Tidal Flats and Associated Tidal Channels

Weimer, Robert J.; Howard, James D.; Lindsay, Donald R.

doi:10.1306/m31424c9

Cited by 38 publications

(9 citation statements)

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“…Macroscale geomorphological units of tidal flats indicate morphological patterns controlling the entire flat system, such as profile geometry, e.g., convex and concave profile morphology (Gao, 2009;Zhou et al, 2016), and zonation of flat sediments (Roberts et al, 2000;Zhang et al, 2018). Mesoscale geomorphological units refer to those features with the length of 1-10 m, including scarps occurring at the boundaries between flat and vegetation (salt marsh plants and mangroves), ridges (Weill et al, 2010;Weill et al, 2012), sand waves (Allen, 1980;Besio et al, 2006), and waterways (Weimer et al, 1982;Pieterse et al, 2016), as well as tidal creeks (Blanton et al, 2002). Microscale geomorphological units, which generally less than 1 m, include flat surface cracks (Gardel et al, 2009), sand grains (Harms, 1969), linear scour pits (Sumer et al, 2001), biological holes (Takeuchi and Tamaki, 2014), and flat surface uplift caused by fish or large burrowing, which usually located in the low tidal zone (Dott and Bourgeois, 1982).…”

Section: Introductionmentioning

confidence: 99%

The Hummocky Patches and Associated Sediment Dynamics Over an Accretional Intertidal Flat

Zhu¹,

Yan²,

Xing³

et al. 2022

Front. Earth Sci.

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Tidal flat system is composed of multiple sub-scale geomorphological units. We found a new mesoscale geomorphological unit on sand-mud mixed intertidal zone along China coast, which was defined as hummocky patches. Hummock patches are most developed in middle tidal flat, with horizontal magnitude of 10–20 m and vertical magnitude of ∼15 cm. Hummocky patches significantly influence local sediment transport, thus affect morphological evolution of tidal flats. In order to understand the formation and development mechanisms of hummocky patches, we collected hydrodynamics, topography, sediment properties, and substrate erosion thresholds data through an in-situ field observation covering a spring-neap tidal cycle over an accretional intertidal flat in Jiangsu, China. We found that sediment characteristics including sorting coefficient (σ: measuring the uniformity of sediment particles) and silt/clay/organic matter/water content are essentially different between hummocky patches and nearby seabed, which leads to spatially varied substrate erosion resistance. The measured erosion thresholds for patches are two times higher comparing to surrounding seabed sediment, which provides foundation for the formation of hummocky patches. Under the impact of periodical tidal currents and waves, surrounding seabed experiences considerably more erosion than patch area, which finally develops to hummocky patches. Therefore, hydrodynamic forces drive the formation and development of patches. The erosion resistance of patches decreases vertically from seabed surface to sublayer, causing initial erosion in the lower sublayer, followed by a mass collapse of the seabed surface layer. Hummocky patches are commonly found in middle tidal zone and their sizes decrease to the shore as tidal currents and waves attenuate with shoreward propagation. Hummocky patches have distinct seasonal variations, which only appear in summer and autumn when wind waves are comparatively lower than winter and spring. We infer the reason is that the strong hydrodynamics caused by winter storms cause larger bottom shear stress than the erosion threshold of hummocky patches, leading to destruction of hummocky patches and a smooth tidal flat surface. This study shed new insight on the knowledge of mesoscale geomorphological units and their formation and development in intertidal flats, which provides crucial information for developing more realistic tidal flat sediment transport and morphological models.

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Section: Introductionmentioning

confidence: 99%

The Hummocky Patches and Associated Sediment Dynamics Over an Accretional Intertidal Flat

Zhu¹,

Yan²,

Xing³

et al. 2022

Front. Earth Sci.

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“…Although polygonal mud‐cracks form by several mechanisms (Tanner, ), their presence is consistent with subaerial exposure (Allen, ) and is considered by some workers to be diagnostic when mud curls are present (Tanner, ). Assuming that their formation was due to desiccation, the largest cracks required exposure of significant duration to develop (Weimer et al ., ). Cracked medusae were subaerially exposed (Hagadorn et al ., ; Young & Hagadorn, ) and medusae excavate moats when subaerially stranded by contracting their bells while trying to escape (Kornicker & Conover, ; Bruton, ).…”

Section: Discussionmentioning

confidence: 97%

“…Deposition of the Elk Mound Group at Blackberry Hill was on marginal-marine sand-flats that experienced periodic subaerial exposure and had fair-weather water depths ≤2 mfeatures consistent with 'classic' tidal sand-flats (MacKenzie, 1972;Weimer & Land, 1972;Weimer et al, 1982). However, unlike typical tidal flats, storm and fair-weather waves exerted a dominant influence on the flats.…”

