The AAPG Canada Region welcomed Rice AAPG Student Chapter for a four day guided transect through the Canadian Rockies. This trip was supported in part by funds provided by SHELL.
Dr. Clinton Tippett (Geoscience Leader), Dr. Kevin Root (Geoscience Leader) and Dr. Malcolm Ross (SHELL – Rice University)
Assistant trip leaders:
Lacey Pyle and Catherine Ross
Alana Semple, Christopher Odezulu, Jingxuan Liu, Joyeeta Bhattacharya, Maryam Nasizadeh, Nancy Zhou, Wey Yi Foo, William Farrell, Yue Yao and Zuyue Zhang
Day 1: Calgary to Lake Louise
Copithorne Ridge, McConnell Thrust at Mount Yamnuska, Lac des Arcs Region, Rundle Thrust Sheet Viewpoint (Harvey Heights), Grassi Lakes Devonian Section above Canmore, Kootenay-Fernie section, Mt. Norquay Overlook, Castle Mountain
Day 2: Lake Louise to Fernie
Lake Louise, Cambrian Facies Change, Marble Canyon, Folds in the Cambrian Chancellor Formation, Redwall Thrust, Radium Hot Pool, Sinclair Canyon, Out-of-sequence Thrusts, Columbia River Overlook, Radium, Toby Formation, Windermere Lake Area, Southern Rocky Mountain Trench, Fort Steele Area, Southern Rocky Mountain Trench, Elko Area
Day 3: Fernie to Waterton
Crowsnest Lake, Cardium Formation, Crowsnest Formation Volcanics, Frank Slide, Triangle Zone of the Outer Foothills
Day 4: Waterton to Calgary
Prince of Wales Hotel, Waterton Field, Triangle Zone structures in the Canyon of the Oldman River, Livingstone Gap, Okotoks “Big Rock” Erratic
“End of the trip group photo” at the Big Rock Erratic
From Left: Jingxuan Liu, Zuyue Zhang, Maryam Nasizadeh, Alana Semple, Catherine Ross, Joyeeta Bhattacharya, Nancy Zhou, Lacey Pyle, Wey Yi Foo, William Farrell, Christopher Odezulu, Clint Tipette, Yue Yao and Malcolm Ross. Behind the lens: Kevin Root
Blog created by:Joyeeta Bhattacharya
The Solar System of Forking Paths: Bifurcations in Planetary Evolution and the Search for Life-Bearing Planets in Our Galaxy
Lenardic A., Crowley J.W., Jellinek A.M., and Weller M.. Astrobiology. June 2016, 16(7): 551-559. doi:10.1089/ast.2015.1378.
—From Rice News…
Rice University scientists propose that life in the solar system could have been very different
If conditions had been just a little different an eon ago, there might be plentiful life on Venus and none on Earth.
The idea isn’t so far-fetched, according to a hypothesis by Rice University scientists and their colleagues who published their thoughts on life-sustaining planets, the planets’ histories and the possibility of finding more in Astrobiology this month.
The researchers maintain that minor evolutionary changes could have altered the fates of both Earth and Venus in ways that scientists may soon be able to model through observation of other solar systems, particularly ones in the process of forming, according to Rice Earth scientist Adrian Lenardic.
The paper, he said, includes “a little bit about the philosophy of science as well as the science itself, and about how we might search in the future. It’s a bit of a different spin because we haven’t actually done the work, in terms of searching for signs of life outside our solar system, yet. It’s about how we go about doing the work.”
Lenardic and his colleagues suggested that habitable planets may lie outside the “Goldilocks zone” in extra-solar systems, and that planets farther from or closer to their suns than Earth may harbor the conditions necessary for life.
Students, staff, professors, and alumni from Rice University, Department of Earth Science attended the AAPG, Annual Convention & Exhibition, Calgary 2016 from June 20th – June 23rd.
