Tuff Beds Research Articles

Influences of Sedimentary Environments and Volcanic Sources on Diagenetic Alteration of Volcanic Tuffs in South China

Permian-Triassic (P-Tr) altered volcanic ashes (tuffs) are widely distributed within the P-Tr boundary successions in South China. Volcanic altered ashes from terrestrial section-Chahe (CH) and marine section-Shangsi (SS) are selected to further understand the influence of sedimentary environments and volcanic sources on diagenetic alterarion on volcanic tuffs. The zircon 206Pb/238U ages of the corresponding beds between two sections are almost synchronous. Sedimentary environment of the altered tuffs was characterized by a low pH and did not experience a hydrothermal process. The dominant clay minerals of all the tuff beds are illite-smectite (I-S) minerals, with minor chlorite and kaolinite. I-S minerals of CH (R3) are more ordered than SS (R1), suggesting that CH also shows a higher diagenetic grade and more intensive chemical weathering. Besides, the nature of the volcanism of the tuff beds studied is derived from different magma sources. The clay mineral compositions of tuffs have little relation with the types of source volcanism and the depositional environments. Instead, the degree of the mixed-layer clay minerals and the REE distribution are mainly dependent upon the sedimentary environments. Thus, the mixed-layer clay minerals ratio and their geochemical index can be used as the paleoenvironmental indicator.

Utilizing U–Pb CA-TIMS dating to calibrate the Middle to Late Jurassic spore-pollen zonation of the Surat Basin, Australia to the geological time-scale

Wainman, C.C., Hannaford, C., Mantle, D. & McCabe, P.J., April.2018. Utilizing U–Pb CA-TIMS dating to calibrate the Middle to Late Jurassic spore-pollen zonation of the Surat Basin, Australia to the geological time-scale. Alcheringa XX, xx-xx.Spore-pollen palynostratigraphy is commonly used to subdivide and correlate Jurassic continental successions in eastern Australia and thus aid the construction of geological models for the petroleum and coal industries. However, the current spore-pollen framework has only been tenuously calibrated to the geological time-scale. Age determinations are reliant on indirect correlations of ammonite and dinoflagellate assemblages from New Zealand, the North West Shelf of Australia and Southeast Asia to the standard European stages. New uranium-lead chemical abrasion thermal ionization mass spectrometry (U–Pb CA-TIMS) dates from 19 tuff beds in the Middle–Upper Jurassic Injune Creek Group of the Surat Basin enables regional spore-pollen palynostratigraphic zones to be precisely dated for the first time. These results show the base of the APJ4.2 and APJ4.3 subzones are similar in age to previous estimates (Middle Jurassic, Bathonian) from indirect palynostratigraphic correlation. However, the base of the APJ5 Zone and the APJ6.1 Subzone may be somewhat younger than previously estimated, possibly by as much as 2.5 and 4.2 Myrs, respectively. The continued utilization of U–Pb CA-TIMS dates will further refine the absolute ages of these zones, improve the inter- and intra-basinal correlation of Middle–Upper Jurassic strata in eastern Australian basins and greatly enhance intercontinental correlations.Carmine Christopher Wainman [carmine.wainman@adelaide.edu.au] and Peter James McCabe [peter.mccabe@adelaide,edu.au] Australian School of Petroleum, University of Adelaide, SA, 5005, Australia; Carey Hannaford [carey.hannaford@mgpalaeo.com.au] and Daniel Mantle [dan.mantle@mgpalaeo.com.au] MGPalaeo Pty Ltd, 5 Arvida Street, Malaga, WA, 6090, WA, Australia.

