Remember there is no container to find here! Think of this Earthcache as more of a geology field trip. To claim credit for this cache you will observe some rocks near the posted coordinates and then answer some questions. Observing the rocks will enable you to answer the questions listed in the “Logging Requirements” section below.
Cautions:
- Some of the cliffs are cordoned off for safety and to prevent accelerated erosion caused by foot traffic. Do not cross into the areas which are cordoned off.
- Some of the nearby conglomerate is undercut and weakly adhered. There is no need to walk on the conglomerates. For safety you should stay away from steep portions of the conglomerate layers.
- Some portions of the sandstone are steep. The sandstone is decomposing which means loose sand and poor footing. For safety you should stay away from the steep sandstone faces.
- Some combinations of high tides or high surf may create hazardous conditions at or near the exposed trace fossils. Use good judgment and do not proceed if there is any danger of being caught by a wave!
Point Lobos State Natural Reserve:
- All features are protected – do not collect rocks, plants, sea life, etc.
- Stay on designated trails
- Bicycles allowed on paved roadways only
- Do not disturb wildlife
- No dogs allowed – not even if confined to your motor vehicle
- Fee area - $10 per motor vehicle, senior discount for age 62 and up - $9 per motor vehicle.
Logging Requirements:
- Locate some of the Trace Fossils – tread lightly so as to not wear down the fossil traces. The snapshot above is an example of the first type of trace for which you will be searching.
- The trace shown above is believed to have been left by an animal as it made its way through the soft sediment – feeding along the way. Pick a representative example and estimate the average number of side lobes per foot and then describe the dimensions of a typical side lobe.
- There are also some simpler types of preserved burrows nearby. These are less complex, but still interesting because of the variety seen here. Find an example of a burrow and describe the dimensions and characteristics of the burrow.
- Use the “Send Message” feature in my profile to send your findings. Be sure to mention that the message is about “GC4P5RX – Weston Beach Ichnofossils Earthcache.”
- Go ahead and post your found log online – please do not post your answers to the logging requirement in your online log. I will contact you only if your answers are not clear.
- Feel free to post any snapshots of your activities at the Earthcache site, so long as the posted snapshots do not reveal the answers to the logging requirement questions.
Ichnofossils
“Ichnofossils” is the scientific term for trace fossils. Trace fossils aren’t like the fossils with which most people are familiar. When one thinks of fossils, then fossilized dinosaur bones are likely to top the list. One might also think of other “typical” fossils such as the shells of nautiloids or the teeth of ancient sharks. These are all directly fossilized parts of animals. One may also find fossilized plants such as “petrified” wood or the imprints of leaves. “Trace fossils” are different in that they are signs of activity preserved in stone. The activities may be burrowing for food, burrowing for shelter, nesting, walking or crawling. The best known fossil traces are probably dinosaur “trackways.”
There are several types of trace fossils near the Earthcache coordinates. One type was left as ancient sea creatures made their way through soft sediments. The pattern doesn’t match any known to be left by modern sea creatures so it is not possible to state with certainty what sort of creature left them. The most widely accepted interpretation of these traces is that a bivalve (a type of mollusk – think of a clam or geoduck) left them. The feeding pattern left by the bivalve consists of a main track with side lobes. The side lobes were presumably created as the bivalve extended its siphons upward – alternately to each side of the main track. As you observe these traces keep in mind that the trace is very three dimensional – but you are only seeing a cross-section depending on how much of the sediment layer was weathered away.
No need to feel bad if you don’t perceive the three dimensional nature of these traces. The earliest descriptions interpreted the feeding traces seen above as fossilized seaweed. I had assumed the traces were tracks left by sea creatures crossing on top of sediment. That was before receiving expert advice from a geologist who volunteers as a docent at Point Lobos State Natural Reserve.
The other types of trace fossils here were also left by burrowing animals. Some burrows show signs that they were filled by the animal that created them – perhaps with sediment which had passed through the digestive tract of the burrowing animal. Look for tubular structures resembling stacked “pillows.” The contents of some nearby burrows have been replaced with siderite (iron carbonate). These vertical burrows are seen primarily in cross section where they exposed at the weathering surface. Contact with oxygen causes rusty discoloration of the siderite.