Late Cenozoic Sediments Research Articles

Análisis Icnológico y Paleoambiental de la Aloformación Punta San Andrés (Plio-Pleistoceno), Provincia de Buenos Aires, Argentina

ICHNOLOGICAL AND PALEOENVIRONMENTAL ANALYSIS OF THE PUNTA SAN ANDRÉS ALLOFORMATION (PLIO-PLEISTOCENE), BUENOS AIRES PROVINCE, ARGENTINA. Late Cenozoic deposits that crop-out in the costal cliffs of Buenos Aires Province, have been the center of paleontological studies since the beginnings of the twentieth century. The presence of structures related to biological activity in these deposits has been pointed out by several authors. However, they have never been studied in a holistic way, taking into account all of the structures and not only those related to a single group. Amongst the diversity of trace fossils related to invertebrate activity, burrows are the most abundant and two different morphologies can be recognized: (1) unwalled meniscate burrows referred to Taenidium serpentinum, and (2) walled meniscate burrows interpreted as Beaconites coronus. Other trace fossils found in these paleosols are spherical chambers assigned to Castrichnus incolumis. Trace fossils of vertebrate activity are mostly caves. The largest ones are attributed to the activity of Pampatheriidae or Eutatini (Xenarthra, Cingulata) and the smallest ones to the activity of various types of Caviomorpha (Mammalia, Rodentia) including the families Echimyidae, Octodontidae, Cavidae and Chinchillidae. Trace fossils related to flora are root molds and rhizoconcretions. Ichnological analysis allowed some paleoclimatic inferences. The presence of chambers and burrows associated with earthworm activity suggests soils affected by seasonally dry periods. These observations confirm prior paleoclimatic interpretations based on micromorphological study of the paleosols and sedimentological work.

THE ULTRAFINE COMPONENT RECORD FROM THE LATE CENOZOIC SEQUENCE IN THE CENTRAL TARIM BASIN AND ITS PALAEOCLIMATIC IMPLICATIONS

Grain size data from the Hongbaishan section reveal that the late Cenozoic deposits in the central Tarim basin generally contains an ultrafine component,which has an consistent modal size of 0.87μm and a variable proportion of 0.3%~10%.For the same lithological unit,proportions of the ultrafine component are quite distinctive along with the alternation of lithology.Aeolian sand owns the lowest value,loess has slightly higher value but lower than that of the fluvial deposits,whereas lacustrine clay maintains the highest value.Nevertheless,the long-term variations of the ultrafine component in different sediments show a similar trend,implying that same factor contributed to the long-term changes.Intensities of the chemical weathering and/or pedogenisis probably play the leading role in driving the changes.The abrupt decreasing of the ultrafine component at 2.8 Ma indicates a dramatic weakening of the chemical weathering and/or pedogenisis,which in turn suggest a significant strengthening of aridity in the Tarim basin.

Late Cenozoic shelf delta development and Mass Transport Deposits in the Dutch offshore area – results of 3D seismic interpretation

AbstractIn this study, seismic stratigraphic criteria have been used to characterise the evolution of the Southern North Sea (SNS) shelf-delta system that progressively filled the Southern North Sea basin during Plio-Pleistocene times. Based on the prograding and down-stepping architecture of the shelf-delta sequence it is inferred that deposition occurred during a time of high sediment supply and overall sea-level lowering. During this time the delta slopes failed several times, creating at least 30 internally coherent Mass Transport Deposits (MTDs) mainly grouped in common areas, affecting the same clinoform set and partially sharing the basal shear surface (groups of MTDs). The most important features of the studied MTDs are 1) the dominance of brittle deformation; 2) the small amount of material removal from the headwall domain (lack of completely depleted areas above the basal shear surface); and 3) the lack of an emergent toe domain above the un-failed sediment located basinward, although proper confining geometries for the MTD are not detected. Therefore, the studied MTDs can neither be classified as frontally confined nor as frontally emergent but they are a new intermediate type of submarine landslides which has not been described before. These characteristics suggest that the mass movement ceased relatively soon after initiation of failure. Incisions on top of the MTDs suggest the presence of erosive flows. These flows were probably generated due to a concentration of the drainage in the negative morphology the failure event left behind in the upper sector of the slope. The stronger progradational character of the reflections on top of MTDs confirms a concentration of drainage after the erosional phase too.The interplay between high sediment supply and constant or even decreasing accommodation space (caused by constant or decreasing sea-level) is supposed to be the main precondition for slope instability for most of the MTDs in this study area. Slope failures themselves can also be considered a preconditioning factor by the creation of local very high sedimentation rates (see groups of MTDs). Salt-induced seismicity and storm waves' effect superimposed on high frequency sea level fall are considered the most important triggering factors.

