Middle Miocene Time Research Articles

Madbi-Biyadh/Qishn (!) petroleum system in the onshore Masila Basin of the Eastern Yemen

The Masila Basin is one several onshore Mesozoic basins in Yemen. However, a full petroleum system, with its essential elements and processes, has not been assigned yet. In this study, one petroleum system in the Masila Basin was identified and named Madbi-Biyadh/Qishn (!) petroleum system. An extensive overview study showed that the main source and reservoir rocks in the Masila Basin are the Upper Jurassic Madbi shales and Lower Cretaceous Biyadh/Qishn sandstones, respectively; hence it appears that the most important effective petroleum system of the Masila Basin becomes the Madbi-Biyadh/Qishn (!) petroleum system. Organic-rich shales of the upper part of the Madbi Formation, deposited during the upper Jurassic, constitute the main source rock of the crude oils in the basin. These shales contain high total organic carbon content (TOC >2.0 wt.%) and predominantly algal Type II with minor Type I kerogen. The Madbi shales are mature and, at the present time, are within the oil window with determined vitrinite reflectance values in the range of 0.53–0.91 Ro%. The Biyadh/Qishn sandstones are the main reservoir and were deposited in braided river channels, shoreface and shallow-marine environments, and consist of fine to coarse-grained, moderate to well sorted grains. Seal rocks are Cretaceous limestone and shales of the Qishn and Harshiyat Formations and Tertiary shales. Overburden rocks include the Cretaceous rocks and the Tertiary sediments deposited simultaneously with development of the traps during Oligocene–Middle Miocene time. Burial/thermal histories models demonstrate that hydrocarbon generation from the Madbi shales commenced in the Late Cretaceous and maximum rates of hydrocarbon expulsion occurred during the Early Tertiary. Geochemical oil-source rock correlation studies showed that regional distribution of the oil fields almost overlap with the previously constructed pod of active Madbi shales indicating that oil migrated from the active Madbi source rock to trapping sites via vertical migration pathways through faults as a result of Tertiary rifting during Oligocene–Middle Miocene time.

A fossil palm leaf impression from ∼11.2 Ma old, Siwalik deposits of Kangra Valley, Himachal Pradesh

We report here, a fossil palm leaf from Lower Siwalik sediments, tied to nearby palaeomagnetically dated 11.2 Ma old beds exposed in the Baner Khad, near Ranital, Himachal Pradesh. The palm fossil leaf impression has been placed in the genus Palmacites sp. (Family: Arecaceae) based on its diagnostic features such as large palmate leaf without hastula and costa (midrib), showing coriaceous texture, leaflets diverging from the base of the lamina with prominent midrib and parallel venation. This finding may indicate presence of tropical to subtropical climatic conditions in the Himalayan foothills around Kangra Valley in the Middle Miocene time.

Miocene basin development and volcanism along a strike-slip to flat-slab subduction transition: Stratigraphy, geochemistry, and geochronology of the central Wrangell volcanic belt, Yakutat-North America collision zone

