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At least 325 records · Page 18Linked to original sources

USGS2014

Quaternary ostracode and foraminiferal biostratigraphy and paleoceanography in the western Arctic Ocean

The stratigraphic distributions of ostracodes and selected calcareous benthic and planktic foraminiferal species were studied in sediment cores from ~ 700 to 2700 m water depth on the Northwind, Mendeleev, and Lomonosov Ridges in the western Arctic Ocean. Microfaunal records in most cores cover mid- to late Quaternary sediments deposited in the last ~ 600 ka, with one record covering the last ~ 1.5 Ma. Results show a progressive faunal turnover during the mid-Pleistocene transition (MPT, ~ 1.2 to 0.7 Ma) and around the mid-Brunhes event (MBE, ~ 0.4 Ma) reflecting major changes in Arctic Ocean temperature, circulation and sea-ice cover. The observed MPT shift is characterized by the extinction of species that today inhabit the sea-ice free subpolar North Atlantic and/or seasonally sea-ice free Nordic Seas ( Echinocythereis sp., Rockallia cf. enigmatica , Krithe cf. aquilonia , Pterygocythereis vannieuwenhuisei ). After a very warm interglacial during marine isotope stage (MIS) 11 dominated by the temperate planktic foraminifer Turborotalita egelida , the MBE experienced a shift to polar assemblages characteristic of predominantly perennial Arctic sea-ice cover during the interglacial and interstadial periods of the last 300 ka. These include the planktic foraminifera Neogloboquadrina pachyderma , the sea-ice dwelling ostracode Acetabulastoma arcticum and associated benthic taxa Pseudocythere caudata , Pedicythere neofluitans , and Polycope spp. Several species can be used as biostratigraphic markers of specific intervals such as ostracodes Rabilimis mirabilis — MIS 5 and P. vannieuwenhuisei extinction after MIS 11, and foraminiferal abundance zones Bulimina aculeata — late MIS 5 and Bolivina arctica — MIS 5-11.

Marine Micropaleontology↗

USGS2008

Trace-element budgets in the Ohio/Sunbury shales of Kentucky: Constraints on ocean circulation and primary productivity in the Devonian-Mississippian Appalachian Basin

The hydrography of the Appalachian Basin in late Devonian-early Mississippian time is modeled based on the geochemistry of black shales and constrained by others' paleogeographic reconstructions. The model supports a robust exchange of basin bottom water with the open ocean, with residence times of less than forty years during deposition of the Cleveland Shale Member of the Ohio Shale. This is counter to previous interpretations of these carbon-rich units having accumulated under a stratified and stagnant water column, i.e., with a strongly restricted bottom bottom-water circulation. A robust circulation of bottom waters is further consistent with the palaeoclimatology, whereby eastern trade-winds drove upwelling and arid conditions limited terrestrial inputs of siliciclastic sediment, fresh waters, and riverine nutrients. The model suggests that primary productivity was high (~ 2??g C m- 2 d- 1), although no higher than in select locations in the ocean today. The flux of organic carbon settling through the water column and its deposition on the sea floor was similar to fluxes found in modern marine environments. Calculations based on the average accumulation rate of the marine fraction of Ni suggest the flux of organic carbon settling out of the water column was approximately 9% of primary productivity, versus an accumulation rate (burial) of organic carbon of 0.5% of primary productivity. Trace-element ratios of V:Mo and Cr:Mo in the marine sediment fraction indicate that bottom waters shifted from predominantly anoxic (sulfate reducing) during deposition of the Huron Shale Member of the Ohio Shale to predominantly suboxic (nitrate reducing) during deposition of the Cleveland Shale Member and the Sunbury Shale, but with anoxic conditions occurring intermittently throughout this period. ?? 2008 Elsevier B.V.

Palaeogeography, Palaeoclimatology, Palaeoecology↗

USGS2015

An early to mid-Pleistocene deep Arctic Ocean ostracode fauna with North Atlantic affinities

An early to middle Pleistocene ostracode fauna was discovered in sediment core P1-93-AR-23 (P23, 76.95°N, 155.07°W) from 951 meter water depth from the Northwind Ridge, western Arctic Ocean. Piston core P23 yielded more than 30,000 specimens and a total of about 30 species. Several early to mid-Pleistocene species in the genera Krithe , Echinocythereis , Pterygocythereis , and Arcacythere are now extinct in the Arctic and show taxonomic affinities to North Atlantic Ocean species. Our results suggest that there was a major ostracode faunal turnover during the global climate transitions known as the Mid-Pleistocene Transition (MPT, ~ 1.2 to 0.7 Ma) and the Mid-Brunhes Event (MBE, ~ 400 ka) reflecting the development of perennial sea ice during interglacial periods and large ice shelves during glacial periods over the last 400,000 years.

