Correlation Of Rocks Research Articles

The northbrae rhyolite of Berkeley (California, USA) constrains motion of the proto-Hayward Fault

ABSTRACT Right-lateral transform motion associated with the Pacific-North American plate boundary in the modern-day San Francisco Bay Area occurs across a series of sub-parallel fault zones. Much of this motion is accommodated east of the San Andreas Fault by the faults of the East Bay fault system. A major tool for reconstructing the spatial and temporal history of fault motion is the correlation of offset Neogene volcanic rocks. These Neogene volcanics within the California Coast Ranges formed in association with the slab gap that grew as the Mendocino Triple Junction migrated northward. Some of the volcanic centres have been variably offset by subsequent strike-slip faulting. A felsic volcanic unit exposed in Berkeley, CA, known as the Northbrae rhyolite has variably been interpreted to be one of these Neogene volcanic units or to be a Mesozoic volcanic unit associated with the Coast Range ophiolite. A new U-Pb zircon date of 11.10 ± 0.09 Ma confirms the Neogene volcanic interpretation. This date is indistinguishable from previously published Ar/Ar dates from the Burdell Mountain volcanics of the North Bay region as well as a new U-Pb zircon date of 11.07 ± 0.10 Ma. In addition to the indistinguishable ages, similarities in bulk lithology, zircon crystallization/dissolution textures, and zircon trace element geochemistry are consistent with these rhyolites being associated with the same volcanic centre. This correlation implies that 40 ± 5 km of right-lateral offset occurred to the west of the modern-day position of the Hayward-Rodgers Creek fault zone. This offset represents ∼ 20% of the total offset along the East Bay fault system. A proto-Hayward Fault with a different geometry than that of the present-day played a significant role in the evolution of the fault system. This result highlights the dynamic spatiotemporal variability of strike-slip faults along transform margins.

The effect of weathering on cohesion in granitic fault rocks: A case study from the Yeongdeok Fault, South Korea

Weathering can alter fault-rock cohesion, which is an important criterion in the classification of fault rocks, and can also alter fault-rock mechanical and hydraulic properties. To investigate the effects of weathering on fault rocks, we studied relatively fresh and weathered fault rocks collected from a drill core and outcrop, respectively, of a granitic fault zone (the Yeongdeok Fault, a northern branch of the Yangsan Fault) on the southeastern Korean Peninsula. At the studied outcrop, the Yeongdeok Fault has juxtaposed Triassic granite against Cretaceous sedimentary rocks. Granitic fault rocks in the outcrop are incohesive, whereas the drill core includes both cohesive and incohesive granitic fault rocks. A detailed correlation of the fault rocks from the drill core with those from the outcrop reveals that some incohesive fault rocks from the outcrop are weathered cataclasite. Cataclasites from the drill core are composed of feldspar, plagioclase, and quartz fragments embedded in a matrix of quartz, plagioclase, muscovite, and chlorite. Locally, foliation defined by the preferred orientation of muscovite is developed. The weathered cataclasite comprises quartz, plagioclase, and feldspar fragments, with a fine-grained matrix composed mostly of clay minerals. The measured Chemical Index of Alteration (CIA) values for cataclasite and weathered cataclasite are 47–49 and 60–67, respectively. Measurements of hydraulic properties show that weathered cataclasite has higher porosity and permeability compared with unweathered cataclasite. Physical and chemical weathering are interpreted to have increased the fracture density of the weathered cataclasite and enhanced the dissolution of vein minerals, respectively. These processes have not only contributed to the higher permeability and porosity of the weathered (cf. unweathered) cataclasite but have also resulted in a loss of cohesion. When cohesion is lost due to weathering, distinguishing between cataclasite and fault breccia becomes challenging. Our study demonstrates that the cohesion-based classification of fault rocks becomes limited for fault rocks with CIA value more than 60.

