Proper species concepts of planktonic foraminifera are essential for paleo-environmental studies. Although subtle but key differences indicate the existence of sibling species, the quantitative ...morphological variability of foraminifera tests remains still poorly documented. We present morphological analyses of over 7500 oriented specimens of the subgenus Menardella (globorotalid foraminifera) at a time-slice at 3.2 Ma (Mid-Pliocene). Size, frequency distribution and linear test measurements were collected with an automated device, the robot AMOR. We performed morphometric investigations in a total of 19 samples distributed worldwide. Among formally established menardellid morpho-species, eight different morphotypes are recognized. The geographic variation in morphotype abundance allows for the recognition of five menardellid provinces among the tropical Atlantic, Indian and Pacific Ocean. Results suggest that during the Mid-Pliocene, the formal morpho-species Globorotalia (Menardella) menardii is in fact composed of two distinct morphotypes, which differ in size range, morphological variability and biogeography. Morphological characterization of the morpho-species Globorotalia (M.) multicamerata reveals the occurrence of three distinct morphotypes, which may represent an adaptation to their vertical distribution in the water column.
•The morphological diversity of Pliocene menardellid is studied in a 3.2Ma time slice.•We examine 19 ODP sites distributed worldwide using an automated device.•We investigate test size and morphology to define menardellid morphotypes.•Eight different morphotypes are recognized, showing specific biogeography.•The morpho-species G. menardii is composed of two distinct morphotypes.
A beach deposit on the southern end of the Baudo Mountain Range, at an elevation of ∼2.0 m above the backshore of the modern beach, was dated at ∼2870 years using optically stimulated luminescence ...dating. The calculated average uplift rate necessary to raise this deposit is 0.7 mm/yr. This rate combines the long-term regional deformation associated with the subduction of the Nazca Plate under the South American Plate and the collision of the Choco Block microplate against the South American continent, as well as uplift from local faults. We propose that rapid emergence probably as several pulses, each involving decimeter scale coseismic uplift, is likely to have occurred to elevate the beach above the intertidal zone and offset destructive wave erosion.
•A raised beach at ∼2.0 m above the backshore of the modern beach was osl dated at ∼2870 yrs.•An average uplift rate of 0.7 mm/yr was calculated to raise the beach above the intertidal zone.•The uplift rate includes both a regional and a local component.•Shallow focus, ≥Magnitude 6.5 earthquakes close to the coast can produce coseismic uplift.•The uplift rate is representative of the Holocene for the southern Baudo Range.
Interpretation of industrial multichannel seismic profiles and well data are used to identify the main tectonic features of the Gulf of Guayaquil (GG) area. These include two E‐W trending major ...detachments: the Posorja and the Jambelí detachment systems, which represent half grabens with oppositely dipping detachments, to the south and to the north, respectively. The NE‐SW trending Puná‐Santa Clara fault system developed as a transfer fault system between the Posorja and the Jambelí detachments. The Esperanza and the Jambelí basins exhibit 3–4 km of sediment that accumulated during the past 1.6–1.8 Myr. The Puná‐Santa Clara fault system bounds the Esperanza and the Jambelí basins, evidencing that the evolution of these basins is tightly controlled by the two detachments at depth. To the west, the N‐S trending Domito fault system bounding the Posorja detachment system and the Esperanza basin to the west acted as a transfer zone between the shelf area and the continental slope. The Pliocene series show no significant variations in thickness throughout the Gulf of Guayaquil area suggesting that no important tectonic deformation occurred from 5.2 to 1.8–1.6 Ma. The major period of tectonic deformation in the Gulf of Guayaquil area occurred during the Pleistocene times. Three main tectonic steps are identified. From early Pleistocene to ∼180 ka, major subsidence occurred along the Esperanza and Jambelí basins. From ∼180 to ∼140 ka, most of the Gulf of Guayaquil area was above sea level during the isotope substage 6 low stand. From ∼140 ka to Present, tectonic activity is restricted along the normal faults bounding the Esperanza basin, the Tenguel fault, and the Puná‐Santa Clara and Domito fault systems. A N‐S trending tensional stress regime characterizes the Pleistocene times throughout. The northward drifting of the North Andean block is proposed to control the tectonic evolution and associated subsidence of the Gulf of Guayaquil area. It is also accepted that the collision of the Carnegie ridge with the trench axis has to play a major role in controlling the North Andean block northward drift. Because the Carnegie ridge subduction is possibly an ongoing process, which began prior to the Pliocene, we postulate the along‐strike morphology of the ridge at the origin of interplate coupling variations. The subduction of an along‐strike positive relief of the ridge is proposed at the origin of the major tectonic reorganization of the GG area occurring at ∼1.8–1.6 Ma.
