Neogene Sedimentary Basins Research Articles

Can surface samples be used to infer underground permeability structure? A test case for a Neogene sedimentary basin in Horonobe, Japan

We measured gas permeability of Neogene sedimentary rocks from Wakkanai, Koetoi and Yuchi Formations in the Horonobe area in northern Hokkaido, Japan. Measurements were done at room temperature and during pressure cycling to simulate underground conditions. Fresh intact samples from surface outcrops yielded a similar range of permeabilities as did intact samples from drill cores, within lithological variations. Comparison of laboratory and in-situ measurements has revealed that the permeability of Wakkanai Formation (middle to late Miocene, siliceous mudstone) from in-situ measurements is bounded by the permeability of brecciated specimen on the upper side and by the permeability of intact specimens on the lower side. Fragments in fault breccia are smaller than sample size and laboratory data should be applicable to natural fault rocks. Permeability of fractured specimens falls in between those upper and lower bounds, and complex scale issues will not be important in determining upper and lower bounds of permeability. The hydraulic conductivity values from in situ tests for Koetoi Formation (late Miocene to Pliocene, diatomaceous mudstone) are similar to those of the gas permeability of intact specimens. Effects of faults and fractures on permeability seems to be minor for this formation, and this was confirmed by permeability measurements with fractured samples. The hydraulic conductivity values from in situ tests for Yuchi Formation are lower than estimates from laboratory tests by within an order of magnitude. Thus permeability measurements in laboratory on fresh surface samples (intact, fractured and brecciated), combined with geological survey on the development of faults and fractures, leads to quantitative estimates, even if not complete, of underground permeability structures.

Interaction between the controls on fluvial system development: tectonics, climate, base level and river capture – Rio Alias, Southeast Spain

ABSTRACTFluvial systems in uplifting terrain respond to tectonic, climatic, eustatic and local base‐level controls modified by specific local factors, such as river capture. The Rio Alias in southeast Spain is an ephemeral, transverse‐to‐structure fluvial system. The river drains two interconnected Neogene sedimentary basins, the Sorbas and Almeria basins, and crosses two major geological structures, the Sierras de Alhamilla/Cabrera and the Carboneras Fault Zone. Regional epeirogenic uplift resulted in sustained fluvial incision during the Quaternary, punctuated by major climatically driven periods of aggradation and dissection, which created a suite of five river terraces. The river terrace sequence was radically modified in the late Pleistocene by a major river capture (itself a response to regional tectonics), localized tectonic activity and eustatic base‐level change. The Rio Alias is defined by four reaches; within each the climatically‐generated, region‐wide, fluvial response was modified by tectonics, base‐level change or river capture to varying degrees. In the upper part of the basin (Lucainena reach), climate was the dominant control on river development, with limited modification of the sequence by uplift of the Sierra Alhamilla and local drainage reorganization by a local river capture. Downstream of the Sierra Alhamilla in the Polopus reach, the climatic signal is dominant, but its expression is radically modified by the response to a major river capture whereby the Alias system lost up to 70% of its pre‐capture drainage area. In the reach adjacent to the Carboneras Fault Zone (Argamason reach), modification of the terrace sequence by local tectonic activity and a resultant local base‐level fall led to a major local incisional event (propagating c. 3–4 km upstream from the area of tectonic disturbance). At the seaward end of the system (El Saltador reach) Quaternary sea‐level changes modified the patterns of erosion and incision and have resulted in steep incisional terrace profiles. The signals generated by regional tectonics and the Quaternary climate change can be identified throughout the basin but those generated by ongoing local tectonics, river capture and sea‐level change are spatially restricted and define the four reaches. The connectivity of the system from the headwaters to the coast decreased through time as incision progressed, resulting in changes in local coupling characteristics. Copyright © 2012 John Wiley & Sons, Ltd.