Stratigraphy, geochronology, and paleoenvironments of Miocene - Pliocene boundary of San Fernando, Belén (Catamarca, northwest of Argentina)

The Santa María-Hualfín Basin was proposed as a regional synchronous lithostratigraphic depocenter in the geological province of Northwestern Pampean Ranges, Northwestern Argentina. However, new 40Ar–39Ar dating indicates that deposits toward the east, in Santa María Valley (Santa María Department), are younger than the western depocenter in San Fernando (Belén Department). Therefore, it would be more appropriate to study these valleys as separate basins, each one with its own tecto-sedimentary features. The east basin, named in this paper Villavil-Quillay, constitutes an elongated independent basin that developed along the front of the eastern Puna bordering with Papachacra and Durazno Ranges. This basin is composed of more than 3000 m of mudstone, sandstone, conglomerates, volcaniclastic and pyroclastic deposits. Villavil-Quillay basin develops onto a peneplain of Precambrian and lower Cambrian rocks, most of which are metamorphic and granites rocks. The sedimentary fill consists of Cretaceous? and Cenozoic continental deposits. The Cenozoic record is composed of a) the Santa María Group (Miocene-Pliocene), formed by Las Arcas, Chiquimil, Andalhuala and Corral Quemado Formations, and b) the Punaschotter unit (Puna's Gravels in German, Pleistocene). This study involves the Andalhuala, Corral Quemado and Punaschotter deposits cropping out in San Fernando area. The set of identified facies assemblage corresponding to the Andalhuala Formation shows a vertical variation of fluvial sub-environments, varying from permanent sandy braided rivers to gravel rivers and aeolian dunes culminating in an alluvial dry cycle. While facies assemblages of the Corral Quemado Formation allow inferring the development of ephemeral water bodies from secondary channels on the floodplain, the Punaschotter conglomerates indicate the development of gravel channels and bars. Three samples of tuffs interbedded in the sedimentary levels of Andalhuala Formation were dated indicating that the Miocene-Pliocene boundary is represented in this area. The lower tuff beds, outcropping at the southwest of San Fernando Sur, provided an age of 5.59 ± 0.04 Ma (late Miocene, Messinian). The others tuffs beds, both outcropping at the west-northwest of San Fernando Norte and overlaying the first one, gave an age of 4.79 ± 0.15 Ma and 4.72 ± 0.08 Ma (early Pliocene, Zanclean), respectively. These absolutes ages, together with the results of a sedimentological analysis, indicate that westward from San Fernando River, much of the areas mapped as Corral Quemado Formation correspond to the Andalhuala Formation; while part of the area considered as Punaschotter unit must be assigned to Corral Quemado Formation. Also, a thick tuff bed, recognized at the contact of Corral Quemado and Punaschotter, was considered as the previous one dated in 3.66 Ma, in Puerta de Corral Quemado locality.

Soft sediment deformation structures in a lacustrine sedimentary succession induced by volcano-tectonic activities: An example from the Cretaceous Beolgeumri Formation, Wido Volcanics, Korea

The Cretaceous Beolgeumri Formation is composed of laminated mudstones intercalated with sandstones, chert, and a bed of lapilli tuff that were deposited in a lacustrine environment at the terminal part of a regional strike-slip fault systems on the southwestern Korean Peninsula. The Beolgeumri Formation contains various types of soft sediment deformation (SSD) structures that are characterized by a wide extent (<4km), lateral continuity (<200m), and vertical repetition. The SSD structures can be classified into six categories based on their morphological features and deformation styles: 1) fold structures, 2) load structures, 3) water-escape structures, 4) rip-down structures, 5) boudin structures, and 6) synsedimentary fault structures. Field examination of SSD structures together with an analysis of the sedimentological records of the Beolgeumri Formation indicate that the SSD structures formed largely by liquefaction and/or fluidization triggered by ground shaking during earthquakes. To constrain the timing of the development of SSD structures in the Beolgeumri Formation, we conducted sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon age dating of block sized lithic clasts bearing volcaniclastic deposits that conformably underlie (the Mangryeongbong Tuff) and overlie (the Ttandallae Tuff) the Beolgeumri Formation. The Mangryeongbong and Ttandallae Tuffs have ages of 86.63±0.83Ma and 87.24±0.36Ma, respectively, indicating that the Beolgeumri Formation was deposited during a short interval between major volcanic eruptions. The large lithic clasts of volcaniclastic deposits suggest that the Beolgeumri Formation was deposited adjacent to an active volcanic edifice(s). Syndepositional magmatic activities are suggested by the occurrence of a lapilli tuff bed in the Beolgeumri Formation and an igneous intrusion (intermediate sill) that is crosscut by a sand dike, as well as the similar age results of the underlying and overlying volcaniclastic deposits. Thus, we infer that the earthquakes that caused the development of SSD structures in the study area were closely related to syndepositional magmatic activities, as is the case for modern tectonic earthquakes around active volcanoes.