The Antiñir‐Copahue fault zone (ACFZ) is the eastern orogenic front of the Andes between 38° and 37°S. It is formed by an east vergent fan of high‐angle dextral transpressive and transtensive faults, ...which invert a Paleogene intra‐arc rift system in an out of sequence order with respect to the Cretaceous to Miocene fold and thrust belt. 3.1–1.7 Ma volcanic rocks are folded and fractured through this belt, and recent indicators of fault activity in unconsolidated deposits suggest an ongoing deformation. In spite of the absence of substantial shallow seismicity associated with the orogenic front, neotectonic studies show the existence of active faults in the present mountain front. The low shallow seismicity could be linked to the high volumes of retroarc‐derived volcanic rocks erupted through this fault system during Pliocene and Quaternary times. This thermally weakened basement accommodates the strain of the Antiñir‐Copahue fault zone, absorbing the present convergence between the South America and Nazca plates.
The slip distribution of the 12 November 1996, Mw = 7.7, Peru earthquake is determined using broadband teleseismic waveforms, a differential SAR interferogram (interferometric synthetic aperture ...radar InSAR), and a fault parametrization allowing slip and rupture velocity to vary along the rupture plane. Both data sets are inverted jointly to limit the trade‐off between the space and time aspects of the rupture. The earthquake fault plane is located at the subduction interface; it strikes parallel to the trench and dips 30° NE. By inverting synthetic data, we show how the InSAR and teleseismic data are complementary and how the joint inversion produces a gain in the spatial and temporal resolution of the slip model, even with a SAR interferogram that covers only part of the coseismic deformation. The rupture of the 1996 Peru event initiated on the southern flank of the subducted Nazca ridge and propagated unilaterally toward the southeast (along strike) for more than 100 km at a depth between 20 and 40 km. The area of maximum slip (6–7 m) is located 50 km southeast of the hypocenter. The total seismic moment is 4.4 × 1020 N m (our joint inversion). The source time function is approximately 60 s long and presents three major pulses of moment release. The dominant one, which occurred between 30 and 45 s, does not correspond to the area of largest slip but to the rupture of a wide zone located about 100 km away from the hypocenter where slip reaches only 2–3 m. Computed coseismic coastal uplift correlates well with the location of raised marine terraces and with the topography of the coastal cordillera, suggesting that these features may be related to the repetition of 1996‐type events at the interface between the Nazca ridge and the South American plate.
Nazca Trophy Head Vessel
How They Lived : An Annotated Tour of Daily Life through History in Primary Sources: Ancient and Medieval World,
2016
Reference
Convergent margins often exhibit spatial and temporal correlations between trench curvature, overriding plate shortening and topography uplift that provide insights into the dynamics of subduction. ...The Andean system, where the Nazca plate plunges beneath continental South America, is commonly regarded as the archetype of this class of tectonics systems. There is distinctive evidence that the degree of mechanical coupling between converging plates, i.e. the amount of resistive force mutually transmitted in the direction opposite to their motions, may be at the present-day significantly higher along the central Andean margin compared to the northern and southern limbs. However quantitative estimates of such resistance are still missing and would be desirable. Here we present laboratory models of subduction performed to investigate quantitatively how strong lateral coupling variations need to be to result in trench curvature, tectonic shortening and distribution of topography comparable to estimates from the Andean margin. The analogue of a two-layers Newtonian lithosphere/upper mantle system is established in a silicone putty/glucose syrup tank-model where lateral coupling variations along the interface between subducting and overriding plates are pre-imposed. Despite the simplicity of our setup, we estimate that coupling in the central margin as large as 20% of the driving force is sufficient to significantly inhibit the ability of the experimental overriding plate to slide above the subducting one. As a consequence, the central margin deforms and shortens more than elsewhere while the trench remains stationary, as opposed to the advancing lateral limbs. This causes the margin to evolve into a peculiar shape similar to the present-day trench of the Andean system.
► We employ analog models of subduction. ► We investigate the effect of mechanical-coupling gradients of trench curvature, shortening and uplift of the overriding plate. ► These observations along the Andean margin may be reconciled by strong gradient of mechanical coupling in the present-day.
High‐precision relocations of intermediate‐depth earthquakes (80–130 km) below the Central Andes reveal a fine‐scale double‐layered Wadati‐Benioff zone (WBZ). Upper and lower band of seismicity are ...separated by about 9 km and occur at the top of the oceanic crust and in the uppermost oceanic mantle, respectively. Analysis of focal mechanisms and waveform similarities indicate that fluid processes are causing the events. Earthquakes in the oceanic crust occur on pre‐existing normal faults due to hydraulic embrittlement from metamorphic dehydration, and on subvertical faults that connect the two layers in a narrow depth range. Extensional faulting predominates in both layers, indicating that slab pull forces are the dominant stress source superseding possible unbending forces in this segment of the Nazca plate.
PDF
