Lacustrine Depositional Systems Research Articles

Geomorphology and sedimentary sequence evolution during the buried stage of paleo-uplift in the Lower Cretaceous Qingshuihe Formation, Junggar Basin, northwestern China: Implications for reservoir lithofacies and hydrocarbon distribution

The evolution of large-scale paleo-uplifts within sedimentary basins controls the sedimentary provenance, depositional systems and hydrocarbon distributions. This study aims to unravel changes in paleo-geomorphology, interpret sedimentary sequence evolution, and investigate favourable reservoir types and the hydrocarbon distribution during the buried stage of a long-term eroded paleo-uplift, taking the Lower Cretaceous Qingshuihe Formation (K1q) in the Junggar Basin as an example. These research topics have rarely been studied or are poorly understood. This study integrates current drilling production data with outcrop and core analyses, drilling well logs, 3D seismic data interpretations, grading data, physical property comparisons and identified hydrocarbon distributions.After more than 20 million years of differential river erosion and weathering in arid conditions, the large-scale Chemo paleo-uplift within the hinterland area of the basin formed a distinctive valley–monadnock paleo-geomorphology prior to the deposition of K1q. Since the Early Cretaceous, tectonic subsidence and humid conditions have caused the base level (lake level) to rise, leading to backfilling of valleys and burial processes. Two systems tracts in the target strata of K1q, consisting of distinctive depositional systems, can be identified: (1) a lowstand systems tract (LST), which is confined within incised valleys and is mainly composed of gravelly braided rivers and rarely occurring debris flows and (2) an extensive transgressive systems tract (TST), which developed into an almost flat landform and consists of braided river delta to lacustrine depositional systems. Overall, the physical properties of braided river reservoirs in the LST are better than those of the braided river delta reservoirs in the TST. However, the inhomogeneous distributions of carbonate cements cause differences in the physical properties of conglomerate reservoirs in the LST. However, for sandstones in both the LST and TST, coarser grain sizes and better sorting result in better physical properties. Altogether, four types of reservoir can be identified in the study area: Jurassic inner monadnock reservoirs, K1q LST stratigraphic onlap reservoirs, LST structural reservoirs and TST structural reservoirs.

Estimation of palaeo-slope and sediment volume of a lacustrine rift basin: A semi-quantitative study on the southern steep slope of the Shijiutuo Uplift, Bohai Offshore Basin, China

The sequence architecture and depositional systems of the Palaeogene lacustrine rift succession in the southern steep slope of the Shijiutuo Uplift (SU) in Bohai Offshore Basin (BOB) were investigated using combined 3-D seismic, well log and core data. Four second-order/composite sequences and seven third-order sequences were identified. A detailed analysis revealed fan delta, braid delta and lacustrine depositional systems in the third-order sequences 7 (SQ7). Eleven seismic facies were chosen in the SQ7 to calculate the area and sediment budget. We also calculated the palaeo-slope parameters in the southern steep slope of the SU, including the gradient of basin margin fault slope belt, the shape, average width, average height, width/height ratio and cross sectional area of palaeo-valley. The gradient of the fault slope break belt was inversely proportional to the area and volume of sediments. The higher gradient corresponded to the smaller area and volume of sediments. The width and cross sectional area of palaeo-valleys dominated the volume and facies of sediments. A larger cross sectional area of a palaeo-valley involved much more sediments supply and more favorable conditions for the origin of large-scale deltas. Because of favorable sediment transportation path and existence of large-scale braid delta, the eastern part of the SU formed better quality reservoir than that in the west.

Sedimentology and seismic geomorphology of a lacustrine depositional system from the deep zone of the Gaoyou Sag, Subei Basin, eastern China

ABSTRACTSandstones of the Dainan Formation in the Gaoyou Sag of the Subei Basin are important hydrocarbon reservoirs. This paper studies the sedimentary facies and sandstone dispersal patterns in the Gaoyou Sag, based on the analysis of sedimentology and seismic geomorphology. The data used in this study include lithological data, wire-line-log data and three-dimensional (3D) seismic data. The target strata are the Eocene Daiyi Member (E2d13, E2d12 and E2d11) and the lower Dai'er Member (E2d25), which belong to three third-order sequences. Five types of depositional systems were identified in the Dainan Formation based on core observation and log-facies analysis. They are, respectively, delta, fan delta, sub-lacustrine fan, nearshore subaqueous fan and lacustrine system. Stratal slices from 3D seismic volumes have been used to map the sandstone dispersal patterns and to document the evolution of the depositional systems within these third-order sequences and associated systems tracts. In the low-stand systems tract and the high-stand systems tract, sandstones of delta, fan delta and nearshore subaqueous fan were well developed and can be delineated by stratal slices showing distinct progradation towards the deep lake centre. In the transgressive systems tract, sandstones are less common. Stratal slices indicate that the depositional environments of individual third-order sequences evolved from gravel-rich or sand-rich fans to lacustrine mudstones, and finally to mixed sandstone–mudstone fans. Sandstone dispersal patterns appear to be primarily controlled by syn-sedimentary faults, and generally sandstone thickness decreases with distance from the syn-sedimentary faults. Deltas and fan deltas have different characteristics in sand-body thickness because they have different sedimentary subfacies. The proposed geomorphology and sedimentary evolution of the lacustrine depositional system may aid in the prediction of potential reservoir distribution in the Gaoyou Sag.

