Thick Sedimentary Sequence Research Articles

Nonlinear inversion of isostatic residual gravity data from Montage Basin, northern Gulf of California

The flexural isostatic response to surface loads is used to estimate the crustal thickness in northwestern Mexico and Southwestern USA. This estimate is used to compute an isostatic regional gravity, which, subtracted from Bouguer gravity anomalies, led to the isostatic residual gravity anomaly at Montage Basin. This basin is located between the southern portion of the Mexicali Valley and the northern Gulf of California, it roughly has an extension of [Formula: see text] wide, and it shows a gravity minimum reaching approximately [Formula: see text]. Montage Basin is within the extensional province of the Gulf of California, where rifting is currently an ongoing geologic process, and deep exploratory wells drilled by Petróleos Mexicanos have shown that the basin accommodates thick sedimentary sequences greater than 5 km. The interpretation of the isostatic residual gravity anomaly is considered as a nonlinear inverse problem, constrained using density as a function of depth derived from Gardner’s equation applied to dual time [Formula: see text]-logs, assuming isostatic equilibrium and considering the basin as a subsurface load that is compensated at depth by a mass of unknown shape and density. The outcome of the inverse problem suggests that Montage Basin accommodates as much as 7.5 km thick sedimentary sequences and a compensating mass at a minimum depth of 13 km.

Assimilation of sulfate and carbonaceous rocks: Experimental study, thermodynamic modeling and application to the Noril’sk-Talnakh region (Russia)

Most of the intrusions in the Noril’sk-Talnakh region (Siberia) are hosted in thick sedimentary sequences including abundant evaporitic and terrigenous sedimentary rocks. Three mafic-ultramafic intrusions in this region contain unusually thick massive sulfide deposits, which represent one of the world’s largest economic concentrations of Ni, Cu and PGE. The interaction of Siberian magmas with sulfate and organic matter-rich sedimentary rocks has been proposed as a possible mechanism for the origin of these exceptional sulfide deposits but the interaction process and the reaction paths have never been fully investigated. Here we clarify, by both experimental petrology and thermodynamic modeling, how sulfate and organic matter assimilation occur in mafic-ultramafic magmas, affecting magma composition, crystallization and sulfide saturation.Interaction experiments were conducted at conditions relevant to the emplacement of Noril’sk type intrusions (1200°C, ∼80MPa) to simulate the assimilation of sulfate and/or organic compounds by ultramafic magmas. We used a picrite from Noril’sk1 intrusion, and coal and anhydrite from the area as starting materials. The experimental results show that the incorporation of anhydrite into the magma occurs by chemical dissolution in the melt, which increases the magma’s sulfur content, but suppresses sulfide saturation and reduces olivine crystallization. Extreme assimilation leads to sulfate saturation in the magma and high dissolved sulfur contents of 0.9±0.1wt% S. Conversely, coal assimilation promotes sulfide segregation and magma crystallization, while decreasing the dissolved H2O content of the melt and increasing the amount of coexisting fluid phase.We also employed gas-melt thermodynamic calculations to quantify the effect of these assimilations on the redox conditions and the S content of the magma, and investigate the role of temperature, pressure, and initial gas content of the magma in the assimilation process. We quantify how sulfate assimilation strongly oxidizes the magma and increases its S content; both effects are intensified by increasing pressure (from 50 to 100MPa in this study), decreasing temperature (from 1350 to 1200°C in this study), and decreasing amounts of fluid phase initially coexisting with the magma (from 2 to 0wt%). The interaction with organic matter (CH in this study) induces a strong reduction of the magma, even for extremely low degrees of assimilation (few tenths of wt%), and the dehydration of the melt.We therefore suggest that in the Noril’sk-Talnakh district (1) additional S was supplied to mantle derived magmas by the assimilation of evaporitic rocks, and was transported during magma ascent in the form of dissolved, oxidized S; (2) a substantial reduction of the magma inducing sulfide segregation and important crystallization then occurred due to the interaction with carbonaceous sediments. This mechanism can potentially produce massive sulfide deposits by important sulfate assimilation (locally higher than 3wt% CaSO4) and minor organic matter assimilation (few tenths of wt% CH); however, if one of the two steps does not occur, or the assimilation in (1) is not large enough, disseminated sub economic or no sulfide deposits are produced. We conclude that exceptional conditions favoring substantial assimilation of sediments are needed to generate exceptional ore deposits like those of the Noril’sk-Talnakh district.

