Tectonic controls on Quaternary landscape evolution in the Ventura basin, southern California, USA, quantified using cosmogenic isotopes and topographic analyses

The quantification of rates for the competing forces of tectonic uplift and erosion has important implications for understanding topographic evolution. Here, we quantify the complex interplay between tectonic uplift, topographic development, and erosion recorded in the hanging walls of several active reverse faults in the Ventura basin, southern California, USA. We use cosmogenic 26Al/10Be isochron burial dating and 10Be surface exposure dating to construct a basin-wide geochronology, which includes burial dating of the Saugus Formation: an important, but poorly dated, regional Quaternary strain marker. Our ages for the top of the exposed Saugus Formation range from 0.36 +0.18/−0.22 Ma to 1.06 +0.23/−0.26 Ma, and our burial ages near the base of shallow marine deposits, which underlie the Saugus Formation, increase eastward from 0.60 +0.05/−0.06 Ma to 3.30 +0.30/−0.41 Ma. Our geochronology is used to calculate rapid long-term reverse fault slip rates of 8.6−12.6 mm yr−1 since ca. 1.0 Ma for the San Cayetano fault and 1.3−3.0 mm yr−1 since ca. 1.0 Ma for the Oak Ridge fault, which are both broadly consistent with contemporary reverse slip rates derived from mechanical models driven by global positioning system (GPS) data. We also calculate terrestrial cosmogenic nuclide (TCN)-derived, catchment-averaged erosion rates that range from 0.05−1.14 mm yr−1 and discuss the applicability of TCN-derived, catchment-averaged erosion rates in rapidly uplifting, landslide-prone landscapes. We compare patterns in erosion rates and tectonic rates to fluvial response times and geomorphic landscape parameters to show that in young, rapidly uplifting mountain belts, catchments may attain a quasi-steady-state on timescales of <105 years even if catchment-averaged erosion rates are still adjusting to tectonic forcing.

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.

Carbon and oxygen stable isotope record of upper Kimmeridgian shallow-marine ramp carbonates (Iberian Basin, NE Spain): the imprint of different burial and tectonic histories

Bulk carbon and oxygen stable isotopes of ancient shallow-marine carbonates can record the effects of multiple palaeoenvironmental factors, but also the imprint of several post-depositional processes, which may alter the original marine isotopic composition. In this study, carbon and oxygen stable isotope analyses were performed on bulk carbonate, bivalve calcitic-shell (Trichites) and calcite vein samples from two stratigraphic sections (Tosos and Fuendetodos, present-day distance 15km), representing proximal inner- and distal mid-ramp environments, respectively, of the uppermost Kimmeridgian ramp facies deposited in the northern Iberian Basin (NE Spain). These successions underwent different diagenetic pathways that altered the primary marine isotopic composition in each section in different ways. Different burial histories, tectonic uplift and a variable exposure to meteoric diagenesis from the end of the Kimmeridgian to the Cenozoic (following Alpine tectonic uplift) are reflected in the different alteration patterns of the carbon and oxygen stable isotope signatures. A significant deviation to lower values in both δ13O and δ18O is recorded in those carbonates mostly exposed to meteoric diagenesis (distal mid-ramp Fuendetodos section), because of post-depositional tectonic uplift (telogenesis). On the other hand, the deposits mainly affected by burial diagenesis (proximal inner-ramp Tosos section) only record low δ18O with respect to expected values for pristine Kimmeridgian marine carbonates. The different burial and tectonic uplift histories of these deposits in each sector, due to their different tectonic evolution in this part of the basin, resulted in a variable degree of diagenetic resetting. However, in spite of the different diagenetic resetting reported of the carbon and oxygen stable isotope signatures in each section, these carbonates show similar cement types in termsof fabrics and cathodoluminescence properties. The diagenetic resetting reported for these carbonates prevents the use of the δ13O and δ18O records for addressing palaeoenvironmental interpretations, but instead highlights useful features regarding the variable diagenetic overprint of the studied shallow-marine carbonate successions concerning their specific post-depositional history.

Age constraints on surface deformation recorded by fossil shorelines at Cape Range, Western Australia: Comment

Sandstrom et al. (2020) present new elevation and age data for a flight of four marine terraces preserved along the western limb of the Cape Range anticline in western Australia. Their interpretation of these data provides an alternative estimate for the amount of tectonic deformation that has occurred since terrace formation. They conclude that less tectonic uplift has occurred in the region than previously reported and posit that their study provides a template for reducing the uncertainty associated with last interglacial paleoshoreline reconstructions.