Constraints on the history and topography of the Northeastern Sierra Nevada from a Neogene sedimentary basin in the Reno-Verdi area, Western Nevada

Neogene (Miocene–Pliocene) sedimentary rocks of the northeastern Sierra Nevada were deposited in small basins that formed in response to volcanic and tectonic activity along the eastern margin of the Sierra. These strata record an early phase (ca. 11–10 Ma) of extension and rapid sedimentation of boulder conglomerates and debrites deposited on alluvial fans, followed by fluvio-lacustrine sedimentation and nearby volcanic arc activity but tectonic quiescence, until ∼ 2.6 Ma. The fossil record in these rocks documents a warmer, wetter climate featuring large mammals and lacking the Sierran orographic rain shadow that dominates climate today on the eastern edge of the Sierra. This record of a general lack of paleo-relief across the eastern margin of the Sierra Nevada is consistent with evidence presented elsewhere that there was not a significant topographic barrier between the Pacific Ocean and the interior of the continent east of the Sierra before ∼ 2.6 Ma. However, these sediments do not record an integrated drainage system either to the east into the Great Basin like the modern Truckee River, or to the west across the Sierra like the ancestral Feather and Yuba rivers. The Neogene Reno-Verdi basin was one of several, scattered endorheic (i.e., internally drained) basins occupying this part of the Cascade intra-arc and back-arc area.

Tectono-Sedimentary evolution and geochronology of the Middle Miocene Altınapa Basin, and implications for the Late Cenozoic uplift history of the Taurides, southern Turkey

The Tauride range in southern Turkey is flanked and overlain by Neogene sedimentary basins. To the south and on top of the high range, these basins are mainly marine, whereas poorly studied intramontane basins dominated by continental deposits are exposed to the north. In this paper, we study the stratigraphy and structure of the continental Altınapa Basin, and provide 40Ar/39Ar geochronology for volcanic deposits in the stratigraphy. The stratigraphy can be subdivided into a Lower Group, displaying ~400m of fining upward fluvio-lacustrine sediments, unconformably overlain by an Upper Group with ~500m of lacustrine deposits, andesitic lavas and volcaniclastic sediments. 40Ar/39Ar dating of three volcaniclastic samples across the Upper Group provide 11.8–11.6Ma ages. The Altınapa Basin is an extensional basin, which formed predominantly due to N–S to NE–SW directed stretching. The main basin forming phase occurred during deposition of the Lower Group, prior to 11.8Ma. Paleostress inversion analyses demonstrate uniaxial stress, with highly variable extension directions that are consistent with currently observed seismicity patterns. The Middle Miocene extension history of the Altınapa Basin is consistent with a regional pattern of Middle Miocene NE–SW to NW–SE extension north of the Cyprus subduction zone. This suggests that the Cyprus subduction zone has been in retreat relative to central Anatolia since at least Middle Miocene time. The continental Altınapa Basin is currently at an elevation of ~1km, whereas partly contemporaneous marine sediments in the Mut Basin that lies on top of the Tauride range are elevated to 2km. This shows strong late Cenozoic differential uplift in southern Turkey, with at least 1km more uplift of the Tauride range than of the intramontane basins to the north. We conclude that the current high elevation of the Taurides is related to late Neogene extension and does not result from the late Cretaceous to perhaps Oligocene folding and thrusting that deformed the rocks in the range.

Cosmogenic burial ages reveal sediment reservoir dynamics along the Yellow River, China