Magnetostratigraphy and environmental magnetism in a Pleistocene sedimentary sequence, Marcos Paz, Argentina

Late Cenozoic sediments exposed in a quarry in the locality of Marcos Paz (Buenos Aires province) were studied by applying paleomagnetism and environmental magnetism. The whole sequence, with the exception of the recent soil, belongs to the Pleistocene and is integrated by clayey silts (sandy) and also by a layer of fine sand. Eleven different depositional/postdepositional units, numbered in descending order from unit 1 to 11, were determined. The units 1, 2 and 3 in the upper portion of the geological section should be assigned to Brunhes ( 0.78 Ma). Matuyama magnetozone includes some subzones of normal polarity that should be assigned to the subchron Jaramillo (0.99 Ma) and to the subchron Olduvai (1.9 Ma). The reverse polarity levels determined at the bottom of the profile should be assigned to the lower Matuyama (>1.9 Ma). The highest volume susceptibility values are recorded in the less pedogenized sediments (400 × 10−5), while the lowest values are always obtained in gleyed horizons (30 × 10−5). The data support the wind-vigor magnetoclimatological model, although affected by different pedogenesis degrees and weathering as demonstrated by the behavioral pattern of chemical elements.

EVIDENCE OF NEOGENE TO QUATERNARY FAULTING AND SEISMOGENIC DEFORMATION ALONG THE NAMAQUALAND COAST, SOUTH AFRICA

This paper reports on the results of a systematic investigation into evidence of near-surface and surface deformation of Late Cenozoic sediments along the West Coast of South Africa. Regional studies were supplemented by the investigation of pit faces in diamond mines owned by De Beers Consolidated Mines (Pty) Ltd between Hondeklip Bay and Kleinsee and inspection of exploratory trench logs kept by Alexkor at Alexander Bay. The results provide the first substantiation for previous unverified reports of neotectonic faulting in Pliocene to Pleistocene formations along the Namaqualand coast. Associated deformation of unconsolidated marine sediments suggests that the faulting was seismogenic. The interpretations of some of the observed features remain preliminary and the age of the structures is in most cases not well constrained. Some of the faulting at Hondeklip Bay is clearly younger that 3 Ma and the youngest surface rupture observed may be of latest Pleistocene age. This style of reactivation of coast-parallel Mesozoic or older faults is similar to that recently described in Namibia, and known Quaternary reactivation of the Kango fault system in the Southern Cape.

Pliocene freshwater pollen-bearing deposits in the Mizerna-Nowa borehole, West Carpathians, Poland

This paper describes sedimentology and palynology of freshwater plant-bearing late Cenozoic (Pliocene sensu lato) deposits drilled at Mizerna, the eastern part of the Nowy Targ Intramontane Depression, West Carpathians, South Poland. Our data were obtained from a newly-analysed 39-m thick succession from the Mizerna-Nowa borehole, containing spores, pollen and freshwater organic-walled algal micro-remains. They shed light on the palaeoenvironmental conditions of the Nowy Targ Intramontane Depression, where the Mizerna palaeolake once formed.

Tectonic and geoelectric structures of rift basins in the Baikal region

The article summarizes results of tectonophysical and geoelectric studies of rift basins in the Baikal region. Their sedimentary cover is intersected by faults, which induce shallow soft deformations in Late Cenozoic sediments. The faults observed in the internal part of the basins correlate with zones of contrast change in the deep structures of the crystalline basement and sedimentary layers. They offset the top of the basement and bottom of the sedimentary layers, and constitute zones of lower resistivity values. Significant variations of electrical parameters can be due to redistribution of conducting fluids in a geological massif, which allows discriminating water-bearing faults from water-free ones. Taken as a whole, the tectonic structure of the basins is best defined by the presence of shallow deformation zones, an asymmetrical morphology and fault-block pattern of both the sedimentary infill and basement of the basins.