Late Cenozoic Erosion in New Zealand

<p>Uplift and erosion are roughly equal in the Southern Alps of New Zealand and the following rates have been determined: tectonic uplift 620 +/- 20 Mt y^-1, river load 700 +/- 200 Mt y^-1, offshore deposition 580 +/- 110 Mt y^-1. The tectonic uplift is the result of oblique collision between the Indian and Pacific plates, with the edge of the Pacific plate being upturned and uplifted as the Southern Alps, crustal narrowing of 22 mm y^-1 being converted to uplift along a curved fault plane. Almost all rock eroded from the Southern Alps is carried as suspended load by rivers. River bedload is of minor importance, and its abrasion adds to the suspended load. The estimated suspended load amounts to 265 Mt y^-1, but with a single exception only normal load have been sampled, and the additional abnormal load from earthquake-caused landslips is estimated to double the normal load. The river load estimate is confirmed in part by spot checks from sediment accumulated in onshore traps. A model proposed for the growth of the Southern Alps from a peneplain shows that the range attained steady state about 1.5 My after uplift started. With uplift initial non steady state, flat topped mountains like those that remain in Otago, become steady state spiky mountains. The range as a whole is in steady state, though the individual mountains change. The offshore deposition rates agree with the river load and tectonic uplift estimates and thus provide substantial confirmation for the steady state model.</p>

Late Cenozoic Erosion in New Zealand

<p>Uplift and erosion are roughly equal in the Southern Alps of New Zealand and the following rates have been determined: tectonic uplift 620 +/- 20 Mt y^-1, river load 700 +/- 200 Mt y^-1, offshore deposition 580 +/- 110 Mt y^-1. The tectonic uplift is the result of oblique collision between the Indian and Pacific plates, with the edge of the Pacific plate being upturned and uplifted as the Southern Alps, crustal narrowing of 22 mm y^-1 being converted to uplift along a curved fault plane. Almost all rock eroded from the Southern Alps is carried as suspended load by rivers. River bedload is of minor importance, and its abrasion adds to the suspended load. The estimated suspended load amounts to 265 Mt y^-1, but with a single exception only normal load have been sampled, and the additional abnormal load from earthquake-caused landslips is estimated to double the normal load. The river load estimate is confirmed in part by spot checks from sediment accumulated in onshore traps. A model proposed for the growth of the Southern Alps from a peneplain shows that the range attained steady state about 1.5 My after uplift started. With uplift initial non steady state, flat topped mountains like those that remain in Otago, become steady state spiky mountains. The range as a whole is in steady state, though the individual mountains change. The offshore deposition rates agree with the river load and tectonic uplift estimates and thus provide substantial confirmation for the steady state model.</p>

Pore structural characteristics and methane adsorption capacity of transitional shale of different depositional and burial processes: a case study of shale from Taiyuan formation of the Southern North China basin

Pore structural characteristics and methane adsorption capacity are two significant aspects affecting shale gas potential, but the impact of deposition and burial processes on these two aspects is not clear. Hence, the shale samples of Taiyuan Formation deposited continuously and experienced multi-stage tectonic uplift in Fuyang-Bozhou area of Southern North China Basin were collected in this study. Based on the total organic carbon content analysis, mineral composition determination, low-pressure CO2 and N2 adsorption, high-pressure methane adsorption and argon ion polishing-field emission scanning electron microscope observation. The impact of depositional and burial processes variation on shale reservoir physical properties and adsorption performance is studied. The results display that the pore types of shale samples which were continues deposited and experienced multi-stage tectonic uplift have no obvious differences, while the pore volume as well as specific surface area (SSA) of micropores and mesopores of shale samples under multi-stage tectonic uplift are larger significantly. Meanwhile, the roughness of shale pores increases also. The decrease of loading pressure caused by multi-stage tectonic uplift may be the main factor for the pore structure changes of shale sample. Compared with the continuous deposited samples, the shale samples under multi-stage tectonic uplift have stronger methane adsorption capacity, which is relevant to the greater SSA of micropores as well as mesopores. This study provides an example and new revelation for the influence of depositional and burial processes on shale pore structure and methane adsorption capacity.