Research Article| September 01, 2011 Cosmogenic burial ages reveal sediment reservoir dynamics along the Yellow River, China Xiaofei Hu; Xiaofei Hu 1Key Laboratory of Western China's Environmental Systems, Ministry of Education, Lanzhou University, Lanzhou 730000, P.R. China Search for other works by this author on: GSW Google Scholar Eric Kirby; Eric Kirby 2Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA Search for other works by this author on: GSW Google Scholar Baotian Pan; Baotian Pan 1Key Laboratory of Western China's Environmental Systems, Ministry of Education, Lanzhou University, Lanzhou 730000, P.R. China Search for other works by this author on: GSW Google Scholar Darryl E. Granger; Darryl E. Granger 3Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana 47907, USA Search for other works by this author on: GSW Google Scholar Huai Su Huai Su 1Key Laboratory of Western China's Environmental Systems, Ministry of Education, Lanzhou University, Lanzhou 730000, P.R. China Search for other works by this author on: GSW Google Scholar Author and Article Information Xiaofei Hu 1Key Laboratory of Western China's Environmental Systems, Ministry of Education, Lanzhou University, Lanzhou 730000, P.R. China Eric Kirby 2Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA Baotian Pan 1Key Laboratory of Western China's Environmental Systems, Ministry of Education, Lanzhou University, Lanzhou 730000, P.R. China Darryl E. Granger 3Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana 47907, USA Huai Su 1Key Laboratory of Western China's Environmental Systems, Ministry of Education, Lanzhou University, Lanzhou 730000, P.R. China Publisher: Geological Society of America Received: 27 Dec 2010 Revision Received: 31 Mar 2011 Accepted: 08 Apr 2011 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2011 Geological Society of America Geology (2011) 39 (9): 839–842. https://doi.org/10.1130/G32030.1 Article history Received: 27 Dec 2010 Revision Received: 31 Mar 2011 Accepted: 08 Apr 2011 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Xiaofei Hu, Eric Kirby, Baotian Pan, Darryl E. Granger, Huai Su; Cosmogenic burial ages reveal sediment reservoir dynamics along the Yellow River, China. Geology 2011;; 39 (9): 839–842. doi: https://doi.org/10.1130/G32030.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Burial dating using cosmogenic 26Al and 10Be is an emerging technique for establishing chronologies of fluvial deposits ranging in age from ca. 0.5 Ma to 5 Ma. The determination of burial age, however, requires an assumption that sediment is buried with a known initial 26Al/10Be ratio. Using a sequence of well-dated fluvial terraces along the Yellow River in Lanzhou, China, we demonstrate that this assumption may be violated when upstream sediment sources include Neogene sedimentary basins. Samples of fluvial gravel from six terraces yield burial ages ranging from ca. 0.83 Ma to 2.81 Ma. Comparison of these results to independent ages determined from magnetostratigraphic and loess-paleosol studies demonstrates a high degree of correspondence between ages in the lower three terraces. In the higher terraces, however, burial ages are systematically too old, implying a previous burial history. These results can be exploited to place quantitative constraints on the provenance of sediment in the terrace deposits. Our results reveal that rapid incision and excavation of late Neogene sedimentary basins ca. 1.7 Ma led to injection of fluvial sediment with low initial 26Al/10Be ratios. Dilution of this source through time occurred as incision progressed into upstream bedrock ranges. Our results suggest that cosmogenic nuclides can illuminate the timing of long-term storage and remobilization of sediment in continental-scale river systems. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Structuring and evolution of Neogene transcurrent basins in the Tellian foreland domain, north-eastern Tunisia

The Neogene sedimentary basins (Serravallian to Quaternary) of the Tellian tectonic foreland in north-eastern Tunisia formed within the overall NE-SW sinistral strike-slip tectonic framework of the Ras El Korane-Thibar and El Alia-Teboursouk fault systems. From stratigraphic logs, structural cross sections and interpretation of 2D seismic lines and boreholes, the pre-Neogene basement can be interpreted to be structured according to Eocene (NW-SE) compressional and Oligocene extensional phases. This basement comprises structural highs (anticlines and horsts) and subsiding areas (synclines, half-grabens and grabens) formed during the Neogene. The subsiding areas are delineated by faults striking N030E, N-S and N140E, defining (i) narrow, strongly subsiding synclines, (ii) lozenge-shaped basins and (iii) trapezoidal basins. The architecture of their fill results from the sedimentary balance between tectonics and eustatism. Halokinesis and clay diapirism (driven by Triassic and Neogene evaporites and clays) also played an important role in basin evolution, contributing to the formation of domes and diapirs along active faults.

Rupturing in overpressured crust during compressional inversion—the case from NE Honshu, Japan

Inboard from the subduction interface in NE Honshu, the crustal seismogenic zone which overlies the dehydrating subducting slab is generally from 10 to 20 km deep. Arc-normal shortening is manifested by patterns of geodetic strain accumulation and by a predominance of moderate-to-steep reverse faulting, reflecting compressional inversion which has been ongoing since the Late Pliocene. Several strong recent earthquakes have involved reverse-slip rupturing on inherited normal faults along the margins of Miocene extensional basins flanking the magmatic arc both to the east and to the west. From focal mechanism analyses and aftershock distributions, the mainshocks involved close-to-pure reverse slip on faults dipping at 40–60° along the basin margins. These earthquakes represent increments of the continuing compressional inversion which is not far advanced, however, because in several instances the fault hangingwalls are occupied by Neogene sedimentary basins which are still, locally, up to 6 km deep. On the assumption of horizontal maximum compressive stress, rupturing during these earthquakes took place on faults poorly oriented for frictional reactivation, often approaching the lock-up angle expected for standard rock friction. Continued reactivation of such structures, in preference to the formation of more favourably oriented low-dipping thrusts, requires near-lithostatic ( P f → σ 3) but probably heterogeneous fluid-overpressuring within the lower half of the seismogenic zone. A range of geophysical evidence—local occurrence of bright-spot reflectors, low-velocity zones, anomalous Vp/Vs ratios, and high electrical conductivity—support the existence of a fluid-rich (H 2O ± CO 2), variably overpressured mid-crust which extends into the lower half of the upper crustal seismogenic zone, especially in the vicinity of the major fault systems. Subhorizontal magmatic sills and arrays of hydrothermally filled extension fractures formed by hydraulic fracturing when lithostatic fluid-pressures are locally attained ( P f > σ v = σ 3) provide plausible explanations for local development of bright-spot reflectors in the subvolcanic regions and the areas flanking the magmatic arc, respectively. The seismogenic upper crust in NE Honshu is therefore functioning as a brittle stress guide under compressional stress, confining overpressured hydrothermal fluids in the mid-crust that are probably derived from a combination of magmatic intrusion and prograde metamorphism within the crust, as well as from the underlying dewatering slab. Fault failure in such settings is at least partly driven by overpressured fluids infiltrating the lower seismogenic zone. Episodic failure in the brittle carapace leads to fluid discharge along transiently permeable rupture zones (fault-valve action). Cycling of fluid pressures between near-lithostatic values prefailure and sub-lithostatic values postfailure may induce time-dependent changes in physical parameters (seismic velocities, reflectivity, electrical conductivity) within the lower seismogenic zone.

