Eocene To Early Miocene Research Articles

Magmatic and tectonic fabrics in the Upper Jurassic La Hoya Pluton, North Patagonian Batholith (~43°S) as a record of the early stages of the Andean deformation

The magmatic record of the North Patagonian Batholith starts in Middle Jurassic times and rapidly grew in Early Cretaceous times, where it experienced its main building phase. Slightly after, in the Late Cretaceous, the North Patagonian fold and thrust belt experienced its first contractional deformation pulse. The La Hoya Pluton is an Upper Jurassic shallow intrusive body emplaced in the North Patagonian Andes in the proximities of the city of Esquel in Argentina. Its excellent exposures, which bear magmatic and high- and low-temperature solid-state deformation structures, are studied in this work through field, microstructural, and AMS studies. The initial shape of the pluton could be envisaged as having a geometry compatible with coalescent laccoliths, given by the presence of subhorizontal magmatic to solid-state foliations with associated E-W or N–S trending magmatic to solid-state lineations. These magmatic structures, which bear a mild solid-state overprint, were probably formed during progressive pluton cooling. Moreover, the nature of these structures suggests that the pluton cooled fast at shallow crustal levels, indicating that they are probably related to its emplacement processes that started, at least, in Late Jurassic times. Contrastingly, NW-SE and NE-SW trending high-angle subvertical fractures and low-temperature mylonitic zones with steeply plunging lineations, which are compatible with an E-W shortening direction, cut the previously formed subhorizontal magmatic structures. These compressive structures found in the La Hoya Pluton were probably developed during the Late Cretaceous main stage of contractional deformation. The contractional deformation is constrained to have happened before the intrusion of undeformed basaltic dikes crosscutting the mylonitized areas of the La Hoya Pluton. These dikes have an 40Ar-39Ar age in plagioclase of 42.15 ± 0.40 Ma and geochemical features typical of volcanic arcs above a subduction zone. Their geochemical signature is sensitive to the process of arc resumption after the Paleogene waning of arc activity, as it is transitional between the alkaline-like signature of Pilcaniyeu Belt (~57.8–42; Paleocene-Eocene) and the predominantly slab-derived magmas of El Maitén Belt (~37–19; Late Eocene-Early Miocene). These dikes probably formed part of the early stages of the El Maitén Belt.

Southward-Directed Subduction of the Farallon–Aluk Spreading Ridge and Its Impact on Subduction Mechanics and Andean Arc Magmatism: Insights From Geochemical and Seismic Tomographic Data

Since the initial proposal of the past existence of a southward-directed mid-ocean ridge-subduction interaction in the Andes during Late Cretaceous-Paleogene times, several studies have been devoted to uncover the tectonomagmatic evidence of this process. The collision of a spreading ridge against a subduction margin provoke important tectonomagmatic changes; including between them variations in arc-related magmatic activity and in the plate-margin stress regime. However, the cryptic nature of the geological record often hampers assessing the influence and along-strike evolution of this process. In this study, we integrate new isotopic data with previous field and geochemical data on Andean arc-related magmatism, together with seismic tomography to track the main tectonic changes that affected the Andes between 35° and 42oS from Latest Cretaceous to early Miocene times. In particular, we carry out a new tomotectonic analysis combining the regional bedrock record of the Late Cretaceous-early Miocene arc with upper-lower mantle seismic tomography. This analysis allowed us to unravel the main geodynamic changes that affected the Andean active-margin when the Farallon-Aluk spreading ridge was subducting. Besides, new isotopic analyses reveal the variable nature of the mantle source that fed the Late Cretaceous-early Miocene arc. Hence, the integration of geological, geochemical and geophysical data, together with new isotopic data studying the geochemical composition of the main Andean arc-related magmatic units in three main periods: 1) Latest Cretaceous-early Paleocene; 2) Early Paleocene-late Eocene; 3) Late Eocene-early Miocene, allow us to understand with an unprecedented detail the geochemical and spatio-temporal evolution of the passage of this spreading ridge along the Andean margin

Tajik Basin and Southwestern Tian Shan, Northwestern India‐Asia Collision Zone: 2. Timing of Basin Inversion, Tian Shan Mountain Building, and Relation to Pamir‐Plateau Advance and Deep India‐Asia Indentation