New geochronologic, geochemical, sedimentologic, and compositional data from the central Wrangell volcanic belt (WVB) document basin development and volcanism linked to subduction of overthickened oceanic crust to the northern Pacific plate margin. The Frederika Formation and overlying Wrangell Lavas comprise >3 km of sedimentary and volcanic strata exposed in the Wrangell Mountains of south-central Alaska (United States). Measured stratigraphic sections and lithofacies analyses document lithofacies associations that reflect deposition in alluvial-fluvial-lacustrine environments routinely influenced by volcanic eruptions. Expansion of intrabasinal volcanic centers prompted progradation of vent-proximal volcanic aprons across basinal environments. Coal deposits, lacustrine strata, and vertical juxtaposition of basinal to proximal lithofacies indicate active basin subsidence that is attributable to heat flow associated with intrabasinal volcanic centers and extension along intrabasinal normal faults. The orientation of intrabasinal normal faults is consistent with transtensional deformation along the Totschunda-Fairweather fault system. Paleocurrents, compositional provenance, and detrital geochronologic ages link sediment accumulation to erosion of active intrabasinal volcanoes and to a lesser extent Mesozoic igneous sources. Geochemical compositions of interbedded lavas are dominantly calc-alkaline, range from basaltic andesite to rhyolite in composition, and share geochemical characteristics with Pliocene–Quaternary phases of the western WVB linked to subduction-related magmatism. The U/Pb ages of tuffs and 40 Ar/ 39 Ar ages of lavas indicate that basin development and volcanism commenced by 12.5–11.0 Ma and persisted until at least ca. 5.3 Ma. Eastern sections yield older ages (12.5–9.3 Ma) than western sections (9.6–8.3 Ma). Samples from two western sections yield even younger ages of 5.3 Ma. Integration of new and published stratigraphic, geochronologic, and geochemical data from the entire WVB permits a comprehensive interpretation of basin development and volcanism within a regional tectonic context. We propose a model in which diachronous volcanism and transtensional basin development reflect progressive insertion of a thickened oceanic crustal slab of the Yakutat microplate into the arcuate continental margin of southern Alaska coeval with reported changes in plate motions. Oblique northwestward subduction of a thickened oceanic crustal slab during Oligocene to Middle Miocene time produced transtensional basins and volcanism along the eastern edge of the slab along the Duke River fault in Canada and subduction-related volcanism along the northern edge of the slab near the Yukon-Alaska border. Volcanism and basin development migrated progressively northwestward into eastern Alaska during Middle Miocene through Holocene time, concomitant with a northwestward shift in plate convergence direction and subduction collision of progressively thicker crust against the syntaxial plate margin.

Quantifying crustal extension and shortening in the back‐arc region of Northeast Japan

The Northeast Japan (NEJ) arc has experienced strong extension in the early to middle Miocene time and contractive deformation since Pliocene time. We determine the amounts of the Miocene extension and Pliocene contraction along four transects across the NEJ arc by area‐balancing restoration using seismic reflection, gravity, and surface geologic data. We find that the Miocene extension is as much as 31–56 km while the Pliocene‐Quaternary contraction is only 10–15 km. The style of the Miocene extension in the back‐arc region of NEJ is highly asymmetric; the zone of concentrated extension is characterized by a breakaway fault on the west, a rollover basement anticline on the east, and abnormally deep (∼10 km) basins and strongly rotated fault blocks in between, suggesting the existence of a large‐scale detachment fault at a mid‐crustal level beneath the extended zone. We reveal that the Pliocene‐Quaternary contractive surface deformation in the back‐arc region of NEJ resulted principally from positive tectonic inversion of the underlying detachment fault. Previous works have suggested that Andean‐type orogens have often experienced negative and positive inversions alternately in their back‐arc regions. Although the former has been well documented, for example, for the Cenozoic North American Cordillera, the latter has rarely been reported because subsequent contraction has obscured the older structures. Since the NEJ arc is still at an incipient stage and hence its older structures are well preserved, our study provides an important example of positive tectonic inversion of Andean‐type orogens.

Basin modelling and source rock evaluation in the Guyana Basin

The Guyana Basin contains a world-class source rock of Late Cretaceous age, but no hydrocarbon fields have yet been discovered offshore. In order to evaluate source rock maturity, we used basin modelling software to model a grid of interpreted 2D seismic sections and combined the 2D modelling results to build a basin-wide model. The burial depth, temperature, and transformation ratio of the Cretaceous source rocks were calculated from the end of the Cretaceous to the present, and mapped over the entire basin. The modelling results show that regional uplift during Late Cretaceous–middle Miocene time slowed the maturation of the Cretaceous source rock in the basin except in the south-eastern depocentre. In this depocentre, the oil window was reached during the Palaeogene, by which time few reservoir and seal rocks had been deposited. For the rest of the basin, uplift of the Waini arch and the middle Miocene regional uplift slowed maturation of the source rock. Possible reservoirs that could have received hydrocarbons from the south-eastern depocentre include Cretaceous-middle Miocene clastic rocks that pinch out against the southern flank of the Waini arch and stratigraphic traps along the shelf.

