sediment that had been carried across a barrier island and dumped in the 

 adjoining bay by catastrophic storms, such as hurricanes. One such fan, 

 measuring 4-1/4 by 4 miles (6.9 by 6.4 km), occurs at the north end of St. 

 Joseph Island, on the central Texas coast. It grades northeastward into a 

 subaerial tidal delta. The surface facies of these two features and the 

 adjoining barrier island nucleus, as well as the geometry of the component 

 sediment bodies, are described in detail. The data upon which descriptions 

 and interpretations are based were obtained by digging trenches and pits, up 

 to 8 ft (2.4 m) deep. 



The washover fan is fed via a low-level washover channel, Vincent 

 Slough, which is cut through the barrier island nucleus. The fan is accret- 

 ing laterally into the adjoining bay, Aransas Bay, through the deposition of 

 shell debris and sand that are derived from the inner neritic zone of the 

 continental shelf. Periodic hurricane surges, both flood and ebb, deposit 

 large volumes of sediment in Aransas Bay. The washover fan thus built up is 

 25 to 30 in. (63.5 to 76.2 cm) thick at its periphery and thickens to more 

 than 50 in. (127 cm) near its apex. It is composed predominantly of an 

 imbricate set of sheet sands, each 3 to 15 in. (7.6 to 38.1 cm) thick. Each 

 washover sand rests on a sharp scour base and consists of a shell placer at 

 the base that grades upward into horizontally laminated, shell-free, clean 

 sand . 



The washover fan is a two-part feature. One part is still actively 

 prograding, albeit very slowly, and mainly consists of sand of the washover 

 sand, eolian flat, low-mound, and high-mound sand facies. The second part is 

 stagnant, and hurricane surge has been excluded from it for some considerable 

 time. The lower half of the stagnant fan segment is dominated by the 

 washover sand facies, while the upper half is dominated by muddy sand to mud 

 of the marsh, mudflat, and pond facies. The superimposed eolian mounds 

 consist of low-mound, high-mound sand, and high-mound mud facies. With 

 exclusion of the scouring action of hurricane surge waters, eolian mounds on 

 the stagnant fan segment are prograding laterally unimpeded, thus slowly 

 changing the distributary channel pattern and reducing channel dimensions. 



Radiocarbon dates show that the tidal delta began to form at least 2,400 

 years ago; the washover fan began to form about 1,700 years ago. Progra- 

 dation was rapid at first but subsequently slowed considerably. Progradation 

 has been minimal since about 450 years before present. (Author) 



Armon, J. W. 1979. "Landward Sediment Transfers in a Transgressive Barrier 

 Island System, Canada," in Leatherman, S. P., ed., Barrier Islands: From the 

 Gulf of St. Lawrence to the Gulf of Mexico, Academic Press, New York, N.Y., 

 pp 291-319. 



The largely transgressive Malpeque barrier system in the southern Gulf 

 of St. Lawrence, Canada, was investigated to assess the influence of a 

 restricted sea environment on barrier island morphology and dynamics. Wave 

 dimensions are restricted by the limited wind fetches and shallow-water 

 depths in the southern Gulf, and the islands are protected from storm action 

 for 2-4 months in winter by shorefast ice. The barrier islands in the 

 transgressive section of this barrier system are narrow, 150 to 450 m in 

 width, with the dune zone commonly dominated by the seawardmost dune. The 

 continuous dune cover restricts overwash during storms, and the well- 

 vegetated dune surface limits sand transport landward of the seawardmost 



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