Sunday, January 8, 2023

Snapshots from holiday fieldwork - Purisima Formation, northern California

 Normally I make these sorts of posts on twitter and facebook as occasional photos with captions, but they're easy blog posts to make - and I ought to just get back in the habit of posting more regularly like this. I made it out to California to visit family just before the holidays, and did a few field trips out along the coast - which, combined with trips to the Monterey Bay Aquarium and California Academy of Sciences with my mom, made for a very busy trip! These are photos from several different Purisima Formation localities from three different half days of fieldwork, in approximate order.


A large, tabular fragment of the Santa Cruz Mudstone that had been eroded and reworked into the basal bioturbated diatomites of the Purisima Formation. There are some small bivalve borings on this fragment; this, and the considerably more indurated condition relative to surrounding Purisima matrix is some of the evidence that the Santa Cruz Mudstone was already lithified by the time the Purisima was deposited - shockingly fast, since the minimum age of the older unit is about 7.5 Ma and the maximum age of the Purisima here is 6.9 Ma.

 
A potato-shaped bone! Looks like a mysticete whale bulla. Found in the lower 15 cm of the Purisima Formation. 


After a few taps with the chisel, it's pretty clearly a nearly complete tympanic bulla of a balaenopterid whale - balaenopterids are humpbacks/fin/blue/minke whales.
 

And it's out - the sigmoid process broke off in a second piece but I recovered it as the hole began to fill with a slurry of mud and saltwater - and it stuck right back in. Close to 100% complete; collecting right above the formation contact is challenging since the bullae tend to rest right on top of the Santa Cruz Mudstone, which is indurated, and bullae are highly susceptible to fracturing - as a result, they come out in pieces unless you can carefully pop off a big chunk of matrix. This one was fortunately at least 10 cm above the base so I had quite a better margin. I'll post pics once I get this prepped out.

 


A frustrating jumble of ribs and vertebrae of a small dolphin. I spotted a small skull here in 2013 while visiting from California and showed a colleague where it was in the hopes that they could collect it, but they never bothered, and it was completely eroded away by the time I finished up my Ph.D. in 2015. This is less than a meter away and I suspect it's the same specimen. A bit of a shame.

 


A great example of pholad clam borings - ichnogenus
Gastrochaenolites - in a chunk of Purisima Formation diatomite! There's even a fragment of a piddock clam above my thumb. 


Somebody's braincase or skull roof - not sure whose yet. It *seems* hollow, which would suggest bird - though there are no salt glands. If the hollowness is just apparent from staining along the fracture, then this would more likely be the frontals from some kind of fish. Either way, new diagnostic record for this assemblage as I've not seen this morphology before in the Purisima!


 I found a dauntingly large baleen whale skull near the base of the section of one locality - it's not too far from the nearest parking lot, but it would be a 200-300 lb plaster jacket. I'm not sure how much of it will have survived this latest thrashing from the incredible suite of atmospheric river storms the Northern California coast has received over the past week.


 Here's the photo annotated and reversed shown side by side with the braincase of the early diverging balaenopterid whale
Marzanoptera tersillae: this specimen is very likely something like Parabalaenoptera or "Cetotheriophanes".

 


 Ravens are a regular sight out on the coast these days.

 


 A thoracic vertebra from a large dolphin or small baleen whale about 15 feet up in the roof of a sea cave - probably been eroding out for a year or more.

 


This section of the Purisima Formation has a number of large-scale trace fossils, some of which can be a couple meters wide, called
Teichichnus pescaderoensis - basically known from the deeper water, middle shelf facies of the Purisima as well as the somewhat younger Rio Dell Formation of Humboldt County.


 Some smaller
Teichichnus pescaderoensis a little distance away.


 One of several phosphatic bonebeds in the Purisima Formation - I routinely check these, clast by clast, to see if any teeth, earbones, or other diagnostic specimens are eroding out. No such luck at this location this time.


A tiny little anemone in a small tidepool - I think this is an aggregating anemone, Anthopleura elegantissima.
 

A strand of giant kelp, Macrocystis pyrifera. I'm devastated that there's no kelp here in the Carolinas.

A bunch more aggregating anemones in a small Purisima tidepool - Anthopleura elegantissima.


