Geology topics

Kenneth A. Farley

Publications and source records attributed to Kenneth A. Farley.

4 recordsLinked to original sources

USGS2025

Cosmic dust reveals dynamic shifts in central Arctic sea-ice coverage over the past 30,000 years

Arctic sea-ice loss affects biological productivity, sustenance in coastal communities, and geopolitics. Forecasting these impacts requires mechanistic understanding of how Arctic sea ice responds to climate change, but this is limited by scarce long-term records. We present continuous 30,000-year reconstructions of sea-ice coverage from the Arctic Ocean based on measurements of two isotopes, thorium-230 and extraterrestrial helium-3, whose burial ratio changes with sea-ice coverage. We found that the central Arctic was perennially covered by sea ice during the last glaciation. Sea-ice cover retreated during the deglaciation approximately 15,000 years ago, culminating in seasonal sea-ice coverage in the warm early Holocene, before ice coverage increased into the late Holocene. Sea-ice changes closely correlate with biological nutrient consumption, supporting projections of a nutrient-starved central Arctic Ocean with continued sea-ice loss.

Science↗

USGS2023

Report of the Science Community Workshop on the proposed First Sample Depot for the Mars Sample Return Campaign

The Mars 2020/Mars Sample Return (MSR) Sample Depot Science Community Workshop was held on September 28 and 30, 2022, to assess the Scientifically-Return Worthy (SRW) value of the full collection of samples acquired by the rover Perseverance at Jezero Crater, and of a proposed subset of samples to be left as a First Depot at a location within Jezero Crater called Three Forks. The primary outcome of the workshop was that the community is in consensus on the following statement: The proposed set of ten sample tubes that includes seven rock samples, one regolith sample, one atmospheric sample, and one witness tube constitutes a SRW collection that: (1) represents the diversity of the explored region around the landing site, (2) covers partially or fully, in a balanced way, all of the International MSR Objectives and Samples Team scientific objectives that are applicable to Jezero Crater, and (3) the analyses of samples in this First Depot on Earth would be of fundamental importance, providing a substantial improvement in our understanding of Mars. At the conclusion of the meeting, there was overall community support for forming the First Depot as described at the workshop and placing it at the Three Forks site. The community also recognized that the diversity of the Rover Cache (the sample collection that remains on the rover after placing the First Depot) will significantly improve with the samples that are planned to be obtained in the future by the Perseverance rover and that the Rover Cache is the primary target for MSR to return to Earth.

Meteoritics and Planetary Science↗

USGS2022

Geochemical insights into formation of enigmatic ironstones from Rio Grande rise, South Atlantic Ocean

Rio Grande Rise (RGR) is an intraplate oceanic elevation in the South Atlantic Ocean that formed at a hotspot on the Mid-Atlantic Ridge during the Cretaceous. In spreading center and hotspot environments, ironstones form mainly by biomineralization of reduced Fe from hydrothermal fluids or oxidation of sulfide deposits. However, RGR has been considered aseismic and volcanically inactive for the past 46 Ma. Here, we investigate the origin of ironstones collected from the summit of RGR using multiple techniques: petrographic observations, X-ray diffraction, U-Th/He geochronology, and chemical composition. The ironstones from RGR consist of finely laminated goethite containing igneous rock fragments, carbonate fluorapatite, and calcite. Our results suggest that Fe oxyhydroxides were precipitated by Fe-oxidizing bacteria forming bacterial mats. The bacterial Fe mats underwent compaction, dewatering, goethite crystallization, and cementation that created the ironstone deposits. U-Th/He geochronology reveals protracted goethite minimum ages extending from the late Miocene to the Quaternary, probably due to multiple generations of mats, slow mineralization rates, and Fe-oxide dissolution-reprecipitation cycles. Flame-like goethite structures underneath FeMn crusts and a chimney-shaped goethite sample with a central channel indicate that the dewatering fluid flowed upward through the deposits, or a thermal fluid source may have been introduced from below the ironstone deposits. High Fe/Mn ratios, low trace metals contents (Ni + Co + Cu), and very low Fe/REY ratios suggest ironstone precipitation from a hydrothermal fluid; however, REY SN plots and bivariate Ce SN /Ce SN ⁎ versus Y SN /Ho SN and Ce SN /Ce SN ⁎ versus Nd plots are inconclusive, and a proximal source of magma was unlikely during the period of mat formation. Given this evidence, we hypothesize that a geothermal circulation system may have facilitated ironstone mineralization at RGR.

Marine Geology↗

USGS2018

Thermochronometry across the Austroalpine-Pennine boundary, Central Alps, Switzerland: Orogen-perpendicular normal fault slip on a major ‘overthrust’ and its implications for orogenesis

Fifty‐one new and 309 published thermochronometric ages (nine systems with closure temperatures ranging from ~450 to 70°C) from the Graubünden region of the Central Alps demonstrate that a pronounced thermal mismatch between the Austroalpine allochthon (Alpine “orogenic lid”) and the Pennine zone persisted until at least 29 Ma and, allowably, until circa 18 Ma. The observed mismatch supports previous suggestions that the famous “overthrust” between the Austroalpine allochthon and the Pennine zone, historically regarded as primarily an Eocene top‐north thrust fault, is in fact primarily an Oligocene‐Miocene normal fault that has a minimum of 60 km of displacement with top‐south or top‐southeast sense of shear. Two hallmarks of Alpine geology, deposition of the foredeep Molasse and emplacement of the Helvetic nappes, appear to be coeval, peripheral manifestations of crustal thickening via the interposition of the Pennine zone as a northward intruding wedge between the Austroalpine “lid” and the European cratonic margin, with the Helvetic system (European margin) acting as the “floor” of the wedge. We presume the Penninic wedge is driven by the buoyant rise of subducted crust no longer able to remain attached to the descending slab. If so, emplacement of the Pennine wedge could have occurred mainly after Adria was juxtaposed against cratonic Europe.

Tectonics↗