Deep Marine Basin Research Articles

Geochemical constraints on the depositional environment of Upper Devonian radiolarian cherts from Loei, north-eastern Thailand

Late Devonian radiolarian chert sequences in the Indochina block of north-eastern Thailand are exposed in a narrow belt located to the east of Loei province. The analyzed radiolarian cherts were collected from Chiang Klom, Sumnoi and Pha Samyod localities. They are characterized by high silica content (>90 wt.%), high aluminum content and low iron content (Al2O3/(Al2O3 + Fe2O3): geomeans 0.91, 0.88 and 0.92). The Al/(Al + Fe + Mn) values are high in both cherts and interbedded shales (geomean 0.89). High Si/(Si + Al + Fe) ratios are observed in cherts (geomean 0.97) and slightly low in shales (geomean 0.69), whereas Fe2O3/TiO2 values are low (geomean 5.91). For rare earth element (REE) analysis, the cherts exhibit low La abundances (geomean 4.31, 3.59 and 4.22), slightly negative Ce anomalies (Ce/Ce*: geomean 0.81, 0.76 and 0.93), intermediate ratios of North American Shale Composite (NASC) normalized Lan/Cen (geomean 1.33, 1.37 and 1.12) and intermediate Lan/Ybn values (0.79, 0.94 and 1.22). In the interbedded shales, REE characteristics are more or less equal to the cherts. The results indicate that these late Devonian radiolarian cherts were deposited in a continental margin environment. High Si/(Si + Al + Fe) values indicate a biogenic origin of the cherts, however, additional silica content in the cherts could be the result of diagenetic alteration. Intermediate positive Eu anomalies (Eu/Eu*: geomean 1.32, 1.25 and 1.44) are interpreted as the result of detrital feldspar contribution corresponding to the distinctive low content of Fe. Geological evidences from the field support volcanic activities during the Late Devonian-Early Carboniferous. Weathered materials and fragments of basalts and andesites would possibly be supplied to the basin during chert sedimentation. These geochemical constraints indicate that, in western portion of Indochina, deep marine basin was closed before Late Devonian which was followed by the incursion of Early Carboniferous orogeny.

Determining the Predominant Governing Parameters of the Bed-Load Equations for Sediment-Laden Rivers on the Continental Shelf

Abstract Sediment transport between the emerged land masses and deep marine basins is a fundamental process that affects the exploitation of resources and protection of the environment and its ecosystems. Sediment transport models on the continental shelf are often very complex and subject to semiempirical or empirical equilibrium transport equations that relate sediment fluxes and turbulence to physical properties such as velocity, depth, and characteristic bed-load sediment particle sizes. In engineering applications, errors in these physical properties affect the accuracy of the sediment fluxes. The present analysis details the importance of physical properties to the bed-load fluxes and suggests which parameters have more influence on the final result by providing insight into the relative strengths, weaknesses, and limitations of all the selected 52 bed-load equations for noncohesive particles (sand and gravel are treated separately). Various parameters were first investigated individually to pinpoin...

GEOCHEMICAL AND PETROLOGICAL CHARACTERISTICS OF LATE TRIASSIC BASIC VOLCANIC ROCKS FROM THE KOCALI COMPLEX; SE TURKEY: IMPLICATIONS FOR THE TRIASSIC EVOLUTION OF SOUTHERN TETHYS

The Kocali Complex in SE Anatolia is mainly composed of tectonically imbricated slices of pelagic rock suits (pelagic limestones; cherts; etc); platform carbonates; clastics; serpentinites and basic volcanics. It can be subdivided into four main parts as the Tarasa Unit; the Konak Unit; the Cilo Limestones and the Kale Ophiolite. In this paper; geochemical characteristics of basic volcanic rocks associated with pelagic sediments (radiolarian cherts; pelagic limestones; etc) have been studied along four stratigraphical sections (the Tarasa; the Bulam-2; the Korun-1 and the Korun-2) in the Konak and the Tarasa Units. The age of the volcanic sequences have been assigned to Late Triassic (middle Carnian to Rhaetian) based on the radiolarian data from the associated pelagic rock units. Geochemical data indicates the presence of two different types of Late Triassic volcanic rock groups characterized by E-MORB-type (Group-1 volcanites from the Tarasa Unit formed by mixing of OIB and MORB-type melts) and OIB-type (Group-2 volcanites from the Konak Unit) mantle sources. None of the samples from the Kocali Complex has characteristics of N-MORB type mantle source and was affected by crustal contamination. Based on these data; it can be suggested that all these volcanic rocks formed in a marginal oceanic basin away from the ocean ridge. The presence of Radiolaria and Bivalvia-bearing pelagic limestones and cherts associated to the basic volcanic rocks in the Kocali Complex also emphasize that they all formed in deep marine basin. Geochemical characteristics of Late Triassic volcanics in the Kocali Complex have great similarities and well-correlative to the coeval volcanics previously studied in the Southern Tethyan Belt (e.g. the Baer-Bassit region in NW Syria; the Mamonia Complex in SW Cyprus and the Antalya Nappes in SW Turkey). Taking into the consideration of the geochemical data obtained from Late Triassic basic volcanics in the Kocali Complex and geochemical characteristics of the coeval volcanics in the adjacent units in the Southern Tethyan Belt; it can be suggested that rifting age of the Southern Tethyan Oceanic Basin in SE Anatolia is probably earlier than early Late Triassic (middle Carnian time).

