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1.
The initially obtained data characterize organic-walled phytoplankton (dinocysts), nannoplankton, spores, and pollen from the Upper Argun, Alkun, and Lower Assa deposits of the Fiagdon and Mairamadag sections situated on the southeast of North Ossetia (North Caucasus) in the Alkun Formation stratotype area. The lithology of the formation is described, and its position in the Oligocene-Miocene succession is considered. According to the analyzed data on organic-walled phytoplankton from the Fiagdon and Mairamadag sections, the transitional late Oligocene-early Miocene dinoflora from the top of the Argun Formation and the lower part of the Alkun Formation is in general of the Miocene aspect. Based on the dinocysts, deposits from the upper part of the Alkun Formation coupled with the Assa Formation are attributed to the lower Miocene. The entire interval of the studied deposits corresponds to the acme subzone Def of the Ebu Zone in the Mediterranean dinocyst zonation by D. Zevenboom, where it spans the top of the Chattian and lower part of the Aquitanian Stage. Nannoplankton assemblages from the Alkun deposits are tentatively correlated with the nannoplankton assemblage of Zone NN1 in the standard zonation by E. Martini. It is impossible to date precisely the Alkun Formation based on nannoplankton, as the respective deposits are lacking index species and characteristic taxa of the standard zonation. The dominance of the cosmopolitan species Cyclicargolithus floridanus is a peculiar feature of nannoplankton assemblages from the Alkun Formation. Palynological data are used to consider the dynamics of the evolution of the vegetation cover and climate. Four episodes of relative cooling are distinguished against a background of warm-temperate climatic conditions in general. The most significant episodes occurred in the mid-Alkun time and during the early phase of the Assa time.  相似文献   

2.
This study describes the lithostratigraphic character of mid-Cenozoic (Oligocene-Pliocene) sequences in different parts of the northeastern Mediterranean area and offers a detailed stratigraphic correlation for this region. The sequences concerned are drawn from the Camardi area (south-central Anatolia), the Adana Basin, the Misis Mountains and the Kyrenia Range (northern Cyprus) and the submerged Florence Rise (west of Cyprus). The stratigraphic relationships identified here indicate the following: (a) Following the middle Eocene (Lutetian) regression there was uplift throughout the entire region; (b) Episodes of fluvial and lacustrine deposition in intramontane settings ensued in most of this region during the late Eocene/early Miocene interval; (c) Following a regionally extensive phase of tectonic compression, major marine transgression commenced in the late Oligocene in northern Cyprus and in the early Miocene in adjacent southern Turkey, with the exception of the Ecemi§ Fault Zone where continental deposition continued; (d) These Oligo-Miocene transgressive sequences comprise a broadly diachronous complex of both shallow and deeper marine facies, including reefal carbonates, littoral clastics, basinal shales and fan-turbidites; (e) Deeper marine Miocene facies persisted longer in the Misis area and in northern Cyprus; (f) A regional regression occurred throughout most of the area during the late Serravallian to Tortonian interval and is marked by the abrupt, locally discordant appearance of extensive shallow marine, deltaic and fluvial deposits; (g) Continued regression in the Messinian led to the formation of significant evaporite deposits in the western and southern parts of the region, but localized uplift of the Misis area is attested by the initial deformation of the Neogene rocks there and the absence of Messinian sediments from this area; (h) In the Pliocene there was extensive emergence of the northern parts of the region interrupted by brief marine incursions. The present-day drainage pattern was established at this time; (i) Marine conditions persisted longer in northern Cyprus, where emergence occurred only in the latest Pliocene.  相似文献   

