Pliocene Time Research Articles

Miocene and Pliocene paleoclimate of the Dry Valleys region, Southern Victoria land: a geomorphological approach

The Dry Valleys region is a hyper-arid, cold polar desert. Modern climate varies systematically with increasing elevation and distance from the coast. We distinguish three microclimate zones on the basis of varying precipitation, wind direction, relative humidity, temperature, and soil-moisture content. Zone 1 represents coastal, Zone 2 intermediate, and Zone 3 far-western areas of the Dry Valleys region. Soil-moisture content and relative humidity are the key parameters that control the areal distribution of solifluction terraces, gelifluction lobes, polygonal ground, scree slopes, and soil development in Zones 1, 2 and 3. The coastal Zone 1 shows active solifluction terraces, gelifluction lobes, levees, streams, debris flows, mudflows, and subxerous soils. The intermediate Zone 2 contains little evidence for modern downslope movement; here active gelifluction lobes, debris flows, and streams are largely restricted to north-facing slopes with high moisture content. The inland Zone 3 lacks evidence for significant modern downslope movement. There are no active solifluction terraces, stream channels, debris flows, or levees in Zone 3. Instead, Zone 3 shows Miocene- and Pliocene-age sand wedges, avalanche cones, and desert pavements. The mid-Miocene landsurface of Zone 3 is preserved to a remarkable degree. The antiquity and longevity of paleoforms in Zone 3 can be readily demonstrated by the topographic position of dated ashfall deposits. Our chronology comes from laser-fusion 40Ar/ 39Ar analyses of in-situ ashfall deposits that rest at, or just below, the ground surface in Zones 2 and 3 ( Marchant et al., 1993a,b,c, 1995). The lack of gelifluction lobes, solifluction terraces, rills, levees, and stream channels on in-situ Miocene- and Pliocene-age deposits in Zone 3 indicates that here mean-annual air temperature, soil moisture content, and relative humidity did not reach levels that now occur in Zones 1 and 2. The present mean-annual air temperature and relative humidity of Zones 1 and 2 are about −17 °C/ 75% and −27 °C/ 45%, respectively. The implication is that climatic wanning of the magnitude necessary for East Antarctic Ice Sheet deglaciation predicted by some glaciological models (e.g., about 20 °C above present values according to Huybrechts, 1993) and growth of vascular vegetation in the Transantarctic Mountains (e.g., Webb and Harwood, 1993) could not have occurred during Pliocene time. In addition, the preservation of Miocene-age ashfall deposits, avalanche cones, and delicate desert pavements strongly suggest that no wet-based, erosive glaciers advanced into the far western Dry Valleys region above 1200 m elevation during late Pliocene time. Overall, our paleoclimate record from the Dry Valleys region implies an enduring East Antarctic Ice Sheet since Middle Miocene time. This makes it difficult to ascribe large-scale Pliocene sea-level fluctuations to ice-volume variations on the East Antarctic craton.

Late Cenozoic sedimentation and uplift history on the mid-Norwegian continental shelf

Four Mid(?)/Late Cenozoic sedimentary units are recognised on the mid-Norwegian continental shelf: (1) A thin Miocene unit, (2) a “deltaic complex” variously dated to be of Oligocene or Early Pliocene age; (3) A Late Pliocene-Early Pleistocene low angle prograding unit and (4) a Mid/Late Pleistocene blanketing diamicton. The deltaic complex which extends along the Norwegian coast from the Lofoten Islands in the north to at least 62°45′N, is inferred to be the result of regional uplift of Fennoscandia during Oligocene or Early Pliocene times. As a result of further uplift and regional glaciations during the Late Pliocene-Early Pleistocene, a system of low angle prograding sequences of mainly glacigenic sediments were deposited. Inferred glacial erosional forms suggests periods of grounded ice on the continental shelf. The sedimentary regime was dominated by subglacial sediment input to the shelf edge and later reworking by gravity flows down the continental slope. At first most of the sediments within the study area were derived from the Lofoten area in the northeast. Later the progradation had a more east-west direction. During the Late Pliocene/Early Pleistocene period the shelf edge prograded about 100 km, and an average sedimentation rate of 42 cm/10 3 years is found.