Dynamics of deformation and sedimentation in the northern Sierras Pampeanas: An integrated study of the Neogene Fiambala basin, NW Argentina

The thick-skinned Sierras Pampeanas morphotectonic domain of western and northwestern Argentina (27°S–33°S) is characterized by reverse-fault–bounded basement blocks that delimit internally deformed, Neogene sedimentary basins. Foreland-basin evolution in this part of the Andes is still not very well understood. For example, challenging questions exist as to how thick-skinned deformation develops, if there are distinct spatiotemporal trends in deformation and exhumation, how such deformation styles influence sedimentation patterns, and whether or not broken foreland basins are related to regional plate-tectonic processes, such as flat-slab subduction. The Fiambala basin of the northwestern Sierras Pampeanas is the largest of several intermontane basins in the transition to the southern margin of the Puna Plateau. This basin preserves a thick continental Neogene sequence that provides information on the dynamics of thick-skinned deformation and resulting sedimentation. The Fiambala basin contains ~4 km of fluvial-alluvial sedimentary rocks that comprise the Tamberia, Guanchin, and Punaschotter Formations. U-Pb geochronology of ashes intercalated within the Fiambala stratigraphic sequence demonstrates that these sedimentary rocks are late Miocene to Pliocene (8.2 ± 0.3 Ma to 3.05 ± 0.4 Ma) in age. Sedimentology and provenance data indicate that the source of the Tamberia Formation was located to the west of the modern western basin-bounding range. The Guanchin and Punaschotter Formations record input from local sources, including the modern basin-bounding range to the west and the southern Puna Plateau to the north, suggesting reorganization of the catchment area at ca. 5.5 Ma. The coarsening-upward trends recorded by the fluvial Tamberia and Guanchin Formations indicate enhanced tectonics and relief during sedimentation. The Punaschot-ter conglomerates record alluvial-fan sedimentation and local sources. Fault kinematic data document a contractional regime, characterized by E-W and NE-SW shortening, active throughout the middle-late Miocene and Pliocene. Furthermore, a comparison between the Fiambala basin and similar sedimentary basins in the Sierras Pampeanas (e.g., Bermejo foreland basin) and the Eastern Cordillera leads us to propose that the study area originally constituted an integral part of a continuous and more extensive foreland-basin system (thin-skinned) for much of its early history. Our data suggest coeval intrabasin deformation along strike from the Bermejo region northward to the Eastern Cordillera. The coeval change at ca. 6 Ma from a regional to more compartmentalized (thick-skinned) tectono-sedimentary environment in the regions adjacent to the Eastern Cordillera, the southern Puna margin, and other sectors within the Sierras Pampeanas domain may thus reflect a regional tectonic process related to flat subduction. Our data, combined with existing sedimentological and petrological evidence, imply that the passage from steep to flat subduction occurred synchronously from ~30°S to ~26°S.

