Belt Basin Research Articles

Continental-scale drainage reorganization during Mesoproterozoic orogenesis: Evidence from the Belt Basin of western North America

The Mesoproterozoic Belt Basin of the northwestern United States and southwestern Canada contains a 5–20-km-thick metasedimentary succession deposited during an important transition in the Precambrian development of North America. Key unresolved issues for the Belt Basin include the chronology of deposition, sources of siliciclastic sediment, and regional paleogeography during Laurentian orogenesis. To address these topics, we acquired detrital zircon U-Pb geochronologic data for eastern exposures of the Belt-Purcell Supergroup in the Lewis thrust salient along the USA-Canada border. To define an integrated chronostratigraphic and provenance framework for the Belt Basin, we calculated maximum depositional ages and qualitatively and quantitatively compared our geochronologic data set to a compilation of Laurentian igneous and metamorphic zircon U-Pb ages using multidimensional scaling and an inverse Monte Carlo model. The results suggest a stratigraphic age range of ca. 1495–1380 Ma, constituting a depositional duration of ~115 m.y. with an average sediment accumulation rate of ~40 m/m.y. for the studied locality (extrapolated to ~155 m/m.y. for the basin depocenter). Variations in sediment provenance are expressed by three distinct intervals within the Belt-Purcell Supergroup. The lower Belt Supergroup succession (Waterton to lower Helena Formations; ca. 1495–1440 Ma) is dominated by Paleoproterozoic and Archean grains derived from the northeastern Canadian Shield. The middle Belt Supergroup succession (upper Helena to Sheppard Formations; ca. 1440–1420 Ma) displays mixed early Mesoproterozoic, late Paleoproterozoic, and Archean zircon age groups. The upper Belt Supergroup succession (Gateway to Roosville Formations; ca. 1420–1380 Ma) contains almost entirely late Paleo-proterozoic zircons sourced from the south (Yavapai-Mazatzal and Mojave crustal provinces). We interpret sediment provenance to reflect a continental-scale, fluvial drainage reorganization during middle Belt Supergroup deposition that can be linked to the recently recognized Picuris orogeny.

Recently Identified Mesoproterozoic Strata in South‐Central Idaho Document Late‐Stage Rifting of the Nuna Supercontinent in Western Laurentia

AbstractSedimentary basins are valuable archives of tectonic processes involved in continental rifting. The northern Rocky Mountains preserve the Belt Supergroup, one of the most complete records of Mesoproterozoic strata on Earth; however, debate remains about its tectonic origin. We investigated a recently identified package of Mesoproterozoic strata at Leaton Gulch near Challis, Idaho, using a combination of traditional and newer sedimentological tools. Results suggest that the Leaton Gulch stratigraphic section was deposited in a fluvial setting ca. 1,380–1,317 Ma, spanning the poorly documented interval between late Belt Supergroup deposition at ∼1,370 Ma and recently characterized Deer Trail Group strata that are less than 1,300 Ma. Detrital zircon age distributions from Leaton Gulch demonstrate a similar provenance signature to Missoula Group rocks of the upper Belt Supergroup; however, Leaton Gulch strata are up to ∼70 Ma younger than most prior age constraints on Belt Supergroup rocks. Regional metabentonites (interpreted as metamorphosed reworked tuffs) found within Leaton Gulch and Missoula Group strata show dominantly radiogenic εHf(t), with a range of −8 to +15, interpreted as a mix of primary mantle and remelted metasedimentary sources. Zircon trace element data of the metabentonite from Leaton Gulch suggest a 1,450–1,300 Ma geochemically consistent and moderate–high silica melt source. Collectively, the strata of Leaton Gulch record basin sedimentation during a critical window of Mesoproterozoic time. We speculate that sedimentation during late‐stage Belt Supergroup deposition thickened and stepped westward, abandoning the main Belt basin, culminating with breakup of the Nuna Supercontinent.

