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Paleozoic Equatorial Records of Melting Ice Ages (PERMIA)
Paleozoic Equatorial Records of Melting Ice Ages (PERMIA)
In delving into geological history, the Late Paleozoic Ice Age (LPIA) takes on special significance in current climate studies as our unique reference for understanding "climate change in an icehouse on a vegetated Earth" (Montañez and Soreghan, 2006). Towards the close of the LPIA, particularly during the Carboniferous-Permian Transition (~304-290 Ma), a noticeable shift occurred on continental environments—from expansive wetlands dominated by a mix of aquatic and terrestrial tetrapods in the Carboniferous, to more arid environments dominated by terrestrial biota in the Permian (Fig. 1).
Current modeling suggests that this shift was protracted and spatially diachronous, with the Late Paleozoic Cutler Group in southern Utah, USA, potentially possessing the earliest records of continental aridification and associated biotic changes (Pardo et al., 2019). Yet, full comprehension is forestalled by imprecise age-constraints and incomplete paleoclimate records due to inaccessible outcrop exposures.
Figure 1: (Left) Earth during the Carboniferous Period, dominated by large coal forests; (right) Earth during the early Permian Period which was dominated by more arid environments
Figure 2: Photo-scans of the Elk Ridge-1 Core, from Stine et al., 2024 (in review).
To resolve these issues my co-authors and I, developed the Paleozoic Equatorial Records of Melting Ice Ages (PERMIA) research project. A highly multidisciplinary effort, PERMIA seeks to construct a robust biochronology for the fossil assemblages of Utah’s Cutler Group that is correlated to globally-indexed marine biozones, magnetostratigraphy (including astronomically-tuned magnetic cyclostratigraphy), and paleoclimate proxies.
As a member of PERMIA, and as a post-doctoral researcher at the IRM, my focus has been examining outcrop in addition to processing the Elk Ridge-1 core (Fig. 2). This legacy core, collected in 1981 within what is now Bears Ears National monument, recovered a significant portion of the Hermosa Group and overlying lower Cutler Group, making it an ideal archive for studying paleoenvironmental change during the C–P transition
While the analysis of the Elk Ridge-1 core is an ongoing process, substantial insights have already been gleaned from an examination of the polished working halves. This has included a refined lithostratigraphy in addition to the measurement of geophysical properties, such as magnetic susceptibility and natural gamma-radiation (Fig. 3). Moving forward, the next phase of our work will focus on refining the core's age. To achieve this, we plan to employ biostratigraphy (led by co-PI Adam Huttenlocker) and geochemical-isotopes (co-PI Randy Irmis). These complementary approaches will contribute to a more nuanced understanding of the core's chronological framework, enabling me to design a more targeted and efficient sampling strategy for subsequent geochronologic analyses at the IRM, including magnetic polarity stratigraphy and rock-magnetic cyclostratigraphy.
Finally, Elk Ridge-1 is currently being analyzed with an XRF core scanner for elemental concentrations, complementing existing geophysical data. This, along with planned environmental-magnetic investigations, will contribute to constructing, for the first time, a detailed paleoenvironmental model for the lower Cutler beds, anchored by robust age constraints.
Figure 3: Preliminary geophysical and lithological data from the Elk Ridge-1 Core, modified from Stine et al., 2024 (in review).
Investigating Miocene Mediterranean–Atlantic Gateway Exchange (IMMAGE)
Investigating Miocene Mediterranean–Atlantic Gateway Exchange (IMMAGE)
Marine gateways are pivotal for global ocean dynamics, facilitating the exchange of water, heat, and nutrients. The Gibraltar Strait, a critical gateway, played a key role in the Atlantic–Mediterranean exchange. Notably, during the Messinian Salinity Crisis, the opening of the Gibraltar Strait (Fig. 4) may have caused the influx of highly dense and salty Mediterranean water into the Atlantic. This event could have influenced thermohaline circulation, potentially contributing to the development of permanent glaciation in the northern hemisphere during the Late Cenozoic. The IMMAGE project, Investigating Miocene Mediterranean–Atlantic Gateway Exchange, delves into the global paleoclimatic impacts of the Late Miocene opening of the Mediterranean Sea. Requiring an amphibious drilling strategy, IMMAGE will utilize cores collected during IODP Expedition 401 (December 2023 -- February 2024) and upcoming ICDP campaigns, making it the first Land-2-Sea Project.
This multi-year, interdisciplinary initiative aims to quantify how the inception of a Mediterranean-Atlantic marine gateway effected global climate, ocean circulation, comprehend environmental changes, and test hypotheses related to unprecedented overflow dynamics. In doing so, IMMAGE provides valuable insights into the profound impact of gateway configurations on Earth's climate and marine systems (link to prospectus).