Tectono-sedimentary and hydrocarbon potential analysis of rift-related successions in the Dehui Depression, Songliao Basin, Northeastern China

In this study, we use seismic reflection, well-log and core data to investigate the basin structure and sedimentary filling of the Upper Jurassic and Lower Cretaceous in the Dehui Depression, Songliao Basin, Northeastern China. The Late Jurassic-Early Cretaceous Dehui Depression is an active-fault bounded graben. Unconformity and vertical variations on fault activity reveal that the syn-rift stage of the basin can be subdivided into four sub-stages: (i) early syn-rift stage (Huoshiling Formation), which is composed mainly of fan-delta and shallow lacustrine depositional systems; (ii) rift-climax stage (Shahezi Formation), which consists of sublacustrine fan, fan-delta and deep lacustrine depositional systems; (iii) late syn-rift stage (Yingcheng Formation), which is composed of fan-delta and shallow lacustrine depositional systems; (iv) rift-depression transition stage (Denglouku Formation), which is composed of braid delta and shallow lacustrine depositional systems. Fault evolution and episodic rifting control the basin geomorphology, and thus influenced the depositional systems of each stage, while the climate influenced the sediment type. Besides, our estimation on the hydrocarbon exploration potential of the rift-related successions in Dehui Depression shows that they can sustain the formation of medium-large gasfield.

Formation and accumulation of lower Jurassic tight gas sands field in Kekeya area of Tuha Basin, northwestern China

The lower Jurassic in Kekeya area of Tuha Basin contains great tight gas sand resources. This study reveals the geologic controls on the formation and accumulation of tight gas sand reservoirs in Kekeya area comprehensively and systematically, based on tectonic evolution, depositional setting, source rock characteristics, reservoir properties, charging-accumulation history and mechanisms. Our study reveals that tectonics and depositional systems play important roles in the tight gas sand petroleum system. Located at the thrust fold belt of Tuha Foreland Basin with continuous stratigraphic succession of braided fluvial – deltaic – lacustrine depositional systems, the lower Jurassic in Kekeya area contains favorable petroleum geologic conditions for the tight gas sands field. The source rocks contain abundant organic matters dominated by gas-prone type III kerogens and started generating primarily gas in early burial stage. The tight sand reservoirs are mainly composed of medium to coarse grained feldspathic litharenites with primary reservoir space as remnant interparticle pores, solution enlarged intraparticle pores as well as micro-fractures. The more active burial compactions and chemical diagenesis in coal-bearing stratigraphy along with the fast subsidence rate in Tuha Basin are responsible for the tightness of the sand reservoir. The favorable source – reservoir – seal arrangement along with the right timing of hydrocarbon generation, the developing of overpressure in source rocks as well as faulting and fracturing contribute to the widespread accumulation of tight gas sands in lower Jurassic in Kekeya area. The findings in this study would provide reference and guide for future exploration and development of tight gas sand fields in this area and in other basins.

Comparison of lacustrine successions and their palaeohydrological implications in two sub‐basins of the Triassic Cuyana rift, Argentina