Palaeogeography, Palaeoclimatology, Palaeoecology↗

USGS2007

A ~25 ka Indian Ocean monsoon variability record from the Andaman Sea

Recent paleoclimatic work on terrestrial and marine deposits from Asia and the Indian Ocean has indicated abrupt changes in the strength of the Asian monsoon during the last deglaciation. Comparison of marine paleoclimate records that track salinity changes from Asian rivers can help evaluate the coherence of the Indian Ocean monsoon (IOM) with the larger Asian monsoon. Here we present paired Mg/Ca and δ 18 O data on the planktic foraminifer Globigerinoides ruber (white) from Andaman Sea core RC12-344 that provide records of sea-surface temperature (SST) and δ 18 O of seawater (δ 18 O sw ) over the past 25,000 years (ka) before present (BP). Age control is based on nine accelerator mass spectrometry (AMS) dates on mixed planktic foraminifera. Mg/Ca-SST data indicate that SST was &sim;3 °C cooler during the last glacial maximum (LGM) than the late Holocene. Andaman Sea δ 18 O sw exhibited higher than present values during the Lateglacial interval ca 19–15 ka BP and briefly during the Younger Dryas ca 12 ka BP. Lower than present δ 18 O sw values during the BØlling/AllerØd ca 14.5–12.6 ka BP and during the early Holocene ca 10.8–5.5 ka BP are interpreted to indicate lower salinity, reflect some combination of decreased evaporation–precipitation (E–P) over the Andaman Sea and increased Irrawaddy River outflow. Our results are consistent with the suggestion that IOM intensity was stronger than present during the BØlling/AllerØd and early Holocene, and weaker during the late glaciation, Younger Dryas, and the late Holocene. These findings support the hypothesis that rapid climate change during the last deglaciation and Holocene included substantial hydrologic changes in the IOM system that were coherent with the larger Asian monsoon.

Quaternary Science Reviews↗

USGS2010

Quaternary Sea-ice history in the Arctic Ocean based on a new Ostracode sea-ice proxy

Paleo-sea-ice history in the Arctic Ocean was reconstructed using the sea-ice dwelling ostracode Acetabulastoma arcticum from late Quaternary sediments from the Mendeleyev, Lomonosov, and Gakkel Ridges, the Morris Jesup Rise and the Yermak Plateau. Results suggest intermittently high levels of perennial sea ice in the central Arctic Ocean during Marine Isotope Stage (MIS) 3 (25-45 ka), minimal sea ice during the last deglacial (16-11 ka) and early Holocene thermal maximum (11-5 ka) and increasing sea ice during the mid-to-late Holocene (5-0 ka). Sediment core records from the Iceland and Rockall Plateaus show that perennial sea ice existed in these regions only during glacial intervals MIS 2, 4, and 6. These results show that sea ice exhibits complex temporal and spatial variability during different climatic regimes and that the development of modern perennial sea ice may be a relatively recent phenomenon. ?? 2010.

