Tuff Levels Research Articles

Short note. A new U-PB age for the Talampaya Formation: Stratigraphic and paleoclimatic implications

This paper presents a new U–Pb zircon age of 253.40 ± 1.06 Ma for the middle part of the Talampaya Formation, which is consistent with the previously reported dating of 252.38 ± 0.22 Ma at the top of the unit. The age herein presented was obtained from a tuff level intercalated into a fluvial sequence formed by finning-up cycles of massive conglomerates, cross-bedded sandstones, and laminated sandy mudstones interpreted as deposited by sandy meandering rivers with dominant sandy floodplains. In this context, a vitric tuff from a floodplain located 140 m from the base of the unit provided the zircons dated by the combination of LA-ICP-MS (Laser Ablation – Inductively Coupled Plasma – Mass Spectrometry).The radiometric age of 253.40 ± 1.06 Ma confirms the relocation of the Talampaya Formation in the Late Permian and demonstrates that at least the upper half and probably the whole of this unit was deposited during the Lopingian, a time interval scarcely represented in South America. This assumption is consistent with the age of 249.66 ± 0.11 Ma (early Triassic) reported in the overlying La Veteada Formation.The new age presented has paleoclimatic implications regarding the worldwide climatic aridification event that occurred at the end of the Late Paleozoic since it gives a relatively precise approximation to the onset of the aridization in this part of Gondwana during the Lopingian (circa 252.38 Ma).

Revisión de la Formación La Veteada en su estratotipo (La Rioja, Argentina): edad, estratigrafía y significado paleoambiental

The La Veteada Formation, in the Sierra de Famatina (west of Argentina), is one of the few records of Early Triassic age in South America verified by isotopic age and palynological assemblages. This unit is composed of sandstones, mudstones, shales, limestones, and marls, with some levels of gypsum, chert, and tuff levels. In its stratotype, the La Veteada Formation rests on Late Permian red beds of the Talampaya Formation and is covered by Neogene breccias and conglomerates belonging to the Del Crestón Formation. The unit is divided into three associations of sedimentary facies. Facies association A (80 m thick) is a red bed succession composed of mudstone and fine-grained sandstone, together with some levels of chert and gypsum. Facies association B (58 m thick) is greenish-gray to yellowish-gray and comprises limestones, marls, shales, and fine- to coarse-grained sandstones. This facies includes stromatolites and several levels of shales and marls where rich palynological assemblages were recovered. Finally, facies association C (24 m thick) is made up of yellowish-gray marls, mudstones, and sandstones. In this section, stromatolites are missing, thin levels of gypsum appear, and evidence of subaerial exposition as mud cracks and raindrop imprints are frequent at the top of the facies. The lithology, sedimentary structures, and vertical stacking of facies suggest that the La Veteada Formation was deposited in a lacustrine environment, which evolved from a shallow ephemeral playa lake system (facies association A) to a perennial lake, in which carbonate production increased compared to clastic sedimentation (facies association B). Regarding the facies association C, the increase in clastic supply, the missing stromatolites, and the presence of gypsum levels suggest a progressive shallowing of the lake and the likely transition to a palustrine environment. The Early Triassic age of the La Veteada Formation is indicated from two different lines of research. Firstly, a zircon U-Pb age of 249.66±0.11 Ma obtained from a tuff level at the middle part of the facies association A. Secondly, the presence of palynological species identified in other Early Triassic units worldwide. The La Veteada Formation records the filling of the embryonic extensional basins formed at the earliest Triassic. Moreover, this unit shows the evolution of depositional environments after the late Permian massive extinction event.

Clay mineral assemblages as indicators of paleoenvironmental and diagenetic dynamics in the Neogene Fiambalá Basin, NW Argentina