AbstractContinental carbonates are rich in palaeoclimatic, palaeoenvironmental and palaeontological information. While carbonate accumulation mechanisms have been described for many types of continental environments, especially in extensional basins, there are still uncertainties that existing facies models fail to address. The Triassic Cerro de las Cabras and Cerro Puntudo formations are alluvial–fluvial–lacustrine sequences that represent a part of the sedimentary infill of two sub‐basins of the Cuyana Basin during the early stages of the Triassic rift in west‐central Argentina. Previous work has provided absolute dates, confirming that these deposits are coeval (Anisian) allowing a comparative study of carbonate sedimentation in an extensional tectonic context. The description and origin of freshwater carbonate deposits and their surrounding siliciclastic sediments in specific areas of the Cuyana rift, gives insight into the major factors that control carbonate precipitation in all rift basins, including the characterization of the palaeohydrology and the importance of provenance. The Cerro de las Cabras Formation represents an ephemeral, playa‐lake depositional system with subaerial exposure and pedogenesis. Its aggradational succession corresponds to the evaporative facies association lake type, diagnostic of underfilled lake basins where persistently closed surface hydrology can lead to thick evaporites. However, this formation lacks thick evaporites and has microbialitic limestones, pointing to an open groundwater supply. The Cerro Puntudo Formation represents an alkaline playa‐lake system fed by groundwater and ephemeral surface‐water input. The unit is an aggradational–minor progradational succession, pointing to a fluctuating profundal facies association, suggesting a balanced‐filled lake type. These two synchronous, lacustrine depositional systems were influenced by tectonics and climate. Provenance and hydrology are key controls in carbonate accumulation in continental rift basins that must be included in future facies models for continental carbonates. Comparison with other rift basins suggests that application of lake‐type characterizations coupled with palaeohydrology and provenance patterns will aid in developing new sedimentation models for freshwater limestones in extensional settings.

Early–Middle Jurassic evolution of the northern Yangtze foreland basin: a record of uplift following Triassic continent–continent collision to form the Qinling–Dabieshan orogenic belt

The northern Yangtze foreland basin system was formed during the Mesozoic continental collision between the North and South China plates along the Mianlue suture. In response to the later phase of intra-continental thrust deformation, an extensive E–W-trending molasse basin with river, deltaic, and lake deposits was produced in front of the southern Qinling–Dabieshan foreland fold-and-thrust belt during the Early–Middle Jurassic (201–163 Ma). The basin originated during the Early Jurassic (201–174 Ma) and substantially subsided during the Middle Jurassic (174–163 Ma). A gravelly alluvial fan depositional system developed in the lower part of the Baitianba Formation (Lower Jurassic) and progressively evolved into a meandering river fluvial plain and lake systems to the south. The alluvial fan conglomerates responded to the initial uplift of the southern Qinling–Dabieshan foreland fold-and-thrust belt after the oblique collision between the Yangtze and North China plates during the Late Triassic. The Qianfoya Formation (lower Middle Jurassic) mainly developed from shore-shallow lacustrine depositional systems. The Shaximiao Formation (upper Middle Jurassic) predominantly consists of thick-bedded braided river delta successions that serve as the main body of the basin-filling sequences. The upward-coarsening succession of the Shaximiao Formation was controlled by intense thrusting in the southern Qinling–Dabieshan fold-and-thrust belt. Palaeogeographic reconstructions indicated an extensive E–W foredeep depozone along the fold-and-thrust belt during the Middle Jurassic (174–163 Ma) that was nearly 150 km wide. The depozone extended westward to the Longmenshan and further east to the northern middle Yangtze plate. The northern Yangtze foreland basin was almost completely buried or modified by the subsequent differential thrusting of Dabashan and its eastern regions (Late Jurassic to Cenozoic).

Tectono-stratigraphy of Lower Cretaceous Tanan sub-basin, Tamtsag Basin, Mongolia: Sequence architecture, depositional systems and controls on sediment infill

Tanan sub-basin is an active-fault bounded basin. The spatial distribution and temporal evolution of depositional systems were significantly influenced by tectonics. Fault movement and stages of basin development controlled the subsidence rates and the potential for erosion and the rate of sediment supply. Distinct stages of rift evolution during the early Cretaceous can be recognized, namely the early syn-rift, rift climax and late syn-rift stages. Three types of lacustrine sequence, consisting of distinctive depositional systems, are distinguished: (1) the early syn-rift sequences (SQ1 + SQ2), which are composed mainly of fan delta and shallow lacustrine depositional systems; (2) the rift climax sequences (SQ3) which developed in response to rapid and differential tectonic subsidence rates, and consist of fan delta, deep lacustrine and sublacustrine fan depositional systems; and (3) the late syn-rift sequences (SQ4) which are comprised of braided-delta and shallow lacustrine depositional systems. Each of the three lacustrine sequence architectures stands for a particular stage of basin fill and reflects variable rates of basin subsidence. Within each sequence, depositional systems and their stacking patterns are interpreted to have been a function of the interaction between tectonics and sediment supply. Differential subsidence across the basin, related to rotation of fault blocks, resulted in the formation of distinct paleomorphologies in different structural settings. These settings were fault-scarp zones controlling the development of fan-deltas, fault-terrace zones controlling the development of fan-delta and sublacustrine fans, half-graben dip-slope zones controlling the development of braided river and braided deltas, and intra-basinal fault-break zones controlling the development of sublacustrine fans. During the late syn-rift stage, active tectonism, displacement on the boundary faults had ceased. At this stage the depositional systems and their stacking patterns were dominantly related to the sediment supply rates, and not to tectonic activity.