Late Cenozoic paleogeographic evolution of northeastern Nevada: Evidence from the sedimentary basins

Field and geochronologic studies of Neogene sedimentary basins in northeastern Nevada document the paleogeographic and geologic evolution of this region and the effects on major mineral deposits. The broad area that includes the four middle Miocene basins studied—Chimney, Ivanhoe, Carlin, and Elko, from west to east—was an upland that underwent prolonged middle Tertiary exposure and moderate erosion. All four basins began to retain sediments at ca. 16 Ma. Eruption of volcanic flows in the Chimney and Ivanhoe basins produced short-lived (ca. 2 Ma), lacustrine-dominated basins before the dams failed and the streams drained to the southwest. In contrast, early, high-angle, normal faulting induced fluvial to lacustrine sedimentation in the Carlin and Elko basins, and volcanic flows further blocked drainage in the Carlin basin until the basin drained at ca. 14.5 Ma. The Elko basin, with continued synsedimentary faulting, retained sediments until ca. 9.8 Ma and then drained west into the Carlin basin. Sediment buildup in all basins progressively buried existing highlands and created a subdued landscape. Relatively minor post-sedimentation extension produced early north-northwest–striking normal faults with variable amounts of offset, and later east-northeast–striking normal faults with up to several kilometers of vertical and left-lateral offset. The earlier faults are more pronounced east of the Tuscarora Mountains, possibly reflecting a hanging-wall influence related to uplift of the Ruby Mountains-East Humboldt core complex on the east side of the Elko basin. The later faults are concentrated along the north-northwest–trending northern Nevada rift west of the Tuscarora Mountains. The area west of the rift contains major tilted horsts and alluvium-filled grabens, and differential extension between this more highly extended region and the less extended area to the east produced the intervening east-northeast–striking faults. The Humboldt River drainage system formed as the four basins became integrated after ca. 9.8 Ma. Flow was into northwestern Nevada, the site of active normal faulting and graben formation. This faulting lowered the base level of the river and induced substantial erosion in upstream regions. Erosion preferentially removed the poorly consolidated Miocene sediments, progressively reexposed the pre-middle Miocene highlands, and transported the sediments to downstream basins. Thus, some ranges in the upstream region are exhumed older highlands rather than newly formed horsts. In addition, the drainage system evolution indicates that northern Nevada has become progressively lower than central Nevada since the middle Miocene. Mineral belts with large Eocene gold deposits are exposed in uplands and concealed beneath Neogene basin units in the study area. Also, numerous epithermal hot-spring deposits formed at and near the paleosurface in the Chimney, Ivanhoe, and Carlin basins as those basins were forming. The Neogene geologic and landscape evolution had variable effects on all of these deposits, including uplift, weathering, supergene enrichment, erosion, and burial, depending on the events at any particular deposit. As such, this study documents the importance of evaluating post-mineralization processes at both regional and local scales when exploring for or evaluating the diverse mineral deposits in this area and other parts of the Basin and Range region.

The impact of a major Quaternary river capture on the alluvial sediments of a beheaded river system, the Rio Alias SE Spain

The Rio Alias is a transverse river system developed within the Sorbas and Almeria Neogene sedimentary basins within the Internal Zone of the Betic Cordillera, southeast Spain. Headwaters of the Rio Alias rise in the southern margins of the Sorbas basin following a superimposed transverse course across the Sierra Alhamilla/Cabrera and its associated boundary faults. A major river capture event within the Sorbas Basin (c.70 ka) created a situation whereby the Rio Alias abruptly lost c. 70% of its drainage area. Such an extensive loss of drainage area led to significant modification of the fluvial system in both upstream and downstream zones on the capturing stream, and downstream on the beheaded system. On the beheaded Rio Alias, a combination of terrace mapping, clast identification/analysis, field descriptions of pedological development and mineral magnetic analysis allows the relative timing of the capture event to be confirmed. Examination of the fluvial architecture of the Quaternary terrace deposits reveals significant changes in bedform geometry, involving a reduction in bedform height, degree of channelisation and maximum clast size in the post-capture sediment assemblage. The post-capture evolution of the Rio Alias has been heavily influenced by the river capture event, highlighting the need for further analysis of beheaded drainage systems and their influence on developing landform assemblages.