AbstractThe Tajik basin and southwestern Tian Shan constitute the northwestern tip of the India‐Asia collision zone. Basin inversion formed the thin‐skinned Tajik fold‐thrust belt, outlined by westward convex fold trains, underlain by a décollement in Jurassic evaporites. The belt's leading edge—the Uzbek Gissar—and its transpressional northern lateral margin—the Tajik Gissar—constitute the thick‐skinned foreland buttresses. Apatite fission‐track data indicate ~40‐ to 15‐Ma reheating by sediment burial in the Tian Shan. In the Gissar and the Tajik fold‐thrust belt, apatite fission‐track and (U,Th)/He ages date the major phase of shortening/erosion between ~12 and 1 Ma, with exhumation to 2‐ to 3‐km crustal depths within a few Myr after onset of shortening. Shortening spread immediately across the fold‐thrust belt, typical for belts floored by a detachment in ductile rocks, and into the foreland buttresses. Reactivation concentrated in the internal (eastern) fold‐thrust belt with the thickest evaporates. The youngest ages (~6.6–1.6 Ma) occur along the Vakhsh thrust, the active erosional front of the fold‐thrust belt in the northeastern Tajik basin, where it narrows between the converging Tian Shan and Pamir. Our study links major events in the Pamir hinterland with the Tajik basin and Tian Shan foreland. In the late Eocene–early Miocene, the advancing Pamir‐plateau crust loaded the foreland, inducing subsidence, reheating, and early shortening. Basin inversion and major shortening/transpression in the foreland buttresses from ~12 Ma onward were synchronous with the subcrustal indentation of Indian lithosphere into the Tajik‐Tarim basin lithosphere and the onset of its rollback beneath the Pamir.

Integrated seismic and well-log analysis for the exploration of stratigraphic traps in the Carbonera Formation, Llanos foreland basin of Colombia

The Llanos foreland basin of Colombia is the country's most prolific oil producer, with the most known oil fields found in normal fault traps created during flexure of the foreland basin. The objective of the study is to evaluate the potential of stratigraphic traps in the Late Eocene-Early Miocene Carbonera Formation, a 400-1800 m-thick reservoir unit with numerous traps related to unfaulted, sand-prone fluvial deposits. We integrated 700 km2 of 3D seismic data with eight wells near the ~8600 bcd Cubiro field in the central area of the Llanos foreland. Interpretations of well logs and stratal slices through multi-attribute and iso-frequency amplitude cubes show that the Carbonera Formation contains tectonically-controlled, sinuous channel belts seen on seismic lines as strong, high-amplitude, concave reflections with variable width-to-depth ratio. Well logs through the Carbonera Formation record two regressive-transgressive cycles with greater preservation of non-reservoir, shaly transgressive deposits within the intermediate Carbonera members 5 and 3, and sandy, lowstand deposits in the lower and uppermost Carbonera members 7 and 1, respectively. Seismic and gamma-ray facies analyses allowed the distinction of prospective, sand-rich point bars, scrolls, and basal lag deposits from non-prospective, mud-rich abandoned channels. Stratal slices within the Carbonera Formation show changes from Late Eocene-Early Oligocene, northeast-flowing channel belts of a main axial fluvial system -proposed to be the proto-Meta River-, to a Late Oligocene southeast-flowing tributary channels interpreted as a result of eastward flexural migration, enhanced accommodation from loading of the Eastern Cordillera and a shift from an underfilled to overfilled foreland basin.

Mid-Miocene initiation of the Aimunike-Oulongbuluke Range in the NE Qaidam Basin, implications for the growth of the Tibetan Plateau

ABSTRACT Constraining the initial age of the Northern Qaidam Thrust Belt is critical for studying the growth of the Tibetan Plateau. This study presented insights from field observations and seismic profiles, to constrain the structural pattern and the initial age of the eastern segment of the Northern Qaidam Thrust Belt during the Cenozoic. Our research suggested the Aimunike and the Oulongbuluke uplifts, as well as the Ounan Depression between them have been uplifted during the mid-Miocene, and as a result underwent widespread denudation to remove the late Eocene-early Miocene sequences over them. After that, this area was subsided and accepted the deposition of the mid-Miocene to the Pliocene strata. A second phase of thrusting occurred in the Quaternary as those faults initiated in the mid-Miocene rejuvenated. Our results together with the previous studies suggested the N-S compressional stress over the NE Tibetan Plateau strengthened substantially during the mid-Miocene, leading to a widespread plateau growth at that time.

