桑托斯盆地白垩系盐下Barra Velha组叠层石灰岩沉积环境探讨
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摘要
通过对桑托斯盆地盐下Barra Velha组叠层石灰岩进行岩石学、地球化学等方面的研究,提出簇状、指状和近球形叠层石是叠层石灰岩的主要组构,不同组构的发育路径可能与沉积环境有关。叠层石多呈集合体的形式发育,宏观上可见上下叠置和左右相连等组合方式,其中湖水直接沉淀的亮晶和以微生物为媒介形成的泥晶是组成叠层石灰岩的主要物质,叠层石灰岩的形成受到微生物的影响显著。叠层石灰岩中高硅、高镁含量以及正偏的碳、氧同位素特征都表明其形成于盐度较高的蒸发封闭湖盆的水体环境。叠层石灰岩中多数仅为数厘米高的叠层石集合体,表明高位水体持续时间仅在千年左右或更短,而不同高度的叠层石集合体在垂向上的频繁交替出现则表明水体深度存在频繁的波动。
By using lithological and geochemical methods, the depositional environment of stromatolitic limestone of pre-salt Barra Velha Formation in Santos Basin, offshore Brazil, was analyzed. It is concluded that the dominating fabric of stromatolitic limestone consist of shrub, finger-like and spherulitic stromatolites, which relate to depositional environment evolutionarily. From a macroscopic view, many stromatolites occur in aggregation with overlaid and adjacent pattern. The main consitution of stromatolite are made of sparry calcite precipitated directly from lake water and microbial-mediated micrite. The stromatolites, although not produced by microorganism directly, are influenced significantly by microorganism. That the high contents of magnesium and silicon, and the positive depletion in carbon and oxygen isotopes, which have been measured from stromatolitic samples, indicate a saline environment with intensive evaporation, mirroring a closed lacustrine system. Stromatolite aggregates with several centimeters in height are widespread, which implies the depth of water favored stromatolite growth did not last long, perhaps on a millennium scale or even shorter, and that stromatolites grown with different and alternate height vertically shows that the frequent fluctuation in water depth was common during that period.
By using lithological and geochemical methods, the depositional environment of stromatolitic limestone of pre-salt Barra Velha Formation in Santos Basin, offshore Brazil, was analyzed. It is concluded that the dominating fabric of stromatolitic limestone consist of shrub, finger-like and spherulitic stromatolites, which relate to depositional environment evolutionarily. From a macroscopic view, many stromatolites occur in aggregation with overlaid and adjacent pattern. The main consitution of stromatolite are made of sparry calcite precipitated directly from lake water and microbial-mediated micrite. The stromatolites, although not produced by microorganism directly, are influenced significantly by microorganism. That the high contents of magnesium and silicon, and the positive depletion in carbon and oxygen isotopes, which have been measured from stromatolitic samples, indicate a saline environment with intensive evaporation, mirroring a closed lacustrine system. Stromatolite aggregates with several centimeters in height are widespread, which implies the depth of water favored stromatolite growth did not last long, perhaps on a millennium scale or even shorter, and that stromatolites grown with different and alternate height vertically shows that the frequent fluctuation in water depth was common during that period.
引文
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[2]Leinfelder R R,Schmid D U.Mesozoic reefal thrombolites and other microbolites[M]//Riding R,Awramik S M.Microbial sediments.Berlin:Springer,2000:289-294.
[3]Riding R,Awramik S M.Preface[M]//Riding R,Awramik S M.Microbial sediments.Berlin:Springer,2000:i.
[4]邓超,白国平,仲米虹,等.巴西桑托斯盆地含油气系统划分与评价[J].海相油气地质,2014,19(3):35-42.
[5]康洪全,程涛,李明刚,等.巴西桑托斯盆地油气成藏特征及主控因素分析[J].中国海上油气,2016,28(4):1-8.
[6]Santos E D,Ayres H F,Pereira A,et al.Santos microbial carbonate reservoirs:A challenge[C].Offshore Technology Conference,October 29-31,2013,Rio de Janeiro,Brazil.
[7]IHS Basin Monitor.Santos Basin[R].2012.
[8]Bochacs K M,Lamb-Wozniak K,Demko T M,et al.Vertical and lateral distribution of lacustrine carbonate lithofacies at the parasequence scale in the Miocene Hot Spring limestone,Idaho:An analog addressing reservoir presence and quality[J].AAPG Bulletin,2013,97(11):1967-1995.
[9]Jones G D,Xiao Yitian.Geothermal convection in South Atlantic subsalt lacustrine carbonates:Developing diagenesis and reservoir quality predictive concepts with reactive transport models[J].AAPG Bulletin,2013,97(8):1249-1271.
[10]Riding R.Abiogenic,microbial and hybrid authigenic carbonate crusts:Components of Precambrian stromatolites[J].Geologia Croatica,2008,61(2):73-103.
[11]Riding R.The nature of stromatolites:3500 million years of history and a century of research[M]//Reitner J,Queric N V,Arp G,et al.Advance in Stromatolite Geobiology.Berlin:Springer,2011:29-74.
[12]Frantz C M,Petryshyn V A,Marenco P J,et al.Dramatic local environmental change during the Early Eocene Climatic Optimum detected using high resolution chemical analyses of Green River Formation stromatolites[J].Palaeogeography,Palaeocli matology,Palaeoecology,2014,405(3):1-15.
[13]Alonso-Zarza A M,Tanner L H.Carbonates in continental settings:Facies,environments,and processes[M].Netherlands:Elsevier,2010:1-48.
[14]Vasconcelos C,McK enzie J A,Bernasconi S,et al.Microbial mediation as a possible mechanism for natural dolomite formation at low temperatures[J].Nature,1995,377(6546):220-222.
[15]Laval B,Cady S L,Pollack J C,et al.Modern freshwater microbialite analogues for ancient dendritic reef structures[J].Nature,2000,407(6804):626-629.
[16]Casanova J,Hillaire-Marcel C.Late Holocene hydrological history of Lake Tanganyika,East Africa,from isotopic data on fossil stromatolites[J].Palaeogeography,Palaeoclimatology,Palaeoecology,1992,91(1/2):35-48.
[17]Petryshyn V A,Corsetti F A,Berelson W M,et al.Stromatolite lamination frequency,Walker Lake,Nevada:Implications for stromatolites as biosignatures[J].Geology,2012,40(6):499-502.
[18]Sibley D F.Unstable to stable transformations during dolomitization[J].Journal of Geology,1990,98(5):739-748.
[19]Land L S.The application of stable isotopes to studies of the origin of dolomite and to problems of diagenesis of clastic sediments[M]//Arthur M A,Anderson T F,Kaplan I R,et al.Stable Isotope in Sedimentary Geology.SEPM Short Course Note 4,1983:1-22.
[20]Piovesan E K,Nicolaidis D D,Fauth G,et al.Ostracodes from the Aptian-Santonian of Santos,Campos and Espírito Santo basins,Brazil[J].Journal of South American Earth Sciences,2013,48(12):240-254.
[21]Poropat S F,Colin J P.Early Cretaceous ostracod biostratigraphy of eastern Brazil and western Africa:An overview[J].Gondwana Research,2012,22(3/4):772-798.