LENS ON SEPTARIAN NODULES

Septarian Nodule, Dan Bowen, 2020 Tucson Gem and Mineral Show

An exceptional polished septarian nodule with an ammonite heart. Septarian concretions or septarian nodules are concretions containing angular cavities or cracks, called "septaria." These septaria can be filled 

The word comes from the Latin word septum; "partition", and refers to the cracks/separations in this kind of rock.

The process that created the septaria that characterize septarian concretions remains unclear. A number of mechanisms have been proposed, including the dehydration of clay-rich, gel-rich, or organic-rich cores; shrinkage of the concretion's center; expansion of gases produced by the decay of organic matter; or brittle fracturing or shrinkage of the concretion interior by either earthquakes or compaction.

The cracks or patterns you see here are highly variable in shape and volume, as well as the degree of shrinkage they indicate. Although it has commonly been assumed that concretions grew incrementally from the inside outwards, the fact that radially oriented cracks taper towards the margins of septarian concretions is taken as evidence that in these cases the periphery was stiffer while the inside was softer, presumably due to a gradient in the amount of cement precipitated.

A spectacular example of septarian concretions, which are as much as 3 meters (9.8 feet) in diameter, are the Moeraki Boulders. These concretions are found eroding out of Paleocene mudstone of the Moeraki Formation exposed along the coast near Moeraki, South Island, New Zealand. They are composed of calcite-cemented mud with septarian veins of calcite and rare late-stage quartz and ferrous dolomite.

Beautiful smaller septarian concretions are found in the Kimmeridge Clay exposed in cliffs along the Wessex Coast of England. As as you walk the beach, look for exposures of Speeton Clay beds D6 and D7, the bentonite horizons that weather to yellow colouration. Beneath the Speeton Shell Bed cliff exposures is an exposure of Kimmeridge Clay, UK. This outcrop contains concretions that show the characteristic 'turtle-stone' patterns of these septarian nodules.

Photo top: Dan Bowen, Chair, VIPS, 2020 Tucson Gem and Mineral Show.

References: Humberside Geologist No. 14, Humberside Geologist Online, The geology of East Yorkshire coast.http://www.hullgeolsoc.co.uk/hg146t.htm

Dale, P.; Landis, C. A.; Boles, J. R. (1985-05-01). "The Moeraki Boulders; anatomy of some septarian concretions". Journal of Sedimentary Research. 55 (3): 398–406.

Milliken, Kitty L.; Picard, M. Dane; McBride, Earle F. (2003-05-01). "Calcite-Cemented Concretions in Cretaceous Sandstone, Wyoming and Utah, U.S.A." Journal of Sedimentary Research. 73 (3): 462–483. Bibcode:2003JSedR..73..462M. doi:10.1306/111602730462. ISSN 1527-1404.

AMMONITES: INDEX FOSSILS

Ammonites were prolific breeders that evolved rapidly. If you could cast a fishing line into our ancient seas, it is likely that you would hook an ammonite, not a fish. They were prolific back in the day, living (and sometimes dying) in schools in oceans around the globe.

We find their fossilized remains (and plenty of them) in sedimentary rock from all over the world. In some cases, we find rock beds where we can see evidence of a new species that evolved, lived and died out in such a short time span that we can walk through time, following the course of evolution using ammonites as a window into the past. For this reason, they make excellent index fossils.

An index fossil is a species that allows us to link a particular rock formation, layered in time with a particular species or genus found there. Generally, deeper is older, so we use the sedimentary layers rock to match up to specific geologic time periods, rather the way we use tree-rings to date trees. Photo: Dan Bowen, 2020 Tucson Gem and Mineral Show.

HOLCOPHYLLOCERAS MEDITERRANEUM

There is tremendously robust suturing on this lovely ammonite, Holcophylloceras mediterraneum, (Neumayr 1871) from Late Jurassic (Oxfordian) deposits near Sokoja, Madagasgar.

They were a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids — octopuses, squid, and cuttlefish) than they are to shelled nautiloids such as the living Nautilus species.

Ammonites first appeared about 240 million years ago, though they descended from straight-shelled cephalopods called bacrites that date back to the Devonian, about 415 million years ago, and the last species vanished in the Cretaceous–Paleogene extinction event.

The shells had many chambers divided by walls called septa. The chambers were connected by a tube called a siphuncle which allowed for the control of buoyancy with the hollow inner chambers of the shell acting as air tanks to help them float. We can see the edges of this specimen's shell where it would have continued out to the last chamber, the body chamber, where the ammonite lived. Picture a squid or octopus, now add a shell and a ton of water.