Chronostratigraphy of the Pliocene–Pleistocene boundary in forearc basin fill on the Pacific side of central Japan: Constraints on the spatial distribution of an unconformity resulting from a widespread tectonic event

The upper Ikego Formation (Pliocene) and the Urago Formation (Pliocene to Lower Pleistocene) have been examined for their lithostratigraphy, calcareous nannofossil biostratigraphy, and magnetostratigraphy. Both formations are forearc basin fills exposed on the Miura Peninsula on the Pacific side of central Japan. The boundary between these formations has been previously treated as the western extension of the Kurotaki Unconformity, which was considered to be related to widespread tectonic change at ca. 3 Ma in the Japanese forearc region. However, the presence of the unconformity on the Miura Peninsula remains unclear due to sparse lithostratigraphic and chronostratigraphic data around the boundary between the both formations. In the study area, the Ikego Formation consists mainly of sandy mudstone and the Urago Formation of sandstone and muddy sandstone; both formations contain numerous tuff beds. Key tuff beds and the last appearance of Discoaster tamalis have been identified in the upper Ikego Formation and the lower Urago Formation, allowing these formations to be considered conformable. The following continuous stratigraphic markers were identified (in ascending order): top of the Mammoth Subchronozone (3.21 Ma); base (3.13 Ma) and top (3.05 Ma) of the Kaena Subchronozone; last appearance of Discoaster tamalis (2.76 Ma); the widespread tuff bed KGP (ca. 2.5 Ma); and the last appearance of Discoaster pentaradiatus (2.41 Ma). Sedimentation rates are almost constant among these age-controlled horizons, which indicates continuous sedimentation from 3.2 to 2.4 Ma. The results indicate that the Kazusa Group conformably overlies the Miura Group on the Miura Peninsula, which provides a well-established continuous stratigraphic section for analyses of regional paleoenvironmental and tectonic evolution in the Japanese forearc region.

U-Pb Age and Hf Isotopic Compositions of Magmatic Zircons from a Rhyolite Flow in the Porcellanite Formation in the Vindhyan Supergroup, Son Valley (India): Implications for Its Tectonic Significance

AbstractThe Porcellanite Formation in the basal Semri Group of the Proterozoic Vindhyan Supergroup, exposed along the Son River Valley, India, primarily consists of intercalated silicified felsic tuff beds (porcellanite), rhyolitic breccia, and shale. Lensoid patches of very coarse-grained rhyolite occur in a stretch of about 10 km near the eastern end of the valley. These are newly interpreted as rhyolite flows, with flow structures including aligned volcanic fragments and phenocrysts, a few of which are ∼10-cm-long feldspars. Microphenocrysts consist of fragments of patchy perthite and quartz, with subordinate Fe-oxide minerals set in a very fine-grained groundmass of quartz and feldspar. Volcanic rock fragments and fiamme are common. Bulk chemical compositions of nine samples also identify them as rhyolite (SiO2 = 75.24%; Na2O + K2O = 7.06%, CaO = 1.66%). Rare earth element distribution is typical of granitic rocks, with a negative Eu anomaly of 0.57. The samples are enriched in U, Th, La, and Rb and d...