Upper Jurassic Reefs from the Russian Western Caucasus: Implications for the Eastern Black Sea

Exposures of Upper Jurassic reef outcrops in the Russian western Caucasus provide excellent field analogues for possible reef-complex reservoir targets imaged on seismic reflection data from the northern Shatskiy Ridge, eastern Black Sea. The reefs at outcrop can be generally grouped into coral-dominated, siliceous sponge-microbialite and microbialite types. Coral-dominated reefs occur as isolated patchy and massive forms, and can be subdivided into higher-diversity and low-diversity types. The former developed at shallow-water platform margins and in platform interiors, whilst the latter occurred in deeper-water mid-shelf settings. Siliceous sponge-microbialite and microbialite reefs occur as lenses and mounds that were restricted to deeper-water mid-outer shelf environments. The reefs developed on two Late Jurassic carbonate platforms in the Russian western Caucasus: the north Caucasus platform to the north and South Adler platform to the south. These platforms were separated by a deep marine (Greater Caucasus) basin, along the margins of which thick shallow-water coral-dominated reefs formed. The southwestern margin of the north Caucasus platform probably represented a reef barrier-slope-basinal system that was structurally controlled. At the northeastern margin of this platform, in the Laba River region, inner ramp coral-dominated reefs pass northwards into deeper-water siliceous sponge- and microbialite-dominated reefs. The South Adler platform may extend offshore into the eastern Black Sea and the coral-dominated reefs that crop out at its northern margin form potential exploration analogues. The palaeowater depth of the possible isolated reef complexes imaged on the Shatskiy Ridge is unclear. If they were deposited in shallow-water, the coral-dominated reefs examined in the north Caucasus or South Adler carbonate platforms may form suitable analogues. Alternatively, if they were developed in deeper water they may be equivalent to the siliceous sponge and microbialite reefs examined in the Laba River region.

Channel structures formed by contour currents and fluid expulsion: significance for Late Neogene development of the central North Sea basin

Abstract Channel horizons, delimiting a major Pliocene sedimentary prism in the central North Sea basin, have been investigated in the context of oceanographic, climatic and tectonic controls, using 3D seismic and well data from the UK and Norwegian sector. Aggrading channel structures, forming 700–2500 m wide and 75–150 m deep linear to arcuate troughs, superimpose the truncated distal part of the prism in the northern Central Graben. The origin of the aggradational channel and prism complex is related to differential deposition and erosion by contour currents that intensified as tectonic subsidence formed a deep marine basin (>600 m) with open connections to the Atlantic and Norwegian Sea. The largest channel troughs appear to be filled with consolidated sediments and emerge from areas where the Neogene strata is pierced by salt diapir chimneys. From Early Pleistocene ( c . 2.5 Ma) the channels were subject to progressive burial by rapid clinoform progradation. Based on the seismic observations, a depositional model is proposed that relates contourite channel development to fluid expulsion from salt diapir structures and fracture zones extending from lower Miocene strata. The sedimentary prism accumulated over a Late Miocene/Early Pliocene Unconformity marked by incised channels that are reminiscent of a northward diverging drainage system. This erosive low-stand development is probably related to late Alpine compression, which promoted uplift in the British Isles and the Channel region. The ensuing subsidence of the central North Sea, associated with concomitant uplift of the Norwegian–Danish Basin, generated the present southwestward dip of 0.5–0.8° of the basal unconformity. The Late Miocene compressional phase followed by rapid basin depending during Pliocene to early Pleistocene suggests that present concepts of North Sea basin development have to be re-evaluated.

