Palynological analysis of 228 outcrop samples from the Kenai, Seldovia, and Tyonek quadrangles, Cook Inlet region, Alaska

Zippi, Pierre A.

doi:10.14509/23723

Cited by 6 publications

(21 citation statements)

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“…In contrast to the tabular sand bodies found in the Tyonek Formation, those in the Beluga Formation are generally lenticular. Palynological analyses from these outcrops yield an early late to late Miocene depositional age [ Zippi and Loveland , ]. In the subsurface type section located on the west side of the basin, the Beluga Formation consists of intercalated claystone, sandstone, siltstone, and coal, and generally lacks massive sandstone beds and massive coal seams [ Calderwood and Fackler , ].…”

Section: Facies Descriptions and Interpretationsmentioning

confidence: 85%

“…We measured four stratigraphic sections (total thickness of 104 m; TY‐1, TY‐3, TY‐4, TY‐2) that comprise a composite stratigraphic section that records up‐section variations in lithofacies and provenance. Palynological analyses from this section indicate middle Miocene deposition [ Zippi and Loveland , ], which is in agreement with the age assignment based on plant megafossils [ Wolfe et al ., ]. The base of the Tyonek Formation is erosive into underlying Triassic‐Jurassic chert and greenstone.…”

Section: Facies Descriptions and Interpretationsmentioning

confidence: 99%

“…Near the Capps Glacier (Figure b), several hundred feet of exposed Tyonek Formation consists of siltstone succession more than 9 m thick, thin fine‐grained, ripple cross‐laminated sandstone, and lenticular bodies of thicker fine‐grained, ripple cross‐laminated sandstone up to 3 m thick [ LePain et al ., ]. Palynological analyses from these outcrops suggest a middle to late middle Miocene depositional age [ Zippi and Loveland , ]. In the subsurface type section located offshore on the west side of the basin, the Tyonek Formation consists of massively bedded, fine‐grained to medium‐grained sandstone, siltstone, and thick coal [ Calderwood and Fackler , ].…”

Section: Facies Descriptions and Interpretationsmentioning

confidence: 99%

“…We measured three stratigraphic sections with a total thickness of 95 m (Figure ). Palynological analyses from these sections suggest a late Miocene depositional age [ Zippi and Loveland , ], which is in agreement with the assigned age based on plant leaf megafossils [ Wolfe et al ., ]. The most common lithofacies, in order of decreasing abundance, are trough (St) and planar (Sp) cross‐stratified sandstone, massive sandstone (Sm), massive (Fsm) and horizontally bedded siltstone (Fsm), ripple‐laminated siltstone (Fsr), and coal.…”

Section: Facies Descriptions and Interpretationsmentioning

confidence: 99%

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Miocene‐Recent sediment flux in the south‐central Alaskan fore‐arc basin governed by flat‐slab subduction

Finzel

Enkelmann

2017

Geochem Geophys Geosyst

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The Cook Inlet in south‐central Alaska contains the early Oligocene to Recent stratigraphic record of a fore‐arc basin adjacent to a shallowly subducting oceanic plateau. Our new measured stratigraphic sections and detrital zircon U‐Pb geochronology and Hf isotopes from Neogene strata and modern rivers illustrate the effects of flat‐slab subduction on the depositional environments, provenance, and subsidence in fore‐arc sedimentary systems. During the middle Miocene, fluvial systems emerged from the eastern, western, and northern margins of the basin. The axis of maximum subsidence was near the center of the basin, suggesting equal contributions from subsidence drivers on both margins. By the late Miocene, the axis of maximum subsidence had shifted westward and fluvial systems originating on the eastern margin of the basin above the flat‐slab traversed the entire width of the basin. These mud‐dominated systems reflect increased sediment flux from recycling of accretionary prism strata. Fluvial systems with headwaters above the flat‐slab region continued to cross the basin during Pliocene time, but a change to sandstone‐dominated strata with abundant volcanogenic grains signals a reactivation of the volcanic arc. The axis of maximum basin subsidence during late Miocene to Pliocene time is parallel to the strike of the subducting slab. Our data suggest that the character and strike‐orientation of the down‐going slab may provide a fundamental control on the nature of depositional systems, location of dominant provenance regions, and areas of maximum subsidence in fore‐arc basins.