Eurasian ice-sheet dynamics and sensitivity to subglacial hydrology

ABSTRACTIce-stream dynamics are strongly controlled by processes taking place at the ice/bed interface where subglacial water both lubricates the base and saturates any existing, underlying sediment. Large parts of the former Eurasian ice sheet were underlain by thick sequences of soft, marine sediments and many areas are imprinted with geomorphological features indicative of fast flow and wet basal conditions. Here, we study the effect of subglacial water on past Eurasian ice-sheet dynamics by incorporating a thin-film model of basal water flow into the ice-sheet model SICOPOLIS and use it to better represent flow in temperate areas. The adjunction of subglacial hydrology results in a smaller ice-sheet building up over time and generally faster ice velocities, which consequently reduces the total area fraction of temperate basal ice and ice streaming areas. Minima in the hydraulic pressure potential, governing water flow, are used as indicators for potential locations of past subglacial lakes and a probability distribution of lake existence is presented based on estimated lake depth and longevity.

English

Numerous publications analyze the origin of Arsenic and Fluoride, their behavior and distribution in groundwater indicating the importance in understanding the relation between their occurrence with other physical and chemical properties. Here, such properties associated with elements of the landscape in the plain of the Chaco-Pampean region are discussed. The landscape is represented by hills, lagoons and plains used for agricultural purposes. Water was sampled in mills, piezometers and lagoons following sections with different topographic elevation, soil type and vegetation in nine field campaigns from 2011 to 2013. Results in Lincoln are compared to localities in Trenque Lauquen, Pehuajó and Carlos Casares. Hydro geochemical modeling assisted to define composition and origin of the water from local mineralogy in soil and subsoil. Three major water groups were defined HCO3-Na, HCO3>Cl-Na and HCO3>Cl>SO4-Na. Piezometers were located at the top and base of hills with the presence of Acuic Hapludolls – Natric thapto Hapludolls, and Typic Natraqualfs with halophytic vegetation, respectively. Arsenic and Fluoride presence was not fully explained by groundwater chemistry type and association with HCO3-, Na+, salinity and pH, although generally were linked to alkaline soil and halophyte vegetation. High Arsenic and Fluoride presence in groundwater are explained by discharge flows travelling long distances through a thick sedimentary sequence; relative low concentration is refereed to local travelling flows recharged in nearby high terrain. Groundwater origin and its relations with other elements of the landscape permitted an understanding of groundwater functioning and to anticipate a general situation with respect Arsenic and Fluoride contents. In the present study this criterion is applied to analyze the relation of the occurrence of Arsenic (as total Arsenic, TAs) and Fluoride (F-) content in water of the Lincoln region in the Buenos Aires province of Argentina. Key words: Arsenic, fluoride, discharge and recharge zone, groundwater flow system, soil, natural vegetation.

The Mesohellenic trough and the Thrace Basin. Two Tertiary molassic Basins in Hellenides: do they really correlate?

Based on lithostratigraphic and structural data, as well as geological mapping, the mollasic Thrace Basin (ThB) in NE Greece (including the Paleogene deposits of the Axios Basin) was compared with the Mesohellenic Trough (MHT) in NW Greece. Both basins are characterized by a thick sedimentary sequence of molassic-type strata (3-5km thickness) of Tertiary age, overlain unconformably by Miocene- Pliocene and Quaternary deposits. Molassic sedimentation started almost simultaneously in both areas during the Mid-Upper Eocene but it finished in different time, in the Mid-Upper Miocene for the MHT and the Upper Oligocene for the ThB, respectively. Sedimentation in ThB was also linked with an important calc-alkaline and locally shoshonitic magmatism of Eocene-Oligocene age. We interpreted the MHT as a polyhistory strike-slip and piggy-back basin, above westward-emplacing ophiolites and Pelagonian units on the cold Hellenic accretionary prism. In contrast to MHT, the ThB evolved as a Paleogene supra-detachment basin above the strongly extended during the Eocene-Oligocene Hellenic Hinterland. The syn-depositional magmatic products, linked possibly with subduction processes in Pindos or Axios ocean(s). In any case, MHT and ThB are related to inferred oblique convergence of the Apulia plate and the internal Hellenic units.

