Cenozoic Geology Research Articles

How a New Cenozoic Geology and Glacial History Paradigm Explains Anomalous Monongahela River Drainage Basin Topographic Map Evidence, PA, WV and MD, USA

A recently proposed and fundamentally different Cenozoic geology and glacial history paradigm (new paradigm) is used to explain previously reported and other anomalous Monongahela River drainage basin drainage system evidence (observable on detailed topographic maps in the form of barbed tributaries, asymmetric tributary drainage basins, large abandoned meander cutoffs, and poorly explained transverse drainages and abandoned transverse drainages). The north-oriented Monongahela River drainage system according to the accepted Cenozoic geology and glacial history paradigm (accepted paradigm) originated during preglacial times and was blocked by continental icesheets to form today’s Ohio River. Based on Missouri River drainage basin topographic map evidence the new paradigm predicts the Monongahela River drainage system developed during immense and prolonged south- and southwest-oriented continental icesheet melt water floods. The new paradigm also predicts icesheet caused regional uplift created a deep “hole” in which a thick icesheet was located and which forced south-oriented melt water floods to flow in southwest directions along the deep “hole’s” southeast rim (now the Ohio River-Atlantic Ocean drainage divide) until continued deep “hole” rim uplift and the deep valley headward erosion from space being opened up by icesheet melting reversed the flow direction to create the north-oriented Monongahela River drainage system. This new paradigm interpretation explains previously reported and other anomalous Monongahela River drainage system topographic map evidence and suggests the Monongahela River drainage system developed while a continental icesheet melted and not during preglacial time as has been commonly reported.

Structures and sand injectites in Oligocene deep-lacustrine deposits, Bach Long Vi island, Gulf of Tonkin, Vietnam: Integrating UAV imaging with modern field work methods

Located at the junction between the Beibuwan Basin and the Song Hong Basin in the Gulf of Tonkin, the Bach Long Vi (BLV) island offers a rare window into the Cenozoic geology of Indochina and surrounding region. The island exposes 5 km-long continuous outcrop of weakly to moderately dipping Oligocene deep-lake deposits along the coastline. Using integrated UAV imaging and modern field methods, we characterized the deformation on the island at unprecedented level of details, and then related these features to regional tectonic events. BLV's mudstone-rich succession was intruded by pervasive sand injectites which consist of three main types: linear dikes, irregular dikes, and irregular sandstone bodies. Linear dikes and irregular dikes are found throughout most of the island. Linear dikes are steeply dipping, trend dominantly ENE, and tends to be thicker close to the top of the island stratigraphy. Irregular dikes have contorted shapes both in plan view and cross-section, and often connect adjacent linear dike segments. Irregular sandstone bodies are located toward the highest part of the island stratigraphy, and are characterized by depositional sands modified by sand injection processes. Most of the sand injectites on BLV constitute an interconnected complex that formed at the same time, probably in the late Oligocene during syn-rift. Sand injectites are later cross-cut by NW-SE left-lateral and its conjugate NE-SW right-lateral strike-slip faulting. The inferred ENE-trending maximum principal stress and NNW-trending minimum principal stress of this deformation is compatible with the regional end-Oligocene inversion as indicated by seismic data.

Use of Topographic Map Evidence to Locate a New Cenozoic Glacial History Paradigm’s Deep “Hole” Rim in Northeast New Mexico and Southern Colorado, USA

A recently proposed Cenozoic geology and glacial history paradigm requires a thick North American continental ice sheet to have been located within an ice sheet created and occupied deep “hole” and predicts large south-oriented meltwater floods flowed across the deep “hole’s” southern rim before rim uplift progressively diverted floodwaters toward the Mississippi River valley, which in time became the only deep “hole” southern exit (the accepted paradigm does not recognize such an ice sheet created deep “hole”). Possible locations for the new paradigm deep “hole” rim in Great Plains regions east of the Sangre de Cristo Mountains are considered with the one being the Purgatoire-Canadian River drainage divide in the Raton Mesas area along the Colorado-New Mexico border and a second being the Canadian-Pecos River (Arkansas River-Gulf of Mexico) drainage divide in San Miguel County (NM). Detailed topographic maps indicate streams of what could have been south-oriented melt water once crossed the two studied drainage divides with headward erosion of the northeast-oriented Purgatoire River drainage basin diverting south-oriented water toward the east-oriented Arkansas River (and Mississippi River valley) while headward erosion of east-oriented Canadian River tributary valleys beheaded south-oriented flow to the south-southeast oriented Pecos River (flowing to the Rio Grande River–which then flows to the Gulf of Mexico). While the Purgatoire-Canadian River drainage divide has some deep “hole” rim characteristics, those characteristics disappear in an eastward direction and the Canadian River, like the Purgatoire River, is an Arkansas River tributary. East-oriented Canadian River headwaters and tributary valley headward erosion diverted south-oriented flow from the Rio Grande River to the Mississippi River valley (via the Canadian and Arkansas Rivers), which means the new paradigm’s deep “hole” rim southern margin should be located along or near the Arkansas River-Gulf of Mexico drainage divide.