Evolution Features and Controlling Factors of Depositional Systems of Paleogene-Neogene in Maxian Area, the Northern Margin of Qaidam Basin

According to the comprehensive detailed analysis of data such as, drilling core, logging and outcrop section, four kinds of sedimentary facies, namely, proluvial fan, braided river, shallow water braided river delta, and oxidative lacustrine, are recognized in Paleogene-Neogene of Maxian area in the northern margin of Qaidam basin. The evolution features of the sedimentary systems were analyzed in details: at the early forming stage of the lake basin (Paleocene-Eocene), proluvial fan -braided river depositional systems were developed in the study area. At the middle flourishing stage of the lake basin (Oligocene-Middle Pliocene), the main sedimentary systems were braided river-shallow braided river delta-oxidative lacustrine. Then the study area was dominated by proluvial fan-braided river-oxidative lacustrine depositional systems in the regression stage of the lake basin (Late Pliocene). The range of the depositional systems in low frequency sedimentary cycle was controlled by the multi-cycle tectonic uplifts and squeezing action of mountains around the study area. Paleoclimate and ancient landform controlled the high frequency change of the lacustrine level and supplied an advantage for the development of shallow braided river delta and oxidative lacustrine facies.

Oligocene-Miocene Kailas basin, southwestern Tibet: Record of postcollisional upper-plate extension in the Indus-Yarlung suture zone

Research Article| July 01, 2011 Oligocene–Miocene Kailas basin, southwestern Tibet: Record of postcollisional upper-plate extension in the Indus-Yarlung suture zone P.G. DeCelles; P.G. DeCelles † Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA †E-mail: decelles@email.arizona.edu Search for other works by this author on: GSW Google Scholar P. Kapp; P. Kapp Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar J. Quade; J. Quade Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar G.E. Gehrels G.E. Gehrels Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2011) 123 (7-8): 1337–1362. https://doi.org/10.1130/B30258.1 Article history received: 25 Jan 2010 rev-recd: 26 May 2010 accepted: 24 Jun 2010 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation P.G. DeCelles, P. Kapp, J. Quade, G.E. Gehrels; Oligocene–Miocene Kailas basin, southwestern Tibet: Record of postcollisional upper-plate extension in the Indus-Yarlung suture zone. GSA Bulletin 2011;; 123 (7-8): 1337–1362. doi: https://doi.org/10.1130/B30258.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Kailas basin developed during late Oligocene–early Miocene time along the Indus-Yarlung suture zone in southwestern Tibet. The >2.5-km-thick basin-filling Kailas Formation consists of a lower coarse-grained proximal conglomerate and more distal fluvial sandstone member, a lacustrine shale and sandstone member, and an upper red-bed clastic member. Felsic tuffs and trachyandesite layers are locally present. Detrital and igneous zircon U-Pb ages indicate deposition of most of the Kailas Formation between ca. 26 and 24 Ma. The Kailas Formation was deposited by alluvial-fan, low-sinuosity fluvial, and deep lacustrine depositional systems in buttress unconformity upon andesitic volcanic (ca. 67 Ma) and granitoid (ca. 55 Ma) rocks of the Gangdese magmatic arc. Abundant organic material, fish and amphibian fossils, and sparse palynomorphs suggest that Kailas lakes developed in a warm tropical climate, quite different from coeval basins in central Tibet, which formed at high elevation in a dry climate. Provenance and paleocurrent data indicate that the bulk of the Kailas Formation was derived from the northerly Gangdese magmatic arc (Kailas magmatic complex). Only during the latest stages of basin filling was abundant sediment derived from the southerly Tethyan Himalayan thrust belt in the hanging wall of the Great Counter thrust. Kailas basin stratigraphy resembles a classic lacustrine sandwich and is most consistent with deposition in an extensional or transtensional rift that developed along the suture zone some 30 m.y. after the onset of Indo-Eurasian intercontinental collision. Correlative coarse-grained syntectonic strata similar to the Kailas Formation crop out along a >1300 km length of the Indus-Yarlung suture zone, suggesting that the basin-forming mechanism recorded by the Kailas Formation was of regional significance and not exclusively related to local kinematics near the southeastern end of the Karakoram fault. We propose that extension of the southern edge of the Eurasian plate was caused by southward rollback of underthrusting Indian continental lithosphere, followed by slab break-off. Alternating episodes of hard and soft collision, associated with regional contraction and extension, respectively, in the Tibetan-Himalayan orogenic system may have been related to changing dynamics of the subducting/underthrusting Indian plate. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Disruption of playa–lacustrine depositional systems at the Permo-Triassic boundary: evidence from Vyazniki and Gorokhovets on the Russian Platform