Erratum to: Cenozoic giant coal-bearing basin belt discovered in China’s sea area

Erratum to: Cenozoic giant coal-bearing basin belt discovered in China’s sea area

Timing of the Transition From Sevier‐ to Laramide‐Style Tectonism in Southwestern Montana Based on the Provenance of the Frontier Formation, North American Cordillera

AbstractThe Upper Cretaceous Frontier Formation in southwestern Montana is coeval with the transition from Sevier‐ to Laramide‐style tectonism in the Idaho‐Montana sector of the North American Cordillera. To better constrain the timing of initial exhumation above the Laramide‐style Blacktail‐Snowcrest arch, we use biostratigraphic data, sandstone petrography, and detrital zircon (DZ) geochronology to determine the provenance and depositional age of the Frontier Formation. Near Lima Peaks, erosion of Lower Cretaceous strata from the frontal Sevier‐style Tendoy thrust sheet provided sediment to the foreland basin. In the Western Centennial Mountains, sediment sources included those same sources as well as Neoproterozoic and Cambrian strata and Mesoproterozoic plutons in the Belt basin. In contrast, near the Gravelly Range, sediment eroded from Pennsylvanian‐Upper Cretaceous strata atop the Blacktail‐Snowcrest basement‐cored uplift, documenting unroofing to Pennsylvanian‐Permian stratigraphic levels by 87–85 Ma. Palynology corroborates recycling into the Frontier Formation, including from the underlying Blackleaf Formation. The ubiquitous presence of 100–85 Ma DZ ages coupled with different interpreted source regions suggests that an ash‐fall source contributed young zircon grains to the Frontier Formation. The timing of exhumation above the Blacktail‐Snowcrest arch provided by these new data presented herein suggest that Laramide‐style tectonism in Idaho‐Montana may be unrelated to shallow‐angle subduction within a narrow corridor as envisioned by current models. Instead, upper plate controls, such as the locations of inherited faults and basement highs, the distribution and thickness of pre‐orogenic sedimentary cover, and the availability of detachment surfaces, may be responsible for Laramide‐style tectonism during early Late Cretaceous time.

The delta-fluvial evolution of a lacustrine basin with gentle slope and low sedimentation rate: A case study of the Fudong Slope, Junggar Basin, Northwest China

Gentle slope belts of lacustrine basins are important areas for the generation of stratigraphic petroleum reservoirs controlled by sedimentary systems. Based on coring, well logging, 3D seismic and analytical test data, the sedimentary system and sandbody distribution characteristics of the Jurassic Toutunhe Formation (J2t) in the Fudong slope of the Junggar Basin were analysed. The results indicated that the Fudong slope showed the characteristics of low sediment input. Sediments mainly originated from the Shaqi uplift, and the sediment input gradually weakened from the early to the late J2t stages. The sedimentary system evolved from a delta to a meandering river, resulting in a delta front facies in the 1st member (J2t1) and a meandering river facies in the 2nd (J2t2) and 3rd (J2t3) members of the Toutunhe Formation. A sedimentary evolution pattern for the gentle slope with low sediment input was established. Thick deltaic sandbodies developed locally in the J2t1 stage. However, meandering rivers with high sinuosities predominantly developed and resulted in a striped geometry in the J2t2 and J2t3 members. Moreover, the meandering sandbodies exhibited an anastomosing morphology after multistage superposition. The channel and point bar facies in J2t2 were more developed than those in J2t3 because of sediment input differences. Under low-sediment input conditions, the sedimentary environment of the gentle slope belt in the lacustrine basin was controlled by changes in the palaeoclimate, palaeogeomorphology, gradient (slope) and base level. Palaeoclimate was the main factor controlling the evolution of the sedimentary environment. Palaeogeomorphology and slope controlled the distribution of sedimentary microfacies, channel sinuosity and sandbodies. Base-level change restricted the sandbody superimposition style. Under the low sediment input conditions of the Fudong slope, the subaqueous distributary channels of the delta environment and the point bars of the meandering river environment in the transitional belt of the Fudong slope are the main potential targets for stratigraphic petroleum reservoirs, whilst the 2nd member of the Toutunhe Formation (J2t2) is the main favourable interval for stratigraphic reservoir exploration.

