Getting out into the field is so important as a geoscientist. We can learn so much from field trips with our peers and colleagues. At the end of this edition, we will journey to Poland for a recap of the 2024 AAPG Europe Region Conference held in late May—a great example of geoscientists learning from the field and from each other. Next up? AAPG’s International Conference & Exhibition and corresponding field trips are coming up in Oman from 30 September–2 October.
Rasoul Sorkhabi
Editor, Core Elements
Paleozoic Shales of the Midcontinent United States
Image courtesy of AAPG Bulletin
The U.S. shale revolution of the past 15 years hinges on Paleozoic plays. In a recent article in the AAPG Bulletin, researchers from Arkansas have characterized the black shale formations of Cambrian-Carboniferous age from the Midcontinent USA.
Basins and formations: The study focuses on the:
Illinois Basin: Cambrian-age shales (Mt. Simon, Eau Clair, and Tunnel City); Late Devonian age (New Albany)
Cherokee and Forest City Basins: Pennsylvanian-age shales (Excello, Little Osage, Hushpuckney, Stark, Muncie, Vilas, Eudora, Heebner)
Ozark Dome area: Mississippian-age shales (Chattanooga and Fayetteville)
Ouachita Mountains: Ordovician shales (Collier, Mazarn, Womble, Polk Creek), Mississippian shale (Stanley), Pennsylvanian shales (Jackfork and Atoka)
Samples and analyses: Sixty-nine outcrop shale samples from 21 stratigraphic formations were analyzed for total organic carbon and elemental concentrations.
The proxies evaluated were for: paleoredox, Mo concentration, Mo/total organic carbon, basin restriction signatures (Cd/Mo and Co-Mn), and paleosalinity (Sr/Ba ratios).
Classifications: The depositional environments for petroleum source rocks may be oxic (oxygen-present), anoxic (oxygen-absent), or dysoxic (having low oxygen concentration). Anoxic environments best preserve organic matter that generates oil and gas.
Study goals: The geochemical data were used to better understand depositional environments of metalliferous black shales across the Midcontinent.
Findings:
The Cambrian Mt. Simon, Eau Claire, and Tunnel City samples in the northern part of the study area were deposited under oxic marine conditions influenced by marine upwelling.
Ordovician shales from the Ouachita Mountains and Pennsylvanian shales from the Cherokee and Forest City Basins were likely formed under anoxic, open marine conditions.
Devonian shales from the Ozark Dome and the Illinois Basin were likely deposited under anoxic to dysoxic conditions.
The Mississippian Fayetteville Shale in the Ozark Dome formed under a range of oxic to anoxic conditions.
Pennsylvanian shales in the Ouachitas were deposited under oxic marine conditions.
Why it matters:
Shale deposition has played an important role in Earth’s paleo-climate evolution. Studies of global anoxia events are particularly important for historical geology.
Organic-rich, thermally mature shale formations in the U.S. will continue to supply considerable volumes of oil and gas, and geologic appraisal of these formations help better production practices.
Carbon Capture and Storage (CCS) is at the forefront of sustainability initiatives. Join AAPG Academy and AspenTech for this upcoming webinar on 25 June at 9am CDT that will teach you better execution of CCS projects utilizing geologic modeling workflows.
You'll walk away with expert insights that'll enable you to:
1️⃣ Streamline the site selection process through high-level reservoir screening 2️⃣ Ensure project viability by performing reservoir characterization and building 3D models for flow simulation and geomechanical assessments 3️⃣ Reduce risks through a comprehensive geological uncertainty analysis 4️⃣ Increase productivity by facilitating rapid model updates with newly acquired data throughout the project lifecycle
Ogrodzieniec castle on top of the Upper Jurassic carbonate buildup; Courtesy of Piotr Krzywiec
A friend of mine and fellow geoscientist, Piotr Krzywiec, recently co-chaired the AAPG Europe Region Conference in Kraków, Poland, where a lot of great geoscience information was shared. Krzywiec shared his notes with me. Here are the highlights:
Conference stats:
The two-day conference included 24 technical sessions with 132 oral and 54 poster presentations. More than 270 people from 100 different companies across 29 countries attended.
Pre-conference field trip: This one-day field trip focused on the Upper Jurassic Carbonate sediment of the Carpathian foreland basin.
These formations lie within the Polish Jura Chain that stretches from Kraków in the southeast toward Częstochowa and Wieluń in the northwest.
Since the 1970s, numerous wells and seismic images have described these Upper Jurassic deposits in the subsurface, beneath Miocene or Cretaceous sedimentary cover.
In the outcrop, the Jurassic carbonate buildups often form tall hills due to their resistance to erosion. Medieval defense towers or castles were built on top of many of them.
Second field trip: The event also offered atwo-day field trip to the Carpathian fold-and-thrust belt—the so-called “Outer Carpathian”—which contains surface seeps of oil and gas known for centuries.
In the mid-19th century, the oil industry developed as distillation of kerosene became an industrial technology in this region. In the early 20th century, the region was “the third-largest oil producing region in the world.”
During the field trip, the group visited Miocene sediments, including the famous Wieliczka salt mine.
Attendees examined petroleum source and reservoir rocks in the field within the deepwater flysch sediments. They also viewed corresponding subsurface seismic images.
One of the highlights of the trip was visiting the Museum of Petroleum Industry in Bóbrka, where the first modern commercial oil mine was established in the mid-19th century by the Polish engineer Ignacy Łukasiewicz.
The bottom line: Let’s recall this famous line from Harold Reed from 1940: “The best geologist is the one who has seen the most rocks.” Get out there and see as many as you can. These conferences are a great way to do so.
What’s next: The upcoming AAPG International Conference & Exhibition in Muscat, Oman (30 September to 2 October) will feature field trips before and after the conference, including:
Oman Geological Heritage: The Semail Ophiolite (29 September): One of the largest and textbook outcrops of oceanic crust rocks
Visit to Earth 44.01 CO2 Injection Site (29 September)
Geology of the Late Cretaceous Natih Intra-shelf Basin (3 October): Outcrops of shallow-water Upper Cretaceous carbonates that offer prolific oil and gas reservoirs underground
Al Jabal Al Akhand and Wadi Al Muaydin: A Window into Middle Eastern Petroleum Geology (3 October): A full sequence of Cryogenian to Cretaceous sedimentary rocks in Oman
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