Chapter 20 Current tectonic activity along the Sagaing Fault, Myanmar indicated by alluvial fans

In the area to the north of Sagaing, fault-parallel ridges, alluvial fans, sag ponds, scarp lines, fault furrows, offset streams, a lowland plain hosting a lacustrine basin, river terraces and elevated flat-surfaces are the striking geomorphic features adjacent to the Sagaing Fault. The present study concentrates on the nature and development of the younger alluvial fans and the older fanglomerates located along the fault, in order to document the tectonic history of the Sagaing Fault. Alluvial fans and associated features can be a valuable record of tectonic activity (Nemec & Kazanci 1999) as they commonly develop along fault scarps, and thick sequences of syntectonic sediments have frequently been deposited on the actively subsiding side of the major fault (Reineck & Singh 1980; Collinson 1981). This chapter ties field-based geological studies, associated with satellite-image observations and interpretation of sedimentological data, to reconstruct the history of the alluvial fans along the Sagaing Fault in the area of Sagaing. Located between the Ayeyarwady (Irrawaddy) River and the Yemyet Inn (Lake) in Sagaing township, Central Myanmar, the study area extends northwards from Sagaing for a distance of 40 km. Topographically, the area consists of two fault-parallel north–south ridges: the Minwun Ridge in the west, and the Sagaing Ridge in the east. The latter, about 30 km long and studded with religious edifices, is much broader and higher than the former, the highest point at Mingun Taung (Hill) is 406 m above sea level. The two ridges, often considered as transpressive features (Win Swe 1981; Bertrand & Rangin 2003), are divided by a wide fault valley; just north of Kyaukta Village is the Yega Inn, a sag pond 1.2 km long. North of this lake, the valley becomes less conspicuous as the Minwun Ridge plunges beneath and locally emerges from the alluvial fan …

Permian-Triassic palynofloral transition in Sohagpur Coalfield, South Rewa Gondwana Basin, Madhya Pradesh, India

A 1300 m thick sedimentary sequence in borehole SNB–1 around Jaisinghnagar area in the western part of the South Rewa Basin has been lithologically designated as the Pali Formation. However, palynological investigation reveals presence of three distinct palynoassemblage zones belonging to late Permian, early and late Triassic ages in ascending order. Palynoassemblage I (Striatopodocarpites magnificus–Crescentipollenites fuscus) recorded between a depth of 1213.40–1164.10 m showing dominance of striate bisaccate pollen taxa chiefly―Striatopodocarpites ovatus, Faunipollenites varius and Crescentipollenites fuscus in association with Alisporites ovalis, Lunatisporites pellucidus, Densipollenites indicus and Lahirites rarus is late Permian (Raniganj) in age. Palynoassemblage II (Lundbladispora densispinosa–Densoisporites playfordii) recorded between a depth of 1054.30–956.00 m and showing dominance of cavate/cingulate spores, like Lundbladispora microconata, Densoisporites complicatus along with Kraeuselisporites rallus, Lapposisporites lapposus, Playfordiaspora crenulata, Goubinispora indica, Klausipollenites schaubergeri, Limatulasporites fossulatus and Reduviasporonites chalastus indicates an early Triassic age. Palynoassemblage III (Aulisporites astigmosus–Falcisporites nuthallensis) recorded between a depth of 404.40–53.60 m and characterized by the dominance of Aulisporites astigmosus along with Falcisporites nuthallensis, Tikisporites balmei, Dubrajisporites unicus, Enzonalasporites densus, Leschikisporites aduncus, Lunatisporites rhaeticus, Lueckisporites virkkiae, Playfordiaspora vellata, Polycingulatisporites crenulatus, Cingulizonates indicus, Neoraistrickia taylori and Aratrisporites fischeri is equated with late Triassic (Supra–Panchet) age.
 The Permian–Triassic boundary is delineated at the contact of coal/shale bearing upper part of the Middle Member and lower part of the Upper Member of the Pali Formation (between 1164.10–1075.15 m depth). At the P/T boundary, the abrupt change of the palynoflora is marked by the disappearance of the striate bisaccate pollen grains and appearance of non–striate bisaccate grains in association with cingulate–cavate/zonate trilete spores. The Permian/Triassic palynofloras recorded in South Rewa Basin show close similarities with those of the uppermost Bainmedart Coal Measures (McKinnon Member) and Flagstone Bench Formation of east Antarctica.

