We have drilled a second core through the ice to bedrock, and are done at our first site. Unfortunately, the helicopter that we need to move the heavy pieces to our second planned spot is down for regular maintenance until next Monday, June 21. That means the team must wait it out at the relatively sheltered “saddle camp” until then.
Here are two spectacular pictures, taken from the helicopter, of the landscape we are up against.
Yesterday we completed our first ice core at the Northwall Firn Glacier, down to bedrock, penetrating 30 meters through the glacier, until we hit bottom. The ice seems to contain visible layers all the way down–a sign that yearly accumulations have been preserved, instead of melding into each other. This means we should be able to extract a good climate record from this ice. There also appears to be some organic matter near the bottom, which could be carbon-14 dated to establish age.
The first 23 meters of core were immediately slung out by helicopter, stored in a special box, and delivered to a freezer in Tembagapura, the nearest town down the mountain.
Today, the team completed another 18 meters of coring in a second location near to the first core. (We drill two cores near each other so that we have duplicates with which to verify our data.) We hope to fly more ice out tomorrow, pending good weather.
Photos here courtesy of David Christenson/Freeport McMoRan.
The Crotone Basin accumulated sediments for nine million years before the forearc uplifted above sea level. Each layer of sand, clay, and conglomerate in the basin contains information about the environment at the time that layer was deposited.
About six million years ago, halite and gypsum were deposited in the Crotone Basin. Geologists refer to both rocks as evaporites. All bodies of water on the Earth’s surface contain dissolved ions, most commonly sodium (Na+), chloride (Cl-), magnesium (Mg2+), calcium (Ca2+), and sulfides (SO42-). When water starts to evaporate, the dissolved ions bond together and precipitate out of the solution, forming evaporites (halite = NaCl, salt; gypsum = CaMg2SO4). Most commonly we find evaporites in deserts environments that sometimes receive influxes of water, like the Great Salt Lake in Utah. Since halite and gypsum are found in the Crotone Basin, we think that water must have evaporated from the basin about six million years ago.
As it turns out, evaporite deposits are found across the Mediterranean Sea during the same time period. Drill cores have turned up three kilometers of evaporites in some areas. To crystallize this much salt over such a wide area, geologists think that the entire Mediterranean Sea must have evaporated–an event called the Mediterranean Salinity Crisis (or Messinian Salinity Crisis) which lasted from 5.96 million years ago to 5.33 million years ago.
The Mediterranean Sea is located in the desert latitudes, where evaporation exceeds precipitation. The water level remains constant because water from the Atlantic Ocean enters the basin through the Straits of Gibralter.
But this wasn’t always the case. During the Messinian, a global sea level drop and local tectonics caused the land at the Straits to rise, cutting off the Mediterranean from the ocean. Since evaporation was so high, the water level dropped, concentrating the dissolved ions, and crystallizing evaporites; just like the Dead Sea in Israel, which crystallizes halite on its seafloor. Halfway through the Salinity Crisis, the four kilometers of water that filled the Mediterranean disappeared. A vast, desert basin is all that remained.
Nano and I are studying Messinian river deposits. Before and after the Salinity Crisis, rivers carried sediments from the mountains west of the basin. During the Messinian, however, something different happened.
The rivers seem to have flowed from east to west, exactly opposite from today. They may also have carried chert, a rock made of silica and formed only within deep ocean basins. Chert is not found in the mountains to the west, but is found offshore below current sea level. This suggests there may have been mountains east of the Crotone Basin during the Salinity Crisis.
So, how did the mountains form and where did they go? The water in the Mediterranean Sea pushes down on and depresses the crust, much as glaciers do on land. If water is removed (as it was during the Salinity Crisis), the crust rebounds. Therefore, uplift and local tectonics may have formed mountains of deep-sea rock east of Calabria. When the the Mediterranean Sea came flooding in, the mountains would have been obliterated.
With the blessing of two wonderful days of clear weather, all our equipment was moved into place this morning. The ice coring can now begin. We anticipate finishing the drill assembly today and drilling by mid-morning tomorrow at three sites on the Northwall Firn glacier: the two “domes” and the saddle, where the team will look for ice-filled crevasses with sonar while the first dome is being drilled.
All that will remain after this is the simple matter of getting the ice from this glacier back to our freezer facility in Ohio without melting. (And this is not a simple matter!)
Photos here are courtesy of Scott Hanna and David Christenson of Freeport McMoRan.