ARKOSE SANDSTONES OF THE KEBEKTA GROUP OF THE UGUI GRABEN (ALDAN SHIELD): AGE, SOURCES, AND DEPOSITION SETTING

The paper presents the results of U-Pb (ID-TIMS) and U–Th–Pb (LA-ICP-MS) geochronological studies of baddeleyite from dolerite dikes of the Sulumat Complex and detrital zircon from red arkose sandstones of the Kebekta Group of the Ugui graben, the Aldan Shield. It has been established that the Kebekta Group have an age of 2.011.87 Ga. The sources of the Kebekta Group deposits were the Archean (2.92–2.52 Ga) igneous and metamorphic complexes of the Chara-Olekma geoblock and the zone of its junction with the West Aldan megablock of the Aldan Shield, as well as unidentified on the present erosion level the Paleoproterozoic (ca. 2.01 Ga) complexes. The obtained geochronological data do not contradict the correlation of terrigenous rocks of the Kebekta Group of the Ugui graben and the Kemen Group of the Kodaro-Udokan trough. The deposition of arkose sandstones of the Kebekta Group correlates in age with the glaciations in Australia and Sweden (ca. 1.9–1.8 Ga) associated with the formation of the Columbia/Nuna supercontinent. It also cannot be ruled out that the deposition of the rocks of the Ugui graben was related to the inflow of glacial material into the intracontinental extensional basin from the southern and/or western (in modern coordinates) framing of the Chara-Olekma geoblock at the stage of collapse of the Paleoproterozoic orogen.

Identification of Alteration Zones Based on Resistivity and Induced Polarization Geoelectric Survey

Air Putih, Lebong Regency's geothermal field, is near gold mining. The relationship between the two can be illustrated in the type of rock alteration. The study aims to identify the rock alteration zone caused by the Air Putih, Lebong Regency geothermal system. It was described by the correlation of rocks' resistivity and chargebility values based on geoelectric measurement. Two tracks spread along the Air Putih tour, with a track length of 240 meters, were used to see variations in resistivity and chargeability values and the depth of geothermal potential due to deeper current penetration to determine the alteration zone in the study area. The results of field measurements are in the form of 2D models processed with Res2DinvX64 software. According to analysis, the subsurface rock lithology in the research area is relatively the same because the location of the two measurement lines is still close together; namely, there are wet valley rocks and alterated rock layers. Pores cause rock layers found in conductive areas in the rock filled with fluid or water at high temperatures. It is evidenced by the detection of manifestations on the surface in the form of warm soil, warm rocks, steamy soil, and small holes containing water grains. The higher the temperature and pressure, the lower the value of rock-specific resistance. At the Air Putih tourist area of Lebong Regency, it is found that it is a zone of prophylitic alteration containing several minerals of andesite lava, breccia, tuff, and soil.

Vodorazdelny Granitic Pluton, Subpolar Urals, and Problems of Correlation of Pre-Ordovician Granitoids and Volcanic Rocks of the Northern Part of the Lyapin Anticlinorium

Vodorazdelny Granitic Pluton, Subpolar Urals, and Problems of Correlation of Pre-Ordovician Granitoids and Volcanic Rocks of the Northern Part of the Lyapin Anticlinorium

Correlation of Neogene Oil and Paleogene Source Rocks in the Middle Huanghekou Sag, Bohai Bay Basin

Several billion-ton Neogene oil fields have been successfully discovered in the middle Huanghekou sag over the past few years. However, the source of the crude oil needs to be clarified, and the relevant oil-source correlation was less carried out. Six source rocks of the third member of the Paleocene Shahejie Formation (Es3) from five wells and sixteen Neogene crude oil samples from nine wells in the middle Huanghekou sag were investigated for the oil-source correlation with the biomarkers and carbon and hydrogen isotopes of saturated hydrocarbon monomers. The distribution characteristics of n-alkanes, C19/C23 ratio of tricyclic terpanes, long-chain tricyclic terpene ratios (ETR), C24 tetracyclic terpane to C26 tricyclic terpene, and distribution characteristics of conventional steranes suggest that the Es3 parent material is of a mixed-source input from terrestrial higher plants and aquatic phytoplankton. The gammacerane to C30 hopane ratio is low, ranging from 0.094 to 0.134, with a mean value of 0.118; the Pr/Ph ratio is less than 1.5. The Neogene oils show the characteristics of a saturated hydrocarbon biomarker similar to Es3. The carbon and hydrogen isotopes of saturated hydrocarbon monomers also corroborate the oil-source correlation from the depositional environment and parent material source, which characterize the low salinity of the water during the Es3 sedimentary period, which was a brackish or a freshwater delta deposition under weak oxidation–weak reduction conditions. The parity dominance of CPI and OEP values (both greater than 1), higher ratios of Ts/Tm (1.174 to 1.383, mean 1.278) and the C29Ts/C29 norhopane, high values of diahopane and diasterane contents (C30diaH/C30H, C27diaS/C27S), and hopane and sterane isomerization parameters (%22S, %20S, %ββ) confirm that the Es3 source rock samples are mature enough to provide crude oil for the middle Huanghekou sag. The biomarker characteristics of regional Neogene crude oil are significantly different from those of Es4 source rocks in the surrounding depressions (sags), indicating the Es4 strata’s absence in the middle Huanghekou sag. Suitable traps need to be discovered around the hydrocarbon-generating center of the Es3 source rock for oil and gas exploration in the future.