Origin and provenance of 2 Ma–2 Ga zircons ejected by phreatomagmatic eruptions of Pliocene basalts in southern Slovakia

U–Pb ages of zircons recovered from Pliocene pyroclastic deposits in northern part of the Cenozoic intra-Carpathian back-arc basin (Pannonian Basin) span the interval from Pliocene (2.2 Ma) to Paleoproterozoic (Orosirian–Rhyacian, 1850–2115 Ma). The scattered U–Pb ages reflect eruption ages of the host basaltic volcanic centres, two episodes of post-Eocene magmatic crustal growth, and the possible tectonic affiliation, provenance and age of the subjacent basement or the sedimentary basin detritus sampled by the basaltic magma. The youngest zircons define the maximum ages of phreatomagmatic eruptions during the Late Miocene–Pliocene extension. These zircons are distinguished from older zircons by Zr/Hf (40–90) and Th/U ratios (0.5–4.5) as well as super-chondritic εHf(t) values ranging from + 7 to + 14, indicating mantle-derived parental magmas. The locally increased Th/U ratios (up to 8) accompanied by Zr/Hf > 60 are diagnostic of evolved phonolite parental melt. Hence, the youngest zircons can be interpreted as antecrysts, originating from evolved melts cogenetic with the host alkali basalts. In contrast, older zircons represent xenocrysts scavenged by the uprising basalt from surrounding rocks. Subordinate Eocene–Early Oligocene (29–38 Ma) sub-group of zircon xenocrysts is coincidental with the magmatism and volcanism along the Periadriatic lineament and the middle-Hungarian zone. The Early Miocene (18 Ma) cluster is coeval with the deposition of the Bükk Mountains felsic ignimbrite correlated with the onset of the back-arc extension that triggered Miocene sedimentation within the Pannonian Basin. The Eocene–Early Oligocene zircons have been likely scavenged from pyroclastic and ash-fall deposits of the Palaeogene retroarc basin subjacent to the Miocene basin infilling. Sub-chondritic εHf(t) values between − 2.5 and − 8 in the Eocene–Early Miocene zircons attest their crystallization from subduction-related felsic-to-intermediate melts containing large amounts of recycled crustal material. Palaeozoic–Proterozoic zircons create a heterogeneous population with variable trace element abundances and εHf(t) values. The determined age clusters are reminiscent of some basement units cropping out recently in Central Western Carpathians. Zircon Hf isotope data indicate recycling of up to 3.4 Ga old mafic crust and also the presence of 2 Ga old juvenile mafic crust. These units had either underlain the northern part of the Pannonian Basin during Pliocene or had been exposed during the deposition of Miocene clastic sediments. The absence of Mesoproterozoic, Grenvillian zircons (0.9–1.8 Ga) in the pre-Cenozoic population of zircon xenocrysts is provisionally interpreted as indicating the evolution of the zircon source area within the west-African Craton.

Ichnofacies distribution in the Eocene-Early Miocene Petra Tou Romiou outcrop, Cyprus: sea level dynamics and palaeoenvironmental implications in a contourite environment

Ichnological analysis of the carbonate contourite drift at the Petra Tou Romiou outcrop (southern Cyprus) reveals a relationship between sea level dynamics, shoreline position, sedimentation rate, flow hydrodynamics and trace fossil assemblages. The base of the outcrop is composed of chalky deposits showing the Zoophycos ichnofacies attributes. The transition to the first contouritic interval beds is marked by the gradual disappearance of Zoophycos and dominance of horizontal traces. This change is caused by a gradual sea level fall determining an increase in proximity and energy conditions in the environment that favoured the development of distal Cruziana ichnofacies. Upper contouritic interval beds contain abundant burrow systems with vertical components. Increased ichnodiversity, particularly among vertical morphologies, coincides with the appearance of Teichichnus, Gyrolithes and rare Ophiomorpha, revealing a transition to the proximal Cruziana ichnofacies, related with the maintenance of the previous trend toward more proximal and higher energy settings. The differentiated ichnofacies in the Petra Tou Roumiou carbonate drifts are controlled by complex interactions between variable environmental factors with sea level dynamics playing a major role.