The climate of the Crotone Basin is marked by cold, wet winters and hot, dry summers. We arrived last year, on our first trip, in the middle of a six-month drought that lasted from April to September.
I love how life figures out a way to flourish. Flowers in a riverbed; Snails on a thorn bush; Spiders spinning webs in a field.
Herds of sheep and goats roam the fields of the Crotone Basin. We were hiking through these fields and met a goat herder and his dogs. Herders often share invaluable information about the land, and show us useful paths and roads through the maze of brush and thorns.
The goats are amazing creatures. They can climb trees and stand on the small branches to find tasty leaves; they are wonderfully agile.
Fences like this are found across Calabria, to protect harvests from goats, sheep, and cattle herds.
This is an example of a gate in one of these fences: just slipping the loop of wire off the top opens the gate. It’s a wonderful contraption that keeps herds in their place, but allows people to go anywhere.
Fires are a common sight in June in the Crotone Basin. After the wheat harvest (going on right now), the farmers burn their fields to resupply nutrients and prevent wildfires during the dry season.
Near the town of Casabona, farmers have been burning the grasslands surrounding the town to stave off wildfires later in the season.
Nano and I usually take a packed lunch of panini (sandwiches) and fruit with us into the field. Around midday, we start looking for trees to shade us from the sun while we eat. Sitting by Lake Ampollino for lunch one day, Nano and I were joined by a neighboring dog that got our scraps.
Last year I was collecting a sample of sediment from a riverbed and spent the day walking up the Neto River to find a good location. When I finished, I noticed a road high on one side of the valley. I climbed to the road and found a tunnel with no lights inside. I looked to see if I could walk around it but found only a shear cliff. My options were to climb back down into the river or walk through the tunnel. So, I began walking.
Gradually, the darkness took over. I stopped about 15 meters in, when I couldn’t see my hand in front of my face, waiting for my eyes to adjust. They never did. With my hand on the wall of the tunnel, I slowly stepped forward into the smell of rainwater and sound of creatures moving around. I thought I knew darkness, but not like this. After what felt like hours, I saw a light signaling the tunnel end and practically ran. When I reached daylight, my excitement was quickly dulled. Not 20 meters away loomed a second tunnel. I thought, “Hey, if I made it through the last one, I can do this one.” Then I see the sign “Galleria: 458m”. No way! Half a kilometer long! I turn back and see a sign from the tunnel I just walked through “Galleria: 427m”. Oh. I’m glad I didn’t see that sign on the way into the first tunnel. I shrug and begin walking toward the second tunnel. But then, I hear what sounds like a huge truck coming through the tunnel behind me. For the next three minutes, car after car after car come through the tunnels. When there’s a break, I begin to walk through the second tunnel. But before long, I see the light from a car coming behind me. Several more cars pass including one that stops just ahead but continues on. Eventually, I make it out of the tunnel and a car pulls over. In Italian, the driver asks, “Where is your car? The gate closes at 5 pm. What are you doing?” I tell him “My car is on the other side of the gate, don’t worry.” He looks back at the tunnels I just walked through and says, “Your car is on the other side?” “Yes,” I say, “Don’t worry.” He gives me a skeptical look and drives off.
This year, Nano and I traveled the same road but when we turned around we found the gate shut. We were locked inside the road! Just as I was about to attempt picking a lock for the first time, a man pulled up on the other side and called his father who arrived 10 minutes later with the key.
Nano and I have arrived in the Crotone Basin, where we’re staying in a place that Italians call an “agriturismo,” which is like a bed and breakfast that also serves lunch and dinner. Our little place is unique even among agriturismos. It is called Canciumati (can-chew-ma-tea), a house with four generations living under one roof. The family rents three rooms on the first floor to tourists, visitors, and friends, that remain unoccupied most of the year. For income, the family depends on the olive grove that surrounds the property, which also supplies the olives and olive oil we’ve been relishing. Calabria’s hot, dry summers and cold, wet winters provide the perfect conditions for the trees to flourish.
Last year, Nano and I visited an agriturismo that has a 2000-year-old olive tree on its property! For the first part of our field season, Nano and I will be in the Crotone Basin in the forearc of a subduction system. Usually, the forearc is found below sea level, but in Calabria parts of the forearc are located 1200 meters above sea level. What difference does that make? I’ll put it this way: one million years ago, before Calabria began to rise, Italy did not have a toe to its boot, and only a few islands would have existed between Salerno and Sicily!