Active Faulting of Landforms along the Tuosuhu-Maoniushan Fault and Its Seismotectonic Implications in Eastern Qaidam Basin, China

Abstract The fold-and-thrust belt along the northern margin of the Qaidam basin is a typical active tectonic belt located in the northeast Tibetan Plateau. This belt is at a high risk of strong earthquakes with magnitudes larger than 6, as shown by multiple recorded events during 1962–2009. The lack of detailed late Quaternary surficial faulting data and systematic seismotectonic studies has posed difficulties in properly assessing the seismic risks and understanding the ongoing geodynamics in this region. In this study, we mapped the geomorphic features and fault traces from high-resolution satellite images and field investigations of the Tuosuhu-Maoniushan fault (TMF). Field photogrammetry was conducted to obtain deformation measurements using a DJI M300 real-time kinematic (RTK) drone. The TMF displaces the Holocene and late Pleistocene alluvial terraces in the eastern Qaidam basin. This fault dips to the south in the west and central segments (as a boundary of the Denan depression) and to the north in the eastern segment along the piedmont of the Maoniushan Mountains. The vertical slip rate is estimated to be 0.37 ± 0.08 mm/yr, which is similar to that of the active southern Zongwulongshan fault. By integrating our investigations with the previously published studies on deep structures and Cenozoic geology of the region, we propose a deep-seated thrust model for the seismotectonics of the northern margin of the Qaidam basin. The Aimunike, Tuosuhu-Maoniushan, southern Zongwulongshan, and Zongwulong faults, along with many folds, form an active compressional zone. The complex across-strike structures and along-strike segmentation could facilitate the release of strain through earthquakes of magnitude 6–7 in this broad seismotectonics belt, rather than through strong surface-rupturing events resulting from a single mature large fault.

How a New Cenozoic Geology and Glacial History Paradigm Explains Topographic Map Drainage System and Erosional Landform Evidence: Elbert and Lincoln Counties, Colorado, USA

Detailed topographic map drainage system and erosional landform evidence such as drainage route orientations, drainage divides, divide crossings (low points on drainage divides), erosional escarpments, and similar features in the east central Colorado Elbert and Lincoln County region are considered as pieces of a complex but solvable drainage history puzzle. A satisfactory solution to date has eluded investigators who have worked from the accepted Cenozoic geology and glacial history paradigm (accepted paradigm) perspective in which climatic and tectonic factors operating over long time periods lead to what might be considered to be a randomly determined regional drainage history. A new and fundamentally different Cenozoic geology and glacial history paradigm (new paradigm) in which immense and prolonged south-oriented continental ice sheet meltwater floods flowed across the Elbert and Lincoln County area which at that time was near the rising rim surrounding a thick continental icesheet created and occupied deep “hole”. Map evidence documents how northeast-oriented Republican River headwaters valleys eroded headward across must have been large southeast-oriented floods probably moving toward what at that time would have been an actively eroding and deep east-oriented Arkansas River valley head and how those massive southeast-oriented floods subsequently lowered the Colorado Piedmont surface before being beheaded and reversed when the deep northeast- and east-oriented South Platte River valley eroded headward to create in an identifiable sequence (from east to west) what are now long north-oriented South Platte River tributaries. New paradigm predicted massive and prolonged south-oriented meltwater floods flowing across what must have been a rising region explains much, if not all of the Elbert and Lincoln County detailed topographic map drainage system and erosional landform evidence.

How a New Cenozoic Geology and Glacial History Paradigm Explains Arkansas-Red River Drainage Divide Area Topographic Map Evidence in and near Pontotoc County, Oklahoma, USA