Evolution of a nearshore and coastal macrotidal sand transport system, Queen Charlotte Islands, Canada

Abstract An extensive (40 km) coastal plain is prograding on the north coast of the Queen Charlotte Islands off the Pacific margin of Canada while the entire 120 km eastern coast of Graham Island is actively eroding. At the junction of these two systems is Rose Spit, which extends northeastward at a point of sediment transport convergence. Historical bathymetrical data and aerial photographs indicate that a spit platform extends 10 km to the northeast and at least four portions (up to 4 km in length) of the platform bank have become emergent since 1911. The area is seismically active and subject to storm-related sediment transport events superimposed on strong semi-diurnal tidal flows. The rapid emergence of the offshore banks and the net coastal changes are primarily controlled by: (1) convergence of sediment transport between the waters of Hecate Strait to the south and Dixon Entrance to the north, particularly during winter storms; and (2) localized tectonic uplift. Sediment is transported north from the shallow waters of Hecate Strait by southeasterly winter storms and east, by longshore transport, along the accreting northern coast of the Queen Charlotte Islands to converge at Rose Spit. A ‘hydraulic fence’ has formed resulting in the creation of the elongate spit platform with emergent sand bars, east of the spit. Transpressional folding has occurred in this area east of the Queen Charlotte Fault, which separates the North American and Pacific Plates. This has resulted in localized uplift since Pliocene time, complementing the accretion process.

Surface expression of the Chicxulub crater

Analyses of geomorphic, soil, and topographic data from the northern Yucatan Peninsula, Mexico, confirm that the buried Chicxulub impact crater has a distinct surface expression and that carbonate sedimentation throughout the Cenozoic has been influenced by the crater. Late Tertiary sedimentation was mostly restricted to the region within the buried crater, and a semicircular moat existed until at least Pliocene time. The topographic expression of the crater is a series of features concentric with the crater. The most prominent is an approximately 83-km-radius trough or moat containing sinkholes (the Cenote ring). Early Tertiary surfaces rise abruptly outside the moat and form a stepped topography with an outer trough and ridge crest at radii of approximately 103 and approximately 129 km, respectively. Two discontinuous troughs lie within the moat at radii of approximately 41 and approximately 62 km. The low ridge between the inner troughs corresponds to the buried peak ring. The moat corresponds to the outer edge of the crater floor demarcated by a major ring fault. The outer trough and the approximately 62-km-radius inner trough also mark buried ring faults. The ridge crest corresponds to the topographic rim of the crater as modified by postimpact processes. These interpretations support previous findings that the principal impact basin has a diameter of approximately 180 km, but concentric, low-relief slumping extends well beyond this diameter and the eroded crater rim may extend to a diameter of approximately 260 km.

Fold amplification and parasequence stacking patterns in syntectonic shoreface carbonates

Kinematic models for fault-related folding may be examined by estimating amplification and limb-tilt rates using the stratigraphies of syndeformational strata. The methodology behind such analyses is described with reference to a case study from the Maghrebian thrust belt of Neogene age from central Sicily. High biostratigraphic resolution is provided by Pliocene strata that were deposited across the Marcasita anticline during deformation. The coastal carbonate facies of the rocks record variations of relative base-level and tilt histories. Foraminifera and nannoplankton faunal assemblages, from interbedded and laterally continuous pelagic sediments, bracket the age of the strata, and sequence stratigraphic boundaries are used to correlate relative time lines through the depositional architecture. These chronostratigraphic data are incorporated into a depositional model to quantify the rates of uplift and sedimentation. Offlapping parasequences record progressive tilting of the fold limb. Regionally, other sections also show this offlapping relationship, but the rate of offlap varies, thus putting constraints on the uplift history across several profiles of the fold. Tilt rates for late Pliocene time, based on an astronomically calibrated time scale, are estimated at 1°/28 k.y., with uplift rates (relative to long-term sea level) of 1 m/k.y. The methodology may be applied to study along-axis variations in fold amplification or regional variations in deformation rate. The parasequence stacking patterns and their implied deformation rates are inconsistent with simple fault-bend fold and kink-band models. They are better explained by detachment folding and tightening of a preexisting anticline in conjunction with continued propagation of an underlying thrust.

