Patterns & Processes in Rockfall Dynamics from 1977-2022

 

The author in about 1977.  My dog Blackie in the foreground.

Since 1977 when I was 17 I have been fascinated by the dynamic nature of our coast here along the Monterey Bay.  I can never go down to the same shore twice; it’s in constant flux, never the same as it was the day before.  One of the things that I have been tracking as a paleontologist here are the rockfalls that are continually happening as a coastal erosional process.  These rockfalls are singularly amazing, not only in

Capitola Beach looking toward New Brighton, early 1900's and 2019.

their size and scope, but in the history of our bay that they reveal.  With each new fall, like turning the pages of a book, new information comes to light and a more complete picture of the history of our bay begins to form in my mind.  This process is a decadal revelation; only imaginable over long periods of time, with emergent information coming to light in the longer scale that is not visible from year to year.  Not year-to-

The scale of some of these rockfalls is immense.  Here is Susan for perspective.

year; but more expansive time over 10-, 20-, 30-, and 40-years that allows one to understand geological time, Deep Time, better.  With each turn of the page, new and varied creatures are revealed that were not known before and more details of the ancient physical oceanography of the California coast emerges with each new strata set that comes to the light of day.  Interacting with a single place over a large expanse

My dog Blackie and I taking a break from prospecting, The Point, 1980.

of time such as this can engage one in processes that are not visible in the day to day.  There is a larger periodicity of non-random dynamic processes that overlies a place such as this.  Some of those processes present themselves to me, others may only be inferred over even larger expanses of time, not known to a single life span.  I will end with a quote from one of my favorite authors, Pulitzer Prize winning Wallace Stegner

Rockfall 10.20 is a series of interconnected and developmentally related rockfalls, 2020.

who has written some of my most comforting literature on the American west.  I came to know Wallace, or rather his writing, through my father, who I did not really know at all in the sense of “father” since he past away when I was 5.  From a longing to know who my father was, I was introduced to Wallace, since my father and Wallace

grew up in the same small Canadian town together, Eastend, in the early 1900’s.  In reading the words of Stegner it allowed me to feel close to the father I never knew, and at the same time allowed me to learn an appreciation for a sense of place.  This is a quote from one of Wallace’s last essays, the year before he died at age 84; from “The

Sense of Place” by Wallace Stegner. Copyright 1992 by Wallace Stegner. Reprinted by permission of Random House, Inc. “So I must believe that, at least to human perception, a place is not a place until people have been born in it, have grown up in it, lived in it, known it, died in it – have both experienced and shaped it, as individuals, families, neighborhoods, and communities, over more than one generation. Some are born in their place, some find it, some realize after long searching that the place they left is the one they have been searching for. But whatever their relation to it, it is made a place only by slow accrual, like a coral reef.”  I hope you all have a strong sense of place, wherever that may be, however diversified, however tangible or conceptual. In this particular place on Earth I am comforted, because it recalls the work of Wallace Stegner, who in turn certainly knew my father, and by such circuitous routes I, too, can know my father.

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Olivella's graveyard at Pandora's Cave!

Here is Olivella's Graveyard (now referred to the genus Callianax) at Pandora's Cave, New Brighton State Beach; the first shell bed unconformably overlying the finer sandstone layer immediately below it.  One can see here bivalves such as Leukoma and Macoma, a naticid, perhaps Natica clausa, and the Nassariids Demondia californicus and Nassarius.  Portions of this shell layer, which does not stretch continuously for the entire length of the section and is thus more aptly referred to as a Lag or Shell Bed or Lens, consists partly of concreted shell blobs and loosely concentrated shells in which the gastropods are preserved mostly whole and the bivalves are predominantly broken prior to burial.  Olivella's Graveyard represents a moderately shallow water (27-46m) storm deposit and is one of many dozens of examples of "missing time", or  unconformities, in the evolutionary record of our Monterey Bay where once-existing layers have been eroded away by storms during the Pliocene Period about 3 million years ago, never to be seen again.

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Life's Perfect Circle...

