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Sand dune cross-beds can be large, such as in the Jurassic-age erg deposits of Navajo Sandstone in Canyonlands National Park. Aztec Butte shown here Formation of cross-stratification Schematic of eolian cross-bedding Close up of cross-bedding and scour, Logan Formation, Ohio Tabular cross-bedding in the Navajo Sandstone in Zion National Park Tabular cross-bedding in the South Bar Formation in ...
These structures are within sedimentary bedding and can help with the interpretation of depositional environment and paleocurrent directions. They are formed when the sediment is deposited. Cross-bedding Cross-bedding is the layering of beds deposited by wind or water inclined at an angle as much as 35° from the horizontal. [1]
A bedding surface is three-dimensional surface, planar or curved, that visibly separates each successive bed (of the same or different lithology) from the preceding or following bed. Where bedding surfaces occur as cross-sections, e.g., in a 2-dimensional vertical cliff face of horizontal strata, are often referred to as bedding contacts .
Hummocky cross-stratification from the Book Cliffs, Utah. Hummocky cross-stratification from the Arisag Formation (Silurian), Nova Scotia. Hummocky cross-stratification is a type of sedimentary structure found in sandstones. It is a form of cross-bedding usually formed by the action of large storms, such as hurricanes. It takes the form of a ...
Cross-bedding – the axis of a trough cross bed or the down-dip direction of a tabular cross bed point the direction of paleo flow. Current ripple marks – will have the short side of the ripple pointing down stream. Sole markings/flute casts – the short, steep side will point up stream, and the long, tapered side points down stream.
Very small cross-lamination means that the ripple height is roughly one centimeter. It is lenticular, wavy and flaser lamination. Small Small cross-bedding are ripples set at a height less than ten centimeters, while the thickness is only a few millimeters. Some ripples that may fit this category are wind ripples, wave ripples, and current ripples.
Schematic illustrations of two styles of graded bedding: left: normal grading; right: inverse grading. Schematic illustrations of two styles of graded bedding: left: normal grading; right: coarse tail grading. In geology, a graded bed is a bed characterized by a systematic change in grain or clast size from bottom to top of the bed.
Cross-bedding in Zion National Park, Utah.Both the tangential bases on the cross beds and the truncations of overlying layers can be used as a way up indicator. A dinosaur footprint preserved in positive relief is a trace fossil indicating the bottom (or sole) of the bed (Lower Jurassic Moenave Formation, southwestern Utah).