Quaternary Science Reviews↗

USGS2000

Using submarine lava pillars to record mid-ocean ridge eruption dynamics

Submarine lava pillars are hollow, glass-lined, basaltic cylinders that occur at the axis of the mid-ocean ridge, and within the summit calderas of some seamounts. Typically, pillars are ~1-20 m tall and 0.25-2.0 m in diameter, with subhorizontal to horizontal glassy selvages on their exterior walls. Lava pillars form gradually during a single eruption, and are composed of lava emplaced at the eruption onset as well as the last lava remaining after the lava pond has drained. On the deep sea floor, the surface of a basaltic lava flow quenches to glass within 1 s, thereby preserving information about eruption dynamics, as well as chemical and physical properties of lava within a single eruption. Investigation of different lava pillars collected from a single eruption allows us to distinguish surficial lava-pond or lava-lake geochemical processes from those operating in the magma chamber. Morphologic, major-element, petrographic and helium analyses were performed on portions of three lava pillars formed during the April 1991 eruption near 9°50'N at the axis of the East Pacific Rise. Modeling results indicate that the collected portions of pillars formed in ~2-5 h, suggesting a total eruption duration of ~8-20 h. These values are consistent with observed homogeneity in the glass helium concentrations and helium diffusion rates. Major-element compositions of most pillar glasses are homogeneous and identical to the 1991 flow, but slight chemical variations measured in the outermost portions of some pillars may reflect post-eruptive processes rather than those occurring in subaxial magma bodies. Because lava pillars are common at mid-ocean ridges (MORs), the concepts and techniques we present here may have important application to the study of MOR eruptions, thereby providing a basis for quantitative comparisons of volcanic eruptions in geographically and tectonically diverse settings. More research is needed to thoroughly test the hypotheses presented here. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

Earth and Planetary Science Letters↗

USGS2025

Using distance sampling with camera traps to estimate densities of ungulates on tropical oceanic islands

Reliable population estimates are one of the most elementary needs for the management of wildlife, particularly for introduced ungulates on oceanic islands. We aimed to produce accurate and precise density estimates of Philippine deer ( Rusa marianna ) and wild pigs ( Sus scrofa ) on Guam using motion-triggered cameras combined with distance sampling to estimate densities from observations of unmarked animals while accounting for imperfect detection. We used an automated digital data processing pipeline for species recognition and to estimate the distance to detected species. Our density estimates were slightly lower than published estimates, consistent with management to reduce populations. We estimated the number of camera traps needed to obtain a 0.1 coefficient of variation was substantial, requiring > ten-fold increase in camera traps, while estimates with precision of 0.2 or 0.3 were more achievable, requiring doubling to quadrupling the number of camera traps. We provide best practices for establishing and conducting distance sampling with camera trap surveys for density estimation based on lessons learned during this study. Future studies should consider distance sampling with camera traps to efficiently survey and monitor unmarked animals, particularly medium-sized ungulates, in tropical, oceanic island ecosystems.

Journal of Tropical Ecology↗

USGS2009

Inputs of fossil carbon from wastewater treatment plants to U.S. Rivers and oceans

Every day more than 500 million cubic meters of treated wastewater are discharged into rivers, estuaries, and oceans, an amount slightly less than the average flow of the Danube River. Typically, wastewaters have high organic carbon (OC) concentrations and represent a large fraction of total river flow and a higher fraction of river OC in densely populated watersheds. Here, we report the first direct measurements of radiocarbon ( 14 C) in municipal wastewater treatment plant (WWTP) effluent. The radiocarbon ages of particulate and dissolved organic carbon (POC and DOC) in effluent are old and relatively uniform across a range of WWTPs in New York and Connecticut. Wastewater DOC has a mean radiocarbon age of 1630 ?? 500 years B.P. and a mean ?? 13 C of -26.0 ?? 1???. Mass balance calculations indicate that 25% of wastewater DOC is fossil carbon, which is likely derived from petroleumbased household products such as detergents and pharmaceuticals. Thesefindings warrant reevaluation of the "apparent age" of riverine DOC, the total flux of petroleum carbon to U.S. oceans, and OC source assignments in waters impacted by sewage. ?? 2009 American Chemical Society.

Environmental Science & Technology↗

USGS1999

Variability in bacterial community structure during upwelling in the coastal ocean

Over the last 30 years, investigations at the community level of marine bacteria and phytoplankton populations suggest they are tightly coupled. However, traditional oceanographic approaches cannot assess whether associations between specific bacteria and phytoplankton exist. Recently, molecular based approaches have been implemented to characterize specific members of different marine bacterial communities. Yet, few molecular-based studies have examined coastal upwelling situations. This is important since upwelling systems provide a unique opportunity for analyzing the association between specific bacteria and specific phytoplankton in the ocean. It is widely believed that upwelling can lead to changes in phytoplankton populations (blooms). Thus, if specific associations exist, we would expect to observe changes in the bacterial population triggered by the bloom. In this paper, we present preliminary data from coastal waters off New Jersey that confirm a shift in bacterial communities during a 1995 upwelling event recorded at a long-term earth observatory (LEO-15) in the Mid-Atlantic Bight. Using PCR amplification and cloning, specific bacterial 16S ribosomal RNA sequences were found which were present in upwelling samples during a phytoplankton bloom, but were not detected in non-bloom samples (surface seawater, offshore sites or sediment samples) collected at the same time or in the same area. These findings are consistent with the notion of specific associations between bacteria and phytoplankton in the ocean. However, further examination of episodic events, such as coastal upwelling, are needed to confirm the existence of specific associations. Additionally, experiments need to be performed to elucidate the mechanisms leading to the specific linkages between a group of bacteria and a group of phytoplankton.

