Paleomagnetic Isochrons, Unsteadiness, and Non-Uniformity of Sedimentation in Miocene Fluvial Strata of the Siwalik Group, Northern Pakistan

McRae, Lee E.

doi:10.1086/629418

Cited by 57 publications

(13 citation statements)

References 29 publications

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“…i05-i06 years) tend to have smaller ranges than those calculated over short time intervals (e.g. 104-105 years) due to the f 0.1 Ma error, and because periods of deposition, erosion, and non-deposition tend to be averaged (McRae, 1990). Sediment accumulation rates that could be calculated over relatively short time intervals by interpolating dates between palaeomagnetic reversals are unreliable because of errors associated with absolute age dates, potentially large differences in local deposition rates between channel-belt and floodplain deposits, and sedimentary hiatuses associated with palaeosols (i.e.…”

Section: Utran Kasmentioning

confidence: 87%

Intra‐ and extrabasinal controls on fluvial deposition in the Miocene Indo‐Gangetic foreland basin, northern Pakistan

Zaleha

1997

Sedimentology

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The Miocene Siwalik Group (upsection, the Chinji, Nagri, and Dhok Pathan Formations) in northern Pakistan records evolving fluvial systems within the Himalayan foreland basin. Sedimentological variations are evaluated with respect to local, regional, and global controls on fluvial deposition and basin filling.Thick (5 m to tens of metres) sandstones are composed of channel bar and fill deposits of low-sinuosity, meandering and braided rivers which formed large, low-gradient sediment fans (or 'megafans'). River flow was dominantly toward the south-east. The proportion of thick sandstones varies in all Siwalik sections on three scales, and reflects similar variations in palaeochannel size and grain size:(1) small-scale variations are generally tens of metres thick, and reflect the alternation of thick sandstones (channel-belt deposits) and mudstone-dominated strata (overbank deposits) through the section; (2) medium-scale variations are roughly one-hundred to a few hundreds of metres thick, and primarily correspond to changes in channel-deposit thickness, but also to the degree of superposition of channel deposits and/or to changes in the number of channel-belt deposits per unit of section; and (3) large-scale variations (formation-scale) are greater than one km thick, and primarily correspond to changes in channel-deposit thickness. Time-scales of small-, medium-, and large-scale variations appear to be on the order of lo4, lo5 and lo6 years, respectively. The Chinji-Nagri transition is characterized by increases in channel-deposit proportion, sandstone thickness, palaeochannel size and discharge, mean grain size of sandstones, and sediment accumulation rates; and a decrease in avulsion period. The Nagri-Dhok Pathan transition is characterized by decreases in channel-deposit proportion, sandstone thickness, palaeochannel size and discharge, mean grain size of sandstones, and avulsion period; and a further increase in sediment accumulation rates. Formation boundaries across the Potwar Plateau decrease in age toward the west. The Chinji-Nagri transition ranges in age from z 10.9-12.7 Ma, and the Nagri-Dhok Pathan transition ranges in age from z 9.3-10.1 Ma.Small-scale variations are attributable to repeated river avulsions triggered by autocyclic processes and/or mountain-front tectonism (e.g. faulting, earthquakes). Medium-scale variations are attributable to local changes in the position of large sediment fans, also triggered by autocyclic processes and/or mountain-front tectonism. The Chinji-Nagri transition records the diversion or establishment (possibly due to river piracy) of a larger river system in the area. River diversion or piracy probably took place within the mountain belt and is attributable to 0 1997 International Association of Sedimentologists 369 370 M. J. Zaleha increasing and spatially variable mountain-belt uplift rates, and possibly the development of associated mountain-front deformational structures. The Nagri-Dhok Pathan transition records the diversion of the larger river system out of the...

