Constraints on Moon's orbit 3.2 billion years ago from tidal bundle data

The angular momentum of the Earth-Moon system was initially dominated by Earth's rotation with a short solar day of around 4 hours duration. Since then, Earth gradually transferred angular momentum through tidal friction to the orbit of the Moon, resulting in an increasing orbital radius and a deceleration of Earth's rotation. Geologic observations of tidal deposits can be used to verify and constrain models of lunar orbital evolution. In this work we reexamine the oldest tidal record suitable for analysis from the Moodies Group, South Africa with an age of 3.22 billion years. Time frequency analysis of the series of thicknesses of the sandstone layers yields a periodicity at 15.0 layers, taking into account the possibility of missing laminae. Assuming a mixed tidal system, the duration of two neap-spring-neap cycles was 30.0 lunar days for dominant semidiurnal or 30.0 sidereal days for dominant diurnal tides. We derive the relationship between this observation and the past Earth-Moon distance and re-visit related published work. We find that the Earth-Moon distance 3.22 billion years ago was around 70% of today's value. The Archean solar day was around 13 hours long with around 700 solar days per year. The ratio of solar to lunar tide-raising torque controls the leakage of angular momentum from the Earth-Moon system, but deviation from the assumed ratio of 0.211 results in only moderate changes. A duration of a postulated 21-hour atmospheric resonance shorter than 200 million years would be consistent with our observation; it would significantly alter Earth-Moon distance

In situ S‐isotope compositions of sulfate and sulfide from the 3.2 Ga Moodies Group, South Africa: A record of oxidative sulfur cycling

Sulfate minerals are rare in the Archean rock record and largely restricted to the occurrence of barite (BaSO4). The origin of this barite remains controversially debated. The mass‐independent fractionation of sulfur isotopes in these and other Archean sedimentary rocks suggests that photolysis of volcanic aerosols in an oxygen‐poor atmosphere played an important role in their formation. Here, we report on the multiple sulfur isotopic composition of sedimentary anhydrite in the ca. 3.22 Ga Moodies Group of the Barberton Greenstone Belt, southern Africa. Anhydrite occurs, together with barite and pyrite, in regionally traceable beds that formed in fluvial settings. Variable abundances of barite versus anhydrite reflect changes in sulfate enrichment by evaporitic concentration across orders of magnitude in an arid, nearshore terrestrial environment, periodically replenished by influxes of seawater. The multiple S‐isotope compositions of anhydrite and pyrite are consistent with microbial sulfate reduction. S‐isotope signatures in barite suggest an additional oxidative sulfate source probably derived from continental weathering of sulfide possibly enhanced by microbial sulfur oxidation. Although depositional environments of Moodies sulfate minerals differ strongly from marine barite deposits, their sulfur isotopic composition is similar and most likely reflects a primary isotopic signature. The data indicate that a constant input of small portions of oxidized sulfur from the continents into the ocean may have contributed to the observed long‐term increase in Δ33Ssulfate values through the Paleoarchean.Centre National de la Recherche ScientifiqueDeutsche ForschungsgemeinschaftH2020 European Research Counci

The Malolotsha Klippe: Large‐Scale Subhorizontal Tectonics Along the Southern Margin of the Archean Barberton Greenstone Belt, Eswatini

Whether Archean tectonics were horizontally or vertically dominated is controversially discussed because arguments bear on the kinematics and thermal state of the Archean mantle and constrain the mode of formation of the earliest continental crust. Highly deformed strata of Archean greenstone belts figure prominently in this debate because they record long periods of time and multiple deformation phases. Among the best-preserved greenstone belts counts the Barberton Greenstone Belt (BGB) of southern Africa. Geological mapping of part of the southern BGB in Eswatini (Swaziland), combined with U-Pb zircon dating, shows that the region preserves a tightly re-folded imbricate thrust stack in which metavolcanic and -volcaniclastic strata of the Onverwacht Group, deposited at 3.34–3.29 Ga, have been thrust on top of ca. 3.22 Ga siliciclastic strata of the Moodies Group. The structurally highest element, the Malolotsha Syncline, forms a tectonic klippe of substantial size and is >1,450 m thick. Forward modeling of a balanced cross section indicates that this thrust stack was part of a northwestward-verging orogen along the southern margin of the BGB and records a minimum horizontal displacement of 33 km perpendicular to its present-day faulted, ductily strained and multiply metamorphosed margin. Because conglomerate clasts indicate a significantly higher degree of prolate strain which extends further into the BGB than at its northern margin, late-stage tectonic architecture of the BGB may be highly asymmetrical. Our study documents that the BGB, and perhaps other Archean greenstone belts, preserves a complex array of both vertically- and horizontally-dominated deformation styles that have interfered with each other at small regional and short temporal scales

Reassessing evidence of Moon–Earth dynamics from tidal bundles at 3.2 Ga (Moodies Group, Barberton Greenstone Belt, South Africa)