We are trying to determine how and why this uplift began. Nano and I have identified a surface that we think existed near sea level one million years ago. This surface is a geological “contact” between the granite bedrock of Calabria and a fluvial conglomerate, or river deposit, on top of it. A contact is the surface where two different types of rock are touching. Contacts can be sedimentary, related to changes in deposition (a clay bed on top of a sandstone bed) or tectonic, related to faulting. The sedimentary contact we are measuring is now high above sea level and has been eroded and dissected by rivers, so it is only present in small pieces. To map this surface, we are walking up river gorges, climbing mountains and traversing numerous goat and cow paths until we see the contact. Then we record our location with GPS (latitude, longitude, and elevation), take pictures, sketch and record interesting features and move on to find another contact.
When we put all our points on a map, we will be able to see the shape of the surface. The shape (or morphology, as geologists call it) of the surface will reveal much about how the land was uplifted: if the surface we map is now flat, then the land must have risen straight up. This is like submerging a piece of ice in water and then letting go, the ice will rise straight up to the top. If the surface we map is now tilted, then the land rose faster on one side than the other. It’s like opening a cooler. When you grab the handle and start to pull it open, the side by your hand raises high into the air while the side connected to the hinge remains close to its original starting height.
In early May, Scott Nooner and I returned to Malawi to retrieve our seismic equipment and finally lay eyes on the data recorded over the last 4 months. Picking them up was vastly easier than putting them out. In contrast to the days studying out-dated maps and driving down dirt roads looking for sites, and hours of hard labor under the hot African sun digging holes and constructing vaults, recovery required only minutes at each site to shut down the equipment and safely stow it in plastic cases in the back of our rented truck. It took us about a day to recover all the equipment that we spent a week installing. Since we recovered the seismic equipment so quickly, we had time to collect new GPS data, too.
Although retrieving the seismic equipment proved easy, transporting numerous 50-lb boxes from one side of the world to the other is not trivial, as we discovered during the deployment. Our hasty departure in January prevented us from obtaining US customs documentation that would have simplified the export/import process, and our seismic equipment had to return from Malawi the way it came in – as checked luggage. We wrested ten ~50-lb pieces of baggage to the check-in counter at the Lilongwe airport, and handed over all of our remaining dollars plus a fistful of Malawi Kwacha for excess baggage fees. Checking in for each subsequent leg of the trip, we braced ourselves to part with more money. Even for the few pieces of equipment that we transported back to the US via a commercial shipper, we faced interesting challenges. The Karonga DHL office lacks a scale, so shipping agents and our Geological Survey colleagues made competing guesses as to the weight of our boxes and compromised on the average when charging us shipping fees.
Far and away the best part of recovering instruments is the chance to take a first look at the data, and our new dataset from Malawi did not disappoint. While sipping complementary wine on the long flight from Johannesburg to Atlanta, I perused the recordings from our seismometers. While (thankfully) there were no recurrences of the damaging events from December, to my delight I saw that we have recorded a remarkably persistent series of aftershocks. For our purposes, the more aftershocks, the merrier! We plan to determine the location of each aftershock to map out the structures below Earth’s surface that caused the large sequence of earthquakes in December. Stay tuned…..
While installing our seismic network in Malawi, we interacted with everyone from scientists to schoolteachers, and journalists to villagers. The opportunity to provide information and education to Malawians has been the most rewarding aspect of our effort. We trained local scientists and technicians on seismic equipment and data analysis, and educated the public on earthquakes and earthquake monitoring both in person and via media interviews. The Malawi Geological Survey Department (MGSD) prompted our visit by requesting assistance in monitoring aftershocks, and we hope that this temporary seismic deployment will empower them to obtain resources and training for a permanent seismic network.
Because we deployed our seismic stations near schools, clinics and other centers of village life, we met a wide spectrum of Malawians. Everyone we spoke with expressed interest in our undertaking and wanted to know more about the chindindindis (earthquakes in Tumbuka). In the village of Mpata, 5 miles west of Karonga, a crowd gathered around a laptop balanced on the hood of our 4×4 as Jim showed them aftershocks in newly downloaded data; the audience peppered him with pertinent questions about the East African Rift and earthquakes beneath Lake Malawi. Curious policeman looked on as I retrieved seismic records from a station positioned near a checkpoint ~10 miles north of Karonga, inquiring when and where the next earthquake would occur. Science teachers in Mlare helped us install a station near their school and received an impromptu lesson in plate tectonics and seismology.
Journalists from newspapers, radio stations and national TV programs also interviewed us during our visit, which allowed us to communicate with a larger audience about possible causes of the earthquakes and the benefits of monitoring them.