 

I am happy to share that I’m adding a new position as Paleontology Collections Advisor at the Santa Cruz Museum of Natural History to my schedule! I officially began my career as a paleontologist with the museum 46 years ago now, in 1976 when I was 16. It brings me unparalleled joy to now be working with the museum once again, completing my life's circle with the original institution that I began with all those years ago. https://www.santacruzmuseum.org/

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“Final Extraction, How-To with Frenamya”

 

The *last* stage of fossil preparation typically ends with extracting it from the block of rock that it was removed with, shown here with a 4-5 million year old clam

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New record of a previously unknown species from the Pliocene of Monterey Bay!

WY890.1: Turcica brevis was described from the the Pliocene of the Central Valley but this is the first record from Monterey Bay! .

 

“An Ancient Skate of Monterey Bay”

 

This is WT744, the *upper jaw*, or palatoquadrate, from the skull of a 2-3 million year old skate, related to stingrays, from the ancient Monterey Bay. Its scientific name is Raja sp cf. R. binoculata. It was discovered in one of the now well-known and most favorite layers, or shell beds, in the upper part of the Purisima Formation of Santa Cruz, CA. The other creatures that this skate was preserved alongside of include Princess Slipper snails (Grandicrepidula princeps), Arc Clams (Anadara trilineata), Giant Barnacles (Balanus aff. B. proxinubilus), and many others, and all represent a nearshore environment for this creature. In point of fact, when Chaco and Yoshi and I are out in the water on the modern reef here we can still disturb living skates resting on the bottom; they then gently flap their flippers up into the floating kelp fronds and it’s always an exciting meeting for all of us.

The rock that it came from had what we call “rip clasts” in it: chunks of angular mudstone that were broken off, or ripped, from the layer of mudstone below it during an erosional event, or regression, representing a period where there was a lowering of sea level. We have now mapped several dozen of these erosional events, called unconformities, preserved in our study area. All together they represent the dynamic geological history of our bay, itself mirroring the dynamic changes happening Globally over deep time and thus influencing and creating a dynamic biological evolutionary history as a result.

This upper jaw is not actually bone, but rather the cartilage precursor of bone found in all sharks, skates, and rays. Being soft rather than hard like bone, cartilage is less likely to be preserved in the fossil record and more rare. In fact, body cartilage of sharks, skates, and rays is even rarer and not found here at all as far as I know; presumably because mouth cartilage had to be slightly more calcified and hard structurally to do its job, and thus preserved more commonly. You will notice in the beginning of the video the hexagonal pattern of the fossilized jaw tissue that is a key feature of fossilized cartilage.

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“An Example of Remarkably Well-Preserved fossils”

 

Sometimes creatures are preserved astonishingly well that it boggles the mind!  From Dinosaur skin impressions, to frozen mammoths and glass insect fossils, the world of fossil preservation is incredibly bewildering!  And such was the case with the whole, unfilled, baby Arc Clams, Anadara trilineata, shown here.  Preserved so well, without a gap between the two valves of the shell, no ocean sediment filled into the inner area of the shell and the shells are “empty”.  These shells were likely moved very little from their original burial spot, so as to preserve both valves together.  Almost universally, fossil clams are discovered with sediment-filled interiors, meaning they were moved around on the bottom of the sea floor before being buried.  Even clams that are preserved “in-situ” or in life-position are usually preserved with sediment filling inside the two valves, making these clams extremely exceptionally, uber rare.  Additionally, almost universally the surrounding rock exerts a degree of pressure on a fossil and can even break, squish, or completely pulverize the organism.  

These Arc Clams seem to have avoided that.  Clams can live either in the sediment, or infaunal, or on the sediment, or epifaunal, at the bottom of the ocean; the two most common lifestyles–there are others.  This particular species lived just below the sediment-water interface.  Reconstructing the ancient lifestyle of this clam was the focus of one of my earliest research papers as a young paleontologist at U.C. Berkeley back in 1984.  I was able to use the commensal marine Polychaete worm Polydora, which leaves a scar on the shell of Anadara, as a proxy measure to reconstruct the lifestyle orientation of these ancient fossils from 4 million years ago.  Commensalism is when two creatures share an ecological relationship that neither harms (parasitism) nor benefits (symbiosis) the two species involved.  The link to the manuscript, and some of the diagrams used, appear below.

Thompson, W., 1984.  Anadara from the Purisima Formation along the Monterey Bay

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