Faculty – André W. Droxler
Adjunct – Vitor Abreu, Paul M. (Mitch) Harris, Stephanie Shipp
Alumni – Vitor Abreu, Martha Lou Broussard, Gary Couples, Gulce Dinc, Hunter Lockhart, Bob Milam, Jack Neal, Stephanie Shipp, Joan Spaw, Richard Spaw, Nana Xu, and Jim Tucker
Students – Heath H. Hopson and Pankaj Khanna
The list of talks and poster presentations given by Rice are mentioned below:
- Transgressive Lag of Flat Rip-up Clasts – Substratum for Initial Growth of Upper Cambrian Large Microbial Bioherms. André W. Droxler, Heath, H. Hopson, Pankaj Khanna, Jacob, M. Proctor, Daniel J. Lehrmann, Paul (Mitch) Harris. Session – Geobiology of Carbonate Systems (SEPM)
- Investigating Upper Cambrian Microbial Reefs (Mason, Texas) – Unconventional Approach in Mapping and Quantifying their different scales. Pankaj Khanna, André W. Droxler, Heath, H. Hopson, Daniel J. Lehrmann, Paul (Mitch) Harris. Session – Unconventional Carbonate Reservoirs II (SEPM)
Poster Presentations –
- Distinct Growth Phases of an Upper Cambrian Microbial Reef Complex; Depositional Environment Indicators (James River, Mason County, Texas). Heath H. Hopson, Pankaj Khanna, Meron, Fessahaie , André W. Droxler, Paul (Mitch) Harris , Daniel J. Lehrmann. Session – Additional AAPG Student Research Poster Session II
- Uppermost Pleistocene Coralgal Reefs and Upper Cambrian Microbial Reefs: Morphologies and Sea Level-Induced Evolution (?). Pankaj Khanna, André W. Droxler, Daniel J. Lehrmann, Jeffrey Nittrouer, Paul (Mitch) Harris. Session – Additional AAPG Student Research Poster Session II
Highlights of the AAPG Annual Convention & Exhibition at Calgary –
1. Adjunct Prof. Vitor Abreu (Rice University) – Taking charge as President of SEPM 2016-17
From Left to Right – Pankaj Khanna (PhD Candidate), Adjunct Prof. Vitor Abreu, Heath H. Hopson (Masters Candidate)
2. The Rice group also met few alumni during the meeting
From Left to Right – Hunter Lockhart (Former Rice Student – current Associate Geologist at BHP Billiton), Heath H. Hopson (Masters Candidate), Prof. André W. Droxler, Gulce G. Dinc (Former Rice Student – current – Geophysicist at ION Geophysical), and Pankaj Khanna (PhD Candidate)
3. The Carbonate Research Group – Rice University
From Left to Right – Pankaj Khanna (PhD Candidate), Prof. André W. Droxler, Heath H. Hopson (Masters Candidate)
4. Dinner at an AAPG event
Prof. Bill Fischer (UT) and Martha Lou
5. SEPM meetings – Monday evening – 21st June
From Left to Right – Prof. Vitor Abreu (SEPM President) , Jack Neal (ExxonMobil), and Prof. A. W. Droxler
6. SEPM Poster session – 22nd June
Adjunct Prof. Paul M. (Mitch) Harris and Prof. A. W. Droxler
Additionally the Carbonate research group went to Canadian Rockies to visit some Cambrian Microbial outcrops as well as few other outcrops.
- On the way to Helen lake microbial outcrops – Rick Sarg (CSM) and wife Ana
From Left to Right – Prof. Rick Sarg, Ana, Heath H. Hopson (Masters Candidate), and Pankaj Khanna (PhD Candidate)
2. Helen Lake Cambrian Microbial Outcrop
3. Devonian Carbonate outcrops near Canmore, Alberta
4. Sulphur Spring, Jasper National, Alberta
5. Athabasca Glacier, Jasper National National Park
If you would like to know more about the AAPG ACE meeting, Calgary, or about the field trip the Carbonate research group went on after the meeting then kindly let me know firstname.lastname@example.org.
ESCI 546 “Advance Topic in Basin Sedimentology and Stratigraphy ” participated in a field trip to County Clare, western Ireland, from May 2nd to May 12th, 2016. The class visited sea-cliff exposures of rocks found in the Western Irish Namurian Basin (WINB), which were deposited during the Upper Carboniferous (326 Ma – 317 Ma). The deposits represent a variety of sedimentary depositional environments, including fluvial-deltaic to deep water turbidites. The rocks were later obscured by fold-thrust related deformation associated with the Variscan (Hercynian) orogeny, brought on by rift-related deformation during the breakup of Pangaea. The WINB is an ideal location to evaluate the interconnectedness of the various sedimentary environments, in particular, linking the physical processes that shape the internal stratigraphy.
The first part of the class trip included a five day “basin overview” led by Professor Jim Best of the University of Illinois at Urbana–Champaign (UIUC), who has 30 years of experience working in the WINB. During this tour, students self-organized to develop research projects for the range of depositional environments. Students were then provided three days to work among the outcrops to pursue their respective projects. On the final day, these students led the class through the outcrops, presenting their specific findings.
Professors: Jeffrey A. Nittrouer, Jim Best (UIUC)
Post-doc: Hongbo Ma
Students: Andrew Moodie, Brandee Carlson, Sam Zapp, Simon Chan, Garrett Lynch, Brian Demet, Chenliang Wu, Pulkit Singh
Visiting Student: Matthew Czapiga (UIUC)
Teaching Assistant: Tian Dong
Day 1 Loop Head Cliffs: Ross Fm. (Deep Water Turbidite)
We arrived in Shannon, Ireland, on the morning of May 3rd. In the early afternoon, after settling into our rental home in Kilkee, we visited cliff exposures of the Ross Fm. near the Loop Head lighthouse. The Ross Fm. is a sandstone unit, interpreted as deep-water turbidite fan deposits. Among the lobes are a few channel features higher in the stratigraphic section. The Ross Fm. is the thickest near the Shannon Estuary (~380 m) and thins to the north, in the general direction of paleo flow.
Day 2 Northern County Clare: Visean Fm. (Basement Limestone) and Clare Shale Fm.(Deep Water Shale)
We drove north for 2 hours from Kilkee to the south of Galway Bay at the northern end of County Clare. Here, we visited the Burren Fm., a Visean limestone unit that forms the basement of the WINB. This unit is interpreted to be a shallow-water carbonate deposit, likely associated with a shelf setting. The unit contains variety of fossils, including rugosa corals and brachiopods.