We worked side by side with scientists and technicians from the MGSD every day of our visit. They taught us local geology, local customs, and local language, and made our joint endeavor possible by facilitating contacts with national and regional officials. In return, we brought them seismic monitoring equipment, helped them deploy it, and taught them new techniques for analyzing the resulting data. Although the MGSD is charged with monitoring earthquakes within the Malawi rift valley, their efforts are severely hampered by paucity of data and lack of training. Only two seismic stations exist in Malawi (provided by Africa Array), and university-level courses in seismology are almost non-existent. The data and training of MGSD employees provided by our temporary deployment following the Karonga earthquakes will help mitigate these problems in the short term; we hope that this experience will equip the MGSD with the ammunition to argue for more national and international resources for seismic monitoring in Malawi over the longer term.
Mike and I head out today for Cerro Gorra, leaving Jay and Barbara at Lago Cardiel to finish the stratigraphy. What wonderful people; I am so grateful to have had the opportunity to do field work with them.
We drive to Lago Argentino, where Mike is meeting a new research team for a separate project. We have just enough time to stop at the Perito Moreno glacier in Los Glaciares National Park. The only glaciers I’ve seen before have been quiet and still but this one cracks and grumbles as we watch. The sound of breaking ice echoes through the valley; the noise seems outsized for the quantity of ice.
I still can’t imagine how ice like this once coursed through valleys to blanket huge parts of Patagonia. The glacier I’m looking at is enormous; a tourist boat near its base looks like a wind-up-toy. I’m trying to comprehend how much snow would be needed to make this glacier grow thicker and hundreds of miles longer. It’s a lot easier to understand how a glacier can grind up mountains to make dust.
Anyway, I’m back in Rio Gallegos safe and sound. Tomorrow I return our rental car and get back on a plane for Buenos Aires and then New York. Mike has our samples in a bag; he’s going to FedEx them back to the States in a cardboard box. Hopefully they’ll arrive intact. This has been an incredible field experience, and I’m incredibly thankful to Gisela and Mike for arranging the trip. I hope we get some good data!
Last night I made dinner. I’ve never cooked over an open fire—only on a tiny gas-powered stove on backpacking trips–but Jay and Barbara have been teaching me how. Dinner was edible. Jay built the fire last night, but tonight I’m hoping to do the whole thing start to finish. Wish me luck.
We left Cerro Gorra this morning after spending all of yesterday taking dust samples and studying the Cerro’s stratigraphy. We were looking for ancient dust stuck in lake sediments. Dust floating in the air falls onto the lake and sinks to the bottom, where it gets trapped in mud. Normally, we’d have to drill a core into the bottom of the lake to get at these sediments, but drilling takes time and money. Lucky for us, the local climate and geology let us sample these sediments without drilling.
The lake’s water level has fallen over the last 20,000 years, leaving its ancient bottom sediments exposed. When a stream cuts through the layers of sediment, you can see the whole depositional record of the lake. We stood in the stream bed looking at its banks, and the layers of sediment deposited as the lake waxed and waned.
“Look,” says Jay, pointing to cobble layer between the sediments, “There’s an old shoreline with shells in it!” A few inches above the cobble layer was a layer of organic material. We hacked out chunks of sediment from those layers with our trowels and stuck them in Ziploc bags. Jay added shells from the layers to date their age. Once the shells are dated, we can estimate the age of the sediments.
Now we continue to the other side of the lake, stopping at Rio Bayo, on the north shore. We’re just about to move on to another area with better stratigraphy when we spot shells with brownish-green markings, different from the white shells we’ve been seeing for days. Finding pigmented shells comes as a surprise, though it shouldn’t since not all shells are bleached white once the organism inside dies.
Surprise number two: we find another kind of shell, fragile and scallop-like, the size of quinoa grains that break as soon as you touch them. Surprise number three: while collecting pigmented shells, we realize there are actually two different types. They look similar until you notice the wider aperture and tighter whorls of one species, plus other variations in shape. Once we see the difference, though, it’s hard not to hit yourself over the head and say “Stupid! Of course they’re different!”
This trip reminds me how easy it is to see what you want to see. Looking more closely at a shell or shoreline is how science advances, but learning to be this observant is incredibly difficult.
Reconstructing a shoreline history takes skill. Today we’re using altimeters to establish the elevation of Lago Cardiel’s former shorelines. We also continue to look for shells to help us date the lake’s past shorelines, a task that requires strong powers of observation.
