Short communication: Forward and inverse models relating river long profile to monotonic step-changes in tectonic rock uplift rate history: A theoretical perspective under a nonlinear slope-erosion dependency

The long profile of rivers is widely considered as a recorded of tectonic uplift rate. Knickpoints form in response to rate changes and faster rates produce steeper channel segments. However, when the exponent relating fluvial incision to river slope, n, is not unity, the links between tectonic rates and channel profile are complicated by channel dynamics that consume and form river segments. Here, we explore non-linear cases leading to channel segment consumption and develop a Lagrangian analytic model for knickpoint migration. We derive a criterion for knickpoint preservation and merging, and develop a forward analytic model that resolves knickpoint and long profile evolution before and after knickpoint merging. We further propose a linear inverse scheme to infer tectonic history from river profiles when all knickpoints are preserved. Our description provides a new framework to explore the links between tectonic uplift rates and river profile evolution when n is not unity.

Cosmogenic nuclide dating of the sediments of Bulmer Cavern: Implications for the uplift history of southern Northwest Nelson, South Island New Zealand

<p>The landscape of Northwest Nelson shows evidence of significant tectonic activity since the inception of the Austro-Pacific plate boundary in the Eocene. Evidence of subsidence followed by rapid uplift from the Eocene to the late Miocene is preserved in the sedimentary basins of Northwest Nelson. However, the effects of erosion mean there is very little evidence of post-Miocene tectonic activity preserved in the Northwest Nelson area. This is a period of particular interest, because it coincides with the onset of rapid uplift along the Alpine Fault, which is located to the south, and the very sparse published data for this period suggest very low uplift rates compared to other areas close to the Alpine Fault. Cosmogenic nuclide burial dating of sediments preserved in Bulmer Cavern, indicate an uplift rate of 0.13mm/a from the mid-Pliocene to the start of the Pleistocene and 0.067mm/a since the start of the Pleistocene. The Pleistocene uplift rate is similar to other published uplift rates for this period from the northern parts of Northwest Nelson, suggesting that the whole of Northwest Nelson has experienced relative tectonic stability compared to other areas close to the Alpine Fault during this period. The mid-Pliocene uplift rate is possibly the first precisely constrained uplift rate in the area for this period, and suggests that there has been a progressive decrease in uplift rates from much higher rates in the late Miocene.</p>

Cosmogenic nuclide dating of the sediments of Bulmer Cavern: Implications for the uplift history of southern Northwest Nelson, South Island New Zealand

<p>The landscape of Northwest Nelson shows evidence of significant tectonic activity since the inception of the Austro-Pacific plate boundary in the Eocene. Evidence of subsidence followed by rapid uplift from the Eocene to the late Miocene is preserved in the sedimentary basins of Northwest Nelson. However, the effects of erosion mean there is very little evidence of post-Miocene tectonic activity preserved in the Northwest Nelson area. This is a period of particular interest, because it coincides with the onset of rapid uplift along the Alpine Fault, which is located to the south, and the very sparse published data for this period suggest very low uplift rates compared to other areas close to the Alpine Fault. Cosmogenic nuclide burial dating of sediments preserved in Bulmer Cavern, indicate an uplift rate of 0.13mm/a from the mid-Pliocene to the start of the Pleistocene and 0.067mm/a since the start of the Pleistocene. The Pleistocene uplift rate is similar to other published uplift rates for this period from the northern parts of Northwest Nelson, suggesting that the whole of Northwest Nelson has experienced relative tectonic stability compared to other areas close to the Alpine Fault during this period. The mid-Pliocene uplift rate is possibly the first precisely constrained uplift rate in the area for this period, and suggests that there has been a progressive decrease in uplift rates from much higher rates in the late Miocene.</p>

Late Pleistocene Tephrostratigraphy of the Eastern Bay of Plenty Region, New Zealand

