Tectonic vs. climate forcing in the Cenozoic sedimentary evolution of a foreland basin (Eastern Southalpine system, Italy)

This paper discusses the Cenozoic interaction of regional tectonics and climate changes. These processes were responsible for mass flux from mountain belts to depositional basins in the eastern Alpine retro‐foreland basin (Venetian–Friulian Basin). Our discussion is based on the depositional architecture and basin‐scale depositional rate curves obtained from the decompacted thicknesses of stratigraphic units. We compare these data with the timing of tectonic deformation in the surrounding mountain ranges and the chronology of both long‐term trends and short‐term high‐magnitude (‘aberrant’) episodes of climate change. Our results confirm that climate forcing (and especially aberrant episodes) impacted the depositional evolution of the basin, but that tectonics was the main factor driving sediment flux in the basin up to the Late Miocene. The depositional rate remained below 0.1 mm year^?1 on average from the Eocene to the Miocene, peaking at around 0.36 mm year^?1, during periods of maximum tectonic activity in the eastern Southern Alps. This dynamic strongly changed during the Pliocene–Pleistocene, when the basin‐scale depositional rate increased to an average of 0.26 mm year^?1 (Pliocene) and 0.73 mm year^?1 (Pleistocene). This result fits nicely with the long‐term global cooling trend recorded during this time interval. Nevertheless, we note that the timing of the observed increase may be connected with the presumed onset of major glaciations in the southern flank of the Alps (0.7–0.9 Ma), the acceleration of the global cooling trend (since 3–4 Ma) and climate variability (in terms of magnitude and frequency). All these factors suggest that combined high‐frequency and high‐magnitude cooling–warming cycles are particularly powerful in promoting erosion in mid‐latitude mountain belts and therefore in increasing the sediment flux in foreland basins.     

Chronology and tectonic controls of Late Tertiary deposition in the southwestern Tian Shan foreland, NW China

Magnetostratigraphy from the Kashi foreland basin along the southern margin of the Tian Shan in Western China defines the chronology of both sedimentation and the structural evolution of this collisional mountain belt. Eleven magnetostratigraphic sections representing ～13 km of basin strata provide a two‐ and three‐dimensional record of continuous deposition since ～18 Ma. The distinctive Xiyu conglomerate makes up the uppermost strata in eight of 11 magnetostratigraphic sections within the foreland and forms a wedge that thins southward. The basal age of the conglomerate varies from 15.5±0.5 Ma at the northernmost part of the foreland, to 8.6±0.1 Ma in the central (medial) part of the foreland and to 1.9±0.2, ～1.04 and 0.7±0.1 Ma along the southern deformation front of the foreland basin. These data indicate the Xiyu conglomerate is highly time‐transgressive and has prograded south since just after the initial uplift of the Kashi Basin Thrust (KBT) at 18.9±3.3 Ma. Southward progradation occurred at an average rate of ～3 mm year^?1 between 15.5 and 2 Ma, before accelerating to ～10 mm year^?1. Abrupt changes in sediment‐accumulation rates are observed at 16.3 and 13.5 Ma in the northern part of the foreland and are interpreted to correspond to southward stepping deformation. A subtle decrease in the sedimentation rate above the Keketamu anticline is determined at ～4.0 Ma and was synchronous with an increase in sedimentation rate further south above the Atushi Anticline. Magnetostratigraphy also dates growth strata at <4.0, 1.4±0.1 and 1.4±0.2 Ma on the southern flanks the Keketamu, Atushi and Kashi anticlines, respectively. Together, sedimentation rate changes and growth strata indicate stepped migration of deformation into the Kashi foreland at least at 16.3, 13.5, 4.0 and 1.4 Ma. Progressive reconstruction of a seismically controlled cross‐section through the foreland produces total shortening of 13–21 km and migration of the deformation front at 2.1–3.4 mm year^?1 between 19 and 13.5 Ma, 1.4–1.6 mm year^?1 between 13.5 and 4.0 Ma and 10 mm year^?1 since 4.0 Ma. Migration of deformation into the foreland generally causes (1) uplift and reworking of basin‐capping conglomerate, (2) a local decrease of accommodation space above any active structure where uplift occurs, and hence a decrease in sedimentation rate and (3) an increase in accumulation on the margins of the structure due to increased subsidence and/or ponding of sediment behind the growing folds. Since 5–6 Ma, increased sediment‐accumulation (～0.8 mm year^?1) and gravel progradation (～10 mm year^?1) rates appear linked to higher deformation rates on the Keketamu, Atushi and Kashi anticlines and increased subsidence due to loading from both the Tian Shan and Pamir ranges, and possibly a change in climate causing accelerated erosion. Whereas the rapid (～10 mm year^?1) progradation of the Xiyu conglomerate after 4.0 Ma may be promoted by global climate change, its overall progradation since 15.5 Ma is due to the progressive encroachment of deformation into the foreland.     