3.
The Early Permian Gondwana regime succession of the Nilawahan Group is exposed only in the Salt Range of Pakistan. After a prolonged episode of non-deposition that spanned much of the Palaeozoic, the 350?m thick predominantly clastic sequence of the Nilawahan Group records a late glacial and post-glacial episode in which a range of glacio-fluvial, marine and fluvial environments evolved and accumulated. The Early Permian succession of the Salt Range has been classified into four formations, which together indicates a changing climatic regime during the Early Permian in the Salt Range region. The lower-most, Tobra Formation unconformably overlies a Cambrian sequence and is composed of tillite, diamictite and fresh water facies, which contain a floral assemblage (Gangamopteris and Glossopteris) that confirms an Asselian age. The Tobra Formation is overlain by marginal marine deposits of the Dandot Formation (Sakmarian), which contain an abundant brachiopods assemblage (Eurydesma and Conularia). Accumulation of the Dandot Formation was terminated by a regional sea-level fall and a change to the deposition of the fluvial deposits of the Warchha Sandstone (Artinskian). The Warchha Sandstone was deposited by high sinuosity meandering, avulsion prone river with well developed floodplains. This episode of fluvial sedimentation was terminated by a widespread marine transgression, as represented by the abrupt upward transition to the overlying shallow marine Sardhai Formation (Kungurian). The Early Permian Gondwana sequence represented by the Nilawahan Group is capped by predominantly shallow shelf carbonate deposits of the Tethyan realm. The sedimentologic and stratigraphic relationship of these four lithostratigraphic units in the Salt Range reveals a complex stratigraphic history for the Early Permian, which is mainly controlled by eustatic sea-level change due to climatic variation associated with climatic amelioration at the end of the major Gondwana glacial episode, and the gradual regional northward drift to a lower latitude of the Indian plate.  相似文献   

4.
Stream profile analysis of the Koralm Range (Eastern Alps)   总被引：1，自引：0，他引：1  
  相似文献   

5.
The interaction of river and marine processes in the fluvial to marine transition zone fundamentally impacts delta plain morphology and sedimentary dynamics. This study aims to improve existing models of the facies distribution, stratigraphic architecture and preservation in the fluvial to marine transition zone of mixed-process deltas, using a comprehensive sedimentological and stratigraphic dataset from the Middle Miocene Lambir Formation, Baram Delta Province, north-west Borneo. Eleven facies associations are identified and interpreted to preserve the interaction of fluvial and marine processes in a mixed-energy delta, where fluvial, wave and tidal processes display spatially and temporally variable interactions. Stratigraphic successions in axial areas associated with active distributary channels are sandstone-rich, comprising fluvial-dominated and wave-dominated units. Successions in lateral areas, which lack active distributary channels, are mudstone-rich, comprising fluvial-dominated, tide-dominated and wave-dominated units, including mangrove swamps. Widespread mudstone preservation in axial and lateral areas suggests well-developed turbidity maximum zones, a consequence of high suspended-sediment concentrations resulting from tropical weathering of a mudstone-rich hinterland. Within the fluvial to marine transition zone of distributary channels, interpreted proximal–distal sedimentological and stratigraphic trends suggest: (i) a proximal fluvial-dominated, tide-influenced subzone; (ii) a distal fluvial-dominated to wave-dominated subzone; and (iii) a conspicuously absent tide-dominated subzone. Lateral areas preserve a more diverse spectrum of facies and stratigraphic elements reflecting combined storm, tidal and subordinate river processes. During coupled storm and river floods, fluvial processes dominated the fluvial to marine transition zone along major and minor distributary channels and channel mouths, causing significant overprinting of preceding interflood deposits. Despite interpreted fluvial–tidal channel units and mangrove influence implying tidal processes, there is a paucity of unequivocal tidal indicators (for example, cyclical heterolithic layering). This suggests that process preservation in the fluvial to marine transition zone preserved in the Lambir Formation primarily records episodic (flashy) river discharge, river flood and storm overprinting of tidal processes, and possible backwater dynamics.  相似文献   

6.
据新的地层划分方案及大量钻井、露头和岩心资料,详细研究了鄂尔多斯盆地华池地区延安组延9油层组（Y9）沉积体系特征及演化,认为延9油层组主要为河流沉积,是延10油层组的继承与发展,发育有辫状河、辫状型曲流河和网状河3种类型的河流。Y39油层是辫状河发育的油层,Y29油层在继承Y39油层河流的基础上发育辫状型曲流河,Y19油层则是在前两期逐渐填平补齐之后,在准平原条件下发育的网状河沉积。华池地区延9油层组发育辫状河-辫状型曲流河和网状河两种河流沉积模式。  相似文献   

