Exploring the wonders of geology in response to young-Earth claims...

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Thursday, June 23, 2011

Grand Canyon, AZ to Logan, UT — A Geology Photo Tour

I've decided that this blog has too many words!

So to compensate, I have littered this post with geology-related photos from the past month. These pictures are in no particular order (chronological, geographic, or even logical), so forgive the randomness. Click on the pictures to view in full size. Also, please feel free to share, but link to the original source if applicable. Enjoy!

Antelope Island, Utah

Antelope Island is well known for its population of American Bison. This bison is grazing on vegetation that is growing in Holocene lake sediments, which formed during Lake Bonneville's life and fall (esp. ~12,000 B.C. to present). Quartzite boulders, like those in the background, litter the landscape, and have eroded from nearby outcrops of the Cambrian Tintic Quartzite (equivalent to the Tapeats Sandstone of the Grand Canyon). If Lake Bonneville were to refill, large boulders such as these would be found amid 'calm-water' sediments. These sediments overly much older sedimentary/igneous rock, but are separated from them by an erosional unconformity. A similar phenomenon is found at the base of the Grand Canyon, where Proterozoic Quartzite boulders are cited as evidence for catastrophic deposition by young-Earth (Flood) geologists.

The bedrock of Anteleope Island ranges in age from Mesoproterozoic, igneous basement (Farmington Canyon Complex) to Cambrian sedimentary rocks. Sandwiched somewhere in the middle (and beneath the bison in this photo) is a Neoproterozoic diamictite. This particular diamictite preserved evidence of glaciation from one of the Cryogenian 'Snowball Earth' events, during which glaciation extended to the tropics. At that time, Utah formed the northern shore of a large, equatorial continent.

A granodioritic gneiss boulder of the ~1.8 billion-year-old Farmington Canyon Complex, which comprises the basal outcrop of the Wasatch Range and a bulk of the basement rock for northern Utah.

Eastern shores of Antelope Island, and a great example of Walther's Law of Facies in action. As the lake recedes, marshland will advance over what used to be shoreline and lake-bottom sediments. Thus a geologic cross section of the region will reveal a transition from fine-grained, calcareous mudstone to oolitic sandstone to organic-rich, calcareous siltstone with fragments of grasses/shrubs. Each layer will appear to be flat, when in fact deposition occurred in adjacent environments on a gentle slope.
Why are sedimentary rocks so flat? Despite the relief generated by the bounding mountain ranges, most sedimentary basins are extremely flat. Since topographic highs (i.e. mountain ranges) provide sediment to the basin, they will not be preserved in the geologic record, except as detrital fragments in the valley sediments. With the aid of radiometric dating, geologists study the composition of sedimentary rocks through time to reconstruct the tectonic (or structural) history of a sedimentary basin. 
Shoreline sands in the Great Salt Lake are comprised of oolitic carbonate (i.e. tiny snowballs of calcium carbonate). Minor sand bars, seen above in the foreground, will form thin sets of oolitic grainstone (limestone) with low-angle cross bedding. Thin lenses of silty mudstone should also form between bed sets, as wind and stagnant water cover the sand with dust between storms. Avian footprints are common on the beach (namely, seagull). Although wave action commonly erases the visible evidence, prints of the heavier gulls will be preserved a few centimeters below the surface as carbonate grains/mud are compacted beneath their feet. One time, I found the fully articulated skeleton of a seagull (meat-free, but a few feathers still intact) buried in the carbonate sand. How are bird skeletons (e.g. Archaeopteryx) preserved in lake carbonates? Now I know! Fossilization requires 'rapid' burial, but not that rapid.

Bingham Canyon Copper Mine (Rio Tinto/Kennecott), Utah

Difficult to describe or capture in a single photograph. This mine is big— the largest open-pit copper mine in the world, in fact. In addition to copper, the mine produces economical supplies of gold, molybdenum, and sulfuric acid. Yes, I learned that from the video in the visitor's center...and a personal tour through the core lab!

Up, down, up, down—non-stop delivery of ore and waste. Note the bulldozer and full-size pickup for scale.