Gymnospermous woods from the Late Cenozoic sediments of Rajasthan, western India

The paper describes two gymnospermous woods, namely Araucarioxylon Kraus, 1870 and Podocarpoxylon Gothan, 1905 from the Late Cenozoic sediments (Shumar Formation) of district Jaisalmer, Rajasthan, western India. The woods indicate favourable climatic conditions for the growth of mesic vegetation in Rajasthan till Plio-Pleistocene time compared to the xeric vegetation and drier conditions in the area today.

A catalogue of late Cenozoic tephra beds in the Klondike goldfields and adjacent areas, Yukon Territory1Yukon Geological Survey Contribution 010.

Many distal tephra beds exist in the late Cenozoic sediments of the Klondike goldfields and nearby areas. They come from volcanoes in the Wrangell volcanic field and the eastern Aleutian arc and represent large-magnitude eruptions. During the course of our tephrochronological studies in this region over the last 40 years, we have discovered 196 tephra occurrences and 50 distinctive tephra beds. The location of these sites and the distinguishing features of each of these tephra beds are presented in the form of a catalogue, which we hope will provide a stimulus for present and future tephrochronological studies in the Yukon Territory. These data are presented as a series of tables, as follows: location, stratigraphic context, petrography, geochemical characteristics, including major- and trace-element composition of glass shards, major-element composition of Fe–Ti oxides, classification, and age determinations. A new classification scheme is presented in which the rhyolitic and dacitic tephra beds are grouped into three classes: adakite, transitional, and typical arc.

Neodymium isotopic variations of the late Cenozoic sediments in the Jianghan Basin: Implications for sediment source and evolution of the Yangtze River

The Yangtze River originates from eastern Asia and is one of the most important components of the East Asia river system. In this study we applied bulk Nd isotopic analysis to identify the sediment provenance in the Jianghan Basin, middle Yangtze River and tried to provide useful information on the evolvement of the Yangtze River. The fine-grained (<0.058 mm) sediment samples were selected from a continuous borehole in the Jianghan Basin and analyzed for Nd isotopic compositions. The 143Nd/ 144Nd ratios vary between 0.512042 and 0.512239, with an average of 0.512144. The ε Nd(0) values vary between −11.6 and −7.8, with an average of −9.6. Nd isotopic compositions cannot provide compelling evidence to prove whether the Pliocene sediments in the Jianghan Basin were influenced by the source rocks in the Jinshajiang area characterized by extremely high (positive) ε Nd(0) values. While these source rocks made a great contribution to the Jianghan Basin during the Quaternary. Less negative ε Nd(0) values reflect preferential erosion of source rocks in the Jinshajiang drainage. The Nd variations reflected changes in erosion patterns during the Quaternary. Based on the provenance analysis of the Jianghan Basin sediments, we propose that the Yangtze River appears to develop into a large river similar as the modern Yangtze no later than the beginning of the Quaternary.

Magnetostratigraphy and magnetic parameters of a sedimentary sequence in Punta San Andres, Buenos Aires, Argentina