In one short stretch there might be a dime-sized snail shell almost indistinguishable from the millions of white, rounded pebbles on this ancient beach. A few meters away, we might have to readjust our eyes to search for tufa, or smoothed glass fragments (people left bottles on the shore, which wore down like sea glass). Most often, we don’t know what we’re looking for, so we shuffle around looking staring at our feet as if trying to find a lost contact lens.
Barbara, Jay’s wife, is a master at finding stuff. She spotted a piece of nacre—the shiny part of an oyster shell–about the size of a quarter. I have no idea how she picked it out from the grayish-blue rocks around it. The fragment must have come from a pretty big oyster. Could giant freshwater oysters once have lived here?
As the hunt continues, Mike finds an oyster chunk as long as a stick of gum, and I discover a saucer-sized fragment, and another, the size of my palm.
What are these things? I picture a filter feeder big enough to eat a flamingo. With each fragment we find, it becomes obvious that these oysters probably originated from the sea. Jay says we’re on the edge of a drainage delta, so these oyster fragments may have been carried downstream from their fossil beds and deposited here.
These bivalves also appear to be ancient. Mike remembers finding similar oysters several years ago near a rock outcropping at least as old as the Miocene, the geological period that spanned from 23 to 5 million years ago.
Such is the nature of fieldwork: a constant gathering, synthesizing and imagining of information. How can I build a story about this place that incorporates all of the latest clues?
Today we’re looking for live snails so that we can measure how much carbon-14 they are incorporating into their calcite shells. Carbon-14 is a rare isotope of carbon that decays radioactively–organisms incorporate carbon-14 into their tissues and shells while they are alive, and as soon as they die, the carbon-14 starts decaying away. We can estimate how much carbon-14 there should have been in a shell, for instance, when the organism died, and we can measure how much is left: the difference tells us how long the shell has had to decay its carbon-14 away. Different organisms incorporate carbon differently, though, and it’s useful to get a modern sample (e.g. one that is alive, using carbon, when we find it) to compare to the older samples we find. The air is hot and still and the tufa coating on the rocks around us reflecs the sunlight, making the day feel hotter and brighter. We stalk snails in tiny inlets and pools, sifting through pebbles and combing through thick algae that will eventually decompose into tufa. We squat by the side of the lake for at least an hour but don’t see any signs of life, not even zooplankton. We can see flamingoes standing in the water at a distance, and other birds wheeling in the sky but what are they eating? Perhaps there are fish somewhere in this giant lake, but at its shoreline, all I can see is algae.
Later on, in the afternoon, we explore a stream cut that Jay had noticed, called Cerro Gorra. The stream had cut cleanly through former lake shores, leaving beautiful stratigraphic sections. We will spend time here in the next few days studying the layers and looking for shells.
A rapid technical response to the damaging earthquakes in Malawi produces both humanitarian and scientific benefits, and we hoped that both scientific and international assistance agencies would support our effort. Our seismic field effort serves two purposes: (1) to provide badly needed seismic equipment and technical training to the Malawi Geological Survey department (MGSD); and (2) to obtain unique data from very close to the earthquake sources to develop a better scientific understanding of faulting in the East African Rift. Funding has proven difficult, however, and our experience suggests that a technical component to earthquake response often falls through the cracks of the broader relief effort.
The Malawi earthquake sequence spawned a modest international response by several organizations with complementary and overlapping goals. The US Agency for International Development (USAID), through the Office of Foreign Disaster Relief (OFDA), and international organizations (e.g., Red Cross) provided direct humanitarian response: food, water, shelter, and other necessities for the displaced people of Karonga. Two scientists from the US Geological Survey (USGS), with support from USAID, provided a post-earthquake assessment based on field observations of damage and faulting, which constituted the official US government technical response.
Our technical response parallels those efforts, and is typical for the US academic community; individual scientists with existing contacts in and working knowledge of the effected region provide seismological field equipment, analysis, and training. Responding to the earthquakes in a timely manner required an almost instantaneous commitment on our part. Within two days after the largest event, IRIS had mobilized instruments and the funding necessary to ship them to the field. Lamont-Doherty Earth Observatory (LDEO) and the Earth Institute (EI), both at Columbia University, promised to “backstop” our effort – in other words, cover our travel and field expenses while we sought external funding for our effort. Both have strong and long-standing commitments to mitigating earthquakes, hazards, and human suffering worldwide, including in East Africa and Malawi. The project would have immediately stalled without this support.