Lithofacies and age data of Jurassic foreslope and basin sediments of Rudabánya Hills (NE Hungary) and their tectonic interpretation

Lithofacies and age data of Jurassic foreslope and basin sediments of Rudabánya Hills (NE Hungary) and their tectonic interpretationJurassic sedimentary rocks of the Telekesvölgy Complex (Bódva Series), Telekesoldal Complex (Telekesoldal Nappe) and the Csipkés Hill olistostrome in Rudabánya Hills (NE Hungary) were sampled for microfacies studies and interpretation of the depositional environments. The Telekesvölgy Complex is made up of reddish to greenish marl, occasionally containing limestone olistoliths — gradually progresses from the Norian Hallstatt Limestone of the Bódva Series — then grey marl, which may correspond to the latest Triassic Zlambach Formation. This variegated marl progresses into grey marl and calcareous marl, containing crinoid fragments. It may be interpreted as a hemipelagic facies, relatively close to submarine highs. Bajocian to Lower Bathonian black shales, rich in radiolarians and sponge spicules representing typical deep pelagic facies, are also assigned to the Telekesvölgy Complex. The Telekesoldal Complex represents a mélange-like subduction-related complex that consists of black shales, sandstone turbidites and olistostrome beds, and deposited by gravity mass flows. A relatively deep marine basin in the proximity of a submarine slope is likely to be the depositional environment of this unit. The clasts of the olistostromes are predominantly Middle to Upper Triassic pelagic limestones, rhyolite and basalt. Subduction related nappe stacking of the ocean margin during the Middle to Late Jurassic may have created suitable conditions for this sedimentation pattern. Bajocian-Callovian age of the complex was proved by the revision of the radiolarian fauna and new palynological data, the first from the Jurassic of the Aggtelek-Rudabánya Hills. The Csipkés Hill olistostrome consists of carbonate turbidite beds containing Jurassic platform derived foraminiferal and olistostrome horizons with Middle-Upper Triassic limestone clasts of red Hallstatt facies.

Coarse-grained sediment delivery and distribution in the Holocene Santa Monica Basin, California: Implications for evaluating source-to-sink flux at millennial time scales

Research Article| September 01, 2009 Coarse-grained sediment delivery and distribution in the Holocene Santa Monica Basin, California: Implications for evaluating source-to-sink flux at millennial time scales Brian W. Romans; Brian W. Romans 1Department of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Building 320, Stanford, California 94305, USA *Current address: Chevron Energy Technology Co., San Ramon, California 94583, USA. E-mail: brian.romans@chevron.com Search for other works by this author on: GSW Google Scholar William R. Normark; William R. Normark 2U.S. Geological Survey, Coastal and Marine Geology Division, 345 Middlefield Road, Menlo Park, California 94025, USA Search for other works by this author on: GSW Google Scholar Mary M. McGann; Mary M. McGann 2U.S. Geological Survey, Coastal and Marine Geology Division, 345 Middlefield Road, Menlo Park, California 94025, USA Search for other works by this author on: GSW Google Scholar Jacob A. Covault; Jacob A. Covault 1Department of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Building 320, Stanford, California 94305, USA Search for other works by this author on: GSW Google Scholar Stephan A. Graham Stephan A. Graham 1Department of Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Building 320, Stanford, California 94305, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2009) 121 (9-10): 1394–1408. https://doi.org/10.1130/B26393.1 Article history received: 22 Dec 2007 rev-recd: 09 Dec 2008 accepted: 17 Dec 2008 first online: 02 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 Brian W. Romans, William R. Normark, Mary M. McGann, Jacob A. Covault, Stephan A. Graham; Coarse-grained sediment delivery and distribution in the Holocene Santa Monica Basin, California: Implications for evaluating source-to-sink flux at millennial time scales. GSA Bulletin 2009;; 121 (9-10): 1394–1408. doi: https://doi.org/10.1130/B26393.1 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 SocietyGSA Bulletin Search Advanced Search Abstract Utilizing accumulations of coarse-grained terrigenous sediment from deep-marine basins to evaluate the relative contributions of and history of controls on sediment flux through a source-to-sink system has been difficult as a result of limited knowledge of event timing. In this study, six new radio-carbon (14C) dates are integrated with five previously published dates that have been recalibrated from a 12.5-m-thick turbidite section from Ocean Drilling Program (ODP) Site 1015 in Santa Monica Basin, offshore California. This borehole is tied to high-resolution seismic-reflection profiles that cover an 1100 km2 area of the middle and lower Hueneme submarine fan and most of the basin plain. The resulting stratigraphic framework provides the highest temporal resolution for a thick-bedded Holocene turbidite succession to date, permitting an evaluation of source-to-sink controls at millennial (1000 yr) scales.The depositional history from 7 ka to present indicates that the recurrence interval for large turbidity-current events is relatively constant (300–360 yr), but the volume of sediment deposited on the fan and in the basin plain has increased by a factor of 2 over this period. Moreover, the amount of sand per event on the basin plain during the same interval has increased by a factor of 7. Maps of sediment distribution derived from correlation of seismic-reflection profiles indicate that this trend cannot be attributed exclusively to autogenic processes (e.g., pro-gradation of depocenters). The observed variability in sediment accumulation rates is thus largely controlled by allogenic factors, including: (1) increased discharge of Santa Clara River as a result of increased magnitude and frequency of El Niño–Southern Oscillation (ENSO) events from ca. 2 ka to present, (2) an apparent change in routing of coarse-grained sediment within the staging area at ca. 3 ka (i.e., from direct river input to indirect, littoral cell input into Hueneme submarine canyon), and (3) decreasing rates of sea-level rise (i.e., rate of rise slowed considerably by ca. 3 ka). The Holocene history of the Santa Clara River–Santa Monica Basin source-to-sink system demonstrates the ways in which varying sediment flux and changes in dispersal pathways affect the basinal stratigraphic record. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Step-over in the structure controlling the regional west tilt of the Sierra Nevada microplate: eastern escarpment system to Kern Canyon system

