摘要
钦州盆地是中国东南部大地构造格架中的一个独特构造单元.本文研究了其中的志留系—中泥盆统连续沉积的巨厚的类复理石建造.这套沉积具有浊积和等深流沉积的双重特点.综合各项资料可认为:这是一套形成于陆隆处的受等深流改造的低密度浊积岩.它反映了被动大陆边缘的板块构造背景,与国内外古代和现代的等深流沉积均可进行对比.
Qinzhou Basin is located in Guangxi Province, South China, extending in NE- SW direction, 200km long and 50-70km wide.Its southwest part passes through the Tonkin Gulf then ended in Vitnarn.It
is bounded on the east and west by two deep faults.
This basin had had a continuous history from Silurianor earlier) to Permian during which the Silurian-Middle Devonian flyschoid formation and Upper Devonian-Lower Permian siliceous-muddy formation formed.The basin is a particuliar tectonic unit in South China because of no uncomformity between the Silurian and Devonian System.Its tectonic feature is very different from adjacent regions' in cither geological history or rock formation.
The Silurian-Middle Dcvonian flyschoid formation here, about 9500m thick, is composed of sandstone, siltstone and mudstone of which make up rhythmic succcsions with thickness of about 50cm per unit.Conglomcrate can only be seen on some part of the bottom of the Silurian.Many kinds of fossil such as graptolitc, tentaculitid and trilobite contained, most of them are planktonic (few nectonic) and cosmopolitan taxa.Inferably, seawatcr circulation and animal cxchangement between this basin and outer oceans may have taken place during that period.
Onthe studies of field occurencc, sedimentary structure and texture, and grain-size analyses etc., it is proposed the origin and tectonic setting of the formation.Tt has a that higher maturity of both mineral and texture than typical turbidite. The average sandstone/ mudstone value (in thickness) is about 2.Framcwork minerals are chiefly quartzes.There are graded beddings, lead structures and other characteristics of turbidite on one hand, and little crossbcddings, Row marks, imbricated texture of mineral grains or faecle pellets, and other diagnostics of traction flow deposits on the other hand. Sedimentary structure and grain-size analyses show a transitional feature between turbidctc and fluvisl (or tractive current) deposit, only possibly the latter represented a submarine river-a contour currcnt.lt is important
that there are a kind of very thin (0.5±cm) mudslonc (or fairly sorved sandstone) intcrclated into much thicker sandstone (or mudstone) . Such rocks arc very much like to the muddy contouritc (or sandy one ) described by Stow & Lovcll ( 1979) Especially, the presence of bimodal directions c.g.downslope and alongslope at about 90 ° is a key indicater in dctermination of
Furthermore, the sandstone here are chiefly graywackc, most of them are one, and very similar to those of passive continantal margin type of the contouritc can also be contrasted with those in the world .
Summing up the above mentioned, it is concluded Silurian-Middle Devonian flyschoid formation of the Qinzhou Basin is a low dcnsty turbiditc which abviously were reworked or superimposcd by paleocontour current.They formed on a contincntal rise the tectonic sctting of the Atlantic type of east continental margin.
出处
《沉积学报》
CAS
CSCD
北大核心
1989年第3期21-29,共9页
Acta Sedimentologica Sinica
