The UNSOLVED MYSTERY of Hummocky Cross-Stratification (Geologists are STILL seeking answers)
Автор: Dr. Anton's Rock-o-Rama
Загружено: 2025-05-02
Просмотров: 1486
Hummocks and hummocky cross-stratification, what's the difference and who cares? That's a question that gets asked a LOT by geologists, engineers, and drillers and it's an important one! Geologists have known about the mysterious and distinctive sedimentary structure known as hummocky cross-stratification (HCS for short) since the 1970s. We’ve recorded HCS in outcrops, cores, and image logs and have a good idea of where and how they form.
BUT…nobody has ever witnessed them form either in the natural world or in a lab experiment! Why not?
We know they form on storm-dominated shorelines, below fair weather wave base and above storm wave base. They have an erosive base and a depositional bedding that suggest they form by internal waves breaking on the shoreline, forming an upslope swash run-up, followed by the backwash, with modification by the waves building the hummock. Since they form during storms in turbid water, it’s maybe not surprising nobody has witnessed them being generated firsthand.
We'll visit a textbook (literally) outcrop of HCS in Utah's famous Book Cliffs, where sandy shorefaces prograded into the Western Interior Seaway during the Cretaceous. Storm waves reworked sand delivered by rivers into HCS beds in the lower shoreface. Now, those deposits have been uplifted and eroded for us to explore. Let's look at some rocks!
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