Abstract: Permo-Triassic sections at Vyazniki and Gorokhovets provide evidence on terrestrial events at, or close to, the Permo-Triassic boundary, the time of the largest ever mass extinction. The sedimentary succession records the overrun of a muddy playa–lacustrine depositional system by major channel belts transporting sand-grade sediments. Biostratigraphy of sections at Vyazniki and Gorokhovets (Zhukov Ravine) shows that this event occurred either at the very end of the Permian or 8 m above in the sections. The timing and nature of this event, which records increased sediment flux from the Ural Mountains, is closely comparable with that from the Southern Uralian Foreland Basin. The Vyazniki and Gorokhovets sections are 800 km from the mountain front and in a separate depositional basin, which strengthens the case that increased sediment flux from the Urals at the Permo-Triassic boundary is related to devegetation of upland catchments (increasing sediment yield) and a switch toward low-frequency but high-magnitude discharge events (increasing sediment delivery). The interbedding of fluvial and aeolian deposits provides further evidence for climatic instability and extremes in the Early Triassic. Supplementary material: Detailed reports on the ostracodes and fossil fish remains from the Zhukov Ravine sections are available at http://www.geolsoc.org.uk/SUP18402 .

The Taravilla lake and tufa deposits (Central Iberian Range, Spain) as palaeohydrological and palaeoclimatic indicators

Lacustrine and tufa deposits from Laguna de Taravilla (Iberian Range, Guadalajara province, Spain, 40°39′ N, 1°59′ W, 1100 m a.s.l.) have been analyzed using sedimentological, mineralogical, geochemical and palynological techniques. A preliminary chronological framework is presented, based on U/Th, 14C AMS, 210Pb and 137Cs analyses. The lacustrine–tufa system developed in a hanging tributary valley of the Upper Tajo River and is composed of a large perched springline tufa build-up, and a barrage tufa dam that impounds Laguna de Taravilla. The Taravilla tufa stable-isotope compositions are similar to other examples in central and southern Spain and they plot in the same field as other lowland European stream tufas. These values are coherent with the range of isotopic compositions measured in the Taravilla spring and lake water. Several sediment cores retrieved from the Laguna de Taravilla have been dated with 14C AMS and analyzed using a multiproxy approach including magnetic properties, sedimentology, geochemistry, stable isotopes, palynology and ostracode assemblages. Sedimentary facies analyses show the dominance of clastic depositional processes in the lacustrine depositional system and suggest the potential of the sequences as palaeoflood records. Sands and coarse silts reflect periods of increased alluvial activity of the inlet. The dominance of clastic depositional processes and the input of detrital carbonate hinder the use of lake mud stable-isotope compositions as environmental indicators. Phases of increased tufa growth occurred during the Late Pleistocene (Last Glacial to Interglacial transition from oxygen isotopic stage 6 to 5) and during the Late Glacial and Early Holocene. Although the Taravilla chronology does not allow a detailed analysis of flood frequency, the reconstructed evolution is coherent with the palaeoflood history of the Tajo River for the last 2000 years, particularly with an increase during the last 500 years. The increase in flood frequency coincides with other evidence of wetter and colder climate and environmental change in Central Spain and in Europe during the Little Ice Age.

Spherical and columnar, septarian, 18O‐depleted, calcite concretions from Middle–Upper Permian lacustrine siltstones in northern Mozambique: evidence for very early diagenesis and multiple fluids