Two-dimensional basement modeling of central loop transient electromagnetic data from the central Azraq basin area, Jordan

Thick sedimentary sequences are deposited in the central area of the Azraq basin in Jordan consisting mostly of hyper-saline clay and various evaporates. These sediment successions form the 10km×10km large Azraq mudflat and are promising archives for a palaeoclimatical reconstruction. Besides palaeoclimatical research, the Azraq area is of tremendous importance to Jordan due to groundwater and mineral resources. The heavy exploitation of groundwater has lead to a drastic decline of the water table and drying out of the former Azraq Oasis. Two 7 and 5km long transects were investigated from the periphery of the mudflat across its center using a total of 150 central loop transient electromagnetic (TEM) soundings. The scope of the survey was to detect the thickness of sedimentary deposits along both transects and to provide a basis for future drilling activities. We derive a two-dimensional model which can explain the TEM data for all soundings along each profile simultaneously. Previously uncertain depths of geological boundaries were determined along both transects. Particularly the thickness of the deposited mudflat sediments was identified and ranges from 40m towards the periphery down to approximately 130m at the deepest location. Besides that, the depth and lateral extent of a buried basalt layer was identified. In the basin center the groundwater is hyper-saline. The lateral extent of the saline water body was determined precisely along both transects. In order to investigate the detectability of the basement below the high conductive mudflat sediments an elaborate two-dimensional modeling study was performed. Both, the resistivity and depth of the basement were varied systematically. The basement resistivity cannot be determined precisely in most zones and may range roughly between 1 and 100Ωm without deteriorating the misfit. In contrast to that, the depth down to the basement is detected accurately in most zones and along both transects. Varying the depth of the basement or removing it completely results in a poor data fitting and, therefore, proves its significance. From the modeling study we derived bounds for the resistivity and depth of the base layer as a measure of their uncertainty.

Dynamic carbonate sedimentation on the Northern Line Islands Ridge, Palmyra Basin

The Line Islands Ridge (LIR), located south of the Hawaiian Islands between 7°N and 1°S, is one of the few large central Pacific regions shallower than the regional carbonate compensation depth. Thick sequences of carbonate sediments have accumulated around the LIR despite it being located in the sediment-starved central tropical Pacific. The LIR is an important source of carbonates to the surrounding region and deposition around the LIR has expanded the equatorial Pacific carbonate sediment tongue by about 5% of its total area. Furthermore, sediments on the ridge are potentially important paleoceanographic archives. A recent survey at the crest of the LIR finds evidence for high current activity, significant erosion, but overall net sediment deposition. Currents are strong enough to form sediment waves and lee drifts in the Palmyra Basin, at the northern terminus of the LIR. Sediments along the LIR are pelagic foraminiferal sands that are easily eroded and flow out into the surrounding abyssal plain in active submarine channel systems. As channels migrate, pelagic sediments fill in the abandoned channel arms. Despite significant sediment losses from the top of the ridge, 1.3km of sediment has accumulated in the upper Palmyra Basin over basement formed 68 to 85millionyears ago (Ma). Late Neogene erosion may be more extensive than earlier erosion cycles, in response to reduced sediment production as the Palmyra Basin exited the high productivity equatorial latitudes. Sediments with good stratigraphic order needed for paleoceanographic study are limited in this dynamic sedimentary environment, but can be found with proper survey.