Late Eocene–Pliocene basin evolution in the Eastern Cordillera of northwestern Argentina (25°–26°S): regional implications for Andean orogenic wedge development

AbstractImportant aspects of the Andean foreland basin in Argentina remain poorly constrained, such as the effect of deformation on deposition, in which foreland basin depozones Cenozoic sedimentary units were deposited, how sediment sources and drainages evolved in response to tectonics, and the thickness of sediment accumulation. Zircon U‐Pb geochronological data from Eocene–Pliocene sedimentary strata in the Eastern Cordillera of northwestern Argentina (Pucará–Angastaco and La Viña areas) provide an Eocene (ca. 38 Ma) maximum depositional age for the Quebrada de los Colorados Formation. Sedimentological and provenance data reveal a basin history that is best explained within the context of an evolving foreland basin system affected by inherited palaeotopography. The Quebrada de los Colorados Formation represents deposition in the distal to proximal foredeep depozone. Development of an angular unconformity at ca. 14 Ma and the coarse‐grained, proximal character of the overlying Angastaco Formation (lower to upper Miocene) suggest deposition in a wedge‐top depozone. Axial drainage during deposition of the Palo Pintado Formation (upper Miocene) suggests a fluvial‐lacustrine intramontane setting. By ca. 4 Ma, during deposition of the San Felipe Formation, the Angastaco area had become structurally isolated by the uplift of the Sierra de los Colorados Range to the east. Overall, the Eastern Cordillera sedimentary record is consistent with a continuous foreland basin system that migrated through the region from late Eocene through middle Miocene time. By middle Miocene time, the region lay within the topographically complex wedge‐top depozone, influenced by thick‐skinned deformation and re‐activation of Cretaceous rift structures. The association of the Eocene Quebrada del los Colorados Formation with a foredeep depozone implies that more distal foreland deposits should be represented by pre‐Eocene strata (Santa Barbara Subgroup) within the region.

Lateral extrusion in the Eastern Alps revisited: Refining the model by thermochronological, sedimentary, and seismic data

This study comprises a reassessment of the classical model of lateral extrusion in the Eastern Alps by using recently published geochronological data, sedimentary ages from intramontane basins, ages and distribution of magmatic rocks, and information from seismic profiles. Extrusion‐related faulting continuously propagated from the western toward the central eastern part of the Eastern Alps during Oligocene to Middle Miocene times. This is confined by oblique convergence between the Adriatic and European plates. During Middle Miocene times, extrusion became not only lateral in terms of parallel to the trend of the Eastern Alps, but was characterized by a displacement vector at a high angle to the strike of the orogen. This resulted in the exhumation of the Schladming and Pohorje blocks that were exhumed within extensional bridges at the northern and southern terminations of the Pöls‐Lavanttal fault system, respectively. From Middle Miocene to recent times, extrusion was controlled by overall extension between the Dinaric and Carpathian subduction zones. The influence of north directed compression triggered by the northward moving Adriatic plate diminished, and the influence of the retreating Carpathian subduction zone increased. This gave rise to Miocene volcanism that is exclusively found east of the Dinaric subduction zone. We therefore consider that lateral extrusion in the Eastern Alps can be subdivided into distinct tectonic phases, with less pronounced eastward extension‐related displacement between Late Oligocene and Middle Miocene times. As soon as the Eastern Alps passed the Dinaric subduction zone, the entire domain became highly extensive.

Direct dating of Eocene reverse faulting in northeastern Tibet using Ar-dating of fault clays and low-temperature thermochronometry

Paired together, fault gouge dating and low-temperature thermochronometry overcome the limitations and assumptions inherent in each independent technique. Here we establish timing of brittle faulting along the West Qinling fault of northeastern Tibet by dating several size fractions of fault gouge clay that represent variable populations of illite polytypes. Results show that the authigenic or fault-generated component of illite formed at 50 ± 8 Ma and that the detrital component formed at 236 ± 7 Ma indicating a Middle Eocene age of faulting and a Middle Triassic age of the wall rocks. Comparing this dataset with published thermochronology from hanging wall rocks supports the interpretation that the West Qinling fault initiated at ~ 50 Ma and continued until at least Middle Miocene time and that authigenic clay growth occurred at ambient temperatures of ~ 110 °C. Lack of overprinting of younger clay ages at this site may indicate that rocks were out of the thermal window for authigenic clay formation during later faulting episodes. The potential for temperature to control illite growth has implications for interpretation of authigenic illite ages and their relationship to deformation episodes within fault zones.