Parvimico materdei gen. et sp. nov.: A new platyrrhine from the Early Miocene of the Amazon Basin, Peru

Three field seasons of exploration along the Río Alto Madre de Dios in Peruvian Amazonia have yielded a fauna of micromammals from a new locality AMD-45, at ∼12.8°S. So far we have identified the new primate described here as well as small caviomorph rodents, cenolestoid marsupials, interatheriid notoungulates, xenarthrans, fish, lizards and invertebrates. The site is in the Bala Formation as exposed where the river transects a syncline. U-Pb dates on detrital zircons constrain the locality's age at between 17.1 ± 0.7 Ma and 18.9 ± 0.7 Ma, making the fauna age-equivalent to that from the Pinturas Formation and the older parts of the Santa Cruz Formation of Patagonian Argentina (Santacrucian). The primate specimen is an unworn M1 of exceptionally small size (equivalent in size to the extant callitrichine, Callithrix jacchus, among the smallest living platyrrhines and the smallest Eocene-Early Miocene platyrrhine yet recorded). Despite its small size it is unlike extant callitrichines in having a prominent cingulum hypocone. Based on the moderate development of the buccal crests, this animal likely had a diet similar to that of frugivorous callitrichines, and distinctly different from the more similarly-sized gummivores, Cebuella and C. jacchus. The phyletic position of the new taxon is uncertain, especially given the autapomorphic character of the tooth as a whole. Nevertheless, its unusual morphology hints at a wholly original and hitherto unknown Amazonian fauna, and reinforces the impression of the geographic separation of the Amazonian tropics from the more geographically isolated southerly parts of the continent in Early Miocene times.

The continental crust contributes to magmatic hydrothermal gold deposit in Ciemas, West Java, Indonesia: Constraints from Hf isotopes of zircons and in situ Pb isotopes of sulfides

Multiple periods of arc magmatism induced by the subduction of the Indian-Australian Plate northward developed on Java Island, and multistage porphyry-epithermal metallogenic systems occurred within the Late Eocene-Early Miocene and the Late Miocene-Early Pleistocene magmatic belts. These porphyry-epithermal metallogenic systems have obvious spatial variations. In West Java, there are large populations of low-sulfidation type epithermal deposits, while East Java and its east are characterized by the occurrences of porphyry deposits. However, the newly discovered Ciemas deposit in West Java, a Middle Miocene (~17 Ma) porphyry-epithermal Au deposit, provides an opportunity for further understanding the porphyry-epithermal mineralization in Java. To elucidate the controlling factors of porphyry-epithermal mineralization in West Java, we analyzed the Hf isotopies of zircons from the igneous rocks and in situ Pb isotopes of sulfides (galena, pyrite, arsenopyrite) in the Ciemas deposit. The results show that the zircons εHf (t) of igneous rocks are uniform with an average value of −11.5 ± 0.39, and the peak value of TDM2 is 1500–1650 Ma, suggesting the Middle Miocene arc magmatism in Ciemas suffered intense crustal contamination. The Pb isotopic compositions of sulfides are very uniform and have high amounts of radiogenic lead. The mean ratios of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb are 39.343 ± 0.059, 15.73 ± 0.015 and 18.854 ± 0.025, respectively, indicating that the mineralization materials of the Ciemas gold deposit mainly originated from ancient continental crust. The multistage arc magmatism induced by the subduction of the Indian-Australian Plate northward beneath Java Island control the porphyry and epithermal mineralization in Java. The Middle Miocene arc magmatism in Ciemas contaminated intensely by the Sundaland, and the ancient continental crust provides the main metal source for the Ciemas deposit in West Java.

New age constraints on the Lan Sang gneiss complex, Thailand, and the timing of activity of the Mae Ping shear zone from in-situ and depth-profile zircon and monazite U-Th-Pb geochronology