Tectono-sedimentary processes along an active marine/lacustrine half-graben margin: Alkyonides Gulf, E. Gulf of Corinth, Greece

ABSTRACT The Alkyonides half‐graben is separated from the Gerania Range to the south by active faults whose offshore traces are mapped in detail. The East Alkyonides and Psatha Faults have well‐defined, Holocene‐active tip zones and cannot be extrapolated from the onshore Skinos Fault into a single continuous surface trace. During the late Quaternary, catchments draining the step‐faulted range front have supplied sediment to alluvial fans along a subsiding marine ramp margin in the hangingwall of the Skinos Fault, to shelf ledge fans on the uplifting footwall to the East Alkyonides Fault and to the Alepochori submarine fan in the hangingwall of the latter. During late Pleistocene lowstand times (c. 70–12 ka), sediment was deposited in Lake Corinth as fan deltas on the subsiding Skinos shelf ramp which acted as a sediment trap for the adjacent 360 m deep submarine basin plain. At the same time, the uplifting eastern shelf ledge was exposed, eroded and bypassed in favour of deposition on the Alepochori submarine fan. During Holocene times, the Skinos bajada was first the site of stability and soil formation, and then of substantial deposition before modern marine erosion cut a prominent cliffline. The uplifting eastern shelf ledge has developed substantial Holocene fan lobe depositional sequences as sediment‐laden underflows have traversed it via outlet channels. We estimate mean Holocene displacement rates towards the tip of the Psatha Fault in the range 0.7–0.8 mm year^?1. Raised Holocene coastal notches indicate that this may be further partitioned into about 0.2 mm year^?1 of footwall uplift and hence 0.5–0.6 mm year^?1 of hangingwall subsidence. Holocene displacement rates towards the tip of the active East Alkyonides Fault are in the range 0.2–0.3 mm year^?1. Any uplift of the West Alkyonides Fault footwall is not keeping pace with subsidence of the Skinos Fault hangingwall, as revealed by lowstand shelf fan deltas which show internal clinoforms indicative of aggradational deposition in response to relative base‐level rise due to active hangingwall subsidence along the Skinos Fault. Total subsidence here during the last 58 kyr lowstand interval of Lake Corinth was some 20 m, indicating a reduced net displacement rate compared to estimates of late Holocene (< 2000 bp ) activity from onshore palaeoseismology. This discrepancy may be due to the competition between uplift on the West Alkyonides Fault and subsidence on the onshore Skinos Fault, or may reflect unsteady rates of Skinos Fault displacement over tens of thousands of years.     

The sedimentary and tectonic evolution of the Amur River and North Sakhalin Basin: new evidence from seismic stratigraphy and Neogene–Recent sediment budgets

The North Sakhalin Basin in the western Sea of Okhotsk has been the main site of sedimentation from the Amur River since the Early Miocene. In this article, we present regional seismic reflection data and a Neogene–Recent sediment budget to constrain the evolution of the basin and its sedimentary fill, and consider the implications for sediment flux from the Amur River, in particular testing models of continental‐scale Neogene drainage capture. The Amur‐derived basin‐fill history can be divided into five distinct stages: the first Amur‐derived sediments (>21–16.5 Ma) were deposited during a period of transtension along the Sakhalin‐Hokkaido Shear Zone, with moderately high sediment flux to the basin (71 Mt year^?1). The second stage sequence (16.5–10.4 Ma) was deposited following the cessation of transtension, and was characterised by a significant reduction in sediment flux (24 Mt year^?1) and widespread retrogradation of deltaic sediments. The third (10.4–5.3 Ma) and fourth (5.3–2.5 Ma) stages were characterised by progradation of deltaic sediments and an associated increase in sediment flux (48–60 Mt year^?1) to the basin. Significant uplift associated with regional transpression started during this time in southeastern Sakhalin, but the north‐eastward propagating strain did not reach the NE shelf of Sakhalin until the Pleistocene (<2.5 Ma). This uplift event, still ongoing today, resulted in recycling of older deltaic sediments from the island of Sakhalin, and contributed to a substantially increased total sediment flux to the adjacent basinal areas (165 Mt year^?1). Adjusted rates to discount these local erosional products (117 Mt year^?1) imply an Amur catchment‐wide increase in denudation rates during the Late Pliocene–Pleistocene; however, this was likely a result of global climatic and eustatic effects, combined with tectonic processes within the Amur catchment and possibly a smaller drainage capture event by the Sungari tributary, rather than continental‐scale drainage capture involving the entire upper Amur catchment.     