Incised Pleistocene valleys in the Western Belgium coastal plain: Age, origins and implications for the evolution of the Southern North Sea Basin

The Belgian coastal plain occupies a key position as it is located at the transition between the Southern North Sea Basin and the Strait of Dover. It is characterized by thick sequences (>20m) of Pleistocene terrestrial and littoral sediments. Yet the wider stratigraphical and palaeo-environmental significance of these sediments received little attention. In this paper we draw on the results of a recent sedimentological study based on >100 drillings that spans the Pleistocene sequence, and present new biostratigraphical (pollen, foraminifera, ostracods) data, all revealing a complex history of deposition. The record includes evidence of the development of incised-valley systems that were initiated in the late Middle and Late Pleistocene. Five phases of fluvial incision can be identified. The majority of the infills are deposited in an estuarine environment that passes into a fluvial environment land inward, except the Weichselian infill which has a predominant fluvial origin. The greatest part of the most seaward located zone of the western coastal plain was free of valley incisions, there, shallow marine sediments built up the record. Local biostratigraphical investigations provide a timeframe. The result is placed in a regional context.

An examination of the fluid inclusions of the well RP3-1 at the Halahatang Sag in Tarim Basin, northwest China: Implications for hydrocarbon charging time and fluid evolution

The well RP3–1 lies in the Tarim Basin, which is located in the southern Xinjiang Uygur Autonomous Region in northwest China. This region is one of the world's largest frontier basins. Drilling data that we collected on the well RP3–1 reveal a 2398–7066m thick sedimentary sequence, containing Ordovician to Tertiary strata. The Yijianfang (O2yj) formation of the Middle Ordovician sequence is one of the most important reservoir stratums. The O2yj formation consists mainly of bioclast and intraclast limestones. Two different fluid types are identified by the associations they have with veinlets, which are colors caused by petroleum inclusions under UV light. Early-stage petroleum fluids are characterized by a blue-white color under UV-epifluorescence microscopy, and early-stage aqueous fluid inclusions are mainly homogenized between 54 and 102°C, with salinities ranging from 12.0 to 16.7wt% NaCl equiv. Late-stage petroleum fluids are characterized by a yellow color under UV-epifluorescence microscopy, and late-stage, aqueous-fluid inclusions are mainly homogenized between 85 and 135°C, with salinities ranging from 2.0 to 8.0wt% NaCl equiv. In order to obtain accurate measurements of both the trapped temperature (Ttrap) and pressure (Ptrap) of these fluids, we use 10 pairs of petroleum inclusions and coeval aqueous fluid inclusions to measure the intersection of a number of isochors. The Ttrap of early-stage fluids we surveyed were between 82 and 97°C, with the Ptrap ranging from 97 to 259 bars. In contrast, the Ttrap of late-stage fluids were between 141 and 170°C, with Ptrap values ranging from 430 to 608 bars. When combined with the regional buried history, the early-stage fluids charged from 422Ma to 412Ma BP, and the late-stage fluids charged from 20Ma to 6Ma BP.

Nubian Sandstone reservoir characteristics: sedimentological and petrophysical evaluation in the Southern Gulf of Suez, Egypt

The Nubian Sandstone is a thick sequence of clastic and thin carbonate sediments in the Jebel El Zeit section of eastern Egypt. The sequence is composed mainly of sandstone with shale and minor carbonate interbeds and was deposited in continental and fluviomarine to marine settings. Petrographically, quartz arenite and quartz wacke are the main facies of Nubian Sandstone. They have different secondary components, cement and matrix types, reflecting their different depositional environments and diagenetic histories. The Nubian Sandstone is one of the most prolific hydrocarbon reservoirs in the Gulf of Suez oil province.The Nubian Sandstone has good reservoir quality with porosity varying from 10% to 29%, and permeability of up to 5000 millidarcies. The quality of the reservoir depends on its proportions of shale, diagenetic history and the depth of burial (compaction). X-ray diffraction and scanning electron microscope analyses indicate that kaolinite is the main clay mineral and is derived from the alteration of potash feldspar. Enhancement of oil recovery from the reservoirs of the Nubian Sandstone can be achieved by alkaline injection to dissolve the kaolinite.