Regional Cenozoic uplift and subsidence events in the southeastern North Sea

The Paleocene topography of the Fennoscandian Shield is indicated by outbuilding towards the Central Trough and the Ringkøbing-Fyn High. From Eocene until Pliocene time three events of relative vertical movements are indicated by changes in outbuilding directions and reflection termination patterns in the central North Sea. The first event of uplift was in the Eocene and resulted in relative uplift of the Mid North Sea High and contemporary subsidence east of it, indicated by a change in outbuilding from north to west. A second event of uplift is indicated to the north of the study area at the Eocene-Oligocene boundary by renewed southward outbuilding in the Norwegian-Danish Basin. In Miocene until Early Pliocene time a relatively stationary, almost east-west striking, basin margin was probably located to the north along the Tornquist Zone as indicated by the continued outbuilding towards the Ringk0bing Fyn High. A third event of relative uplift is indicated east of the study area by changes in the Pliocene outbuilding pattern. After the first event of uplift it appears that the deepest parts of the Eocene North Sea Basin were located more easterly than the deepest parts are today. Apparently the two latest uplift events north and east of the study area were related to movements of, or along the Tornquist Zone or to regional uplift of the Fennoscandian Shield finally resulting in the presentday configuration of the North Sea.

Pliocene‐Quaternary sedimentation and Alpine Fault related tectonics in the lower Cascade valley, South Westland, New Zealand

Abstract Study of Pliocene and Quaternary sediments west of the Alpine Fault in the Cascade valley, South Westland, New Zealand, has allowed determination of Alpine Fault displacement rate and coastal uplift rate over the last 3.5 m.y. Exposures of the Pliocene Halfway Formation (latest Opoitian‐Waipipian) are composed of marine sand and conglomerate deposited in c. 200–1000 m water depth. Beds are gently dipping and weakly deformed, with the direction of principal shortening oriented at a high angle to the Alpine Fault and plunging gently northwest (c. 107340°). Fiordland‐derived clasts indicate a minimum of 95–100 km of lateral offset on the Alpine Fault since deposition of Halfway Formation. Paleogeographic evidence suggests that first‐order features of the drainage were similar in Pliocene time to those of the present day. Quaternary moraines and fluvioglacial sediments are subdivided on the basis of composition and morphology into five groups: Cl (oldest) to C5 (youngest). The Cl deposits have a prov...

Evolution of a trench‐slope basin within the Cascadia subduction margin: the Neogene Humboldt Basin, California