7.
Widespread Cenozoic sediments in and around the Tibetan Plateau (TP) are thought to have played an important role in explaining the process of the India-Asia collision as well as its interactions with global and regional paleoclimate. However, high-resolution temporal frameworks of sedimentary sequences and controls on geological and climatic events are still absent. To study the abovementioned issues, we investigate the Oligocene-Miocene lacustrine sequences (the Dingqinghu Formation) of the Lunpola Basin, central TP. In this work, cyclostratigraphic analyses are conducted with gamma ray log and pollen data to establish a high resolution temporal framework ranging from ca. 25.4 to 18.0 Ma for the sections. Along these sections, sediment accumulation rates are calculated with orbital signals to monitor clastic input of the lake basin; elemental, palynological, and isotopic data are summarized to depict the paleoclimate and paleoelevation evolution of this drainage system. Integrating all these clues together, we sort out a chronological list of events including lake basin, tectonics, and paleoclimate: regional uplift took place at 23.7 Ma; simultaneously, a distinct lake-basin transition characterized by accelerated sediment accumulation rate is recognized; about 0.2 Ma later at 23.5 Ma, catchment scale drought occurred and maintained to the end of the sections. Our results demonstrate that paleoclimate did not impose decisive influence on the late Oligocene-early Miocene evolution of the lake basin; instead, regional uplift and its associated accelerated exhumation of the source area resulted in the lake-basin transition and paleoclimatic drought. After reviewing the Oligocene-Miocene sedimentary records distributed in and around the TP, we argue that the 23.7 Ma geological event of the Lunpola Basin is probably not a single case but a regional effect of a dramatic tectonic transition of the plateau.  相似文献   

8.
Low, nearly continuous terraces of similar age are present along streams in drainage basins that range in size from Drift Creek (190 km2) to the Umpqua River (11,800 km2) in the Oregon Coast Range. Radiocarbon ages from near the bose of fluvial sediments underlying these terraces are clustered at about 9000-11,000 14C yr B.P. Beveled bedrock surfaces (straths) that underlie the fluvial sediments are 1-8 m above summer stream levels and are present along most of the nontidal reaches of the rivers that we studied. Where exposed, the bedrock straths are overlain by 2-11 m of fluvial sediment that consists of a bottom-stratum (channel) facies of sandy pebble-cobble gravel and a top-stratum (overbank) facies of sandy silt or silt. Eight radiocarbon ages from the fluvial sediments allow correlation of the lowest continuous terrace over a wide area and thus indicate that a regional aggradation episode occurred in Coast Range drainage basins during the Pleistocene-Holocene transition. The cause of such widespread aggradation is unknown but may be related to climate-induced changes in the frequency of evacuation of colluvium from hollows, which are common in all drainage basins in the region.  相似文献   

9.
The transition from the shallow marine Upper Muschelkalk Sea to the Lower Keuper fluvial plain represents the most diachronous facies shift of the entire Germanic Triassic. The type-section of the fluvial Lower Keuper (Erfurt Formation) is described in detail for the first time including biostratigraphic dating of the Muschelkalk/Keuper boundary. The type-section is integrated into a NNE-SSW cross section through the Central European Basin, and the Muschelkalk/Keuper facies shift is constrained by high-resolution conodont and ceratite biostratigraphy. Thus, the fundamental changes in palaeogeography, shifts of facies belts and stratal pattern architecture are visualised. Forced by a rapid transgression from Tethyan waters, the shallow marine Upper Muschelkalk Sea attained its maximum flooding in the lower conodont zone 2 (sequens/pulcher to philippi/robustus zones). Subsequent slow continuous regression to the South was accompanied by step-by-step progradation of coastal to fluvial plain environments of the Lower Keuper, culminating in a fluvial plain extending to South Germany. Based on stratal patterns, an improved sequence-stratigraphic interpretation for the Upper Muschelkalk/Lower Keuper interval is suggested. In combination with biostratigraphic arguments, the new sequence-stratigraphy points to a revised correlation of this interval within the Tethyan Triassic, incorporating the positions of the Anisian/Ladinian and Fassanian/Longobardian boundaries.  相似文献   