AbstractCalcite septarian concretions from the Permian Beaufort Group in the Maniamba Graben (NW Mozambique) allow controls on the composition and nature of diagenetic fluids to be investigated. The concretions formed in lacustrine siltstones, where they occur in spherical (1 to 70 cm in diameter) and columnar (up to 50 cm long) forms within three closely spaced, discrete beds totalling 2·5 m in thickness. Cementation began at an early stage of diagenesis and entrapped non‐compacted burrows and calcified plant roots. The cylindrical concretions overgrew calcified vertical plant roots, which experienced shrinkage cracking after entrapment. Two generations of concretionary body cement and two generations of septarian crack infill are distinguished. The early generation in both cases is a low‐Mn, Mg‐rich calcite, whereas the later generation is a low‐Mg, Mn‐rich calcite. The change in chemistry is broadly consistent with a time (burial)‐related transition from oxic to sub‐oxic/anoxic conditions close to the sediment–water interface. Geochemical features of all types of cement were controlled by the sulphate‐poor environment and by the absence of bacterial sulphate reduction. All types of cement present have δ13C ranging between 0‰ and −15‰(Vienna Peedee Belemnite, V‐PDB), and highly variable and highly depleted δ18O (down to 14‰ Vienna Standard Mean Ocean Water, V‐SMOW). The late generation of cement is most depleted in both 13C and 18O. The geochemical and isotopic patterns are best explained by interaction between surface oxic waters, pore waters and underground, 18O‐depleted, reducing, ice‐meltwaters accumulated in the underlying coal‐bearing sediments during the Permian deglaciation. The invariant δ13C distribution across core‐to‐rim transects for each individual concretion is consistent with rapid lithification and involvement of a limited range of carbon sources derived via oxidation of buried plant material and from dissolved clastic carbonates. Syneresis of the cement during an advanced stage of lithification at early diagenesis is considered to be the cause of development of the septarian cracks. After cracking, the concretions retained a small volume of porosity, allowing infiltration of anoxic, Ba‐bearing fluids, resulting in the formation of barite. The results obtained contribute to a better understanding of diagenetic processes at the shallow burial depths occurring in rift‐bound, lacustrine depositional systems.

Multiple rifting pulses and sedimentation pattern in the Çameli Basin, southwestern Anatolia, Turkey

The neotectonic development of western Anatolia was characterized by the formation of numerous graben-type basins, which have been well documented by general mapping, although the cause and timing of the Neogene regional tectonic extension remain controversial. Previous interpretations of the origin and evolution of these Neogene basins were based mainly on regional-scale tectonic inferences, rather than detailed basin-fill analysis. The present study of the terrestrial intramontane Çameli Basin in the western Taurides combines detailed facies analysis with biostratigraphic dating (mammalian and molluscan fossils) and documents three pulses of crustal extension that are reflected in changes in the palaeogeography and sedimentary architecture of the basin. Development of the Çameli graben commenced in the Vallesian time (early Tortonian), and is marked by alluvial-fan, fluvial and lacustrine depositional systems, with freshwater molluscan fauna. A second pulse of tectonic extension occurred in the late Ruscinian time (early–middle Pliocene), producing a new normal fault that split the basin longitudinally into two compartments. The lake environment expanded and deepened, coastal peat-forming mires developed and abundant mammal fauna appeared by the early Villanian time (middle Pliocene), with the lacustrine deposits onlapping the basin-margin and intrabasinal fault escarpments. The lacustrine environment subsequently shrank, as the progradation of axial river deltas and basin-margin fan deltas caused water shallowing and shoreline regression. A third pulse of extension occurred at the end of Villanian time (late Pliocene), when the development of a new generation of normal faults further split the basin into still narrower half-graben compartments. The third pulse of rifting is estimated to have accounted for little more than 10% of the sub-basinal crustal extension, but caused the most striking changes in the basin palaeogeography and drainage pattern. The inward development of the successive normal faults indicated a high-rate crustal extension. This is the first regional case study of a terrestrial neotectonic graben employing detailed sedimentary facies analysis and mammal biostratigraphy and providing a time-stratigraphic framework for the rifting pulses in western Anatolia.

Tectono-stratigraphic evolution of an Early Miocene incised valley-fill (Derinçay Formation) in the Mut Basin, Southern Turkey

An Early Miocene (Early Burdigalian) incised valley-fill was produced through development of an alluvial system during active extension and block rotation in the Mut Basin. Five phases of alluvial activity have been recognized and are linked to specific tectono-stratigraphic factors. The entrenchment phase (phase 1) was a response to a rapid decrease in accommodation caused by a combination of sea-level fall and accelerated tectonism that occurred around the basin during active extension. A lacustrine depositional system that pre-dated entrenchment was abruptly succeeded by an erosional fluvial system. The initial erosion, the entrenchment phase was followed by the deposition of ephemeral meandering fluvial facies and later by high sinuosity sandy meandering fluvial facies. During the aggradational phase (Phase 2), coarser-grained, lower sinuosity meandering river facies were vertically stacked in response to successive periods of fault-block rotation and basinal subsidence. The thickest stratigraphic interval was deposited during this time. Simultaneously in a basinward position, finer-grained distal facies were deposited. The succeeding backfilling phase (Phase 3) was marked by further fault-block rotation and an increase in the catchment area that resulted in higher flow regime and more sediment input. A further increase in accommodation space due to block rotation resulted in the retreat of facies belts, and the deposition of a retrogradational stacked gravelly low-sinuosity meandering facies during the early transgressive phase (Phase 4). In the downstream part of the alluvial valley, fluvio-deltaic and non-marine transitional facies were deposited and progressively retreated landwards during marine flooding. Phase 5 marks the main interval of Early Miocene marine transgression (a combination of global eustasy and regional epeiric subsidence). During this time, the facies belts within the incised valley-fill were dominated by estuarine and lagoonal facies assemblages, while the distal parts of the alluvial valley became completely flooded with marine waters. At the end of the transgressive phase, in the uppermost early Burdigalian, the estuarine and lagoonal facies migrated further inland, while shallow-marine sediments (reefal limestones) were deposited in distal parts of the now-drowned valley, blanketing the pre-existing topography.