Travelling to the south, we moved upsection to the “St. Brendan’s Well” outcrop to locate the contact between the Visean Limestone and the Clare Shale. The Clare Shale Fm. is the lowest unit of the WINB sedimentary fill, and consists of a deep marine black shale. At the contact of the Clare Shale and Visean Limestone is a phosphate rich bed, ~ 8 cm thick, interpreted to be a condensed section likely associated with an open marine environment, where sedimentation is extremely minimal.
Day 3 Point of Relief: Deep Water Deposit (Ross Sandstone Fm.) and Slope Deposit (Gull Island Fm.)
We visited the Bridge of Ross and the Ross Fm. to examine the sedimentary structures found within the turbidite deposits. One of the most famous structures here is the Ross Slide, a highly deformed, inter-bedded mudstone and sandstone unit, which contains various soft sediment deposition features, including sand volcanoes and syndepositional folds. The Ross Slide is more recently interpreted as a slump deposit, whereby external forces caused liquefaction of sand and mud and initiated motion that produced significant folding and deformation. The Ross Slump is very laterally extensive (10’s of kilometers long), and this significant size is considered to be associated with a seismic event as triggering the the deformation.
Moving up Section, we examined the contact between the Ross Fm. and the Gull Island Fm., identified by a thin layer of mud with a goniatite (ammonoid) band, which is likely associated with a condensed open-marine section.
The Gull Island Fm. is interpreted as a slope deposit, whereby numerous failures trigger mass transport of sediment that ultimately feed the Ross Fm. turbidite deposits. The Gull Island Fm. contains various styles of soft sediment deformation, including slides, slumps, growth faults, and mud volcanoes.
At end of the day, we visited the Tullig Cyclothem, the formation atop the Gull Island. Here, this cyclothem represents alternating sequences of fluvial-delatic and near-shore, shallow marine deposits, indicated by a classic coarsening upward deltaic sequence of interfingering pro delta, interdistributary bay, and fluvial-deltaic deposits. The middle to upper Tullig Cyclothem is characterized by channels of various sizes, and the Upper Tullig sandstone possesses bedforms and terrestrial plant fossils, indicating a fully fluvial depositional setting.
Day 4 Trusclieve: Fluvial-Deltaic Deposit (Tullig Cyclothem and Kilkee Cyclothem)
We took a boat ride on the Shannon Estuary, in order to observe cliff exposures of the Middle to Upper Ross Fm., and the underlying Clare and and Visean Limestone. The upper Ross Fm. contains numerous feeder channels that routed sediment to the fan lobe deposits of the Ross Fm.
Later, we drove to Trusklieve to visit the Tullig Cyclothem in detail, specifically, the changes in vertical stacking patterns. Stratigraphic Sequences of the Tullig Cyclothem at Trusklieve show that an overall coarsening upward trend is pervasive (as described above). Moving up section, there is an increase in the frequency of amalgamated channels bodies, which possess bedforms, barforms, and terrestrial plant fossils, all of which indicate a land-based fluvial-deltaic environment.
Overlaying this fluvial section is a thick transgressive mudstone that contains various types of marine fossils, including zoophycos, which is a trace fossil left behind by the movement of polychaete worms. Above this mudstone is a marine mud bed, rich with goniatites, and representing the final stage of the Tullig transgression. Overlying this is the Kilkee Cyclothem, which progrades overtop and marks of the onset of a new fluvial-deltaic progradation.
Day 5 Killard: Fluvial-Deltaic Deposit (Tullig Cyclothem)
We drove several kilometers north of Trusklieve to examine the Tullig Cyclothem at Killard Bay. We observed similar coarsening upward sand bodies, as well as sedimentary structures and plant fossils that are quite similar to those observed at Trusklieve. An interesting question arose regarding this outcrop: Why do the bedform foresets dip at such a shallow angle, much lower than angle of repose? Hongbo Ma is investigating this phenomenon, and has some interesting findings based on ongoing studies in the modern Huanghe River (China) which could be used to compare to the Tullig channel dunes.
Day 6-8 Group Project
May 8th – 10th
Students self-organized into four groups of two people each, and pursued independent research projects, conducted at various field sites for the range of depositional environments. On May 10th, each team presented the results of their individual projects to the class. The following list describes the student groups and their respective project depositional environments:
Fluvial-deltaic (Trusklieve and Killard): Brandee and Andrew
Pro-Delta/Shelf (Point of Relief and Killard): Chen and Sam
Slope (Point of Relief): Garrett and Brian
Turbidite (Bridge of Ross): Pulkit and Simon
Day 9 Cliffs of Moher
We visited the Cliffs of Moher on the northern end of County Clare. This location is distal part of the WINB, where it contains a condensed section of all the previously visited sedimentary formations. At the highest point of Cliff of Moher, stands the O’Brien’s Tower, an observation tower build by local landlord in the early 1800s. Standing by the tower, we had a spectacular view of the Loop Head peninsula and north Atlantic, which is a great way to conclude this wonderful trip.
I am Adeene Denton, a senior in this Earth Science department, and that means I’m graduating in a very short time because Rice has decided that I am worthy even if I still feel like I have so, so much to learn. I want to thank the department and look back on what it did for me, and all of us.