Figure 4: Model of the Miocene opening of the Mediterranean (from Capella et al., 2019)
Figure 5: Photo of myself with the rest of the members of the IMMAGE team during the 2023 Summer meeting at the University of Bristol, U.K.
As a member of IMMAGE (Fig. 5), my objective is to construct a high-resolution geophysically-based climate model for Late Miocene sequences. This involves utilizing environmental magnetic proxy data, anchored by paleomagnetic and rock-magnetic cyclostratigraphic age controls. To this end, I will serve as an on-board scientist during IODP Expedition 401 from December 2023 -- February 2024 (link here).
During the summer of 2024, I will collect oriented samples from the collected cores and return them to the IRM for further analysis.
The Blackwater Draw Formation – A North American Continental Record of the Middle Pleistocene Transition?
The Blackwater Draw Formation – A North American Continental Record of the Middle Pleistocene Transition?
The Early-Middle Pleistocene Transition (MPT) refers to a period that occurred ~1.2-0.5 Ma when the frequency of Earth's glacial-interglacial cycles shifted from one dominated by the ~41,000-yr obliquity cycle (i.e., changes in the planet's tilt) to one dominated by the ~100,000-yr eccentricity cycle (i.e. when the shape of the planet's orbit around the sun shifts from more elliptical to more circular).
The post-MPT world corresponded to prolonged periods of cooling, leading to much more expansive continental ice sheets (Fig. 6), increased aridity ,and thus large deposits of aeolian loess on the continents. In places such as the Chinese loess plateau, these loess deposits have been crucial to better understanding the effects of the MPT on continental systems. However, in order to more fully understand the global effects of the MPT, more data is required from other continents. The challenge lies in the fact that many Quaternary loess deposits in North America are relatively thin (∼20 m or less) and with few exceptions are no older than the penultimate glacial period (LGM) (ca. 110 ka) (Fig. 7a) (Muhs, 2018).
Figure 6: Model of the extent of the Laurentide Ice sheet prior to the MPT (top row) and after the MPT (bottom row). Note that the ice sheet reaches its greatest extent post-MPT (bottom left corner). Figure modified from Stine (2022) (dissertation)
Figure 7:(A) The North American loess deposits continent during the LGM, (B) Geographic extent of the Southern High Plains showing areas discussed in the text. Figure modified from Stine et al. (2020).
A notable exception is the Quaternary Blackwater Draw formation that mantles the Southern High Plains in North America (Fig. 7) (Holliday, 1989; Holliday et al., 1996). Existing age control of the BDF indicates that these sediments span at least the last 1.4 Ma and potentially up to the last 2.0 Ma, therefore it is likely that the MPT is recorded within this formation (Fig. 8) (Holliday, 1989; Patterson and Larson, 1990; Imbrie et al., 1993; Gustavson and Holliday, 1999).
While studying at the University of Texas at Dallas, I conducted a thorough investigation into the environmental magnetic properties of the Blackwater Draw type-site. Through the correlation of these magnetic attributes with comprehensive textural and geochemical datasets, my co-authors and I discerned a distinct zone characterized by heightened weathering and magnetic depletion (Fig. 8)(for more detail refer to my papers Stine et al., 2020; 2021). Although there is a suggested link between this zone and the onset of the MPT, the challenge in precisely dating the type-site introduces ambiguity to this conclusion.
Figure 8: Environmental magnetic results from the Blackwater Draw type-site compared to geochemical and textural data. Figure modified from Stine et al. (2020; 2021).
Figure 9: Top left -- A photo of myself collecting samples at the Blackwater Draw-type site. Top right -- Collecting preserved core of the Blackwater Draw formation in Bushland, TX. Bottom -- Photo of the Bushland-cores after splitting at the CSD facility.
In order to establish a more robust age model, we sought to obtain a more preserved record of the sediments by conducting a core-drilling operation in the vicinity of Bushland, Texas. This successfully resulted in the acquisition of three closely spaced parallel cores (Fig. 9), each recovering ~12 meters of the Blackwater Draw Formation. One of these cores is presently located at Texas Tech University, where the geochemical properties are being measured by graduate students under the supervision of Professor Dustin E. Sweet. The remaining two cores were transported to the University of Minnesota (UMN), where they underwent splitting (Fig. 9) and geophysical measurements (including magnetic susceptibility and natural gamma rays) utilizing the advanced equipment at the Continental Scientific Drilling Facility (CSD).
In the upcoming Spring semester of 2024, under my supervision, the paleomagnetic properties of the core will be meticulously measured by undergraduate student Ruby Sandell. Her research endeavors will be supported through funds awarded to her via the UMN Undergraduate Research Opportunities Program (UROP), contributing valuable insights to our broader scientific investigation. For more information on the UROP program, please click this link.
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