A new Cenozoic geology and glacial history paradigm (new paradigm), fundamentally different from the accepted Cenozoic geology and glacial history paradigm (accepted paradigm), describes a thick North American continental icesheet (located where continental icesheets are usually reported to have been) which by deep erosion and uplift of surrounding regions created and occupied a deep “hole” (the accepted paradigm does not see this thick ice sheet or the deep “hole”). Unusual erosional landform features in the southeast Oklahoma Pontotoc County region including the asymmetric Canadian-Red River drainage divide, a large escarpment-surrounded basin in which most south-oriented Clear Boggy Creek headwaters begin, and a large escarpment-surrounded upland on which the south-oriented Blue River begins, are used to test the new paradigm’s ability to use large and prolonged south-oriented melt water floods to explain previously unexplained or poorly explained detailed topographic map drainage system and erosional landform evidence. Numerous low points (referred to as divide crossings) indicate large and prolonged south-oriented melt water floods did flow across what is now the Canadian-Red River drainage divide (an interpretation also consistent with Clear Boggy Creek escarpment-surrounded basin and Blue River escarpment-surrounded upland shapes). The new paradigm described massive and prolonged melt water floods also account for previously unrecognized deep regional erosion (which is determinable from detailed topographic map evidence). East-oriented Canadian River valley headward erosion (from the Arkansas River valley) diverted the long-lived south-oriented meltwater floods to the Arkansas River valley and to what ultimately became the deep “hole’s” only southern exit. Previous southeast Oklahoma drainage history interpretations (made from the accepted paradigm perspective in which Rocky Mountain glacier melt water flowed to east-oriented rivers) do not provide adequate water volumes or flow directions to explain the detailed topographic map drainage system and erosional landform evidence, which the new paradigm’s massive and prolonged south-oriented melt water floods do explain.

Late cenozoic geology and geomorphology of the Laguna de Agnia Area, Argentina

Laguna de Agnia is located within an endorheic basin in arid extra-Andean Patagonia. A variety of erosional and depositional landforms, most of which are relict, are well preserved in the basin. Geological, geomorphological, and sedimentological studies, 14C and 40Ar/39Ar ages, and paleomagnetic data allow us to modify the published interpretation of the late Cenozoic stratigraphy of the area and provide an improved understanding of local landscape evolution, and paleoenvironments and paleoclimates in the region. The basin formed during or before the late Oligocene. Miocene pyroclastic deposits, which are widely distributed in this part of Patagonia, were not found within the basin. However, a bajada sloping down toward the east side of the lake likely dates to the Miocene. Basalt lava flows reached the west margin of the Laguna de Agnia depression 3.39 ± 0.02 Ma. A lacustrine phase is manifest in numerous shorelines and related features east of and above the modern lake. This shoreline system, one of the most extensive in Patagonia, provides evidence for high paleo-lake levels associated with cooler and wetter conditions during the late Pleistocene and even in some periods during the Holocene, when Southern Hemisphere Westerlies were more intense than today.

Nature of the pre-collisional lithospheric mantle in Central Tibet: Insights to Tibetan Plateau uplift

The properties of accreted terranes in a large collisional orogen determine, in large part, the nature and subsequent development of the orogen. In this paper we present a detailed study of Late Mesozoic sodic mafic magmatic rocks from Central Tibet. These sodic mafic rocks from Bandatso provide an excellent opportunity to assess the nature and evolution of pre-collisional lithospheric mantle in the Himalayan–Tibetan region, and will thus aid our understanding of the evolution of the orogeny. The Bandatso sodic mafic rocks are characterised by marked oceanic island basalt (OIB)-like enrichment in incompatible elements, such as Nb (up to 139 ppm) and light rare-earth elements. This Late Mesozoic (ca. 148 Ma and 90 Ma) mafic magmatism is likely to be the result of two-stage mantle evolution in the northern Qiangtang. The late Jurassic rocks were derived from carbonated lithosphere metasomatized by subducted oceanic sediments during flat subduction. Whereas the late Cretaceous basanites were likely derived from interaction of lithosphere with upwelling asthenosphere induced by removal of lithosphere that had previously been thickened by relamination. Our study suggests the presence of an inherited carbonated lithospheric mantle beneath the northern Qiangtang prior to continental collision. The conclusions from this work suggest that the enrichment of the mantle source of Cenozoic potassic rock closely related to plateau uplift, more likely result from continental subduction after the late Cretaceous (ca. 90 Ma). These conclusions will help our understanding of the Cenozoic geology of this multi-terrane collision system and uplift mechanism of the Tibetan Plateau.

Cenozoic volcanism, tectonics and mineralisation of Woodlark Island (Muyuw), eastern Papua