ABSTRACTThe Neogene Humboldt (Eel River) Basin is located along the north‐eastern margin of the Pacific Ocean within the Cascadia subduction zone. This sedimentary basin originated near the base of the accretionary prism in post‐Eocene time. Subduction processes since that time have elevated strata in the south‐eastern portion of the basin above sea level. High‐resolution chronostratigraphic data from the onshore portion of the Humboldt Basin enable correlation of time‐equivalent lithofacies across the palaeomargin, reconstruction of slope‐basin evolution, and preliminary delineation of climatic and tectonic influence on lithological variation. Emergent basin fill is divided into five lithofacies which clearly document shoaling of the inner trench slope from deep‐water environments in early Miocene time to paralic environments in Pleistocene time. The oldest strata consist of hemipelagic mudstones and minor debris‐flow breccias deposited in a deep‐water setting during elevated sea level. These strata are overlain by glauconite‐rich, fine‐grained turbidites which heralded an increasing influx of terrigenous detritus. Water depths shoaled earlier in the eastern basin area as the palaeoshoreline prograded seaward. Turbidite deposition ceased in the eastern basin area at about 2‐2 Ma, whereas 22 km to the west, turbidite deposition continued until about 1‐8 Ma. Lithofacies at the western study site change abruptly across a middle Pleistocene unconformity from outer shelf to paralic deposits. In the east, a more complete Pleistocene section records transition from outer to inner shelf, beach and fluvial environments.The Humboldt Basin lithofacies sequence is overprinted by eustatic control of sediment source. Comparison of sediment character with palaeoceanographic conditions indicates dominance of hemipelagic facies during periods of elevated sea level in the middle Miocene and early Pliocene when depocentres were isolated from terrigenous sediment. Glauconite‐rich facies were mobilized from an upper slope setting following these periods of elevated sea level and redeposited in a deep‐marine environment. Pleistocene shoreline lithofacies display glacio‐esutatic control of depositional environment by recording several cycles of nearshore to fluvial progressions.General models of accretionary prism behaviour and trench‐slope basin evolution are compatible with the overall coarsening‐upward lithofacies sequence filling the Humboldt Basin. Early structural barriers precluded deposition of terrigenous material except from locally derived debris flows; subsequent shoaling and burial of deactivated thrust‐folds enabled turbidity flows to reach the basin floor.However, late‐stage tectonism apparently controlled the onset of coarse‐grained deposition in this sequence. Significant sand‐rich turbidite deposition began in the middle Pliocene, synchronous with tectonic uplift of the southern basin margin. Conversely, cessation of turbidite deposition in the eastern basin area in latest Pliocene time was synchronous with growth of anticlinal structures which again blocked widespread dispersal of turbidity flows. This middle Pliocene to Holocene period of crustal shortening is synchronous with continued reduction in spreading rate along the southern Juan de Fuca ridge, and probably reflects partial coupling between the subducting lithosphere and the overlying accretionary prism.

Plio‐Quaternary megasequence geometry and its tectonic controls within the Maghrebian thrust belt of south‐central Sicily

ABSTRACTSequence stratigraphy in marine foredeep and thrust‐top basins is controlled by the conventional variations in eustatic sea‐level and sedimentation rate together with tectonics. Vertical motions reflect combinations of subsidence due to regional flexure and uplift on local thrust anticlines which act to modify the volume and shape of accommodation space together with syn‐depositional slopes. Plio‐Pleistocene successions on Sicily were deposited in thrust‐top and foredeep basins, above and ahead of evolving structures of the Maghrebian fold and thrust belt. Collectively the sediments represent a single megasequence defined at its base by a maximum flooding surface of earliest Pliocene age following reconnection with global sea‐level at the end of the Messinian. The internal stratigraphy of this megasequence consists of Trubi chalks, blue marls and a coastal calcarenite package with subordinate silciclastic sand. Plankton biostratigraphy allows these facies to be placed in a chronostratigraphic framework. Regionally the upper assemblage progrades away from the orogenic hinterland, recording a tectonically forced regression in response to regional uplift from late Pliocene times. This uplift may be associated with isostatic unloading in the orogenic hinterland due to tectonic collapse of the more internal thrust sheets. Prior to this, flexure from orogenic loading is inferred to have been sufficient for regional subsidence locally to outstrip uplift associated with the growth of some thrust structures. For shallow‐water facies the competition between thrust‐related uplift and flexural subsidence can be investigated from the stacking patterns of parasequence sets. For structures developed at greater palaeobathymetries receiving fine‐grained pelagic sediment, active tectonics may be recognized from depositional hiatuses.

Palaeogeography, subsidence and thermal history of the Neogene Styrian Basin (Pannonian basin system, Austria)