<p>This thesis has produced the compilation of a complete tephrostratigraphic record of the eastern Bay of Plenty, New Zealand. About fifty Late Pleistocene tephras (i.e. those older than the Rotoiti eruption), ranging in age from c. 600 to 50 ka, are recorded in a terrestrial sequence of loess and paleosols in the eastern Bay of Plenty. Tephra correlations are based on the distinctive physical characteristics of the airfall beds and confirmed by microprobe analysis of glass shards ("fingerprinting"). Chemical analysis of hornblendes and titanomagnetites is used as a supplementary correlation tool where the tephras are too weathered to retain glass. The eastern bay of Plenty deposits are divided into seven subgroups with their boundaries marked either by major tephras or by significant changes in the paleo-climate indicator deposits such as loess and paleosols. These subgroups, and their estimated age ranges, are: Age control on the eastern Bay of Plenty tephras has been obtained by fitting the paleoclimatic information inferred from field observations to the Low Latitude Stack (LLS) and SPECMAP oxygen isotope curves, with correlations to a few well dated eruptives providing key time planes within this record; in particular, the Mamaku Ignimbrite (correlates to the Kutarere Tephra), and the Kaingaroa (Kaingaroa), Matahina (Matahina) and Rangitaiki (Kohioawa) Ignimbrites. Tentative correlations of several eastern Bay of Plenty tephras to the western, coastal central, and Southeast-central Bay of Plenty areas (Tauranga Matata cliffs and Reporoa, respectively) have been achieved. Three additional subgroups are proposed: the Welcome Bay (with at least 6 tephras) in the west, the Ohinekoao (14 tephras) in the coastal central, and the Reihana (13 tephras) in the southeast-central Bay of Plenty; all of which overlap in time with the eastern Bay of Plenty stratigraphy. The tephras recorded in the Bay of plenty have been used to estimate the ages of formation and uplift rates for many of the landforms that are observed throughout the region. A tectonic regime of subsidence in the west towards Tauranga, block faulting on either side of the subsiding Whakatane Graben in the central Bay of Plenty, and further large scale block faulting towards the far eastern margin of the Bay of Plenty has been proposed. Activity at the Okataina Volcanic Centre is now thought to have initiated at or before c. 370 ka, with the eruption of the Paerata Tephra. This tephra has a distribution pattern consistent with an Okataina source, and contains abundant cummingtonite, which is a signature mineral within tephras from the Okataina Volcanic Centre during the late Quaternary time period. However, the much older, but less well understood, Reeves-A and Wilson Tephras - both with estimated ages of c. 0.5 Ma - also contain cummingtonite, which indicates that activity may have been initiation at a much earlier time, or that a volcanic centre other than Okataina has produced cummingtonite. Activity in the Rotorua Volcanic Centre prior to the eruption of the Mamaku Ignimbrite is also indicated, as is activity at the Reporoa Volcanic Centre prior to the Kaingaroa Ignimbrite eruption.</p>

Late Pleistocene Tephrostratigraphy of the Eastern Bay of Plenty Region, New Zealand

<p>This thesis has produced the compilation of a complete tephrostratigraphic record of the eastern Bay of Plenty, New Zealand. About fifty Late Pleistocene tephras (i.e. those older than the Rotoiti eruption), ranging in age from c. 600 to 50 ka, are recorded in a terrestrial sequence of loess and paleosols in the eastern Bay of Plenty. Tephra correlations are based on the distinctive physical characteristics of the airfall beds and confirmed by microprobe analysis of glass shards ("fingerprinting"). Chemical analysis of hornblendes and titanomagnetites is used as a supplementary correlation tool where the tephras are too weathered to retain glass. The eastern bay of Plenty deposits are divided into seven subgroups with their boundaries marked either by major tephras or by significant changes in the paleo-climate indicator deposits such as loess and paleosols. These subgroups, and their estimated age ranges, are: Age control on the eastern Bay of Plenty tephras has been obtained by fitting the paleoclimatic information inferred from field observations to the Low Latitude Stack (LLS) and SPECMAP oxygen isotope curves, with correlations to a few well dated eruptives providing key time planes within this record; in particular, the Mamaku Ignimbrite (correlates to the Kutarere Tephra), and the Kaingaroa (Kaingaroa), Matahina (Matahina) and Rangitaiki (Kohioawa) Ignimbrites. Tentative correlations of several eastern Bay of Plenty tephras to the western, coastal central, and Southeast-central Bay of Plenty areas (Tauranga Matata cliffs and Reporoa, respectively) have been achieved. Three additional subgroups are proposed: the Welcome Bay (with at least 6 tephras) in the west, the Ohinekoao (14 tephras) in the coastal central, and the Reihana (13 tephras) in the southeast-central Bay of Plenty; all of which overlap in time with the eastern Bay of Plenty stratigraphy. The tephras recorded in the Bay of plenty have been used to estimate the ages of formation and uplift rates for many of the landforms that are observed throughout the region. A tectonic regime of subsidence in the west towards Tauranga, block faulting on either side of the subsiding Whakatane Graben in the central Bay of Plenty, and further large scale block faulting towards the far eastern margin of the Bay of Plenty has been proposed. Activity at the Okataina Volcanic Centre is now thought to have initiated at or before c. 370 ka, with the eruption of the Paerata Tephra. This tephra has a distribution pattern consistent with an Okataina source, and contains abundant cummingtonite, which is a signature mineral within tephras from the Okataina Volcanic Centre during the late Quaternary time period. However, the much older, but less well understood, Reeves-A and Wilson Tephras - both with estimated ages of c. 0.5 Ma - also contain cummingtonite, which indicates that activity may have been initiation at a much earlier time, or that a volcanic centre other than Okataina has produced cummingtonite. Activity in the Rotorua Volcanic Centre prior to the eruption of the Mamaku Ignimbrite is also indicated, as is activity at the Reporoa Volcanic Centre prior to the Kaingaroa Ignimbrite eruption.</p>