Cenozoic geology of Woodlark Island was influenced by events prior to the onset of continental rifting at ca 8 Ma and the slightly later commencement of seafloor spreading in the eastern Woodlark Basin between ca 6 and 3.6 Ma. The embryonic Woodlark Island consisted of latest Paleocene(?)–Eocene shallow marine, deep-water shelf and turbidite deposits (Loluai Formation) and small submarine and emergent mafic volcanic centres (Utavai Basalt Member). Platform carbonates extended across the Woodlark Basin in the late Oligocene–middle Miocene (Nasai Limestone). Onset of middle Miocene eruptions in the north-northeast-trending Okiduse Volcanic Zone (OVZ) was localised in the similarly trending Kulumadau Horst and Graben Zone (KHGZ). Volcanic centres flanked major structures in the 12.5 km wide horst and graben zone, suggesting a link between volcanism and extensional tectonics. It was not an island arc settling, and there are neither andesites nor an obvious subduction zone. Offshore the KHGZ is connected with the similarly trending Nubara Fault, the plate boundary between the Solomon Sea Plate and Woodlark Plate. Contrasting volcanic deposits were erupted from volcanoes of the OVZ, viz. Mt Kabat Eruptive Centre, Uvarakoi Caldera, Watou Mountain Eruptive Centre and Suloga Harbour Tuff Cone. The epithermal Busai and Kulumadau gold deposits are located in the KHGZ. They are hosted by porous and permeable crystal lithic lapilli tuff beds in the Monasiy Tuff (Uvarakoi Caldera). Emplacement of thick dolerite sills (Auyed Dolerite) occurred post-middle Miocene. Sill emplacement coincided with the ca 6–3.6 Ma commencement of seafloor spreading in the eastern Woodlark Basin. A major phase of extensional tectonics along the KHGZ commenced post-middle Miocene and has persisted to the Holocene. Uplift was accompanied by rapid erosion and the widespread deposition of poorly to chaotically sorted gravels (Na’ku’iel Conglomerate). KEY POINTS Middle Miocene volcanism occurred from four volcanic centres in the north-northeast-trending Okiduse Volcanic Zone. Volcanism was confined to the similarly north-northeast-trending Kulumadau Horst and Graben Zone. Volcanism was not located in an island arc setting, as there are neither andesites nor an obvious subduction zone. A major phase of extensional tectonics along the horst and graben zone commenced post-middle Miocene and has persisted to the Holocene. Both the epithermal Busai and Kulumadau gold deposits exhibit lithological controls (porosity and permeability) on ore deposition.

Geology of China and adjacent regions: An introduction

This introduction outlines the papers collected in the special issue “Geology of China and Adjacent Regions”. The papers focus on scientific issues from Archean to Cenozoic geology in the areas including Northwest Pacific to western Central Orogenic Belt concerning tectonics, geophysics, petrology, geochemistry, mineral deposit, and energy resources. A tectonic framework of China and adjacent regions is briefly introduced.

Insights into the Cenozoic geology of North Beirut (harbour area): biostratigraphy, sedimentology and structural history

The biostratigraphy and sedimentology of the outcrops and bedrock recently exposed in archaeological excavations around the harbour area of Beirut (~5 km²) unlock the geological and structural history of that area, which in turn are key to understanding the hydrocarbon and hydrogeological potential of the region. A key location (Site 2) of a studied outcrop section and newly uncovered bedrock is on the northern foothill cliff of East Beirut (Achrafieh). The outcrop section of carbonates is of Eocene beds overlain by conformable Miocene beds. The excavation of the slope bordering the outcrop uncovered a bedrock section of an early Pliocene shoreline of carbonate/siliciclastic sands at its base and topped by a beach-rock structure. The early Pliocene age of the shoreline section is dated by an assemblage of planktonic foraminifera that includes Sphaeroidinellopsis subdehiscens, Sphaeroidinella dehiscens and Orbulina universa. The Eocene carbonates of Site 2 extend the coverage of the previously reported Eocene outcrops in the harbour area. They form a parasequence of thin-bedded, chalky white limestones that includes the youngest fossil fish deposits in Lebanon (Bregmaceros filamentosus). The deposits are dated as early Priabonian by their association with the planktonic foraminiferal assemblage of Porticulasphaera tropicalis, Globigerinatheka barri, Dentoglobigerina venezuelana, Globigerina praebulloides, Turborotalia centralis and Borelis sp. The Middle Miocene carbonates that conformably overlie the early Priabonian, parasequence include a planktonic foraminiferal assemblage of Globigerinoides trilobus, Orbulina universa and Borelis melo. Elsewhere, in the harbour area, the preserved Eocene limestones are also overlain by conformable Miocene carbonate parasequences of Langhian-Serravallian age. Younger argillaceous limestone beds of the Mio/Pliocene age occur in the eastern central part of the harbour area and enclose an assemblage of Truncorotalia crassaformis, Globorotalia inflata and Orbulina universa. The three markers of old and recently raised structural blocks in the harbour area are a Lutetian/Bartonian marine terrace in the south west corner, a lower Pliocene shoreline carbonate section in the north east side and a Holocene raised beach of marine conglomerates in the north east corner of the area. The locations of these paleo-shorelines, less than 2 km apart, indicate a progressive platform narrowing of North Beirut since the Paleogene. This study underpins the geological complexity of the region and contributes to understanding the underlying geology, which will be needed for future regional archaeological, hydrocarbon and hydrogeological exploration.