K-Ar evidence for a Mesozoic thermal event superimposed on burial diagenesis of the Upper Silesia Coal Basin

K-Ar dating of mixed-layer illite-smectite from clay fractions extracted from pyroclastic horizons was used to address the controversy about the age and mechanism of the thermal alteration of Carboniferous rocks from the Upper Silesia Coal Basin (USCB). The clay fractions were also investigated by X-ray diffraction in order to select for dating samples possibly rich in illitesmectite, and to evaluate the K-Ar dates for possible contamination by K-bearing pre-diagenetic minerals, of pyroclastic or epiclastic origin. The K-Ar dates document intense Variscian tectonic burial illitization produced by thrusting (~290 Ma) in the SW of the basin, and the lack of intense burial illitization in the NE, which is consistent with sedimentological models of the basin. The burial illitization in its final phase (<30%S in illite-smectite) involved incorporation of measurable amounts of ammonium cation in the illite structure (substitution for K). Advanced illitization in the NE of the basin is much younger than its tectonic inversion (uplift and erosion started in Permian), and the corresponding K-Ar dates have to be interpreted as the result of a Mesozoic thermal event, which produced widespread pervasive illitization at shallow depth. This event was dated at 175 Ma, but it may have started earlier and could have lasted longer. This conclusion is consistent with widespread evidence of a major Mesozoic thermal event all over Central Europe, produced by rifting and lithospheric thinning during the opening of the Tethys and Atlantic oceans. This study demonstrates that smectite illitization histories may be very complex, and that the nature of the illitization mechanism results in mixed K-Ar dates encompassing pro-longed or multiple illitization histories. Dating of several grain-size fractions may help to unravel such histories. When a calibration using data from Neogene sedimentary basins is applied, vitrinite reflectance and %S in I-S indicate similar palaeotemperatures of tectonic burial diagenesis in the USCB, but they produce very different estimates of the temperature of the thermal event.

La tectonique active de la région nord-algérienne

Active tectonics in Algeria is located in the northern part of the country, mainly in the Tell system. In this region, located at the Africa–Eurasia boundary, the tectonic activity expresses the convergence between the two main plates. This leads to the closure of the Neogene sedimentary basins and the ongoing Tell building. Offshore, present deformation affects the abyssal plain located close to the continent, by folding of the Plio-Quaternary sediments cover. Along the slope and the continental platform, active structures with a continental extension crosscut this region. The coastal tectonics generates the coastal uplift as it was shown during the last Boumerdes earthquake of 21 May 2003, where an average uplift of 0.50 m was measured. Onshore, the earthquakes occur along the boundaries of the Neogene sedimentary basins that are located along the coast. These basins underwent compressional deformations giving anticlines, reverse faults or thrust faults oriented NE–SW to NW–SE. These later active structures generated the most important earthquakes. In the High Plateau and the Saharan Atlas, a weak seismic activity is recorded. To cite this article: A. Yelles-Chaouche et al., C. R. Geoscience 338 (2006).

A field guide to the Neogene sedimentary basins of the Almería province, south-east Spain by A. E. Mather, J. M. Martín, A. M. Harvey and J. C. Braga, International Association of Sedimentologists, Blackwell Science, 2001. No. of pages: 350. (soft covers)

A field guide to the Neogene sedimentary basins of the Almería province, south-east Spain by A. E. Mather, J. M. Martín, A. M. Harvey and J. C. Braga, International Association of Sedimentologists, Blackwell Science, 2001. No. of pages: 350. (soft covers)

Palaeomagnetic constraints on the geodynamic evolution of the Gibraltar Arc

AbstractSubduction zone roll‐back was recently put forward as a convincing model to explain the geometry and evolution of the Gibraltar Arc. For other subduction‐related arc systems of the Mediterranean, such as the Calabrian Arc and the Hellenic Arc, palaeomagnetic rotation data from Neogene extensional basins provided important constraints on geodynamic evolution models. Here, we present the results of a palaeomagnetic study of 13 continuous sections that are located in E–W transects across the Neogene sedimentary basins of Morocco and Spain. They provide evidence that no significant rotation about vertical axes has occurred in the Gibraltar Arc since the late Tortonian. Comparison with other Mediterranean arc systems shows strong similarities as regards geodynamic evolution. The timing of rotation in the Gibraltar Arc is markedly older than in the Calabrian and Hellenic arcs, and suggests that it is related to the first Neogene extensional phase of the western Mediterranean in which the Algerian–Provençal Basin opened.

Tectonic evolution and deep to shallow geometry of Nagamachi-Rifu Active Fault System, NE Japan

The Nagamachi-Rifu fault is an active reverse fault which trends NE-SW across the central part of Sendai City for over 21 km distance. The fault does not emerge at the surface and, accompanied with the Dainenji-yama fault, shows wedge thrusting in the Tertiary sediments. The amount of net slip of the master part of the Nagamachi-Rifu fault is estimated to be one mm/year. Seismic reflection profiles across the fault plus a gravity anomaly reveal the thicker Neogene sediments on the hanging wall rather than on the footwall. The Neogene sedimentary basin was formed by normal faulting in early Miocene under an extensional stress regime associated with the formation of the northern Honshu rift system. Due to shortening deformation since the Pliocene, this Miocene normal fault reactivated as a reverse fault. Judging from the CMP deep seismic reflection profile and location of the 1998 M5.0 Sendai earthquake, the deep geometry of the Nagamachi-Rifu fault is listric.