 
 More anemones! These can be differentiated from the giant green anemones based on their uniformly small size (derived from clonal reproduction) and the cotton-candy pink color of the tentacle tips.
 
 Better luck! This is the rostral spine of a sawshark, Pristophorus - the third I've collected from this locality. These specimens are amongst the youngest sawshark specimens from the eastern North Pacific, where they are now extirpated.

I used to ignore crustacean remains (when I was a dumbass graduate student) but now am keenly aware that the crustacean fossil assemblage is both poorly known from the Purisima Formation and barely published, unlike the massive mollusk assemblage. This appears to be a small cancrid crab, perhaps Cancer or Metacarcinus, in a phosphatic nodule - you can see the right claw there with the chela and dactyl.


 Invertebrate burrows cross-cutting ash beds in the Purisima. Beautiful ichnology thanks to the high contrast in the sediment color - normally everything is churned up with nearly invisible burrow boundaries.


 No visit to this locality is complete without paying my respects to the hole I dug when I was 19 doing my first whale dig - there used to be a sand dune here, but that eroded away in fall 2005 just a few months later. The cliff has slowly eroded back by about 30-50 cm. The skull was eventually described as the holotype of
Balaenoptera bertae - the first species I ever named.


 
Tresus pajaroanus, one of our California Pliocene index fossils - an extinct relative of the Pacific gaper clam, Tresus nuttalli. Modern Tresus generally inhabits sandy and gravelly bottoms, though most of the Tresus pajaroanus fossils I've found seem to be in middle shelf settings (e.g. highly bioturbated silty sandstones). This was probably a choice meal for extinct temperate latitude walruses (stay tuned).


 One of the larger specimens I collected from the Purisima this trip - I thought it was a walrus rostrum at first, but now I admittedly have no clue what the hell it is. I'll have to prep it out next week.


 A small patch reef of the extinct slipper shell
Crepidula princeps - uncommon in the Purisima, but most commonly found in middle shelf facies.

 

Mmmm, who's hungry? A sperm whale carcass we came across.


 Occasionally you find nice little pebbles of opal out on the coast.

 


I found a number of stranded ochre stars,
Pisaster ochraceus - all of them were alive, and all were tossed back into the surf. I've never seen them out there before - and it was nice seeing so many without any evidence of sea star wasting disease. I did some tidepooling while out there and saw more Pisaster than I have since before the wasting disease outbreak began, giving me some real hope for our sea star populations.This one is unusually plump with short arms.



 A rare murex type shell - Muricidae - perhaps the genus
Forreria according to prior communication with Chuck Powell. I collected this one - any potentially age informative mollusk gets collected.

Whale skull #2 - this one is a bit further away, a bit of a hike, but it's also fun-sized - a little Herpetocetus braincase! Everything from the middle of the orbits is missing, but it should have a fantastic vertex even if the earbones are gone (periotics may be present). I left this one in place and we'll return to excavate it this summer.

Hopefully now you can see it - and if not, there's a marked up version below.

 


Not only is there a braincase, but the posterior end of one of the mandibles, and some ribs! Also, it's preserved within a scallop shellbed, so some of these scallops will hopefully prep out nicely. Also, there's a good chance of digging down into the beach sand and recovering more of the skull if it was also encased in a concretion as there's a conveniently located fissure in the rock that it likely fell right into.

Back to more freshly dead stuff. On the second day, the tail flukes of our stinky whale friend were above the water - about 3 meters apart. I was unsure if this was a fin whale or not - absolutely not a humpback owing to the smooth edge, and way too big for a minke whale. Other possibilities included a smallish blue whale or sei whale.


 However, finding the mandible with a couple of teeth in situ made this identification extremely easy - sperm whale,
Physeter macrocephalus.


 A particularly enormous sea nettle (
Chrysaora fuscescens) I saw - easily about 50-60 cm across. The individuals you see in exhibits like at the Monterey Bay Aquarium and California Academy of Sciences are small, young individuals about 20-30 cm in bell diameter - apparently these can reach monstrous sizes of a meter in bell diameter! I had no idea. When I saw this I questioned if I had found something like a lion's mane jelly, but no, a monster sea nettle!


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