Cenozoic giant coal-bearing basin belt discovered in China’s sea area

Cenozoic giant coal-bearing basin belt discovered in China’s sea area

The Asmari Formation Petrophysical Parameters in the Abu Ghirab Oil Field of the Zagros Fold Belt Basin, Southeastern Iraq, Using Well Log Data Interpretation

The current study represents the evaluation of petrophysical characteristics, lithological analysis, and identification of the Asmari Formation for the main and sub-reservoir units in the Abu Ghirab oil field, Maysan, southeast of Iraq. This petrophysical assessment was accomplished using the interpretations of well log data to know the properties of the Asmari Formation reservoir. The available logs such as resistivity, gamma ray, neutron and density logs were converted to digital data using the Diger Sotware. The lithic properties of the reservoir like porosity, total shale saturation, oil and water saturation were interpreted and calculated using the interactive petrophysics software. The lithic and mineral study was completed and the type of mineral filling was known through the cross-plot of the porosity logs for different wells. The petrophysical properties were calculated and represented on the CPI profile. Depending on the petrophysical characteristics, the Asmari Formation was divided into main and sub units, which are: Jeribe-Euphrates and its sub-units A1, A2, and A3; Upper Kirkuk unit and B1, B2, B3, B4 sub-units; and Middle-Lower Kirkuk unit and C subunit. The results showed that the reservoir has economic oil productivity. The subunits B2, B3 in Upper Kirkuk were characterized by high effective porosity values and high hydrocarbon content, and they are the highest produced units in Upper Kirkuk in studied wells. The vary on lithology represents as dolomites in the Jeribe, Euphrates, limestones in the Kirkuk group, and the mineral components were calcite and dolomite.

Detrital zircon U-Pb geochronology of the Lunpola basin strata constrains the Cenozoic tectonic evolution of central Tibet

The Cenozoic tectonic evolution of central Tibet plays an important role in the growth of the Tibetan plateau. Paleoelevation studies show that the central Tibetan plateau hosted an east-west trending belt of basins in the Paleogene, but how they relate to the regions uplift history remains unclear. This study addresses the uplift history of the central Tibetan plateau by focusing on Lunpola basin strata deposited in the Cenozoic through detrital zircon basin provenance and zircon geochemical indicators for crustal-thickening. U-Pb dating of detrital zircon demonstrates that the Lunpola basin was mainly derived from mixed sources composed of Paleozoic–Mesozoic sedimentary rocks of the Lhasa terrane, the Cretaceous igneous rocks of the northern Lhasa terrane, and the Paleozoic–Mesozoic sedimentary rocks of southern Qiangtang terrane. The modal framework-grain composition of sandstone samples from the basin strata indicates a recycled orogen as the source. Sandstone composition analysis reveals an increase in the volcanic component with time associated with a pulse of quartz grains in the middle Eocene. We interpret such observations to indicate input from early Cretaceous clastic sediments belonging to the Duba Formation and the Baingoin Plutonic Complex, which imply passive exhumation along the hanging wall of the Gerze-Siling Co thrust. Trace element geochemistry of zircon grains demonstrates an increase in europium anomaly (Eu/Eu*), which we interpret to reflect ∼20 km crustal thickening in central Tibet from the Eocene to Oligocene, as well as an increase of >3 km surface elevation which partly was induced by the Cenozoic sedimentary accumulation. This significant uplift event may have been associated with convective removal of a thickened Tibetan lithosphere that in turn led to magmatic inflation of the Tibetan crust.

The Belt Basin (Rocky Mountains): Composition of Sedimentary Complexes and Some Features of Its Sedimentary Filling

The Belt Basin (Rocky Mountains): Composition of Sedimentary Complexes and Some Features of Its Sedimentary Filling

Evidence of Mid-Cretaceous carbon cycle perturbations and OAE2 recorded in Cenomanian to middle Campanian carbonates of the Zagros fold–thrust belt basin, Iran