Reconciling the geological history of western Turkey with plate circuits and mantle tomography

We place the geological history since Cretaceous times in western Turkey in a context of convergence, subduction, collision and slab break-off. To this end, we compare the west Anatolian geological history with amounts of Africa–Europe convergence calculated from the Atlantic plate circuit, and the seismic tomography images of the west Anatolian mantle structure. Western Turkish geology reflects the convergence between the Sakarya continent (here treated as Eurasia) in the north and Africa in the south, with the Anatolide–Tauride Block (ATB) between two strands of the Neotethyan ocean. Convergence between the Sakarya and the ATB started at least ~ 95–90 Myr ago, marked by ages of metamorphic soles of ophiolites that form the highest structural unit below Sakarya. These are underlain by high-pressure, low-temperature metamorphic rocks of the Tavşanlı and Afyon zones, and the Ören Unit, which in turn are underlain by the Menderes Massif derived from the ATB. Underthrusting of the ATB below Sakarya was since ~ 50 Ma, associated with high-temperature metamorphism and widespread granitic magmatism. Thrusting in the Menderes Massif continued until 35 Ma, after which there is no record of accretion in western Turkey. Plate circuits show that since 90 Ma, ~ 1400 km of Africa–Europe convergence occurred, of which ~ 700 km since 50 Ma and ~ 450 km since 35 Ma. Seismic tomography shows that the African slab under western Turkey is decoupled from the African Plate. This detached slab is a single, coherent body, representing the lithosphere consumed since 90 Ma. There was no subduction re-initiation after slab break-off. ATB collision with Europe therefore did not immediately lead to slab break-off but instead to delamination of subducting lithospheric mantle from accreting ATB crust, while staying attached to the African Plate. This led to asthenospheric inflow below the ATB crust, high-temperature metamorphism and felsic magmatism. Slab break-off in western Turkey probably occurred ~ 15 Myr ago, after which overriding plate compression and rotation accommodated ongoing Africa–Europe convergence. Slab break-off was accommodated along a vertical NE trending subduction transform edge propagator (STEP) fault zone, accelerating southwestward slab retreat of the Aegean slab. The SE Aegean slab edge may have existed already since early Miocene times or before, but started to rapidly roll back along the southeastern Aegean STEP in middle Miocene times, penetrating the Aegean region in the Pliocene.

Rotation history of Chios Island, Greece since the Middle Miocene

Superimposed on a regional pattern of oroclinal bending in the Aegean and west Anatolian regions, the coastal region of western Anatolia, shows a complex and chaotic pattern of coexisting clockwise and counterclockwise rotations. Here, we report new palaeomagnetic data from the eastern Aegean island of Chios, to test whether this fits the regional palaeomagnetic pattern associated with the Aegean orocline, or should be included in the narrow zone of chaotic palaeomagnetic directions. Therefore, a combined palaeomagnetic study of Miocene sediments and volcanic rocks has been carried out. Thermal and AF demagnetization of a 130-m thick Middle Miocene succession from the Michalos claypit allowed a stable component of both polarities to be isolated while rock magnetic experiments showed that the main magnetic carrier is magnetite. When compared with the Eurasian reference, the mean declination of 348 ± 5.1° implies 15° of counterclockwise rotation since Middle Miocene times. The obtained shallow inclination of 38 ± 6.7° was corrected to 61.8 ± 3.9°, by applying the elongation/inclination correction method for inclination shallowing. This result is similar to the expected inclination of 58° for the latitude of Chios. The palaeomagnetic analysis (demagnetization treatment and corresponding rock magnetic measurements) of the volcanic rocks identify a stable, predominantly normal, ChRM with poorly constrained mean declination of about 290 ± 19.8° based on five successfully resolved components. The significantly different palaeomagnetic results obtained from an island as small as Chios (and a very short distance), and the relatively large rotation amounts do not fit the regional palaeomagnetic direction of Lesbos and basins in northwestern Turkey which show little or no significant rotation. We thus prefer to include Chios in the coastal zone of chaotic rotations, which may represent a previously inferred tectonic transfer zone that accommodates lateral differences in extensional strain within the Aegean back-arc.

