The Moenkopi Formation

Moenkopi Formation with ancient riverbed marks at capital reef national park Ut

Moenkopi Formation slopes in Canyonlands national park Ut

Swimming dinosaur tracks Capital reef national park Ut. Compared to 50mm lens cap

The age of the Moenkopi Formation ranges from the early Triassic to the middle Triassic period. The Moenkopi Formation generally contains thinly bedded mudstones and sandstones with a wide variety of ripple marks and some trace fossils. Secondary gypsum veins cut through the formation. The Moenkopi formation can contain localized fossils, but most exposures are devoid of fossils. Actual bone is even more rare. During the initial deposition of the Moenkopi, the climate was hot and dry. Then during later members, it progressively got wetter.  It was deposited due to tidal, and also nearshore, shallow marine, and some floodplain.
    In the Moenkopi formation there are six subdivisions that are recognized. In upward sequence these are the Timpoweap member, the lower red member, the Virgin limestone member, the middle red member, the Shnabkaib member, and the upper red member. There are four general members deposited in the Capitol Reef region; the Black Dragon member (the lowest deposited under marine conditions, and capped by beach sands and fluvial deposits.), the Sinbad Limestone member(deposited under shallow marine conditions)  , the Torrey member (over laying the Sinbad Limestone),  and the Moody Canyon member (deposited under wide spread, uniform, low energy marine conditions.)  Sometimes you will encounter trackways of reptiles and amphibians that lived along the lake and streams of this pre-dinosaur landscape. While the formation was still fairly young, small animals crossed it and left tracks that then left fossils. By the Marine, depositing into the west were gray mudstone and limestone. Several periods had relatively with high sea level.  Which became embedded in sharp, to the dominant red sandstone and mudstone of the Moenkopi. The Moenkopi is known for it’s well preserved ripple marks and mud cracks.  The polygonal shape mud cracks were formed when cohesive sediment, such as mud or clay, dries out, contracts, and shrinks due to scorching heat from the sun. The ripples are formed when shallow water flows across a non-cohesive bed (silt, gravel, sand etc.). The force of the water pulling at clastic debris produces the ripples.