The Cenomanian to middle Campanian succession of the Zagros fold-thrust belt basin in Iran was investigated to evaluate the sedimentologic and geochemical response to Oceanic Anoxic Event 2 (OAE2), the Cenomanian–Turonian Boundary Event (CTBE) and Mid Cenomanian Event I (MCEI). The succession was examined at the Chenareh anticline locality, which is situated between the two main tectonic zones of the Zagros fold-thrust belt basin. Petrographic analysis led us to define 10 carbonate microfacies and a shale petrofacies that were deposited in four facies belts: tidal flat, lagoon, shoal, and open marine within a larger platform ramp environment. Carbon isotope and trace element data indicate that the Coniacian to middle Campanian Ilam Formation formed within anoxic to dysoxic settings, with lower amounts of water/rock interaction compared to the underlying Sarvak Formation. Carbon isotope chemostratigraphy allows the CTBE and MCEI evidence to be distinguished within the Zagros Basin, however, values measured by this study are depleted compared to other published chemostratigraphic records of the event. The results, therefore, demonstrate that diagenesis or a local CTB hiatus affected the record of these global events in the study area at the Zagros Basin.

Neoproterozoic Windermere Supergroup Near Bayhorse, Idaho: Late‐Stage Rodinian Rifting Was Deflected West Around the Belt Basin

AbstractConflicting models of Rodinian rifting have been proposed to explain the recognized variation in the Neoproterozoic and early Cambrian tectonostratigraphic architecture of the western Laurentian margin. However, discrimination among rift models is hampered by limited exposure and metamorphism of the rocks. Southeastern Idaho preserves more than 6 km of Neoproterozoic and Cambrian strata. In contrast, along the inferred continuation of the margin in east central Idaho, correlative rocks are missing across the Lemhi arch. Our field mapping and U‐Pb dating studies, located approximately 50 km west of the Lemhi arch unconformity, focused on a succession of regionally extensive rocks that were previously assigned an Ordovician age. We show that ~1.5 km of strata here overlies a ~667 Ma reworked felsic tuff and was intruded by a 601 ± 27 Ma gabbro sill; we thus redesignate these rocks as Cryogenian and Ediacaran in age. These rocks are overlain by a ~1 km thick Ediacaran to middle Cambrian quartzite. Middle Ordovician quartzites overlie these middle Cambrian strata, indicating that though Neoproterozoic and lower Cambrian rocks are present west of the Lemhi arch, upper Cambrian and Lower Ordovician rocks are thin or absent. Comparison of this redesignated section to the closest correlative sections suggests an initial stage of symmetric rifting followed by later asymmetric rifting. We suggest that prerifting ~1,370 Ma magmatism within the Belt basin produced lithospheric rigidity that influenced the final stage of rifting and produced heterogeneity in the geometries of structural domains similar to those documented in other well‐defined, modern rift margins.

Mapping the 3D extent of the Stillwater Complex, Montana—Implications for potential platinum group element exploration and development

Geophysical models characterize the exposed and interpreted buried extent of the Stillwater Complex, critical for understanding the origin of the layered mafic intrusion and its associated high-grade platinum group element resources. The 3D models, constrained by gravity, magnetic, xenolith, seismic, borehole, and rock property data indicate that the likely maximum extent of the Stillwater Complex beneath Phanerozoic cover is ~10 times greater than its outcrop, ~2240 km2. The thickness values are poorly constrained but vary from ~7000 to 12,000 m, depending on crustal and mantle density variations and depths to the top of the lower crust and mantle. This thickness may include dense metasedimentary units of the basin into which the Stillwater Complex intruded. Using the modeled thickness results in a volume estimate of ~24,700 km3, albeit poorly constrained. New analyses of xenoliths from the Cretaceous Sliderock and Suzie Peak intrusions produce ages of 2706–2716 Ma, corresponding to the age of the Stillwater Complex, and 2813 Ma, corresponding to the age of Archean gneissic basement. Seismic reflectors in inferred Archean crystalline basement, possibly including the Stillwater Complex, dip ~25–30° north, with segments dipping as much as 70° north. Layered reflectors beneath the Phanerozoic sedimentary section and above the inferred Archean crystalline basement may represent metasedimentary units, perhaps a southern extension of the Mesoproterozoic Belt Basin. The potential field models and the seismic reflection data suggest that the Stillwater Complex was dipping northward prior to deposition of Cambrian strata, perhaps uplifted in the late Archean or Proterozoic as previously proposed, and that during Laramide times, faulting and intrusions highly disrupted the complex. Temperature measurements from boreholes help constrain the depths of feasible mining of the complex.