Low-temperature thermochronology in the Peruvian Central Andes: implications for long-term continental denudation, timing of plateau uplift, canyon incision and lithosphere dynamics

Abstract: In Peru, the western edge of the 4.5 km high Western Cordillera is cut by a >3 km deep canyon. To understand incision by the Cotahuasi–Ocoña River and the regional uplift history of this orogenic plateau capped by volcanic rocks, 26 crystalline rock samples were collected for low-temperature thermochronology from vertical profiles parallel and perpendicular to the canyon. Rock cooling histories confirm that most plateau denudation had occurred prior to 24 Ma but plateau incision peaked after c . 14–9 Ma in response to rapid surface uplift. The abrupt occurrence of a rock heating event is also detected during middle Miocene time. This was either a response to the emplacement of low-conductivity, regionally extensive ignimbritic caprock or a response to crustal-scale fluid circulation caused by wet melting of the overriding plate when magmatism resumed c . 24 Ma. The potential for thermochronology to provide information on past geothermal gradients is discussed, showing how it can be used as a proxy for understanding change in subducting slab dynamics, with oscillations in subduction angle having perhaps been the main on–off switch for magmatism in this Cordilleran setting. Supplementary material: Fission-track and apatite (U–Th)/He results and apatite chemistry indicators are available at http://www/geolsoc.org.uk/SUP18405 .

A new species ofDiplocynodon(Crocodylia, Alligatoroidea) from the Late Eocene of the Massif Central, France, and the evolution of the genus in the climatic context of the Late Palaeogene

AbstractThe genusDiplocynodonis widely recorded in Europe from Early Eocene up to Middle Miocene times. A fragmented but almost complete skull of a new species ofDiplocynodonis reported from the Late Eocene locality of Domérat, northern border of the Massif Central (Allier), France. The present skull provides an important basis for comparison with other members of the genus and complements a fossil record full of gaps despite the large number of vertebrate localities spanning the Cenozoic. The new taxon occurs at a key period for climate evolution with conditions marking the transition from a greenhouse to an icehouse world. The response of crocodylian assemblages to this climatic shift is discussed in light of evidence for their decline in diversity from the Eocene period onward.

Cretaceous–Neogene tectonic evolution of the northern margin of the Black Sea from seismic reflection data and tectonic subsidence analysis

Abstract Three fundamental stages of the Cretaceous–Neogene tectonic evolution of the Odessa Shelf and Azov Sea (northern margins of western and eastern Black Sea basins, respectively) have been documented from the analysis of reinterpreted regional seismic profiling and one-dimensional (1-D) subsidence analysis of 49 wells, for which the stratigraphic interpretation was recently revised. (1) An initial active rifting stage began within the Early Cretaceous (not later than Aptian–Albian times) and continued until the end of the Santonian in the Late Cretaceous ( c . 128–83 Ma). A system of half-grabens with mainly south-dipping normal faults developed on the Odessa Shelf at this time. The most profound faulting, accompanied by volcanic activity, occurred in the NE–SW orientated Karkinit-Gubkin rift basin at the boundary between the Eastern European and Scythian platforms. The footwalls of half-grabens were exposed above sea level and subject to erosion at this time. Active extensional processes affected the western part of Azov Sea and, while the onset and cessation of these cannot be tightly constrained, they are compatible with the well constrained results from the Odessa Shelf. (2) The second tectonic stage is one of passive post-rift thermal subsidence that lasted from the Campanian (Late Cretaceous) until the end of the Middle Eocene (83–38.6 Ma). (3) The third stage of basin evolution is one of inversion tectonics in a compressional setting. Discrete inversion events occurred at the end of the Middle Eocene, during the Late Eocene, during the Early Miocene and at Middle Miocene times ( c . 38.6 Ma, c . 35.4 Ma, c . 16.3 Ma, c . 10.4 Ma, respectively) and typical inversion structures developed on the Odessa Shelf, some parts of which were uplifted and significantly eroded (down to the Lower Cretaceous succession). The southern part of the Azov Sea, opening into the northernmost eastern Black Sea basin, subsided rapidly during this time; thereafter, until the Quaternary, rapid subsidence was limited to its southeastern part, which was incorporated into the Indolo-Kuban foreland basin of the Greater Caucasus orogen.