There are not enough words to explain how grateful I am to this department, or to express what it has done for me. It was in my classes here that I learned how to think like a scientist, how to frame my questions and shape my logic. This department taught me how to think as it fed me information, and it gave me some of the best friends I’ve ever had in the cohort that I graduate with this year.
Very few of the Earth Science majors graduating this year came in to Rice as Earth Science. This is common – maybe it’s because most of us were barely taught earth science in high school, if at all. Maybe it’s because we thought we should be engineers – or lawyers, in my case – based on the people we knew were successful back home. I came in to Rice convinced that I would be a lawyer or a politician, and the metric of my success would be measured by the quality of the suits I would wear or the slickness of my vocabulary.
Then I discovered the Earth Science department, in a crazy turn of events that led to me taking Dr. Alan Levander’s ESCI 324 as a freshman – a class that turned out to be incredibly hard for a humanities major who hadn’t taken physics since freshman year of high school, but also incredibly rewarding. When Alan traced the Earth’s formation back to the Big Bang, vividly describing how the swirling dust of the planetary disk formed the hot, wobbly Earth, I knew I was hooked for life. I wanted to understand the Earth more than anything – from how the mountains rise and fall to the stratification of its interior to its rapidly changing atmosphere and everything in between.
Since then, I’ve taken as many classes in this department as possible, and gotten to know so many absolutely amazing, inspirational people. I want to thank the professors of this department for teaching and inspiring me, for instilling all of us with knowledge and making it fun at the same time. Thank you to Dr. Alan Levander, who taught my first Earth Science class, and ensured that I would one day write this. To Dr. John Anderson, Dr. Jerry Dickens, and Dr. Jeff Nitrouer, for introducing us to sedimentation, to rivers and oceans and keeping us from drowning in our workloads. To Dr. Juli Morgan for teaching us that rocks, like college students, are also subject to stress and strain. To Dr. Cin-Ty Lee and Dr. Raj Dasgupta for teaching us our rocks and minerals, so hopefully I will never misidentify a brick as a rock again. To Dr. Helge Gonnermann for taking us out into the field where we learned how to make theoretical knowledge really, really practical, and that geology does not mean one right answer. To Helge and Dr. Adrian Lenardic for helping with my senior thesis and making sure I produce good scientific work and can explain it well. Thank you to all the other professors I have met and worked with – Dr. Dale Sawyer, Dr. Carrie Masiello, Dr. Colin Zelt, and everyone else. If I am a good scientist at all, it is because all of you were there to teach and help me.
It was with this department and its people that we learned that science is not bright and shiny and we pushed onwards anyway – that science sometimes means spending five hours in the lab only to realize that you set the wrong spot size on the laser, or trying to find the bug in your code and see that it’s a missing semicolon in the third line. But that breakthrough moment – that moment is worth everything. That moment when you are standing in the middle of nowhere, looking at the notes on your field map that is so worn it’s tattered, and suddenly the pieces fall together and you know.
We joined this department because we all wanted to know, deep in ourselves, how the earth works. How to map it, how it shapes itself, how it was born and where it will go. Now, we go to grad school or to jobs or to keep figuring ourselves out, still not entirely sure of our passions, but so much surer of our directions than when we came in. I am who I am because of the incredible people in this department, and I am forever grateful that I found this place and these rocks and these humans who love rocks right along with me. There are eleven undergrads leaving Rice, but we are coming out as capable scientists, ready to pursue completely different life paths. We came here looking to understand how the earth works. Maybe an era or an eon from now, we’ll know.
It was a nice and sunny Saturday when we started our journey on I-10 going west of Houston. We crossed Pleistocene and thin Pliocene rocks until we were near the Little Low Miocene Hills of Columbus, a very small strip. Finally, we arrived at our first stop where lower Cretaceous rocks onlap onto basement rocks. We noticed that Oligocene rocks were missing.
Walnut Formation Road Cut (Stop 1)
Location N 030.29947 W 097.82767
Elevation: 297 m
At this stop, we saw Glenrose basement rock overlain by Walnut Formation (110 Ma). The lithology of the Walnut Formation is a lime mud marl (limestone), and the beds seen are horizontal and fissile. The beds contain fossils and some of the fossils found include the famous Devil’s toenail (exogyra), oyster, snails and warm burrows. The worm burrows are indicative of a depositional environment with ubiquitous bioturbation. Since it was quiet enough for worms to burrow and mud to be deposited, we speculated that the depositional environment was lagoonal. If this is the case, it could be an indicator of paleo sea level.
There is an enigma surrounding the Walnut formation. If it was formed close to sea level, how is it that the elevation is now 297 m today? The question of when and how the Llano Uplift (part of the Edwards Plateau) occurred is still a mystery in geology. Some researchers have pinned it to Oligocene time. As far as how it occurred, several theories exist: (1) magmatic underplating from ultramafic intrusions along the Balcones Escarpment; (2) a flexural response from forebulge to the coastal basin; and (3) Jurassic salt moving to the surface, causing Cretaceous rocks to slide and creating offset.
