【摘要】 <正> 对现代砂泥质潮坪研究,不仅有益于弄清潮汐沉积作用,而且为探讨古潮坪沉积,寻找有关矿产提供依据。近年来我们对弶港潮坪调查研究表明,该潮坪是以古长江和旧黄河组成的三角洲为基础,并在两股强潮流以弶港为顶点辐聚辐散控制下所形成的滩面宽阔,潮沟发育,向海开敞的潮坪。本文着重探讨潮坪不同地貌单元沉积物的特点和相标志。不妥之处,望祈指正。更多还原

【Abstract】 Field investigation and laboratory analysis have shown that the Jianggang tidal flat has developed its own characteristic features neither similar to North Sea tidal flat nor to Shanghai tidal flat due to its unique geographical position, hydraulic regime as well as the local sediments available.1. Jianggang lidal flat is a non-barred open sea tidal flat with large tidal range and rather gentle-sloping surface (slope=0.20‰。). The main causal factors which control its development are two strong tidal currents, i.e., the southwestly-moving tidal current of Yellow Sea revolving wave and the northwestly-moving tidal current of East China Sea translational wave, which converge and diverge with Jianggang as their center. The Jianggang tidal flat located at Changjiang River Mouth developed and superimposed upon the ancient sand shoale reworked from the submerged pre-existing Changjiang Delta and its constitutional materials were derived from the ancient Changjiang River and Yellow River fluvial sediments. Now the Jianggang tidal flat is prograding seaward at a rate of 100-200 meters annually, while its aggradational rate is about 5-7 centimeters per year.2. Topography of the tidal flat governs the frequency, water depth and duration of the time so it can also govern the physical environment of the individual subfacies.With the decrease of the flow velocity and energy from subtidal to supra-tidal area, grain size gradually changes from fine sand in subtidal zone to medium-fine silt in supratidal zone with a concomitant increase in mud content and deterioration in sorting; the stratification types change, in the same trend, from large-scale bidirectional cross-stratification, herringbone stratification and reactivation surface through small-scale ripple-lamination, wavy-flaser-lenticular stratification and interlayered (sand/mud or sand/silt) stratification and ultimately to parallel-lamination in supratidal zone; marine fauna generally increases in amount from supra-to, subtidal zone,while the biodistarbance gradually decreases seaward as both deposition and erosion intensify toward subtidal area.In addition, from supra-to sub-tidal area, as water energy increase, the maturity of mineral composition enhances in contrast to a relative concentration of clay minerals in supratidal area where hydrodynamic comparatively quiet.3. Tidal channels are well-developed in the Jianggang tidal flat, which are characterized with relatively large scale, intensified scouring and rapid lateral migration. Vertical profile analysis has shown that about 60-80% of the deposits below middle tidal flat is subject to more or less tidal channel reworking. The typical tidal channel deposits show the following features:1) upward-fining variation is quite clear; 2) bi-saltation population, (reflecting the bidirectional nature of formational agents(flow),) in probability graph is common; 3) from bottom upward, the following stratifications occur successively: lag deposits and scour-and-fill structure, longitudiual cross-stratification, bidirectional oriented cross-stratification, herringbone stratification, etc. These features, together with its dominant marine or transitional between terrigeneous and shallow marine fauna constitution, can easily distinguish the tidal channel deposits from those of fluvial facies.4. Sand layers coarser than under-and overlying sediments ars frequently found intercalated in the tidal flat deposits, showing hydrodynamically disharmony. These interstratified sand layers vary from 5 to 10 centimeters in thickness, contain shells or other coarse organic fragments and have a scoured or sharp-contacted basal boundary and a sharp or gradational top surface. Produced by unusual stom tidal action, these sand layers are the relatively important deposits in the tidal flat and have relative high accumulation and preservation potential due to the episodic nature of their formation.更多还原