Past orbital parameters of the Moon are difficult to reconstruct from geological records because relevant data sets of tidal strata are scarce or incomplete. The sole Archean data point is from the Moodies Group (ca 3.22 Ga) of the Barberton Greenstone Belt, South Africa. From the time-series analysis of tidal bundles from a well-exposed subaqueous sand wave of this unit, Eriksson and Simpson (Geology, 28, 831) suggested that the Moon’s anomalistic month at 3.2 Ga was closer to 20 days than the present 27.5 days. This is in apparent accordance with models of orbital mechanics which place the Archean Moon in a closer orbit with a shorter period, resulting in stronger tidal action. Although this study’s detailed geological mapping and section measuring of the site confirmed that the sandstone bed in question is likely a migrating dune, the presence of angular mud clasts, channel-margin slumps, laterally aggrading channel fills and bidirectional paleocurrents in overlying and underlying beds suggests that this bedform was likely located in a nearshore channel near lower-intertidal flats and subtidal estuarine bars; it thus carries risk of incomplete preservation. Repeated measurements of foreset thicknesses along the published traverse, measured perpendicular to bedding, failed to show consistent spectral peaks. Larger data sets acquired along traverses measured parallel to bedding along the 20.5 m wide exposure are affected by minor faulting, uneven outcrop weathering, changing illumination, weather, observer bias and show a low reproducibility. The most robust measurements herein confirm the periodicity peak of approximately 14 in the original data of Eriksson and Simpson (Geology, 28, 831). Because laminae may have been eroded, the measurements may represent a lower bound of about 28 lunar days per synodic month. This estimate agrees well with Earth–Moon dynamic models which consider the conservation of angular momentum and place the Archaean Moon in a lower orbit around a faster-spinning Earth

Reassessing evidence of Moon–Earth dynamics from tidal bundles at 3.2 Ga (Moodies Group, Barberton Greenstone Belt, South Africa)

Past orbital parameters of the Moon are difficult to reconstruct from geological records because relevant data sets of tidal strata are scarce or incomplete. The sole Archean data point is from the Moodies Group (ca 3.22 Ga) of the Barberton Greenstone Belt, South Africa. From the time-series analysis of tidal bundles from a well-exposed subaqueous sand wave of this unit, Eriksson and Simpson (Geology, 28, 831) suggested that the Moon’s anomalistic month at 3.2 Ga was closer to 20 days than the present 27.5 days. This is in apparent accordance with models of orbital mechanics which place the Archean Moon in a closer orbit with a shorter period, resulting in stronger tidal action. Although this study’s detailed geological mapping and section measuring of the site confirmed that the sandstone bed in question is likely a migrating dune, the presence of angular mud clasts, channel-margin slumps, laterally aggrading channel fills and bidirectional paleocurrents in overlying and underlying beds suggests that this bedform was likely located in a nearshore channel near lower-intertidal flats and subtidal estuarine bars; it thus carries risk of incomplete preservation. Repeated measurements of foreset thicknesses along the published traverse, measured perpendicular to bedding, failed to show consistent spectral peaks. Larger data sets acquired along traverses measured parallel to bedding along the 20.5 m wide exposure are affected by minor faulting, uneven outcrop weathering, changing illumination, weather, observer bias and show a low reproducibility. The most robust measurements herein confirm the periodicity peak of approximately 14 in the original data of Eriksson and Simpson (Geology, 28, 831). Because laminae may have been eroded, the measurements may represent a lower bound of about 28 lunar days per synodic month. This estimate agrees well with Earth–Moon dynamic models which consider the conservation of angular momentum and place the Archaean Moon in a lower orbit around a faster-spinning Earth