ANDROGYNOCERAS OF YORKSHIRE

A stunning example of the ammonite Androgynoceras from the Yorkshire Coast, England.

The Geology of Yorkshire in northern England shows a very close relationship between the major topographical areas and the geological period in which their rocks were formed. The rocks of the Pennine chain of hills in the west are of Carboniferous origin whilst those of the central vale is Permo-Triassic.

The North York Moors in the north-east of the county are Jurassic in age while the Yorkshire Wolds to the southeast are Cretaceous chalk uplands.

The plain of Holderness and the Humberhead levels both owe their present form to the Quaternary ice ages. The strata become gradually younger from west to east. Much of Yorkshire presents heavily glaciated scenery as few places escaped the direct or indirect impact of the great ice sheets as they first advanced and then retreated during the last ice age. This beauty is in the collection of the deeply awesome Harry Tabiner.

MIDDLE TRIASSIC HUMBOLDT RANGE

Looking out over the Middle Triassic exposures of the Humboldt Mountain Range.

These hills were the site of the 1905 Expedition of the University of California’s Department of Geology in Berkeley funded by the beautiful and bold, Annie Alexander, the women to whom the UCMP owes both its collection and existence. Annie brought together a paleontological crew to explore these localities and kept an expedition journal of their trip which is now on display at the University of California Museum of Paleontology at Berkeley.

Annie's interest was the ichthyosaurs and she was well pleased with the results. They dodged rattlesnakes and tarantulas, finding many new specimens as they opened up new quarries in the hills of the Humboldt Range of Nevada.

Ichthyosaurs range from quite small, just a foot or two, to well over twenty-six metres in length and resembled both modern fish and dolphins. The specimens from Nevada are especially large and well-preserved. They hail from a time, some 217 million years ago, when Nevada, and parts of the western USA, was covered by an ancient ocean that would one day become our Pacific Ocean. Many ichthyosaur specimens have come out of Nevada. So many, in fact, that they named it their State Fossil back in 1977.

Fossil fragments and complete specimens of these marine reptiles have been collected in the Blue Lias near Lyme Regis and the Black Ven Marls. More recently, specimens have been collected from the higher succession near Seatown. Paddy Howe, Lyme Regis Museum geologist, found a rather nice Ichthyosaurus breviceps skull a few years back. A landslip in 2008 unveiled some ribs poking out of the Church cliffs and a bit of digging revealed the ninth fossil skull ever found of a breviceps, with teeth and paddles to boot.

Specimens have since been found in Europe in Belgium, England, Germany, Switzerland and in Indonesia. Many tremendously well-preserved specimens come from the limestone quarries in Holzmaden, southern Germany.

AMMONITE: INDEX FOSSILS

Ammonites first appeared about 240 million years ago, though they descended from straight-shelled cephalopods called bacrites that date back to the Devonian, about 415 million years ago, and the last species vanished in the Cretaceous–Paleogene extinction event.

They were prolific breeders that evolved rapidly. If you could cast a fishing line into our ancient seas, it is likely that you would hook an ammonite, not a fish. They were prolific back in the day, living — and sometimes dying — in schools in oceans around the globe. We find ammonite fossils — and plenty of them — in sedimentary rock from all over the world. In some cases, we find rock beds where we can see evidence of a new species that evolved, lived and died out in such a short time span that we can walk through time, following the course of evolution using ammonites as a window into the past.

For this reason, they make excellent index fossils. An index fossil is a species that allows us to link a particular rock formation, layered in time with a particular species or genus found there. Generally, deeper is older, so we use the sedimentary layers rock to match up to specific geologic time periods, rather the way we use tree-rings to date trees. A handy way to compare fossils and date strata across the globe.

UPPER CRETACEOUS NANAIMO GROUP AT HORNBY ISLAND

Hornby is a delightful island off the east coast of Vancouver Island, just east of Denman Island. Texada and Lasqueti lie just to the west of Hornby. It is home to about 1,000 residents made up of artists, retirees and those wanting to enjoy the quiet, rural, community-oriented lifestyle.

Hornby Island is formed from sediments of the upper Nanaimo Group which are also widely exposed on adjacent Denman Island and the southern Gulf Islands. Peter Mustard, a geologist from the Geologic Survey of Canada, did considerable work on the geology of the island. It has a total stratigraphic thickness of 1350 m of upper Nanaimo Group marine sandstone, conglomerate and shale.