Carving intracrater layered deposits with wind on Mars

AbstractCrater basins on Mars host thick sedimentary sequences, which record the environments of early Mars. These basin fills commonly exhibit mound morphologies thought to arise from aeolian erosion of initially crater filling strata. This study presents transport‐based models explaining how mounds could be carved by wind. Wind tunnel experiments generated morphologies similar to those observed on Mars, and numerical modeling of flow over a crater using large‐eddy simulation (LES) demonstrated a positive feedback between topographic focusing of flow and erosion potential. Observations of yardangs, dunes, and wind streaks, all proxies for wind direction, largely agree with model results. Where mound strata origins have been interpreted, basal subaqueous deposits are overlain by aeolian deposits. This stratigraphic progression, culminating in wind‐driven excavation, is consistent with a global desiccation event. The occurrence of sedimentary mounds only on Noachian terrain argues that this event was related to late Noachian climatic change.

High-intensity geomagnetic field ‘spike’ observed at ca. 3000 cal BP in Texas, USA

Abstract By observing the fluctuations in direction and intensity of the Earth's magnetic field through time, we increase our understanding of the fluid motions of the Earth's outer core that sustain the geomagnetic field, the geodynamo. Recent archaeomagnetic studies in the Near East have found extremely rapid increases – ‘spikes’ – in geomagnetic field intensity at ca. 3000 yr cal BP. These observations have proved problematic for our current understanding of core-flow. However, until now, these geomagnetic spikes had not been observed outside of the Near East, where they have been preserved in metallurgical slag and fired, mud brick walls. We present a new, fully oriented, geomagnetic secular variation and relative palaeointensity (RPI) record for the last 17,000 yr from Hall's Cave, Texas, whose complete, >3.8 m thick sedimentary sequence spans from the present to 16 , 850 ± 110 RC yr BP (Modern to 20,600 cal BP). Within the stable, cool climate of the cave, pedogenic and bioturbation processes are negligible to non-existent, thereby limiting post-depositional physical and geochemical alteration of the magnetic record. The sub-aerial and subterranean setting of the sedimentary sequence in Hall's Cave enabled us to collect oriented palaeomagnetic cubes from a previously excavated stratigraphic section. The palaeomagnetic samples yielded high-quality vectors. An age model for the sequence, determined using 15 AMS 14C-dates on individual bones from microvertebrates, was combined with the palaeomagnetic data to construct a secular variation record. The record is in broad agreement with predictions by Holocene field models for the site's location. However, starting ca. 3000 yr ago, the RPI data indicate an almost four-fold increase in geomagnetic field intensity lasting several hundred years. This record presents well-dated evidence, obtained using conventional techniques, for the existence of a geomagnetic intensity spike in North America that is contemporaneous with the shorter duration, decadal-scale spikes reported from the Near East.

Geochemical Evidence for Provenance, Tectonic Settings and Presence of Gas Hydrate in Mud Volcano Sediments of Andaman Islands

Abstract Mud volcanoes are one of the land / seafloor expressions of the expulsion of argillaceous material from deeper areas, generated by an extrusion activity involving the transfer of sediments, liquids and gas from subsurface to the land / seafloor. Eruption of mud volcano has been recorded historically in 1843, 1879, 1907, 1983, 2003, and 2004 in Bara tang in Middle and Diglipur in North Andaman Islands. Exceeding of threshold pressure of pressured gas and/ or liquid breaks upward through the overlying sediment frequently following existing zone of weakness and flow out sub aerially or subaqueous condition. Venting structure of mud volcanoes are the most important natural seepage features with fluid, gases and sediments from the earth’s surface. Most of the terrestrial mud volcanoes are located in convergent plate margin with thick sedimentary sequences as seen in Alpine-Himalayan, Caribbean and Pacific organic belts. The occurrence of mud volcanoes is controlled by several factors, such as tectonic activity, sedimentary loading due to rapid sedimentation and the existence huge thickness of fine-grained sediments and continuous hydrocarbon accumulation. Tectonic setting discrimination diagrams based on major, minor and trace elements suggest a shale provenance in an oceanic island arc. The correlation of K2O with other elements, abundance of Al2O3, Ba, Th suggest that these elements are primarily controlled by the dominant clay minerals. The compositional immaturity of the analyzed mud volcano sediments is typical of sub ducted-related environments, and their SiO2/Al2O3 and K2O/Na2O ratios reflect their oceanic island arc settings.