Miocene–Recent tectonic and climatic controls on sediment supply and sequence stratigraphy: Canterbury basin, New Zealand

The well‐constrained seismic stratigraphy of the offshore Canterbury basin provides the opportunity to investigate long‐term changes in sediment supply related to the formation of a transpressive plate boundary (Alpine Fault). Reconstructions of the relative motion of the Australian and Pacific plates reveal divergence in the central Southern Alps prior to ～20.1 Ma (chron 6o), followed by increasing average rates of convergence, with a marked increase after ～6 Ma (late Miocene). A strike–slip component existed prior to 33.5 Ma (chron 13o) and perhaps as early as Eocene (45 Ma). However, rapid strike–slip motion (>30 mm yr^?1) began at ～20.1 Ma (chron 6o). Since ～20.1 Ma there has been no significant change in the strike–slip component of relative plate motion. Sedimentation rates are calculated from individual sequence volumes that are then summed to represent sequence groups covering the same time periods as the tectonic reconstructions. Rates are relatively high (>22 mm yr^?1), from 15 to ～11.5 Ma (sequence group 1). Rates decrease to a minimum (<15 mm yr^?1) during the ～11.5–6 Ma interval (sequence group 2), followed by increased rates during the periods of ～6–2.6 Ma (21 mm yr^?1; group 3) and 2.6–0 Ma (～25 mm yr^?1; group 4). Good agreement between sedimentation and tectonic convergence rates in sequence groups 2–4 indicates that tectonism has been the dominant control on sediment supply to the Canterbury basin since ～11.5 Ma. In particular, high sedimentation rates of 21 and ～25 mm yr^?1 in groups 3 and 4, respectively, may reflect increased plate convergence and uplift at the Southern Alps at ～6 Ma. The early‐middle Miocene (～15–11.5 Ma) high sedimentation rate (22 mm yr^?1) correlates with low convergence rates (～2 mm yr^?1) and is mainly a response to global climatic and eustatic forcing.     

Tectonic evolution of the Himalaya constrained by detrital 40Ar–39Ar, Sm–Nd and petrographic data from the Siwalik foreland basin succession, SW Nepal

⁴⁰Ar–³⁹Ar dating of detrital white micas, petrography and heavy mineral analysis and whole‐rock geochemistry has been applied to three time‐equivalent sections through the Siwalik Group molasse in SW Nepal [Tinau Khola section (12–6 Ma), Surai Khola section (12–1 Ma) and Karnali section (16–5 Ma)]. ⁴⁰Ar–³⁹Ar ages from 1415 single detrital white micas show a peak of ages between 20 and 15 Ma for all the three sections, corresponding to the period of most extensive exhumation of the Greater Himalaya. Lag times of less than 5 Myr persist until 10 Ma, indicating Greater Himalayan exhumation rates of up to 2.6 mm year^?1, using one‐dimensional thermal modelling. There are few micas younger than 12 Ma, no lag times of less than 6 Myr after 10 Ma and whole‐rock geochemistry and petrography show a significant provenance change at 12 Ma indicating erosion from the Lesser Himalaya at this time. These changes suggest a switch in the dynamics of the orogen that took place during the 12–10 Ma period whereby most strain began to be accommodated by structures within the Lesser Himalaya as opposed to the Greater Himalaya. Consistent data from all three Siwalik sections suggest a lateral continuity in tectonic evolution for the central Himalayas.     

Pliocene onset of rapid exhumation in Taiwan during arc–continent collision: new insights from detrital thermochronometry

The Coastal Range in eastern Taiwan contains the remnants of the Pliocene–Pleistocene retro‐foredeep basin of the ongoing Penglai orogeny. These sedimentary successions record the earliest exhumation of the Central Range, Taiwan. We dated detrital Plio‐Pleistocene sediments in the Coastal Range using multiple thermochronometers [fission‐track, zircon (U–Th)/He and U/Pb dating] to document changes in exhumation rate through time. Fission‐track grain ages in 2–4‐Myr‐old sediments were not reset by the Penglai orogeny and reflect the early stage removal of the sedimentary cover. This early stage, when exhumation rates were low, could encompass both the accretionary wedge phase of the orogen and the early arc–continent collision. Sediments younger than 2‐Myr‐old yield Pliocene zircon fission‐track grain ages and suggest that exhumation, transport and deposition occurred within 0.4–1.5 Myr. The recorded onset of rapid exhumation in the Pliocene is contemporaneous with other major tectonic changes in the region, including an increase in subsidence rate in both the pro‐ and retro‐foredeep basins and a change in the wedge kinematics from internal shortening to underplating.     