10.
Tectonic deformation of the land surface is known to influence the gradient, water and sediment discharge and the grain-size of modern fluvial systems. Any change in these variables alters the equilibrium of a fluvial system, potentially causing a change in channel morphology. 3D seismic data from the Tertiary (Miocene) age, Upper Frio Formation, Kelsey Field, South Texas, in the US are used to examine changing fluvial channel morphology through time during a period of active growth of a rollover anticline in the hangingwall of a normal fault (the Vicksburg Fault). The studied interval varies between 22 and 47 m thick, and spans several hundred thousand years. It consists of an alternation of fluvial sandstones, overbank mudstones and coal. Seismic extractions show the evolution of sinuous fluvial channels during a phase of growth fault activity. Prior to growth, a single sinuous channel is imaged. During growth, the fluvial system became decapitated by a developing rollover anticline, and a highly sinuous drainage network formed, with frequent avulsion events, headward propagation of streams and related stream capture. Increased channel sinuosity was spatially associated with increased avulsion frequency in the area down dip to the east of the rollover anticline, more than 10 km from the active fault. More than 25 m of relative accommodation developed on the flank of the growing rollover anticline compared with on the crest. The increased channel sinuosity is interpreted as reflecting an increase in longitudinal valley slope analogous to observations made in flume experiments and modern river systems. The increase in avulsion frequency is attributed to increased aggradation as the rivers adjusted back to equilibrium grade following the increase in slope.  相似文献   

11.
ABSTRACT
An anomalous sequence of thick fossiliferous marine shale of late Oligocene-early Miocene age, here termed the Opuama Shale Member, occurs within the paralic Agbada Formation in the subsurface of the western Niger Delta. The Opuama Shale fills a deep palaeochannel which was cut into Eocene-early Oligocene paralic beds. Planktonic and benthic foraminifera suggest that deposition in the channel began in the late Oligocene-early Miocene at outer shelf-slope depths, and that by the late early Miocene the channel had filled to shallow neritic depths. The channel, which is believed to be of submarine origin, is termed the Opuama canyon. The Opuama canyon originated during the pronounced early-Middle Oligocene drop in sea-level, and was cut by turbidity currents. It was filled, during the major late Oligocene-early Miocene rise of sea-level.
The location of the Opuama canyon in the western re-entrant of the Niger Delta supports Burke's (1972) conclusion that the western and eastern (where ancient submarine canyon fills are known) re-entrants of the delta are potential sites for ancient submarine canyons. Burke based his conclusion on the observation that the eastern and western re-entrants of the modern delta are areas where opposing longshore drifts converge and generate turbidity currents which cut submarine canyons.  相似文献   

12.
Relics of a thick, widely spread, fluvial sequence of Early Miocene age are scattered throughout southern Israel, eastern Sinai, the Dead Sea Rift Valley and the western margins of the Jordanian Plateau. These relics are mainly preserved in structural lows, karstic systems, and abandoned stream valleys. The paleogeography of this fluvial system was reconstructed based on the relations between the sequence remnants and the main structural and morphological features of the southeastern Levant region.Three sedimentary associations were identified in the Miocene sequence: a lower part dominated by locally derived clastic sediments; a thicker middle part, composed mostly of far-field allochthonous clastic sediments; and an upper part composed of local as well as allochthonous sediments. The two lower parts are regionally distributed whereas the upper part is syn-tectonic and confined to the Dead Sea basin and the Karkom graben in the central Negev. The composition of the far-field allochthonous sediments points to a provenance of Precambrian crystalline rocks of the Arabo-Nubian massif that were exposed along the uplifted shoulders of the Red Sea Rift as the upper drainage basin of the fluvial system. The diverse mammal remains found in this fluvial sequence suggest a complex of savanna, forests and fluvial habitats similar to those of present East Africa, with monsoon-type rains, which were the dominant water source of the rivers.The thickness of the Miocene sequence in the central Negev is at least 1700 m, similar to that of the subsurface sequence encountered in the Dead Sea basin. This similarity suggests that both were parts of an extensive subsiding sedimentary basin that developed between the Neo-Tethys and the uplifted margins of the Red Sea.The relations between the reconstructed pre-depositional landscape of southern Israel during the Early Miocene and the overlying fluvial sequence indicate that the entire area was buried under several hundred meters of fluvial sediments, reflecting a subsidence of the northern margins of the African continent (Arabian plate) before its breakup and the splitting of the Sinai–Israel subplate by the Dead Sea Transform.During the early Middle Miocene the subsidence was inversed as the mountainous backbone of Israel was uplifted. The uplift triggered a large scale denudation that removed the thick Early Miocene fluvial sequence from the Negev and transported the eroded sediments northwestward toward the eastern Mediterranean basin. Additional uplift during the late-Middle Miocene was associated with entrenchment of the Be’er Sheva Valley between the Judea Mountains in the north and the Negev Highlands in the south. This valley was flooded by the sea during the Late Miocene.We suggest that the formation of the Early Miocene subsiding basin at the northern edge of the Arabian sub-plate predated the breakup of the Arabian plate by the DST. The inversion of the subsiding regime, which led to the establishment of the Negev Highlands seems to be intimately related to the detachment of the Sinai–Israel sub-plate from the Arabian plate during the Middle Miocene.  相似文献   