Section: Blackberry Hill Depositional Systemmentioning

confidence: 97%

Cambrian wave‐dominated tidal‐flat deposits, central Wisconsin, USA

2018

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In central Wisconsin, Cambrian strata of the Elk Mound Group record deposition on open-coast, wave-dominated tidal flats. Mature, mediumgrained quartz arenite is dominated by parallel-bedding with upper-flow regime parallel-lamination, deposited during high-energy storms that also produced three-dimensional bedforms on the flats. Abundant wave ripples were produced as storms waned or during fair weather, in water depths ≤2 m. Indicators of variably shallow water (washout structures and stranded cnidarian medusae) and subaerial exposure (adhesion marks, rain-drop impressions and desiccation cracks, including cracked medusae) are abundant. Parallel-bedded facies preserve a Cruziana ichnofacies, similar to other Cambrian tidal-flat deposits. Flats were dissected by small, mainly straight channels, the floors of which were grazed intensely by molluscs. Most channels were ephemeral but some developed low lev ees, point bars and cut-banks, probably reflecting stabilization by abundant microbial mats and biofilms. Channels were filled with trough cross-bedding that is interpreted to have been produced mainly during storm runoff. The strata resemble deposits of open-coast, wave-dominated tidal flats on the east coast of India and west coast of Korea. Ancient wave-dominated and open-coast tidal flats documented to date appear to have been limited to mud-rich strata with 'classic' tidal indicators such as flaser bedding and tidal bundles. The Cambrian (Miaolingian to early Furongian) Elk Mound Group demonstrates that sandy, wave-dominated tidal flats also can be recognized in the stratigraphic record.

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“…In contrast. Late Paleozoic (Carboniferous) to Recent tidal environments contain a predominance of mud in upper tidal facies (Ginsburg, 1975;Weimer et al, 1982;Klein, 1985); because tidal-flat facies models have been based on these Recent mud-dominated tidal sequences, recognition of Lower Paleozoic tidal deposits have been difficult (Dott and Byers, 1980;Klein, 1980;Moiola, 1980). For example, units previously interpreted as simple blanket sands that formed under wave-dominated coastal systems such as the Middle Cambrian Flathead Sandstone of Wyoming and Montana, the Lower Ordovician St. Peter Sandstone of the midcontinent, and the Mt.…”

Section: Aspects Of Cambro-ordovician Sedimentationmentioning

confidence: 99%

“…2). Assuming horizontal time lines in Figure 4, a minimal breadth of the Black Hills Cambro-Ordovician shelf intertidal zone may have approximated 25-35 km, which far exceeds the 7-km average of modem macrotidal coasts (Klein, 1980;Weimer et al, 1982). The closest modem analog that can be compared to the Deadwood-Aladdin intertidal zone is the Yellow Sea macrotidal flat of southwestern South Korea, with a tidal-flat width ranging from 8-25 km (Klein, 1980;Alexander et al, 1991).…”

Section: Aspects Of Cambro-ordovician Sedimentationmentioning

confidence: 99%

Significance of nearshore trace-fossil assemblages of the Cambro-Ordovician Deadwood Formation and Aladdin Sandstone, South Dakota

Stanley¹,

Feldmann²

1998

Annals of the Carnegie Museum

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The Cambro-Ordovician Deadwood Form.ation and Aladdin Sandstone represent intertidal and subtidal, nearshore deposystems that contain few well-preserved body fossils, but contain abundant trace fossils. The present study uses the much neglected trace-fossil fauna to describe the diverse paleoenviroemeets represented in the Deadwood-Aladdin deposystems, and to better understand the environmental conditions that controlled benthic life in the Early Paleozoic.The Deadwood-Aladdin ichnotaxa can be separated into three distinct assemblages based on the changing sedimentologic and hydrodynamic conditions that existed across the Cambro-Ordovician shelf. Trace-fossil assemblages and corresponding lithofacies characteristics indicate that the Deadwood-Aladdin deposystems formed within an intertidal-flat and subtidal-shelf environment.Based on the distribution and numbers of preserved ichnotaxa, the intertidal flat can be subdivided further into an ecologically stressful inner sand-flat environment, and a more normal marine outer sand-flat environment, both of which belong to a mixed, SkoUthos-Cruziana softground ichnofacies. The inner sand flat is characterized by low diversity, low numbers, and a general lack of complexly constructed ichnotaxa. Trace fossils common to both assemblages tend to be smaller in the inner flat compared to the outer sand flat. Taphonomic effects, such as substrate type and sediment heterogeneity, also aid in differentiating between the inner and outer sand-flat assemblages.The subtidal shelf environment is categorized in the Cruziana ichnofacies. Ichnological evidence of periodic tempestite deposition and hardground development within this subtidal regime is manifested by high diversity and low abundance of ichnogenera.

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Tidal Flats and Associated Tidal Channels

Cited by 38 publications

References 0 publications

The Hummocky Patches and Associated Sediment Dynamics Over an Accretional Intertidal Flat

The Hummocky Patches and Associated Sediment Dynamics Over an Accretional Intertidal Flat

Cambrian wave‐dominated tidal‐flat deposits, central Wisconsin, USA

Significance of nearshore trace-fossil assemblages of the Cambro-Ordovician Deadwood Formation and Aladdin Sandstone, South Dakota

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