Evolution of the Grenada and Tobago basins and implications for arc migration

The tectonic mechanisms controlling how volcanic arcs migrate through space and geologic time within dynamic subduction environments is a fundamental tectonic process that remains poorly understood. This paper presents an integrated stratigraphic and tectonic evolution of Late Cretaceous to Recent volcanic arcs and associated basins in the southeastern Caribbean Sea using seismic reflection data, wide-angle seismic refraction data, well data, and onland geologic data. We propose a new tectonic model for the opening of the Grenada and Tobago basins and the 50–250-km eastward jump of arc volcanism from the Late Cretaceous Aves Ridge to the Miocene to Recent Lesser Antilles arc in the southeast Caribbean based on the mapping of three seismic megasequences. The striking similarity of the half-graben structure of the Grenada and Tobago basins that flank the Lesser Antilles arc, their similar smooth basement character, their similar deep-marine seismic facies, and their similar Paleogene sediment thickness mapped on a regional grid of seismic data suggest that the two basins formed as a single, saucer-shaped, oceanic crust Paleogene forearc basin adjacent to the now dormant Aves Ridge. This single forearc basin continued to extend and widen through flexural subsidence during the early to middle Eocene probably because of slow rollback of the subducting Atlantic oceanic slab. Rollback may have been accelerated by oblique collision of the southern Aves Ridge and southern Lesser Antilles arc with the South American continent. Uplift and growth of the southern Lesser Antilles arc divided the Grenada and Tobago basins by early to middle Miocene time. Inversion of normal faults and uplift effects along both edges of the Lesser Antilles arc are most pronounced in its southern zone of arc collision with the South American continent. The late Miocene to Recent depositional histories of the Grenada and Tobago basins are distinct because of isolation of the Grenada basin by growth and uplift of the Neogene Lesser Antilles volcanic ridge.

Geological development of the Central and South Vietnamese margin: Implications for the establishment of the South China Sea, Indochinese escape tectonics and Cenozoic volcanism

The Vietnamese margin forms a key region to the understanding of escape tectonics and the development of the South China Sea (SCS). The existing geological reconstructions of the region are restricted to studies of single basins, are based on limited amounts of geophysical data or analysis of onshore geological features. These models are critically assessed on the basis of interpretation of the most comprehensive 2-D digital seismic database published to date within the area combined with a thorough analysis of existing literature, and a new model is presented. The Vietnamese margin is underlain by a series of Paleogene rift basins established through southeastward extrusion of Indochina. The East Vietnam Boundary Fault (EVBF) forms the almost 1000 km long seaward continuation of the left-lateral Ailao Shan-Red River Shear Zone (ASRRSZ). Toward the southern half of the Phu Khanh Basin the EVBF breaks up into discrete segments and splays into the SE-directed Tua Hoa Fault Zone. Paleogene faults splayed from the EVBF and the Mae Ping Shear Zone and accommodated the coeval motion of these two major left-lateral structural lineaments. During the late Oligocene, basin inversions offshore occurred contemporaneously with initial right-lateral inversion along the Mae Ping Shear Zone and the onset of major uplift of the metamorphic core complexes along the ASRRSZ. It is suggested that a dramatic change of the regional stress pattern occurred in response to the northward movement of India and the effective coupling of the West Burma Block and India, the later resulting in broadening of the indenting continental mass. After the mid-Oligocene, left-lateral movements across the offshore EVBF decreased and eventually ceased. Later, onshore sinistral movements were accommodated by internal shortening and local clockwise block rotations within the Shan-Thai Terrain. Renewed rifting offshore south Vietnam resulted from the jump of the SCS spreading axis and subsequent Neogene southwestward propagation of continental break-up. The Neogene opening of the SCS is viewed as a consequence of a slab-pull associated with subduction of the proto-SCS underneath Borneo as offshore Neogene escape tectonism had virtually ceased. During this phase of rifting, right-lateral transtension is inferred along N to NW oriented fault zones in the Phu Khanh and the Nam Con Son basins. Rifting and by inference seafloor spreading continued until the end of middle Miocene time although at significantly reduced rates during the final 5–10 Ma. Termination of seafloor spreading is marked by a distinct latest middle Miocene unconformity in the Nam Con Son and the southern Phu Khanh basins. Neogene volcanism resulted in the build-up of several magmatic structures across the central and South Vietnamese margin and induced reactivation of older faults in the Phu Khanh Basin. The offshore magmatism heralded widespread volcanism onshore southern Indochina associated with a latest Neogene uplift and denudation event. The uplift led to significantly increased siliciclastic accumulation rates offshore, which repressed widespread carbonate deposition.