Fisson-track constrains on superposed folding in the Beishan orogenic belt, southernmost Altaids

The Hongyanjing inter-arc basin, is located at the central part of Beishan Orogenic College (BOC), Gansu Province, northwest China. Thick sequences of Permian sediments were strongly folded, forming extremely spectacular superposed folds. To better understand the thermal history of Hongyanjing inter-arc basin and to potentially constrain the timing of deformation, apatite fission track thermochronology method was applied on two superposed folds in the Hongyanjing Basin. Samples from the basin, yield central AFT ages ranging from ∼206 to 118 Ma. AFT peak ages were largely consistent between samples and can divided into three groups: 245, 204–170 and 112–131 Ma. Subsequent thermal history modeling of the samples from the Hongyanjing Basin can be summarized as follows: (1) thermal reheating by sedimentary burial at ∼ 260 to ∼220 Ma; (2) major cooling from ∼220 to ∼180 Ma; (3) an episode of very slow subsequent cooling from ∼180 to 65 Ma (∼80 °C) to present-day outcrop temperatures. Sediments in the Hongyanjing Basin were folded forming F1 fold during the early to late Triassic (∼240–∼220 Ma), by regional stress, and at the time that the adjacent Xingxingxia shear zone started to become active. It is further suggested that the F2 folding occurred at ∼225–219 Ma. The deformation age of F2 should be extended to 180 Ma based on our thermal history modeling for the Hongyanjing Basin, which show a rapid exhumation and cooling at the late Triassic to early Jurassic (∼220–∼180 Ma). In our interpretations, the F1 folding is therefore thought to be related to the final closure of the Paleo-Asian Ocean, while the F2 folding occurred at ∼225–180 Ma associated with a major pulse of orogenesis in the BOC.

Early Wisconsinan (MIS 4) glaciation on Haida Gwaii, British Columbia, and implications for biological refugia

Sea cliffs at Cape Ball on Graham Island, British Columbia, expose a thick sequence of Pleistocene sediments deposited during at least two glaciations. In sequence, from the base of the section, the units are (1) stony mud, (2) till, (3) silt, sand, and peat, (4) stony mud, (5) laminated sand and silt, (6) cross-bedded sand, and (7) till. Of special interest is unit 4, a massive to weakly stratified mud containing scattered stones that was deposited during the penultimate Pleistocene glaciation (marine isotope stage (MIS) 4). This unit contains wood and marine shell fragments that have yielded non-finite radiocarbon ages. Sand and silt with thin stringers of peat (unit 3) directly underlie this stony mud, and returned an optical age of 57.3 ± 5.7 ka. The stony mud is unconformably overlain by ponded sediments (unit 5) and advance outwash (unit 6) and till (unit 7) deposited during the Fraser Glaciation (MIS 2). The optically dated unit and a correlative peat and silty sand unit at a nearby exposure have pollen spectra with almost 100% non-arboreal pollen. Very low values of tree pollen, coupled with high frequencies of sedges, grasses, composites, Ericales, and the arctic−alpine indicator Koenigia islandica, indicate tundra vegetation and a cold climate. Abundant coprophilous Sporormiella (69%–91%) and Sordaria type (14%–47%) fungal spores in the peat samples indicate the former presence of grazing mammals at Cape Ball during MIS 4. During the MIS 3 interstade, subalpine forest existed at low elevations on Graham Island, providing environments suitable for the development of genetically distinct bird and mammal populations that survived in lowland refugia during the Fraser Glaciation.