Neotectonics and Plio-Quaternary landscape development within the eastern Huércal-Overa Basin (Betic Cordilleras, southeast Spain)

The Huércal-Overa Basin is one of a series of Neogene sedimentary basins located within the Betic Cordillera of southeast Spain. Its geological and geomorphological history has been controlled by tectonic activity culminating in basin inversion during the Plio-Quaternary. Deformation of the Huercal-Overa Basin is associated with left-lateral strike-slip faulting in relation to its position within the Trans-Alboran shear zone. In this paper, we focus upon the eastern portion of the Huercal-Overa Basin and make the first attempt to reconstruct the long-term landscape development during the Plio-Quaternary. This is done through integration of geological and geomorphological data obtained through field observations and GIS and remote sensing techniques. In particular, this paper provides a case study that contributes to the understanding of landscape development within tectonically active shear zones. Within the eastern part of the Huércal-Overa Basin, the main tectonic activity is associated with the left-lateral strike-slip Lorca-Alhama fault (oriented NE–SW). During the Late Pliocene and Early Pleistocene, the interaction of this fault with older Miocene ENE–WSW to E–W orientated structures formed a subsiding area with pull-apart basin characteristics termed the Cubeta del Saltador. Subsidence within the Cubeta del Saltador enabled sedimentary infilling by braided rivers with sediment being derived from the Sierra de Las Estancias to the north and the Sierra de Almagro to the south. Sedimentary deformation has resulted in the development of a series of progressive unconformities, angular unconformities and faulting within the alluvial sediments. Towards the end of this stage of landscape development, an increase in tectonic activity resulted in the creation of elevated tectonic highs in the north (Alto de la Garita del Diablo) and east (Loma de Garcı́a) of the Cubeta del Saltador. From the middle Pleistocene onwards, a progressive decrease in tectonic activity is recorded. Alluvial sediments infilled the Cubeta del Saltador. These were dominated by braided river sediments that formed part of a fan-shaped alluvial distributary system derived from the Sierra de las Estancias to the north. In contrast, smaller debris-flow-dominated alluvial fans were derived from the Sierra de Almagro along the southern margin. Currently, the study area presents an asymmetric configuration, reflecting the different topographic characteristics of the northern and southern limiting mountain fronts.

Explosive silicic volcanism of the Yellowstone hotspot: The ash fall tuff record

Unaltered silicic ash fall tuffs are abundant in Neogene sedimentary basins of the western U.S. and constitute an important record of explosive silicic volcanism in this region. In particular, ash fall tuffs from silicic volcanic centers along the Yellowstone hotspot track are common in these basins and provide a detailed record of explosive volcanism along the hotspot track. The available hotspot ash fall tuff record commences at ca. 16 Ma, shortly after the initiation of hotspot silicic volcanism at ca. 16.5 Ma, and continues through the most recent explosive eruptions in the late Pleistocene. Post–16 Ma hotspot silicic volcanism has been dominated by eruption of metaluminous ash flow tuffs and rhyolites, and ash fall tuffs produced by these eruptions dominate the Yellowstone hotspot ash fall tuff record. Evaluation of a well-dated composite sequence of 142 of these tuffs reveals systematic variation in magma composition, magma temperature, eruption frequency, and, possibly, volumetric discharge as the hotspot migrated eastward from the western edge of the North America craton to its current location in the Yellowstone Plateau. On the basis of these variations, three primary stages of metaluminous rhyolite magmatism (M stages) are recognized: M1 (16.0–15.2 Ma), M2 (15.2–7.5 Ma), and M3 (7.5–0 Ma). Each of these stages is marked by distinctive magma compositions, eruption frequencies, and magma temperature ranges and trends, with an overall decline in average eruption frequency and magma temperature from stage to stage. The partitioning of explosive hotspot volcanism into stages likely reflects variation in the style and intensity of the interaction between the mantle anomaly powering the hotspot magmatic systems and a spatially and temporally heterogeneous lithosphere along the hotspot track. Although the ash fall tuff record does not provide definitive constraints on the nature of these variable interactions, correlations between changes in eruption frequency, ash fall tuff discharge, and magma temperature point to variable input of mantle basalt into hotspot crustal magmatic systems as a first order control on intensity of explosive volcanism. As future studies reveal more about the processes controlling the variations in hotspot silicic volcanism, a fuller understanding of both the nature of silicic magmatism and the nature of the Yellowstone hotspot should emerge.

