Eocene facies successions and environments in the Southern Llanos basin, Colombia

This work presents the facies analysis and depositional environment for the Eocene rocks in the southern Llanos Basin (SLLB) and southern Llanos Foothills. Cores and outcrop samples were analyzed by palynology and detrital zircon U-Pbgeochronology. In this paper, we present ages for the facies and two important paleosol markers. The lower member of the Mirador Formation consists of amalgamated sandstones and conglomerates accumulated in a braidad channel belt. The lower Mirador is 33 m thick and early Eocene in the Foothills, whereas in the SLLB, it ist is 22 m thick and middle Eocene in age; it pinches out approximately 33 km to the east. The fluvial facies rests over an unconformity marked by a mature and intensively-weathered paleosol developed over Paleocene, Cretaceous and older rocks to the east. This mature paleosol was dated by U-Pb detrital zircon geochronology as middle to late Paleocene. At the top of the lower Mirador, we describe an interval of sandstones with root casts capped by a thin layer of coal or coaly mudstone. This facies succession evolved as A compound paleosol is a polygenetic soil that marks a change from well-drained conditions under a subaerial vegetation cover to poor-drained conditions of marsh and swamps, which halt vegetation growth, which is incorporated as coal or coaly mudstone, see the section of Facies Successions. At the top of the lower Mirador facies and recorded the cessation of the fluvial system and its stabilization by vegetation. The coal layer marked the posterior rise on the water table and flooding. Detrital zircon U-Pb geochronology dated this compound paleosol as middle Eocene. Above the fluvial facies of the lower Mirador, shallow marine facies deposited during the middle and late Eocene in the Foothills and western SLLB. The marine facies consist in shelf mudstone and shoreface sandstone in a coarsening upward trend. These facies correspond to the C8 member of the Carbonera Formation. The correlative middle Eocene facies to the east of the SLLB are carbonaceous mudstones and coals that were deposited in swamp-marsh and lagoon environments in backshore to coastal-plain environments during the middle Eocene. The fluvial and coastal plain, as well as the marine facies, fossilized an erosional relief less than 50 m high, corresponding to a paleo-landscape. The paleo-landscape was carved at the end of the Paleocene and is capped by the intensely-weathered paleosol indicating subaerial exposition. The paleo-landscape was modeled over Paleocene, Cretaceous, Paleozoic, and basement rocks toward the east and south of the basin. This paleo-landscape lasted until the end of the middle Eocene in the studied area. The Fluvial reservoirs are not continuous but distributed along channel belts composed of channels and braided bars in an NW direction. The marine shoreface reservoirs are distributed as swaths of sandstones in a perpendicular direction to the fluvial belts. These reservoirs have excellent seal rocks above. The plays include fluvial valley sandstones and buried hills of Cretaceous sandstones.

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Detrital zircon geochronology of metasedimentary rocks in the southern Omineca Belt, Canadian Cordillera

Canadian Journal of Earth Sciences ◽

10.1139/e91-112 ◽

1991 ◽

Vol 28 (8) ◽

pp. 1254-1270 ◽

Cited By ~ 42

Author(s):

Gerald M. Ross ◽

Randall R. Parrish

Keyword(s):