Clay mineral characterization is a valuable tool for unraveling the evolution of continental sedimentary basins. The Fiambalá basin is a foreland Andean basin located in the Southwest of the province of Catamarca (Argentina), on the flat subduction segment. In order to characterize its paleoenvironment and post-depositional evolution, petrographic, X-ray diffraction (XRD), and scanning microscopy (SEM-EDS) studies were carried out in detrital and volcaniclastic samples from the Tambería, Guanchín, and Rodados de la Puna Fms. Petrographic and XRD analyses show a predominance of phyllosilicates, quartz, plagioclase, and low proportions of feldspar and anhydrite, sporadic calcite, analcime, heulandite, and hematite. In the XRD fraction <2 μm, minerals from the smectite and illite groups dominate, with lower proportions of chlorite and kaolinite. An analyzed tuff level presents smectite solely in this fraction. The textural-compositional analyses of SEM-EDS show that illite and chlorite have a detrital origin. Their preservation would be consistent with the dominance of an arid climate in the region during the erosion and deposition of material from the source areas. The smectites are of the magnesium-rich beidellite-montmorillonite type and, together with the zeolites would be authigenic as a product of the alteration of both the volcanic material and magnesian detrital phases (chlorite and biotite), possibly under the influence of an alkaline environment related to the arid climate. From a thermal point of view, the presence of smectite throughout all stratigraphic succession allows interpreting maximum temperatures that, even in the deepest levels of the basin, inhibit the development of prograde phases (such as smectite/illite and smectite/chlorite mixed-layered) and allow the preservation of smectite. Based on the authigenic clays present in the basin, paleogeothermal gradients of between 13 and 18 °C/km (considered a fill of 4000 m thick) and between 8 and 11 °C/km (considered a fill of 6000 m thick) could be estimated.

Toward a chronostratigraphy of the Paleocene-Eocene sedimentary record in northwestern Argentina

The Santa Bárbara Subgroup of the Salta Group in northwestern Argentina represents a key sedimentary record to understand the geological, biological, and climatological changes that occurred in South America during the Paleogene. However, the lack of absolute ages in these non-marine successions have prevented conclusive interpretations and correlations at a regional-scale. In this contribution, we present an integrative study based on sedimentological and stratigraphic approaches, a paleontological review, and, for the first time, an absolute age from a tuff level in the upper section of the Mealla Formation. We propose the following scenario: 1) Cycles of low and high accommodation stages that can be tracked at basin-scale providing a criterion to regional correlations; 2) An U–Pb zircon age of 58 Ma, which combined with previously estimated ages for Santa Bárbara Subgroup indicate that this unit is constrained between 61 and 49? Ma; 3) On view of this new age the fossil-bearing levels of the Mealla Formation fill a hiatus of more than 4 Myr in the South American vertebrate record for the middle to late Paleocene, reshaping our understanding of the early evolutionary stages of this fauna. Our results represent a robust first step to achieve reliable regional correlations and an integrative comprehension of the evolution of the Salta Basin and its fossil biota.

High-precision U-Pb CA-ID-TIMS calibration of the Permian Lueckisporites-dominated assemblages in westernmost Gondwana: inferences for correlations

Palynology is one of the most useful tools for constructing biostratigraphic charts in the late Paleozoic basins of South America, but the lack of radiometric ages often makes it difficult to establish the precise age of the biozones. This paper focuses on two points: (i) the description of new Argentinian palynological assemblages referred to the Lueckisporites/Weylandites (LW) Biozone and (ii) the application of a new isotopic age that enables more confident large-scale correlations with the neighboring Paraná Basin of Brazil. The palynofloras were recovered from the upper part of the De La Cuesta Formation that crops out in the retroarc basin of the Paganzo Basin, more specifically obtained from mudstones intercalated with limestones, cherts, and tuffs interpreted as being deposited in a shallow water body. The assemblages are characterized by an abundance of bi-taeniate pollen grains of the Lueckisporites complex and multitaeniate pollen grains such as Lunatisporites, Protohaploxypinus, Striatopodocarpidites, Tornopollenites, and Vittatina. Colpate pollen grains are also represented by Marsupipollenites and Pakhapites. A U-Pb CA-ID-TIMS age of 278.84 ± 0.22 Ma, obtained from a tuff level interstratified with the fossiliferous strata, allows the age of the LW Biozone in the Paganzo Basin to be constrained for the first time and the adjustment of the record Lueckisporites virkkiae in Gondwana. Moreover, this date enables precise correlations with other basins, such as the San Rafael Basin (Yacimiento Los Reyunos Formation) in Argentina and the Brazilian Paraná Basin (Iratí Formation).