Hydrobiologia↗

USGS2004

Deep and bottom water export from the Southern Ocean to the Pacific over the past 38 million years

The application of radiogenic isotopes to the study of Cenozoic circulation patterns in the South Pacific Ocean has been hampered by the fact that records from only equatorial Pacific deep water have been available. We present new Pb and Nd isotope time series for two ferromanganese crusts that grew from equatorial Pacific bottom water (D137-01, "Nova," 7219 m water depth) and southwest Pacific deep water (63KD, "Tasman," 1700 m water depth). The crusts were dated using 10 Be/ 9 Be ratios combined with constant Co-flux dating and yield time series for the past 38 and 23 Myr, respectively. The surface Nd and Pb isotope distributions are consistent with the present-day circulation pattern, and therefore the new records are considered suitable to reconstruct Eocene through Miocene paleoceanography for the South Pacific. The isotope time series of crusts Nova and Tasman suggest that equatorial Pacific deep water and waters from the Southern Ocean supplied the dissolved trace metals to both sites over the past 38 Myr. Changes in the isotopic composition of crust Nova are interpreted to reflect development of the Antarctic Circumpolar Current and changes in Pacific deep water circulation caused by the build up of the East Antarctic Ice Sheet. The Nd isotopic composition of the shallower water site in the southwest Pacific appears to have been more sensitive to circulation changes resulting from closure of the Indonesian seaway.

Paleoceanography↗

USGS2007

Flux and age of dissolved organic carbon exported to the Arctic Ocean: A carbon isotopic study of the five largest arctic rivers

The export and Δ 14 C-age of dissolved organic carbon (DOC) was determined for the Yenisey, Lena, Ob', Mackenzie, and Yukon rivers for 2004–2005. Concentrations of DOC elevate significantly with increasing discharge in these rivers, causing approximately 60% of the annual export to occur during a 2-month period following spring ice breakup. We present a total annual flux from the five rivers of ∼16 teragrams (Tg), and conservatively estimate that the total input of DOC to the Arctic Ocean is 25–36 Tg, which is ∼5–20% greater than previous fluxes. These fluxes are also ∼2.5× greater than temperate rivers with similar watershed sizes and water discharge. Δ 14 C-DOC shows a clear relationship with hydrology. A small pool of DOC slightly depleted in Δ 14 C is exported with base flow. The large pool exported with spring thaw is enriched in Δ 14 C with respect to current-day atmospheric Δ 14 C-CO 2 values. A simple model predicts that ∼50% of DOC exported during the arctic spring thaw is 1–5 years old, ∼25% is 6–10 years in age, and 15% is 11–20 years old. The dominant spring melt period, a historically undersampled period, exports a large amount of young and presumably semilabile DOC to the Arctic Ocean.

Global Biogeochemical Cycles↗

USGS2009

Impact of a permanent El Niño (El Padre) and Indian Ocean Dipole in warm Pliocene climates

Pliocene sea surface temperature data, as well as terrestrial precipitation and temperature proxies, indicate warmer than modern conditions in the eastern equatorial Pacific and imply permanent El Niño–like conditions with impacts similar to those of the 1997/1998 El Niño event. Here we use a general circulation model to examine the global-scale effects that result from imposing warm tropical sea surface temperature (SST) anomalies in both modern and Pliocene simulations. Observed SSTs from the 1997/1998 El Niño event were used for the anomalies and incorporate Pacific warming as well as a prominent Indian Ocean Dipole event. Both the permanent El Niño (also called El Padre) and Indian Ocean Dipole (IOD) conditions are necessary to reproduce temperature and precipitation patterns consistent with the global distribution of Pliocene proxy data. These patterns may result from the poleward propagation of planetary waves from the strong convection centers associated with the El Niño and IOD.