These are partially exposed in the Campanian to the lower Maastrichtian outcrops at Collishaw Point on the northwest side of Hornby Island. Four formations underlie the island from oldest to youngest, and from west to east: the Northumberland, Geoffrey, Spray and Gabriola.

During the upper Cretaceous, between ~90 to 65 Ma, sediments derived from the Coast Belt to the east and the Cascades to the southeast poured seaward to the west and northwest into what was the large ancestral Georgia Basin. This major forearc basin was situated between Vancouver Island and the mainland of British Columbia.

The island's soils have developed from marine deposits of variable texture, except for the higher elevations and steeper slopes where weathered clastic sedimentary rock provides the parent material. Most of Hornby's soils are sandy or gravelly, but some deep black loams occur in the northwestern part and many of the sands at the southern end have loam-textured topsoils.

Collishaw Point, known locally as Boulder Point, Hornby Island

Podzols are common and the bleached sand grains associated with their eluvial (A2, Ae or E) horizons lend a salt-and-pepper appearance to many forest trails. In most cases, though, the E is not very thick and may, in fact, be discontinuous. For this reason, the soils were mostly classified as Brown Podzolic in a soil survey published in 1959.

All of the island's soils are strongly acidic in their natural state except for those which have developed on shoreline shell middens.

And it is to the shore that many are drawn — locals, tourists, geologists and paleontologists alike. Hornby is a wonderful place to explore. The island is beautiful in its own right and the fossils from here often keep some of their original shell or nacre which makes them quite fetching.

The Nanaimo Group as a whole represents largely coarse-grained units deposited in deep-sea fan systems. In this environment, deeper channels continuously cut through successive shale and sandstone bodies. The channels funnelled density currents into the basin, while also building levee deposits. Turbidity currents travelled down the channels, and also overtopped the levees spilling across backslope areas. The sequential sediment formations, from significantly coarse-grained sandstones and conglomerates to fine silts and shale units of the Nanaimo Group, are considered to be partly due to eustacy, but more significantly related to relative sea-level changes induced by regional tectonics in an active forearc setting.

The Northumberland Formation consists of a massive, dark-grey mudstone which is locally interlaminated and interbedded with siltstone and fine-grained sandstone.

There are abundant calcium carbonate concretions, parallel and current ripple laminations, clastic dikes and folded layers due to slumping. In the Gulf Islands to the south, this formation has been found to contain abundant and diverse foraminifera indicating marine paleodepths of 150-1200 m.

The more resistive Geoffrey Formation consists of thick-bedded sandstone and conglomerate. It is highly channelized, and some sandstone has exposed parallel and ripple laminations. The Spray Fm exposed on the east end of the island is a massive olive-grey mudstone with interlaminations of sandstone.

Furthest to the east, the youngest exposures on Hornby Island are from the Gabriola Formation, which outcrops on the eastern peninsula. This is again a thick-bedded and channelized sequence of conglomerates and massive sandstone with minor mudstone interbeds. South, in the Gulf Islands, this formation has contained ammonites, gastropods and pelecypods. Paleowater-depth from foraminiferal assemblages has been set at 200 m.

Katnick, D.C. and P.S. Mustard (2001): Geology of Denman and Hornby Islands, British Columbia (NTS 92F/7E, 10); British Columbia Geological Survey Branch, Geoscience Map 2001-3.

England, T.D.J. and R. N. Hiscott (1991): Upper Nanaimo Group and younger strata, outer Gulf Islands, southwestern British Columbia: in Current Research, Part E; Geological Survey of Canada, Paper 91-1E, p. 117-125.

LIVING FOSSIL: HEDGEHOGS

This little cutie is a Western European hedgehog, Erinaceus europaus, in the subfamily Erinaceinae (Fischer, 1814). They are native to western Europe, Asia, Africa and have been introduced (oops!) to New Zealand.

There are seventeen species of hedgehog in five genera. They share distant ancestry with the family Soricidae (shrews) and the gymnures.

Hedgehogs are considered "Living Fossils" as they have changed very little over the past 15 million years. These small mammals are loners with their own kind but live in close proximity to our human population. They dwell in inhabited areas, farmland, deciduous forests and desert. You'll know them by their distinctive spiny look (which may remind you of very tasty chocolates from Purdy's in Canada) and their adorable piglike snorts and grunts as they make their way through the underbrush looking for tasty snacks.