U-PB ages and environmental evolution of the De La Cuesta Formation (late Paleozoic): Record of the Choiyoi Volcanism in the retroarc area of the Paganzo Basin, Western Gondwana

This paper examines the relationship between the sedimentation in the retroarc Paganzo Basin and the activity of the magmatic arc developed in the neighboring Andean Cordillera during the Late Pennsylvanian-Cisuralian. The temporal relationships between the Choiyoi Volcanism (Andean region) and the retroarc Paganzo Basin were investigated according to three lines of research: 1. Sedimentology and lithostratigraphy of the De La Cuesta Formation, 2. Geochronology and, 3. Biostratigraphy.Paleoenvironmental studies indicate that small alluvial fans (facies association A) and braided river (facies association B) deposits prevailed in the lower third of the De La Cuesta Formation, which includes a thin intercalation of shallow marine sediments only present in the western part of the area (facies association C). A progressive decrease in the energy of the fluvial systems occurred at the middle part of the unit, where dominant finning-upward successions correspond to meandering rivers (facies association D). In contrast, interbedded sandstones and mudstones were subsequently deposited by low-energy ephemeral rivers (facies association E). Finally, the upper third of the De La Cuesta Formation corresponds to eolian sandstones (facies association F) and shallow water bodies deposits, including evaporites, limestones, and tuffs (facies association G) sedimented under semiarid to arid conditions with periods of explosive volcanism.A U–Pb age of 278.84 Ma was obtained from a tuff level at the uppermost part of the De La Cuesta Formation (facies association G). This age, together with one previously obtained of 311.89 ± 0.21 Ma corresponding to the base of the unit, indicate that the De La Cuesta Formation is Moscovian-Kungurian in age and that it was mostly deposited before the main phase of the Choiyoi magmatism, synchronically with the so-called Pre-Choiyoi magmatism. Furthermore, a rich palynological assemblage belonging to the Lueckisporites/Weylandites Biozone (LW), recovered from deposits of the facies association G, is equivalent to the Lueckisporites virkkiae (Lv) Biozone from the Paraná Basin (Brazil), pointing out a Kungurian age for these biostratigraphic units.The new radiometric age and the palynological taxa recovered from the top of the De La Cuesta Formation (facies association G) confirm a Kungurian age for this interval, establishing a key level for correlation between the sedimentation in the retroarc with the onset of the Choiyoi Volcanism in the magmatic arc.

A high-precision U–Pb zircon age constraints the timing of the faunistic and palynofloristic events of the Carnian Ischigualasto Formation, San Juan, Argentina

The Late Triassic represents records many of the most critical biotic crises in life-history (from Carnian to the end-Triassic extinction, ETE). Some hypotheses propose that these life changes were linked with shifts in the environmental setting during the initial stages of the Pangea breakup. These crises were likely not sudden events but a series of step-changes that reached their peak at the end of the Triassic. The Carnian-Norian Ischigualasto Formation is a world-renown terrestrial sequence that records both the Triassic Dinosaur Diversification Event (DDE) and at least one crucial terrestrial environmental and biotic turnover. A notable increase in humidity and volcanism was the setting of critical faunal replacement represented by the passage of the Hyperodapedon-Exaeretodon-Herrerasaurus to Exaeretodon tetrapod biozones. That environmental modification, together with the paleofaunistic turnover, has been accurately constrained by a new high-precision CA-TIMS U/Pb zircon age of 228.91 ± 0.14 Ma obtained from a tuff layer located in the exact stratigraphic position of the major biotic-paleoenvironmental disturbance in the middle part of the Valle de la Luna Member, at ~310 m from the base of the Ischigualasto Formation. Palynological assemblages containing the first records in westernmost Gondwana of European Tethyan and Onslow palynological species are also recognized close to the dated tuff level. Thus, this age is the first isotopic record for the Onslow Microflora diagnostic species in Gondwana. Moreover, the CA-TIMS date promotes a discussion about the accurate chronostratigraphic position for the beginning (after the Carnian Pluvial Event) of a series of environmental-biological disturbances that culminated at the end of the Triassic.

Sedimentary and geochronological studies on tuff levels from Triassic strata in the Nanzhao Basin, North Qinling Orogenic Belt, and their geological significance