Alpine Rockwall Erosion Patterns Follow Elevation-Dependent Climate Trajectories

Mountainous topography reflects an interplay between tectonic uplift, crustal strength, and climate-conditioned erosion cycles. During glaciations, glacial erosion increases bedrock relief, whereas during interglacials relief is lowered by rockwall erosion. In the first landscape-scale, multi-process investigation of postglacial rockwall erosion patterns, we show that paraglacial, frost cracking and permafrost processes jointly drive rockwall erosion. Field observations and modelling experiments demonstrate that all three processes are strongly conditioned by elevation. Our findings provide a multi-process explanation for the increase of rockwall erosion rates with elevation across the European Alps. As alpine basins warm during deglaciation, changing intensities and elevation-dependent interactions between periglacial and paraglacial processes result in elevational shifts in rockwall erosion patterns. Future climate warming will shift the intensity and elevation distribution of these processes, resulting in overall lower erosion rates across the Alps, but with more intensified erosion at the highest topography most sensitive to climate change.

U-Pb speleothem geochronology reveals a major 6 Ma uplift phase along the western margin of Dead Sea Transform

The timing of vertical motions adjacent to the Dead Sea Transform plate boundary is not yet firmly established. We utilize laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb geochronology of carbonate cave deposits (speleothems) to constrain paleo-groundwater levels along the western margin of the Dead Sea Transform and provide a proxy for the timing of large-scale incision and tectonic uplift. Phreatic speleothems can form in caves that are located slightly below the groundwater level. Tectonic uplift and/or base level subsidence can trigger incision of canyons and induce a drop in the groundwater table. This can cause dewatering of the caves, cessation of the deposition of phreatic speleothems, and initiation of growth of vadose speleothems. The transition between deposition of phreatic and vadose speleothems can therefore reflect tectonic or erosive events. We obtained 102 U-Pb ages from 32 speleothems collected from three cave complexes across a 150-km-long, north-to-south transect. These ages indicate that phreatic deposition began between 14.68 ± 1.33 and 11.34 ± 1.62and ended by 6.21 ± 0.59 Ma. Later, vadose speleothems grew intermittently until the Quaternary. These results suggest an abrupt drop in the water table starting at ca. 6 Ma with no re-submergence of the caves. We interpret this to indicate river incision of ∼150−200 m that was driven by uplift and folding of the western margin of the Dead Sea Transform and by inland morpho-tectonic, base-level subsidence in the Dead Sea area. The observed timing corresponds with a change in the Euler pole of the plates motion along the Dead Sea Transform. The growth period of phreatic speleothems suggests groundwater level stability and limited vertical tectonic motions between 14 Ma and 6 Ma.

Geomorphologic Evolution of Northern Tibetan Plateau in the Quaternary: Tectonic and Climatic Controls

Situated in the northwestern Qinghai-Tibet Plateau, the Qaidam Basin is the largest Cenozoic terrestrial intermountain basin in the world. It is an ideal place for understanding the coupling control of tectonics and climate on sedimentary evolution. Although numerous studies on the Quaternary sedimentary evolution of the Qaidam Basin have been done, most of which are of local, conceptual and qualitative in nature. In this study, we investigated the entire Qaidam Basin and its surrounding mountains quantitatively as a single entity to probe the Quaternary evolution of the basin-range system in the northern Qinghai-Tibet Plateau. We used a Basin and Landscape Dynamics (Badlands) modeling algorithm that is capable of modeling landscape evolution by simulating erosion, sediment transport and deposition in a source-to-sink context by considering climate changes and tectonic uplift. We have simulated the evolution of the Qaidam Basin and its surrounding mountains since 2.5 Ma quantitatively. Both tectonic uplift and climate changes appear to have a direct impact on the denudation and deposition rates, but the impact varies through time. The deposition in the Qaidam Basin was mainly affected by tectonic movement during the period of 2.5 Ma to 0.6 Ma, reaching a maximum deposition thickness of 2130 m at the end of 0.6 Ma, but was prevailed by climate after 0.6 Ma during the last four glacials-interglacials, reaching a maximum deposition thickness of 3200 m. The Qilian Mountains and the Kunlun Mountains contributed the bulk sediments to the Qaidam Basin around 35% and 40%, respectively. The Altun Mountains made a significant contribution to the sediments in the Qaidam Basin during the early Quaternary from 2.5 Ma to 2.4 Ma due to a high denudation rate. The findings provide new insights for analyzing geomorphic and landscape evolution as well as source-to-sink systems in the Northern Qinghai-Tibet Plateau.