Mesozoic–Cenozoic geological evolution of the Himalayan-Tibetan orogen and working tectonic hypotheses

The Himalayan-Tibetan orogen culminated during the Cenozoic India – Asia collision, but its geological framework and initial growth were fundamentally the result of multiple, previous ocean closure and intercontinental suturing events. As such, the Himalayan-Tibetan orogen provides an ideal laboratory to investigate geological signatures of the suturing process in general, and how the Earth9s highest and largest orogenic feature formed in specific. This paper synthesizes the Triassic through Cenozoic geology of the central Himalayan-Tibetan orogen and presents our tectonic interpretations in a time series of schematic lithosphere-scale cross-sections and paleogeographic maps. We suggest that north-dipping subducting slabs beneath Asian continental terranes associated with closure of the Paleo-, Meso-, and Neo-Tethys oceans experienced phases of southward trench retreat prior to intercontinental suturing. These trench retreat events created ophiolites in forearc extensional settings and/or a backarc oceanic basins between rifted segments of upper-plate continental margin arcs. This process may have occurred at least three times along the southern Asian margin during northward subduction of Neo-Tethys oceanic lithosphere: from ∼174 to 156 Ma; 132 to 120 Ma; and 90 to 70 Ma. At most other times, the Tibetan terranes underwent Cordilleran-style or collisional contractional deformation. Geological records indicate that most of northern and central Tibet (the Hoh-Xil and Qiangtang terranes, respectively) were uplifted above sea level by Jurassic time, and southern Tibet (the Lhasa terrane) north of its forearc region has been above sea level since ∼100 Ma. Stratigraphic evidence indicates that the northern Himalayan margin of India collided with an Asian-affinity subduction complex – forearc – arc system beginning at ∼60 Ma. Both the Himalaya (composed of Indian crust) and Tibet show continuous geological records of orogenesis since ∼60 Ma. As no evidence exists in the rock record for a younger suture, the simplest interpretation of the geology is that India – Asia collision initiated at ∼60 Ma. Plate circuit, paleomagnetic, and structural reconstructions, however, suggest that the southern margin of Asia was too far north of India to have collided with it at that time. Seismic tomographic images are also suggestive of a second, more southerly Neo-Tethyan oceanic slab in the lower mantle where the northernmost margin of India may have been located at ∼60 Ma. The geology of Tibet and the India – Asia suture zone permits an alternative collision scenario in which the continental margin arc along southern Asia (the Gangdese arc) was split by extension beginning at ∼90 Ma, and along with its forearc to the south (the Xigaze forearc), rifted southward and opened a backarc ocean basin. The rifted arc collided with India at ∼60 Ma whereas the hypothetical backarc ocean basin may not have been consumed until ∼45 Ma. A compilation of igneous age data from Tibet shows that the most recent phase of Gangdese arc magmatism in the southern Lhasa terrane initiated at ∼70 Ma, peaked at ∼51 Ma, and terminated at ∼38 Ma. Cenozoic potassic-adakitic magmatism initiated at ∼45 Ma within a ∼200-km-wide elliptical area within the northern Qiangtang terrane, after which it swept westward and southward with time across central Tibet until ∼26 Ma. At 26 to 23 Ma, potassic-adakitic magmatism swept southward across the Lhasa terrane, a narrow (∼20 km width), orogen-parallel basin developed at low elevation along the axis of the India – Asia suture zone (the Kailas basin), and Greater Himalayan Sequence rocks began extruding southward between the South Tibetan Detachment and Main Central Thrust. The Kailas basin was then uplifted to >4 km elevation by ∼20 Ma, after which parts of the India – Asia suture zone and Gangdese arc experienced >6 km of exhumation (between ∼20 and 16 Ma). Between ∼16 and 12 Ma, slip along the South Tibetan Detachment terminated and east-west extension initiated in the northern Himalaya and Tibet. Potassic-adakitic magmatism in the Lhasa terrane shows a northward younging trend in the age of its termination, beginning at 20 to 18 Ma until volcanism ended at 8 Ma. We interpret the post-45 Ma geological evolution in the context of the subduction dynamics of Indian continental lithosphere and its interplay with delamination of Asian mantle lithosphere.

