bluuebunny/crossref_metadata_2025_split huggingface dataset:
Facies belts of the Middle America Trench and forearc region, southern Mexico: results from Leg 66 DSDP
Authors: Moore J. Casey , Watkins Joel S. , McMillen Kenneth J. , Bachman Stephen B. , Leggett Jeremy K. , Lundberg Neil , Shipley Thomas H. , Stephan Jean-Francois , Beghtel Floyd W. , Butt Arif , Didyk Borys M. , Niitsuma Nobuaki , Shephard Les E. , Stradner Herbert 
Published: May 2008

Summary

The Middle America Trench SE of Acapulco is flanked by a steep canyon-incised slope and narrow shelf, showing one of a variety of sedimentary facies patterns possible at convergent margins. Piston and drill cores from this region define eight facies belts including: (1) a pelagic facies of brown clay, (2) an outer slope mud facies, (3) a trench sand facies, (4) a foraminiferan-free facies on the lower slope, (5) a foraminiferan-bearing facies on the mid-slope, (6) a laminated mud facies on the upper slope, (7) a shelf facies of sand and mud, and (8) a canyon facies of sand and gravel. The superposition of trench and lower slope sediment during accretion results in a fining upward sequence reflecting a gradual uplift of the seafloor through the trench sediment-plume. The lower limit of the foraminiferan-bearing facies is defined by the absence of
in situ
calcareous foraminiferans and is controlled by the calcite compensation depth. The upper slope laminated mud facies probably reflects the depth range of the oxygen minimum zone.

In the Leg 66 area sedimentation rates are high in the trench and on the outer and lower slope, decrease on the mid-slope, and increase again on the shelf. On the inner shelf, waves and currents concentrate sand which funnels through a prominent submarine canyon, bypassing the mud-dominated slope and accumulating in the trench. A terrigenous sediment-plume generated by trench turbidity flow causes accelerated sediment accumulation to about 500 m above and 40 km seaward of the trench. The volume of material transported by the trench sediment-plume is five or six times greater than that moved by the shelf sediment-plume which supplies detritus to the shelf, upper slope and mid-slope environments.
Tectonic processes along the Middle America Trench inner slope
Authors: Shipley Thomas H. , Ladd John W. , Buffler Richard T. , Watkins Joel S. 
Published: May 2008

Summary
The relationship between sedimentation and structural variations observed in geophysical data provides insight into tectonic processes on the convergent Middle America Trench margin. We observe that some of the hemipelagic and pelagic oceanic sediments seem to continue relatively undeformed beneath the lowermost slope. Trench sediment bodies restricted to ponds in the vicinity of submarine canyons are incorporated into the lower slope by folding and thrust faulting. This offscraping (shallow accretion) at the base of the Middle America Trench slope appears at least partly dependent on the presence of trench fill. The internal structure of the so-called accretionary zone, the top of which is usually identified on seismic reflection profiles by a prominent zone of diffractions, is rarely resolved in the seismic reflection data. The shallow part of the accretionary zone along much of the margin may consist of deformed slope sediments since down-section increase in both folding and other deformation are observed in the seismic reflection and drill data. Beneath the undeformed and deformed slope sediments, offscraped trench fill may occur if trench fill was present in the ancient trench. The deeper part of the accretionary zone representing the bulk of the volume is not resolved in the reflection data but may consist of other sediments or crustal rocks added by an underplating process at deeper structural levels.
Sedimentation in different tectonic environments of the Middle America Trench, southern Mexico and Guatemala
Authors: McMillen Kenneth J. , Enkeboll Robert H. , Moore J. Casey , Shipley Thomas H. , Ladd John W. 
Published: May 2008

