GeologyDiscussion Archives - Bliss Photographics

You Have to be Swift

Well a “White Throated Swift” if I read my audubon ID correctly. They are silly fast birds. Getting one launching from it’s home…. lol. My reaction time isn’t as fast as in my youth. As a geologists I’m less interested in the bird instead of the WONDERFUL geology behind it. I’m always thinking about Cretaceous river systems operating up here in the rock record. Geologists read rocks like a book. The local rocks make for a great story ! ..

Transition to geology:

Indeed this Swift is a cliff dweller exiting that dark subsoil homestead built out of the Cretaceous Hell Creek/Lance formation Cretaceous River bottom sediment exposed here. Those various “rocks” are all different kinds of mudstone “pebbles”. These were rolled down a very large paleo-river. Each rock torn up from the clay river bottom up stream then rounded along the way. There is a nice mix of clast sizes represented in the wall. The current velocity in that paleo-river obviously carried these pebbles to cobble sizes down river only to dump them here at this spot. That river lost it’s ability to carry this material leaving it behind for me to observe 66 million years later. No fossils in this debris which represents the source’s likely-hood of having bones in the clay. (way long discussion ommitted).

Somewhat more recently, rain water has very carefully washed the sand away from the pebbles showing this well exposed “cobblestone surface that is resultant from that pre-historic river depositional event. Notice I didn’t say “flood”. Floods wash sediment down stream as well as scouring clay chunks out of the floor of the stream. It’s the cessation of that flood that leaves this kind of debris as these transported mud clasts behind. Slower velocity drops the suspended and saltated load instantly. This pile of river gravel was eventually covered by another river cycle of deposition. The next depositional event overlapping rinse and repeat millions of times. The same river swept back and forth across the Cretaceous piedmont filling the epi-continenal sea at the time. Dinosaurs skinny dipped in these rivers sands/cobbles.

Location: Bliss Dinosaur Ranch, Wyoming/Montana borderlands (Wyotana)

Title: You Have to be Swift

SkyScape Prairie Dog Hills (off season)

The perspective on this wide angle shot was amazing to me and I see this view regularly. Wyoming is on the left and Montana is on the right looking west right down the 45th parallel. (1/2 way precisely between the Equator and the North Pole coincidentally) This became a well dissected landscape. Rocks fractured due to freezing ice/ dry cycles is a huge process.. Boulders break into smaller and smaller iterations with enough time. Each sand grain thus formed actuates from the motion of wind and water. One sand grain at a time, the hillocks wear down, wash to the Gulf of Mexico

I stand on Cretaceous age sands but the Olive green tainted hills distant are younger age. Their rocks formed from sediments washed over 130 miles away from the BigHorn Mountains. This outwash from that massive tectonic uplift so far away transported here in the form of a “Fangclomerate” deposit. Those beds deposited eons after debris from the Big Horns filled up the tectonic “bathtub” . Located at their eastern mountain front (called the Powder River Basin).

The current rivers/hydrologic regime wore many thousands of feet of that debris off the older sediments I stand on. That just to expose them to the sky. All the dirt/rocks/sediment that USED to be above me, is currently all in transport to or in the Gulf of Mexico’s Mississippi River Delta. Just like the Prairie Dog Hills are made of sediments in Transport From the BigHorns (their source), to the gulf of Mexico (sink). Ultimately all of this ground will wash into the Gulf. That is assuming all precesses we observe today, continue into the future (a primary assumption in Geology/science)

Location: Bliss Dinosaur Ranch, Wyoming/Montana borderlands (Wyotana)

Title: SkyScape Prairie Dog Hills