This contribution focuses on polarity changes and magnetic parameters obtained in late Cenozoic sediments exposed on the cliffs in San Andrés, Chapadmalal, Buenos Aires province. The sedimentary section studied comprises the Vorohué, San Andrés, Miramar and Arroyo Seco Formations. The upper layers of Vorohué and the base of San Andrés showed records of normal polarity and were attributed to the Gauss Normal Polarity Chron (>2.6 Ma). The main portion of San Andrés Formation appears to have been deposited during lower and middle Matuyama Polarity Chron, including the Normal Polarity Subchron Olduvai (1.78–2.02 Ma). Miramar Formation contains polarity changes that should be assigned to Middle Matuyama/Jaramillo (1.05 Ma) and to Jaramillo/Upper Matuyama (0.99 Ma). The upper portion of the Miramar Formation and the lower one of the Arroyo Seco Formation show reverse polarity levels and were assigned to the Upper Matuyama (>0.78 Ma). Finally, the upper part of Arroyo Seco Formation seems to have been deposited during the Brunhes polarity chron (<0.78 Ma). Noticeable differences of magnetic records are obtained when comparing loess and paleosols values with calcic horizons values. LF susceptibility values range between 380 × 10−8 m3/kg and 20 × 10−8 m3/kg, of which the lowest values correspond to the calcic horizons. The outcome confirms previous results in the sense that neither of the existing magnetoclimatological models (wind and pedogenetic models) adequately account for the complexities of the Pampean loess. Clearly, the entrainment of dense magnetic iron oxides minerals was more efficient during stormy, dry (glacial) periods than during humid ones. Weathering and pedogenesis produce the decrease of susceptibility values, among other epigenetic processes. Thus, it follows that the decrease of magnetic values by weathering of parent materials depends on the geographic location of loess deposits.

Cosmogenic nuclide burial ages and provenance of Late Cenozoic deposits in the Sichuan Basin: Implications for Early Quaternary glaciations in east Tibet

Collision between the Indian and the Eurasian plates since the early Cenozoic produces one of the world’s most remarkable continental escarpments between the Tibetan Plateau and the adjacent Sichuan Basin. Yet Tertiary sediments are rare in the Sichuan Basin; the oldest preserved Late Cenozoic deposits called Dayi conglomerates directly overlie the Cretaceous or Jurassic red beds. Using cosmogenic 10Be and 26Al burial dating, we obtain deposition ages of ∼2.0 Ma and catchment erosion rates of ∼400 mm/ka for the Dayi conglomerates. Zircon U–Pb age distributions suggest derivation of these conglomerates from the Songpan-Ganzi flysch, the Pengguan complex and Late Permian and Triassic granite plutons in the headwater regions of the Min Jiang (Jiang, a Chinese term, means river). The formation of the poorly-sorted, sub-angular to sub-rounded and tens-centimeter-sized deposits in the western margin of the Sichuan Basin, after long distance transportation, is best explained by glacial activity ∼2.0 Ma ago in east Tibet.

Palynofacies analysis of Late Cenozoic sediments from the Undulating Pampa (Argentina): first results

Palynofacies analysis of Late Cenozoic sediments from the Undulating Pampa (Argentina): first results

Magnetostratigraphy of sediments from the Yumu Shan, Hexi Corridor and its implications regarding the Late Cenozoic uplift of the NE Tibetan Plateau

The Yumu Shan, located on the northernmost margin of the North Qilian Shan, contributes key information for deciphering the deformation and uplift of the NE Tibetan Plateau. This paper presents magnetostratigraphic results from Late Cenozoic sediments in the Yumu section of the northwestern Yumu Shan. The upper Shulehe Fm., Yumen Conglomerates Fm., and Jiuquan Gravels Fm., were deposited before ∼5.23 Ma, during the periods ∼3.58 to perhaps ∼1.77 Ma, and after ∼0.8 Ma, respectively. Four significant tectonic episodes occurred at ∼5.89 Ma, ∼3.58 Ma, during ∼2.88–2.58 Ma, and ∼0.9–0.8 Ma, based on sedimentation, magnetic susceptibility and angular unconformities. Being synchronous with tectonic activity throughout the NE Tibetan Plateau, these tectonic ages do not support the northward growth model for the NE Tibetan Plateau during the Late Cenozoic.