The Sierra Nevada and Great Valley are coupled, and behave as a semi-rigid microplate. The microplate formed as it was calved off the western edge of the Nevadaplano in the late Miocene, at which time westward regional tilting began. Tilting is controlled by west-side-up normal faulting primarily along the eastern Sierra escarpment system. Uplift and exhumation along the eastern Sierra are balanced by subsidence and sedimentation along the western Great Valley. The west tilt of the microplate is expressed by the west slope of a regional relict landscape surface that developed across much of the Sierra Nevada basement, and by the westward continuation of the surface as the basal Eocene nonconformity of the west-dipping Great Valley Tertiary section. The rigid behaviour of the microplate breaks down along its southern ∼100–150 km segment as expressed by seismicity, pervasive faulting and the development of a deep marine basin, the San Joaquin Basin (SJB), whose facies and palaeogeographic patterns diverge from regional patterns of the rest of the Great Valley. The disrupted state of the southern segment of the microplate resulted from its Late Cretaceous position above a regional lateral ramp in the underlying Franciscan-related subduction megathrust. The Kern Canyon fault system began its polyphase history as a complex oblique dextral shear zone above the megathrust lateral ramp. It was remobilized in the Neogene as an oblique transfer structure partitioning differential extension between the southern Sierra Nevada and the SJB. In Quaternary time, the Kern Canyon zone was again remobilized as a west-side-up normal fault system whose geomorphic and structural expressions are best developed south of ∼36.4° N. This normal fault system controls the west tilt of the relict landscape surface in the southern Sierra region, as well as the west dip pattern in the strata of the adjacent SJB. To the east of the Kern Canyon normal fault system, the relict landscape surface slopes continuously southwards from the high eastern Sierra into a low-lying, multiply extended terrane. Thus, from ∼36.4° N southwards, the west tilt along the western Sierra and the west dip of the adjacent Great Valley strata are controlled by the Kern Canyon system. Fresh normal scarps along the eastern Sierra escarpment system become more subdued and ultimately die out southwards from ∼36.4° N. Thus, currently, the controlling structure for the west tilt of the microplate steps westwards in the south from the eastern escarpment system over to the Kern Canyon system.

Characterizing Spatial and Temporal Variability of Dissolved Gases in Aquatic Environments with in situ Mass Spectrometry

The TETHYS mass spectrometer is intended for long-term in situ observation of dissolved gases and volatile organic compounds in aquatic environments. Its design maintains excellent low mass range sensitivity and stability during long-term operations, enabling characterization of low-frequency variability in many trace dissolved gases. Results are presented from laboratory trials and a 300-h in situ trial in a shallow marine embayment in Massachusetts, U.S.A. This time series consists of over 15000 sample measurements and represents the longest continuous record made by an in situ mass spectrometer in an aquatic environment. These measurements possess sufficient sampling density and duration to apply frequency analysis techniques for study of temporal variability in dissolved gases. Results reveal correlations with specific environmental periodicities. Numerical methods are presented for converting mass spectrometer ion peak ratios to absolute-scale dissolved gas concentrations across wide temperature regimes irrespective of ambient pressure, during vertical water column profiles in a hypoxic deep marine basin off the coast of California, U.S.A. Dissolved oxygen concentration values obtained with the TETHYS instrument indicate close correlation with polarographic oxygen sensor data across the entire depth range. These methods and technology enable observation of aquatic environmental chemical distributions and dynamics at appropriate scales of resolution.