Influence of dissolution/reprecipitation reactions on metamorphic greenschist to amphibolite facies mica 40Ar/39Ar ages in the Longmen Shan (eastern Tibet)

AbstractLinking ages to metamorphic stages in rocks that have experienced low‐ to medium‐grade metamorphism can be particularly tricky due to the rarity of index minerals and the preservation of mineral or compositional relicts. The timing of metamorphism and the Mesozoic exhumation of the metasedimentary units and crystalline basement that form the internal part of the Longmen Shan (eastern Tibet, Sichuan, China), are, for these reasons, still largely unconstrained, but crucial for understanding the regional tectonic evolution of eastern Tibet. In situ core‐rim 40Ar/39Ar biotite and U–Th/Pb allanite data show that amphibolite facies conditions (~10–11 kbar, 530°C to 6–7 kbar, 580°C) were reached at 210–180 Ma and that biotite records crystallization, rather than cooling, ages. These conditions are mainly recorded in the metasedimentary cover. The 40Ar/39Ar ages obtained from matrix muscovite that partially re‐equilibrated during the post peak‐P metamorphic history comprise a mixture of ages between that of early prograde muscovite relicts and the timing of late muscovite recrystallization at c. 140–120 Ma. This event marks a previously poorly documented greenschist facies metamorphic overprint. This latest stage is also recorded in the crystalline basement, and defines the timing of the greenschist overprint (7 ± 1 kbar, 370 ± 35°C). Numerical models of Ar diffusion show that the difference between 40Ar/39Ar biotite and muscovite ages cannot be explained by a slow and protracted cooling in an open system. The model and petrological results rather suggest that biotite and muscovite experienced different Ar retention and resetting histories. The Ar record in mica of the studied low‐ to medium‐grade rocks seems to be mainly controlled by dissolution–reprecipitation processes rather than by diffusive loss, and by different microstructural positions in the sample. Together, our data show that the metasedimentary cover was thickened and cooled independently from the basement prior to c. 140 Ma (with a relatively fast cooling at 4.5 ± 0.5°C/Ma between 185 and 140 Ma). Since the Lower Cretaceous, the metasedimentary cover and the crystalline basement experienced a coherent history during which both were partially exhumed. The Mesozoic history of the Eastern border of the Tibetan plateau is therefore complex and polyphase, and the basement was actively involved at least since the Early Cretaceous, changing our perspective on the contribution of the Cenozoic geology.

Chapter 7 Cretaceous geology of Myanmar and Cenozoic geology in the Central Myanmar Basin

This chapter presents an account of the Cretaceous System and its tectonic setting in Myanmar, sedimentary sequences of the Bago Yoma, Central Myanmar and the fluvial architecture of the Irrawaddy Sandstone in the Salin Basin. Myanmar can be divided into four north–south-trending belts – the Shan Plateau, Shan Scarp, Central Myanmar Basin and Indo-Burma Ranges (Figs 7.1a & 7.2a) – which lie on two basement blocks (Stephenson & Marshall 1984; Pivnik et al. 1998; Mitchell et al. 2012; Metcalfe 2013). The Shan Scarp and the Myanmar Central Basin lie on the West Burma Block, whereas the Shan Plateau belongs to the Sibumasu Block. To the west, the Indo-Burma Ranges have been interpreted as an accretionary wedge that resulted from the oblique subduction of the Indian Plate beneath the Burma Plate (Maurin & Rangin 2009). Southwards-prograding deltaic sedimentation with syn-tectonic deep-marine sloping to shallow marine sandstones are recorded in Neogene siliciclastic sequences in the westernmost part of Yakhine (Rakhine) Coastal Ranges (Kyi Khin et al. 2014, 2017). Fig. 7.1. ( a ) Regional tectonic map of Myanmar, showing the Myanmar Central Basins (MCB), Mogok Metamorphic Belt (MMB), Wuntho Massif (WTM), Victoria Massif (VM), Tagaung Myitkyina Belt (TMB), Poppa Volcano (P) and Sagaing Fault (modified after Bertrand & Rangin 2003). HB, Hukaung Basin; CB, Chindwin Basin; MB, Minbu Basin; P, Popa Volcano; BYSB, Bago Yoma-Sittaung Basin; PEB, Pyay Embament Basin; IRB, Irrawaddy Delta Basin. ( b ) Location of the northern Bago Yoma area and surrounding geological units (modified after Kyi Khin 1991). Fig. 7.2. ( a ) Tectonic framework and sub-basins of the Central Basin in Myanmar (after Pivnik et al. 1998). ( b ) General outcrops, lithology, structural pattern and study section of the Taungni-Pingadaw area (modified from Naing Maw Than 1993). The Shan Plateau is characterized by a distinctive Cambrian–Triassic succession, similar …

The discovery of a low-angle normal fault in the Taurus Mountains: the İvriz detachment and implications concerning the Cenozoic geology of southern Turkey*