Combined Multifactor Evidence of a Giant Lower-Mantle Ring Structure below the Eastern Mediterranean

In the Arabian-Northern African region, interaction of the Nubian, Arabian and Eurasian plates and many small tectonic units is conspicuous. In order to better understand this interaction, we use satellite derived gravity data (retracked to the Earth’s surface) recognized now as a powerful tool for tectono-geodynamic zonation. We applied the polynomial approximation to the gravity data which indicated the presence of a large, deep ring structure in the eastern Mediterranean centered below the Island of Cyprus. Quantitative analysis of residual gravity anomaly provides an estimate of the deep anomalous body’s upper edge at a depth of about 1700 km. Computations of the residual gravity anomalies for the lower mantle also indicate presence of anomalous sources. The GPS vector pattern coinciding with the gravity trend implies counter clockwise rotation of this structure. Independent analyses of the geoid isolines map and seismic tomography data support the existence of a deep anomaly. Paleomagnetic data analysis from the surrounding regions confirms a counter clockwise rotation. Numerous petrological, mineralogical, geodynamical and tectonic data suggest a relation between this deep structure and near-surface processes. This anomaly sheds light on a number of phenomena including the Cyprus gravity anomaly, counter clockwise rotation of the Mesozoic terrane belt and asymmetry of basins along continental transform faults.

Facies architecture and sediment infilling processes in intrabasinal slope belts of lacustrine rift basins, Zhanhua Depression, Bohai Bay Basin

Abstract Intrabasinal slope belts, which were previously thought to lack sandy sediments, have been largely understudied due to their distance from their sediment provenance. Thus, our study sought to conduct a comprehensive geological study of the facies architecture and sediment infilling processes in the intrabasinal slope belts of the Zhanhua Depression during the Paleogene using seismic data, drill cores and well logs. Three distinctive depositional systems were identified: near-shore subaqueous fan, shallow/deep lakes, and braided-river delta. The facies architecture and sediment infilling processes were primarily characterized by different stages of diversiform tectonic geomorphologies in cyclothem motifs of rift lacustrine basins. The geomorphological characteristics of the Shahejie Formation exhibited multiple alternating uplifts and sags, resulting in multiple intra- and extra-basinal sediment provenances, while those of the Dongying Formation displayed a single depocenter with a wide and gentle geomorphology derived from several extra-basinal sediment provenances. Coarse-grained sediments formed near-shore subaqueous fans, primarily accumulated on the slopes around the Kenli Uplift during the member 3 of the Shehejie Formation interval; medium- and fine-grained sediments deposited in the proximal and distal environment of the delta front and sandy sediments formed thick-bedded sandy beach bars on subaqueous uplifts during member 2 of the Shehejie Formation interval; ultrafine-grained, fine-grained, and carbonate sediments deposited as thin-bedded carbonate banks and sandy beach bars in a shallow/deep lake during member 1 of the Shehejie Formation interval; and fine-to medium-grained sediments abundantly accumulated in the proximal environment of the delta front by passing the uplifts and infilling the slopes during the Dongying Formation interval. This integrated study demonstrates the effectiveness of a process-based analytical approach and depositional models in predicting facies architecture and sediment infilling processes. Furthermore, it provides guidelines for oil and gas exploration in intrabasinal slope belts of rift basins.

The armored burrow Nummipera eocenica from the upper Eocene San Jacinto Formation, Colombia: morphology and paleoenvironmental implications

The ichnospecies Nummipera eocenica occurs in thick-bedded, tabular bioclastic massive sandstone of the upper Eocene San Jacinto Formation in the San Jacinto Fold Belt Basin, Colombia. Nummipera eocenica is a vertical to oblique burrow locally displaying a conical shape. The lining structure of the specimens studied consists of uniformly distributed lepidocyclinids and operculinids, with tests typically dipping towards the burrow wall, and well-compacted lining. The burrow infill is identical to the host rock, a bioclastic sandstone with abundant bivalve fragments. The diagnosis of Nummipera is emended to include as components of burrow lining all representatives of the Subclass Rotaliana characterized by being lenticular to discoidal in shape. In the San Jacinto Formation, Nummipera eocenica is present in the transition between deltaic mouth-bar and carbonate platform deposits.

