ABSTRACT

The surface textures of quartz sand grains from locations along the Florida Gulf Coast are compared with those from other environments. High-magnification studies consistently show the predominance of chemical over physical textural features, which is to be expected in low- to moderate-energy coastal environments. Because of multiple reworking of these sediments, detailed environmental interpretations are difficult but not impossible. Distinctions are commonly quite subtle.

The great influence of the crystal structure of quartz on the physical and chemical surface features precludes the normal method of rapid scanning of several grains per sample by the electron microscope. Therefore, a statistical approach is suggested using a combination of Nomarski differential interference-contrast microscopy and scanning electron microscopy. A relatively high percentage of the total surface areas of large numbers of grains can be studied in detail by this method.

Stereopairs of scanning electron micrographs illustrate numerous surface textural features produced by a variety of sedimentary processes and environments.

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FIGURE 1. Idealized figure of quartz, showing relationship of percussion figures to different crystal planes (after Frondel, 1962).

FIGURE 2a. Idealized development of faces of quartz crystal, showing orientations of various etch figures.

FIGURE 2b. Rates of solution shown on left-handed quartz sphere. Outlines represent body remaining after long attack by hydrofluoric acid. Left figure -- view looking down c-axis with original crystal outline indicated. Right figure -- view perpendicular to prism face illustrating much higher rate of solution along direction of c-axis (after Frondel, 1962).

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FIGURE 3. Range chart showing distribution of surface features in various environments (modified from Karpovich, 1969).

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FIGURES 4-7 Histograms showing relationship among surface feature density and distribution, 5 different processes, i.e., eolian (physical impact in air), glacial, surf action, chemical [solution (--), and silica deposition-recrystallization (+)], and 4 individual environments. Surface features not in definite process categories were placed between classes where they most commonly occur. However, gradation between processes occur among most of features (See Fig. 3). Fig. 4 -- Beach at Marco Island exhibits moderate wave-energy (20 to 40 cm) and marks near southern end of quartz drift system (Cape Romano, Florida). Fig. 5 -- Wisconsin glacial outwash from Little Miami River valley, Cincinnati, Ohio, showing wide variety and abundance of surface features characteristic of this environment. Fig. 6 -- Dominance of chemical processes demonstrated by textures seen on the Grass Island beach on o-wave energy coast (2 to 3 cm) near Adams Beach (Florida "big bend"). Fig. 7 -- Dune at Royal Bluff, southwest of Carrabelle, Florida, containing abundant relicts of past environmental history despite silica deposition and iron-staining that has occurred in 2,000 to 7,000-year (Pilkey and Gorsline, 1961) history since stabilization was achieved.

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EXPLANATION OF PLATE 1

Scanning electron micrographs of quartz grains

Figure

1. Complex of oriented triangles developed at different levels by chemical solution. Chemical steps and linear grooves well developed on this grain from Adam Beach, "Big Bend", Florida. Slightly curved grooves only mechanical feature on stereopair, 2,000X.
2. Complex pattern of curved solution features dominate this grain from Flint River, Georgia. Fine pattern represents diagenetic features, 1,950X.
3. Mechanical impact v's on grain from high-energy beach at Sebastian Inlet, central east coast, Florida. Orientation of these mechanical features may be related to crystallographic structure of quartz. Stereopair, 4,800X.
4. Flat pitted surface exhibits large impact v's, irregular small-scale indentations, small-scale conchoidal fractures, and breakage blocks. Sebastian Inlet beach, 950X.
5. Oriented triangles and diagenetic features predominate on this Ft. Walton Beach, Florida, sample. Mechanical impact v's have same orientation as triangles. Solution, acting on these chemically active surfaces, are modifying v's to triangles. Stereopair, 2,350X.
6. Quartz-kink dislocation exposed by fresh breakage block. Smooth upper surface marked by mechanical pits created in high-energy Georgetown Co., South Carolina, beach environment. Recrystallization has begun on dislocation surface with micro-slickensides, 2,100X.
7. Extensive, smooth, nearly featureless surface found on high-energy beach (Sebastian Inlet) grain. Effect of crystal structure demonstrated by lower, more protected surface being covered with impact features. Oriented solution features seen on slopes to left, recrystallization surface occurs on lower left, 2,400X.
8. Oriented chemical triangles in upper left only distinct features on this nearly smooth featureless grain surface from Tampa Bay, Florida, 1,350X.
9. Smooth quartz grains from Sebastian Inlet with few impact v's under high magnification, despite coming from high-energy beach, 120X.

EXPLANATION OF PLATE 2

Scanning electron micrographs of quartz grains

1. Imbricated trigonal recrystallization formed on grain from moderate-energy beach at Marco Island, South Florida. This is 4th step in proposed development of quartz grains by recrystallization, 4,200X.
2. Complex of perfectly oriented triangles, including well-developed concentric triangles on grain from lighthouse Point, Florida, on low-energy Apalachicola Peninsula. Few oriented impact v's also present. Presence of imperfectly developed (1 poorly formed and 2 prominent sides) oriented triangles, in addition to above forms, may represent nearly complete evolutionary cycle. Some slightly curved grooves and recrystallization can also be seen, 2,000X.
3. Grain from Marco Island beach with several breakage blocks. Smooth, relatively featureless plane on upper surfaces may represent 2nd proposed stage of recrystallization, while lower right portion of grain is on more advanced stage, 650X.
4. Middle stage of recrystallization on grain from dune, St. Joseph State Park, Florida. Stereopair, 2,100X.
5. Well-developed oriented triangles and oriented impact v's on sample from moderate-wave energy, St. Vincent Island beach near Apalachicola, Florida, 95X.
6. Oriented fractures or platelets on grain from Royal Bluff dune near Carrabelle, Florida. Stereopair, 2,100X.
7. Smooth, frosted eolian grain from Royal Bluff on Apalachicola Peninsula, Florida. Note flat pitted surface and graded arcs over most of surface. Lower surface shows oriented triangles--probably remnants from earlier littoral history, 175X.
8. Complex chemical etch patterns developed on frosted eolian Royal Bluff grain. Iron-staining removed prior to examination of grain by SEM. Figure H, I 220X; Figure I 636X.
9. Complex chemical etch patterns developed on frosted eolian Royal Bluff grain. Iron-staining removed prior to examination of grain by SEM. Figure H, I 220X; Figure I 636X.