The contribution of peat compaction to total basin subsidence: implications for the provision of accommodation space in organic‐rich deltas

Provision of accommodation space for aggradation in Holocene deltaic basins is usually ascribed to eustatic sea‐level rise and/or land subsidence due to isostasy, tectonics or sediment compaction. Whereas many Holocene deltas contain peat, the relative contribution of peat compaction to total subsidence has not yet been quantified from field data covering an entire delta. Subsidence due to peat compaction potentially influences temporal and spatial sedimentation patterns, and therefore alluvial architecture. Quantification of the amount and rate of peat compaction was done based on (1) estimates of the initial dry bulk density of peat, derived from a relation between dry bulk density and organic‐matter content of uncompacted peat samples and (2) radiocarbon‐dated basal peat used to reconstruct initial levels of peat formation of currently subsided peat samples. In the Rhine‐Meuse delta, peat compaction has contributed considerably to total basin subsidence. Depending on the thickness of the compressible sequence, weight of the overburden and organic‐matter content of peat, subsidence of up to approximately 3 m in a 10‐m thick Holocene sequence has been calculated. Calculated local subsidence rates of peat levels are up to 0.6 mm year^?1, averaged over millennia, which are twice the estimated Holocene‐averaged basin subsidence rates of 0.1–0.3 mm year^?1 in the study area. Higher rates of subsidence due to compaction, on the order of a few mm year^?1, occur over decades to centuries, following a substantial increase in effective stress caused by sediment loading. Without such an increase in effective stress, peat layers may accumulate for thousands of years with little compaction. Thus, the contribution of peat compaction to total delta subsidence is variable in time. Locally, up to 40% of total Holocene accommodation space has been provided by peat compaction. Implications of the large amount of accommodation space created by peat compaction in deltaic basins are: (1) increased sediment trap efficiency in deltas, which decelerates delta progradation and enhances the formation of relatively thick clastic sequences and (2) enhanced local formation of thick natural levees by renewing existing accommodation space.     

Early Tertiary evolution of the North Alpine Foreland Basin of the Swiss Alps and adjoining areas

We present a new palaeogeographic reconstruction of the Helvetic zone based on the palinspastic restoration of 18 recently published and new retrodeformed structural cross‐sections through the Swiss Alps, Haute Savoie (France) and Vorarlberg (Austria). The reconstruction resulted in two palaeogeographic maps, one of the pre‐Mesozoic basement, the other for the sedimentary cover of the Helvetic shelf including the Nummulitic deposits of the Palaeocene–Eocene, which mark the onset of the North Alpine Foreland Basin of the Alps. Based on the palaeogeographic maps and a precise dating of the Nummulitic deposits, we established maps of the facies distribution including the estimated positions of the ancient coastlines and their evolution through time. The North Alpine Foreland Basin started as a narrow flysch basin in Palaeocene–Eocene times. Emplacement of the Penninic nappes led to the formation of a mélange on the active margin of this basin. This early foreland basin and its active margin migrated to the NW in Early Eocene times at a rate of about 10 mm yr^?1. The maps also reveal a general progressive north‐ and westward propagation of the Eocene coastline between 50–34 Ma and during the Oligocene until approximately 32 Ma. Coastline propagation reveals strongly varying rates both spatially and temporally, and is ca. 1–2 mm yr^?1 between 50 and 37 Ma and approximately 20 mm yr^?1 between 37 and 32 Ma. Evolution and orientation of the Tertiary coastlines infers that the early development of the North Alpine Foreland Basin was mainly controlled initially by eustatic sea‐level fluctuations superimposed on flexural subsidence. After 37 Ma, we suggest a tectonically controlled coastline evolution in response to the collision of the European and Adriatic margins.     