The putative earliest Cambrian trilobite–brachiopod association in southern Sichuan Basin of South China

ABSTRACT Parabadiella is considered the earliest trilobite representative in South China and was originally recovered from the mid-upper part of the Guojiaba Formation, in Liangshan section. Previous studies suggested that the earliest brachiopod co-occurred with the oldest trilobite, and the Parabadiella–Eoobolus association from the Xihaoping Member (Cambrian Series 2, Stage 3), in southern Shaanxi was considered the first trilobite–brachiopod assemblage zone in South China. Therein, brachiopods occur together with trilobites recovered in Well JS103 seemingly extending the First Appearance Datum deeply in the lower Cambrian at the central Yangtze Platform. Well JS103 is a shale gas exploration well that targets the lower Cambrian Jiulaodong Formation in southern Sichuan Basin. The uppermost fossiliferous layers are siliciclastic rocks nearly 10 metres thick. Here, two distinct trilobite zones are found, including the lower Parabadiella Zone and the upper Wutingaspis–Eoredlichia Zone. Additionally, the lowermost part of the Guojiaba Formation is poorly fossiliferous, and ranges from 200 to 250 metres in thickness. Thus, the discovery of the brachiopod–trilobite assemblage provides new insights into the biostratigraphy in Sichuan and is of great potentials for biostratigraphic correlation of the siliciclastic rocks in the western margin of the Yangtze Platform.

Organic Geochemistry and Oil-Source Correlation of Oil Seepages and Potential Source Rocks in Qiangtang Basin, China.

Different viewpoints on the oil-source correlation of the Angdarco paleo-reservoir in the Qiangtang Basin, northern Tibet, China, have seriously affected oil and gas exploration in this area. In this work, based on the results of biomarker analysis on six oil seepage samples and 11 potential source rock samples, the oil source of the oil seepages in the Angdarco area was examined by correlating the composition characteristics of n-alkanes, multiple factors of biomarkers, correlograms of biomarker parameters, and δ13C values of individual n-alkanes between oil seepages and potential source rocks. In addition, the sedimentary environment and thermal maturity characteristics of the potential source rocks were also discussed. The biomarkers indicated that the potential source rocks of the Lower Jurassic Quse Formation (J1q) presented characteristics of littoral sediments, deposited under suboxic conditions, while the potential source rocks of the Middle Jurassic Buqu Formation (J2b) were deposited in a marine sedimentary environment and presented characteristics of a low mature to mature stage. The potential source rocks of the Middle Jurassic Xiali Formation (J2x) were deposited in a low-salinity environment and presented characteristics of low-mature source rocks. Finally, the oil seepages of the Buqu Formation were deposited in a suboxic littoral environment and presented characteristics of a low mature to mature stage. It is concluded that the oil seepages in the Angdarco paleo-reservoir were mainly sourced from the Lower-Jurassic Quse oil shales. This work provides a scientific basis for the exploration of paleo-reservoirs in the southern Qiangtang Basin.