Thrust faults and extensional detachment faults in Cretan tectono-stratigraphy: Implications for Middle Miocene extension

The revised tectono-stratigraphy of Crete and especially of the “Phyllites–Quartzites” complex demonstrated the distinction of the probable Paleozoic low-medium grade metamorphic rocks of the Arna unit from the underlying Permo–Triassic phyllites and associated carbonate sediments (Trypali facies) of Western Crete unit as well as the overlying Permo–Triassic phyllites and associated sediments of the Tyros/Ravdoucha Beds at the base of the Tripolis unit. The pre-existing mixture of the above tectono-stratigaphic units in a single complex created a number of misinterpretations as far as stratigraphy, metamorphism and interpretation of low angle faults as thrusts or detachments. Especially in cases where the inferred tectonic contact concerns the transition between the Tyros Beds and the base of the Tripolis carbonate platform there is no structural omission and therefore the contact represents a minor disharmonic sliding surface and not a detachment. Based on the revised tectono-stratigraphic analysis the determination of the structural omission for each tectonic contact was possible and several detachments were described for the first time. Footwall rocks of the detachments comprised several tectonic units usually from the lower nappes and hanging wall rocks comprised several tectonic units usually from the upper nappes. The detachment may separate not only metamorphosed units in the footwall (Mani, Western Crete, Arna) from non metamorphosed units in the hanging wall (Tripolis, Pindos and higher nappes) but also all other possible combinations from the Cretan nappe pile. Extension in Crete started in the Middle–Late Miocene with the formation of extensional detachment faults. The reported extensional structures of Oligocene to Early Miocene age do not correspond to crustal extension of Crete but to localized shear zones related to nappe stacking and the exhumation of metamorphic rocks. Extensional detachments in Crete form a tectonic horst through two oppositely dipping E–W-trending zones; one dipping north, related to the opening of the Cretan basin, and the other dipping south, related to the formation of the Messara supra-detachment basin. The deformation history of units within Crete can be summarized as: (i) compressional deformation producing arc-parallel east–west-trending south-directed thrust faults in Oligocene to Early Miocene time; (ii) extensional deformation along arc-parallel, east–west-trending detachment faults in Middle Miocene time, with hanging wall motion to the north and south; and (iii) Late Miocene–Quaternary transtensional deformation along high-angle normal and oblique normal faults that disrupt the older arc-parallel structures.

Climate forcing by iron fertilization from repeated ignimbrite eruptions: The icehouse–silicic large igneous province (SLIP) hypothesis

During middle Eocene to middle Miocene time, development of the Cenozoic icehouse was coincident with a prolonged episode of explosive silicic volcanism, the ignimbrite flare-up of southwestern North America. We present geochronologic and biogeochemical data suggesting that, prior to the establishment of full glacial conditions with attendant increased eolian dust emission and oceanic upwelling, iron fertilization by great volumes of silicic volcanic ash was an effective climatic forcing mechanism that helped to establish the Cenozoic icehouse. Most Phanerozoic cool-climate episodes were coeval with major explosive volcanism in silicic large igneous provinces, suggesting a common link between these phenomena.

Neogene uplift of central eastern Patagonia: Dynamic response to active spreading ridge subduction?