Detrital zircon U-Pb ages of Late Cenozoic sediments from the Yangtze delta: Implication for the evolution of the Yangtze River

Detrital zircon grains of Late Cenozoic sediments dated back to ca. 3.6 Ma from core DY03 in the Yangtze delta were dated by LA-ICP-MS, in order to investigate the sedimentary provenance and to find some clue for the evolution of the Yangtze River. Most of the detrital zircon U-Pb ages are distributed at 100–300 Ma, 350–550 Ma, 600–1000 Ma, 1400–2000 Ma and 2200–2800 Ma, which correspond well with the main tectonic and magmatic events in the Yangtze drainage. The detrital zircon age patterns show distinct difference between the 3 samples below 189.8 m and other 6 above 189.8 m. 43%–55% zircons in the 3 samples below 189.8 m fall within Cretaceous, while ages from 150 to 2800 Ma are distributed with no obvious peaks, which indicate the sedimentary provenance may be limited to the lower Yangtze drainage. The 6 samples above 189.8 m show similar age patterns, and the ages are relatively evenly distributed, indicating the sedimentary provenance broadened distinctly. All 6 samples deposited later than ca. 3.2 Ma show age information from the upper Yangtze drainage (including the Emeishan large igneous province), indicating that the Three Gorges may have already been cut through by then.

Composition and Provenance History of Late Cenozoic Sediments in Southeastern Bolivia: Implications for Chaco Foreland Basin Evolution and Andean Uplift

Abstract The Chaco foreland basin marks the eastern edge of the Andean orogenic system and contains up to 7.5 km of mostly nonmarine siliciclastics, thus providing an opportunity to study the detrital record of late Cenozoic Andean geodynamics and paleogeography. Sandstones from the southern Bolivian Chaco foreland basin testify to variable contributions from the craton and the Andean foreland fold-and-thrust belt in the context of an eastward-advancing orogen. Sandstone and conglomerate petrography of the Oligocene to Recent strata exposed in the Chaco Basin show an overall trend towards reduced mineralogical maturity, corresponding to diminishing transport distance, increasing topographic gradient and changing depositional environment from arid continental plain (Oligocene to middle Miocene Petaca sandstone) through marginal marine (middle Miocene to late Miocene Yecua sandstone) and braided fluvial settings (late Miocene Tariquia sandstone) to semihumid alluvial-fan environments (late Miocene to Recent Guandacay and Emborozu formations). Paleocurrent patterns of pre-tectonic sediments record westward transport. The late Miocene transitional-marine Yecua Formation sediments show a complex shoreline-related pattern. Syntectonic strata (Tariquia, Guandacay, and Emborozu formations) filling the foreland basin indicate dominant east-directed sediment transport from the advancing Andean orographic front. Because the Eastern Cordillera provided a drainage barrier to Altiplano erosion, sandstones of the Chaco Basin do not directly record Andean volcanism or Altiplano uplift; however, climatic inferences from changing facies and petrographic composition suggest major uplift and formation of orographic barriers between 14 and 7 Ma.

Late Cenozoic deposits at Reedy Glacier, Transantarctic Mountains: implications for former thickness of the West Antarctic Ice Sheet

Deposits corresponding to multiple periods of glaciation are preserved in ice-free areas adjacent to Reedy Glacier, southern Transantarctic Mountains. Glacial geologic mapping, supported by 10Be surface-exposure dating, shows that Reedy Glacier was significantly thicker than today multiple times during the mid-to-late Cenozoic. Longitudinal-surface profiles reconstructed from the upper limits of deposits indicate greater thickening at the glacier mouth than at the head during these episodes, indicating that Reedy Glacier responded primarily to changes in the thickness of the West Antarctic Ice Sheet. Surface-exposure ages suggest this relationship has been in place since at least 5 Ma. The last period of thickening of Reedy Glacier occurred during Marine Isotope Stage 2, at which time the glacier surface near its confluence with the West Antarctic Ice Sheet was at least 500 m higher than today.