Magnetic polarity stratigraphy of the Neogene foreland basin deposits of Nepal

The early Miocene Dumri Formation and middle Miocene–Pliocene Siwalik Group were deposited in the Himalayan foreland basin in response to uplift and erosion in the Himalayan fold‐thrust belt. We report magnetostratigraphic data from four sections of these rocks in Nepal. Three of these sections are in the Siwalik Group in the hanging wall of the Main Frontal thrust, and one section is from the Dumri Formation in the hanging wall of the Main Boundary thrust (MBT). Thermal demagnetization experiments demonstrate that laminated siltstones yield palaeomagnetic data useful for tectonic and magnetostratigraphic studies whereas other lithofacies yield data of questionable reliability. Magnetostratigraphic data have been acquired from 297 sites within a 4200‐m‐thick section of Siwalik deposits at Surai Khola. The observed sequence of polarity zones correlates with the geomagnetic polarity time scale (GPTS) from chron C5Ar.1n to chron C2r.2n, spanning the time frame ca. 12.5–2.0 Ma. At Muksar Khola (eastern Nepal), 111 palaeomagnetic sites from a 2600‐m‐thick section of the Siwalik Group define a polarity zonation that correlates with the GPTS from chron C4Ar.2n to chron C2Br.1r, indicating an age range of ca. 10.0–3.5 Ma. At Tinau Khola, 121 sites from a 1824‐m‐thick section of the Siwalik Group are correlated to chrons C5An.1n through C4r.1n, equivalent to the time span ca. 11.8–8.1 Ma. At Swat Khola, 68 sites within a 1200‐m‐thick section of lower Miocene Dumri Formation are correlated with chrons C6n through C5Bn.2n, covering the time span ca. 19.9–15.1 Ma. Together with previous results from Khutia Khola and Bakiya Khola, these data provide the first magnetostratigraphic correlation along nearly the entire NW–SE length of Nepal. The correlation demonstrates that major lithostratigraphic boundaries in the Siwalik Group are highly diachronous, with roughly 2 Myr of variability. In turn, this suggests that the major sedimentological changes commonly inferred to reflect strengthening of the Asian monsoon are not isochronous. Sediment accumulation curves exhibit a 30–50% increase in accumulation rate in four of the five sections of the Siwalik Group, but the timing of this increase ranges systematically from ～11.1 Ma in western Nepal to ～5.3 Ma in eastern Nepal. If this increase in sediment accumulation rate is interpreted as a result of more rapid subsidence owing to thrust loading in the Himalaya, then the diachroneity of this increase suggests lateral propagation of a major thrust system, perhaps the MBT, at a rate of ca. 103 mm year^?1 across the length of Nepal.     

Origin of the in situ stress field in south-eastern Australia

The in situ stress field of south‐eastern Australia inferred from earthquake focal mechanisms and bore‐hole breakouts is unusual in that it is characterised by large obliquity between the maximum horizontal compressive stress orientation (S_Hmax) and the absolute plate motion azimuth. The evolution of the neotectonic strain field deduced from historical seismicity and both onshore and offshore faulting records is used to address the origin of this unusual stress field. Strain rates derived from estimates of the seismic moment release rate (up to ～10^?16 s^?1) are compatible with Quaternary fault–slip rates. The record of more or less continuous tectonic activity extends back to the terminal Miocene or early Pliocene (10–5 Ma). Terminal Miocene tectonic activity was characterised by regional‐scale tilting and local uplift and erosion, now best preserved by unconformities in offshore basins. Plate‐scale stress modelling suggests the in situ stress field reflects increased coupling of the Australian and Pacific Plate boundary in the late Miocene, associated with the formation of the Southern Alps in New Zealand.     

Late Quaternary aggradation rates and stratigraphic architecture of the southern Po Plain,Italy

The Po River Basin, where accumulation and preservation of thick sedimentary packages are enhanced by high rates of tectonic subsidence, represents an ideal site to assess the relations between vertical changes in stratigraphic architecture and sediment accumulation rates. Based on a large stratigraphic database, a markedly contrasting stratigraphy of Late Pleistocene and Holocene deposits is reconstructed from the subsurface of the modern alluvial and coastal plains. Laterally extensive fluvial channel bodies and related pedogenically modified muds of latest Pleistocene age are unconformably overlain by Holocene overbank fines, grading seaward into paralic and nearshore facies associations. In the interfluvial areas, a stiff paleosol, dating at about 12.5–10 cal ky BP, marks the Pleistocene–Holocene boundary. Across this paleosol, aggradation rates (ARs) from 16 radiocarbon‐dated cores invariably show a sharp increase, from 0.1–0.9 mm year^?1 to 0.9–2.9 mm year^?1. Comparatively lower Pleistocene values are inferred to reflect fluvial activity under a low‐accommodation (lowstand and early transgressive) regime, whereas higher ARs during the Holocene are related to increasing accommodation under late transgressive and highstand conditions. Holocene sediment accumulation patterns vary significantly from site to site, and do not exhibit common trends. Very high accumulation rates (20–60 mm year^?1) are indicated by fluvial channel or progradational delta facies, suggesting that extremely variable spatial distribution of Holocene ARs was primarily controlled by autogenic processes, such as fluvial channel avulsion or delta lobe switching. Contrasting AR between uppermost Pleistocene and Holocene deposits also are reported from the interfluves of several coeval, alluvial‐coastal plain systems worldwide, suggesting a key control by allogenic processes. Sediment accumulation curves from adjacent incised valley fills show, instead, variable shapes as a function of the complex mechanisms of valley formation and filling.     