Lithology and biostratigraphy of Upper Cretaceous marine deposits from the Haţeg region (Romania): Palaeoenvironmental implications

This paper presents the lithological and biostratigraphical (mainly based on calcareous nannofossils) record of the marine sediments which crop out in the NW and SE Haţeg regions. Upper Cretaceous marine deposition starts in these two regions in the Early Cenomanian (both in the CC9 calcareous nannofossil zone, and within UC1–UC2 biozones, respectively). In NW Haţeg, a hemipelagic sequence composed of red shales and marlstones, followed by white marlstones, probably associated with a deep-water paleoenvironment, marked the beginning of Upper Cretaceous marine sedimentation. In the SE, marine deposition started with sandstones and calcarenites, interlayered with Actaeonella and Ytruvia coquina, indicating an infralittoral paleoenvironment. From the Cenomanian up to the Coniacian, the marine setting becomes progressively shallower in the two Upper Cretaceous marine depositional Haţeg areas; this change is marked by the occurrence of outer shelf deposits in the NW and inner shelf sediments up to infralittoral ones in the SE. These deposits are followed by lower Santonian–upper Campanian turbidites in the NW, and by Lower Santonian–Campanian pro parte red marlstones and Upper Campanian turbidites, in the SE. The marine sedimentation ends, in NW Haţeg, with distal turbidites, Late Campanian in age (placed in the CC22 calcareous nannofossil zone, in the UC15d subzone respectively, slightly above the first occurrence of the nannofossil Uniplanarius trifidus). Towards the end of the Campanian, conglomerates and sandstones with Actaeonella and Ytruvia coquina, yielding reworked nannofloras (including Late Campanian taxa), occur in SE Haţeg. Associated with the paroxysmal Laramian tectonic phase, continental deposition started, probably within the Campanian/Maastrichtian boundary interval, both in the NW and SE parts of the Haţeg region. During the Late Cretaceous interval, different paleoenvironmental settings may be distinguished in the NW Haţeg (where a deep marine basin developed for most of the Early Cenomanian up to the Late Campanian interval), and in the SE Haţeg (characterised by an outer oscillating basin with an episodic shallow-water deposition in the same interval). Despite the various backgrounds of the two regions, some common regional events, such as the Early–Middle Cenomanian and the Early Santonian–Early Late Campanian sea level highstand, as well as the Late Cenomanian–Coniacian sea-level lowstand were recognised in both investigated areas.

End-signature of deep-marine basin-fill, as a structurally confined low-gradient clastic system: the Middle Eocene Guaso system, South-central Spanish Pyrenees

The ca 300 m thick Guaso system is the youngest part of the ca 4 km thick deep-marine fill of the Middle Eocene Ainsa basin, Spanish Pyrenees. It is overlain by 150 to 200 m of fine-grained slope, prodelta and deltaic sediments. The ca 25 discrete deep-marine sandbodies within the Ainsa basin accumulated over ca 10 Myr, making eustasy the most likely control for coarse sand deposition (probably the ca 400 kyr Milankovitch mode). The first-order control on basin-scale accommodation, however, was tectonically-driven subsidence. Previously, the Guaso sandbodies were interpreted as linked to deep erosional, canyon-like features, but here it is argued that they are laterally extensive sandbodies, built by lateral-switching of 3 to 10 m deep erosional channels, and confined only by basin structure during deposition. The Guaso system represents the end of deep-marine deposition in a structurally-confined, delta-fed, low-gradient clastic system. The critical end-signature of deep-marine deposition was a phase of differential tectonic uplift above the underlying (Boltaña) thrust creating a narrower and shallower basin morphology, thus allowing sedimentation to create a low-gradient clastic system. Then, the next eustatic sea-level fall was insufficient to permit the cutting of canyons or deeply-incised slope channels, as had been the case earlier when the topographic relief between shelf and basin was at least several hundred metres greater. Such low-gradient clastic systems may characterize the end-signature for the infill of other shallowing-up deep-marine basins where a tectonic driver on subsidence is removed and/or differential uplift/subsidence leads to reduced sea floor gradients, leaving eustasy and sediment flux as the principal control on sediment supply.