The Ivriz detachment fault has been determined on the southern border of the Ulukisla basin separating the metamorphic Bolkar Group of the Taurus Mountains and the Paleocene-Lower Eocene Halkapinar formation of basin deposits. The fault dips towards the north and has kinematic indicators (asymmetric grain/grain aggregate porphyroclasts, oblique foliation, and S-C fabrics), suggesting a top-to-the-N-NE sense of shearing. The clastic material originating from the Bolkar Group in the sedimentary units of the Ulukisla basin demonstrates that the detachment fault could have been be active during Latest Cretaceous-Eocene times. The Ivriz detachment may have initiated as part of a high-angle breakaway fault (the Aydos main breakaway fault) in the south of the Ulukisla basin. The breakaway fault then rotated to a low-angle normal fault and its northern continuation played an important role in the exhumation of the Central Anatolian Crystalline Complex. This implies that the Upper Cretaceous-Eocene sedimentary basins in central Anatolia were supradetachment basins rather than collision- or arc-related basins as previously suggested.

Cenozoic geology of the Yolomécatl-Tlaxiaco area, Northwestern Oaxaca, Southeastern Mexico: Stratigraphy, structure and regional significance

The Yolomécatl-Tlaxiaco Area, lies in the rugged Sierra Madre del Sur (SMS) of northwestern Oaxaca (YOTLA), southeastern Mexico. Within the area Cenozoic units unconformably overlie metamorphic, clastic and carbonate rock units of Late Paleozoic to Cretaceous ages as well as the Mixteco/Oaxaca Terrane boundary.The Cenozoic sequence, emphasized herein, includes from botton to top: (1) basal, calcilithitic Early Tertiary Tamazulapam Conglomerate, (2) andesitic lava flows of Nduayaco “Group,” (3–4) Epiclastic/pyroclastic strata composing Yolomécatl Formation (∼40.3 ± 1.0 Ma), and Tayata Pyroepiclastics (5) Early Oligocene (∼32.9 Ma), felsic, pyroclastic Nundichi “Group,” (6) Late Oligocene (∼27.7 ± 0.7 Ma) andesitic lava flows of Nicananduta “Group” containing intercalations of unit (7) ?Chilapa Formation (largely lacustrine). Quaternary deposits unconformably overlie the sequence. The structural record includes NNW-SSE folds in the Mesozoic units, and one in Tayata Pyroepiclastics, as well as numerous fractures/faults of diverse types, whose pattern seems to roughly define four geographic/structural domains, NW, SW, S, and E.The Tertiary sequence records four magmatic and six deformational events: Pre-Late Eocene Extension accommodated by the Tamazulapam fault, along which magma of the Nduayaco “Group” moved upward. The next episode is the earliest Late Eocene extension recorded by the Yucuxaco-Santa Cruz Tayata fault was followed by accumulation of Yolomécatl Formation, Tayata Pyroepiclastics, and synsedimentary emplacement of tuff sheets at ∼40.3 ± 1.0 Ma. After this date, left lateral transpression emplaced a Teposcolula Limestone block over Nduayaco “Group” and ?Yolomécatl Formation, whereas the Tayata Pyroepiclastics was folded into an open anticline. Movement along the Yucuxaco-Santa Cruz Tayayata fault suite influenced accumulation of the Nundichi “Group” strata ca. ∼32.9 Ma. Subsequent ENE-WSW extension affected the Nundichi “Group,” partly placing it in contact with Jurassic limestone blocks. Finally, ca. 27.7 Ma, the Nicananduta “Group” was emplaced.The discrimination of YOTLA's Cenozoic magmatic/deformational events correlates well with that of events previously recognized in the SMS, and to the north along the southwestern margin of North America. However, significant differences persist in terms of number, characterization, age and duration of events that cannot be resolved at present. Anyway, differences are expected due to the inherent diachronic nature of magmatism and deformation across SMS, and the fact that the events reported here took place inland, not around the Mixteco/Oaxaca Terranes block, where most events of these kinds occurred.

Volcanological study of the middle Miocene Okiduse Volcanic Group, Woodlark Island (Muyuw), eastern Papua