Depositional age of the Himenoura Group on the Amakusa‐Kamishima area, Kyushu, southwest Japan: Using zircon U–Pb dating of the acidic tuffs

AbstractThe Upper Cretaceous Himenoura Group in the Amakusa‐Kamishima Island area, southwest Japan is subdivided into the Hinoshima and Amura Formations. In order to determine the numerical depositional age of the formations, zircon U–Pb ages were investigated using laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) for acidic tuff samples from the lower part of the Hinoshima Formation and the upper part of the Amura Formation. Although the two samples contain some accidental zircons, the samples have a definite youngest age cluster and their weighted mean ages are 85.4 ± 1.3 and 81.5 ± 1.1 Ma, respectively (errors are 95 % confidence interval). These age data indicate that the Himenoura Group in the Amakusa‐Kamishima Island area was deposited mainly in the early Santonian to early Campanian which is consistent with biostratigraphic ages. Additionally, zircon age distributions of the two tuff samples from the upper part of the Hinoshima Formation do not show a distinct youngest peak of eruption age but characteristics of detrital zircons suggestive of maximum depositional age of the host sediments. These results demonstrate that the mean age of the youngest zircon age cluster of a tuff sample does not always indicate depositional age of the tuff, and statistical evaluation of age data is effective to determine depositional age of a tuff bed using zircon U–Pb ages.

Neoarchaean banded iron formation within a ∼2620 Ma turbidite-dominated deep-water basin, Slave craton, NW Canada

Banded iron formations (BIFs) are iron- and silica-rich chemical metasedimentary rocks that span much of the Archaean and early Palaeoproterozoic rock record. Given that BIFs precipitated from ambient seawater, they provide an important archive of Earth’s ancient marine environments. Within the Slave craton occurs one of the largest and well-preserved Achaean turbidite basins in the world. Interstratified within the greywacke-mudstone turbidites is BIF that is commonly associated with ferruginous sediments and locally with a felsic tuff bed. Field investigations were conducted at four BIF locations from west to east across the Slave craton. These BIFs are composed of micro- and mesobands of quartz and magnetite, with various amounts of metamorphic grunerite, ferro-actinolite, ferro-hornblende as well as greenalite and stilpnomelane, the latter two are interpreted as retrograde metamorphic phases. As the BIF was deposited in a deep-water turbidite-dominated basin(s), the chemical component was occasionally diluted by clastic detritus, as illustrated by highly variable Al2O3 content, and Al2O3/TiO2 and Cr/Ni that are similar to the clastic sediments. On a layer-by-layer basis, the iron content in the BIF ranges from as low as 4wt.% and up to ∼75wt.% Fe2O3, whereas the SiO2 content ranges from 20wt.% to as high as ∼94wt.%. This, together with a hyperbolic germanium/silicon distribution, suggests that continentally-sourced silica comprised the background precipitation, which was periodically interrupted by pulses of hydrothermally-sourced iron. High-temperature hydrothermal fluids contributed, with an average shale-normalized positive Eu anomaly of 1.92, which indicates input of reduced Eu2+ to the ambient seawater. The BIF shows characteristic aqueous fluid-derived rare earths+yttrium fractionation (Pr/Yb<1) and positive La and Y anomalies. A negative Ce anomaly in parts of the BIF indicates the presence of an oxidizing agent able to fractionate Ce3+ to Ce4+. The age and trace element signature of the felsic tuff is similar to arc-type volcanic rocks, potentially linking the BIF and turbidite basin(s) to the Defeat Suite plutons (ca. 2630–2620Ma). The slow chemical rainout behind BIF deposition presumably took place on the basin plain adjacent to a steep submarine ramp where turbidite currents and slump-generated debris flows, sourced and triggered by the tectonically active arc-terrain, episodically delivered clastic sediment.

