Stop A:The Green - Building Stone Walking Tour of Uptown Charlotte (sitios de interés)
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Stop A: The Green
College Street and 2nd Street
The 1.5 acre urban pocket park known as the Green is located between the 400 block of South Tryon and South College Streets, immediately west of the Charlotte Convention Center. Designed by Wagner Murray Architects of Charlotte, it was completed in 2002 and sits directly on top of a 7-level underground parking structure.
A1: Sandstone blocks in the retaining wall
This fine-grained quartz sandstone was quarried near Crossville, Tennessee. Red iron staining highlights cross-bedding on some specimens. The high quartz content in this sandstone, deposited along the coast of an inland sea that covered most of North America in the Mississippian, about 340 million years ago, has made it a desirable and durable building stone. It is called a fieldstone because it has been left in its natural state.
A2: Sandstone capping retaining walls
This fine-grained, plane-bedded sandstone, used throughout the Green as retaining wall caps, was also quarried near Crossville, TN. One of the capstones on the southern side of the plaza has ripple marks (Figure 3), others have parting lineation (the small ridges evident on bedding planes where the stone has split). This stone was likely formed in a deltaic setting associated with the inland sea mentioned for A1 above, as evidenced by its plant fossils (Figure 4).
Can you find a plant fossil in one of these stones?
A3: Upper sections of the pillars on the ‘Ratcliffe on the Green’ building
This limestone is a packstone (according to the Dunham classification scheme) meaning it is grain supported and the pores between the grains are filled with calcareous mud. It has a fine to medium grained texture (you can see individual grains without magnification), and contains a type of fossilized shell fragments known as bivalved molluscs, such as those visible in Figure 5.
Many limestones form in warm, shallow seas where organisms with shells composed of calcite (CaCO3) accumulate layer by layer and eventually become lithified into a limestone. This example contains fossilized shell fragments and ooids (small spherical grains). Pull out your hand lens, because ooids are particles < 2mm in diameter that form when individual aragonite grains accumulate concentric layers of carbonate as they roll around on the shallow sea floor. Can you find the ooids? How many different other fossils can you observe in this building stone?
A4: Pillar bases on the ‘Ratcliffe on the Green’ building
This light colored packstone is composed of medium to coarse-grained skeletal fragments of shells, peloids and possibly ooids. The skeletal fragments are best seen on the cut edges of the blocks.