Geology of Chief Joseph Pass, Wyoming: Crest of Rattlesnake Mountain anticline and escape path of the Eocene Heart Mountain slide

ABSTRACT Rattlesnake Mountain is a Laramide uplift cored by Archean gneiss that formed by offset along two reverse faults with opposing dips, the result being an asymmetric anticline with a drape fold of Cambrian–Cretaceous sediments. Rattlesnake Mountain was uplifted ca. 57 Ma and was a structural buttress that impeded motion of upper-plate blocks of the catastrophic Heart Mountain slide (49.19 Ma). North of Pat O’Hara Mountain anticline, Rattlesnake Mountain anticline has a central graben that formed ca. 52 Ma (U-Pb age on vein calcite in normal faults) into which O- and C-depleted fluids propagated upward with hydrocarbons. The graben is defined by down-dropped Triassic Chugwater shales atop the anticline that facilitated motion of Heart Mountain slide blocks of Paleozoic limestones dolomite (i.e., the Ordovician Bighorn Dolomite and Mississippian Madison Limestone) onto, and over, Rattlesnake Mountain into the Bighorn Basin. Heart Mountain fault gouge was also injected downward into the bounding Rattlesnake Mountain graben normal faults (U-Pb age ca. 48.8 ± 5 Ma), based on O and C isotopes; there is no anisotropy of magnetic susceptibility fabric present. Calcite veins parallel to graben normal faults precipitated from meteoric waters (recorded by O and C isotopes) heated by the uplifting Rattlesnake Mountain anticline and crystallized at 57 °C (fluid inclusions) in the presence of oil. Calcite twinning strain results from graben injectites and calcite veins are different; we also documented a random layer-parallel shortening strain pattern for the Heart Mountain slide blocks in the ramp region (n = 4; west) and on the land surface (n = 5; atop Rattlesnake Mountain). We observed an absence of any twinning strain overprint (low negative expected values) in the allochthonous upper-plate blocks and in autochthonous carbonates directly below the Heart Mountain slide surface, again indicating rapid motion including horizontal rotation about vertical axes of the upper-plate Heart Mountain slide blocks during the Eocene.

Synthesis of Recent Paleoseismic Research on Quaternary Faulting in the Eastern Tennessee Seismic Zone, Eastern North America: Implications for Seismic Hazard and Intraplate Seismicity

ABSTRACT Causes of intraplate seismicity remain a great unsolved problem, in contrast with plate-boundary seismicity. Modern seismicity records frequent seismic activity in plate-boundary seismic zones, but in fault zones where seismic activity is not frequent, plate boundary or intraplate, resolution of prehistoric earthquake activity is critical for estimating earthquake recurrence interval and maximum expected magnitude. Thus, documenting prehistoric earthquakes is crucial for assessing earthquake hazard posed to infrastructure, including nuclear reactors and large dams. The ∼400 km long eastern Tennessee seismic zone (ETSZ), United States, is the third most active seismic zone east of the Rocky Mountains in North America, although the largest recorded ETSZ earthquake is only Mw 4.8. Ironically, it is the least studied major eastern U.S. seismic zone. Recent ETSZ field surveys revealed an 80 km long, 060°-trending corridor containing northeast-striking Quaternary thrust, strike slip, and normal faults with displacements ≥1 m. It partially overlaps a parallel trend of seismicity that extends 30 km farther southwest, suggesting this active faulting zone may extend ∼110 km within part of the ETSZ. Near Dandridge, Tennessee, a thrust fault in French Broad River alluvium records two earthquakes in the last 40,000 yr. About 50 km southwest near Alcoa, Tennessee, a thrust fault cuts Little River alluvium and records two earthquakes between 15,000 and 10,000 yr ago. About 30 km farther southwest at Vonore, Tennessee, a thrust fault displaces bedrock ≥2 m over colluvium, and alluvium is normal faulted >2 m. This corridor, just west of the Blue Ridge escarpment, overlies a steep gradient in midcrustal S-wave velocities, consistent with a basement fault at hypocentral depths. The corridor faults may be connected to a basement fault or localized coseismic faults above a blind basement fault. Our current data suggest at least two Mw≥6.5 surface rupturing events in the last 40,000 yr.