Seismogenic faulting of the sedimentary sequence and laterally variable material properties in the Zagros Mountains (Iran) revealed by the August 2014 Murmuri (E. Dehloran) earthquake sequence

We present source models for the August 2014 Murmuri (Dehloran) earthquake sequence in the Zagros Mountains of Iran. An Mw6.2 mainshock was followed by an aftershock sequence containing five events of Mw ≥ 5.4. Models of P and SH waveforms show that all events had dominantly thrust-faulting mechanisms, and had centroid depths that place them within the thick sedimentary sequence, above the crystalline basement. The combination of our estimated focal mechanisms, relative relocations of the event hypocentres and the surface displacement patterns observed using InSAR imply that the mainshock and largest aftershock ruptured different fault planes and both contributed to the surface deformation. The fault planes both slipped in horizontally elongated patches, possibly due to rheological layering limiting the updip and downdip extent of rupture. The slip vector of the Murmuri mainshock implies that the decollement beneath the Lorestan Arc is weaker than any such feature beneath the Dezful Embayment, providing an explanation for the plan-view sinuosity of the range-front of the Zagros Mountains.

Preliminary data from Valle Giumentina Pleistocene site (Abruzzo, Central Italy): A new approach to a Clactonian and Acheulian sequence

Valle Giumentina is a Pleistocene open-air site in Central Italy (Abruzzo). Nine archaeological layers occur in the last 25 m of a 70 m thick sedimentary sequence. In the 1950s, the various archaeological layers were attributed to the Clactonian, Acheulian and Levalloisian traditions. Recent multidisciplinary fieldwork and studies (2012–2016) acquired new archaeological, chronostratigraphical and paleoenvironmental data. This contribution presents the preliminary results of the ongoing excavation of layer 42-ALB. This is a paleosol located at 4 m depth, at the top of a lacustrine deposit directly below the coarse deposits associated with the last major erosive event. Faunal remains consisted essentially by Cervus elaphus. The lithic series is characterized by a specific flake production system: only a part of the block is reduced, and platforms and surfaces are not prepared. Several methods are used, including the SSDA (système par surfaces de débitage alternées). Backed flakes are frequent. Numerous blanks are transformed by intensive or marginal retouch. Functional objectives are multiple, as shown by different tool structures and use-wear traces. Valle Giumentina 42-ALB is a butchery site used briefly but frequently during warmer substages occurring during an overall cold period. The “Clactonian” industry of Valle Giumentina is often considered as simple or expedient: we demonstrate its real technical complexity and its functional significance. Comparisons are made with other European sites.

Influence of calcite decarbonation on the frictional behavior of carbonate-bearing gouge: Implications for the instability of volcanic flanks and fault slip

The impact of heat, readily provided by magma, circulating hot fluids, or rapid fault slip on carbonate substrata is an important factor in determining the flank stability of volcanoes and the mechanical behavior of faults in areas where carbonate lithologies are prevalent. The mineralogy and mechanical properties of carbonate rocks are demonstrably altered by thermally induced decarbonation. While previous studies have considered the role of decarbonation in bulk strength loss at subvolcanic conditions and dynamic weakening during coseismic fault slip, little is known about the effects of decarbonation on the frictional properties of carbonate rocks during both the nucleation and inter-seismic phases. Here, we present results from experiments performed on a portlandite-rich material, a typical hydrous product of the decarbonation reaction. To evaluate frictional strength, stability, and healing at shallow crustal conditions, we sheared gouge layers of this material under saturated conditions at room temperature and at velocities comparable to those involved in earthquake nucleation. Our data indicate that the reaction of calcite to portlandite results in a distinct change in the mechanical behavior of the gouge. Decarbonated shear zones are (1) frictionally weaker at higher normal stresses, (2) more frictionally unstable, and (3) likely to regain their frictional strength more quickly than unaltered calcite-rich zones. The occurrence of portlandite could be key for interpreting the stability of volcanic flanks that root into carbonate substrata and for seismogenic normal faults located within thick sedimentary sequences, and thus provide a better understanding of the hazards they pose.