The influence of rock uplift rate on the formation and preservation of individual marine terraces during multiple sea-level stands

Marine terraces are a cornerstone for the study of paleo sea level and crustal deformation. Commonly, individual erosive marine terraces are attributed to unique sea-level high stands based on the reasoning that marine platforms could only be significantly widened at the beginning of an interglacial. However, this logic implies that wave erosion is insignificant at other times. We postulate that the erosion potential at a given bedrock elevation datum is proportional to the total duration of sea-level occupation at that datum. The total duration of sea-level occupation depends strongly on rock uplift rate. Certain rock uplift rates may promote the generation and preservation of particular terraces while others prevent them. For example, at rock uplift of ~1.2 mm/yr, the Marine Isotope Stage (MIS) 5e (ca. 120 ka) high stand reoccupies the elevation of the MIS 6d–e mid-stand, favoring creation of a wider terrace than at higher or lower rock uplift rates. Thus, misidentification of terraces can occur if each terrace in a sequence is assumed to form uniquely at successive interglacial high stands and to reflect their relative elevations. Developing a graphical proxy for the entire erosion potential of sea-level history allows us to address creation and preservation biases at different rock uplift rates.

Nonrigid Bookshelf Kinematics of Northeastern Tibet: Constrains from Fault Slip Rates around the Qinghai Lake and Chaka-Gonghe Basins

The Elashan fault (ELSF) and Qinghainanshan fault (QHNF), two major faults developed around the Qinghai Lake and Chaka-Gonghe basins, are of great importance for investigating the deformation model of the internal northeastern Tibetan Plateau. However, their late Pleistocene slip rates remain poorly constrained. In this study, we combine high-resolution topography acquired from unmanned aerial vehicles (UAV) and geomorphological dating to calculate the slip rates of the two faults. We visited the central ELSF and western QHNF and measured displaced terraces and stream channels. We collected 10Be samples on the surface of terraces to constrain the abandonment ages. The dextral slip rate of the central segment of the Elashan fault is estimated to be 2.6±1.2 mm/yr. The uplift rates since the late Pleistocene of the Elashan and Qinghainanshan faults are 0.4±0.04 mm/yr and 0.2±0.03 mm/yr, respectively. Comparing the geological rates with the newly published global positioning system (GPS) rates, we find that the slip rates of the major strike-slip faults around the Qinghai Lake and Chaka-Gonghe basins are approximately consistent from the late Pleistocene to the present day. The overall NE shortening rates by summing up the geological slip rates on major faults between the East Kunlun and Haiyuan faults are ~3.4 mm/yr, smaller than the geodetic shortening rates (~4.9 to 6.4 mm/yr), indicating that distributed deformation plays an important role in accommodating the regional deformation. By analyzing the geometrical and kinematic characteristics of the major faults surrounding the basins, we suggest that the kinematic deformation of the internal northeastern Tibet is a nonrigid bookshelf model that consists of counterclockwise rotation (~0.8° Myr-1) and distributed thrusting.

Supplemental Material: Lateral variation in slab window viscosity inferred from global navigation satellite system (GNSS)–observed uplift due to recent mass loss at Patagonia ice fields

Modeling method, Table S1 (newly obtained uplift rates for the ten continuous GNSS sites shown in Figure1A),Table S2 (slab window viscosity values and RMS data), supplemental figures, and the weekly solutions for GNSS data used in the study.<br>

Supplemental Material: Lateral variation in slab window viscosity inferred from global navigation satellite system (GNSS)–observed uplift due to recent mass loss at Patagonia ice fields

Modeling method, Table S1 (newly obtained uplift rates for the ten continuous GNSS sites shown in Figure1A),Table S2 (slab window viscosity values and RMS data), supplemental figures, and the weekly solutions for GNSS data used in the study.<br>