Look for them in the evening in hedgerows and undergrowth as they hunt for frogs, toads, snails, bird eggs, grassroots, berries, insects, worms and snakes. They fatten themselves up in preparation for hibernation. They'll find a nice burrow or built a nest in leaves or compost heaps. In Europe, they generally hibernate by October or November and become active again in March to mid-April once temperatures reach over 15 degrees.

JURASSIC STILL LIFE

This beautiful block, an ancient Still Life of the Jurassic (Callovian) hails from outcrops near Anwil, a municipality in the district of Sissach in the canton of Basel-Country in Switzerland.

It is a tremendous block showing the fauna from that time. Ammonites and Trigonia are clustered together. This specimen was found and prepared by the talented Tim Haye. Tim made the find during his inspection of a 2014 excavation through the Bern and Basel Museums.

PALEONTOLOGIE FRANCAISE

Paléontologie Française: Alcide d'Orbigny

L'un des grands classiques, Paléontologie Française: Zoologique Et Géologique de Tous les Animaux Mollusques Et Rayonnés Fossiles de France, Comprenant Leur Application A la Reconnaissance des Couches; Terrains Crétacés, Supplément. Voici une citation de cette édition:

"Eepl. Des fig. Pl. 4, fig. 4, cône alvéolaire de grandeur naturelle, vu de profil; a la tige: la partie ombrée est ce qu'on connaît en nature, le reste est supposé fig.

Le même, vu en dessus; fig. 3, godet terminal, supposé d'après les lignes d'accroissement; fig. 4, coquille entière, supposée d'après les lignes d'accroissement marquées sur le cône alvéolaire; fig. 5, la figure 2 grossie, la partie non ombrée supposée; fig. 6, la figure grossie; et, partie supposée; b, partie positive; fig. 7, cône alvéolai're vu en dessus, avec son siphon ventre, de ma collection."

PRIMITIVE PTERASPIDOMORPHS

The oldest and most primitive pteraspidomorphs were the Astraspida and the Arandaspida.

They evolved in shallow equatorial seas, as a large diverse and widespread group of armoured, jawless fishes: the Pteraspidomorphi. The first of three groups of ostracoderms.

The Pteraspidomorphi are divided into three major groups: the Astraspida, Arandaspida and the Heterostraci. You'll notice that their taxon names contain 'aspid', which means shield. This is because these early fishes and many of the Pteraspidomorphi possessed large plates of dermal bone at the anterior end of their bodies. This dermal armour was very common in early vertebrates, but it was lost in their descendants.

Arandaspida is represented by two well-known genera: Sacabampaspis, from South America and Arandaspis from Australia. Arandaspis have large, simple, dorsal and ventral head shields. Their bodies were fusiform, which means they were shaped sort of like a spindle, fat in the middle and tapering at both ends. Picture a sausage that is a bit wider near the centre with a crisp outer shell.

Photo by Nobu Tamura (http://spinops.blogspot.com) - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=19460450

JUVENILE HAMITES SUBROTUNDUS

A tremendously delicate juvenile Hamites subrotundus (J. Sowerby 1814) from Upper Albian outcrops in Mallorca, the largest of the Spanish Balearic Island in the Mediterranean. It is famous for its limestone mountains and Roman and Moorish remains. As you can see here, it is also home to some rather nice fossils including this specimen of Hamites subrotundus.

While H. subrotundus is generally a Middle Albian species, this specimen was found in the lower part of Upper Albian in the Cristatum zone by José Juárez Ruiz. José had to piece this lovely together from seven fragments. His labour of love was worth the effort. The final piece is sheer perfection and a beautiful specimen approximately 2.5 cm long.

Mallorca and the other Balearic Islands are geologically an extension of the Betic Cordillera of Andalusia. They are made up of sediments deposited in the Tethys Sea during the Mesozoic.

Exploring the islands, you can collect from deposits from the Triassic, Cretaceous, Jurassic, and Neogene periods. The limestone outcrops contain many foraminifers of the species Globigerina.

We also see lovely examples of Hamites (Hamites) subrotundus in the Euhoplites loricatus zone; Euhoplites meandrinus subzone from the Middle Albian (Lower Gault) of Folkestone, Kent, UK. Photo, preparation and in the collection of the deeply awesome José Juárez Ruiz. Wright C. W. 1996. Treatise on Invertebrate Paleontology (Part L Mollusca 4 Revised) Volume 4: Cretaceous Ammonoidea