The Mae Ping shear zone (MPSZ) is one of four major strike-slip systems in Thailand and a key structural element in some models of the Cenozoic tectonic evolution of Southeast Asia. In northwestern Thailand, the MPSZ exposes a ∼5-km-wide core of intensely deformed high-grade metamorphic and minor undeformed magmatic rocks, the Lan Sang gneiss complex (LSGC). Despite previous efforts to determine the chronology of the LSGC and, ultimately, the MPSZ, the evolution of this gneiss complex remains incompletely resolved. Here we present new zircon and monazite U-(Th-)Pb LA-(MC-)ICP-MS ages and whole-rock geochemical analyses from three peraluminous, high-K (meta)igneous granitic rocks (augen gneiss, sheared granodiorite, undeformed subvolcanic dike) of the LSGC. Our zircon U-Pb dating suggests that the granitic protolith of the augen gneiss intruded metasedimentary basement of Sibumasu as early as ∼235–220 Ma. Zircon rim and monazite U-(Th-)Pb ages from the same sample attest to periods of metamorphic recrystallization and overgrowth in the Late Triassic-Early Jurassic, Early Cretaceous and Eocene. The latter event had started by ∼45 Ma and culminated in partial melting of the basement gneisses and the intrusion of granodiorite magma into the LSGC at ∼35 Ma, contemporaneous with ductile deformation along the MPSZ. A late undeformed subvolcanic dike that crosscuts the mylonitic fabric of the calc-silicate and marble core of the MPSZ, dated in this study at ∼22 Ma, may indicate that ductile shearing had ceased by that time. Thus, our study provides the first evidence for Late Eocene-Early Miocene magmatism in the LSGC.

Geomorphologic and Glacial Evolution of the Cachapoal and southern Maipo catchments in the Andean Principal Cordillera, Central Chile (34°-35º S)

We present here a reconstruction of the post late Miocene landscape evolution of the western slope of the Andean Cordillera Principal near 34°20’ S. We base our analysis on the available geological information, a morphological characterization of the landform assemblages in the Cachapoal and southern Maipo catchments, and the first 10Be exposure ages for moraines in this area. The Cachapoal drainage basin is characterized by a variety of morphological features, like an elevated low-relief surface, volcanoes and lava flows on valley slopes, U-shaped valley sections, roches moutonnées, and large glaciated areas. Different kinds of deposits have been included in the study, such as moraines, lacustrine and landslide deposits, and a well-developed system of fluvial terraces in the more distal part of the Cachapoal catchment. Landslides are mostly developed on rocks of the late Eocene-early Miocene Abanico Formation. and are less frequent in outcrops of the overlying, early to middle Miocene Farellones Formation. We estimate that the lowest end moraine in the Cachapoal catchment is located next to the locality Bocatoma Chacayes (~950 m altitude), though covered by a major landslide. No evidence exist for glacial deposits further down stream in this region. Lateral moraine ridges of the Cachapoal Glacier at Los Cerrillos yielded 10Be exposure ages of 20.3±2.9 and 21.9±5.3 ka that indicate they are associated with the Last Glacial Maximum (LGM). Holocene moraines exist next to all glacier tongues. Of particular interest in this region is the 12 km-long debris-covered Cachapoal Glacier, the longest valley glacier in the central Chilean Andes, and its distal and proximal moraine deposits. Two lateral moraines adjacent to the present-day Cachapoal Glacier yielded exposure average ages of 13.5±2.4 ka for the external ridge, indicating the Younger Dryas, and 3.8±0.8 ka for the internal ridge, an age that coincides with the 4.2 ka global climatic event that marks the beginning of the Meghalayan Age, at the end of the Holocene. The large size of this moraine on both sides of the ice tongue indicates the great development of the glacier at that time. Some of these ages coincide with ages obtained further north in the Maipo drainage basin, at the latitude of Santiago, and in the eastern flank of the cordillera, however, no pre-LGM deposits were found here, unlike the other mentioned regions. This difference together with the much lower altitude of the LGM moraine deposits in the study region suggests that the Cachapoal catchment is a transition zone to a more humid region further south, and indicates the great need for further reconnaissance and dating of glacial deposits in this Andean region. Our analysis of the geomorphological evolution is consistent with incision start for the Cachapoal Valley in latest Miocene. In this process, glacier incision was apparently not much effective until mid-Pleistocene time, when volcanism was active in the higher regions of the mountain range covering areas not yet incised, whereas in the western Principal Cordillera lavas flowed in deeply incised valleys. Pleistocene glaciers deepened and shaped the already incised valleys, which are presently mostly occupied by rivers.

Palynological Characteristic of the Eocene–Early Miocene of the Kvachina Bay Section, West Kamchatka

Six associations of dinocysts, spores, and pollen of various ages are distinguished in the Cenozoic marine deposits of the Kvachina Bay section as a result of study of stratigraphic occurrence of palynomorphs. Their analysis allowed us to date the deposits of the Tigil and Belesovataya units to the Bartonian–Priabonian and Oligocene–Early Miocene, whereas the overlapping lower part of the Kavran Group is dated to the Early Miocene. The age of dislocated rocks beneath the Tigil Unit is estimated as late Ypresian–?early Lutetian. On the basis of the revealed changes in the ratios of the ecological groups of palynomorphs, conclusions were made about the paleoenvironments in which the formation of strata took place in various time intervals.

