My Favorite Outcrops: Molly Turko

Published
American Association of Petroleum Geologists (AAPG)

Dr. Turko has a passion for unraveling complex geological histories and it has taken her to fascinating field locations where there are still mysteries to solve. Join Molly as she shares her story and her favorite outcrops.

What is your name and your background?

My name is Molly Turko and I am a structural geologist with over 10 years of experience in the oil and gas industry alongside teaching in both the field and the classroom. I received a B.Sc. (2009) and a M.Sc. (2011) in geology from the University of Tulsa followed by a Ph.D. (2019) from the University of Oklahoma where I studied under the infamous Dr. Shankar Mitra.

How did you get interested in geology?

Early in my college career I decided I wanted to be a brain surgeon, but upon failing Biology 101 I realized the medical field was not for me. The following semester I took four Earth Science classes where I thrived and found my niche. My geology professor at the time, Claude Bolze, was a petroleum geologist and taught me that I could actually make money by studying rocks! At the University of Tulsa it was Dr. Bryan Tapp who sparked my interest for structural geology. Especially for southern Oklahoma structural geology where he showed me just how complex the geology can be and that deciphering the tectonic evolution is like unraveling a puzzle and putting the pieces back together. I always like a fun challenge, and southern Oklahoma structural geology was the perfect place to conduct my studies!

Where have you done fieldwork?

Southern Oklahoma including the Wichita, Arbuckle, and Ouachita Mountains. I completed my dissertation on the Wichita Uplift and structures in the Anadarko Basin. I also had the privilege to spend six weeks in Turkey for field camp with the South Dakota School of Mines where we looked at structures along the North Anatolian Fault. I also lead field trip down in southern Nevada and Death Valley where participants visit the Valley of Fire, conduct field exercises in the Muddy Mountains, and Spring Mountains, and also spend a day at Death Valley. In 2021 we plan to lead several field trips down there for Applied Stratigraphix that I am looking forward to, including some field trips in California as well.

Please describe a 2 or 3 of your favorite outcrops
  1. What is so memorable about this outcrop?
  2. Where is it? What is the formation and age? when did you visit it?
  3. What does the outcrop tell us about what was happening geologically?
  4. Are there any analogs? Any in the subsurface, related to energy or mineralization?
Arbuckle Mountains

One of my favorite outcrops is located in the Arbuckle Mountains right off of I-35 (just south of Arbuckle Fried Pies off of Hwy 77D) and easily accessible for anyone. This is what some call the “Heart of the Arbuckle Mountains” where the Devonian age Woodford Shale (a world-renowned source rock) is nearly overturned exposing the multiple bedding layers. Multiple fracture sets and faults are exposed, and it makes for a great field exercise deciphering and unraveling the sequence of faulting and fracturing. The Arbuckle Mountains were uplifted during the Pennsylvanian Orogeny, and this area sits within the footwall of a major fault system, the Washita Valley Fault, that underwent both contractional and strike-slip deformation. While some of the fracture sets are related to folding and uplift, several of the fracture sets are believed to have originated prior to significant deformation. Figuring out which fracture sets belong to which deformation event is part of the fun! I visit the outcrop several times a year while leading field trips to the Arbuckle Mountains, this spot is always a fan favorite.

Wichita Mountains

Another great outcrop in Oklahoma is located in the Wichita Mountains along the Post Oak Falls Trail in the Charons Garden Wilderness Area. It is about a 20 minute hike to get to it but well worth the trek. Along the trail, and just past Post Oak Falls, you will see several basement shear zones within the Cambrian age Quanah Granite. The shear zones can be quite tricky to decipher if the deformation is related to normal faulting during Cambrian rifting, or to thrust faulting during the Pennsylvanian when the failed rift was structurally inverted. By studying the geometry of the shear zone, the drag related structures, and fault lenses you can start to get an idea of the sense of slip. However, as soon as you think you’ve figured it out another section of the fault will change your mind, and since the area has undergone both extension and contraction, even some strike-slip, it’s very reasonable to propose multiple slip directions within a shear zone. Basement shear zones around the world are hot spots for mineral exploration and the Wichita Mountains make a great field area for recognizing and learning more about these types of structures.

Valley of Fire, Nevada

One of my favorite places on earth is the Valley of Fire State Park just east of Las Vegas, Nevada. I usually lead an annual field trip where we study fracture patterns in the Jurassic Aztect Sandstone. We hike a loop trail where we see a right-lateral proto-Riedel shear zone that initiated as en échelon deformation bands with an antithetic (opposite/left-lateral) sense of slip. What results is a sigmoidal form accompanied by conjugate shear fractures. Adjacent to this outcrop are more “simplistic” deformation bands that are essentially shear fractures that develop by crushing porous sandstone grains. The kinematics of these two outcrops represent a time when there was strong lateral compression. This occurred as a large thrust sheet overrode the area during the Cretaceous Sevier Orogeny. During this time, a plume of fluid flowed through these rocks staining them with incredible shades of purple, orange, and white. The Valley of Fire is a great area for understanding the impact of deformation bands on porous sandstone resevoirs, and how these unique fracture trends may lead to compartmentilization.

What are your plans for the future?

I am currently a team member with Applied Stratigraphix as their structural geology expert where we are currently planning and constructing several structural geology courses for 2021. This will include both in-house, online, and field courses. I also consult for the company when opportunities come along. I hope to eventually go back to work full time as a petroleum or structural geologist, or possibly even give the mining or geothermal industry a try! My passion is structural geology, so wherever I end up I hope I can apply those skills. I love knowledge sharing and am slowly working on a website that I hope to have up in 2021 (TurkoTectonics.com) where I can share photos, videos, and discuss consulting opportunities for my company, Turko Tectonics and Structural Geology, LLC (TTSG).

Please recommend two or three good books

I really enjoy the “Roadside Geology of Oklahoma” book that came out this year by Neil Suneson. He did a great job at putting the book together while also providing great photos, GPS locations, and descriptions. I have met Neil on several occasions, he’s a great guy and always puts together great content on Oklahoma geology.

If you are looking for a GIANT coffee table book filled with incredible photos of geology and landscapes I recommend “Geologica: Earth’s Dynamic Forces” by Coenraads and Koivula. My mom bought me this book for graduation years ago and I still find myself pondering through the pages and daydreaming about visiting some of the incredible places.

Another recent publication that I have been enjoying is the “Atlas of Natural and Induced Fractures in Core” by Lorenz and Cooper (2018). If anyone is doing a fracture analysis in core this book is a must! Although I may be a bit bias since these guys were the first ones to teach me all about fractures.

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