The Ordos Basin is the second largest oil‐ and gas‐bearing sedimentary basin in China. This basin formed during the Triassic. At present, the location of the basin margins is still highly debated in the literature, especially its eastern and southern margins. The Triassic Yanchang Formation extensively outcrops in the Ordos Basin, and its distribution can provide a significant constraint on the basin extension. In this study, we focus on the measurement and correlation of the Middle–Late Triassic sedimentary strata from Nanzhao Basin, which is located to the south‐east of the present‐day Ordos Basin. The results of this study indicate that the sedimentary sequence of Triassic strata from Taizishan Formation and Taishanmiao Formation in the Nanzhao Basin is comparable with that of the Yanchang Formation in the Ordos Basin. Tuff intercalations in clastic rocks from Taizishan Formation in the Nanzhao Basin were studied with zircon chronology and Hf isotope analysis. The results show that the tuff sample has concord U–Pb age of 234.6 ± 1.5 Ma, which is considered as the boundary age between Middle and Late Triassic with a similar age in respect to that of the Yanchang Formation. The TDM2 values for the studied sample range from 1.0 to 1.4 Ga with the peak at 1.2 Ga, which is also similar to TDM2 values for tuffs encountered in the Yanchang Formation. On the other hand, the corresponding εHf(t) values of tuff in Nanzhao Basin range from −1.1 to +4.2 with an average of 1.2 and peak at 2, which are different with respect to those of the Yanchang Formation. According to the geochronological data, the tuffs in Nanzhao Basin might be mainly derived from a depleted‐mantle source from Late Meso‐Proterozoic period, and contaminated by a continental Early–Middle Meso‐Proterozoic crust. Therefore, we suggest that in Middle–Late Triassic, the southeastern margin of the Ordos Basin may have extended to Nanzhao area and the different εHf(t) values between tuffs in Nanzhao Basin and present Ordos Basin may be the result of scissor‐type collision of North China Block and South China Block during the Triassic.

Geochemical, palaeontological, and sedimentological approaches of a syn-orogenic clastic wedge: Implications for the provenance of the Permian (Cisuralian) Tunas Formation, Ventania System (Argentina)

The Tunas Formation crops out in the eastern sector of the Ventania System (southwestern Buenos Aires Province, Argentina) and represents the last unit of the Pillahuincó Group (Pennsylvanian–Cisuralian). This work integrates sedimentological, palaeontological, geochemical, and geochronological studies of the uppermost levels of the unit with the aim to enhance its palaeoenvironmental and stratigraphic framework within the Southwest Gondwana context. The analysed succession, of 250 m thick, is dominated by lithic arkoses and feldspathic litharenites composed of crystalline quartz and minor feldspars and volcanic fragments, interbedded with muddy-siltstones and heterolithic deposits with plant fossils. The succession is organized in three thickening- and coarsening-upward packages that correspond to fluvio-deltaic deposits. The plant fossil assemblage includes fronds of Gangamopteris obovata, Glossopteris angustifolia, Glossopteris wilsonii, and Asterotheca sp. cf. A. andersonii, in association with articulate ribbed stems of Paracalamites australis, which are here assigned to the Gangamopteris Zone. The low plant-diversity of the Tunas Formation could be related to the change from postglacial to semiarid-arid conditions evidenced during the Cisuralian in the Southwest Gondwana region where the study area is located. The obtained geochemical results indicate low recycling and sorting of continentally derived sediments with dominant input from the upper continental crust and acidic to intermediate magmatic precursors related to an active continental margin. Previous studies pointed out that the North Patagonian Massif, located SW of the Ventania System, was the source of such materials. Additionally, new LA-ICP-MS U–Pb zircon ages from two tuff levels of the Tunas Formation were considered together with previous U–Pb zircon ages. These suggest that the source of the ash fall deposits could be as far as the pre-Choiyoi volcanism (Late Mississippian–middle Cisuralian) of the Chilean Precordillera and Frontal Cordillera and as close as the Choiyoi volcanism (middle Cisuralian–Lower Triassic) of the Las Matras and Chadileuvú blocks, all located west of the Ventania System. The integrated analyses of the available U–Pb geochronological data also allowed us to constrain the sedimentation age of the uppermost levels of the Tunas Formation to the Artinskian. However, the age interval of the stratigraphic unit should be wider.

Mineralogical and geochemical analysis of sodium bentonites in continental settings: The Uspallata Group (Triassic) of the Cuyana Basin, Mendoza province, Argentina

