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Figure 143. (A) Bottom 2.4 m (7.9 ft) of Scorpion Mound core (from Shinn et al., 1983). Horizontal black bands mark 10-cm (4-in.) intervals. Stars indicate areas that were thin sectioned. Stylolites are irregular interlocking contact surfaces that fit together, usually occurring in homogenous carbonate rocks. The seam is characterized by a concentration of insoluble constituents of the rock. Stylolites are formed by chemical alteration under pressure accompanied by dissolution (Dunnington, 1954). Swarms = >40 stylolites per 10-cm section. ls = limestone. dol = dolomite. ss= sandstone. Bold arrow marks top of underlying massive sandstone, which extends to 16.5 m (54.1 ft) depth (bottom of core). Total thickness of sandstone is not known. (B) Enlarged sections of Scorpion core (from Shinn et al., 1983). Top section shows internal sediment around phylloid algae (envision a bowl of potato chips infiltrated with sand). Note stromatolite in center of lower section (black arrow), stylolite (white arrow), and phylloid algae (red arrows). (C) Sawed, plastic-impregnated sections of experimental core of Portland cement and chicken eggshells that simulate phylloid algae in lime mud (from Shinn et al., 1983). Compare with features visible in Scorpion Mound limestone (B). Note laminated geopetal filling (internal structure that indicates original relation of top to bottom at time of formation; red arrow) associated with fractured eggshells. Also note broken lumps of Portland cement outside eggshell to right of arrow and lack of fracturing typical of lime mud. The lumps simulate collapse breccia in limestone (see, for example, Fig. 83A, 83B). The Scorpion Mound core contained numerous areas of collapse breccia. Large voids in (C) are artifacts of shrinkage during sample preparation.

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Coastal & Marine Geology Program > Center for Coastal & Watershed Studies > Professional Paper 1751