Ancient Ripple Marks

Marine Fossil

Visitors who hike up the South Mesa trail at Chaco Canyon National Historical Park will walk directly over these remnants of an ancient sea. Over time, the sea retreated and the sandy sea floor dried and turned into stone in a process known as lithification. This preserved the shape of the ripple marks. These ripple marks were photographed not only to demonstrate the past environment, but also as a means of preservation. Located directly on a public trail, this paleontological resource may be at a greater risk of degradation than others in the field. As the ripple marks eventually wear away, this model will remain to tell that story.

3D Ripple Marks

Chaco Culture National Historical Park, New Mexico

Alternative Text for the 3D Model

A 3D model. This model shows a fossil of ripple marks captured in stone. The central portion of the image where the ripples occur has a low-relief undulating surface. The surface surrounding the fossil is sandy and covered with small rocks and pebbles. Two rulers are visible in the image and serve as scale bars for the image. The fossil is approximately 1 meter by 1/2 meter. The model can be rotated and tilted using a computer interface.

For those park visitors that hike the back country, ripple marks in bedrock can be seen on the South Mesa Trail. Visitors in this arid can walk former “beach-front property”, remnants of an ancient in-land sea in the now arid Southwest. These ripple marks were photographed not only to demonstrate the past environment, but also as a means of preservations. Located directly on a public trail, this paleontological resources may be at greater risk of degradationf than others in the field. As the ripple marks eventually wear away, this model will remain to tell that story.

The numbers 1-4 appear on the model and link to annotations:

1. Scale. This scale bar is a control stick for use with photogrammetry. The circular targets at each end can be read by the software and the precisely know distance (~28 cm) used to provide measurement to the whole area imaged.
2. Ripple symmetry. The symmetry of a ripple mark can tell you about currents. Symmetric ripples formed in water that was going back and forth, like waves at a beach. Asymmetric ripples were formed in a unidirectional current, like a stream. Here, these are likely the result of tidal currents in a near-shore environment, similar to the ripples seen with the model of the clams and ripples.
3. Why so dark? Iron-rich minerals, such as hematite and siderite, settled on the shallow sea floors. These minerals tun a dark, rusty color after being exposed to oxygen.
4. Modern ichnology. The study of animal tracks and traces is known as ichnology. Here, a passing hiker has left a boot-print in the soft sediments of aeolian sands. Tracks can provide clues to the living animal’s behavior, where as body fossils (i.e., bones, teeth) can provide insights about the appearance of the animal. For these tracks, we can posit that the person was enjoying a hike. These tracks though are ephemeral, and the next storm will likely erase these.

Footnotes:

Why so dark? Iron-rich minerals such as hematite and siderite settled on the shallow sea floors. These minerals turn a dark, rusty color after being exposed to oxygen.

Related Links

• NPS—Chaco Culture National Historical Park
• NPS—National Fossil Day
• NPS—Photogrammetry
• NPS—Fossils and Paleontology
• NPS—Geology

Part of a series of articles titled
Chaco Collections—Paleontology.

Previous:
Ripples and Bivalves

Where this belongs

• Chaco Culture National Historical Park

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