Using precise CA-TIMS ages of volcanic air-fall tuff beds in correlating the Walloon Coal Measures of the Surat Basin, Australia

The Upper Jurassic Walloon Coal Measures of the Surat Basin is one of Australia’s largest and most productive gas provinces. Despite the drilling of over 8500 wells and numerous publications, the stratigraphic framework is poorly defined. The laterally discontinuous nature of the sedimentary facies, including coals and fluvial channel sandstones, makes correlation difficult. The abundance of volcanic air-fall tuff beds within strata across the basin provides a unique opportunity to independently verify existing stratigraphic frameworks. Using the high-precision chemical abrasion thermal ionisation mass spectrometry technique, zircon grains from 28 tuff beds have been successfully dated within an error margin of less than 100 kyr. These dates substantially revise biostratigraphic and lithostratigraphic frameworks. Lithostratigraphic units are diachronous across the basin. In addition, the sparsity of key spore–pollen taxa limits the application of biostratigraphy. The complex interplay of climate and subsidence on facies distributions can now be documented over a time frame of ~4 Ma. Syntectonism played an important role in variable palaeodrainage patterns across the basin, the frequency of fluvial avulsions and preferential sites of peat accumulation through time. The new stratigraphic framework should aid in future exploration for coal seam gas in the area. Dating tuff beds using high-precision dating techniques should also assist in correlation of non-marine strata elsewhere in the world.

Depositional timing of Neoarchean turbidites of the Slave craton—recommended nomenclature and type localities

Two temporally distinct Neoarchean turbidite packages are known to occur in the Slave craton. The older is a greywacke–mudstone succession that includes the renowned Burwash Formation (ca. 2661 Ma). In this study, a previously undated tuff bed is demonstrated to have crystallized at ca. 2650.5 ± 1.0 Ma refining the deposition age of these turbidites between ca. 2661 and 2650 Ma. The younger turbidites are locally distinctive as they contain interstratified banded iron formation (BIF). Previous work demonstrated that the younger turbidites were deposited between ca. 2640 and 2615 Ma, based entirely on maximum depositional ages from detrital zircons. A ∼3 cm thick felsic to intermediate tuff bed was discovered interbedded with these BIF-bearing turbidites. The tuff bed contains a single age population of zircon with a crystallization age of 2620 ± 6 Ma defining the depositional timing of these BIF-bearing turbidites. New U–Pb detrital zircon dates from extensive turbidite sequences in the eastern and central part of the Slave craton are also presented. We use the new and previously published results to recommend nomenclature for these extensive sedimentary rocks in the Slave craton. The ca. 2661–2650 Ma turbidites remain part of the previously ascribed Duncan Lake Group. The younger ca. 2620 Ma turbidites are assigned to the new Slemon Group. Where robust age-data exist, we recommend formation names and include type localities for each.

四国東部の観音寺地域に分布する和泉層群滝久保層の珪長質凝灰岩の LA-ICP-MS によるU–Pb 年代とフィッション・トラック年代

四国東部の観音寺地域に分布する和泉層群滝久保層の珪長質凝灰岩の LA-ICP-MS によるU–Pb 年代とフィッション・トラック年代

U-Pb zircon ages of tuff beds from the Hongzaoshan Formation of the Quanji Group in the north margin of the Qaidam Basin, NW China, and their geological significances.

U-Pb zircon ages of tuff beds from the Hongzaoshan Formation of the Quanji Group in the north margin of the Qaidam Basin, NW China, and their geological significances.

LA-ICP-MS Zircon U—Pb Dating of Acidic Tuff from the Eocene Akasaki Formation, Amakusa, Kumamoto Prefecture, Western Kyushu, Japan: Implications for the Age of the Land Mammal Fauna in Japan

Abstract. We obtained zircon U—Pb ages using LA-ICP-MS for an acidic tuff bed in the upper part of the Akasaki Formation, a basal unit of the Eocene sequence in the Amakusa area, Kumamoto Prefecture, Japan. The U—Pb age of 49.1±0.4 Ma (95% confidence interval) suggests a late early Eocene age. Our result is important for biochronological assessment of the land mammal fauna of the Akasaki Formation. The new age date supports the correlation of the Akasaki mammal fauna with the Bridgerian North American Land Mammal Age.