Summary
Late Pleistocene to Holocene sediment facies and composition within and bordering the Middle America Trench offshore southern Mexico and Guatemala reflect two distinctly different tectonic provinces. The truncated Mexican margin with crystalline rocks onshore and a narrow shelf exhibits a locally thick sandy trench fill. Sand mineralogy of quartz, feldspar, and biotite matches the onshore source terrane. The Guatemalan margin with a volcanic terrane onshore and a wide forearc basin show smaller amounts of predominantly muddy trench fill. Sand composition of volcanic rock fragments, plagioclase, and heavy minerals accurately reflects the volcanic source. Trench fill in both areas corresponds to submarine canyon location, and extensive bypassing of the slope occurs. The outer shelf contributes little sediment to the Mexican slope and trench, the main source being in the littoral zone and inner shelf. Conversely, most Guatemalan slope and trench sand has come from the shelf. Trench fill correlates best with onshore geology, with similar slope sediments in both areas. The Mexican margin with locally thick trench fill displays clear evidence of accretion, the Guatemalan margin with meagre trench fill apparently has not accreted lower plate sediments recently. Possibly, larger volumes of trench fill encourage accretion.
A summary of Deep Sea Drilling Project Leg 67 shipboard results from the Mid-America Trench transect off Guatemala
Authors: von Huene Roland , Aubouin Jean , Azema Jacques , Blackinton Grant , Carter Jerry A. , Coulbourn William T. , Cowan Darrel S. , Curiale Joseph A. , Dengo Carlos A. , Faas Richard W. , Harrison William , Hesse Reinhard , Hussong Donald M. , Ladd John W. , Muzylov Nikita , Shiki Tsunemasa , Thompson Peter R. , Westberg Jean 
Published: May 2008

Summary

The Middle America Trench off Guatemala was transected by 24-channel seismic reflection surveys, seismic-refraction surveys, and drilling with the
Glomar Challenger
. The drilling was done at three sites on the oceanic Cocos plate and four sites on the Caribbean plate. These plates converge at about 10 cm yr
−1
. At all drill sites sediment of upper Miocene to Quaternary age is almost entirely hemipelagic mud with interbedded thin volcanic ash, except in the trench where mud and fine sand turbidites less than 400 000 yr old are ponded. However, the underlying rocks are very different. On the oceanic Cocos plate a basal chalk sequence of lower and middle Miocene age is overlain by a thin section of abyssal clay. At a site only 3 km landward of the trench axis where drilling penetrated the slope deposits we recovered a Cretaceous to lower Miocene claystone sequence resting on a section containing igneous rock of continental affinity. A large net subduction of sediment along with ocean crust has occurred during the present (Miocene-Quaternary) episode of subduction and perhaps parts of the continental framework have been subducted as well. However, no current model satisfactorily explains the surprising occurrence of Cretaceous-Miocene claystone at the foot of the trench slope.
Cenozoic structure, stratigraphy and tectonics of the central Peru forearc
Authors: Kulm L. D. , Thornburg T. M. , Schrader H.-J. , Resig J. M. 
Published: May 2008

SummaryThe central Peru forearc (6°–14°S) is characterized by a variety of structural and tectonic styles. Continental shelf basins, Sechura, Salaverry, and East Pisco, are floored by a block faulted Precambrian to Palaeozoic massif and accumulated as much as 3 km of Cenozoic and probably Mesozoic sediment. The massif rises to form an Outer Shelf High (OSH) covered with disrupted Neogene strata. Structural and stratigraphic relationships suggest several pulses of uplift and subsidence for the massif with the most recent uplift detected on the positive massif features.Upper slope basins are cradled between the OSH and a seaward Upper Slope Ridge (USR) of deformed sediment. Late Eocene and younger clastic sediments, with minor limestone beds, occupy the eastern Trujillo Basin, whereas late Miocene to Pleistocene dolomicrite, micrite and glauconitic micrite are prominent in the western part of the basin. Both the Trujillo and Yaquina Basins (7°–9°30′S) exhibit severe internal disruption caused by compressional stresses. To the south, the Lima Basin (9°30′–13°S) contains similar carbonate lithologies, but this basin and underlying massif have subsided 275 to 500 m Ma−1since Pliocene-Pleistocene time, indicating tensional stresses.Geological and geophysical data show the subducting plate is rupturing by thrust faulting of layer 2 basalts which may form a sediment-basalt mélange in the overlying subduction complex. Because the seaward boundary of the arc massif is not well-defined, several forearc models are presented which allow the subduction complex to range in width from 15 to 60 km.The Peru forearc off Lima (12°S) exhibits many of the tectonic characteristics of the Japan forearc off Honshu, especially the subsiding slope basin and contemporaneous accreting subduction complex.
Forearc and other basins, continental margin of northern and southern Peru and adjacent Ecuador and Chile
Authors: Moberly R. , Shepherd G. L. , Coulbourn W. T. 
Published: May 2008