The Triassic Uspallata Group of the Cuyana rift Basin is characterized by continental deposits including alluvial, fluvial and lacustrine systems, mainly composed of volcaniclastic (reworked) and pyroclastic sediments. The present work focuses on the ash fall tuffs levels (bentonites) in order to understand the origin of their sodium composition since classic worldwide natural sodium bentonites link with marine environments as a source of sodium. The mineralogical attributes and relationship with diagenetic alterations have been explored by petrography, X-ray diffraction, and geochemical analysis. The tuff levels, recorded in the Cerro de las Cabras, Potrerillos and Cacheuta formations, provide the most reliable representation of the composition of the original material and diagenetic alterations due to these levels are devoid of detrital input. Accordingly, they represent key elements to explore the origin of huge bentonite deposits in the basin. In the study units, Na-montmorillonite and analcime, found at concentrations of up to or more than 50 vol%, grew at the expense of vitric components and represent authigenic minerals developed under early diagenesis. Following sedimentological and paleogeographic evidence the alteration of volcanic glass occurred in hydrologically open lacustrine systems that reached saline-alkaline conditions. The changes in the (Na + K)/H+ ratio influenced the formation of Na-montmorillonite and analcime through the succession. In addition, kaolinite is an important alteration mineral that fills cavities, replaces the feldspar grains, and probably the early diagenetic minerals. The origin of kaolinite is due to the combined effects of decomposition of organic matter and incursion of meteoric freshwater during late-stage telogenesis which generated the acidification of pore waters. Based on geochemical proxies, geochronological data and the geodynamic context the input of high volumes of pyroclastic material may thus be the result of explosive volcanism from an arc-subduction complex located to the west at these latitudes. The present work suggests that the composition of Na-rich pyroclastic ashes accumulated in hydrologically-open lake systems which conditioned the formation of sodium bentonites in continental settings.

A new chronostratigraphy (40Ar-39Ar and U-Pb dating) for the middle section of the Burdur-Fethiye Shear Zone, SW Turkey (eastern Mediterranean)

Southwestern Turkey is a tectonically active region where extensional, strike-slip, and compressional tectonics cooccur. The Burdur-Fethiye Shear Zone is located in the middle of this complex area. Understanding the tectonic evolution of this region is crucial, but the controversial Neogene chronostratigraphy does not allow robust synthesis because of poor age control. The middle section of the Burdur-Fethiye Shear Zone includes three basins: the Acipayam, Cameli, and Golhisar basins. All these basins represent restricted portions of ancient larger carbonate lakes. The lacustrine sediments are locally covered or cut by lamproites with sparse intercalations of tuff levels. New 40 Ar- 39 Ar biotite and U-Pb zircon radiometric ages from volcanics and a tuff layer in this study demonstrate that the previously suggested Pliocene ages for these sediments are incorrect and that these Neogene sediments are middle Miocene in age.

Integrated stratigraphy and isotopic ages at the Berriasian–Valanginian boundary at Tlatlauquitepec (Puebla, Mexico)

The integration of calpionellid biostratigraphy, microfacies analysis, UPb geochronology, and strontium chemostratigraphy improves the definition of the Berriasian–Valanginian boundary in the Tlatlauquitepec area and validates the age of calpionellid zones from eastern Mexico in this interval. An age of 139.85 Ma derived from 87Sr/86Sr ratio within the base of Calpionellites Zone defines the Berriasian–Valanginian boundary. Additionally, the 134.0 ± 0.5 Ma UPb age returned by zircon grains from a tuff level exposed at the top of the succession confirms the Valanginian age of the whole analyzed section. Microfacies analysis reveals sea level variations that can be coincident with the KVa1–KVa4 eustatic cycles. These new data suggest that calpionellid biostratigraphy represents the most useful tool for the definition of the Berriasian–Valanginian time boundary in central Mexico and its correlation with the rest of the Tethyan domain.

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.

Astrochronology of the Valanginian–Hauterivian stages (Early Cretaceous): Chronological relationships between the Paraná–Etendeka large igneous province and the Weissert and the Faraoni events

The Geological Time Scale shows large uncertainties on durations and ages of Berriasian to Albian stages (Early Cretaceous), which impact climate and paleoceanographic reconstructions. Here, we provide a new astrochronology of the Hauterivian Stage anchored on (1) recent biostratigraphically well-constrained published radio-isotopic dates, and (2) a previously published astrochronology of the Valanginian Stage. A new duration of the Hauterivian Stage is assessed here at 5.93±0.41myr. The retained age model, anchored on a latest CA-ID-TIMS U–Pb age from a tuff level in the Hauterivian of the Neuquén Basin (Argentina), dates the base of the Valanginian Stage at −137.05±1.0Ma, the base of the Hauterivian Stage at −131.96±1.0Ma, and the top of the Hauterivian Stage at −126.02±1.0Ma. In addition, the onset of the mid-Valanginian Weissert Event is dated at −135.22±1.0Ma and the onset of the Faraoni Event at −126.73±1.0Ma. The duration of the mid-Valanginian carbon-isotope excursion, associated to the Weissert Event, is assessed at 5.85myr, with a rapid phase of increasing δ13C values (0.60myr), a phase of stable δ13C values (1.48myr), and smooth decrease in δ13C values (3.77myr). The calibration provided here highlights that the onset of the activity of the Paraná–Etendeka province and the start of the Weissert Event coincided, suggesting that the Paraná–Etendeka province may have played a major role on the climatic and oceanographic changes during the mid-Valanginian.