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Section: Facies Descriptions and Interpretationsmentioning

confidence: 85%

Section: Facies Descriptions and Interpretationsmentioning

confidence: 99%

Section: Facies Descriptions and Interpretationsmentioning

confidence: 99%

Section: Facies Descriptions and Interpretationsmentioning

confidence: 99%

See 2 more Smart Citations

Miocene‐Recent sediment flux in the south‐central Alaskan fore‐arc basin governed by flat‐slab subduction

Finzel

Enkelmann

2017

Geochem Geophys Geosyst

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“…The samples were processed by Russ Harms of Global Geolab Limited in Medicine Hat, Alberta, Canada, and prepared slides of recovered palynomorphs were analyzed by Dr. Pierre Zippi (Biostratigraphy.com, LLC). The results of the analyses are summarized below and published in Zippi and Loveland (2012). Palynology samples were not collected from strata in the Susitna or Matanuska Valley basins as part of this study.…”

Section: Depositional Agementioning

confidence: 99%

Provenance signature of changing plate boundary conditions along a convergent margin: Detrital record of spreading-ridge and flat-slab subduction processes, Cenozoic forearc basins, Alaska

2015

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Cenozoic strata from forearc basins in southern Alaska record deposition related to two different types of shallow subduction: Paleocene-Eocene spreading-ridge subduction and Oligocene-Recent oceanic plateau subduction. We use detrital zircon geochronology (n = 1368) and clast composition of conglomerate (n = 1068) to reconstruct the upper plate response to these two subduction events as recorded in forearc basin strata and modern river sediment. Following spreading-ridge subduction, the presence of Precambrian and Paleozoic detrital zircon ages in middle Eocene-lower Miocene arc-margin strata and Early Cretaceous ages in lower Miocene accretionary prism-margin strata indicates that sediment was transported to the basin from older terranes in interior Alaska and from the exhumed eastern part of the Cretaceous forearc system, respectively. By middle-late Miocene time, diminished abundances of these populations reflect shallow subduction of an oceanic plateau and associated exhumation that resulted in an overall contraction of the catchment area for the forearc depositional system.In the southern Alaska forearc basin system, upper plate processes associated with subduction of a spreading ridge resulted in an abrupt increase in the diversity of detrital zircon ages that reflect new sediment sources from far inboard regions. The detrital zircon signatures from strata deposited during oceanic plateau subduction record exhumation of the region above the flat slab, with the youngest detrital zircon population reflecting the last period of major arc activity prior to inser-tion of the flat slab. This study provides a foundation for new tectonic and provenance models of forearc basins that have been modified by shallow subduction processes, and may help to facilitate the use of U-Pb dating of detrital zircons to better understand basins that formed under changing geodynamic plate boundary conditions. ., 2015, Provenance signature of changing plate boundary conditions along a convergent margin: Detrital record of spreading-ridge and flat-slab subduction processes, Cenozoic forearc basins, Alaska: Geosphere, v. 11, no. 3,

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Long‐term fore‐arc basin evolution in response to changing subduction styles in southern Alaska

et al. 2016

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Detrital zircon U-Pb and fission track double-dating and Hf isotopes from the Mesozoic and Cenozoic strata in the southern Alaska fore-arc basin system reveal the effects of two different modes of flat-slab subduction on the evolution of the overriding plate. The southern margin of Alaska has experienced subduction of a spreading-ridge (~62-50 Ma) and an oceanic plateau (~40-0 Ma). When a subducting spreading ridge drives slab flattening, our data suggest that after the ridge has moved along strike retro-arc sediment sources to the fore arc become more predominant over more proximal arc sources. Spreading-ridge subduction also results in thermal resetting of rocks in the upper plate that is revealed by thermochronologic data that record the presence of young age peaks found in subsequent, thin sedimentary strata in the fore-arc basin. When a subducting oceanic plateau drives slab flattening, our data suggest that basin catchments get smaller and local sediment sources become more predominant. Crustal thickening due to plateau subduction drives widespread surface uplift and significant vertical uplift in rheologically weak zones that, combined, create topography and increase rock exhumation rates. Consequently, the thermochronologic signature of plateau subduction has generally young age peaks that generate short lag times indicating rapid exhumation. The cessation of volcanism associated with plateau subduction limits the number of syndepositional volcanic grains that produce identical geochronologic and thermochronologic ages. This study demonstrates the merit of double-dating techniques integrated with stratigraphic studies to expose exhumational age signatures diagnostic of large-scale tectonic processes in magmatic regions.

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Palynological analysis of 228 outcrop samples from the Kenai, Seldovia, and Tyonek quadrangles, Cook Inlet region, Alaska

Cited by 6 publications

References 0 publications

Miocene‐Recent sediment flux in the south‐central Alaskan fore‐arc basin governed by flat‐slab subduction

Miocene‐Recent sediment flux in the south‐central Alaskan fore‐arc basin governed by flat‐slab subduction

Provenance signature of changing plate boundary conditions along a convergent margin: Detrital record of spreading-ridge and flat-slab subduction processes, Cenozoic forearc basins, Alaska

Long‐term fore‐arc basin evolution in response to changing subduction styles in southern Alaska

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