U-Pb age of the tuff bed in the Urahoro Group, eastern Hokkaido, northern Japan

U-Pb age of the tuff bed in the Urahoro Group, eastern Hokkaido, northern Japan

Les membres Weberg et Warm Spring de la Formation de Snowshoe dans la région de Suplee, Orégon : Lithofaciès et zonation par ammonoïdés de l'intervalle Aalénien-Bajocien inférieur

This paper documents the stratigraphic information upon which an ammonoid zonation from the lower part of the Snowshoe Formation in the Suplee area was originally established (Taylor, 1988). Ammonoid ranges from 22 measured stratigraphic sections reveal about 60 ammonoid species distributed among eight zones encompassing the late Aalenian and part of the early Bajocian stages. The sediments are dominantly volcaniclastic and, as a result, there are numerous tuff beds in the succession. As noted in Taylor (1982) the principal tuff beds (herein designated as units A through F) can be used jointly with the ammonite sequence to give precise correlations from section to section. Utilizing the ammonoids, tuff beds, and facies in combination gives a graphic representation of the westward transgression of the Snowshoe Formation as it enveloped an irregular topography, and lapped onto the topographically high Grindstone High to the west. The ammonoid zonation is significant in that it gives a standard of reference for the biochronology of the late Aalenian and early Bajocian ammonoids in the North American Western Cordillera.

K–Ar ages and petrology of the late Miocene pumices from the Maragheh Formation, northwest Iran

Pumice beds of the Maragheh Formation, which is distributed on the plains at the foot of the late Cenozoic Sahand volcano, NW Iran, consist of the Mordaq tuff bed, lower pumice beds (A and B), middle pumice bed and upper pumice bed, in ascending order. New hornblende and plagioclase K–Ar ages of the pumices from these are: Mordaq tuff bed: 8.14 ± 0.27 Ma, lower pumice beds (A): 7.54 ± 0.22 Ma, lower pumice beds (B): 6.95 ± 0.28 Ma, middle pumice bed: 7.87 ± 0.29 Ma, upper pumice bed: 6.96 ± 0.31 Ma. The middle pumice bed is a flood deposit, and the chemical compositions of glass, hornblende and biotite in pumices overlap those from the lower pumice beds (A). These features indicate that the pumices of the middle pumice bed were derived from a similar source to the lower pumice beds (A). Chemical compositions of pumices from the Maragheh Formation fall in the dacite field of the total alkali-silica (TAS) classification diagram and slightly differ from those of the Plio–Pleistocene rocks from the Sahand volcano. Chemical compositions of late Miocene Maragheh Formation pumices show adakitic features with high Sr contents (698–545 ppm), and low Y (12–8 ppm). It is inferred that the source materials of the adakitic dacite magma were amphibole eclogite or garnet amphibolite originating from the Neo-Thetys plate subducted beneath the Eurasia plate.

Age of the Isomatsu Formation in the Tsugaru Peninsula, northeastern Japan: zircon U-Pb dating of a Miocene green tuff bed

磯松層は中新世のグリーンタフからなり，その既報ジルコンフィッショントラック（FT）年代は層序学的に推定される年代よりも有意に若い．今回筆者らは，若いFT年代が決定されたのと同じジルコンに対してLA-ICP-MS法によるU-Pb年代測定を行った．磯松層下部の火砕岩から約17.7Maの238U-206Pb年代が得られ，これは磯松層下部の堆積年代を近似する，またはその下限を制限する年代と見なされる．磯松層の年代は約17.7Maから約16Maまでの間と考えられ，それを踏まえて筆者らは津軽半島北部の下部中新統の年代層序モデルを改訂した．今回の測定結果は，調査地域またはその近傍でのマグマ活動，磯松層の堆積に示される調査地域における海進，および磯松層堆積時に起こったと考えられるハーフグラーベンの活動に対して，新たな年代制約を与えるものである．