13.
Fine-grained lacustrine, riverine and ash-fall sediments of the Shooting Iron Formation, whose late Pliocene age is established by Blancan gastropods and vertebrates, yield a pollen flora that is essentially similar in composition to the modern pollen rain in the Jackson Hole area. The Pliocene assemblage suggests a climate like that of the Jackson valley and foothills today. These spectra also resemble a Pliocene pollen flora from Yellowstone Park dated at ∼ 2.02 Ma. However, the underlying Miocene Teewinot sediments differ by containing pollen of four exotic deciduous hardwoods (Tertiary relicts) that suggest a summer-moist climate, unlike that of today. The Shooting Iron sediments lie with an angular unconformity on and above the Miocene lake sediments of the Teewinot Formation. Both of these deposits probably preceded the main uplift of the Teton Range based on the absence of Precambrian clasts in the Tertiary valley deposits. Because the Pliocene floras were modern in aspect, a Plio-Pleistocene transition would be floristically imperceptible here. The sequence denotes a protracted period of relative stability of climate during Teewinot time, and a shift in vegetational state (summer-wet trees drop out) sometime between the latest Miocene and latest Pliocene. The Pliocene spectra suggest a dry, cooler climate toward the end of Shooting Iron time.  相似文献   

14.
西藏札达盆地晚上新世—早更新世孢粉组合及其地质意义   总被引：2，自引：0，他引：2  
札达盆地位于青藏高原西南隅的阿里地区,是在中新世晚期约9.6 Ma B.P.形成的一个NW—SE向断陷盆地。该盆地在上新世—早更新世发育一套完整的河湖-冲积扇相地层。在札达县香孜乡西北约1 km处精细实测了上上新统—下更新统香孜剖面。根据前人的古地磁及ESR年龄数据确定下更新统香孜组年龄为2.60~1.67 Ma B.P.。根据孢粉学研究把香孜剖面自下而上划分为3个孢粉组合带(8个孢粉组合),并据此将札达盆地2.75 Ma B.P.以来的气候变化划分为3个阶段:(1)孢粉组合带Ⅰ(孢粉组合1~2),植被为温暖偏湿的常绿与落叶针阔叶混交林,2.67 Ma以后气候逐渐向干旱转变,地层对比时代为晚上新世(2.75~2.60 Ma);(2)孢粉组合带Ⅱ(孢粉组合3~5),发育温凉偏湿的亚高山落叶针阔叶混交林,并在约2.38 Ma逐渐变为针叶林,气候趋向变冷,地层对比时代为早更新世(2.54~2.16 Ma);(3)孢粉组合带Ⅲ(孢粉组合6~8),发育寒冷干旱的高山针叶林,并存在高寒灌丛草甸草原,低海拔处零星分布落叶针阔叶混交林,指示较强的地势差异,地层对比时代为早更新世(2.13~1.86 Ma)。  相似文献   