Faulting, seismic-stratigraphic architecture and Late Quaternary evolution of the Gulf of Alkyonides Basin–East Gulf of Corinth, Central Greece

Swath bathymetry, single‐channel seismic profiling, gravity and box coring, ²¹⁰Pb down‐core radiochemical analyses and sequence stratigraphic analysis in the Gulf of Alkyonides yielded new data on the evolution of the easternmost part of the Gulf of Corinth. Three fault segments, the South Strava, West Alkyonides and East Alkyonides faults, dipping 45, 30 and 45°, respectively, northwards, form the southern tectonic boundary of the Alkyonides Basin. Two 45° southwards dipping segments, the Domvrena and Germeno Faults, form the northern tectonic margin. The Alkyonides Basin architecture is the result of a complex interaction between fault dynamics and the effects of changes in climate and sea/lake level. Chrono‐stratigraphic interpretation of the seismic stratigraphy through correlation of the successive seismic packages with lowstands and highstands of the Late Quaternary indicates that the evolution of the basin started 0.40–0.45 Ma BP and can be divided in two stages. Subsidence of the basin floor during the early stage was uniform across the basin and the mean sedimentation rate was 1.0 m kyear^?1. Vertical slip acceleration on the southern tectonic margin since 0.13 Ma BP resulted in the present asymmetric character of the basin. Subsidence concentrated close to the southern margin and sedimentation rate increased to 1.4 m kyear^?1 in the newly formed depocentre of the basin. Actual (last 100 year) sedimentation rates were calculated to >2 mm year^?1, but are significantly influenced by the presence of episodic gravity flow deposits. Total vertical displacement of 1.1 km is estimated between the subsiding Alkyonides Basin floor and the uplifting Megara Basin since the onset of basin subsidence at a mean rate of 2.4–2.75 m kyear^?1, recorded on the East Alkyonides Fault. Gravity coring in the Strava Graben and in the lower northern margin of Alkyonides Basin proved the presence of whitish to olive grey laminated mud below thin marine sediments. Aragonite crystals and absence of the marine coccolithophora Emiliania huxleyi indicate sedimentation in lacustrine environment during the last lowstand glacial interval.     

Steady, balanced rates of uplift and erosion of the Santa Monica Mountains, California

Topographic change in regions of active deformation is a function of rates of uplift and denudation. The rate of topographic development and change of an actively uplifting mountain range, the Santa Monica Mountains, southern California, was assessed using landscape attributes of the present topography, uplift rates and denudation rates. Landscape features were characterized through analysis of a digital elevation model (DEM). Uplift rates at time scales ranging from 10⁴ to 10⁶ years were constrained with geological cross-sections and published estimates. Denudation rate was determined from sediment yield data from debris basins in southern California and from the relief of rivers set into geomorphic surfaces of known age. First-order morphology of the Santa Monica Mountains is set by large-scale along-strike variations in structural geometry. Drainage spacing, drainage geometry and to a lesser extent relief are controlled by bedrock strength. Dissection of the range flanks and position of the principal drainage divide are modulated by structural asymmetry and differences in structural relief across the range. Topographic and catchment-scale relief are ≈300–900 m. Mean denudation rate derived from the sediment yield data and river incision is 0.5±0.3 mm yr^?1. Uplift rate across the south flank of the range is ≈0.5±0.4 mm yr^?1 and across the north flank is 0.24±0.12 mm yr^?1. At least 1.6–2.7 Myr is required to create either the present topographic or the catchment-scale relief based on either the mean rates of denudation or uplift. Although the landscape has had sufficient time to achieve a steady-state form, comparison of the time-scale of uplift and denudation rate variation with probable landscape response times implies the present topography does not represent the steady-state form.     

Sedimentary evidence for late Messinian uplift of the SE margin of the Central Anatolian Plateau: Adana Basin,southern Turkey

The Adana Basin of southern Turkey, located at the SE margin of the Central Anatolian Plateau in the vicinity of the Arabia‐Eurasia collision zone, is ideally suited to record Neogene and Quaternary topographic and tectonic changes in the easternmost Mediterranean realm. On the basis of our correlation of 34 seismic reflection profiles with corresponding exposed units along the margins of the Adana Basin, we identify and characterize the seismic facies that corresponds to the upper part of the Messinian Handere Formation (ca. 5.45 to 5.33 Ma), which consists mainly of fluvial conglomerates and marls. The seismic reflection profiles indicate that ca. 1100 km³ of the Handere Formation upper sub‐unit is distributed over ca. 3000 km², reflecting local sedimentation rates of up to 12.5 mm year^?1. This indicates a major increase in both sediment supply and subsidence rates at ca. 5.45 Ma. Our provenance analysis of the Handere Formation upper sub‐unit based on clast counting and palaeocurrent measurements reveals that most of the sediment is derived from the Taurus Mountains at the SE margin of the Central Anatolian Plateau and regions farther north. A comparison of these results with the composition of recent fluvial conglomerates and the present‐day drainage basins indicates major changes between late Messinian and present‐day source areas. We suggest that these changes in drainage patterns and lithological characteristics result from uplift and ensuing erosion of the SE margin of the plateau. We interpret the tectonic evolution of the southern flank of the Anatolian Plateau and the coeval subsidence and sedimentation in the Adana Basin to be related to deep lithospheric processes, particularly lithospheric delamination and slab break‐off.     

