FOSSILS OF THE LATHAM SHALE AND CHAMBLESS LIMESTONE
LOWER CAMBRIAN TRILOBITES OF THE LATHAM SHALE
The Latham Shale in San Bernardino County, California, offers the amateur collector a wide range of Lower Cambrian trilobites. According to a few marine paleontologists, this area, which includes the Marble and Providence Mountains, contains the oldest assemblage of these arthropods. The challenge for the fossil hunter is the heat, the long winding trail into the ancient mountains and the sheer effort in finding a whole trilobite (something I was unable to do myself.) There are casts and molds of this elusive arthropod in museums and private collections, which can’t compare in quality to the excellent intact fossils found elsewhere in the world, and yet the variety of trilobite species and the sheer number of specimens in the Latham Shale make it an important site for the study of this period of geologic time. There are, in fact, more species of Olenellus in the Latham Shale (almost always the cephalon) than other locations, as well as rare brachiopods, fossilized algae, and Precambrian crystals beneath this strata. The following drawings are illustrations of intact specimens, rather than actual fossils I extracted from shale. Only one of the specimens shown, Onchocephalus, does not belong to the order of Ollenellidae. (Since I completed these drawings many years ago, I’m quite sure that both amateurs and professional paleontologists have found more species of trilobites in the Latham Shale.)
The following diagram of geological stratigraphy in Marble and Providence Mountains, both above and below the Latham shale, includes a wide variety of marine fossils and an important gem.
Below is a map, showing the course from Route 66 to the Fossil trail, leading up to the fossil beds in the Marble Mountains. Other fossil locations associated with the Latham Shale are found in the nearby Providence Mountains, San Bernardino, California. Another family of Olenellus, Fallotaspis, was discovered in the Inyo-White Mountain area of Eastern California. Immediately above the Latham Shale, discussed in a subsequent section, is the gray colored Chambless Shale, nearly as old, offering excellent specimens of oncolites, which are fossilized cyanobacteria.
The following display from my collection include cephalons from the preceding list of intact trilobites (Olenellus Clarki and Olenellus Fremonti). Originally I had photographed dozens of broken specimens, but there was too much redundancy in the collected fragments, so I exhibited the best of them, including one intriguing specimen containing a brachiopod fossil.
Representative Trilobites and Brachiopod from the Latham Shale, Marble Mountains, California
The Chambless Limestone, though not quite as old and not having Latham Shale’s variety, contains trilobites similar to those found in the Latham Shale, hyoliths, thought by some experts to be primitive molluscs, and oncolites, the fossilized remains of one of the most important life forms on earth. Oncolites, which are merely fossilized slabs of cyanobacteria colonies, are shown in the following section. As living forms today, they are aquatic (in both fresh and salt water) and photosynthetic (i.e. they manufacture their own food). Microscopic and normally unicellure, they often clump into colonies large enough to see as a slimy film floating on water. In spite of being a common and unattractive sight, they are the oldest known fossils, approximately 3.5 billion years old. They are the largest and most important groups of bacteria on earth. Many reservoirs of oil are the products of cyanobacteria activity. They also provide much of the nitrogen in fertilizer for rice and bean cultivation. Most importantly, cyanobacteria have helped shape the course of evolution and ecological change throughout the earth’s history. The oxygen we breathe was generated by cynobacteria during the Precambrian period. Before cyanobacteria, as the first drafts of life, began producing oxygen, the earth’s atmosphere was quite toxic. The most important byproduct of cyanobacteria was the origin of plants, which, beginning with the advent of algae assisted in the proliferation of oxygen. The chloroplast with which plants make food for themselves is made up cynobacteria living inside each plant’s cells. A misconception I’ve still seen in text books and articles is the notion that, because cyanobacteria are photosynthetic and aquatic, they should classified as blue-green algae, but, except for the chloroplast in eukaryotic algae, they are not algae at all but the earliest known bacteria and, according to most scientists, all forms of life.
Cynobacteria, as free floating orgasms or colonies, were already 3.5 billion years old when the Chambless limestone formed above the Latham shale. The oncolites which comprise this strata themselves house other fossils such as trilobites and hyoliths. The fossil exhibited below is shown beside living examples of cyanobacteria.
To zoom in, click on oncolite fossil.