Effective timescales of coupling within fluvial systems

This paper presents a review of the coupling concept in fluvial geomorphology, based mainly on previously published work. Coupling mechanisms link the components of the fluvial system, controlling sediment transport down the system and the propagation of the effects of base-level change up the system. They can be viewed at several scales: at the local scale involving within-hillslope coupling, hillslope-to-channel coupling, and within-channels, tributary junction and reach-to-reach coupling. At larger scales, coupling can be considered as zonal coupling, between major zones of the system or as regional coupling, relating to complete drainage basins. These trends are illustrated particularly by the examples of hillslope-to-channel coupling in the Howgill Fells, northwest England, badland systems in southeast Spain, alluvial fans in Spain, USA and UAE, and base-level-induced dissection of Neogene sedimentary basins in southeast Spain. As the spatial scales increase, so do the timescales involved. Effective temporal scales relate to magnitude and frequency characteristics, recovery time and propagation time, the relative importance changing with the spatial scale. For downsystem coupling at the local scale, the first two are important, with propagation time increasing in importance in larger systems, especially in those involving upsystem coupling related to base-level change. The effective timescales range from the individual event, with a return period of decades, through decadal to century timescales for downsystem coupling, to tens to hundreds of thousands of years for the basinwide response to base-level change. The effective timescales influence the relative importance of factors controlling landform development.

40 Ar/ 39 Ar age of the Cabo de Gata volcanic series and displacements on the Carboneras fault zone, SE Spain

The SW–NE-trending Carboneras fault zone of SE Spain separates a terrain comprising uplifted massifs of the metamorphic basement of the Betic Cordilleras and intervening Neogene sedimentary basins, from the Cabo de Gata volcanic series. Along the southeastern boundary of the Carboneras fault, Burdigalian marls and tuffs, mark the beginning of the volcanic episode, rest unconformably on the basement, and were tilted to the vertical during the earliest stages of movement on the fault zone. 40 Ar/ 39 Ar dating of hornblende grains and igneous clasts from the tuffs constrain the onset of the volcanic episode at 21 Ma, some 4 Ma earlier than previously reported. Volcanic rocks higher in the sequence that overstep unconformably onto the southern edge of the fault zone yielded an age of 11 Ma, thus constraining the earliest episode of motion on the fault zone between these age limits. The main phase of left-lateral strike-slip movement on the Carboneras fault may be later than this time. Movements on more northerly strands of the fault zone, including the uplift of the Sierra Cabrera basement block to the NW, continued at least through Pliocene times. The onset of volcanism is broadly coeval with the unroofing of the orogen by extensional collapse, and supports earlier inferences of very rapid rates of uplift and cooling of the basement rocks.

Local earthquakes seismic tomography in the Betic Cordillera (southern Spain)

A crustal tomographic image, from the surface down to 35 km depth beneath the Betic Cordillera (southern Spain), is obtained using data on local earthquakes recorded at stations from the National and Andalusian Seismic Networks. The velocity structure and the hypocentre locations are derived from the inversion of P first arrival times, using an iterative simultaneous inversion method. The reliability of the results is assessed using different control parameters. The inverted velocity field in the uppermost layers shows a significant lateral variability which reflects most of the large-scale geological features of the Betic Cordillera. Well determined local surface anomalies allow to constrain the location and geometry of the most prominent Neogene sedimentary basins. The upper crust is well resolved throughout the whole region, and is characterized by relatively high velocities in the Internal Betics and in the South Iberian Massif and lower velocities within the External Betics. A relatively well constrained event cluster displays a NNE–SSW trend, and outlines the contact zone between the Internal and the External domains. The middle and lower crustal levels show reliable results beneath the central part of the Betic Cordillera. High averaged velocities are obtained within the South Iberian and the Alboran domains, in contrast to a relatively low velocity anomaly which characterizes the boundary between them. These findings support the hypothesis of the lack of well differentiated crustal levels below the contact zone, while crustal layering is better defined beneath the Alboran and the Iberian domains.