The Isotopic Age and Correlation of Carbonate Rocks of the Ara-Oshei Formation (Tunka Ridge, East Sayan)

Abstract —We present results of Pb–Pb geochronology and Sr- and C- chemostratigraphic study of limestones and dolomites of the Ara-Oshei Formation of the Tunka ridge in East Sayan. The δ13C value of the limestones varies from –0.6 to 2.3‰ PDB, the 87Sr/86Sr ratio is within 0.70851–0.70864, and the Pb–Pb age is 521 ± 21 Ma (MSWD = 0.9). The δ13C value of the dolomites varies from –3.9 to 0.5‰ PDB, the 87Sr/86Sr ratio is 0.70844–0.70882, and the Pb–Pb age is 417 ± 8 Ma (MSWD = 2.5). The U–Pb isotope system of the dolomites was disturbed during the geologic evolution of the region, which led to the rejuvenation of their Pb–Pb age in the Early Devonian. The obtained Sr-chemostratigraphic and Pb–Pb data show that the limestones of the Ara-Oshei Formation accumulated in the early Cambrian. This provides a reliable proof that the limestones are part of the Vendian–Cambrian sedimentary cover of the Tuva–Mongolian massif.

Why is intercontinental correlation within the Lower Cambrian so difficult?

Correlation of Lower Cambrian rocks is hampered because there are no widespread and rapidly evolving organisms such as the later agnostids, graptolites, conodonts, ammonites, or planktonic foramini fers, that might provide the basis for a consistent intercontinental biostratigraphy. Four problems illustrate the issue: 1) the age of the oldest trilobites of China; 2) acritarch correlations between Siberia and Baltica; 3) conflicts between archaeocyath and trilobite correlations; and 4) the location of the Lower Cambrian/Middle Cambrian boundary. There is no basis for an internationally useful set of Lower Cambrian stages at this time.

Carbonate microfacies and depositional model of Triassic Pha Kan and Doi Long Formations, Lampang Group, Sukhothai Zone, Northern Thailand

Triassic carbonate rocks of Pha Kan and Doi Long Formations of Lampang Group consist mostly of carbonate successions deposited in the Sukhothai Zone, northern Thailand. These formations are mixed carbonate and siliciclastic sediments and widely exposed in the Lampang area. These deposits are important for the reconstruction of depositional environments and regional correlations of the Triassic carbonate rocks with respect to the volcanic arc of the Sukhothai Zone during the Triassic. The goal of this study is to analyze the lithology and microfacies of the carbonate rocks of the Pha Kan and Doi Long Formations and reevaluate the existing depositional models and carbonate settings. Both formations have diverse skeletal fossils, including foraminifers, sponges, calcimicrobes, calcareous algae, bivalves, echinoderm spines and fragments, ostracods, gastropods, and other fossils. Based on field observations and microfacies analysis, twelve major facies, corresponding to specific depositional environments within a carbonate setting, have been established. The inferred depositional environment is a carbonate platform with a well-developed lagoon, small-scale reefs, and bioclastic and oolitic shoals, as parts of a carbonate ramp. The microfacies and sedimentological study show that this carbonate system was influenced by the nearby volcanic arc. Consequently, our study shows that the Lampang Group in northern Thailand can be correlated with the Lincang Massif of the western Yunnan Province, PRC and the northwestern Lao PDR.

Glass fission-track ages, composition, and origin of tephra beds in the Upper Cretaceous Kanguk Formation, Banks Island, Arctic Canada

More than 50 conspicuous tephra beds occur in the Kanguk Formation on the southwestern coast of Banks Island. Their glass shards are remarkably well preserved and permit comprehensive characterization, offering the potential for reliable, precise correlation of Upper Cretaceous sedimentary rocks across the three major depocentres of the Arctic Archipelago and adjacent northern continental margin: Sverdrup, Banks, and the Beaufort–Mackenzie basins. Twenty-one tephra beds were analyzed; all have a high-K, peraluminous, rhyolitic composition, with quartz, plagioclase, ilmenite, biotite, and zircon as the dominant minerals. Trace-element concentrations, especially low Nb and Ta, show that the parental magmas formed in a continental-margin subduction environment. Glass fission-track ages range from 100 Ma to younger than 60 Ma, and indicate a very low sedimentation rate giving a very condensed sedimentary sequence on southwestern Banks Island — a sequence that may well contain the K–Pg transition. Source calderas are unknown but most likely are situated in east-central Alaska and the central and northern Kuskokwim volcanic belt, some 1000 to 1500 km distant from southwestern Banks Island. It is also possible that some of the very thin tephra beds come from the Okhotsk–Chukotka volcanogenic belt in northeastern Russia.

