scholarly journals Sediment physico-chemistry associated with natural marsh development on a storm-deposited sand flat

1995 ◽  
Vol 120 ◽  
pp. 271-283 ◽  
Author(s):  
DT Osgood ◽  
MCFV Santos ◽  
JC Zieman
Keyword(s):  
Natural Marsh ◽  
Sand Flat

Caging Manipulations in Marine Soft-Bottom Communities: Importance of Animal Interactions or Sedimentary Habitat Modifications

1980 ◽  
Vol 37 (7) ◽  
pp. 1130-1139 ◽  
Author(s):  
Larry W. Hulberg ◽  
John S. Oliver
Keyword(s):  
Exposure Period ◽  
Sediment Deposition ◽  
Soft Bottom ◽  
Sand Flat ◽  
Elkhorn Slough ◽  
Bottom Communities ◽  
Mobile Species ◽  
Large Numbers ◽  
Competitive Release ◽  
Sand Bottom

Caging manipulations were performed in two marine soft-bottom communities to test two nonexclusive hypotheses: (1) polychaete abundance changes in cages are caused by the presence or absence of particular predators and competitors; (2) polychaete changes in cages are caused by animals responding to cage-induced habitat modifications, especially sediment deposition and erosion.The significant changes in the polychaete community beneath a variety of cages installed on a highly wave-exposed sand bottom could not be explained by the presence or absence of predatory demersal fishes. This result was obtained despite the exclusion of fish which normally consume large numbers of infaunal polychaetes.A caging experiment similar to Woodin's (1974) was performed in the channel of Elkhorn Slough using comparable cages and similar exposure period. In Woodin's experiments, the exclusion of a sedentary tube builder was accompanied by an increase in a mobile deposit feeder. This was interpreted as a competitive release. In our experiment, no sedentary species inhabited the channel and none were excluded; nevertheless, this same mobile species increased inside the cages. Although the importance of potential predators and competitors was not documented in the caging experiments, all of the sand-flat and slough caging results are consistent with the hypothesis that animals respond to sedimentary habitat modifications created by cages. This hypothesis is not considered in most caging experiments in marine soft-bottom communities.

Cycles of sand-flat sandstone and playa–lacustrine mudstone in theTriassic–Jurassic Blomidon redbeds, Fundy rift basin, Nova Scotia: implications for tectonic and climatic controls

1990 ◽  
Vol 27 (3) ◽  
pp. 442-451 ◽  
Author(s):  
Karl A. Mertz Jr. ◽  
John F. Hubert
Keyword(s):  
Fault Zone ◽  
Shallow Lakes ◽  
Alluvial Fan ◽  
Rift Basin ◽  
Sand Flat ◽  
Basin Subsidence ◽  
Evaporite Minerals ◽  
Sand Flats ◽  
Sandy Mudstone

The redbeds of the 220 m Blomidon Formation comprise more than 100 pairs of (i) sand-flat sandstone (distal alluvial fan) and (ii) playa sandy mudstone and (or) lacustrine claystone. These pairs are tectonic autocycles generated by rift-basin subsidence and sagging along the Glooscap fault zone that shifted loci of active fan sedimentation toward and away from the playa surface as fan lobes migrated into topographically low areas.Intervals of intense and prolonged aridity are recorded in many of the sand-flat sandstones and playa sandy mudstones by evaporite minerals, principally gypsum, precipitated by subsurface evolution of a CaSO4–NaCl brine. Aridity is further demonstrated by intense disruption of sediment fabrics beneath evaporite crusts, deep mudcracks, eolian-sandstone layers and patches, and the presence of authigenic Ca–Mg-rich illite–smectite and analcime. During relatively wetter intervals, claystone beds accumulated in shallow lakes that filled the playa depression, lapping onto the sand flats. The claystones lack evaporite minerals and textures, and many are partially bioturbated.The long-term climate became progressively wetter from latest Triassic to earliest Jurassic time, as evidenced by an increase upsection in the ratio of lacustrine claystone to playa sandy mudstone and by less evaporite mineralization in the sand-flat sandstones.

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