ABSTRACTWoodlark Island (Muyuw) is located in a tectonically complex region, one of the few places on Earth where continental breakup is occurring ahead of seafloor spreading. Rifting commenced in the late Miocene (8.8–6 Ma) and is associated with the westward-propagating Woodlark Basin Spreading Centre. The island comprises approximately 850 km2 of raised Pleistocene coral reef and associated sediments with a central, moderately elevated range underlain by the middle Miocene calc-alkaline to shoshonitic Okiduse Volcanic Group (new name). It provides an exposure of upper Cenozoic geology in close proximity to the spreading centre. The Okiduse Volcanic Group is host to most of the island's historical gold and silver production and recently defined mineral resources totalling 1.75 Moz gold. This study uses facies analysis of pyroclastic deposits to develop a detailed geological map of the Okiduse Volcanic Group, with a revision and reinterpretation of the unit. Facies associations suggest that two major volcanic centres erupted synchronously during the middle Miocene (14–12 Ma), referred to as the Watou Mountain Eruptive Centre (new name) and the Uvarakoi Caldera (new name). The mafic–intermediate Watou Mountain Eruptive Centre formed during frequent small eruptions of widely varying style. Strombolian, subplinian, vulcanian and dome-related explosive eruptions occurred, alternating with extrusion of block and ash flow deposits and lava domes. Pyroclastic deposits were rapidly reworked from the steep cone, and were redeposited in a series of coalescing aprons surrounding the volcano. The felsic Uvarakoi Caldera formed during a series of violent explosive eruptions by rapid removal of magma from the underlying chamber, followed by collapse. Plinian and possibly phreatoplinian eruptions, as a result of magma–water mixing in the surface environment, resulted in widely dispersed, highly fragmented tuff deposits. The caldera was modified by widespread erosion following eruptions, resulting in fluvial, laharic and slope-wash deposits. This study highlights lithological controls (porosity and permeability) by various units within the Okiduse Volcanic Group on ore deposition.

Mesozoic–Cenozoic geology of the Scotian Basin

Mesozoic–Cenozoic geology of the Scotian Basin

The provenance of Middle Jurassic sandstones in the Scotian Basin: petrographic evidence of passive margin tectonics 1This article is one of a series of papers published in this CJES Special Issue on the theme of Mesozoic–Cenozoic geology of the Scotian Basin. 2Geological Survey of Canada Contribution 20110319.

The tectonic and geomorphological evolution of the Scotian margin and its hinterland is poorly known between Late Triassic rifting and the Early Cretaceous progradation of major deltas. This study determined sedimentary provenance of Middle Jurassic Mohican Formation sandstones from three wells using heavy minerals and mineral chemistry. Indicator minerals such as xenotime, altered ilmenite, and varietal types of garnet and tourmaline are similar to those in Hauterivian–Barremian sandstones in the western Scotian Basin, which are almost exclusively derived from the Meguma terrane. The wells adjacent to the Canso Ridge have more zircon and less ilmenite, indicating a greater contribution of polycyclic reworking, but with an ultimate source in the Meguma terrane. Zircon and ilmenite were likely derived in part from Carboniferous sandstones in eastern mainland Nova Scotia and Cape Breton Island. Any river drainage from the inboard terranes of the Appalachians either was diverted through the Fundy Basin or entered the easternmost Scotian Basin, where the Mohican Formation is 5.5 km thick, along the linear continuation of the southwest Grand Banks transform. Such sediment did not reach the Canso Ridge, suggesting that the Cobequid–Chedabucto fault zone in Orpheus graben was not a significant physiographic feature. This tectonically controlled paleogeography in the Middle Jurassic is quite different from that during active rifting in the Late Triassic – Early Jurassic. Middle Jurassic quiescence was followed in the Tithonian – Early Cretaceous by renewed tectonic uplift associated with rifting of Grand Banks from Iberia and Labrador from Greenland.

Initial rifting and breakup between Nova Scotia and Morocco: insight from new magnetic models 1This article is one of a series of papers published in this CJES Special Issue on the theme of Mesozoic–Cenozoic geology of the Scotian Basin. 2Earth Sciences Sector Contribution 20120024.

New models of magnetic data are presented that provide insight into the early stages of rifting and breakup between Morocco and Nova Scotia. The margins, which began forming during the Late Triassic rifting and Middle Jurassic separation of the North American and African plates, display considerable variability in deeper crustal structure, faulting style, and basin geometry along their length. The central and northeastern portions of the Nova Scotia margin show characteristics of a magma-poor margin, with a high degree of crustal thinning and a complex ocean-continent transition zone with little direct evidence of volcanism. In contrast, the margin to the southwest of Nova Scotia has clearly recognized characteristics of a volcanic-style rifted margin, including seaward-dipping reflector (SDR) sequences that are interpreted as rift-related volcanic flows overlying basement. These SDRs are coincident with a strong linear magnetic anomaly, the East Coast Magnetic Anomaly (ECMA), which shares many characteristics with the West African Coast Magnetic Anomaly (WACMA). Both magnetic anomalies change character and diminish in amplitude northward along the margins. The new models show the expected decrease in magnetic source material towards the northeastern end of the margin and suggest that modest amounts of igneous material, emplaced at or near the edge of the thinned continental crust, will satisfy the observed anomalies in this magma-poor section of the margin. These new interpretations and supporting evidence indicate volcanism was a factor along much of the margin during early rifting between Nova Scotia and Morocco.