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Section: Utran Kasmentioning

confidence: 87%

Intra‐ and extrabasinal controls on fluvial deposition in the Miocene Indo‐Gangetic foreland basin, northern Pakistan

Zaleha

1997

Sedimentology

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“…Sediment accumulation rates are calculated on the basis of magnetic polarity correlations shown in Figure 5. All rates discussed here are subject to a host of uncertainties, including the errors in magnetic correlations (mentioned previously), errors in the GPTS, resolution of palynological assemblages, uncertainties related to unsteady deposition and stratigraphic completeness, errors in measured stratal thicknesses, and postdepositional thickness changes [ May et al , 1985; Badgley et al , 1986; Gallagher , 1989; McRae , 1990]. One important issue concerns the possibility of significant time gaps within the stratigraphic successions.…”

Section: Magnetostratigraphymentioning

confidence: 99%

“…For the Xining succession, the potential for unconformable time gaps is minimized by several factors. First, the upper and lower age bounds indicate a 10 7 –10 8 year duration of potential deposition, exceeding the 10 0 –10 5 year timescales over which accumulation rates are most sensitive to the effects of unsteady, discontinuous sedimentation [ Sadler , 1981; May et al , 1985; Badgley et al , 1986; McRae , 1990]. Second, the volumetric dominance and large vertical extent of lacustrine facies (Table A3) suggests that (1) erosion of previously deposited sediment, a process common in channelized fluvial systems, was of reduced importance, and (2) deposition was steadier than in a river‐dominated system, as demonstrated by Sadler [1981].…”

Section: Magnetostratigraphymentioning

confidence: 99%

Mesozoic‐Cenozoic evolution of the Xining‐Minhe and Dangchang basins, northeastern Tibetan Plateau: Magnetostratigraphic and biostratigraphic results

et al. 2004

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[1] Accurate stratigraphic ages are crucial to understanding the deformation history of the Tibetan Plateau prior to and during the Indo-Asian collision. Efforts to quantify MesozoicCenozoic ages are hindered by limited fossils and a paucity of volcanic horizons and regionally correlative strata. Magnetostratigraphic and biostratigraphic results from the Xining-Minhe-Longzhong basin complex and Dangchang basin provide an improved chronology of nonmarine basin development over a large region of the northeastern Tibetan Plateau (34-37°N, 101-105°E). Analyses of 171 magnetostratigraphic levels and 24 palynological assemblages (>120 species) indicate Late Jurassic-Early Cretaceous to mid-Tertiary deposition. Although magnetic polarity zonation is incomplete, independent palynological age control partially restricts possible correlations to the Geomagnetic Polarity Timescale. The sediment accumulation record, basin provenance, structural geology, and published thermochronological data support a history of Jurassic exhumation, Late Jurassic-Early Cretaceous fault-related basin initiation, and Cretaceous-Paleogene reduced accumulation. These patterns, which are compatible with Late Jurassic-Early Cretaceous extension and Cretaceous-Paleogene postrift thermal subsidence, were disrupted at about 40-30 Ma, when shortening related to the Indo-Asian collision induced localized range uplift, vertical axis rotation, and amplified subsidence.INDEX TERMS: 1520

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“…Opdyke et al , 1982; Johnson et al , 1982; Tauxe and Opdyke, 1982) has been augmented by additional work in the Pliocene (Khan et al , 1988). The proceeds from these studies have provided the timeframes for a recent analyses of vertebrate evolution and migration (Flynn et al , 1990), of vertical and lateral sedimentation rate fluctuations (Johnson et al , 1988; McRae, 1990b), of thrust belt chronology (Burbank and Reynolds , 1988) and of Himalyan uplift rates from zircon fission‐track ages (Cerveny et al , 1988). The utilization of the magnetostratigraphic record as chronostratigraphic marker in Siwalik sediments (e.g.…”

Section: Magnetostratigraphymentioning

confidence: 99%

Sedimentary Magnetism, Environmental Magnetism, and Magnetostratigraphy

King

Channell

1991

Reviews of Geophysics

280

143

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Paleomagnetic Isochrons, Unsteadiness, and Non-Uniformity of Sedimentation in Miocene Fluvial Strata of the Siwalik Group, Northern Pakistan

Cited by 57 publications

References 29 publications

Intra‐ and extrabasinal controls on fluvial deposition in the Miocene Indo‐Gangetic foreland basin, northern Pakistan

Intra‐ and extrabasinal controls on fluvial deposition in the Miocene Indo‐Gangetic foreland basin, northern Pakistan

Mesozoic‐Cenozoic evolution of the Xining‐Minhe and Dangchang basins, northeastern Tibetan Plateau: Magnetostratigraphic and biostratigraphic results

Sedimentary Magnetism, Environmental Magnetism, and Magnetostratigraphy

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