Lacustrine chalky carbonates: origin, physical properties and diagenesis (Palaeogene of the Madrid Basin, Spain)

The Palaeogene lacustrine chalky carbonates of the Madrid Basin are a peculiar type of very soft and friable carbonate facies with high porosity despite being covered by more than 800 m of sediment. Similar physical properties to those described in marine chalk reservoirs emphasize the interest in analysing and characterizing these carbonate facies within a lacustrine depositional system. Lithologically, they are calcitic and/or dolomitic poorly cemented carbonate muds with no significant amounts of skeletal debris. Clay minerals such as illite, smectite and palygorskite are present between the carbonate crystals. Palygorskite is the most common, covering the carbonate crystals and forming sheets between them. These lacustrine chalky carbonates were formed in the basinal areas of the lake as the result of inorganic carbonate precipitation and/or detrital sedimentation related to episodic reactivation of the adjacent fan systems. Their petrological, geochemical and physical properties indicate that few textural and compositional modifications occurred during diagenesis. Their main physical properties are a very low dry bulk and grain density (1.6–2.2 and 2.62 g/cm 3, respectively) and medium to high porosity (10–40%) due to micropores (<2 μm, 70%) and macropores (>2 μm, 30%). The convergence of lacustrine sedimentation dynamics (rapid sedimentation), the original mineralogy of these calcareous lacustrine muds (relatively stable low-magnesian calcite and dolomite), the early formation of the palygorskite cement of these muds, and the retention of Mg-enriched fluids in the pore system, were decisive in the partial inhibition of calcite cementation, compaction and recrystallization. The chalky carbonates are also intercalated between impermeable littoral carbonate facies that impeded fluid flow through their pore systems.

Palaeoenvironmental reconstruction of a middle Miocene alluvial fan to cyclic shallow lacustrine depositional system in the Calatayud Basin (NE Spain)

ABSTRACT The middle Miocene sedimentary fill of the Calatayud Basin in north‐eastern Spain consists of proximal to distal alluvial fan‐floodplain and shallow lacustrine deposits. Four main facies groups characteristic of different sedimentary environments are recognized: (1) proximal and medial alluvial fan facies that comprise clast‐supported gravel and subordinate sandstone and mudstone, the latter exhibiting incipient pedogenic features; (2) distal alluvial fan facies, formed mainly of massive mudstone, carbonate‐rich palaeosols and local carbonate pond deposits; (3) lake margin facies, which show two distinct lithofacies associations depending on their distribution relative to the alluvial fan system, i.e. front (lithofacies A), comprising massive siliciclastic mudstone and tabular carbonates, or lateral (lithofacies B) showing laminated and/or massive siliciclastic mudstone alternating with tabular and/or laminated carbonate beds; and (4) mudflat–shallow lake facies showing a remarkable cyclical alternation of green‐grey and/or red siliciclastic mudstone units and white dolomitic carbonate beds. The cyclic mudflat–shallow lake succession, as exposed in the Orera composite section (OCS), is dominantly composed of small‐scale mudstone–carbonate/dolomite cycles. The mudstone intervals of the sedimentary cycles are interpreted as a result of sedimentation from suspension by distal sheet floods, the deposits evolving either under subaerial exposure or water‐saturated conditions, depending on their location on the lacustrine mudflat and on climate. The dolomite intervals accumulated during lake‐level highstands with Mg‐rich waters becoming increasingly concentrated. Lowstand to highstand lake‐level changes indicated by the mudstone/dolomite units of the small‐scale cycles reflect a climate control (from dry to wet conditions) on the sedimentation in the area. The spatial distribution of the different lithofacies implies that deposition of the small‐scale cycles took place in a low‐gradient, shallow lake basin located in an interfan zone. The development of the basin was constrained by gradual alluvial fan aggradation. Additional support for the palaeoenvironmental interpretation is derived from the isotopic compositions of carbonates from the various lithofacies that show a wide range of δ18O and δ13C values varying from −7·9 to 3·0‰ PDB and from −9·2 to −1·7‰ PDB respectively. More negative δ18O and δ13C values are from carbonate‐rich palaeosols and lake‐margin carbonates, which extended in front of the alluvial fan systems, whereas more positive values correspond to dolomite beds deposited in the shallow lacustrine environment. The results show a clear trend of δ18O enrichment in the carbonates from lake margin to the centre of the shallow lake basin, thereby also demonstrating that the lake evolved under hydrologically closed conditions.