Transition from Glen Rose to Walnut Formation moving upwards. Glen Rose has harder, regular bedding, where Walnut has muddy Cretaceous limestone.
Close-up of the Walnut Formation. Contains visible shelled organisms and exhibits diffuse bedding.
Ellenberger Group, Honeycut Formation (Stop 2)
Location: N 030.553777 W 098.26020
Elevation: 246 m
The Honeycut Formation is Ordovician in age. About 100 m of limestone has been eroded here in comparison to the Walnut Formation, and this is reflective of the erosional window of the Llano Uplift. The formation is highly laminated and contains bacterial mats (stromatolites which grow on tidal flats). There might also be some stylolites although it is not certain. Barnett Shale, which is Mississippian-Devonian in age, can also be seen at this outcrop, but it is very thin.
In West Texas, the Ellenberger limestone is a major carbonates reservoir where it was exposed, karsted, faulted, and later sealed. The faults here are related to the Ouachita orogeny (which is younger than 300 Ma) and analogous to the Alleghanian orogeny of North America. Although the Honeycut marble is the downthrown side of the fault while the granite is upthrown side, the granite appears to be eroding faster than the marble. The result of this is a reverse topography instead of what we would expect from faulting.
Stromatolite in the Honeycut Formation.
Backbone Ridge (Stop 5)
Location: N 030.64519 W 098.41574
Elevation: 289 m
The Cambrian rocks are beneath the Town Mountain Granite, so we should have been in a graben (central downdrop block), but instead we were standing at a local high point. This is another instance of inverted topography due to erosion of the granite which has relatively low resistance. At this stop, we were standing on normal fault with two more faults running perpendicular in the Cambrian rocks before us. The Lion Mountain green sandstone across the road was formed by worm droppings in an anoxic environment, creating a mineral called glauconite. The sandstone is pelletal in texture and contains white lenses that we identified as trilobite hash. There are little muscovites on the surface of the trilobite deposits suggesting past metamorphism. Underlying the Lion Mountain is the upper Hickory Sandstone containing iron oolites, indicating a ferriferous depositional environment. Above the dark green sandstone we observed a color change to whitish-green and a compositional change to coarser grains containing more quartz. This is indicative of the depositional environment moving inland up the strata with the upper rock likely deposited in a shoreface to backshore setting. The whitish-green then transitions upward into a pink and green rock. The presence of herringbone bedding within this upper section signifies a tidal phase, perhaps an offshore to lagoonal environment. Overall the Lion Mountain Sandstone is less resistant than the overlying strata. Within the whole body we found an oxidized strike slip fault with mellow plunge in the slickenlines.
Predominately strike-slip fault (with some thrusting) in Lion Mountain Sandstone. Directionality indicated by slickenlines on red Fe-stained parts of glauconite on right side of fault.
Students looking at the Lion Mountain Sandstone.
Valley Spring Gneiss and Granite, Inks Lake State Park (Trip 6 PC Guide Stop 3)
Location: N 030.74855 W 098.35748
Elevation: 278 m
Here we saw heavily deformed quartzofeldspathic gneiss among other schists and gneiss. Up to four generations of folds and five associated foliations were able to be identified, all of which except the last were penetrative and seen through the whole area. Granitic dikes and intrusions were present and responsible for local metamorphism.
Granitic dike cutting through the Valley Spring Gneiss.
Distinct F3 fold in the Valley Spring Gneiss.
Valley Spring Gneiss (Trip 6 PC Guide Stop 2)
Location: N 030.75404 W 098.67634
Elevation: 281 m
For our last stop on Day 1, we examined a synform in the Valley Spring Gneiss by the Llano River. We measured the attitudes for several mineral foliations, plotted them on a stereonet, and attempted to match the data to our observations. At another spot by the river, we observed a Valley Spring pluton dated approximately 1250 Ma with a dynamothermal overprint dated 119 Ma. We noted that there was not much foliation in the country rock. The texture of the rock suggests that it was not highly metamorphosed.
Old Valley Spring pluton by the Llano River.
Highway 71 Outcrop (Mosher Day 1 Stop 4)
Location: N 030. 63010 W 098.52912
Elevation: 296 m
At this stop we observed the graphitic Packsaddle Schist. Lightened zones indicate the graphite was volatilized during intrusion, oxidizing the rock along the boundary and bleaching it. Overall the schist is blue in color with white folded quartz veins. It is fairly resistive and contains S1 and S2 folds. Little knots of quartz represent the old fold axis of the formation, and the initial folds appeared to be very ductile. We measured the trends and plunges of various foliations. The folds are typically isoclinal with some shearing, and the plunges of the fold axes range from steep to shallow. Within the schist we observed some vestige of the sedimentary protolith, a dark shale stacked atop a light sand. We noted sheaf folds and contemporaneous multi-directional folding, unique kinematic indicators for shear. The timing of the main assembly of the schist dates to 1140 Ma, predating the intrusion of the Town Mountain Granite. These schists are roughly the same grade as the gneiss we saw the previous day; both were metamorphosed at the amphibolite facies.
Some trends and plunges of fold axes:
- N50ºW, 43º
- N20ºW, 34º
- N40ºW, 15º
- N55ºW, 31º
- N15ºW, 39º
- N60ºW, 12º
Packsaddle Schist containing graphitic layers (dark banding) and folded quartz veins (white).