Deconvolving tectono-climatic signals in deep-marine siliciclastics, Eocene Ainsa basin, Spanish Pyrenees: Seesaw tectonics versus eustasy

The Eocene deep-marine siliciclastic fill of the Ainsa basin, Spanish Pyrenees, gives unprecedented temporal resolution of the causes and timing of coarse clastic sediment supply to a deep-marine basin. Early Eocene tectonic subsidence linked to Pyrenean orogenesis created the Ainsa basin, with water depths of similar to 400-800 m above a foundered shallow-marine mixed carbonate and clastic shelf. The similar to 25 sandbodies or channelized submarine fans in the basin were controlled by the similar to 400 k.y. Milankovitch frequency, with modes at similar to 100 k.y. and similar to 41 k.y. (possibly stacked similar to 23k.y.) influencing bottom-water conditions in the basin, causing periodic stratification in the water column across a submarine sill at the western basin margin (early Boltana anticline). Intrabasinal tectonics defined and controlled the position of eight sandy systems and their constituent fans, in a process of seesaw tectonics, by (1) westward lateral offset stacking of sandy fans due to growth of the eastern side of the basin, represented today by the Mediano anticline, and (2) eastward (orogenward) back stepping of the depositional axis of each sandy system, due to phases of relative uplift of the Boltana anticline. During basin infill, uplift of the Boltana anticline led to increasing basin narrowing and depositional confinement. Unlike the earlier depositional systems, the youngest deep-marine system was fed from a more southern sediment source between the growth anticlines, as was the overlying deltaic system. All the older deep-marine sandy systems were fed from southeast point sources, from canyons and erosional lower-slope channels eroding the growing Mediano anticline. The depositional style outlined in this paper might be common to other active margins where siliciclastic basins evolve between active thrusts.

The tectonic history of Drake Passage and its possible impacts on global climate

This study provides an integrated review of plate tectonic models of the evolution of the Antarctica–Patagonia connection compared to geological records collected on land in Patagonia and Tierra del Fuego, and offshore along the northern edge of the Scotia Sea. A temporal framework for the sedimentary and tectonic events of the North Scotia Ridge and Tierra del Fuego is constructed with additional data compiled from entire Patagonia and the Austral Basin. This review provides robust correlations of seaways and tectonic events along the Scotia and South America plates and indicates that the opening of the Drake Passage was not steady state since ca. 30 Ma. Rather the regions forming the present-day northern limit of this gateway experienced important paleogeographic changes, from deep marine basins to shallow ridges and emerged regions during the late Oligocene and early–middle Miocene time. Our compilation of geological data shows that emergence along the North Scotia Ridge and Tierra del Fuego was achieved at 23–22 Ma, and has been followed by elimination of the Patagoniano Sea in Patagonia, starting at 22–23 Ma and achieved at 20 Ma. This transition towards more continental sedimentation in southern South America is correlated with more shallow marine conditions in the Austral Basin. This succession of events had a strong influence on the general geometry of the Drake Passage, corresponding to a constriction of its northern limit, starting in the window 29–22 Ma and achieved at 21 Ma. This period of active deformation in southern South America also corresponds to a period of the global climate having two anomalies well known from the isotopic records: the Late Oligocene Warming, around 26 Ma and the Mid-Miocene Climatic Optimum which ended between 15 and 14 Ma. The possible effects of the post-Oligocene tectonic evolution of the Drake Passage region on general oceanic circulation are discussed. Causes for the synchronicity between tectonic events and these global warming events are examined.

Southeast Asia's changing palaeogeography

Geology provides the basis for understanding distributions of faunas and floras in Southeast Asia but only via a complex interplay of plate movements, palaeogeography, ocean circulation and climate. Southeast Asia grew incrementally by the addition of continental fragments, mainly rifted from Australia, and added to the margins of Sundaland as a result of subduction. Sundaland was an almost permanent land area from the beginning of the Mesozoic. The addition of the continental fragments of Southwest Borneo and later East Java–West Sulawesi formed a much larger emergent land area by the Late Cretaceous that extended from Indochina to West Sulawesi. Subduction resumed at the Sundaland margin in the Eocene and this led to widespread rifting within Sundaland, and formed one of the most important barriers at its edge, the Makassar Straits. Australia began to collide with Southeast Asia about 25 million years ago, effectively closing the former deep ocean separating the two continents, and forming the region now known as Wallacea. Collision, volcanism, and subduction-related processes have led to rise of mountains but also formed new oceans within this complex region. Plate tectonic movements and collisions were intimately linked to changing topography, bathymetry and land/sea distributions which have in turn influenced oceanic circulation and climate. As the deep-water barrier between Australia and Southeast Asia was eliminated and mountains rose, deep marine basins also formed. Eustatic changes in sea level further contributed to a complex palaeogeography. The present gateway between the Pacific and Indian Oceans is the only low latitude oceanic passage between the world’s oceans, and is an important influence on local and probably global climate. The gateway is likely to have been just as significant in the past. Understanding the geology, then palaeogeography, and then their oceanic and climatic consequences are vital steps on the way to interpreting present distributions of plants and animals.