15.
Altar is a Cu-porphyry deposit related to several small plagioclase porphyry intrusions of the late Miocene formed on the margin of the Flat-Slab segment along the Andean Cordillera in north-west Argentina. New stratigraphic and structural mapping supported by geochemistry and geochronology of pre-ore volcanics at Altar has revealed that a period of ∼6–7 Ma of volcanism during the late Oligocene-early Miocene formed ∼4000 m of volcano-stratigraphic succession making up the Pachón Formation. It represents a period dominated by explosive to effusive eruption in a dynamic arc basin with local ash fall and flow deposition in lacustrine and fluvial sites. Volcanism is typified by medium- to high-K calc-alkaline arc magmatism with a shift from mafic compositions at the base to felsic rocks at the top of the formation containing zircons aged 21.9 ± 0.2 Ma (2 Std.Dev, U–Pb). A clear geochemical separation exists between early Miocene pre-ore volcanics that show signatures akin to non-adakitic, normal arc, extensional tectonic settings conducive of chemical differentiation at shallow crustal levels and correlate with intra-regional Abanico and Farellones Formations; and the middle to late-Miocene Cu-mineralised porphyry intrusions. After a break of ∼9 Ma in the geological record at Altar, these Cu-fertile bodies are emplaced entirely within the Pachón Rhyolite and represent adakite-like magmas with fractionation trends evolving from a lower crustal MASH zone. This distinction is controlled by a change from an extensional to compressive tectonic regime in the region during the middle Miocene in which magmas were stalled in the lower crust for an extended period, subsequently became enriched in metals and then formed several Cu-porphyry bodies which were emplaced during a relatively short period towards the late Miocene.  相似文献   

16.
The Central Patagonian Andes is a particular segment of the Andean Cordillera that has been subjected to the subduction of two spreading ridges during Eocene and Neogene times. In order to understand the Cenozoic geologic evolution of the Central Patagonian Andes, we carried out geochronologic(U-Pb and40Ar/39Ar), provenance, stratigraphic, sedimentologic, and geochemical studies on the sedimentary and volcanic Cenozoic deposits that crop out in the Meseta Guadal and Chile Chico areas(～47°S). Our data indicate the presence of a nearly complete Cenozoic record, which refutes previous interpretations of a hiatus during the middle Eocene-late Oligocene in the Central Patagonian Andes. Our study suggests that the fluvial strata of the Ligorio Marquez Formation and the flood basalts of the Basaltos Inferiores de la Meseta Chile Chico Formation were deposited in an extensional setting related to the subduction of the Aluk-Farallon spreading ridge during the late Paleocene-Eocene. Geochemical data on volcanic rocks interbedded with fluvial strata of the San Jose Formation suggest that this unit was deposited in an extensional setting during the middle Eocene to late Oligocene. Progressive crustal thinning allowed the transgression of marine waters of Atlantic origin and deposition of the upper Oligocene-lower Miocene Guadal Formation. The fluvial synorogenic strata of the Santa Cruz Formation were deposited as a consequence of an important phase of compressive deformation and Andean uplift during the early-middle Miocene. Finally, alkali flood basalts of the late middle to late Miocene Basaltos Superiores de la Meseta Chile Chico Formation were extruded in the area in response to the suduction of the Chile Ridge under an extensional regime. Our studies indicate that the tectonic evolution of the Central Patagonian Andes is similar to that of the North Patagonian Andes and appears to differ from that of the Southern Patagonian Andes, which is thought to have been the subject of continuous compressive deformation since the late Early Cretaceous.  相似文献   

17.
Results from coal‐exploration drilling in the onshore part of the Port Phillip Basin, Victoria, have established stratigraphic and age correlations of the Lower Miocene Werribee Formation brown coal deposits at Bacchus Marsh to similar brown coals at Altona. The coal deposits occur in a northwest‐southeast structural depression (the Parwan Trough) that appears to be a southeast continuation of the Ballan Graben. Recent drilling for potential coal‐bed methane in the trough has provided new data on the deeper stratigraphy not penetrated by earlier drilling, including recognition of an Upper Cretaceous to Eocene Yaloak Formation coal‐bearing interval, similar to the Anglesea area, Ballan Graben and Lal Lal Basin. Up to 200 m of coal‐bearing sediment and minor volcanics underlie the Miocene coal measures. A marine facies transition takes place between the Miocene coal swamps of the Parwan Trough, through barrier sands west of Werribee, to carbonate facies near Geelong. To the south beneath Port Phillip Bay, a similar transition probably occurs between coal swamps of the Parwan Trough and fully marine carbonate environments of the contiguous Sorrento Graben. The palaeogeographical reconstructions suggest a similar coal‐to‐carbonate facies transition as in the adjacent onshore Gippsland Basin.  相似文献   

