. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography SANDS ON THE VIRGINIA SHELF 879 situ subaerial weathering, or weathering in the piedmont source area, it is immediately a func- tion of grain size, and of the consequent chemi- cal microenvironment at the depositional site. To evaluate this hypothesis, we will trace the cycle of iron-stained shelf sand as described in the literature and then present a statistical analysis of the relation of pigment to grain size in our study area. CYCLE OF IRON-STAI
. Collected reprints / Atlantic Oceanographic and Meteorological Laboratories [and] Pacific Oceanographic Laboratories. Oceanography SANDS ON THE VIRGINIA SHELF 879 situ subaerial weathering, or weathering in the piedmont source area, it is immediately a func- tion of grain size, and of the consequent chemi- cal microenvironment at the depositional site. To evaluate this hypothesis, we will trace the cycle of iron-stained shelf sand as described in the literature and then present a statistical analysis of the relation of pigment to grain size in our study area. CYCLE OF IRON-STAINED SANDS The surfaces of quartz grains are chemically active, due in part to unsatisfied bond on the surfaces of the silicate polymer. In fact, quartz grains whose surfaces have been stripped of their inert coatings by acid become so charged with static electricity that they appear "wet" and sticky, and will not sieve properly (J. C. Ludwick, 1969, personal commun.). As a conse- quence of this phenomenon, quartz grains are prone to acquire surficial coatings of hydrous iron oxides, iron-bearing clay minerals, and other materials during any stage of their sedi- mentary history (Fig. 2). The first possible stage is in the source area, either in an iron- precipitating B horizon of a metamorphic or igneous terrane which is serving as a primary source of quartz detritus and ferrous ions, or in the vadose zone of a coastal plain sand unit (Spoljaric, 1971). Under moist, oxidizing con- ditions, the precipitate is initially ferric hydrox- ide [Fe(OH)3] which recrystallizes relatively rapidly to the mineral goethite (HFe02) (Schmalz, 1968). Dehydration may convert the yellow or brown hydroxide to red hematite (Fe203) if the climate includes periodic dry seasons. Under proper conditions, iron-bearing clays may also form on the surface of the quartz grain. Oxidizing river waters transporting iron- stained sand have relatively little effect on the coatings on quartz grains, othe
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