The Neogene Styrian Basin represents an extensional structure on top of a crustal wedge, which was moving eastward during the final stages of the Alpine orogeny. Eastward extrusion was a consequence of continental escape and extensional collapse within the Eastern Alps.In a simple model the evolution of the Styrian Basin can be subdivided into an Early Miocene (Ottnangian to Karpatian) synrift and a subsequent postrift phase. Basement subsidence rates during the synrift phase reached 30 cm/100 yr and more than 2000 m of limnic to marine sediments were deposited. The coincidence of the synrift phase and the formation of pull apart structures along strike-slip zones bordering the eastward moving wedge is evidence for the close genetic relation between extrusion tectonics and basin formation.A Miocene magmatic phase is related to subduction along the Carpathian front. Magmatic activity started during the synrift stage and continued into the postrift stage. Heat flow in the vicinity of the Miocene volcanoes increased dramatically (> 300 mW/m2). A second volcanic phase producing basalts in Plio-Pleistocene times had only little influence on the heat flow pattern.Limnic to marine sediments of the synrift stage are separated by a major unconformity from Middle to Late Miocene (Badenian to Pontian) marine to limnic/fluvial postrift sediments. Sedimentation during the postrift phase was controlled by marine ingressions during Middle Miocene (early Badenian and Sarmatian) times from the south and a subsequent regression with a decline in salinity. Subsidence rates during the postrift stage were mostly below 2.5 cm/100 yr.In Pliocene times subsidence was replaced by uplift, which resulted in erosion of a few hundred metres of sediment. Present-day high heat flows are a consequence of thinned crust beneath the Styrian Basin.

Inversion-controlled uplift of an outer-arc ridge: Nias Island, offshore Sumatra

Abstract This study presents data from Nias Island which lies on an outerarc ridge 150 km to the west of mainland Sumatra. A new stratigraphy, geological map and cross-section of Nias have been produced from field data collected over all the island supplemented with aerial photography, LANDSAT and SAR (synthetic aperture radar) studies and these data form the basis for a new interpretation of the island. Where exposed the basement consists of ophiolitic rocks, originating from a variety of tectonic settings, and with a thin sedimentary cover. Three main sub-basins are identified on Nias. Late Paleogene-Neogene sedimentation in these basins was controlled primarily by major extensional faults though deposition within sub-basins was influenced by the presence of sub-basin transecting faults with significant vertical throws. Two phases of inversion are recognized: the first occurred during the Early Miocene, was limited to western regions and is identified by the presence of a localized unconformity and vitrinite and apatite fission track data. The second inversion initiated in Pliocene times and affected all the sub-basins on Nias. Latest Pliocene-Pleistocene rocks unconformably overlie the Miocene strata. Deformational styles within separate fault-bounded segments vary markedly; structural mapping demonstrates uplift and deformation has been largely controlled by reactivation of sub-basin extensional faults and oblique-slip movements on transecting faults. Diapiric melanges developed during inversion suggesting an intimate relationship between uplift and remobilization of overpressured mudrocks. This study concludes that the uplift of the sub-basins on Nias resulted from inversion of basin successions by reactivation of original major extensional faults rather than on thrust-slices developed in an accretionary prism. Nias does not form part of an accretionary complex; the accretionary prism has developed to the southwest of Nias.

The Jura Thrust Belt: Tectonic History and Prospectivity of a Leading Edge of the Western Alps: ABSTRACT

The Jura Thrust Belt developed in Pliocene times as the result of the late stage of advance to the northwest of the western Alps. The main decollement level is hosted in late and/or middle Triassic salt layers. The belt is superimposed on a Mesozoic platform partially eroded in early Tertiary times. In Oligocene times, the present Jura area was actually a regional high between the Molasse Basin alpine foredeep to the east, and the Bresse rift basin to the west. At depth several isolated and enlongated Stephanian-Permian troughs have been recognized from seismic and well data. They unconformably rest on a Paleozoic basement that was once part of the European segment of the Variscan Thrust Belt. Several small gas fields have been developed in the past and significant oil shows have more recently been tested. Source rocks are generally believed to be late Paleozoic coals and oil shales. Producing horizons are early Triassic continental sandstones with excellent petrophysical characteristics, and slightly less prospective middle Jurassic limestones and dolostones. Untested plays could also be present in the underlying early Permian sandstones. Recent studies have focused on the geometry of the thrust belt through regional laterally coherent balanced sections, and oil-source rockmore » correlations.« less

Minimum 10Be exposure ages of early Pliocene for the Table Mountain plateau and the Sirius Group at Mount Fleming, Dry Valleys, Antarctica