Palaeoproterozoic seismites (fine-grained facies of the Chaibasa Formation, east India) and their soft-sediment deformation structures

Abstract Metamorphosed shales, heterolithic deposits and sandstones build up the Palaeoproterozoic Chaibasa Formation in east India. The shales (referred here to as the fine-grained facies) comprising mudstone (clay and silt size) with some minor amounts of very fine to fine sandstone were deposited below storm wave base in a deep marine basin that simultaneously underwent tectonic activity. This fine-grained facies contains strongly deformed layers, intercalated between undeformed layers. Sedimentological analysis of the deformations indicates that they formed while still in an unconsolidated or slightly consolidated state, partly during and after sedimentation, but before being covered by younger sediments. The types of deformation structures indicate an earthquake-induced origin. Thus, they should be considered as seismites. The soft-sediment deformation structures in the seismites show a wide variety of shapes and other characteristics that appear to depend on their relative position to the epicentre of the earthquake.

Stratigraphy, depositional environments and geodynamic significance of the Upper Bajocian–Bathonian Kashafrud Formation, NE Iran

Abstract A strongly subsiding rift basin in NE Iran, the Kashafrud Basin, opened in the Late Bajocian with the accumulation of more than 2000 m of Upper Bajocian–Upper Bathonian siliciclastic sediments. These sediments comprise the Kashafrud Formation, which crops out along a NW–SE stretch of more than 200 km and occupies a width of 50 km, situated between the Koppeh Dagh and the Binalud Mountains. Ten sections of the formation were logged. Sedimentary environments range from non-marine alluvial fans and braided rivers in the lowermost part of the succession to deltas, succeeded by storm-dominated shelf, slope and deep-marine basin. Monotonous mudstones and turbidites prevail in the deep-marine part of the basin. The thickness and facies of the Kashafrud Formation vary strongly between localities, and reflect distance from the rift margins as well as submarine topography, which was shaped by block tectonics. The Kashafrud Basin is interpreted as the eastern extension of the South Caspian Basin, which entered the rifting stage in the late Early Jurassic and the spreading stage in the Late Bajocian.

Permian and Triassic radiolarians from northern Tibet: correlation between radiolarian and conodont biozones

Abstract Thirty-five radiolarian species, belonging to two assemblages, one from the Changhsingian and the second one from the early Anisian, were recovered from siliceous rocks occurring in Xijirulan orogenic belt, northern Tibet. A new radiolarian species of them, Cryptostephanidium tibetensis, is described. The lower Anisian Eptingium nakasekoi assemblage co-occurs with conodonts belonging to Chiosella timorensis Zone. This fact allows correlation between radiolarian and conodont biozones. The lower Anisian radiolarian assemblage has a high diversity and supports that radiolarian radiation after the end-Permian mass extinction begins in the earliest Anisian. The research on the lithostratigraphic sequence and sedimentology shows that the old land of the Xijirulan orogenic belt, formed by the collision between the Qiangtang and Koh Xil terranes at the latest Early Permian, has disappeared in the early Changhsingian. During the Changhsingian and Triassic, the Xijirulan orogenic belt has become a deep marine basin and was combined with the Bayan Har Basin. This large deep sea basin extended until the end of the Triassic, locally possibly until the Jurassic.

Late Archaean synorogenic basins of the Eastern Goldfields Superterrane, Yilgarn Craton, Western Australia: Part III. Signatures of tectonic escape in an arc-continent collision zone

Siliciclastic supersequences in the Eastern Goldfields Superterrane are remnants of basins that were linear zones of subsidence between intra-terrane faults. Fluvial deposits record proximal to medial braid-plains. Deep-marine canyon and fan deposits were linked across intra-terrane compartments only by mud-rich deposits. Axial depositional systems dominate, with only minor evidence for slope-aprons, although transverse and axial systems are preserved in some fluvial deposits. Basin development occurred during two stages separated by an inversion event, with the Kalgoorlie Terrane recording change from a fluvial to a deep-marine basin and the Kurnalpi Terrane change from distal to proximal deep-marine facies tracts. Sparse palaeocurrents establish that uplift to the north controlled sediment dispersal. Lithofacies stacking is aggradational, whereas abrupt upwards-change in facies tracts is back-stepping within depositional sequences, and between depositional-sequence sets, but forward-stepping between depositional sequences. The stratigraphic architecture is atypical of synorogenic basins but consistent with a strike-slip regime characterised by pulsed uplift-subsidence, steady-state basin lengthening and subsidence, punctuating catastrophic subsidence and lengthening, and tectonic anchoring. The basins are interpreted to have been similar to graben and half-graben of the Western Anatolian extensional province of Turkey, with linear zones of subsidence developing adjacent to strike-slip, oblique-slip or normal dip-slip faults. Controls on stratigraphic patterns are considered to have been regional rather than at the scale of each basin. The envisaged tectonic setting is similar to projected collision between the Philippine Archipelago west of the Philippine Fault and continental crust of the South China Sea, but the orogenic architecture is similar to that of accreted superterranes in the Canadian Cordillera. Interpreted north- or northwest-convergence between the Burtville Terrane to the east and the ancestral Yilgarn continent to the northwest produced a south-propagating orogen, with the Kalgoorlie, Gindalbie, and Kurnalpi Terranes trapped between in a tectonic-escape corridor. Tectonic escape to the south between bounding strike-slip faults produced back-stepping of facies tracts that simulated basin lengthening, whereas forward-stepping of facies tracts was the response to south-propagating uplift.

