9:00am - 9:15am
Analyses of geophysical borehole data of Prees-2 (England) as part of the ICDP JET project
Leibniz Institute for Applied Geophysics, Germany
In the end of 2020, an approx. 650 m deep core was drilled at Prees in Shropshire, England, as part of the ICDP project JET (Integrated Understanding of the Early Jurassic Earth System and Timescale). The main objective of this project is to obtain and characterize a complete and continuous sedimentary archive of the 25 million years of the Early Jurassic. The Early Jurassic period (200-175 million years) was a period of extreme environmental changes: Rapid transitions from cold or ice ages to super-greenhouse events have been documented, including global changes in sea level and organic carbon distribution, as well as mass extinctions.
Knowledge of this part of the Earth's history is supposed to serve as an analogue for present and future environmental changes. The project will provide a "master record" for an integrated stratigraphy (bio-, cyclo-, chemo- and magnetostratigraphy) of this period. In addition, the project will allow the reconstruction of the local and global palaeoenvironment and the driving mechanisms and feedbacks responsible for environmental changes in the Early Jurassic.
The analysis of geophysical borehole measurements contributes to interpretations with respect to the lithological characterization of sediments and their boundaries, but also allows the description of sedimentary cycles related to orbital parameters, insolation and therefore to paleoclimatic history.
First results of these borehole measurements include a lithological classification which is based on cluster analysis of solely physical data. Furthermore, core-log integration has been carried out and a first attempt towards astrochronology and cyclostratigraphy has been made.
9:15am - 9:30am
Reconstruct sedimentation rate and time from downhole logging data at Lake Chalco, Central México
Leibniz Institute for applied Geophysics, Germany
Understanding the evolution of lower latitude climate from the most recent glacial periods to post-glacial warmth in the continental tropical regions has been obstructed by a lack of continuous geological records. Here we present results from a lacustrine record from tropical North America. Specifically, we examine sediments from Lake Chalco, located in the Valley of Mexico, central Mexico (19°30’N, 99°W). The basin represents a hydrological closed system surrounded by the Trans-Mexican Volcanic Belt aging from the Oligocene to the present. We used borehole logging data to conduct a cyclostratigraphic analysis of the Lake Chalco sediments. More than 400 m were logged for several geophysical properties including magnetic susceptibility and spectral gamma radiation (SGR).
SGR is a particularly useful tool as it is non-destructive, fast, affordable, and applicable even in cased boreholes. Among the lake deposit of the Chalco sub-basin, 388 total tephra layers (≥1 mm in thickness) were reported from the core description. Tephra layers with specific gamma-ray signatures present a challenge for extracting the primary signals caused by climatic agents. We propose a protocol to identify tephra layers embedded in other sediments using high-resolution SGR.
After extracting the non-volcanic primary signal, we applied a suite of evolutive cyclostratigraphic methods to the Lake Chalco downhole logging data, with a focus on gamma-ray. The high-resolution gamma-ray results suggest that the Lake Chalco sediments contain several rhythmic cycles with a quasi-cyclic pattern comparable with Pleistocene climate evolution, allowing to calculate of a ~500-kyr time span for the Lake Chalco sediment deposition.
9:30am - 9:45am
Hipercorig Hallstatt History (H3): Accessign a deep time window of Lake Hallstatt´s preHistory
1University of Innsbruck, Austria; 2University of Bern, Switzerland; 3Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Germany; 4Natural History Museum Vienna, Austria; 5Uwitec GmbH, Umwelt und Wissenschaftstechnik, Mondsee, Austria; firstname.lastname@example.org
The new hydraulic coring system Hipercorig was developed to recover undisturbed long cores from deep lacustrine sediment archives that record past environmental conditions and changes (Harms et al., 2020). Here we report initial results from the deep lake drilling project ‘Hipercorig Hallstatt History’, which succeeded to recover two 41m and 51m long cores and to conduct downhole logging in spring 2021 with the Hipercorig System on Lake Hallstatt. This inner-alpine lake, characterized by very high clastic sedimentation rates, is located in the heart of the UNESCO World Heritage region Hallstatt - Dachstein – Salzkammergut, whose early history of Stone Age settlement and salt mining is still not yet fully understood. Also, there is a lack of reliable observational data on past environmental and climatic conditions, and frequencies and impacts of meteorological and geological extreme events of that time, that are needed to holistically understand past environmental-human-environmental interactions. The new >50 m long sediment cores from Lake Hallstatt now overcomes the previous coring-depth limit (16 m subsurface, dated to ~2.3 cal ka BP) and covers a presumably continuous sedimentary succession throughout the Holocene and Late Pleistocene since the retreat of the Traun glacier. Here we present first results from the Hipercorig coring and logging campaign, along with initial results from whole-round core analyses (Multi-Sensor-Core-Logging; and X-ray Computed Tomography) and preliminary Core-Log-Seismic-Integration, revealing unprecedented scientific samples and data, that will provide unique insights into the early development of one of the oldest cultural landscapes in the world.