The Chile Triple Junction (CTJ) episodically migrated northward during the past 14 Ma from 54°S to its present‐day position at 46°30′S, as different almost trench‐parallel spreading segments entered in subduction. This migration resulted in the opening of an asthenospheric window below Patagonia, inducing a disturbance in the regional mantle convection. On the overriding plate, the middle Miocene time corresponds to a major change in the central Patagonian basin dynamics, with a transition from subsidence to generalized uplift. The detailed mapping and the morphological study of post‐middle Miocene terraces evidence regional‐scale trench‐parallel tilt histories that differ depending on latitude. South of 46°30′S, the slopes of the fluvial terraces indicate a change from northward to southward tilt during late Miocene. Terraces younger than the early Pliocene do not show any trench‐parallel tilt. North of 46°30′S, in contrast, only northward tilt, active until the Pleistocene, is recorded. We use a semianalytical model of dynamic topography which suggests that the northward migration of the Chile Triple Junction should be accompanied by a dynamic uplift of the central Patagonian basin. Uplift would cause both north directed and south directed tilt, north and south of the triple junction, respectively, with values of ∼0.1–0.2% 500 km east of the trench. Tilt measured in the southeastern part of the central Patagonian basin (∼0.1%) is comparable to values predicted using the semianalytical model. The dynamic topography associated to the Chile ridge subduction may have exerted a major control on the Neogene dynamics of Patagonia.

Middle to late Miocene chronostratigraphy and development of the northern Gulf of California

Geologic models locate Baja California next to mainland Mexico during the Oligocene and propose opening of the Gulf of California during Miocene times. Outcrop information in the northern part of the Gulf indicates late Miocene marine sedimentation on a continental platform. However, the earliest marine sediments in the region are present in basins sampled by oil exploratory wells in the area, which drilled as much as 5591 m of marine sands to silty clays. Stratigraphic and paleontological data in these wells indicate almost continuous marine sedimentation from middle Miocene times, in maximum water depths of approximately 200 m. The presence of the dinoflagellates Cribroperidinium tenuitabulatum, Diphyes latiusculum and Spiniferites pseudofurcatus, together with the nannofossil Cyclicargolithus floridanus in samples from some of these wells, indicates marine deposition during middle Miocene times in the Tiburón, Consag and Wagner basins in the northern Gulf of California. Our data indicate that in the middle Miocene, a marine proto-gulf basin was formed in the central part of the proto-gulf, probably related to Basin and Range extension. Published data indicate that during late Miocene times, the proto-gulf extended from southeastern California and southern Arizona, to central Baja California and Isla Tiburón. Finally, by Pliocene times, marine sedimentation within the Gulf reached the modern distribution.

The tectonic history of Drake Passage and its possible impacts on global climate

This study provides an integrated review of plate tectonic models of the evolution of the Antarctica–Patagonia connection compared to geological records collected on land in Patagonia and Tierra del Fuego, and offshore along the northern edge of the Scotia Sea. A temporal framework for the sedimentary and tectonic events of the North Scotia Ridge and Tierra del Fuego is constructed with additional data compiled from entire Patagonia and the Austral Basin. This review provides robust correlations of seaways and tectonic events along the Scotia and South America plates and indicates that the opening of the Drake Passage was not steady state since ca. 30 Ma. Rather the regions forming the present-day northern limit of this gateway experienced important paleogeographic changes, from deep marine basins to shallow ridges and emerged regions during the late Oligocene and early–middle Miocene time. Our compilation of geological data shows that emergence along the North Scotia Ridge and Tierra del Fuego was achieved at 23–22 Ma, and has been followed by elimination of the Patagoniano Sea in Patagonia, starting at 22–23 Ma and achieved at 20 Ma. This transition towards more continental sedimentation in southern South America is correlated with more shallow marine conditions in the Austral Basin. This succession of events had a strong influence on the general geometry of the Drake Passage, corresponding to a constriction of its northern limit, starting in the window 29–22 Ma and achieved at 21 Ma. This period of active deformation in southern South America also corresponds to a period of the global climate having two anomalies well known from the isotopic records: the Late Oligocene Warming, around 26 Ma and the Mid-Miocene Climatic Optimum which ended between 15 and 14 Ma. The possible effects of the post-Oligocene tectonic evolution of the Drake Passage region on general oceanic circulation are discussed. Causes for the synchronicity between tectonic events and these global warming events are examined.