Using accelerator mass spectrometry (AMS), we have measured 10Be and 26Al in quartz from granites and sandstones from Table Mountain and Mount Fleming, Antarctica. Our data show that the plateau surface at Table Mountain had formed by early Pliocene time at the latest. Granites fringing but within the Sirius Group at Table Mountain give a minimum exposure age of 2.6 Ma for this deposit. A sandstone clast on the Ferrar dolerite surface just outside and below, and thus postdating, the Sirius Group has a minimum age of 2.9 Ma. Two samples from the Sirius Group at Mount Fleming have 10Be concentrations that have reached secular equilibrium. This deposit is at least 4.8 m.y. old. The Sirius Group at Mount Fleming cannot have been deposited after 3.0–2.5 Ma, as implied by biostratigraphic data. Our dates contradict the hypothesis that in the Pliocene East Antarctica was deglaciated and the climate was significantly warmer and wetter. The preservation of these surfaces indicates a continuous cold desert in the dry valleys since the beginning of the Pliocene. The high 10Be concentrations we have measured cannot be reconciled with uplift of the Transantarctic Mountains at a rate of 1 km/m.y. during the past 3 m.y.

Global sea-level and the (pen-)insularity of late Cenozoic Britain

Abstract During mid-Pliocene times, Britain was surrounded by warm temperate seas. In the south, these received relatively little clastic input, accumulated mainly biogenic sediments, and appear to have allowed free circulation of marine waters between the North Sea and the Atlantic Ocean, either around or across southern Britain. In late Pliocene times, commencing at about 2.5 Ma bp , the first major global sea-level falls associated with northern hemisphere glaciation occurred. At about the same time, climatic changes appear to have accelerated the rate of headwater extension and bedload transport of the principal rivers flowing towards the southern North Sea. The combination of sea-level fall and progressive deltaic progradation into the southern North Sea converted Britain into a European peninsula. By the mid-Quaternary Cromerian stage, the Great European (Ur-Frisia) Delta top was sufficiently moribund, and subject to subsidence, to allow interglacial sea-levels to encroach southwards across it. During the following Anglian Glaciation, impounded glacio-marine or glacio-lacustrine waters appear to have extended southwards, across both the former delta top and the bounding Weald-Artois chalk ridge, into the English Channel. Subsequently a marine connection between the North Sea and the Atlantic Ocean, via the English Channel, was alternately established and broken, as global sea-level rose and fell (synchronously with interglacial and glacial periods), cyclically converting Britain from island to peninsula and back again.

Constraints on age, erosion, and uplift of Neogene glacial deposits in the Transantarctic Mountains determined from in situ cosmogenic 10Be and 26Al

Research Article| December 01, 1995 Constraints on age, erosion, and uplift of Neogene glacial deposits in the Transantarctic Mountains determined from in situ cosmogenic 10Be and 26Al Edward J. Brook; Edward J. Brook 1Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02540 Search for other works by this author on: GSW Google Scholar Erik T. Brown; Erik T. Brown 2Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, Bâtiment 108, 91405, Campus Orsay, France Search for other works by this author on: GSW Google Scholar Mark D. Kurz; Mark D. Kurz 1Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02540 Search for other works by this author on: GSW Google Scholar Robert P. Ackert, Jr; Robert P. Ackert, Jr 1Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02540 Search for other works by this author on: GSW Google Scholar Grant M. Raisbeck; Grant M. Raisbeck 2Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, Bâtiment 108, 91405, Campus Orsay, France Search for other works by this author on: GSW Google Scholar Françoise Yiou Françoise Yiou 2Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, Bâtiment 108, 91405, Campus Orsay, France Search for other works by this author on: GSW Google Scholar Geology (1995) 23 (12): 1063–1066. https://doi.org/10.1130/0091-7613(1995)023<1063:COAEAU>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Edward J. Brook, Erik T. Brown, Mark D. Kurz, Robert P. Ackert, Grant M. Raisbeck, Françoise Yiou; Constraints on age, erosion, and uplift of Neogene glacial deposits in the Transantarctic Mountains determined from in situ cosmogenic 10Be and 26Al. Geology 1995;; 23 (12): 1063–1066. doi: https://doi.org/10.1130/0091-7613(1995)023<1063:COAEAU>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract 10Be and 26Al data from sandstone boulders in three Neogene glacial deposits in the McMurdo Sound–Dry Valleys region of southern Victoria Land, Antarctica, indicate minimum exposure ages of (Approx.)3 Ma and maximum long-term erosion rates of (Approx.)5–12 cm/m.y., supporting the suggestion that polar desert conditions have persisted in the Dry Valleys since at least late Pliocene time. Variation of cosmogenic nuclide production rate with altitude also allows constraints on past uplift rates. Model calculations employing 10Be data indicate little or no uplift in the Dry Valleys region in the past 3 m.y., precluding rapid (≈1 km/m.y.) late Pliocene uplift previously suggested for some parts of the Transantarctic Mountains. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Evolution of an isolated carbonate bank during Oligocene, Miocene and Pliocene times, Cayman Brac, British west Indies