Timpanogos Caves, Utah

American Fork Canyon, as seen from the entrance to Timpanogos Caves. When the caves first formed (some half a million years ago), they were at the same elevation as the river. Coincident uplift of the Wasatch Range and downcutting of the river, however, have since separated the two by ~1,000 vertical feet. Flowstone and riverine sediments within the cave were dated to estimate rates of uplift (less than 1 mm/year, on average).
Helictites and soda-straw stalactites. Variations in climatic conditions (temperature, humidity, precipitation, soil activity) can affect the rate of dripwater flow and calcite precipitation within a cave. This results in seemingly stochastic growth patterns for individual speleothems, pictured above.
When the tour began, we were asked: "What would you do if you found a cave like this for the first time?" I responded, "Take samples!" I don't think the tour guide like my response, but I make no apologies. I would love to take either of these currently forming stalagmites back home with me—well, to the lab, that is. Each stalagmite is about 1.5–2 meters tall.
The inevitable collision course of speleothem formation. Some things just don't last forever...
The closest thing left to 'pristine beauty' in Timpanogos Caves. Not much else to say, except that the 'night' setting on my wife's camera added a very special effect from the artificial lamp placed by the park service.
Brecciation and recrystallization of the host carbonate. When these rocks were deeply buried, the weight of overlying sediment caused the brittle carbonates to fracture. Subsequent fluid flow allowed for the reprecipitation of relatively pure, white calcite (compared to the dark, organic-rich limestone/dolostone surrounding). In other words, these rocks have been lithified for a very long time.

East Canyon Reservoir, Utah

A great day of fishing, interrupted briefly by a dark rain cloud. The positioning of the cloud caused the Wasatch Range (background) to appear rather surreal.
The red conglomerates that outcrop near I-80/I-84 in northeastern Utah are synorogenic to the Sevier Fold-Thrust Belt—a mountain range that runs north-south through northern Utah, southern Idaho, and western Wyoming. During the Late Mesozoic, sedimentary rocks in this region were 'squeezed' together by tectonic forces, causing them to be folded and thrust on top of each other (see cross section here for a more graphic depiction). Pebbles and boulders that comprise the conglomerate above are weathered fragments of earlier Mesozoic and Paleozoic rocks. In other words, the underlying rock layers must have been fully lithified before this conglomerate was deposited in the Late Cretaceous. Since that time, more than a mile of Cenozoic sediments accumulated over the conglomerate before it was exposed here. Synorogenic deposits provide the clearest evidence, I think, for the antiquity of the geologic column. 

Cache Valley (Logan), Utah

May in Cache Valley: ample snowmelt for the summer.

Fault scarps and lacustrine (lake shore) benches are common sights along the Wasatch Range. Can you pick them out?

Layton, Utah

View south toward the Oquirrh Mountains (west of Salt Lake City), which overlook Magna, UT and the south end of the Great Salt Lake. 
The windows of heaven. Antelope Island seen at the bottom right.

Grand Canyon (south rim), Arizona

Outcrop of the Kaibab Limestone, which was deposited in shallow marine conditions during the Permian (~260 million years ago). Four different carbonate lithofacies can be seen in this photo alone, each representing a different depositional environment and different flow regime (i.e. water depth/velocity). The heterogeneity of Grand Canyon sediments has long been overlooked by Flood geologists, who have mistakenly proposed that catastrophic slurries of lime mud and seashells could account for thick carbonates like the Kaibab. Each carbonate layer above differs in 1) grain size and composition, 2) clay vs. carbonate content, 3) cement type and composition, and 4) fossil type and abundance. These differences cannot be explained by hydrodynamic sorting alone (many features, like oncoids, result from algae/bacteria living in the sediments for years). Sedimentary structures provide evidence of weak tides and waves, or even subaerial exposure, but not catastrophic flow in deeper water.

Supai Group (late Mississippian to early Permian). The 'step-like' slope at the base of the picture results from alternating fine and course-grained carbonates and mudstones of the Watahomigi Formation. The cyclic pattern is interpreted to result from 1) long-term variations in sea-level; 2) progradation of carbonate sand bars (think modern Caribbean); or 3) (more likely) a combination of the two. The semi-arid climate of southern Nevada has similarly produced excellent exposures of cyclic carbonates, bearing testimony to a time when a dynamic sea transgressed most of the western United States.

Well, that's all for now! Perhaps I should do this more often? Geology is always explained most effectively by pictures, in my opinion. I welcome any feedback (or corrections?) or additional photos that you'd like to share. Again, please feel free to share any pictures you find here, but link to the original source if applicable (i.e. if reposted online).


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