Detrital Zircon ◽

Bimodal Distribution ◽

Detrital Zircons ◽

Detrital Zircon Geochronology ◽

Early Proterozoic ◽

Metasedimentary Rocks ◽

Basement Rocks ◽

Two Samples ◽

Alberta Basin ◽

Detrital Zircon Ages

We address two problems of Cordilleran geology in this study using U–Pb dating of single detrital zircon grains from metasedimentary rocks: the provenance of the Windermere Supergroup, and the age and correlation of metasedimentary rocks within the Shuswap Complex that are at high metamorphic grade. Because some of these rocks are clearly of North American affinity, the ages of zircons provide indirect constraints on the age and distribution of continental basement from which the zircons were derived.A consistent pattern emerges from ages of about 50 grains from six rocks. Nearly all samples analyzed (48–53°N) are characterized by a bimodal distribution of zircon ages of 1.65–2.16 Ga and > 2.5 Ga, with a distinct lack of ages between 2.1 and 2.5 Ga. Exceptions to this pattern are young zircons from two samples, from Valhalla and Grand Forks – Kettle complexes of southeastern British Columbia, that have grains 1435 ± 35 and 650 ± 15 Ma, respectively. These younger grains are inferred to have been derived from magmatic rocks, and they have no obvious source in either the Canadian Shield or the Alberta subsurface basement to the east. The Early Proterozoic and Archean ages of detrital zircons resemble those of dated basement rocks beneath the Alberta Basin as well as basement exposed within the Cordilleran hinterland (gneisses of Thor–Odin, Frenchman Cap, and Malton regions). However, 2.1–2.4 Ga rocks that are extensive in the subsurface of northern Alberta are not represented in the inventory of detrital zircon ages presented in this paper.This pattern suggests that much of the Cordilleran basement between these latitudes is underlain by Archean crust of the Hearne–Wyoming provinces that may be mantled to the west by an orogenic–magmatic belt of Early Proterozoic (1.7–1.9 Ga) age which may largely have been parallel to the present Cordilleran orogen.

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Detrital zircon geochronology and provenance of the Middle Cambrian Flathead Sandstone, Park County, Wyoming

The Mountain Geologist ◽

10.31582/rmag.mg.54.2.86 ◽

2017 ◽

Vol 54 (2) ◽

pp. 86-103 ◽

Cited By ~ 8

Author(s):

David Malone ◽

John Craddock ◽

Stuart Kenderes

Keyword(s):

Detrital Zircon ◽

Detrital Zircons ◽

The South ◽

Midcontinent Rift ◽

Zircon Age ◽

Middle Cambrian ◽

Detrital Zircon Geochronology ◽

Cheyenne Belt ◽

Basement Rocks ◽

Wyoming Province

We report the results of analyses of detrital zircon from the middle Cambrian Flathead Sandstone from four locations in Park County, WY. The Flathead U-Pb zircon age spectra (n=355) includes one peak at 2702–3345 Ma (95%) and two small age peaks at 1784 Ma (4%) and ∼1830 Ma (1%). Regional paleocurrent data for the Flat-head indicate sediment transport from east to west but the dominant Archean detrital zircons in our sample suite indicates a proximal source in structurally and topographically high Wyoming Province crust. The Archean ages are consistent with the >3.0 Ga fraction being derived from basement rocks present in the northern Beartooth Range and areas further to the west. The 2.8–3.0 Ga grains were derived from the Beartooth-Bighorn magmatic zone, which directly underlies and extends to the south and east of these Flathead sampling localities. The 1.7–1.8 Ga grains were derived from 100s of km to the south and east, in the Cheyenne Belt or more distal Yavapai Province rocks. This 1.7–1.8 Ga crust was uplifted along the Transcontinental Arch during late Precambrian time. The Transcontinental Arch, and perhaps the Midcontinent Rift further to the east as well, prevented easterly-sourced (i.e. Grenville) zircons from reaching the Wyoming Sauk shoreline.

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Detrital zircon geochronology of the Aycross Formation (Eocene) near Togwotee Pass, western Wind River Basin, Wyoming

The Mountain Geologist ◽

10.31582/rmag.mg.54.2.69 ◽

2017 ◽

Vol 54 (2) ◽

pp. 69-85 ◽

Cited By ~ 2

Author(s):

David Malone ◽

John Craddock ◽

Kacey Garber ◽

Jarek Trela

Keyword(s):