18.
Cenozoic marine strata occur in the western, eastern, and central parts of the North Patagonian Andes between ∼43°S and 44°S. Correlation of these deposits is difficult because they occur in small and discontinuous outcrops and their ages are uncertain. In order to better understand the age and sedimentary environment of these strata, we combined U–Pb (LA-MC-ICPMS) geochronology on detrital zircons with sedimentologic and paleontologic (foraminifers and molluscs) studies. Sedimentologic analyses suggest that the Puduhuapi Formation on the western flank of the Andean Cordillera was deposited in a deep-marine setting, the Vargas Formation in the central part of the Andes was deposited at outer-neritic or bathyal depths, and the La Cascada Formation on the eastern flank of the range was deposited in a shallow-marine environment. Geochronologic and paleontologic results indicate that the three marine units were deposited during the late Oligocene-early Miocene interval, although it is not clear whether this occurred during one or more marine incursions in the area. The alluvial(?) conglomeratic deposits of the La Junta Formation, exposed in the proximity of the Vargas Formation outcrops, have a maximum depositional age of ∼26 Ma and could have been deposited during the initial stage of subsidence that affected this region prior to the marine transgression over this area. The occurrence of both Pacific and Atlantic molluscan taxa in the La Cascada and Vargas formations suggests that a marine strait connected both oceans during the accumulation of these units. The new data on the age of the Puduhuapi, Vargas, and La Cascada formations indicate that these units may correlate with lower Miocene marine deposits in the forearc of central and southern Chile (Navidad Formation and equivalent units) and on the eastern flank of the Patagonian Andes (Río Foyel Formation and equivalent units). A late Oligocene−early Miocene age for these marine deposits is a reliable maximum age for the deformation and uplift of the North Patagonian Andes.  相似文献   

19.
Devonian strata near Fowlers Gap and Nundooka Stations, northern Barrier Ranges comprise ～2.7 km of sparsely fossiliferous, fluvially deposited sandstones (Mulga Downs Group). These strata are subdivided into the Coco Range Sandstone (oldest, Emsian‐Eifelian) found west of the north‐trending Nundooka Creek Fault, and the Nundooka Sandstone (youngest, ?Frasnian‐Famennian found east of the fault). Eleven stratigraphic units are mapped and two of these in the Coco Range Sandstone are formally named as The Valley Tank Arenite and Copi Dam Arenite Members. The Coco Range Sandstone and Nundooka Sandstone are tentatively correlated with strata in the Bancannia Trough. Deposition of the Coco Range Sandstone and Nundooka Sandstone was, however, separate from that of the Bancannia Trough, probably due to topographic highs which occurred east of the Western Boundary Fault.

The Coco Range Sandstone is cut by northeast‐trending faults splaying from the Nundooka Creek Fault. These faults have vertical planes and are thought to predate deposition of the Nundooka Sandstone. In the Late Cretaceous the Nundooka Creek and Western Boundary Faults became active and areas west of these faults were uplifted to form Coco Range and Bald Hill. This fossil landscape was progressively buried by deposition of the Palaeocene‐Eocene Eyre Formation until it was half covered by strata. During the Oligocene silcrete of the Cordillo Surface formed and was overlain conformably by the sandy Doonbara Formation (Miocene). Since the Miocene, much of the Eyre Formation has been removed by erosion to exhume a Late Cretaceous landscape. Subsequently in the ?Pliocene there was some faulting along the Nundooka Creek and Western Boundary Faults because locally the Cordillo Surface and the Doonbara Formation dip toward the faults at 30–72°. At three localities there is evidence of probable Quaternary activity on the Nundooka Creek and the Western Boundary Faults (downthrow to the east) suggesting a different style of tectonics from that in the Miocene.  相似文献   

20.
DIFFERENT VARIETIES OF MIOCENE LEUCOGRANITE IN THE ARUN VALLEY—EVEREST—MAKALU AREA:FIELD RELATIONS, PETROLOGY AND ISOTOPE GEOCHEMISTRY1　AritaK .OriginoftheinvertedmetamorphismoftheLowerHimalayas,CentralNepal[J] .Tectonophysics,1983,93:4 3～6 0 . 　BarbarinB .Areviewoftherelationshipsbetweengranitoidtypes,theiroriginsandtheirgeodynamicenvironments[J] .Lithos,1999,4 6 :6 0 5～ 6 2 6 . 3　BurchfielBC ,ChenZ,HodgesKV ,etal.TheSou…  相似文献   

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