The story of Golden begins with the Idaho Spring Formation around 1.7 billion years ago. Made up of the foliated metamorphic rock gneiss, this formation contains the aluminosilicate minerals k-spar, biotite and quartz. Its chemistry, especially its high calcium and carbon content, suggests creation in a subduction zone with deep water deposition of calcite and limestone similar to the modern-day Sea of Japan. After approximately 1.4 billion years of missing geological history, thanks to the Great Unconformity, comes the Fountain Formation {SAY IT HAS CONGLOMERATE}.
This 320 million year old formation is composed of poorly sorted, highly oxidized sediments of the same minerals as the Idaho Springs Formation but with less biotite and amphibole and more hematite. The shallow but wide strain channels of the sediments identify alluvial fans. Gneiss in contact with sediments suggests that serious uplift and erosion occurred.
Altogether, there is evidence of ancestral Rocky Mountains that came up and later eroded, depositing alluvial fans. These alluvial fans coalesced to become a bajada of sediment along the front of the mountains.
As ancestral Rocky Mountains start wearing down and the sea level starts to transgress from the warmer climate, there starts to become less conglomerate and more sandstone toward the top, becoming the Lyons formation. The Lyons sandstone, formed around 280 million years ago, is composed of small fine-grained combination of k-spar and quartz. The fine sand deposits and large cross-beds give evidence that this formation originated from beach dunes.
The Lyons Formation transitions upwards into the Lykins Formation, aged approximately 260 million years.
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The presence of the minerals gypsum, halite, and calcite indicates that the structure was deposited in water. More specifically, the presence of stromatolites and hematite suggests deposition in shallow water. The fact that there was water deposition provides evidence that there was further transgression of sea level. There is also indication of the water being hypersaline (similar to Salt Lake) since the stromatolites came after the Cambrian. Above the Lykins formation is a 100 million years disconformity caused by the Permian Extinction. This mass extinct was caused by huge volcanoes in Siberia and marked the boundary between the Paleozoic and Mesozoic era. This erosional disconformity above the Lykins Formation indicates a regression in sea level. Eventually, sea level started to transgress again leading up to the 160 million-year-old Ralston Creek Shale Formation.
Following the Ralston Creek Formation comes the Morrison Formation dating at around 150 million years. Dinosaur bones found in the formation suggest it originated from the Jurassic period. The Morrison Formation is made up of mostly sandstone composed of paleosols and the minerals hematite, quartz, and clay. Inconsistent thickness sands suggest that deposition occurred in fluvial environments such as rivers and lakes. After about a 50 million-year gap came the 100 million-year-old Dakota Formation. This formation consists of sandstone and shale composed of quartz, hematite, and clay. The symmetrical ripples on the surface, dinosaur footprints, suggest that the area was a beach near water.
The top of the Dakota formation started to become finer and finer as it became Benton and Pierre Shale. The 90 million-year-old Benton formation contains lots of carbon which makes it appealing for petroleum engineers. The Benton eventually became the Pierre Formation around 80 million-years-ago. Their shale provides evidence of marine deposition in the intercontinental seaway as there is indication of further transgression. After the Benton Formation, the sea level started to regress and gave way to the creation of the Foxhills Formation approximately 69 million years ago. Its finely sorted sandstone provides evidence that it was deposited in a beach. The roots and log seen sticking out of the roadcut indicates that the area was a mangrove swamp. This
Golden Geological Sequence Report. (2022, Feb 27). Retrieved from https://paperap.com/golden-geological-sequence-report/