Summary
The continental margin between the Peru-Chile Trench and the west coast of South America is the type example of the Andean margin, where one of the two converging blocks of lithosphere is oceanic and the other is continental. Along Peru and Chile, basement at the coast and under the landward side of forearc basins is dominantly metamorphic and plutonic. Apparently, the edge of continental crust has been stoped away during subduction. The seaward side of basins may be structurally high dams of sediments accreted and deformed by subduction, or they may be horsts of continental basement. Subsurface mapping in the on-shore and off-shore oilfields of the forearc basin of north-western Peru has shown a mosaic of faulted blocks of tensional origin, overlain by low-angle gravity glides. Details of this faulting, however, cannot be seen on single- or multi-channel seismic records of forearc basins, even where they cross the fields. Off northern and southern Peru, forearc basins are separated from one another along strike by culminations of the basement; across strike there may be more than one forearc basin. The pattern of culminations and depressions may be inherited from structures of the oceanic crust and trench. Deeper seismic reflectors of the basins generally dip landward and converge seaward, and show progressive migration shoreward of the centres of deposition. Sediment movement into the basins and down the slopes is by turbidity currents and slumps. Subduction is an efficient process, removing about four-fifths of the trench sediments.
The Progreso Basin under the Gulf of Guayaquil owes its origin to a transform fault, the Dolores-Guayaquil megashear, oblique to the trench. It is a pull-apart basin or rhombochasm opened in the wake of the northward movement of a small plate. A forearc basin at Talara and the adjacent Progreso Basin have substantial hydrocarbon accumulations.
The geology of the western part of the Borbón Basin, North-west Ecuador
Authors: Evans C. D. R. , Whittaker J. E. 
Published: May 2008

Summary

The western part of the Borbón Basin, North-west Ecuador, contains some 5 km of predominantly thin-bedded Tertiary mudstones with rare shallow-water sand-stones, resting on a basement of Cretaceous basalts. The basin is floored by thin, discontinuous, turbiditic carbonates of middle Eocene age, which pass up into a 3 km thick sequence of mudstones, cherty at the base, extending into the mid-Miocene. Shallow-water sandstones accumulated during the late Miocene and early Pliocene and were succeeded by deeper water mudstones, which in the Pliocene, are over 1 km thick and contain resedimented sandstone units. The strata are folded into NE-SW-trending structures, parallel to the mid-slope basement high centred on the Río Verde area. Stratigraphic evidence suggests that much of this folding, and the emergence of the high, post-dates the late Pliocene (
c.
2.9 Ma).

Since the middle Eocene the area has occupied the arc-trench gap between the Ecuador-Colombia oceanic trench, and the volcanic arc of the Andes; it now lies on the oceanward side of the mid-slope basement high.
Ancient plate boundaries in the Bering Sea region
Authors: Marlow M. S. , Cooper A. K. , Scholl D. W. , McLean H. 
Published: May 2008

Summary
Plate tectonic models of the Bering Sea suggest that the abyssal Bering Sea Basin is underlain by oceanic crust, a supposition supported by refraction and magnetic data. The oceanic crust is thought to be a remnant of the Kula(?) plate that was isolated within what is now the Bering Sea when the proto-Aleutian arc began to form between the Alaska Peninsula and Kamchatka in late Mesozoic or earliest Tertiary times. Prior to the formation of the Aleutian arc, the Kula(?) plate moved NW, directly underthrusting eastern Siberia; the plate’s eastern edge either obliquely underthrust or slid past the Bering Sea margin along a transform boundary.
The Koryak Range in eastern Siberia is composed in part of mélange units that include Palaeozoic and Mesozoic allochthonous blocks juxtaposed within a matrix of Cretaceous sedimentary rocks. Structural trends suggest that these blocks were accreted into the Koryak area from the south along an ancient subduction zone formed by underthrusting of the Kula(?) plate.
The base of the Bering Sea continental margin that extends from eastern Siberia to the Alaska Peninsula—the so-called Beringian margin—is underlain by a thick (7–10 km) sedimentary section along the base of the slope. Rocks dredged from the basement exposed farther up the slope (1500–2000 m deep) include shallow-water Upper Jurassic sandstone that is unconformably overlain by shallow-water Eocene to Miocene diatomaceous mudstone. Fauna in the dredge samples indicate that the shelf edge has subsided several kilometres since late Palaeogene time, perhaps in response to the cessation of motion relative to the adjacent oceanic plate and subsequent sediment loading of the oceanic plate.
Uplift of the former plate boundary exposed in the Koryak Range occurred principally in late Cenozoic time, and collapse of the adjacent plate boundary, the Beringian margin, began in earliest Tertiary time and has continued to the present. Both tectonic events occurred after the site of active plate collision shifted south to near the present Aleutian Trench. We are uncertain as to why these two ancient, yet adjacent former plate boundaries should behave so differently, i.e. why one area was folded and uplifted while the other was extensionally deformed and subsided, both apparently in response to the cessation of convergent or strike-slip plate motion.
The Chugach Terrane, a Cretaceous trench-fill deposit, southern Alaska
Authors: Nilsen Tor H. , Zuffa Gian G. 
Published: May 2008