With the LDEO and EI backstop in hand, we sought external funds from the National Science Foundation (NSF) and USAID, highlighting the unique scientific and outreach opportunities offered by a rapid response to these earthquakes (read our proposal here). USAID characterized the activity as too scientific to be in their purview and declined to fund us. NSF acknowledged a modest scientific benefit, but they described the effort as primarily a humanitarian and outreach response. While NSF agreed to provide some support, the amount available for such short-turnaround projects (via the RAPID program) is very small – enough only to return and recover our instruments.
Technical responses such as this one provide scientific and humanitarian benefits alike and strongly complement the larger response effort. The breadth of the impact should increase their fundability – more bang for the buck. But because of the splintered nature of the US response and funding mechanisms, this breadth can be a detriment to obtaining funding – too scientific to be humanitarian, but too humanitarian to be scientific. In our case, we overcame this quandary only with the strong financial support of our home institution. How many technical response efforts never get off the ground because of this funding uncertainty?
Lago Cardiel is much larger than I expected; we can barely see the opposite shore. This side is ringed by low hills and opens up like an apron, broad and gently sloping. As soon as we come through the hills, we notice well-defined former shorelines, which look like soap residue rings around a bathtub.
Shorelines make great natural roads, just as glacial outwash fields are apparently well-suited for airport runways because they are flat and drain well. JFK is built on a glacial outwash plain, Mike tells me.
We drive along until we spot an outcropping of basalt rock and carbonate tufa. Littered over this surface are the tiny white shells of dead snails which once lived near the shore. Their presence indicates that the lake shoreline must have been this high at some point. The shells must have been left when the lake receded.
The lake has grown and shrunk many times over the past 20,000 years. When it grows, it leaves behind a “bathtub ring” of residue around its edge: pebbles smoothed by wave action, carbonate tufas, the remnants of the things that lived at the shore. There are at least three distinct bathtub rings (each of which represents a time when the lake surface was higher than it is today) that we can see in a Google Maps printout we’ve been carrying around. But Scott Stine, a researcher who did his Ph.D thesis on Lago Cardiel, has identified other shorelines beyond the three we can see now.
To date these shorelines, Stine used the carbon-14 dating method on organic material linked to various shorelines to determine their age. His data suggested that the highest shorelines occurred about 10,000 years ago, at a time when the rest of South America was hot and dry. That would mean that this lake got really, really huge, mainly because of rainfall. Jay and Mike are unsure this happened, and think that instead the high shorelines may be older than everyone thinks. Maybe the lake was big about 20,000 years ago—the peak of the last ice age? Dating the shells and tufas again may resolve this question. So we’re looking for the highest shorelines, which is trickier than it might seem. We also have to find good material to date. That’s why Jay nearly jumped up and down with glee when we started finding shells. They’re great for doing carbon-14 analysis since we know the fossils once lived in the former lake. Jay and Mike call out questions as they search. Maybe this is the 55 meter shoreline? Are there other calcifying organisms that lived in the lake?
For most of our drive, I stare out the window and ask Mike questions: “Is that a glacial moraine?” and “How tall were the Andes originally?” and “Why are those sediments white?” He can respond to a stunning number of these questions. I love being around field geologists; the way they make sense out of visual clues that most of us overlook is both mysterious and fascinating.
We drive through a wide, deep canyon, with clearly exposed sedimentary sequences. “What are those dark layers?” I ask, and Mike explains that we’re driving through a Cretaceous sedimentary sequence. Some layers may be siltstone or shale-like deposits laid down when this area was submerged under a shallow sea.
Suddenly, Jay, who is driving ahead of us, stops his truck by the side of the canyon. “I just had to check this out,” he says, pulling his rock hammer out of the truck bed. “Look at this place!” Those dark layers are paleosols, or old layers of organic-rich soils preserved under other sediment, he tells us. And there’s siltstone, he points out. Barbara, his wife, tells us that they’ve found tons of fossils in similar siltstone beds on former trips.
A little further on we see thick, wind-deposited sand beds marked by a layer of volcanic tuff. The sand beds look like the beds forming at the surface today. I don’t know how strong the winds were when those beds were formed or how much sand and dust was in the air but the process that created them is the same that makes sand dunes today. There may have been dinosaurs stomping around and wildly different plants waving in the stiff breezes. But the winds picked up dust particles in the same way they do today. Biology tries out new body plans, reproductive systems and behaviors, and through it all, geology marches forward.