Dating the Triassic continental rift in the southern Andes: the Potrerillos Formation, Cuyo Basin, Argentina

The Triassic successions of western Argentina commonly show thin pyroclastic levels intercalated within thick fluvial and lacustrine terrigenous deposits. The Potrerillos Formation is the thickest Triassic unit in the Cuyo Basin. It is composed of alternating cycles of gravelly- sandy- and muddy-dominated intervals, in which several laterally-continuous tuff horizons occur. U-Pb SHRIMP ages were determined on zircon grains from three tuff levels located between the lowermost and the middle sections of the Potrerillos Formation. The ages for the time of deposition of the tuffs are 239.2 ± 4.5 Ma, 239.7 ± 2.2 Ma and 230.3 ± 2.3 Ma (Middle Triassic). Chemical data indicate that these acid to intermediate volcaniclastic rocks are derived from coeval basic magmas displaying tholeiitic to slightly alkaline signatures. They are associated with the rift stage that followed the extensive post-orogenic volcanism of the Choiyoi Group, that in turn has been ascribed to slab break-off in neighbouring areas. Two of the studied samples also record a subpopulation of inherited zircon grains with crystallisation ages of 260-270 Ma. The latter are considered to be an indirect measurement for the age of the Choiyoi Group in the Cuyo basin. The rift-related Triassic event represents the culmination of the Gondwanian magmatic cycle, and is interpreted as the result of subduction cessation and anomalous heating of the upper mantle previous to the western Gondwana break-up.

The earliest human occupation of North Africa: a reply to Sahnouni et al. (2002)

In a series of papers, Sahnouni et al. (1996, 2002) and Sahnouni and de Heinzelin (1998) have reported the results of their renewed excavations at the important Algerian localities of Ain Hanech and Ain Boucherit, first studied by Arambourg (e.g., Arambourg, 1970, 1979). According to the latest paper by Sahnouni and co-workers (Sahnouni et al., 2002), Ain Hanech would belong to the Olduvai subchron, dated to 1.77–1.95 Ma. This would make it by far the earliest North African site with evidence of hominid presence, and the time-equivalent of Olduvai Bed I, circum- KBS tuff levels at Koobi Fora, and Omo Shungura Member H. However, a review of the evidence put forward by Sahnouni et al. (2002) casts doubt on their conclusions. This evidence consists of 1) paleomagnetism, 2) biochronology, and 3) archaeology. They are discussed in this order below, preceded by a review of the more continuous Moroccan Atlantic sequence.

A study on the geology of the Ţaga region (Cluj district)

2 ABSTRACT. The geological formations from Ţaga area (Cluj District) are Sarmatian in age (in outcrops) and Badenian (under surface). Lithologically, they are represented mainly by sands and sometimes fine sediments (clays, marls), interbedded with volcanic tuffs a low fossil content. The Badenian is the host of gas accumulations, concentrated in dome structures. Localization: the rural community of Ţaga is located East of Cluj District, at the border with Bistriţa - Nasaud District. Relief and hydrography: this region with large hilly areas belongs to the transition zone from the Transylvania (S) towards the Somesan Plateau (N). The highest hills are between 400 to 500 m (the Bocor Hill is over 500 m high). The cuesta relief that corresponds to the unconformable valley slopes is well represented. The main hydrographic collector is the Fizes Valley (from SE to NW) together with its numerous tributaries; within the frame of this valley and its affluents there are extensive marsh lands and lakes formed from a mixed origin (due to natural - earth slipping- and anthropogenous factors). This natural phenomenon originates in tectonic consequences, the rise of the confluence zone of the Fizes Valley, due to diapirism. The most well known lakes are those from Ţaga, Geaca, Catina, and Sântejude. Maxim (1935) examined the evolution of this region's valleys, while Sandulache (1970) covered a study of the lakes. A review of geological research studies: - Koch (1900) - in the Ţaga area the Plain Strata (Stratele de Câmpie) are developed (Middle Miocene). - Wein (1941 - 1942) - focus on the stratigraphy of the Buza-Nasal perimeter, as related to a nondenominated tuff level, and notes the lack of fossils (mentions a few Ervilia examples). - Mârza (1960, 1962) - identifies the Ghiris Tuff in the region and follows it through to Ocna Mures (Uioara), proves its continuity, identifies the geological formations as belonging to the Sarmatian, and discovers more fossil occurrences (Ervilia and Abra), including the fossil level located under the Ghiris Tuff. - Sabau (1984) 3 - his thesis on the Ţaga gas structure focus on the lithology of the formations and their paleonthologic content (micro and macro fauna). 1 Abstract of Geologia perimetrului comunei Ţaga- by I. Mârza (from Monografia comunei Ţaga; in press) 2

