Category FAQs Search : Tidal Bore
Question: Characteristics of tidal-bore deposits and facies associations in theQiantang Estuary, China
Answer:
Abstract
The characteristics of tidal-bore deposition in the Qiantang Estuary are studied on the basis of core strata and
grain-size data, and lateral and longitudinal associations with other sedimentary facies are synthesized. A typical
depositional package by tidal bores and associated flows is generally initiated with (1) an undular/planar erosion
base, overlain by (2) a massive sandy bed, and (3) a sandy bed with parallel laminations or some thinly
heterolithic beds. The depositional units, especially the parallel laminations, are prone to deformation into
convolute bedding, flames, and boiled sand patches with water-escape structures. In the middle estuary, tidalbore
deposits (TBDs) at the main channel and the lower tidal flat transit laterally into alternative beds of TBDs
andz heterolithic beds at the middle tidal flat, and then toward incomplete tidal rhythmites on the higher tidal
flat. TBDs are generally coarser and less sorted than tidal sandy deposits (TSDs), and tidal muddy deposits
(TMDs) have finer grains, less sorting and lower positive skewness than either TSDs or TBDs. Therefore, bivariate
plotting of size parameters is a useful tool to differentiate between these three genetic sedimentary bed types.
Along the axis, three facies divisions are obvious and consist of: (1) linear depositional ridges and erosion troughs
at the outer estuary, (2) TBDs at the middle estuary, and (3) coarse fluvial deposits at the upper estuary. The
tripartite facies model of the Qiantang Estuary is similar to other well-known tide-dominated estuarine facies
models, but it is the first to stress tidal-bore deposition in the sedimentary facies using detailed discriminative
textural and structural characteristics. The approaches offer the potential to better understand tidal-bore
processes and their important role in sediment dispersion and facies formation within modern and ancient
macrotidal to hypertidal estuaries.
Click here to download attachment
(Source: Pustaka Negeri Sarawak, 28 Mar 2022)