Late Archaean synorogenic basins of the Eastern Goldfields Superterrane, Yilgarn Craton, Western Australia: Part I. Kalgoorlie and Gindalbie Terranes

Siliciclastic supersequences of the Kalgoorlie and Gindalbie Terranes post-date ∼2660 Ma deformation, uplift and erosion associated with the amalgamation of arc-related terranes, but were tectonically buried to greenschist or amphibolite facies during the orogenic shortening that accreted the Eastern Goldfields Superterrane to the Yilgarn Craton. The supersequences are synclinal remnants of late-stage basins that were linear zones of subsidence adjacent to north-trending strike-slip faults. Fluvial facies (Merougil, Navajo, Jones Creek, Scotty Creek and Yandal basins) are dominated by sheet sandstones that represent the deposits of medial braid-plains, but proximal channel-and-bar complexes of cobble and boulder conglomerates are also preserved. Submarine facies (Kurrawang basin) range from boulder to pebble conglomerates but are dominantly Bouma turbidites with rare black shales, and record the filling of a proximal canyon that fed a distal submarine fan. Axial depositional systems are preferentially preserved in all basins, but transverse systems are preserved at the base of some fluvial deposits. The gross vertical succession in all basins is from proximal up to distal. The basins developed during two tectonic stages separated by an intervening period of uplift, tilting and erosion, with the southern Kalgoorlie Terrane recording change from a Stage I fluvial to a Stage II deep-marine basin. Stage II fluvial deposits are preserved in the northern Kalgoorlie Terrane and in the Gindalbie Terrane. Sparse palaeocurrents establish sediment dispersal was to the south or southeast, implying uplift to the north or northwest controlled palaeoslopes. Stacking of lithofacies is aggradational and is consistent with limited lateral migration of facies tracts in fault-confined basins. Similar lithofacies and aggradational styles of facies stacking characterise syncollisional sequences of the Cenozoic Coastal Range Basin of Taiwan, and the present-day syncollisional basins of southeastern Taiwan are good analogues of late-stage basins of the Kalgoorlie and Gindalbie Terranes.

Prolonged Permian Triassic ecological crisis recorded by molluscan dominance in Late Permian offshore assemblages.

The end-Permian mass extinction was the largest biotic crisis in the history of animal life, eliminating as many as 95% of all species and dramatically altering the ecological structure of marine communities. Although the causes of this pronounced ecosystem shift have been widely debated, the broad consensus based on inferences from global taxonomic diversity patterns suggests that the shift from abundant brachiopods to dominant molluscs was abrupt and largely driven by the catastrophic effects of the end-Permian mass extinction. Here we analyze relative abundance counts of >33,000 fossil individuals from 24 silicified Middle and Late Permian paleocommunities, documenting a substantial ecological shift to numerical dominance by molluscs in the Late Permian, before the major taxonomic shift at the end-Permian mass extinction. This ecological change was coincident with the development of fluctuating anoxic conditions in deep marine basins, suggesting that numerical dominance by more tolerant molluscs may have been driven by variably stressful environmental conditions. Recognition of substantial ecological deterioration in the Late Permian also implies that the end-Permian extinction was the climax of a protracted environmental crisis. Although the Late Permian shift to molluscan dominance was a pronounced ecological change, quantitative counts of 847 Carboniferous-Cretaceous collections from the Paleobiology Database indicate that it was only the first stage in a stepwise transition that culminated with the final shift to molluscan dominance in the Late Jurassic. Therefore, the ecological transition from brachiopods to bivalves was more protracted and complex than their simple Permian-Triassic switch in diversity.