Paleocene Volcano-Clastic Sequences in the Tuz Gölü Basin, Central Anatolia, Turkey: An Evolution of Petroleum Reservoir Rock Properties Using Logs

The Paleocene unit of the Karap L nar-1/1A and-2/2A wells was studied by subsurface data in the Tuz Gölü Basin. The Karap L nar-1/1A well mainly consists of acidic, andesite, and dasite tuff levels, which was determined according to an M-N plot chart. In the Karap L nar-2/2A well, dasite tuff is characteristic and some levels have rhyolite, glassy rhyolite tuff, and zeolite tuff properties. In the Karap L nar field, formation water salinity is very high (150,000-200,000 ppm), causing low resistivity and porosity values. Petrophysical properties show that tuff sequence total porosity is between 9 and 20%, and the fracture structure indicates that tuff level should be a prospect for hydrocarbon exploration in the Tuz Gölü Basin.

New data on the Volcanic Tuff from Petrestii de Jos (Cluj District)

New Data on the Volcanic Tuff from Petrestii de Jos (Cluj District). The present study was carried out on the cineritic interlayers from Petrestii de Jos (closed quarry from Indolului Valley), in order to present their detailed mineralogical-petrographical features. Previous work already noticed the similarity of this tuff level with Dej Tuff Complex in other areas. The studied outcrop consists of a compact volcanic tuff interlayered with marls and tuffaceous clays. The analytical investigations: chemical analyses, X-ray diffraction, IR spectroscopy and electron microscopy reveal the nature of the diagenetic transformations dominated by zeolitization. Besides clinoptilolite, which is the typical zeolite for Dej Tuff from the Transylvanian Depression, our investigation evidenced also the presence of phillipsite. The process was stepwise: during the primary, syngenetic stage K-clinoptilolite formed, while during the late epigenetic stage Ca-phillipsite crystallized; on behalf of the latter one, Ca- clinoptilolite was also generated. It is worth to mention that the highest amounts of zeolites are to be found in the basal horizon, while this amount decreases in the interlayers associated with the marly-clayey levels. From genetic point of view, the lower horizon in the outcrop represents a primary fall-out tuff. The thin interlayers within the upper horizons are resedimented tuffs. The tuff from Petrestii de Jos represents a cheap raw material located in the neighborhood of the industrial area of Turda town. For using it, only a more detailed research and the removal of the vegetal and soil layer on the top would be necessary.

Middle Triassic magnetostratigraphy and biostratigraphy from the Dolomites and Greece

Magnetostratigrapic and biostratigraphic data across the Anisian/Ladinian (Middle Triassic) boundary were obtained from the Frötschbach/Seceda section from the Dolomites region of northern Italy, and the Vlichos section from the Greek island of Hydra, where the Aghia Triada published section was also resampled. The Frötschbach/Seceda section includes two radiometrically dated (UPb) tuff levels and covers two of the three chief candidates for the position of the base of the Ladinian, namely at the base of the Secedensis Zone or the subsequent Curionii Zone. The Aghia Triada section yields biochronological evidence for the base of the Secedensis Zone, whose significance is, however, critically discussed in the light of the magnetostratigraphic correlation with Frötschbach/Seceda. The Vlichos section can be correlated with Aghia Triada and Frötschbach/Seceda by means of magnetic polarity stratigraphy and sparse fossil occurrences. The satisfactory correlation of the magnetozones allows us to construct a composite geomagnetic polarity sequence tied to Tethyan ammonoid and conodont biostratigraphy for about a 2.4 Myr interval across the Anisian/Ladinian boundary.