9:45am - 10:00am
Latest Achievements with drill core scanning based on Laser Induced Breakdown Spectroscopy applied to 6 meter of drill core through Merensky Reef, Bushveld Complex, South Africa
1Federal Institute for Geosciences and Natural Resources (BGR), Hannover, Germany; 2Mineralogical State Collection Munich (SNSB-MSM), München, Germany
A 6-meter drill core from Merensky Reef, Bushveld Complex, South Africa, was scanned in detail with a drill core scanner based on Laser Induced Breakdown Spectroscopy. The purpose of the investigation was to visualize variations in the chemical composition along the core, and following a mineral classification of the LIBS data, of variations in the mineral chemical composition as well.
The LIBS technology is based on atomic emission spectroscopy, in which the excitation of the atomic species occurs in-situ on the sample surface. The excitation source was a pulsed 50 mJ 1064 nm Nd:YAG laser, and the emitted light was collected with a high-resolution wide-range echelle spectrograph with CCD detector. For validation purposes, selected samples were analysed with bulk chemical analysis and electron probe microanalysis as well.
Distinct trends could indeed be extracted from the 6 m core section through the Merensky Reef. From a saw-cut core surface without further preparation, a continuous record could be extracted consisting of bulk chemical patterns, modal composition, and direct neighbourhood. The data can be used to highlight the presence of unusual patterns and to relate them to Ni, Cu, PGE or other mineralization. When applied to different core sections, it may become an important tool for comparing lateral variability of diagnostic horizons in vertical sequences in layered intrusions such as Merensky Reef and UG-2.
10:00am - 10:15am
The ICDP Oman Drilling Project – Implications from drill core GT1 on magmatic processes beneath fast-spreading mid-ocean ridges
1Leibniz Universität Hannover, Germany; 2Université de Montpellier, France; 3University of Manchester, United Kingdom; 4Christian-Albrechts-Universität zu Kiel, Germany; 5Geoscience Institutions worldwide
A key aim of the ICDP Oman Drilling Project is to constrain magmatic processes beneath fast-spreading mid-ocean ridges. Several drill cores from the Samail ophiolite (Oman), which is regarded as the best-preserved piece of ancient oceanic lithosphere on land, were obtained. Drill core GT1 covers about 400 m from the layered gabbro section between ~1200 and 800 m above the mantle transition zone (maM). The vast majority of the samples recovered are (olivine-) gabbros with a few cm-scale layers of anorthosite, troctolite, and wehrlite. We found a large scale fractionation trend from 800 to 1070 maM in the primary phases olivine, clinopyroxene, and plagioclase that can be subdivided into five smaller trends, each between 25 and 80 m thick. Above 1070 maM, phase compositions change to more primitive compositions over a 15 m thin horizon, revealing decameter-scale fractionation trends between 1090 and 1170 maM. Significant zoning in clinopyroxene, that was absent below, is observed above 1070 maM. These trends are confirmed by bulk rock chemical and mineral trace element data and indicate that fractional crystallization occurred within the layered gabbros. The fabric symmetry varies along the core with significant lineation at the primitive base and top of the core and almost pure foliation dominating the most evolved horizon at about 1070 maM. Variable fabric symmetries and the observed differences in clinopyroxene zoning could result from different liquid/solid ratios caused by on-going fractional crystallization and occasional magma replenishment.
10:15am - 10:30am
The impact of increasing temperature on microbial lipid distributions in the Nankai Trough subduction zone, IODP Exp. 370
1MARUM, University of Bremen, Germany; 2Kochi Institute, JAMSTEC, Japan; 3Mantle Drilling Promotion Office, JAMSTEC, Japan
Site C0023 in the Nankai Through subduction zone was established in 2016 to investigate the temperature limits of deep subsurface life. Here, we report on the detection of intact polar lipids and their degradation products in sediments recovered from this site where temperatures reach values close to the known limit of life of ca. 120°C at the bottom of the core at 1170 m. Lipid biomarkers characteristic for sedimentary methanogens and unclassified heterotrophic archaea were detected within the methanogenic zone where temperatures transition from mesophilic to thermophilic conditions. These include glycerol, butanetriol and pentanetriol dialkyl glycerol tetraethers (GDGT, BDGT, PDGT) and archaeol with glycosidic headgroups. In this zone, elevated intact polar lipid concentrations compared to vegetative cell numbers suggest substantial accumulation of fossil lipids over time at temperatures of ca. 45 to 50°C. A stark decline in both intact lipids and their degradation products below this depth coincides with the onset of the catagenic zone and the subsequent thermal breakdown of organic matter. The detected lipids are degraded at different reaction rates, reflecting their different thermal stabilities. We also observe a selective removal of GDGTs according to the number of rings in their core structure with important implications for the application of these compounds as paleoenvironmental proxies. This study suggests that intact polar lipids provide a time-integrated signal on microbial community distributions and provides insights into abiotic processes affecting their preservation.