Constraints on Moon's Orbit 3.2 Billion Years Ago From Tidal Bundle Data

The angular momentum of the Earth‐Moon system was initially dominated by Earth's rotation with a short solar day of around 5 hr duration. Since then, Earth gradually transferred angular momentum through tidal friction to the orbit of the Moon, resulting in an increasing orbital radius and a deceleration of Earth's rotation. Geologic observations of tidal deposits can be used to verify and constrain models of lunar orbital evolution. In this work we reexamine the oldest tidal record suitable for analysis from the Moodies Group, South Africa, with an age of 3.22 billion years. Time frequency analysis of the series of thicknesses of the sandstone‐shale layers yields a periodicity of 15.0 layers, taking into account the possibility of missing laminae. Assuming a mixed tidal system, the duration of two neap‐spring‐neap cycles was 30.0 lunar days for dominant semidiurnal or 30.0 sidereal days for dominant diurnal tides. We derive the relationship between this observation and the past Earth‐Moon distance and re‐visit related published work. We find that the Earth‐Moon distance 3.2 billion years ago was about 70% of today's value. The Archean solar day was around 13 hr long. The ratio of solar to lunar tide‐raising torque controls the leakage of angular momentum from the Earth‐Moon system, but deviation from the assumed ratio of 0.211 results in only moderate changes. A duration of a postulated 21‐hr atmospheric resonance shorter than 200 million years would be consistent with our observation; it would significantly alter the Earth‐Moon distance.Plain Language Summary: After its formation 4.5 billion years ago, the Moon circled Earth in a low orbit while Earth rotated faster than today around its axis. In the course of time, the Moon gradually evolved to a higher orbit while the rotation of Earth slowed due to the frictional effect of tides. Theoretical models can describe the evolution of the distance between Earth and the Moon with time until today. Counting the thickness of thin sandstone‐shale couplets of known age, which are layered due to tides, can constrain these models. In this work we reexamine the oldest of these geological records in the Moodies Group of South Africa, with an age of 3.2 billion years. The thickness of layers changes with a periodicity of 15 layers which is assumed to originate from varying strengths of currents between successive spring tides. Kepler's third law and the law of conservation of angular momentum allow us to derive the parameters of the lunar orbit from this measurement. According to our analysis, the Earth‐Moon distance was around 70% of today's value 3.2 billion years ago. The faster rotation rate of Earth resulted in a length of day of around 13 hr.Key Points: Time frequency analysis yields 30.0 layers per two neap‐spring‐neap cycles, taking missing laminae in the tidal record into account. Earth‐Moon distance of ca. 70% of today's value 3.2 billion years ago results in a solar day of 13 hr duration. Duration of 21‐hr atmospheric resonance for <200 million years is consistent with our observation, alters estimate of Earth‐Moon distance

Neogene sedimentary and mass-wasting processes on the continental margin off south-central Chile inferred from dredge samples

The active continental margin off south-central Chile (36° to 40°S) is transitional between the tectonically erosive, empty-trench margin north of Juan Fernandez Ridge and the accretionary, trench-filled margin south of the Chile Triple Junction. The small width of the presently active accretionary wedge (maximum width of 25 to 50 km) argues for past phases of tectonic erosion. At present, this sector shows indications of contemporaneous accretion, subduction, and underplating of sediment, as well as readjustment of the slope by various mass-wasting processes. In this context, this study aims to examine the Neogene sedimentary processes on the continental margin from dredge samples recovered during R/V SONNE cruise SO161-5 within this transitional domain using lithology, sandstone petrology, shale mineralogy, and analysis of sedimentary structures. Our results yield that the principal transport of material occurs in high-energy turbidity currents and debris flows via submarine canyons deeply cutting the continental slope, whereas sediment on the shelf is transported by strong coast-parallel bottom currents and trapped by submarine canyons cutting into the shelf. A wide range of mass-wasting processes including slumping, debris flows, evolving to low-density turbidity currents and mud flows, rework the slope sediments. In contrast, thick undisturbed sequences of mostly hemipelagic sediments accumulate in active slope basins, which are largely protected from mass movements. XRD analyses revealed early diagenetic lithification and overall burial depths of up to ∼ 230 mbsf, suggesting a shallow-subsurface cycle of sedimentation, subsidence, diagenesis, uplift, erosion, and resedimentation. The composition of sandstones is dominated by volcanic rock fragments of Andean provenance. Along-strike modal changes reflect a southward increase in glacially denudation and rainfall, the combination of which caused more intense erosion of volcanic rocks and exposure, weathering and, as a result, increased fluvial transport of metamorphic and plutonic rocks to the sea

Comparison of Plate Tectonic Models for the North and Central Atlantic (Paleoceanographic Mapping Project Progress Report No. 20-0487)

Numerous models describing the tectonic evolution of the North and Central Atlantic Ocean have been proposed. However, it is often difficult to quickly evaluate how these models differ. In this study, we have modified a computer program, originally written by Philippe Patriat that graphically displays spreading rates and spreading directions for any pair of plates. Using this program we have analyzed the plate tectonic models proposed by Pitman and Talwani (1972), Sclater et al. (1977), Olivet et al. (1984), Savostin et al. (1986), Klitgord and Schouten (1986), and Srivastava and Tapscott (1986). In addition, we have included the unpublished models of Francheteau (1970), Phillips and Tapscott (1981 ), Molnar and Stork (1983), Rowley et al. (1985), Gahagan et al. ( 1987), and Mueller (1987).UT Institute for Geophysics Paleoceanographic Mapping Project (POMP)Institute for Geophysic

Reconstructions of the Central and North Atlantic Using New Information from Satellite Altimetry (Paleoceanographic Mapping Project Progress Report No. 16-1186)

This series of maps illustrates the tectonic evolution of the Central and North Atlantic for anomaly times A13, A25, A34, M16, and M25 (Figures 1-11). In addition to modeling the relative motions of the five major blocks of continental lithosphere (Europe, Greenland, North America, Africa, Iberia) an attempt was made to reconstruct the tectonic evolution of more complex areas such as northwest Africa, the western Mediterranean, the Norwegian Sea, and the Caribbean.UT Institute for Geophysics Paleoceanographic Mapping Project (POMP)Institute for Geophysic