Antiquity and tectonic lineage of Japanese Islands: New discovery of Archean–Paleoproterozoic Complex

A new rock complex has been discovered from the Tsuwano area of Southwest Japan. This granitic rock complex namely, Tsuwano Complex contains foliated granitic gneiss, massive granitoids, and metaquartzite, forming a distinct unit at the westernmost end of the east-west elongate Maizuru Terrane. The above-mentioned litho-assemblage is characteristically different in appearance from the typical rocks of the Maizuru Terrane as well as the surrounding Jurassic and Permian accretionary rocks. We report here the zircon U-Pb LA-ICP-MS geochronological data of the rocks of this Tsuwano Complex. The comprehensive geochronological data indicate that this complex is much older than the surrounding rocks of the Maizuru Terrane. Zircon cores of the granitic gneiss yield possible magmatic age at ca. 2700 and 2500 Ma, while rim parts show a possible metamorphic age of ca. 1850 Ma. Associated dioritic to tonalitic granitoids also show a comparable age of crystallization at ca. 1850 Ma, indicating Neoarchean granitic rocks suffering a thermal overprinting and associated granitoid magmatism at Paleoproterozoic era. The exposed metaquartzite also yielded Neoarchean detrital zircon grains with the calculated maximum age of deposition at ca. 2430 Ma. While, all the other studied rocks including the grayish granitoids, felsic tuff, and metagabbro yield Paleozoic to Mesozoic ages. This is the first discovery of a Precambrian basement rock complex from the Japanese main islands. Based on the present geochronological dataset, we propose for a correlation and paleo-positioning of these basement rocks on the East Asian cratonic margin and a possible tectonic model of its evolution.

PETROLOGY OF THE CRUSTAL PLUTONIC ROCKS OF NAWEOBA BLOCK, ZHOB OPHIOLITE, BALOCHISTAN, PAKISTAN

Zhob Ophiolite complex is composed of three detached blocks named Omzha, Ali Khanzai and Naweoba blocks. The crustal plutonic section of the Naweoba block is mapped and divided into gabbro and granite. Based on petrographical studies, the gabbros fell in the domain of gabbro, gabbronorite, and hornblende gabbro while granitic rocks fell in the vicinity of quartz-rich granitic rocks, granodiorite, plagiogranite and tonalite. Gabbroic rocks cover the maximum area of the crustal plutonic section and are usually medium-grained while at many places the grain size is quite large to be seen with naked eyes. Minerlogically gabbroic rocks consist of orthopyroxene, clinopyroxene, amphibole and plagioclase. These rocks maybe the fragments of main crustal plutonic section of the Zhob ophiolite. The granitic rocks having mafic minerals dominted in the eastern portion, while the felsic minerals dominted ones are in the west. The eastern side of the granitic body is compact and massive compared to western portion which is quite altered and shattered. Granitic rocks are composed of plagioclase, alkali feldspar and quartz where rutile and Cr-spinel exist in trace amounts. The gabbros of Naweoba block may have formed in a magma chamber as a result of fractional crystallization. While the granites maybe a late magmatic differentiate from the same magma chamber. The close correlation of gabbroic and granitic rocks of Naweoba block with Muslim Bagh, Khanozai and Bela ophiolites suggests their formation in supra subduction zone setting.

ЗНАХІДКА ЗОНАЛЬНОГО ВИДУ – PARKINSONIA PARKINSONI SOWERBY В ЮРСЬКИХ ВІДКЛАДАХ ПЕНІНСЬКОЇ ЗОНИ УКРАЇНСЬКИХ КАРПАТ

У Пенінській зоні Українських Карпат юрські відклади є у вигляді олістолітів – різнорозмірних брил – розміщених у верхньокрейдових утвореннях. Олістоліти не утворюють єдиного безперервного розрізу. Тому детальне палеонтологічне вивчення і датування цих відкладів має прикладне значення і дає змогу відтворити історію геологічного розвитку цієї структурно-фаціальної одиниці. Вивчення найважливішої для стратифікації і кореляції групи палеоорганізмів – амонітів, дало змогу палеонтологічно обґрунтувати вік олістолітів Пенінської зони. В процесі польових досліджень у діючому кар’єрі на околиці с. Приборжавське виявлено амоніт Parkinsonia parkinsoni Sowerby, що є видом-індексом одноіменної верхньої зони байосу біозонального стандарту Міжнародної стратиграфічної шкали і має важливе значення для датування середньоюрських відкладів. Наведено монографічний опис і зображення виду-індексу верхньої зони байосу – Parkinsonia parkinsoni Sowerby, знайденого в юрських відкладах Пенінскої зони Українских Карпат.

