C values have been decreasing during the past 60 years. A composite 600-year δ13C chronology developed from four trees showed that δ13C values remain relatively constant before 1800. After 1800 AD, however, δ13C values became significantly more negative. The trend in wood δ13C values was consistent with that obtained for δ13C values in atmospheric CO2. The results showed that for Qilian juniper, tree-ring δ13C chronology could be established to ascertain fluctuations of the atmospheric δ13C. 相似文献
17.
1 Introduction China’s widespread marine carbonate rock series are mostly characterized by intensive thermal evolution and low abundance of organic matter, especially the Lower Paleozoic carbonate rocks have experienced multi-episodes of tectonics and ap… 相似文献
18.
The long-lived (about 20 yr) bryozoan Adeonellopsis sp. from Doubtful Sound, New Zealand, precipitates aragonite in isotopic equilibrium with seawater, exerting no metabolic or kinetic effects. Oxygen isotope ratios (δ18O) in 61 subsamples (along three branches of a single unaltered colony) range from −0.09 to +0.68‰ PDB (mean = +0.36‰ PDB). Carbon isotope ratios (δ13C) range from +0.84 to +2.18‰ PDB (mean = +1.69‰ PDB). Typical of cool-water carbonates, δ18O-derived water temperatures range from 14.2 to 17.5 °C. Adeonellopsis has a minimum temperature growth threshold of 14 °C, recording only a partial record of environmental variation. By correlating seawater temperatures derived from δ18O with the Southern Oscillation Index, however, we were able to detect major events such as the 1983 El Niño. Interannual climatic variation can be recorded in skeletal carbonate isotopes. The range of within-colony isotopic variability found in this study (0.77‰ in δ18O and 1.34 in δ13C) means that among-colony variation must be treated cautiously. Temperate bryozoan isotopes have been tested in less than 2% of described extant species — this highly variable phylum is not yet fully understood. 相似文献
19.
1IntroductionSoilorganicmatter (SOM)isakeysourceofnutrientsforplantgrowth ,itisessentialforthemaintenanceofsoilstructureanditcontributestotheabilityofsoiltoretainnutrientsandwater.AnimprovedunderstandingofSOMdynamicsiscentraltothedevelopmentofmoreenvironmentallysoundandsustainablepracticesofagriculturalmanagement (Collinsetal.,2 0 0 0 ) .Avarietyofcon ceptualmethodshavebeenusedtodescribetheprocessesofSOMaccumulationandturnover (Jen kinsonandRayner,1 977;Duxburyetal.1 989;Partonetal.,1 99… 相似文献