摘要
研究表明 ,扬子陆块早奥陶世末期至中奥陶世 Darriwilian初期各类沉积呈明显带状分布 ,但南北两侧沉积带分布并不对称。各沉积带总体走向为南西—北东向 ,不同阶段沉积带类型及位置略有变化。自古陆向东南方向 ,早奥陶世末期—中奥陶世初期依次发育近岸砂砾质沉积带 ,近岸砂质、泥质沉积带 ;内陆架泥质夹碳酸盐沉积带 ;浅外陆架碳酸盐夹泥质沉积带 ,含铁泥质碳酸盐沉积带 ,边缘碳酸盐沉积带 ;深外陆架斜坡泥质夹砂质、碳酸盐沉积带 ,泥质夹粉砂质沉积带 ,泥质、碳质沉积带。中奥陶世早期至 Darriwilian初期演变为近岸白云质与陆源碎屑沉积带 ;内陆架碳酸盐与泥、砂质沉积带 ;浅外陆架碳酸盐夹泥质沉积带 ,含铁泥质碳酸盐沉积带 ,边缘碳酸盐沉积带 ;深外陆架斜坡泥质夹砂质、碳酸盐沉积带 ,泥质夹粉砂质沉积带 ,泥质、碳质沉积带。扬子陆块北缘早奥陶世末期—中奥陶世初期发育浅外陆架粉砂质、泥质、碳酸盐沉积带 ,边缘碳酸盐沉积带 ;中奥陶世早期至 Darriwilian初期则包括浅外陆架碳酸盐沉积带 ,粉砂质、泥质 ,外陆架碳酸盐沉积带 。
Based on new chronostratigraphic framework and revised stratigraphic correlation(Table 1), the present paper deals with the sedimentary differentiation of latest Early Ordovician—earliest Darriwilian in the Yangtze Block. According to rock associations and sedimentary features, 9 sedimentary belts are recognized from the old lands southeastward toward the basin during the latest Early—earliest Middle Ordovician (Fig.1), namely: nearshore sand and gravel belt, nearshore sand and mud belt; inner shelf mud carbonate belt; shallower outer shelf carbonate mud belt, ferruginous and argillaceous carbonate belt, marginal carbonate belt; daeper outer shelf mud sand carbonate belt, mud silt belt and argillite carbonaceous shale belt. During the early Middle Ordovician—earliest Darriwilian, most of the sedimentary belts (Fig.2) developed formerly on the outer shelf and the slope remained their geographical positions. However, there were two, instead of three, sedimentary belts occurred in shallow sites; the inner shelf one is characterized by the dominance of carbonate sediments mixed with argillaceous and sandy intercalations. In addition, dolomitic deposits and terrigenous detrital sediments became dominant in the nearshore region. On the northern side of the Yangtze Block proper, three sedimentary belts can be recognized especially during the early Middle Ordovician—earliest Darriwilian. The shallower outer shelf carbonates outcrop only at Hexian, Anhui; the outershelf argillaceous, silty, and carbonate sediments were mainly developed at Mianxian and Susong; the marginal carbonate belt extends approximately from Chuxian to Hongze. It is interesting to note that deeper water sedimentary belts are only incompletely preserved on the northerm side, and a plausible explanation is that they were partially consumed by the later tectonic movements. The distribution pattern of sedimentary belts on the either side of the Yangtze Block is asymmetrical. The south side is thought to be a gentle slope, and the northern side could be a steeper, narrower shelf. Because the Ordovician is largely covered by the Quaternary in the Lower Yangtze area and only a little detailed stratigraphic information is available so far, the extending of the sedimentary belts in this area is just tentatively suggested. Further work is required to connect the corresponding sedimentary belts between the Lowere Yangtze area and the Middle and Upper Yangtze area.
出处
《地层学杂志》
CSCD
北大核心
2002年第4期302-304,共3页
Journal of Stratigraphy
基金
国家基金委特殊学科人才培养基金
南京地质古生物研究所创新基金
中国科学院古生物与古人类学科基础研究特别支持费(980 3 0 3 )
国家自然科学基金 (No.49772 0 87
No.49872 0 0 5
No.4990 2 0 0 1)
国家重点基础研究专项经费 (G2 0 0 0 0 7770 0 )资助