EXPLANATION OF PLATE 3

Scanning electron micrographs of quartz grains

1. Complex development of graded arcs. Small light-colored particles are debris not removed by cleaning techniques. Stereopair, 9,400X.
2. Chemical solution exploiting graded arcs on beach-ridge grain from St. George Island near Apalachicola, Florida. Arcs probably represent relicts from eolian portion of beach-ridge history. Major part of flat pitted surface due to mechanical impact in littoral environment, 1,050X.
3. An oblique view of oriented triangles with conchoidal breakage block in center. All probably relicts from littoral history of Royal Bluff dune grain. Stereopair, 1,700X.
4. Eolian grain adjacent to high-energy North Carolina beach illustrating "popcorn texture". Notice smooth rounded ridges commonly found on eolian grains, 1,350X.

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5. "Popcorn texture" on grain from Southern Ocean recovered from Pleistocene cores. This intermediate stage of recrystallization develops before distinct prisms form and intergrowths terminate in pyramids. High silica content of Antarctic interstitial water probably promotes this process, 2,150X.
6. Unusual oriented T-shaped solution features and linear solution features found on moderate-energy beach grain from Cape San Blas, South of Port St. Joe, Florida. First feature may be impact v's modified by chemical etching. Stereopair, 4,600X.
7. Graded arcs and arc-shaped steps on ice-rafted glacial grain from South Pacific Ocean. Parallel grooves and semi-parallel steps can also be seen. Large features in upper right half may be imbricated breakage blocks. Note fresh appearance of surfaces so characteristic of glacial grains, 5,200X.
8. Nondescript surface of grain from desert dunes, El Paso, Texasgh grain looked clear and vitreous through binocular microscope, iron-stained character of sample is evident, 4,500X.
9. Linear chemical solution features on eolian grain near Panama City, Florida. Rutile inclusion perhaps chemically exploited, 10,300X.

EXPLANATION OF PLATE 4

Scanning electron micrographs of quartz grains

1. Complex of linear and irregular solution features on grain from beach, St. Joe State Park, Florida. Chatter marks on a few linear ridges, diagenetic features quite common. Stereopair, 2,200X.
2. High magnification view, center Figure A. First proposed step in recrystallization, rectilinear solution, and diagenesis all represented, 8,100X.
3. Intricate solution features developed on O-energy Keaton Beach grain from "Big Bend" of Florida. Remnants of physical impact features on uppermost surface. Stereopair, 565X.
4. Diagenetic features on St. Joe State Park dune sand. V-shaped features progress towards normal diagenetic pattern. Are these chatter marks?, 3,800X.
5. Well-developed diagenetic texture, possible inclusion in upper right, St. Joseph State Park, Florida. Stereopair, 3,150X.
6. Diagenesis developed on chemically active surface of grain from flat-topped beach ridge along Gulf Co. Canal, Florida. Apparent chemical deposition occurring on flat surface, 3,050X.
7. Complex solution features as developed on Figure C. Note parallel steps formed by etching. Keaton Beach, Florida. Stereopair, 530X.
8. Semi-parallel and arc-shaped steps on Pleistocene glacial melt-water grain, Cincinnati, Ohio, 7,000X.

EXPLANATION OF PLATE 5

Scanning electron micrographs of quartz grains

1. Effect of different crystal planes on solution features on grain from Grass Island beach, "Big Bend", Florida. Chemical step pattern could be mistaken for imbricated breakage blocks. Diagenetic features on lower left, recrystallization beginning on upper wall. Stereopair, 3,050X.
2. Oriented chemical etch features in lower portion of grain from "fossil" inland dunes near Albany, Georgia. Upper portion, latter stages of recrystallization with development of pyramids, 7,100X.
3. Complex solution forms great depth of chemical etching on grain from berm of Grass Island. Mechanical impact features on top of ridges indicative of active aqueous transport as most recent environment, 950X.
4. Irregular rugged solution features on dune sample from St. Joseph State Park, Florida. These can be mistaken for mechanical semi-parallel steps and breakage blocks, 2,200X.
5. Complex assortment of features lay on different crystal planes exposed by solution. Different orientations of linear solution features alternate with oriented triangles. Top surface of this grain, from tidal marsh of Grass Island, relatively smooth and pitted. Diagenetic feature also evident, 690X.

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PLATE 1.. [Grey Scale] See caption on page 455.

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PLATE 2. [Grey Scale] See caption on page 455.

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PLATE 3. [Grey Scale] See caption on page 455.

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PLATE 4. [Grey Scale] See caption on page 456.

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PLATE 5. [Grey Scale] See caption on page 456.

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