Paleoceanography↗

USGS2020

The ocean's impact on slow slip events

We test the hypothesis that ocean seafloor pressures impart stresses that alter the initiation or termination of transient slow slip events (SSEs) on shallow submarine and near-coastal faults, using simulated seafloor pressures and a new catalog of SSEs in the Hikurangi subduction zone. We show that seafloor pressures may be represented by an average time history over the ~100-km dimensions of the study area. We account for SSE uncertainties and the multiplicity of processes that affect SSEs statistically by estimating the probabilities of rejecting the null hypothesis that SSE initiation or termination pressures are those to be expected by chance sampling of known (modeled) seafloor pressures, with low probabilities indicating some causal connection. No impact of ocean pressure changes on SSE initiation is detectable, but a correlation with their terminations is suggested. SSE slip that weakens the fault and makes it more sensitive to small stress changes may explain results.

Pacific Ocean↗

USGS2026

Tectonic controls on volcanism and associated hydrothermal activity in a sediment-dominated mid-ocean ridge; Escanaba Trough

Mid-ocean ridges, the Earth's most extensive volcanic system, exhibit unique characteristics in sediment-dominant environments. Thick sediment cover insulates the crust and channels fluid along pathways that can lead to the formation of distinct crustal alteration patterns, exceptionally large mineral deposits, and specialized chemosynthetic ecosystems. This study presents an interdisciplinary investigation into the tectonics of the Escanaba Trough, a heavily sedimented axial valley at the southern Gorda Ridge in the Northeast Pacific Ocean. A primary challenge in such environments is overcoming the masking effect of thick sediments on basement structures that control magmatic and hydrothermal activity. We address this by employing three-dimensional (3D) magnetic modeling of high-resolution near-seafloor magnetic data collected by an autonomous underwater vehicle (AUV). The 2022 surveys with AUV Sentry provided data for 3D magnetic susceptibility models, refining our understanding of the geometry of sub-sediment laccoliths/saucer-shaped sills and hydrothermal alteration. In conjunction with a new 1:100,000 scale lithostratigraphic map, we outline the tectonic controls on the emplacement of Escanaba Trough's three main volcanic centers, characterize the geometry of its spreading segments, and provide volumetric data on the distribution of sub-sediment volcanism in the southern Gorda Ridge.

Escanaba Trough, Pacific Ocean↗

USGS2026

Hydrothermal manganese-oxide mineralization of a carbonate ooze, Samoan hotspot region, South Pacific Ocean

Low-temperature hydrothermal manganese oxides occur throughout the global oceans. However, the hydrothermal replacement of a carbonate ooze by manganese oxides is described here for the first time. The 24 samples dredged from three locations around the Territory of American Samoa in the South Pacific Ocean include six samples with remnant carbonate and volcaniclastic sediments, which we refer to as “low Mn,” and 18 samples in which the mineralization is pervasive and has replaced most original sediment, termed “high Mn.” The 18 high-Mn samples exhibit a mean Mn content of 51 wt.%. Higher Li and Mn contents and lower Fe contents in the high-Mn samples indicate a hydrothermal origin and distinguish these samples from hydrogenetic ferromanganese crusts. Mn-oxide layers are up to 90 mm thick, some with columns to 44 mm long and 10 mm wide, the magnitude of which has not been described previously. Samples are composed of birnessite and 10 Å phyllomanganate minerals. Textures of the thickest Mn layers indicate mineralization below the seabed from ascending fluids during multiple hydrothermal pulses. Mineralization took place by complete to partial replacement and cementation of foraminiferal sediments intermixed with volcaniclastic sediments in varying amounts. Our results highlight the production of carbonate sediment-hosted hydrothermal Mn oxides from multiple hydrothermal sources within the Samoan volcanic chain. The potential extensive distribution on the regional scale of this newly described mineralization process and unique element enrichments raise questions about its broader distribution globally and potential importance to hydrothermal processes, element mass balance, and seabed mineral resources.