Cordierite (Added Stop)
Location: N 030.53540 W 098.44107
Elevation: 282 m
The next roadcut we stopped at was notable because of the presence of cement-like cordierite nodules which statically overprint the rock’s foliation. Cordierite is characteristic of high temperature, low pressure contact metamorphism associated with later stage plutonism. It contains no clear crystal structure and is only visible in thin section. Since the cordierite overprints foliation but exhibits none itself, we know that this stage of plutonism postdates folding. The Packsaddle rock here is more schist-like than what we saw at the last stop; the protolith is less obvious.
Packsaddle Schist with cordierite indicated by the weathering pattern. The cordierite is more resistant than the schist.
White Creek Ford (Mosher Day 1 Optional Stop 3)
Location: N 030.45692 W 098.482931
Elevation: 255 m
At this stop, we had an opportunity to see a rock specific to Texas, llanite. Llanite typically has blue quartz phenocrysts and K-feldspar. We saw some of these diagnostic characterics in the rocks surrounding the llanite dike that cut through the area. This dike is dated at 1098 Ma and indicative of late-stage rhyolitic igneous activity. Due to the lack of metamorphic overprint, the area is estimated to be at least 20 million years younger than the Town Mountain Granite not far from there. Further, the surrounding rocks had an aphanitic texture due to being injected into the mix at a shallower depth. They had to formed near the surface to avoid crystal growth and develop this texture.
An interesting feature we observed in this area included veins that were folded. First, in order for the veins to be formed, the rocks had to exhibit brittle behavior by cracking, and then later on exhibit ductile behavior for the veins to then be folded. This brought up the transition between brittle and ductile behavior which can occur due to changes in temperature, overburden pressure, or strain rate. The boudinage of the veins also indicated flow after formation. We also saw some crenulation folding that indicates a later extensional event due to its lack of offset from the main formation.
Classic “boudinage” feature.
Sandy Creek Shear Zone (Mosher Day 1 Stop 3a)
Location: N 030.54169 W 098.56100
Elevation: 292 m
The Sandy Creek Shear Zone is home to unique rocks that were crushed at high pressure and low temperature. We inferred these conditions from the crushed rock grains that lack evidence of recrystallization. At this stop we could also see another rock very specific to Texas, the Town Mountain Granite. This felsic granite appears to have orthoclase, hornblende, K-feldspar, quartz, and mica. The granite owes its pink color to abundant K-spar. In some places, the rock looks very “beat up” in that it has discrete fractures and seems to have undergone violent deformation at temperatures much lower than the solidus of the rock. Very little of the protolith was left untouched. The granite has been sheared but not recrystallized due to its location at shallow depths in the crust.
This formation brought up the brittle vs. ductile deformation question again when we observed that the sheared granite was brecciated to a fine-grained texture. Does the cataclastic but cohesive nature of the rock mean that there was some sort of cataclastic flow? This formation was a prime example of the blurred and ill-defined boundary between brittle and ductile deformation and could perhaps represent some sort of boundary condition between these two categories. The fact that there are mylonites half a kilometer down the road from this formation and its relative location indicates that the Sandy Creek Shear Zone is a point of contact between the Coal Creek and Packsaddle domains.
Brecciated sheared granite exhibiting cataclastic flow.
Augen Gneiss (Mosher Day 1 Stop 3b)
Location: N 030.54169 W 098.56100
Elevation: 292 m
The gneiss here is similar in lithology to the rock at the Sandy Creek Shear Zone. Unlike the previous stop, this rock has been recrystallized after flowing. High-temperature ductile flow and partial melting occurred. This outcrop is a mylonite, meaning that grain size was reduced by plastic deformation during recrystallization. Minerals more resistant to grain size reduction, such as orthoclase feldspar, were rolled during deformation, resulting in clear mineral lineations and classic augen gneiss eye-like feldspar features. These rocks were clearly hotter than at the previous site, yet sit topographically higher, indicating that they likely did not undergo contemporaneous deformation.
Augen gneiss outcrop with mineral lineations lying on a foliation plane.
Red Mountain Ranch (Mosher Day 1 Stop 3c)
Location: N 030.51822 W 098.55237
Elevation: 312 m
Here the cataclastic flow and mylonite from the previous two stops (4 and 5 respectively) are interwoven. This leads us to believe that the two different flow features at their respective sites must represent the early and late stage of the same shear zone. Additionally, this locality is near the transition into the Packsaddle Schist, sitting at the base of the Coal Creek domain.
Interwoven cataclastic flow and mylonite.
Serpentinite Quarry (Mosher Day 1 Stop 2)
Location: N 030.47915 W 098. 63175
Elevation: 332 m
The serpentinite seen at the quarry here is a 6 km long section of the Coal Creek Domain. Derived from ultramafic, low crustal rocks, the serpentinite records a complex history of multiple instances of metamorphism, serpentinization, and deformation. It is thought that the serpentinite was deposited originally as a olivine-rich harzburgite and was subsequently serpentinized during tectonic emplacement. Following emplacement, the unit underwent regional deformation and metamorphism during which it was de-serpentinized. Finally, as granites were emplaced in the area, associated metamorphism anthophyllite grew and, as temperatures fell, serpentinization happened again due to hot water from the granite.