Mechanisms of late Quaternary fault throw‐rate variability along the north central Gulf of Mexico coast: implications for coastal subsidence

Quaternary sea‐level cycles have caused dramatic depocentre shifts near the mouths of major rivers. The effects of these shifts on fault activity in passive margin settings is poorly known, as no studies have constrained passive margin fault throw‐rate variability over 10³ to 10⁵ year time scales. Here we present 11 mean throw rates for the Tepetate–Baton Rouge fault zone along the northern Gulf of Mexico coast in southern Louisiana. These data were obtained by optically stimulated luminescence dating over time scales spanning the last interglacial to the late Holocene. The mean throw rate is ca. 0.22 mm year^?1 during the late Holocene, ca. 0.03 mm year^?1 during the last glacial and at least 0.07 mm year^?1 during the last interglacial. Throw rates averaged over the late Pleistocene to present are spatially uniform within our study area. The temporal variability in throw rates suggests that shifts of the Mississippi River depocentre relative to this fault zone, driven by Quaternary sea‐level cycles, may have imposed a significant control on fault activity. The late Holocene throw rate is at least in the order of magnitude smaller than the rates of land‐surface subsidence in the Mississippi Delta, indicating that this fault zone is not a dominant contributor to subsidence in this region.     

The Pliocene‐Quaternary wedge‐top basins of southern Italy: an expression of propagating lateral slab tear beneath the Apennines

In recent years, contrasting seismic tomographic images have given rise to an extensive debate about the occurrence and implications of migrating slab detachment beneath southern Italy. One of the most pertinent aspects of this process is the concentration of the slab pull force, and particularly its surface expression in terms of vertical motions and related basin subsidence/uplift. In this study we focused on shallow‐water to continental, Pliocene‐Quaternary basins that formed on top of the Apennine allochthonous wedge after its emplacement onto a large foreland carbonate platform domain (Apulian Platform). Due to the thick‐skinned style of deformation controlling the Pliocene‐Pleistocene stages of continental shortening, a high degree of coupling with the downgoing plate appears to characterize the late tectonic evolution of the southern Apennines. Therefore, the wedge‐top basins analysed in this study, although occurring on the deformed edge of the overriding plate, are capable of recording deep geodynamic processes affecting the slab. Detailed stratigraphic work on these wedge‐top basins points to a progressive SE‐ward migration of basin subsidence from c. 4 to c. 2.8 Ma over a distance of about 140 km along the strike of the Apennine belt. Such a migration is consistent with a redistribution of slab‐pull forces associated with the progressive lateral migration at a mean rate in the range of 12–14 cm y^–1 of a slab tear within the down‐going Adriatic lithosphere. These results yield fundamental information on the rates of first‐order geodynamic processes affecting the slab, and on related surface response.     

The Late Cenozoic Eridanos delta system in the Southern North Sea Basin: a climate signal in sediment supply?

ABSTRACT The Eridanos fluvio‐deltaic system, draining most of north‐western Europe, developed during the Late Cenozoic as a result of simultaneous uplift of the Fennoscandian shield and accelerated subsidence in the North Sea Basin. This seismo‐stratigraphic study aims to reconstruct the large‐scale depositional architecture of the deltaic portion of the basin fill and relate it to external controls. A total of 27 units have been recognized. They comprise over 62×10³ km³ in the Southern North Sea Basin alone, and have an average delta surface area of 28×10³ km², which suggests that the size of the drainage area was about 1.1×10⁶ km². Water depth in the depocentre is seen to decrease systematically over time. This trend is interrupted by a deepening phase between 6.5 and 4.5 Ma that can be correlated with the simultaneous occurrence of increased uplift of the Fennoscandian shield, increased subsidence of the Southern North Sea Basin, and a long‐term eustatic highstand. All these observations point to a tectonic control on long‐term average rates of accommodation and supply. Controls on short‐term variations are inferred from variations in rates of sediment supply and bifurcation of the delta channel network. Both rates were initially low under warm, moist, relatively stable climate conditions. The straight wave‐dominated delta front gradually developed into a lobate fluvial‐dominated delta front. Two high‐amplitude sea‐level falls affected the Pliocene units, which are characterized by widespread delta‐front failures. Changes in relative sea level and climate became more frequent from the late Pliocene onward, as the system experienced the effects of glacial–interglacial transitions. Peaks in sedimentation and bifurcation rates were coeval with cold (glacial) conditions. The positive correlation between rates of supply and bifurcation on the one hand, and climate proxies (pollen and δ¹⁸O records) on the other hand is highly significant. The evidence presented in this study convincingly demonstrates the control of climate on time‐averaged sediment supply and channel‐network characteristics, despite the expected nonuniformity and time lags in system response. The presence of a clearly discernible climate signal in time‐averaged sediment supply illustrates the usefulness of integrated seismo‐stratigraphic studies for basin‐wide analysis of delta evolution on geological time scales.     