Summary
The Chugach terrane of southern Alaska extends for approximately 2000 km along the margin of the Gulf of Alaska. A seaward flysch facies of the terrane, the Chugach flysch terrane, represents the fill of a Late Cretaceous trench and consists of structurally deformed turbidites with some mafic volcanic rocks. It is intruded by anatectic granitic plutons of early Tertiary age. The Chugach flysch terrane in most places is bounded to the north by a landward-dipping thrust fault separating it from mélange of the Chugach terrane at least as young as Late Cretaceous. To the south the flysch terrane contains oceanic volcanic rocks and is bounded by faults that separate it from Palaeogene turbidites or upper Mesozoic metavolcanic rocks.
Interpretations of folds and faults in SW Alaska suggest that the Chugach terrane was deformed during NW-directed subduction. Palaeocurrents indicate primarily westward flow along the axis of the outcrop belt, and secondary southward transport. Turbidite facies associations indicate an east-to-west progression from inner-fan to middle-fan, outer-fan, fan-fringe and basin-plain deposits down the axis of the outcrop belt, and a bounding slope facies association to the north. Rock-fragment petrography of sandstone samples from the Chugach terrane indicates derivation from a magmatic arc that was increasingly dissected eastward and from an older subduction complex. The magmatic arc and adjacent shallow-marine forearc basin deposits are located to the north in southern Alaska. Palaeomagnetic data from the Chugach terrane and adjacent deposits indicate original deposition far to the south of the present latitude of Alaska. The entire magmatic arc-forearc basin-trench complex migrated northward in early Tertiary time, when it was probably oroclinally bent and accreted as a mesoplate to Alaska prior to the middle Miocene.
The Barbados Ridge Complex: tectonics of a mature forearc system
Authors: Westbrook G. K. 
Published: May 2008

Summary
The Barbados Ridge Complex is the wide accretionary sediment pile associated with the Lesser Antilles island arc. Its width is so great (>200 km) that a trench no longer exists on the oceanward side of it. This development is a product of the age of the system (>50 Ma) and the thickness of sediment on the ocean floor (0.8 km in the north, >4 km in the south). The northward decrease in elevation of the sediment pile and the variation in the style of initial deformation at the leading edge of the pile are related to the northward change in sediment thickness and type. The region in which deformation is prevalent has a westward limit just west of the axis of the minimum negative Bouguer gravity anomaly. In the south the axis of this minimum is coincident with the Barbados Ridge (an outer ‘sedimentary arc’). The deformed rocks of the accretionary pile are overlain by later sediments, which show varying degrees of deformation, and often occupy small basins.
In the northern part of the complex, the relief and structure of the accretionary pile are complicated by ridges and troughs running east-west across the general trend of structures. These appear to be related to variations in the relief of the subducted oceanic basement.
Sedimentology and structure of the Scotland Group, Barbados
Authors: Pudsey C. J. , Reading H. G. 
Published: May 2008

Summary
The lower to middle Eocene Scotland Group is about 1700 m thick at outcrop and can be divided into: (A) The Lower Scotland Formation consisting of (1) the Walkers Member (500 m): graded turbidite sands and clays, arranged in sand-dominated and clay-dominated packets; (2) the Morgan Lewis Member (200 m): almost all clay, with two sand intervals; (B) the Upper Scotland Formation consisting of (3) the Murphys Member (about 350 m): a thickening and coarsening upward sequence including slumped beds; (4) the Chalky Mount Member (0–250 m): coarse and conglomeratic sands with large slide blocks and minor interbedded muds; (5) the Mount All Member (about 500 m): coarse and fine turbidite sands and clays, much disturbed and displaying no overall sequence. The group was deposited by mass-flow processes in a deep marine environment, probably in a deep-sea trench or a submarine fan.
Current flow was from the SW and mineral composition supports derivation from South American metamorphic rocks. Clay mineralogy shows an upward trend from mainly smectite to mainly kaolinite.
An ENE structural trend is present throughout the island and is anomalous in the present plate-tectonic setting adjacent to a north-south trending island arc. Deformation increases in complexity up the succession; this may be due to sedimentary slumping, partly a result of increasing disturbance by rising mud diapirs. This locally culminated in extrusion of hydrocarbon-rich mud—the overlying Joes River Formation. The Barbados Ridge probably comprises clastic sediments deposited both in a trench and on the Atlantic Ocean floor.
Subduction and tectonics on the continental margin off northern Spain: observations with the submersible
Cyana
Authors: Malod Jacques-André , Boillot Gilbert , Lepvier Claude , Mascle Georges , Taugourdeau-Lantz Josette , Capdevila Raymond , Dupeuble Pierre-Alain , Müller Carla 
Published: May 2008