Late Cretaceous ◽

Detrital Zircon ◽

Inductively Coupled Plasma ◽

Middle Eocene ◽

Detrital Zircons ◽

Zircon Age ◽

Detrital Zircon Geochronology ◽

Inductively Coupled ◽

Wind River Basin ◽

The North

The Aycross Formation is the basal unit of the Absaroka Volcanic Supergroup in the southern Absaroka Range and consists of volcanic sandstone, mudstone, breccia, tuff and conglomerate. The Aycross was deposited during the waning stages of the Laramide Orogeny and the earliest phases of volcanism in the Absaroka Range. U-Pb geo-chronology using laser ablation multicollector inductively coupled plasma mass spectrometry LA-ICP-MS was performed on detrital zircons collected from an Aycross sandstone bed at Falls Campground east of Togwotee Pass. The detrital zircon age spectrum ranged fom ca 47 to 2856 Ma. Peak ages, as indicated by the zircon age probability density plot are ca. 51, 61, and 72 Ma. Tertiary zircons were the most numerous (n = 32), accounting for 42% of the zircon ages spectrum. Of these 19 are Eocene, and 13 are Paleocene, which are unusual ages in the Wyoming-Idaho-Montana area. Mesozoic zircons (n = 21) comprise 27% of the age spectrum and range in age from 68–126 Ma; all but one being late Cretaceous in age. No Paleozoic zircons are present. Proterozoic zircons range in age from 1196–2483 Ma, and also consist of 27% of the age spectrum. The maximum depositional age of the Aycross Formation is estimated to be 50.05 +/− 0.65 Ma based on weighted mean of the eight youngest grains. The Aycross Formation detrital zircon age spectrum is distinct from that of other 49–50 Ma rocks in northwest Wyoming, which include the Hominy Peak and Wapiti Formations and Crandall Conglomerate. The Aycross must have been derived largely from distal westerly source areas, which include the late Cretaceous and Paleocene Bitteroot Lobe of the Idaho Batholith. In contrast, the middle Eocene units further to the north must have been derived from erosion of the Archean basement-cored uplift of the Laramide Foreland in southwest Montana.

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Structural setting and detrital zircon U–Pb geochronology of Triassic–Cenozoic strata in the eastern Central Pamir, Tajikistan

Geological Society London Special Publications ◽

10.1144/sp483.11 ◽

2018 ◽

Vol 483 (1) ◽

pp. 605-630 ◽

Cited By ~ 3

Author(s):

John He ◽

Paul Kapp ◽

James B. Chapman ◽

Peter G. DeCelles ◽

Barbara Carrapa

Keyword(s):

Detrital Zircon ◽

Hanging Wall ◽

Volcanic Rocks ◽

Late Eocene ◽

Geological Mapping ◽

Isotopic Data ◽

Detrital Zircon Geochronology ◽

The North ◽

Central Tibet ◽

Qiangtang Terrane

AbstractIntegration of new geological mapping, detrital zircon geochronology, and sedimentary and metamorphic petrography south of the Muskol metamorphic dome in the Central Pamir terrane provides new constraints on the evolution of the Pamir orogen from Triassic to Late Oligocene time. Zircon U–Pb data show that the eastern Central Pamir includes Triassic strata and mélange that are of Karakul–Mazar/Songpan–Ganzi affinity and comprise the hanging wall of a thrust sheet that may root into the Tanymas Fault c. 35 km to the north. The Triassic rocks are unconformably overlain by Cretaceous strata that bear similarities to coeval units in the southern Qiangtang terrane and the Bangong Suture Zone of central Tibet. Finally, Oligocene or younger conglomerate and interbedded siltstone, the youngest documented strata in the Pamir Plateau proper, record an episode of juvenile magmatism at c. 32 Ma, which is absent in the extant rock record and other detrital compilations from the Pamir but overlaps in age with ultrapotassic volcanic rocks in central Tibet. Zircon Hf isotopic data from the Oligocene grains (εHf(t) ≈ +9.6) suggest a primary mantle contribution, consistent with the hypothesis of Late Eocene lithospheric removal beneath the Pamir Plateau.

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