Coeval development of extensional and contractional features along transform margins: insights from the Diaz Marginal Ridge

The Diaz Marginal Ridge (DMR), on the southern transform margin of South Africa, is a bathymetric feature parallel to the Agulhas Falkland Fracture Zone (AFFZ) that has long been considered an archetype marginal ridge; and yet its origin and evolution remains unconstrained. Using recently acquired seismic data we present a new structural interpretation of the DMR and its association with the evolution of both the AFFZ and the Southern Outeniqua Basin. In contrast to previous scenarios invoking thermo-mechanical explanations for its evolution, we observe a more straightforward structural model in which the genesis of the DMR results from the structural inversion of a Jurassic rift basin. This inversion resulted in the progressive onlap of latest Valanginian-Hauterivian aged stratigraphic units, important for the formation of stratigraphic plays of the recent Brulpadda discovery.Paradoxically, this contraction is contemporaneous with renewed extension observed in the inboard normal faults. The orientation of the DMR and inboard structures have been demonstrated to be controlled by the underlying Cape Fold Belt (CFB) fabric. The onset of motion across the AFFZ shear system led to east-west orientated maximum stress and north-south orientated minimum stress. We propose this stress re-orientation resulted in strain partitioning across existing structures whereby in addition to strike-slip on the AFFZ there was coeval extension and contraction, the nature of which was determined by fault orientation. The fault orientation in turn was controlled by a change in orientation of the underlying CFB. Our model provides new insights into the interplay of changes in regional stress orientation with basement fabric and localised magmatism along an evolving transform. The application of horizontal strain partitioning can provide an explanation of similar features observed on other transform margins.

A snapshot of the earliest stages of normal fault development

Despite decades of study, models for the growth of normal faults lack a temporal framework within which to understand how these structures accumulate displacement and lengthen through time. Here, we use borehole and high-quality 3D seismic reflection data from offshore Norway to quantify the lateral (0.2-1.8 mmyr-1) and vertical (0.004-0.02 mmyr-1) propagation rates (averaged over 12-44 Myr) for several long (up to 43 km), moderate displacement (up to 225 m) layer-bound faults that we argue provide a unique, essentially ‘fossilised’ snapshot of the earliest stage of fault growth. We show that lateral propagation rates are 90 times faster than displacement rates during the initial 25% of their lifespan suggesting that these faults lengthened much more rapidly than they accrued displacement. Although these faults have slow displacement rates compared with data compiled from 30 previous studies, they have comparable lateral propagation rates. This suggests that the unusual lateral propagation to displacement rate ratio is likely due to fault maturity, which highlights a need to document both displacement and lateral propagation rates to further our understanding of how faults evolve across various temporal and spatial scales.

Evolution of rift systems and their fault networks in response to surface processes

Continental rifting is responsible for the generation of major sedimentary basins, both during rift inception and during the formation of rifted continental margins. Geophysical and field studies revealed that rifts feature complex networks of normal faults but the factors controlling fault network properties and their evolution are still matter of debate. Here, we employ high-resolution 2D geodynamic models (ASPECT) including two-way coupling to a surface processes code (FastScape) to conduct 12 models of major rift types that are exposed to various degrees of erosion and sedimentation. We further present a novel quantitative fault analysis toolbox (Fatbox), which allows us to isolate fault growth patterns, the number of faults, and their length and displacement throughout rift history. Our analysis reveals that rift fault networks may evolve through five major phases: 1) distributed deformation and coalescence, 2) fault system growth, 3) fault system decline and basinward localization, 4) rift migration, and 5) breakup. These phases can be correlated to distinct rifted margin domains. Models of asymmetric rifting suggest rift migration is facilitated through both ductile and brittle deformation within a weak exhumation channel that rotates subhorizontally and remains active at low angles. In sedimentation-starved settings, this channel satisfies the conditions for serpentinization. We find that surface processes are not only able to enhance strain localization and to increase fault longevity but that they also reduce the total length of the fault system, prolong rift phases and delay continental breakup.