Paleoenvironments and paleogeography of the Lower and lower Middle Jurassic coal measures in the Turpan-Hami oil-prone coal basin, northwestern China

Detailed facies and paleogeographical analyses of extensive borehole and outcrop data from Lower and lower Middle Jurassic oil-prone coal-bearing sequences in the Turpan-Hami oil-producing basin of northwest China have led to the reconstruction of a basinwide depositional model. A total of 20 distinct lithofacies have been identified and grouped into braided fluvial plain, meandering fluvial plain, braided delta, meandering channel delta, and lacustrine depositional systems. Coal-forming swamps occur in each depositional system, but the preferred sites of accumulation are interdelta bay and lower delta-plain environments in the braided delta and meandering channel depositional systems, and it is in these sites that major oil-prone source rocks are located. A series of age-specific, basinwide, paleogeographical maps have been constructed leading to a depositional model for the basin. Results indicate that the basin experienced cyclic flooding to produce swamps and lakes, and that these characterize the deposition of the Lower and lower Middle Jurassic coal measures. Analyses indicate that both the Bogda and Harlik Mountains were uplifted prior to the Early Jurassic, and a lake separated the two mountain regions during the Early and early Middle Jurassic. From these results, it is interpreted that major oil-prone coal sequences are to be found in the western part of the Taibei depression of the basin, and thus, the full economic potential of the basin has yet to be fully realized.

Fluvial–lacustrine interaction on Skeiðarársandur, Iceland: implications for sandur evolution

Abstract A complex assemblage of fluvial and lacustrine sediments is identified in a major section through proglacial sediments on Skeiðararsandur, south Iceland. High magnitude–low frequency events are identified in both the fluvial and lacustrine sediments. However, much of the sedimentary succession is composed of ‘normal’ low magnitude–high frequency sediments. Retreat of Skeiðararjokull following a surge event created a topographic basin occupied at various times by both fluvial and lacustrine depositional systems and also subjected to a high magnitude jokulhlaup. Previous studies have examined the processes and events occurring on Skeiðararjokull in isolation. This paper improves the understanding of the way in which processes with varying magnitude and frequency regimes interact and contribute to the sedimentary record of proglacial environments.

ABSTRACT: Two Different Types of Nonmarine Source Rocks and Reservoirs of Jurassic Deposits of the Northern Qaidam Basin, NW China

The Qaidam basin, a nonmarine petroliferous basin, is located on the northeastern margin of the Tibet Plateau. It is roughly a diamond shaped, surrounded by the Altyn Tagh Shan Mountains to the northwest, Qilian Shan Mountains to the north, and Kunlun Shan Mountains to the south. Jurassic sedimentary rocks are widely distributed in the northern part of Qaidam Basin, especially in the Lenghu structural belt. The depositional systems of the Northern Qaidam basin during the Jurassic were predominately alluvial, fluvial, deltaic, and lacustrine. Reservoirs and two different types of source rocks (coals and coaly mudstones versus mudstones without a coal component) were identified through analysis of outcrops, core samples, well logs, and seismic data. The distribution of source rocks and reservoirs is related to the depositional system. Non-coal-related source rocks are semi-lacustrine deposits, which are good potential hydrocarbon generators. Reservoirs are channel, point bar, river mouth bar, and turbidite deposits. Except for turbidite deposits, they contain a mixture of primary and secondary pores. Coal-bearing source rocks and coal-related reservoirs are controlled by delta and offshore lacustrine depositional systems, formed under acidic water conditions. The properties of sandstone reservoirs related to coalbearing strata were characterized by low carbonate cement, high siliceous cement, and high kaolinite contents. Diagenesis, especially compaction and siliceous cementation, in the sandstone reservoirs causes low porosity and low permeability. The secondary pores, formed by the solution associated with organic acid, were predominant.