Septarian Nodules

 The name “septarian nodules” is derived from the Latin word “septum,” meaning seven, in reference to partitions dividing cavities. More specifically, the name refers to carbonate-rich nodules having an internal structure comprised of a series of carbonate-filled cracks or cavities, which separate polygonal blocks of hardened sedimentary material, such as mudstone.

The exterior of a septarian nodule, 13 cm tall and 11 cm wide. Utah.

Septarian nodules on the outside are not exactly eye-catching.

The interior of the same nodule, shown above. The interior of a septarian nodule can be, however, very interesting and eye-catching.

The nodules usually form early in the burial history of the muddy sediment before the rest of the sediment hardens into rock. Afterward, compaction causes cracks/cavities to form, and groundwater with dissolved minerals infills the cracks/cavities. Upon evaporation, the minerals crystallize out of the water. 

Septarian nodules, more accurately referred to as septarian concretions, have a smooth rounded exterior, which is normally gray. The mineral-filled cracks in the interior are typically yellow (calcite), but some also can be partially brown (aragonite = another carbonate mineral).

This septarian nodule (12 cm wide and 15 cm tall) was cut (slabbed) in order to show the intricacy of the infilled cavities.

Lastly, I included this slabbed (cut) septarian nodule because it is a nice specimen and one that was used in one of my previous posts (July 17, 2014) entitled "Pseudofossils."The rounded and smooth exterior of most of the septarian nodules have been mistakenly by some collectors as “dinosaur eggs,” which they are NOT! Pseudofossils are inorganic objects.

Rock hounds commonly cut the septarian nodules in half and polish them. They can sell for low to high prices, depending on the complexity of the radiating crack pattern and the variety of the coloration.

Squid and Octopus: Pens, Beaks, and Egg Cases

This is the third and last part of my sequence of posts on cephalopods. Squids and octopods are cephalopods with very poor fossil records. The reason for this is that they have either no or very rarely mineralized body parts.

Modern squid pens: longest one is 11.5 cm;

 the short piece of another one is 5 cm long.

Although squids have "plastic-like" internal structures called "pens," these structures consist of chitin, which is compositionally similar to fingernails and toenails of mammals. Chitin is not mineralized material, hence, it does not get preserved. If you have ever cleaned a squid, the pens have to be removed, before you eat the squid. Technically speaking, the squid pens are semi-transparent gladii = the vestigial internal shell of a squid. They are indeed flexible (allowing squids to live in deep water without being crushed) and help support the internal organs, as well as allow for jet propulsion of the squid.

Squid pens are found often in the stomachs of sperm whales, which are predators of cephalopods.

Modern-day squid jaws (tallest one is 3.7 cm height). They came from a 127-cm (50 inches) long squid and were a gift to me from the late Ralph Ferguson, a shell dealer in Long Beach, California.

Squids, like the nautiloid, sepiid, and octopus, have a two-part jaw (beak). The two parts (mandibles) fit together and function in a scissor-like fashion for tearing their prey apart. Squid beaks consist also of chitin.

The geologic history of octopods (octopus) is little known because of the absence of skeletal structures. The earliest presumed fossil is an impression found in Upper Cretaceous rocks. Argonauta is a pelagic octopus, which lives in tropical to subtropical open oceans but close to the sea surface rather than on the seabed.

The female of the octopus genus Argonauta (there are seven living species) produces a very delicate (egg-shell delicate) calcite (calcium carbonate) brood pouch for transport of its eggs. The exterior of this brood pouch resembles the shell of some Mesozoic ammonoids, but the interior of the brood pouch differs by lacking chambers, chambers walls (septa), and a siphuncle. Brood pouches of Argonauta have been found (rarely) in Miocene deposits of California and elsewhere.

Argonauta hians, a modern-day octopus egg case (4.7 cm maximum diameter) from the Indo-Pacific region.

 Same specimen, showing its spacious and hollow interior.

 The egg cases of Argonauta are paper thin and resemble nautiloid shells, hence their common name has become the "paper Nautilus."

Octopus beak, largest jaw (on the right) 1.5 cm length;

 Marina del Rey, southern California.

It is interesting how similar the beaks are in the different groups of cephalopods, yet each member of the group has its own distinctive beak shapes. Compare the octopus beak, shown here, with the squid beak, shown earlier in this post. "Similar, yet different."