Diachronous evolution of Late Jurassic–Cretaceous continental rifting in the northeast Atlantic (west Iberian margin)

Regional (2‐D) seismic reflection profiles, outcrop, and borehole data are used to characterize the evolution of deep offshore sedimentary basins in southwest Iberia (Alentejo Basin). The interpreted data indicate the bulk of Late Jurassic–earliest Cretaceous subsidence occurred in the present‐day continental slope area, as shown by (1) significant thickening of synrift strata basinward from a slope‐bounding fault system (SFS), west of which the total thickness of sediment can reach more than 9.0 km, and (2) relatively thin Mesozoic strata east of the SFS, where thickening of synrift units against principal faults is limited. Five principal regressive events and their basal unconformities reflect tectonic uplift and relative emersion in proximal basins, which were located on the rift shoulder to subsiding tilt blocks west of the SFS. These regressive events are correlated with major rift‐related events occurring on the deeper margin. Direct comparisons with the Peniche Basin of northwest Iberia reveal that significant portions of the Iberian lower plate margin were uplifted and eroded during the last stages of continental rifting. This process was repeated at different times (and in different areas) as the locus of rifting and continental breakup migrated northward. As a result, two distinct rift axes are recognized in west Iberia, a first axis extending from the Porto Basin to the Alentejo Basin and a second axis located on the outer proximal margin north of 38°30N. In addition, the SFS delimited (1) prograding deposits of Cretaceous‐Paleogene age and (2) late Cenozoic deposits draping the modern continental slope. These latter facts demonstrate that on lower plate passive margins, the relative position of the continental slope is established during the final rifting episode(s) preceding continental breakup.

Stratigraphy of Late Cenozoic sediments of the western Chukchi Sea: New results from shallow drilling and seismic-reflection profiling

The Quaternary history of Beringia and of the Arctic–Pacific marine connection via the Bering Strait is poorly understood because of the fragmentary stratigraphic record from this region. We report new borehole and seismic-reflection data collected in 2006 in the southwestern Chukchi Sea. Sediment samples were analyzed for magnetic properties, grain size, heavy minerals, and biostratigraphic proxies (spores and pollen, foraminifers, ostracodes, diatoms, and aquatic palynomorphs). Two shallow boreholes drilled between the Chukotka Peninsula and the Wrangel Island recovered sediments of two principal stratigraphic units with a distinct unconformity between them. Based on predominantly reverse paleomagnetic polarity of the lower unit and pollen spectra indicative of forested coasts and climate warmer than present, the age of this unit is estimated as Pliocene to early Pleistocene (broadly between ca. 5 and 2 Ma). Attendant sedimentary environments were likely alluvial to nearshore marine. These deposits can be correlated to the seismic unit infilling valleys incised into sedimentary bedrock across much of the study area, and possibly deposited during a transgression following the opening of the Bering Strait. The upper unit from both boreholes contains Holocene 14C ages and is clearly related to the last, postglacial transgression. Holocene sediments in Borehole 2 indicate fast deposition at the early stages of flooding (between ca. 11 and 9 ka) to very low deposition, possibly related to expansive sea ice. Closer to shore, deposition at Borehole 1 resumed much later (ca. 2 ka), likely due to a change in the pattern of coastal erosional processes and/or the demise of a landbridge between the Chukotka Peninsula and the Wrangel Island inferred from studies on mammoth distribution.

Petrogeochemistry and genesis of listwaenite xenoliths in the alkali basalts of the southern Tien Shan

Mesozoic alkaline (subalkaline) mafic rocks from the southern Tien Shan contain numerous listwaenite xenoliths (on average, 50–60% of all xenoliths) and less abundant serpentinites, which develop after nodules of mantle spinel lherzolites and, more rarely, pyroxenites. Various models of listwaenite genesis and the problem of a “listwaenite layer” were considered. The listwaenites consist of three heterogeneous mineral (element) assemblages of different ages: (a) mantle ultrabasic protolith (relics of spinels, pyroxenes, and other minerals); (b) products of shallow-depth serpentinization; and (c) minerals (elements) of hydrothermal-metasomatic carbonation (listwaenitization), which occurred under near-surface conditions but was related to mantle fluids (carbon isotope signatures of carbonates, introduction of Sr, its correlation with CO2, etc.). It cannot be ruled out that the CO2 degassing of the mantle occurred not only in the Mesozoic but also in the Cenozoic. This process was accompanied by the formation of occurrences of chalcophile elements (Hg, Sb, Au, Ag, Zn, Cu, and Pb), F, Ba, and Sr. Late Cenozoic celestite deposits deserve special attention in this context. They form the largest Sr province in the Mediterranean mobile belt and were presumably also related to mantle sources.