The interplay between deformation,erosion and sedimentation in the deep‐water Mexican Ridges foldbelt,western Gulf of Mexico basin

We analyse a regional 2D seismic section of the Mexican Ridges foldbelt (MRFB), western Gulf of Mexico, and construct excess‐area diagrams for each of the structures comprising the foldbelt to estimate shortening, the onset of folding and the degradation of the folded seafloor. From the chronostratigraphy, we derive rates of tectonic and superficial mass transport and illustrate how they change across the MRFB. The resulting tectonic transport in the MRFB is 11.8 km forming a train of twelve buckle folds above a detachment at a depth of ca. 6 s of two‐way travel time, with an average strain of ca. 10%. The fold train grew at a mean uplift rate of ca. 0.21 mm year^?1. Cross‐sectional balancing demonstrates that shortening balances the down‐slip motion of the Quetzalcoatl extensional system (QES), suggesting that horizontal compaction, volume loss and other penetrative deformation mechanisms are negligible. By assuming steady‐state denudation, we are able to distinguish sediments derived locally from sediments transported from distant sources. The constant of mass diffusivity, a parameter controlling the degradation rate, is ca. 0.42 m² year ^?1, which is characteristic of rapid, episodic, superficial mass movements. The combined sedimentation rate from both, local and distal sources is ca. 0.23 mm year ^?1. Those values are not constant; structures proximal to the continental shelf are rising rapidly and are being degraded more intensely than those in the distal part of the MRFB, where sedimentation outweighs tectonic uplift. Our results indicate deformation initiated up to 3 Myr earlier than estimated from stacking patterns. Moreover, we find deformation started synchronously during the Late Miocene throughout the MRFB and not in two episodes as the stacking relations suggest. The discrepancy can be explained by a delay in the sedimentary response to folding. During early fold growth, nearly constant thickness strata are deposited before a progressive unconformity and other converging geometries develop. The development of growth strata is fast in the folds near the QES, which are being uplifted rapidly and degraded vigorously. Under these conditions, the stratigraphic relations give only a broad estimate of the pretectonic/syntectonic limit when compared to the excess‐area method. On the other hand, the development of growth strata took twice as much time for folds near the abyssal plain, which are being uplifted at a slower rate and where degradation is less intense. Consequently, the delay takes more time, and the use of stratigraphic relations introduces an even more pronounced bias towards younger ages in the identification of the onset of folding.     

Tectonic and climatic control on growth and demise of the Phanh Rang Carbonate Platform offshore south Vietnam

The Phan Rang Carbonate Platform located offshore south Vietnam covers more than 15 000 km², making it one of the largest carbonate platforms in the South China Sea. Based on 2‐D seismic analysis, this paper outlines the platform evolution and analyzes the regional tectonic, climatic and oceanic factors that controlled the platform growth and demise. This study of the Phan Rang Carbonate Platform therefore provides an analogue to the regions late Neogene carbonates that form important targets for petroleum exploration. Platform growth initiated during the late middle Miocene along the open marine Vietnamese margin and continued throughout the late synrift to early postrift period of the area terminating around Pliocene time. During this period, the structural grain, local and regional tectonics as well as oceanographic effects exerted major controls on carbonate deposition. Optimal growth conditions existed during initial platform deposition and locally accumulation rates reached ca. 230 m Ma^?1. Late Miocene regional uplift caused subaerial exposure that interrupted platform growth and caused intense karstification. A gradual reestablishment of marine conditions promoted renewed platform growth. However, carbonate production was stressed by increased terrigenous input caused by onshore uplift and by inorganic nutrification of the surface waters. Nutrification probably occurred in response to increased nutrient influx derived from onshore denudation, enhanced periodically by soil ravinement during transgression. The onset or intensification of summer upwelling along the southern platform margin occurred in response to the onshore uplift and most likely contributed to the nutrification. The deteriorated growth conditions and fast subsidence resulted in platform split‐up, backstepping and local drowning. Subsequently, isolated platforms nucleated on structural highs as transgression continued. The remaining platforms thrived for a period but eventually failed to keep pace with subsidence, backstepped and drowned. The longest surviving platform now crops out at the seafloor at ca. 500 m depth.