Drainage Basin Morphometry Analysis in Parts of South Shillong Plateau, Meghalaya: Implications for Landscape Development

The Shillong Plateau is characterized by multiple phases of deformation and number of prominent sets joints/fracture system. The Southern Shillong Plateau unlike the northern part is highly dissected by the scarp faces which are mostly erosional. The area is characterized by deep incising river networks which cuts across many lithological units. To understand the factors influencing the drainage characteristic of the area and landscape development, the present study has been done in context of morphometry, geomorphology and geology of the drainage basin. Fifteen sub basins of 4th order have been selected from the Um Sohrynkew River basin. Drainage morphometry, indices of active tectonism, geology and tectonics and landform features have been worked out for better evaluation of drainage characteristics. The study area forms part of the Meghalaya Precambrian province of upper Proterozoic age. The southern border of the Shillong Plateau is demarcated by Dauki (Also known as Dawki) fault which is a prominent structural lineament. It consists of at least four E-W trending normal faults with occasional reversal. The segment of the Dauki fault in the study area is believed to be active. The present study focuses on the drainage network and the landscape development of the study area where a very strong relationship has been observed between the lithology and structure together with the tectonic activity influencing the drainage pattern in the area.

Morphotectonic Structures along the Southwestern Margin of Lesvos Island, and Their Interrelation with the Southern Strand of the North Anatolian Fault, Aegean Sea, Greece

A hydrographic survey of the southwestern coastal margin of Lesvos Island (Greece) was conducted by the Naftilos vessel of the Hellenic Hydrographic Service. The results have been included in a bathymetric map and morphological slope map of the area. Based on the neotectonic and seismotectonic data of the broader area, a morphotectonic map of Lesvos Island has been compiled. The main feature is the basin sub-parallel to the coast elongated Lesvos Basin, 45 km long, 10–35 km wide, and 700 m deep. The northern margin of the basin is abrupt, with morphological slopes towards the south between 35° and 45° corresponding to a WNW-ESE normal fault, in contrast with the southern margin that shows a gradual slope increase from 1° to 5° towards the north. Thus, the main Lesvos Basin represents a half-graben structure. The geometry of the main basin is interrupted at its eastern segment by an oblique NW-SE narrow channel of 650 m depth and 8 km length. East of the channel, the main basin continues as a shallow Eastern Basin. At the western part of the Lesvos margin, the shallow Western Basin forms an asymmetric tectonic graben. Thus, the Lesvos southern margin is segmented in three basins with different morphotectonic characteristics. At the northwestern margin of Lesvos, three shallow basins of 300–400 m depth are observed with WNW-ESE trending high slope margins, probably controlled by normal faults. Shallow water marine terraces representing the last low stands of the glacial periods are observed at 140 m and 200 m depth at the two edges of the Lesvos margin. A secondary E-W fault disrupts the two terraces at the eastern part of the southern Lesvos margin. The NE-SW strike-slip fault zone of Kalloni-Aghia Paraskevi, activated in 1867, borders the west of the Lesvos Basin from the shallow Western Basin. The Lesvos bathymetric data were combined with those of the eastern Skyros Basin, representing the southern strand of the North Anatolian Fault in the North Aegean Sea, and the resulted tectonic map indicates that the three Lesvos western basins are pull-aparts of the strike-slip fault zone between the Skyros Fault and the Adramytion (Edremit) Fault. The seismic activity since 2017 has shown the co-existence of normal faulting and strike-slip faulting throughout the 90 km long Lesvos southern margin.

SEISMICITY of BAIKAL and TRANSBAIKALIA in 2015

We consider the character of the seismic process in the Baikal and Transbaikalia regions in 2015. 36430 earthquakes with KR≥3 were recorded by seismic stations of permanent and temporary networks during the year due to the sharp increase of a number of seismic events at the north-east of the study region in the area of the large Muyakan seismic activation. 53 earthquakes were felt in the cities, towns and local settlements with an intensity not exceeding 6. The largest Tallaysk earthquake (KR=14.0, Mw=5.1) occurred at the North-Muya Ridge and was followed by few aftershocks. Focal mechanisms were determined for 118 seismic events from P-wave first-arrival polarities and based on seismic moment tensors inverted from the surface wave data. It has been found, that normal faults are realized in the sources of 49 % of earthquakes with the obtained focal mechanisms.

