I thought this was interesting:
You don't need a Ph.D. in geology to know that desert dunes and other desert deposits do not form under roaring flood waters. These require not only time, but also dry land. The Flood of Noah supplies neither. The Old Red Sandstone, which looks for all the world like a collection of fossilized desert dunes, was formed in Devonian times. It has outcrops extending from the British Isles to Poland and Russia's White Sea, and from Germany to Norway (Gilluly, Waters, and Woodford, 1968). Outcrops have even been found in Greenland and North America. In Devonian times, before North America and Europe drifted apart, these dunes covered an entire semi-arid continent.
Several lines of evidence derived from this great geologic formation create difficulties for the flood geology model. For instance, the interfingering of these sandstones with marine sediments shows that the shoreline of this continent advanced and retreated several times. Thus the desert rocks are entangled with rocks that the flood geology model says were formed within the one-year-long flood. Also, redbeds, consisting partly of rust formed above sea level, are also
found in this formation. These would not have been formed in any catastrophic flood. The Old Red Sandstones also contain typical playas, complete with their characteristic cubic salt crystal deposits. These are desert salt-pan deposits formed after the rainy-season lakes evaporate. Today, in the Mojave Desert, playas can become lakes for a couple of weeks, only to dry out again, leaving a crust of salt deposits like those found in the Red Sandstone. Although a few freshwater ponds did exist on this ancient semi-arid continent, they dried up from time to time. So, we find fossil mud cracks in the shales that came from the dried-up pond bottoms, and we find fossil lungfish, a type of fish that can survive drought by building a mud cocoon in the pond bottom and breathing air. Hundreds of square miles of fossil sand dunes in these deposits contain cross-bedding and sand-blasted pebbles (ventifacts) of the sort found in modern desert sand dunes, and in no other kind of modern sediment. These different independent lines of evidence converge to show that the Old Red Sandstones almost certainly formed over thousands of years in a dry climate, not in any kind of flood catastrophe.
The Grand Canyon contains fossil desert dunes and other sediments that to all appearances were deposited on dry land. The Permian Coconino Sandstones in the upper walls of the Grand Canyon have the frosted well-sorted wellrounded sand grains found only in land-deposited sand dunes (Shelton, 1966). Furthermore, many of the laminae of the cross-bedding contain fossil footprints that could only have come from reptiles or other quadrupeds climbing up the face of a slightly damp sand dune in the open air. (Those climbing down the slopes left no tracks because they simply slid.) ICR geologist Dr. Steve Austin has taught the theory that amphibians resting between underwater dunes made the tracks. His theory is very interesting, but rather implausible since the Flood must have been violently dumping several meters' worth of sediment per day. The Canyon's Supai and Hermit Shales, found today beneath the Coconino Sandstones, look exactly like river deltas that formed above sea level (Shelton, 1966). Back in Permian times, many quadrupeds (probably reptiles) left their footprints in the soft delta mud. As the mud baked hard in the sun, it formed cracks. The hardness of the baked mud preserved the footprints and mudcracks until the flooded rivers of the rainy season buried them in fresh mud. These fossil prints and mudcracks are found today, as well as iron oxides that form in the open air, showing that these shales formed above sea level.
The pure quarz Navajo Sandstones of Triassic and Jurassic times in Zion National Park, Utah, also look exactly like desert sand dunes (Gilluly, Waters, and Woodford, 1968). They contain extensive cross bedding of the type found in sand dunes, and the frosted sand grains and sand-blasted pebbles found only in dunes formed on the land.
Certain formations in western Wyoming look exactly like deserts that bordered a fitfully receding sea in Carboniferous times (Houlik, 1973). In particular, the Mississippian Lodgepole Formation contains the type of carbonate deposits and evaporites found forming in tidal flats today. The Amsden formation consists of sabkhas and desert dunes. Sabkhas are a kind of hardpan that forms in deserts after hard water seeps up through the ground by capillary action and evaporates leaving nodules of calcite, andhydrite, and other salts. They are seen forming extensively in Saudi Arabia today. Unless Houlik has grossly erred, these sabkhas, casts of evaporite crystals, and fossil dunes show that these Carboniferous deposits formed in a desert, not a flood.
Several times at the end of the Miocene epoch (six to eight million years ago), the Mediterranean Sea dried up, leaving extensive desert deposits on the sea bottom (Hsu, 1972). The Straits of Gibraltar opened and closed, causing these complex changes, as the Glomar Challenger discovered in 1970 by using echo soundings and deep-sea core samples. Each time the Mediterranean slowly dried up, first calcite precipitated around the rim of the basin of the Balearic abyssal plain, then anhydrites and gypsum further in, and finally rock salt in the center at the deepest point. This is just the order that these salts would precipitate if you set out a large saucer of sea water to dry. Successive dryings of the Mediterranean produced hundreds of meters of evaporites. Not only did evaporites form, but also land deposits like sun-baked mud cracks, wind-blown sand, and sabkha anhydrite nodules. Since algae can only grow where sunlight reaches, the stromatolites (a common algae deposit) found in deep sea core samples show that the Mediterranean sea floor, now two miles deep, was once dry land. The Rhone and Nile rivers cut their canyons thousands of feet below current sea level to feed the desiccated Mediterranean basin. Desert-style alluvial fans accumulated from debris washed by cloudbursts down the slopes of Sardinia; now these deposits lie far under the water. After the Mediterranean refilled with water for the last time, at the beginning of the Pliocene, sediments began to accumulate over the evaporites; the weight of these sediments forced evaporites up through weak spots in the sediments to form salt domes. Some of these salt domes are a few miles across, and hundreds to thousands of feet high. Even though such structures may not be forming today, a dried-up Mediterranean could have easily formed them, whereas flood geology is hard pressed to account for such things.