Recent contributions to the standard Albian/Cenomanian boundary chronology from Hokkaido, Japan: A review for data reintegration and numerical age recalibration

The numerical age of the Albian/Cenomanian (A/C) boundary (=Early/Late Cretaceous Epoch boundary) has recently been updated using new radiometric dates from Hokkaido, Japan. Yet, an element of uncertainty still remains in the age scaling due to inaccurate chronostratigraphic contexts surrounding the tuff beds that have been geochronologically studied in the Oyubari and Soeushinai areas. To ensure stability in the Cretaceous time scale, this paper rigorously reevaluates the current status of Hokkaido A/C chronology, clarifying the limitations and making refinements via proper reintegration of published chronostratigraphic data. In the case of the Oyubari area, its A/C biostratigraphic scheme is limited by near-absence of ammonites and planktonic foraminifera at the Albian–Cenomanian transition, resulting in a large discrepancy in the proposed boundary levels based on these macro- and microfossil taxa. These problems can be solved by solid data integration aided by event- and δ13C-sratigraphy from the adjacent Ashibetsu area, wherein the A/C boundary is well documented by the superior planktonic foraminiferal record. Based on the resultant A/C boundary redefinition for the Oyubari area in conjunction with a simple linear interpolation from two published UPb ages, the A/C boundary age can be independently calibrated to be 100.8 Ma [with ±1.4 Myr uncertainty (=analytical precision)], which is consistent with that currently in use in the Geologic Time Scale 2012 (100.5 ± 0.4 Ma). In the case of the Soeushinai area, its chronostratigraphic framework is limited by rather complex geological structure and vertically/laterally variable lithologies. Moreover, the accuracy of geochronological data from this area is undermined by the fact that the dated tuff levels do not bracket the inferred A/C boundary.

Quantification of kerogen content in organic-rich shales from optical photographs

A novel method for quantifying kerogen content from optical photographs of oil shale is presented. It is applied and extensively validated for the thermally immature Mahogany zone of the Green River Formation. The method produces estimates covering scales of a few hundred microns to several hundred feet. It is simple, cheap, non-invasive, and requires no complex instrumentation other than an ordinary optical camera. Images of dry and water wetted samples are equally applicable, with the latter providing better overall predictions for oil yields less than 60gallons/ton and bitumen-impregnated volcanic tuff beds. Maximum error bounds are ±4wt% total organic carbon or ±10gallons/ton oil yield. Applicability of the method is likely limited in the presence of strong optically absorbing minerals with high spatial variability.

Was there a super-eruption on the Gondwanan coast 477 Ma ago?

Precise zircon and monazite ID-TIMS U–Pb dating of three Lower Ordovician altered ash-fall tuff beds (K-bentonites) in the Cantabrian Zone of NW Iberia yielded coeval ages together with an equivalent previously studied sample (477.5±1 (Gutierrez-Alonso et al., 2007)), of 477±1.3Ma, 477.2±1.1Ma and 477.3±1Ma, with a pooled concordia age (all analyses in the four samples) of 477.2±0.74Ma. A conservative estimation of the volume and mass of the studied K-bentonite beds (using exclusively the CZ data) yields a volume for the preserved deposits of ca. 37.5km3 (Volcanic Explosivity Index — VEI=6, Colossal). When considering other putative equivalent beds in Iberia and neighboring realms (i.e. Armorica, Sardinia) the volume of ejecta associated to this event would make it reach the Supervolcanic–Apocalyptic status (VEI=8, >1000km3). At variance with most known cases of this kind of gigantic eruption events, geological observations indicate that the studied magmatic event was related to continental margin extension and thinning and not to plate convergence. We speculate that a geochronologically equivalent large caldera event recognized in the geological record of NW Iberia could be ground zero of this super-eruption.