Serpentinite quarry at the final stop.
This blog describes the 3-day field trip that the Fall 2015 ESCI 322 class took to northern California with Professors Cin-Ty Lee & Rajdeep Dasgupta and TA Laura Carter, as told by the undergraduate students: Sofia Avendano, Anthony Foster, Alexandra Homes, Garrett Lynch, Oliver Lucier, Ian Mellor-Crummey, Leila Wahab, Shannon Wang, and Sam Zapp.
Marin Headlands (chert):
This site overlooked San Francisco Bay directly across the Golden Gate Bridge. During the Jurassic period, following Pangaea, the Farallon plate subducted underneath the western North American plate.
At this stop we saw silica-rich cherts on top of ancient oceanic crust. The cherts were once laminated sedimentary deposits formed from diatoms and during subduction were scraped off as part of the accretionary prism. These specific cherts formed near the equator, probably during the Jurassic era. In composition, these cherts are 99% silica, but also contain some iron and manganese. This composition arose as iron and manganese were dispelled from the mid-oceanic ridges and deposited within the silicic ooze that becomes chert. We also noticed fractures filled with quartz in the form of white veins. Over to the right we saw darker, older, green bands, which had not been oxidized.
Marin Headlands (pillow basalts):
The pillow basalts here formed from magma that upwelled due to the divergent boundary at the mid-ocean ridge and was erupted underwater. Zoned phenocrysts of plagioclase feldspar were visible, indicating that they grew intrusively before eruption. The surrounding fine grained matrix was extruded on the seafloor where it cooled quickly. The edge of each pillow featured a glassy rind where the surface of the lava body cooled even quicker with direct contact with the water. Layers of chert were deposited on top of these pillows in a marine setting.
Tiburon Peninsula (Eclogite, blueschist, and peridotite, boulder outcrops):
Here we saw a number of boulder outcrops. Eclogite needs high pressure and high temperature conditions to form, so its presence was indicative of subduction zone setting. Chemically, it is very similar to the pillow basalts we saw earlier at the Marin Headlands, suggesting this may be the protolith. However, the eclogite samples we saw were also enriched in sodium, probably from hydrothermal processes, giving a special form of pyroxene: jadeite. In eclogite, the aluminum in the protolith plagioclase is now held in garnet. As it moved back up through the crust, some of the eclogite retrograded into blueschist, greenschist and amphibolite. The heterogeneity of the metamorphic grade may have been caused by uneven distribution of fluids. The kinetics of retrograde metamorphism can be slow, but the presence of fluids makes retrograde metamorphism occur faster.
The last outcrop we saw here was composed of peridotite. It contained orthopyroxene and olivine, so it would be classified as harzburgite. Peridotites with a much greater amount of orthopyroxene are lherzolite. These peridotite xenoliths had a slightly brown / tan coloring due to the weathering at the Earth’s surface. We also saw some serpentinite—altered peridotite—in the area.
Bolinas Lagoon (San Andreas fault, SEALS!):
We observed a rookery of seals accompanied by a lone sea lion as if he meant, through his presence, to elicit an ironical play upon a Danish children’s story. Abreast of these seals, two shovelers swam, feeding, and one merganser swooped through, low, tantalizing the water.
Point Reyes Visitor Center / Earthquake Museum:
Here we did a short nature walk travelling along the path of the San Andreas fault. We saw a fence that was displaced several feet due to previous movement along the fault, which is evidence of an ongoing right lateral strike slip fault.
The beach, the cliffs:
Along Point Reyes on the Pacific Ocean there was a series of cliffs with igneous outcrops that were the roots of a magma chamber from the Cretaceous next to marine sediments from the Miocene, representing a large unconformity. Here, we could see cross cutting relations in the igneous outcrops where magmas of different compositions interacted. The parental magmas were more basaltic, while the more felsic magmas were much more evolved. The intruding felsic magmas were much more viscous, so they mixed in some places but stayed clearly separate in others, and then froze in place. Mixing of the magmas indicated that the surrounding rock was still magmatic mush when they mingled.
Sharper boundaries between two magmas is also visible. This was likely due to the fact that basalt has a higher melting point, so when it cooled, it contracted and pulled some of the surrounding liquid in. These intrusions occurred further inland from the subduction zone, around 10 km below the surface.
Sedimentary Road Cuts, Ione Formation:
In the foothills of the Sierra Nevada, we saw an outcrop on the exposed shoulder of a highway. Sediments had been collected from the Sierra Nevadas and compacted into layers. The layers originated from granodiorite which lost much of its magnesium and iron, leaving behind what became predominantly kaolinite (Al2SiO5). The lower layers of laminated deltaic sediment gave way to cross-bedding features as a fluvial system moved through the area. At the edges of the formation, there was evidence of soft sediment deformation.
We also stopped at Silver Lake for lunch. Beside the lake there were these interesting boulders which appeared to contain clasts of petrified wood. Across the lake we saw large lava flows of andesitic magma, now part of an imposing mountainside.