Geochemistry, Geophysics, Geosystems↗

USGS1996

Late Paleocene Arctic Ocean shallow-marine temperatures from mollusc stable isotopes

Late Paleocene high-latitude (80°N) Arctic Ocean shallow-marine temperatures are estimated from molluscan δ 18 O time series. Sampling of individual growth increments of two specimens of the bivalve Camptochlamys alaskensis provides a high-resolution record of shell stable isotope composition. The heavy carbon isotopic values of the specimens support a late Paleocene age for the youngest marine beds of the Prince Creek Formation exposed near Ocean Point, Alaska. The oxygen isotopic composition of regional freshwater runoff is estimated from the mean δ 18 O value of two freshwater bivalves collected from approximately coeval fluviatile beds. Over a 30 – 34‰ range of salinity, values assumed to represent the tolerance of C. alaskensis , the mean annual shallow-marine temperature recorded by these individuals is between 11° and 22°C. These values could represent maximum estimates of the mean annual temperature because of a possible warm-month bias imposed on the average δ 18 O value by slowing or cessation of growth in winter months. The amplitude of the molluscan δ 18 O time series probably records most of the seasonality in shallow-marine temperature. The annual temperature range indicated is approximately 6°C, suggesting very moderate high-latitude marine temperature seasonality during the late Paleocene. On the basis of analogy with modern Chlamys species, C. alaskensis probably inhabited water depths of 30–50 m. The seasonal temperature range derived from δ 18 O is therefore likely to be damped relative to the full range of annual sea surface temperatures. High-resolution sampling of molluscan shell material across inferred growth bands represents an important proxy record of seasonality of marine and freshwater conditions applicable at any latitude. If applied to other regions and time periods, the approach used here would contribute substantially to the paleoclimate record of seasonality.

Paleoceanography↗

USGS1998

Sulfur in serpentinized oceanic peridotites: Serpentinization processes and microbial sulfate reduction

The mineralogy, contents, and isotopic compositions of sulfur in oceanic serpentinites reflect variations in temperatures and fluid fluxes. Serpentinization of <1 Ma peridotites at Hess Deep occurred at high temperatures (200°–400°C) and low water/rock ratios. Oxidation of ferrous iron to magnetite maintained low ƒO 2 and produced a reduced, low-sulfur assemblage including NiFe alloy. Small amounts of sulfate reduction by thermophilic microbes occurred as the system cooled, producing low-δ 34 S sulfide (1.5‰ to −23.7‰). In contrast, serpentinization of Iberian Margin peridotites occurred at low temperatures(∼20°–200°C) and high water/rock ratios. Complete serpentinization and consumption of ferrous iron allowed evolution to higher ƒO 2 . Microbial reduction of seawater sulfate resulted in addition of low-δ 34 S sulfide (∼15 to ∼43‰) and formation of higher-sulfur assemblages that include valleriite and pyrite. The high SO 4 /total S ratio of Hess Deep serpentinites (0.89) results in an increase of total sulfur and high δ 34 S of total sulfur (mean ∼8‰). In contrast, Iberian Margin serpentinites gained large amounts of 34 S-poor sulfide (mean total S = 3800 ppm), and the high sulfide/total S ratio (0.61) results in a net decrease in δ 34 S of total sulfur (mean ≈ −5‰). Thus serpentinization is a net sink for seawater sulfur, but the amount fixed and its isotopic composition vary significantly. Serpentinization may result in uptake of 0.4–14 × 10 12 g S yr −1 from the oceans, comparable to isotopic exchange in mafic rocks of seafloor hydrothermal systems and approaching global fluxes of riverine sulfate input and sedimentary sulfide output.

Journal of Geophysical Research B: Solid Earth↗

USGS2012

Information on stress conditions in the oceanic crust from oval fractures in a deep borehole

Oval images etched into the vail of a deep borehole were detected in DSDP (Deep Sea Drilling Project) Hole 504B, eastern equatorial Pacific Ocean, from analysis of an acoustic televiever log. Initial speculation as to the origin of these remarkable features considered the intersection of pillow basalts with the wellbore. However, a systematic inspection of these ovals has identified intriguing consistencies in appearance that cannot be explained satisfactorily by a random, coincidental distribution of pillow lavas. As an alternative hypothesis, Mohr-Coulomb failure criterion is used to account for the generation and orientation of similarly curved, stress-induced fractures. Consequently, these oval features can be interpreted as fractures and related directly to stress conditions in the oceanic crust at this site. The azimuth of the oval center corresponds to the orientation of maximum horizontal principal stress (S H ), and the oval width, which spans approximately 180° of the borehole, is aligned vith the azimuth of minimum horizontal principal stress (S h ). The oval height is controlled by the fracture angle and thus is a function of the coefficient of internal friction of the rock.

Geophysical Research Letters↗