STUDI IDENTIFIKASI PERANGKAP HIDROKARBON PALEOGEN - NEOGEN DI PERAIRAN WOKAM ARU UTARA, PAPUA BARAT: DATA UTAMA HASIL SURVEI GEOMARIN III

ABSTRAKPerairan Wokam Aru Utara, Papua Barat merupakan bagian tepi utara passive margin Mesozoik Arafura – Australia. Hasil survei dengan KR. Geomarin III di perairan Wokam 2014 diperoleh lintasan seismik Multi Kanal 1.182 km, dan pemeruman batimetri/sub bottom profiles (SBP) 1.510 km. Metode dilakukan interpretasi penampang seismik hasil survei, pengikatan sumur pemboran dan seismik, analisis petrofisika dan pemetaaan geologi bawah permukaan. Pada penampang seismik telah dilakukan interpretasi aspek struktur geologi dan perlapisan sedimen yang sebelumnya telah diikat dengan data sumur ASA-1X, ASM-1X dan ASB-1X untuk tiga horizon yaitu Top Neogen, Top Paleogen dan Base PaleogenPeta bawah permukaan Paleogen – Neogen menunjukan beberapa klosur yang berpotensi di bagian batas paparan dengan palung Aru serta bagian barat. Pada bagian Tenggara terdapat kenampakan onlapping sedimentasi Tipe struktural yang berkembang sebagai perangkap secara dominan berupa graben – half graben dan tilted faul. Onlaping sedimentasi yang mebaji juga dapat berpotensi.Struktur geologi pada area penelitian secara umum dikontrol oleh sesar utama Zona Sesar Palung Aru Utara di tepian paparan sampai lereng, mengarah utara - timur laut ke selatan - barat daya. Struktur ikutan yaitu sesar-sesar normal mengarah utara - timur laut ke selatan - barat daya di paparan sebelah timur zonar sesar utama.Studi awal potensi migas ini teridentifikasi empat lokasi potensi perangkap hidrokarbon dari umur Paleogen - Neogen, yaitu satu lokasi dari Peta Base Paleogen, dua lokasi Top Paleogen dan satu lokasi Top Neogen. kata kunci: Wokam, Aru, migas, seismik, struktur, interpretasi, jebakan, Geomarin III ABSTRACTThe waters of Wokam North Aru, West Papua are part of the northern edge of the Mesozoic passive margin of Arafura - Australia. Survey results with KR. Geomarin III in the waters of Wokam 2014 obtained a multi-channel seismic trajectory of 1,182 km, and bathymarism/sub bottom profiles (SBP) 1,510 km. The method is to interpret the seismic cross-section of the survey results, tie drilling and seismic wells, petrophysical analysis and mapping the subsurface geology. In the seismic section, an interpretation of the structural aspects of the geology and sediment layers has been carried out previously tied to data from the ASA-1X, ASM-1X and ASB-1X wells for three horizons, namely Top Neogen, Top Paleogene and Base Paleogene.The subsurface map of the Paleogene - Neogeneous surface shows several potential closures in the exposure boundary with the Aru Trench as well as the western part. In the Southeast, there is the appearance of sedimentation onlapping. Structural types that develop as traps are predominantly graben - half graben and tilted fault. The onlaping sedimentation also has potential. The geological structure in the study area is generally controlled by the main fault of the North Aru Trench Zone on the edge of the exposure to the slope, heading north - northeast to south - southwest. Follow-up structures are normal faults pointing north - northeast to south - southwest on the eastern exposure of the main fault zone.This preliminary study of oil and gas potential identified four potential locations for hydrocarbon traps from the Paleogene - Neogene age, namely one location from the Paleogene Base Map, two Top Paleogene locations and one Top Neogen location.Keyword: Wokam, Aru, oil and gas, seismic, structure, interpretation, traps, Geomarin III