The edge of Mono Lake contains massive collections of tufa deposited in towers. We learned that these tufa deposits are a result of the very alkaline water from the lake mixing with calcium rich spring water from the Sierras, which precipitates calcium carbonate (CaCO3). The tufa deposits become visible and form large columns due to the water level of Mono Lake lowering over time. In the past, the springs feeding Mono Lake were drained to provide water for places like Los Angeles and other urban areas, which made more and more of the tufa deposits visible. Only in recent years has this been slowed and Mono Lake protected.
Long Valley Caldera:
The Long Valley Caldera is in the Basin and Range region, which underwent extension. The Caldera was active 2 million years ago, but the last eruption occurred 700,000 years ago and erupted 700,000 m3 of rhyolite. The eruption style was Plinian, which is very explosive, caused by magma fragmentation, and characterized by fine ash. The ash of the eruption spread throughout the western US. There were also resurgent domes with the same magma composition, but with effusive style eruptions since the magmas had already been degassed.
The youngest lava flows were 7,000 years old. Under the Basin and Range extension, decompression allows the mantle to cross the solidus, which leads to alkalic basaltic magmatism. Basalts that re-melt the crust fractionate and form rhyolites, so there are both extremes here: basalts and rhyolites. It is still unclear how basalts skip to rhyolites with no intermediate composition.
The actual magma body was 10 km below the surface. The magma body builds up pressure, creating fractures, and, when the pressure exceeds the yield stress of the rock above, the system evacuates and the roof collapses. This has left a low, flat ~10 x 20 km area. Fumaroles, where magmatic gases were still escaping due to residual heat, were also visible.
Around the caldera, there were also moraines, large sediment mounds moved by glaciation, visible along the outskirts in front of the Sierras.
At the base of the gorge, we saw evidence of a huge rhyolitic ignimbrite, which must have erupted over an incredibly short period of time (estimated at around 6 days). There were three different layers denoting sequential eruptions. The lowest layer was more porous, with many lateral fractures and no evidence of compaction, which indicates that the lowest layer cooled before the weight of the next eruption could deform it. The texture of this tuff was friable, easily breakable, and it was more silicic than the upper layers. The first layer was probably an initial pulse of small eruptions right before the large eruption. Weak precursor eruptions tend to have ashfall rates slower than cooling rates.
The middle layer had a very clear fabric with small pumice ejecta elongated and oriented in the same direction, which shows that the layer was compacted. Thus it cooled slower than the layer below. The strain of the rock can be found from the aspect ratio of the elongated clasts, perpendicular to the bedding. This layer was welded ignimbrite, which contained fiamme, and was formed under high temperature and pressure. Jointing occurred after cooling due to contraction.
The upper layer was mostly ash with pre-existing metamorphic, Paleozoic clasts caught in the ash (lithics). There were also pink pumice clasts that also have an individual fabric, which probably came from a different eruption, and had elongated vesicles caused by compaction. There was no larger scale fabric because there was not enough overpressure to deform the material, so the last eruption must have cooled quickly.
Panum Crater is what remains of a rhyolitic plug-dome volcano. Volcanic eruptions in this area began around 40,000 years ago. Panum Crater itself is approximately dated at 650 years old and is the youngest in the area. The explosion occurred as a magma bubble heated the water table into instant, high-pressure steam. Pumice was the first to be expelled from the volcano, and deposited around the outside of the crater. Following, breccia formed a dome over the crater, followed by lava flows that cooled to obsidian, which dominate the landscape.
The rhyolitic eruptions in the crater produced very silicic lava (roughly 76% SiO2), which is highly viscous and created the two main types of rock we saw: pumice and obsidian. The pumice was very low in density and highly vesicular. The vesicles formed from trapped air bubbles, indicating that the lava solidified quickly. Obsidian had little to no bubbles, but is the same composition as pumice. The obsidian cools quickly forming a glass, evidenced by the black rock’s conchoidal fracturing we saw.
A curious sample of rock we found looked like obsidian but had what looked like mud cracks on its surface. This was actually a breadcrust bomb formed from molten lava chunks flung into the air. The outer surface cooled rapidly, but the inside was still molten, so the gases inside continued expanding. This cracked the surface of the rock, causing it to look like the crust of a bread loaf.
Geologically speaking, obsidian never lasts very long. Devitrification causes glass to be more like rock and less like glass, so It is difficult to find glassy obsidian older than 10 thousand years old. The more vesicular the obsidian is, the faster the rate of devitrification since water gets in the vesicles. Thus, the rock samples at Panum were much younger than the samples at other formations we studied.
Basaltic Phreatic Deposit:
On our way from Panum Crater, we stopped to examine an omega-shaped formation on the side of the road. Upon close inspection, we found the rock to be very fine-grained and soft, with cross-bedding evident on the folds. This was formed when a basaltic flow erupted underwater. When basalt hits groundwater, it fragments and becomes very, very fine-grained, creating the soft texture that we observed instead of the texture we saw in previous basalt deposits. The deformation is very similar to soft-sediment deformation, and most likely occurred when the rock was still warm and ductile. Cross-bedding was likely a result of basaltic ash settling in bodies of water nearby, creating the sloped deformation, and cross-bedding typical of river systems.
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