Modern carbonate sedimentation in the Caribbean Sea commonly occurs on banks that are surrounded and isolated by deep oceanic water. This depositional regime also occurred during the Tertiary, and many islands, such as Cayman Brac, have sequences that evolved in such settings.

Transpression and transtension within different structural levels in the central Aegean region

In the central Aegean region, shortening structures within the Miocene molasse arc known since long ago. Nevertheless recently, most authors have recognized extensional structures within Middle to Upper Miocene granitoids, proposing a Basin and Range type model for the Late Cenozoic evolution of the area. To resolve this problem, structural mapping and mesoscopic analysis of 900 faults sampled from 12 islands have been carried out. Late orogenic uplift of the central Aegean region is the result of a continuous convergence and indentation of the Pelagonian plate by the Apulian plate, that took place throughout the Miocene. Formation of core-complexes can be associated with: (a) large oblique-upthrusts, (b) steeply dipping strike-slip faults, and (c) low-angle normal faults. The latter are produced by low, multidirectional extension, which has affected small crustal regions as adjacent areas underwent transpression. In the late stages of collision the overthickened crust began to collapse due to transtension which was replaced by extension caused by the roll-back of the Hellenic subduction zone in the Lower Pliocene time. This extensional regime has lasted until the present day.

Inherited structural control from repeated Cretaceous to Recent extension in the North Mernoo Fault Zone, western Chatham Rise, New Zealand

The active North Mernoo Fault Zone (NMFZ) is the youngest of three discrete phases of basement-involved extensional faulting to deform the northwestern corner of the continental Chatham Rise since the Cretaceous. The first two phases, inferred to be of Late Cretaceous and Eocene age, respectively, were both part of widespread extensional systems that developed over most of the Chatham Rise region. The third phase, the Late Miocene to Recent NMFZ, developed on the northwestern corner of the rise as a consequence of the interaction between the Chatham Rise plateau and the southern end of the Hikurangi subduction zone. A study of seismic reflection data from the northwestern Chatham Rise has revealed: 1. (1) the detailed structure that relates to each phase of normal faulting; 2. (2) the patterns of fault reactivation during successive episodes of extension; 3. (3) the significant structural control that older deformational fabrics have had on the development of the NMFZ. During the Late Cretaceous phase of extension, two major fault-bounded half-grabens together with other smaller basins developed beneath the upper continental slope. These E-W-trending, S-dipping faults are inferred to have accommodated about 2–7 km of horizontal extension across a 30 km wide region. The early Cenozoic extensional system reactivated some Cretaceous half-graben structures but mainly formed new faults with similar geometry in crust north of the Cretaceous structures. The early Cenozoic faults are inferred to have accommodated about 1–4 km of horizontal extension across a 60-km-wide region. The late Cenozoic NMFZ also reactivated some of the Cretaceous normal faults and almost all of the major early Cenozoic normal faults in this region. In addition, many new extensional structures developed and produced an E-W- to WNW-ESE-trending, southward dipping, domino-style array of faults up to 100 km in width. Although the density of faults in the NMFZ is greater than that of the two previous extensional systems to include this region, the total horizontal extension since late Early Pliocene times is estimated to be no more than 3 km. The common reactivation of old normal faults during the late Cenozoic development of the NMFZ indicates a significant level of structural inheritance from the previous episodes of extension to effect the region. Furthermore, the parallelism between the newly developed faults and the older two extensional systems suggests that the normal faults could be reactivating structures in the Torlesse terrane basement, which in turn relate to an early, Mesozoic phase (> 100 Ma) of accretionary tectonics. The kinematics of active extension within the NMFZ is, therefore, likely to be influenced by the pre-existing structural discontinuities that resulted from a history of poly-phase deformation.