Summary

Short-term latest Mesozoic-early Cenozoic convergence between the Iberian and European plates transformed the passive north Spanish margin into an active margin with southward subduction of the oceanic crust of the Bay of Biscay. This margin became passive again when subduction ceased in late Eocene or Oligocene time. Nine dives with the submersible
Cyana
allowed us to sample the rocks outcropping on the Le Danois Bank slope. A Mesozoic sequence includes shelf limestones of the Dogger to the Lower Cretaceous, and Lower Cretaceous detrital sediments (sandstones, conglomerates, pelites); it overlies a typical Palaeozoic Asturian basement.

The main objective of the diving campaign was to study the structure of these strata in order to elucidate deformation of the continental wall of an active margin during its early stages of evolution, before the formation of an accretionary prism. The occurrence in Lower Cretaceous pelites of a weak schistosity in a reversed fold limb gives evidence of compressive structures, probably northward-verging overfolds. Additional evidence of compressive tectonics is the dislocation of quartz grains and dolomite crystals in Lower Cretaceous sandstones and Jurassic dolomites. These observations suggest that the continental slope in the Le Danois Bank area has a predominantly imbricate structure. Deformation and uplift of the northern Spanish margin appear to be related to the early stages of subduction of the European plate under Iberia.
Subduction in the Hellenic Trench: probable role of a thick evaporitic layer based on Seabeam and submersible studies
Authors: Le Pichon X. , Huchon P. , Angelier J. , Lybéris N. , Boulin J. , Bureau D. , Cadet J.P. , Dercourt J. , Glaçon G. , Got H. , Karig D. , Mascle J. , Ricou L.E. , Thiebault F. 
Published: May 2008

Summary
A Seabeam survey of the Hellenic Trench in 1978 was followed by a submersible survey in 1980. Fifteen dives were completed between 1500 and 3000 m covering 58 km on the bottom and obtaining 48 samples. Thus, the Hellenic Trench is probably now the most intensively studied trench as previous work included seismic reflection, dredging, coring, bottom photography, side-scan sonar and drilling. Because of the high sedimentation rate and the relatively shallow depth, we did not expect outcrops except along faults and in canyons. Active tectonics with numerous faults and folds have been observed. But we have also discovered vertical cliffs with hard rock exposure over a depth range of 1000–1500 m. In this paper, we discuss the nature of the hard rock outcrops observed both on the inner wall and on two hills that we interpret as diapirs. We conclude that at least part of these hard rocks are probably Messinian evaporites and concentrate on the tectonic role of this evaporitic layer in the Hellenic subduction. It is likely that the evaporites do not subduct but tend to pile up in the trench, to form a floating evaporitic basin.
Detailed tectonic trends on the central part of the Hellenic Outer Ridge and in the Hellenic Trench System
Authors: Kenyon N. H. , Belderson R. H. , Stride A. H. 
Published: May 2008

Summary
Extensive new sonograph coverage in the Eastern Mediterranean allows a re-assessment of the complex relief outside the Hellenic Arc. The trenches to the SE and SW of Crete are similar in their plan view appearance, each having predominantly sinuous or curved structures that are interpreted as the surface expression of major thrusts. Thrusting, possibly imbricate, is also suggested on the central, shallowest part of the Hellenic Outer Ridge where interlocking convex-outward, curved structures occur, along with other faults and folds. These are thought to relate to décollement-type displacement within or beneath evaporite sediments. The structural style deduced from the morphology is consistent with a continuing outward radial push of the Hellenic Arc to the SW, S and SE, rather than with a migration to the SW and strike-slip on the SE side of the arc as proposed by other workers.