NOTE: The building pictured above is home to the Geology Department. The fossil in question is in the stones of building 550 which is just a few yards away up the hill.
All rocks have a history which can in part be deciphered from the evidence which the rocks themselves furnish. The rocks in the Quad buildings or others that come from nearby places contain fossils which are known to be the remains of shore clams and snails that lived only during the Cretaceous period, which is relatively late in geological history. Years, the common measure of time, cannot be used to tell how long ago this period was, all that can be said being that in the long series of events that is known these animals lived very late. The fossils found are those whose descendants today live along the shores of tropical or warm temperate oceans. From this it is inferred that the climate was tropical or sub-tropical in the region where, and at the time when, these rocks were laid down. The fossils are similar to others found in similar rocks in Japan. This is evidence that the Cretaceous shores of California and Japan were continuous or nearly so, and that this afforded routes for the migrations and mingling of their two widely separated faunas.
The material in the Quad stones is largely quartz or sand grains that have been cemented together. These grains were carried down by streams from an area which contained an abundant supply of quartzitic material as a source. The material closely resembles the debris that the streams at the present time are carrying down from the Sierras and depositing in the Great Valley. This similarity of material, together with other evidence, suggests the conclusion that the Sierra Nevadas were already in existence during the Cretaceous period. The presence of these marine deposits over the Coast Ranges indicates that while they were being laid down, the Pacific Ocean covered the site of the latter ranges, and possibly the greater part of the Great Valley. These, in brief, are a few high lights recorded by the rocks of the Quad.
-- Lynn Bramkamp, The Stanford Daily, 29 January, 1926
Stanford Sandstone
The sandstone making up the quad buildings is a local rock type, mapped as part of the Chico Formation of Late Cretaceous to Early Tertiary age; it is now interpreted as an unnamed Early Eocene arkosic sandstone (58 to 37 Ma). Opened in 1891, Stanford University was built in the style of California's Spanish missions using the sandstone quarried from the northern end of the Santa Teresa Hills, south of San Jose. A special railway line was built just to haul about 800 cubic feet of stone daily to Stanford form the Greystone Quarry. These sandstones represent some of the oldest stratified sediments overlapping the highly deformed deep water sediments, basalt, and ultramafic rocks of the Franciscan Complex, which underwent deformation during subduction of sea floor beneath California.
This sandstone represents a moderately deep-water subsea fan and channel deposit that is lithologically and stratigraphically identical to rocks of the same age in the Sierra Azul, near Loma Prieta to the southwest. When these sediments were being deposited, you could have sipped margaritas on the beach at the foot of the Sierra Nevada and to visit what is now Stanford would have required a submarine... Fluctuating sea levels and uplift of the land later combined to raise these marine rocks into a "high and dry" position in the modern Santa Teresa Hills.
Geology Professor Elizabeth Miller and her colleagues have done a bit of detective work on our sandstone and know in fairly fine detail where it came from and when. To begin with, they can date it approximately, because there is one (and maybe only one) fossil-like impression of an ancient creature in the thousands of tons of stone quarried for the Quad. This is a Turitella, a common sea snail that has been around for millions of years. Geologists now agree that this one comes from the early Eocene, somewhere around 34 million years ago, give or take. Geologists can also locate the geographical source of our stone. They infer that it must have been in the mountains around what is today Sequoia and Kings Canyon national parks, because they know that since the Eocene, the Pacific Plate has migrated 175 kilometers north, bringing its sediments with it. This migration was an almost unimaginably slow process.
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The Eocene Epoch
The Eocene is the second of five epochs in the Tertiary Period — the second of three epochs in the Paleogene Period — and lasted from about 55.8 to 33.9 million years ago. The oldest known fossils of most of the modern orders of mammals appear in a brief period during the early Eocene and all were small, under 10 kg. Both groups of modern ungulates, Artiodactyla and Perissodactyla, became prevalent mammals at this time, due to a major radiation between Europe and North America.
The early Eocene (Ypresian) is thought to have had the highest mean annual temperatures of the entire Cenozoic Era, with temperatures about 30° C; relatively low temperature gradients from pole to pole; and high precipitation in a world that was essentially ice-free. Land connections existed between Antarctica and Australia, between North America and Europe through Greenland, and probably between North America and Asia through the Bering Strait. It was an important time of plate boundary rearrangement, in which the patterns of spreading centers and transform faults were changed, causing significant effects on oceanic and atmospheric circulation and temperature.
In the middle Eocene, the separation of Antarctica and Australia created a deep water passage between those two continents, creating the circum-Antarctic Current. This changed oceanic circulation patterns and global heat transport, resulting in a global cooling event observed at the end of the Eocene. By the Late Eocene, the new ocean circulation resulted in a significantly lower mean annual temperature, with greater variability and seasonality worldwide. The lower temperatures and increased seasonality drove increased body size of mammals, and caused a shift towards increasingly open savanna-like vegetation, with a corresponding reduction in forests.
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For more detailed information about the formation of the Stanford Sandstone itself, check out Stanford's first EarthCache: Stone River which describes in greater detail the formation, location, and excavation of the sandstone used in the construction of the original university buildings.
In all the sandstone blocks used across all of Stanford Campus, there is one (and only one) known observable fossil. Fittingly it is right here by the Geology Building! Take a close look at the Eocene sandstone near the northwest corner of Building 550. Here you will find Stanford Sandstone's One Singular Sensation: a turritellid gastropod mold. This is your mission. To log this Earthcache, you must find this fossil. Good Hunting.
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Logging requirements:
(You can log your find as soon as the email is sent, but logs with insufficient answer may be deleted)
Send me a note through my caching profile with:
1. The text "GC69TRW One Singular Sensation" on the first line
2. The number of people in your group (put in the log as well).
3. Describe the fossil impression. How big is it? Roughly what shape and what color does it have?
4. How many stone blocks are directly below the block of sandstone containing the fossil? I will also accept the approximate height at which the fossil can be found.
5. Optional (yet encouraged) Post a photo of your GPSs next to the fossil. Then post a photo of you and your party doing your best Turritella impression.
| I have earned GSA's highest level: |
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Sources:
Sandstone & Tile, Stanford Historical Society Fall 2010, Volume 34, Number 3
California Rocks! GEO 116, Continuing Studies, Stanford University
UC Museum of Paleontology Eocene