Revision of the Darriwilian (Middle Ordovician) conodonts documented by Watson (1988) from subsurface Canning Basin, Western Australia

The conodonts documented by Watson form one of the best-known middle Darriwilian faunas from Australia. The present contribution is based on the re-examination of this material. Thirty-one conodont species from the subsurface Goldwyer and Nita formations of the Santalum 1 A drill core section of the Canning Basin, Western Australia are documented and described, including two new species, Belodina watsoni sp. nov. and Scalpellodus percivali sp. nov. The revised fauna is characterized by diagnostic species, namely Histiodella holodentata, Histiodella triangularis, and Eoplacognathus pseudoplanus. It provides compelling evidence to correlate this stratigraphic interval represented by the upper part of the Goldwyer and overlying Nita formations in the Santalum 1 A drill core section to the Histiodella holodentata or Eoplacognathus pseudoplanus biozones of middle Darriwilian age. However, in the Canning Basin, the faunal change signaled by the disappearance of H. holodentata and appearance of E. pseudoplanus reflects shifting of depositional settings from intermediate to outer shelf environments to shallower inner shelf conditions, coinciding with a regional regression event. New taxonomic data also enable more precise regional correlation of middle Darriwilian rocks across the Canning Basin and the Amadeus and Georgina basins in northern-central Australia.Y.Y. Zhen [yong-yi.zhen@planning.nsw.gov.au], Geological Survey of New South Wales, Division of Mining, Exploration and Geoscience, Department of Regional New South Wales, W.B. Clarke Geoscience Centre, 947–953 Londonderry Road, Londonderry NSW, 2753, Australia.

Improving the conceptual understanding of the Darajat Geothermal Field

The Darajat Geothermal Field is the largest vapor-dominated geothermal field in Indonesia with an installed power generation capacity of 271 MWe. For the past 23 years, it has averaged about 90% net capacity factor since commercial operations started in 1994. From the initial 55 MWe, new increments of generation were added in 2000 (95 MWe) and in 2007 (110 MWe; later increased to 121 MWe in 2009). The drilling of wells to support these new increments of generation and continuous resource monitoring has provided key data for integration into the conceptual model and resource simulation modelling.Recent reservoir characterization studies enabled the delineation of surface structures that impact the geothermal system, correlation of surface and subsurface rocks, determination of the orientation of fractures that correlate with feed zones encountered by wells, and better imaging of the reservoir through use of advanced geophysical interpretation methods. The above analyses have helped better define the conceptual model of the Darajat Field and provided information in targeting future make-up wells.Star Energy Geothermal Darajat II (SEGD) takes a proactive approach to manage anticipated and emerging resource performance issues. A good example of this approach is provided by adjustments to the injection of steam condensate from the power plants. Injection initially utilized low productivity wells in the central portion of the field. Field monitoring through geochemical, downhole, and wellhead pressure-temperature (“PT”) measurements indicated that this injection strategy had the potential to adversely affect production from nearby wells by suppressing aquifer boiling and lowering reservoir pressure. Consequently, in 2012, condensate injection was shifted to a new location near the Northeast margin of the field to utilize a well with deep entries. Based on experience and supported with case histories from other vapor-dominated fields, primarily The Geysers, deep injection beneath the feed zones of the production wells is effective at minimizing the impacts of injection breakthrough. Following the change in injection strategy, the central portion of the field has experienced renewed boiling, while only one production well is exhibiting early symptoms of chemical breakthrough from injection in the Northeast.Going forward, expected reservoir management challenges include requirements to add new well pads and target production wells into undrilled areas, localized increased influx of external fluids as the reservoir pressure drops, and reservoir dry-out leading to high superheat levels and reduced well productivity. By continuing to leverage lessons learned to further improve reservoir management processes along with the proactive response to field management issues, SEGD anticipates that Darajat can maintain its production at current levels for the forseeable future.

A greedy variational approach for generating sparse T1-T2 NMR relaxation time distributions.

