【摘要】 澳大利亚西北陆架盆地是一个长期继承性发育的叠合盆地,三叠纪时期处于稳定克拉通大陆边缘拗陷阶段,沉积区基底构造稳定,坡度平缓,发育大型的浅水三角洲。利用钻井、地震以及古生物资料,明确了当时的古地理、古气候与沉积特征:平面上具有三角洲平原分布广、三角洲前缘欠发育、无前积现象等特征;纵向上具有相漂移、地层厚度大、三角洲平原薄煤层普遍发育等特点;沉积作用以单向水流作用为主,正旋回的分支流水道砂体广泛发育;三角洲砂岩分布广,成分成熟较高,但分选磨圆差—中等,互层泥岩中陆源碎屑有机组分丰富,体现了浅水、快速堆积、远距离搬运的特点。平面上西北陆架North Carnarvon以及Browse主力三角洲砂体位于中晚三叠世卡尼期—诺瑞期;而Bonaparte盆地主力砂体位于中三叠世拉丁期—卡尼期。晚三叠世澳大利亚西北陆架北部普遍发生抬升,导致Browse盆地与Bonaparte盆地三叠系发育不全,三角洲规模较小;而西北陆架西南部North Carnarvon盆地地层发育齐全,厚度大,且发育大型三角洲。Pilbara地块、Yilgarn地块以及Kimberley地块为源区三大古陆,其中Pilbara地块与Yilgarn地块大多出露太古代花岗岩类,Kimberley地块以元古代变质结晶岩和沉积岩为主,为盆地提供了充足的碎屑沉积物。利用岩矿资料、磷灰石裂变径迹等资料探讨了大型三角洲的碎屑物来源:North Carnarvon盆地物源主要来自于Pilbara以及Yilgarn地块,Browse以及Bonaparte盆地物源主要来自于Kimberley地块。研究成果表明,在三叠纪全球温室气候背景条件下,特提斯南缘具有发育大型三角洲的特殊古地理背景;大型三角洲发育的地质条件除充足的降雨与丰富的物源供给外,还必须具有稳定持续沉降的构造背景。更多还原

【Abstract】 On the Northwest Shelf of Australia,there is a long-term superimposed basin.It was a continent marginal depression of a stable craton in Triassic characterized by stable structures and gentle gradient.Large deltas were developed.Using the data of drilling,seismic and palaeontology,we discussed in this paper the paleogeography,paleoclimate and sedimentation of the deposits.In a plane view,it is a wide deltaic plain with little deltaic front and no progradational reflections are observed.In the vertical sequence,however,there are thick clastic deposits intercalating thin coal seams,denoting rapid facies changes.The sediments are dominated by.unidirectional water flow.Channel-filling sand bodies with positive rhythms and deltaic sandstones are well developed and distributed.The compositional and textural maturities of the sand are rather high with poor to middle sorting and roundness.Terrigenous organic matters are rich in the mudstone.The main sand body in the North Carnarcon and Browse Basins was deposited in the Carnian period to Norrec period of Triassic,while the main sand body in the Bonaparte Basin was formed during the Ladinian Stage to Carnian period of Triassic.The Northwest Shelf of Australia widely uplifted in late Triassic,resulting in stratigraphic hiatus,shrinkage of deltas in the Browse Basin and Bonaparte Basin.However,the Triassic deltaic deposits are complete and thick in the North Carnarvon Basin,southwestern of Northwest Shelf of Auatralia.The Pilbara Block,Yilgarn Block and Kimberley Block are the three terrestrial zones which providet clastic sediments for the basin.The Pilbara and Yilgarn were mostly exposed then with Archean granitoids,but the Kimberley was exposed to air with Proterozoic metamorphic rocks and sedimentary rocks.Provenance of the deltaic deposits are studied upon mineralogy,apatite fission track and other data.The sediments of North Carnarvon came from the Pilbara and Yilgarn lands and the sediments of Browse and Bonaparte from Kimberley.The global greenhouse in Triassic and the tectonic background at the north edge of the Tethys Ocean are specially significant to the development of large deltas,in addition to adequate rainfall and rich source supply.更多还原