Palynological characteristics of the Eocene–Early Miocene of Kvachina Bay, Western Kamchatka

As a result of studying the stratigraphic distribution of palynomorphs in the Cenozoic marine strata of the Kvachina Bay section, six different age associations of dinocysts, spores, and pollen have been identified. Their analysis made it possible to date the deposits of the Tigil Unit by the Bartonian–Pribonian, the Belesovataya Unit – by the Oligocene–Early Miocene, and the overlying lower part of the Kavranian Series – by the Early Miocene. The age of the dislocated rocks underlying the Tigil Unit is estimated as Late Ypresian–(?) Early Lutetian. On the basis of the revealed changes in the ratios of the ecological groups of palynomorphs, conclusions were made about the paleoenvironmental in which the formation of strata took place in various time intervals.

Minorca, an exotic Balearic island (western Mediterranean)

Despite forming part of the Balearic group of islands, Minorca differs stratigraphically and structurally from Majorca and Ibiza: i) Paleozoic rocks are abundant in Minorca but are very scarce in Majorca and are absent in Ibiza. Eocene-Oligocene sediments are virtually absent in Minorca but crop out extensively in Majorca, ii) Contractional structures in Minorca differ in direction (aligned SW-NE in Majorca and Ibiza and N-S in Minorca) and in age from those in Majorca and Ibiza. In addition, Paleozoic deposits of Minorca do not correlate with those of Sardinia, where in addition the Triassic sediments are not very abundant. Contractional deformation in Sardinia is in part older (late Eocene-early Miocene) than in Minorca (early Miocene?). Given its Neogene clockwise rotation, Minorca cannot be considered a small block dragged by the early Miocene counter clockwise rotation of the Corsica-Sardinia block. Furthermore, the Paleozoic and Mesozoic stratigraphy of Minorca (siliciclasticlate Paleozoic rocks, Triassic Germanic facies and Jurassic carbonates) has affinities with that of the southern part of the Catalan Coastal Ranges. Thus, of all the Balearic islands, Minorca seems to have traveled the farthest during the Valencia Trough rifting with the result that it resembles an exotic island forming part of the Balearic foreland.

Ultra-magnesian olivine-bearing ultramafic lava blocks within Cenozoic accretionary sediments at Shizuoka, Japan: Implications for young, hot plume activity beneath the western Pacific Plate

Ultra-magnesian igneous olivine is thought to crystallize from ultramafic melts and can therefore provide information about physicochemical conditions and the geochemistry and lithology of the source in the context of extremely hot mantle activity. This study focuses on the petrology and mineralogy of the Shizuoka meimechites, a series of ultra-magnesian olivine-bearing ultramafic lava blocks embedded in middle Eocene–early Miocene accretionary sediments at Shizuoka, Japan. Olivine phenocrysts within the Shizuoka meimechites have Fo compositions of ca. 81–92.8 mol%, where Fo = 100 Mg/(Mg + Fe). These ultra-magnesian olivines have trace-element compositions that are indicative of derivation from ultramafic melts that were in equilibrium with peridotitic mantle olivine. Al-in-olivine geothermometry yielded crystallization temperatures of ~1450 °C for Fo92.5–92.8 olivine, higher than the potential temperature of present-day mid-ocean ridge basalt source mantle material and similar to the potential temperatures of some large igneous provinces and ocean island basalts. Primary melt compositions in equilibrium with Fo92.5–92.8 olivine were estimated using the whole-rock compositions of the ultramafic lavas and are meimechitic, with MgO concentrations of ~21.4–27.0 wt% and SiO2 concentrations of 45.4–44.5 wt%. The potential temperature of the source mantle region for these meimechites (Tp) is estimated to be ~1486 °C–1705 °C, which is consistent with the Al-in-olivine geothermometry when considering adiabatic cooling during magma ascent. The relationship between Tp and Al-in-olivine temperature estimates for these lavas is consistent with global examples of ultra-magnesian olivine-bearing lavas. These lavas provide evidence of hitherto unknown Late Cretaceous–early Miocene deep mantle activity beneath the western Pacific region.