Pliocene–Pleistocene fluvial/wave-dominated deltaic sedimentation: the Pamisos delta, southwest Peloponnesus, Greece

AbstractA fluvial /wave-dominated delta was formed during late Pliocene times in southwestPeloponnesus, influenced by NNW—SSE and ENE—WSW trending faults. The depositional patternremained unchanged through early Pleistocene times, when the pre-existing active faults with WNW—ESE extension were combined with an eastward asymmetrical subsidence of the graben. Inthe deltaic environment, marshes, lakes and lagoons were created in the western parts, whereas largequantities of sediments were deposited in the central and eastern parts adjacent to basin marginsof steeper relief.This study combines grain size parameters, total organic matter, carbonate and clay mineralogyand structural analysis to: (a) determine the pattern of sedimentation in sub-environments and (b)create a fluvial/wave-type deltaic depositional model, and distinguish between delta-plain, delta-front and pro-delta environments. The Pliocene-Pleistocene, fluvial/wave-dominated delta model inthis study can be used to predict deltaic sedimentation in analogous basins.

Late oligocene and miocene faulting and sedimentation, and evolution of the southern Rio Grande rift, New Mexico, USA

The distribution of nonmarine lithofacies, paleocurrents, and provenance data are used to define the evolution of late Oligocene and Miocene basins and complementary uplifts in the southern Rio Grande rift in the vicinity of Hatch, New Mexico, USA. The late Oligocene-middle Miocene Hayner Ranch Formation, which consists of a maximum of 1000 m of alluvial-fan, alluvial-flat, and lacustrine-carbonate lithofacies, was deposited in a narrow (12 km), northwest-trending, northeast-tilted half graben, whose footwall was the Caballo Mountains block. Stratigraphic separation on the border faults of the Caballo Mountains block was approximately 1615 m. An additional 854 m of stratigraphic separation along the Caballo Mountains border faults occurred during deposition of the middle-late Miocene Rincon Valley Formation, which is composed of up to 610 m of alluvial-fan, alluvial-flat, braided-fluvial, and gypsiferous playa lithofacies. Two new, north-trending fault blocks (Sierra de las Uvas and Dona Ana Mountains) and complementary west-northwest-tilted half graben also developed during Rincon Valley time, with approximately 549 m of stratigraphic separation along the border fault of the Sierra de las Uvas block. In latest Miocene and early Pliocene time, following deposition of the Rincon Valley Formation, movement continued along the border faults of the Caballo Mountains, Dona Ana Mountains, and Sierra de las Uvas blocks, and large parts of the Hayner Ranch and Rincon Valley basins were segmented into smaller fault blocks and basins by movement along new, largely north-trending faults. Analysis of the Hayner Ranch and Rincon Valley Formations, along with previous studies of the early Oligocene Bell Top Formation and late Pliocene-early Pleistocene Camp Rice Formation, indicate that the traditional two-stage model for development of the southern Rio Grande rift should be abandoned in favor of at least four episodes of block faulting beginning 35 Ma ago. With the exception of two northwest-trending border faults of the Caballo Mountains block that may be reactivated along Eocene compressional structures, the majority of border faults and complementary basins throughout the history of the southern Rio Grande rift were north-trending, which challenges the conventional idea of a clockwise change in stress through time.