We present a nonlinear inversion method for generating sparse solutions to the Fredholm Integral equation describing two-dimensional distributions of nuclear magnetic resonance (NMR) relaxation times or diffusion coefficients. Our greedy variational method approximates the distribution of exponential rate constants using a sum of Dirac delta functions, which constitute our dictionary elements. The greedy nature of the method promotes sparsity in the representation by iteratively increasing the number of terms. The variational component estimates the parameters of the Dirac delta functions from a continuum at each iteration by reducing the least squares misfit to the data. Unlike sparsity promoting linearized inversion methods, where the dictionary is fixed and can exponentially grow in the case of multiple variables or when searching for higher resolution, the greedy component of our method aims to keep the dictionary small while the variational component keeps the dictionary dynamic. We demonstrate our method with synthetic data and experimental measurements of T1-T2 correlations of liquid-saturated porous rocks. The sparsity of the approximate solutions is ideal for real-time processing and transmission in remote or mobile NMR applications such as well logging.

Absolute Age Evidence of Early to Middle Ordovician Volcanism in Peninsular Malaysia

Evidence of Early Palaeozoic volcanism in Peninsular Malaysia is largely represented by felsic Gerik- Dinding meta-volcanic rocks; however, reliable absolute ages for the meta-volcanic rocks are still lacking. This restricts correlation of these meta-volcanic rocks with other Early Palaeozoic East Gondwana Proto- Tethys margin tectonic elements identified in the evolution of Southeast Asia. Here, we report petrographic data and zircon U-Pb age of the Gerik-Dinding metavolcanic rocks. Zircons from three Gerik-Dinding meta-volcanic rock samples yield Early to Middle Ordovician weighted mean 206Pb/238U ages between 480 and 460 Ma. The formation age of the meta-volcanic rocks coincides with the post-collision stage from the final amalgamation of Asian micro-continental fragments with the East Gondwana Proto-Tethys margin. Tectonic processes such as lithospheric delamination during the post-collision period could have induced the hot asthenosphere to underplate the continental crust and trigger crustal anatexis. With these findings, the Early Palaeozoic tectonic history of Peninsular Malaysia needs careful review.

Interrelationship Between Facies Association, Diagenetic Alteration and Reservoir Properties Evolution in the Middle Miocene Carbonate Build Up, Central Luconia, Offshore Sarawak, Malaysia

Carbonate build-ups are proven prolific hydrocarbon reservoirs located around the globe. In Southeast Asia, the carbonates are usually associated with grain-rich facies types. Understanding the carbonate reservoirs in terms of their internal characteristics, depositional environment, diagenesis and their impact on petrophysical properties are essential parts of successful exploration and production strategy. The present study provides a detailed work on carbonate reservoir facies, diagenetic history and reservoir quality including qualitative and quantitative analysis of thin sections of the Miocene carbonate platform, Central Luconia. The Central Luconia carbonates are subdivided into eight lithofacies based on specimens collected from five wells. Detailed lithofacies analysis and correlation of carbonate rocks from Well A and Well B allowed us to reconstruct the evolution of sedimentary environments and relative sea-level changes in a platform during the Early to Middle Miocene of Cycle IV and V. Five lithofacies are identified based on texture, sedimentary structure, grain composition, and fossil contents. These include (1) coated grain to packstone (av. O = 6%, av. Kh = 1 mD), (2) coral (m) lime grainstone (av. O = 14.7%, av. Kh = 6 mD), (3) oncolite lime grain to packstone (av. O = 10%, av. Kh = 4 mD), (4) skeletal lime packstone (av. O = 15%, av. Kh = 4.6 mD), and (5) coral (p) lime mud to packstone (av. O = 4%, av. Kh = 0.5 mD), respectively. Micritization, cementation, fractures, compaction, and dissolution are the dominant diagenetic parameters which are identified. The diagenetic features include dolomitization and dissolution (i.e., leaching) making Well A and Well B unique location to study facies distribution and its implication on reservoir potential. By integrating these parameters, facies 2, 3 and 4 are interpreted as a relatively good quality reservoir, whereas facies 1 and 5 are considered as poor reservoir quality. Among all the diagenetic features, dissolution phenomenon contributes to porosity enhancement and reservoir quality, whereas micritization, compaction and cementation have a negative impact on reservoir quality.