U-Pb monazite ages from the Pakistan Himalaya record pre-Himalayan Ordovician orogeny and Permian continental breakup

The Greater Himalayan Sequence in India and Nepal records crustal thickening processes that took place during and following the onset of India-Asia collision (ca. 54–50 Ma). These resulted in late Eocene–early Miocene kyanite- and sillimanite-grade regional metamorphism, and Oligocene–Miocene crustal anatexis, which formed migmatites and leucogranites. We present new U-Pb monazite data for kyanite- and sillimanite-grade gneisses of the Neoproterozoic to Cambrian Tanawal Formation in the Pakistan Himalaya, which have metamorphic ages of 482.4 ± 7.9 Ma and 464.5 ± 4.0 Ma, respectively. These ages, together with along-strike equivalent rocks in the Lesser Himalaya of India and Nepal, help to define an Ordovician orogeny (the Bhimpedian orogeny, also called the Kurgiakh orogeny) spanning at least from 490 to 460 Ma, which followed Neoproterozoic–Cambrian sedimentation and preceded Late Ordovician–Silurian postorogenic molasse deposition and development of a stable shelf margin at 460–440 Ma. These new ages for peak metamorphism of Neoproterozoic rocks in the Pakistan Himalaya overlap with those of widespread S-type granites that exist along the length of the Lesser Himalaya (e.g., Mansehra, Mandi, and Kathmandu granites), Greater Himalaya (e.g., Nanga Parbat, Kinnaur Kailas, and Ama Drime), and in the North Himalayan domes (e.g., the Tso Morari, Kangmar, and Kampa domes). Thus, based on stratigraphic, metamorphic, and U-Pb geochronological criteria, we equate rocks of the Tanawal Formation gneisses to the Lesser Himalayan rocks to the east and rocks of the Alpurai Group to the Higher Himalaya. Our data also confirm that the Lesser, Greater, and Tethyan Himalaya are all part of a single contiguous plate. Staurolite-grade schists from a higher structural level of the Tanawal Formation record U-Pb monazite ages of ca. 272–267 Ma, indicating the occurrence of Permian regional metamorphism in the area concomitant with major rifting and extrusion of the Panjal Trap volcanics.

GEOHAZARDS IN SANDAKAN TOWN AREA, SABAH, MALAYSIA

The geology of the Sandakan town area provides a favourable setting for geomorphological hazards occurrences. The exposed rocks in the study area and its surrounding vary in types and ages, from Late Eocene-Early Miocene Neogene’s clastic sediment of the Garinono Formation, the Sandakan Formation and Volcanic Facies to vary recent Quaternary alluvial materials which are still being deposited. These rock units are dissected by numerous lineaments with complex structural styles developed during series of regional Tertiary tectonic activities. Rapid urbanization activities have caused changes in the land use. Urbanization processes may contribute to the exposure of impervious surface, loss of vegetation cover, modification of slope gradient and drainage systems. The last decade has seen slope failure, flash flood and erosion events, which have claimed lives, damaged properties and increased the cost of maintenance. The main factors causing geomorphological hazards occurrences in the study area are natural (geology, meteorology, topography and drainage system) and human factors (lack of proper planning, human activities and community’s attitude). Serious efforts to increase the community’s awareness to geomorphological hazards occurrences and reconstruction of natural ecosystem must be taken. To handle this issue, both prevention and mitigation are necessary. At the planning level a multi disciplinary approach to zoning, risk assessment and design with construction practices is recommended. This is to ensure that future activities will not cause further damage to natural environmental condition or ecosystem.

Source rock evaluation of Middle Eocene–Early Miocene mudstones from the NE margin of the Black Sea

Abstract This study comprises the source rock evaluation of 122 Late Middle Eocene–Early Miocene mudstones from the NE margin of the Black Sea. Samples are immature to early mature. The majority of samples have moderate to very good organic richness, poor to moderate source potential and a hydrogen-deficient to gas-prone source rock quality. However, a significant proportion of the samples have good to excellent organic richness and source potential, and an oil- and gas-prone quality derived from amorphous-rich kerogens. These samples would generate significant amounts of oil and associated gas where buried to peak maturity. They come from the lowermost (Rupelian) part of the Maykop Series and the late Bartonian–early Priabonian Kuma Suite or its stratigraphic equivalents. The Rupelian source-rock interval(s) in west Georgia is at least 60 m thick and potentially as much as 200 m thick. It has a source potential index (SPI) of 0.7–2.5 t HC m −2 . The thickness of the Kuma Suite-equivalent source rock interval south of the western Greater Caucasus is unconstrained. Maykop Series source rocks occur in the Black Sea Basin. Prospective Kuma Suite-equivalent samples on both the northern and southern margins of the Black Sea imply that similar sediments may also be present in the basin.

Mesozoic and Cenozoic tectono-thermal reconstruction of the western Bohai Bay Basin (East China) with implications for hydrocarbon generation and migration

Studies on the tectono-thermal evolution of the western Bohai Bay Basin (WBBB), including the Jizhong Sub-basin and Cangxian Uplift, are important for further petroleum exploration and exploitation. This study aims to reconstruct the tectono-thermal history of the WBBB based on a combination of 125 vitrinite reflectance (Ro) data and seven apatite fission track (AFT) and nine apatite (U-Th)/He (AHe) ages. The effective AFT ages range from 60.3 to 97.0Ma, with mean track lengths of 10.86–12.64μm. The variable single-grain AFT ages are explained to be due to the parameter Dpar. The effective AHe ages range from 21.1Ma to 75.0Ma. Two rapid cooling events revealed by the thermal modeling results occurred during the Early-Late Cretaceous (130–90Ma) and Late Eocene-Early Miocene (40–18Ma), respectively. The Fuping Complex, which is located in the western margin of the WBBB and mainly composed of the Paleo-proterozoic high-grade gneisses, experienced the intensive extension-detachment during the Early-Late Cretaceous along with the subduction of the Izanagi Plate, that was probably responsible for the first cooling event. The second cooling event was caused by the subduction of the Pacific Plate during the Middle Eocene-Early Miocene (43–23Ma), as well as the collision of the Indian and Eurasian Plates and the rollback of the subducting Pacific Plate during the Early Miocene (23–18Ma). The WBBB experienced two heat flow peaks of ∼75 and ∼80mW/m2 during the Early Cretaceous and the Late Eocene, respectively. During the Late Eocene-Early Miocene, rapid subsidence in the Baxian Depression (one secondary tectonic unit of the Jizhong Sub-basin) coupled with the rapid uplift in the Cangxian Uplift caused the Shahejie Formation of the middle-upper Eocene to generate gas during the Early Miocene. Meanwhile, tectonic movement during the Early Miocene also caused faults to become migration paths, as revealed by the homogenization temperature of the fluid inclusion. This study provides new insights regarding the tectonic and hydrocarbon evolution of the WBBB.

Hydrocarbon source potential of Eocene-Miocene sequence of Western Sabah, Malaysia

An evaluation of the petroleum generating potential of onshore Eocene-Miocene sequences of Western Sabah, Malaysia was performed based on organic petrological and geochemical methods. The sequences analysed are the Belait, Meligan, Temburong and West Crocker formations of western Sabah. The Belait Formation which is Stage IV equivalent in the offshore represents one of the major source rock/reservoirs of the petroleum-bearing Sabah Basin. The Eocene-Early Miocene West Crocker and Temburong formations are deepwater turbidites whilst the Miocene Meligan and Belait formations are shallow marine fluvio-deltaic deposits. The vitrinite reflectance and pyrolysis Tmax values show that the Belait samples are generally immature for hydrocarbon generation, whereas the Meligan, Temburong and West Crocker samples are in the mature to late maturity stage of hydrocarbon generation. The overall bulk source rock properties of the Belait and Meligan show fair to good petroleum source rock potential with TOC more than 1 wt %, hydrocarbon yield in the range of 400–1300 ppm and moderately high HI for many of the samples. Most of the samples representing the Temburong and West Crocker formations have TOC less than 1 wt% and have no to fair hydrocarbon generating potential. Interestingly, the samples collected in the West Crocker Formation characterized by slump deposits (MTD) have TOC>2 and possess good to excellent hydrocarbon generating potential. The organic matter present in all of the studied formations is mainly of terrigenous origin based on the abundance of woody plant materials observed under the microscope. Consequently, the analysed sequences are predominantly gas prone, dominated by Type III and Type III-IV kerogen except for minor occurrence of mixed oil-gas prone Type II-III kerogen in the Belait Formation and in the slump mass transport deposits (MTD) of the West Crocker Formation.