Mid‐Proterozoic Ferruginous Conditions Reflect Postdepositional Processes

AbstractTo evaluate the mechanics of mid‐Proterozoic environmental iron transport and deposition, we coupled microscale textural and bulk rock magnetic techniques to study the ~1.4‐Ga lower Belt group, Belt Supergroup, Montana and Idaho. We identified a pyrrhotite‐siderite isograd that marks metamorphic iron‐bearing mineral reactions beginning in subgreenschist facies samples. Even in the best‐preserved parts of the basin, secondary overprints were common including recrystallization of iron‐bearing sulfides, base metal sulfides, and nanophase pyrrhotite. Despite these overprints, a record of redox chemistry was preserved in the early diagenetic framboidal pyrite and detrital iron oxides including trace nanoscale magnetite that remained after sulfidization in anoxic and sulfidic sedimentary pore fluids. Based on these results, we interpret the Belt Basin as having oxic waters, at least in shallow‐water environments, with no indication of abundant ferrous iron in the water column; this is consistent with the cooccurrence of early eukaryotic fossils within the same strata.

Sedimentation, earthquakes, and tsunamis in a shallow, muddy epeiric sea: Grinnell Formation (Belt Supergroup, ca. 1.45 Ga), western North America

AbstractInterpreting the deposits of ancient epeiric seas presents unique challenges because of the lack of direct modern analogs. Whereas many such seas were tectonically relatively quiescent, and successions are comparatively thin and punctuated by numerous sedimentary breaks, the Mesoproterozoic Belt Basin of western North America was structurally active and experienced dramatic and continuous subsidence and sediment accumulation. The Grinnell Formation (ca. 1.45 Ga) in the lower part of the Belt Supergroup affords an opportunity to explore the interplay between sedimentation and syndepositional tectonics in a low-energy, lake-like setting. The formation is a thick, vivid, red- to maroon-colored mudstone-dominated unit that crops out in northwestern Montana and adjacent southwestern Alberta, Canada. The mudstone, or argillite, consists of laminated siltstone and claystone, with normal grading, local low-amplitude, short-wavelength symmetrical ripples, and intercalations of thin tabular intraclasts. These intraclasts suggest that the muds acquired a degree of stiffness on the seafloor. Halite crystal molds and casts are present sporadically on bedding surfaces. Beds are pervasively cut by mudcracks exhibiting a wide variety of patterns in plan view, ranging from polygonal to linear to spindle-shaped. These vertical to subvertical cracks are filled with upward-injected mud and small claystone intraclasts. Variably interbedded are individual, bundled, or amalgamated, thin to medium beds of white, cross-laminated, medium- to coarse-grained sandstone, or quartzite. These are composed of rounded quartz grains, typically with subangular to rounded mudstone intraclasts. Either or both the bottoms and tops of sandstone beds commonly show sandstone dikes indicative of downward and upward injection. Both the mudcracks and the sandstone dikes are seismites, the result of mud shrinkage and sediment injection during earthquakes. An origin via passive desiccation or syneresis is not supported, and there is no evidence that the sediments were deposited on alluvial plains, tidal flats, or playas, as has been universally assumed. Rather, deposition occurred in relatively low-energy conditions at the limit of ambient storm wave base. The halite is not from in situ evaporation but precipitated from hypersaline brines that were concentrated in nearshore areas and flowed into the basin causing temporary density stratification. Sandstone beds are not fluvial. Instead, they consist of allochthonous sediment and record a combination of unidirectional and oscillatory currents. The rounded nature of the sand and irregular stratigraphic distribution of the sandstone intervals are explained not by deltaic influx or as tempestites but as coastal sands delivered from the eastern side of the basin by off-surge from episodic tsunamis generated by normal faulting mainly in the basin center. The sands were commonly reworked by subsequent tsunami onrush, off-surge, seiching, and weak storm-induced wave action. Although the Grinnell Formation might appear superficially to have the typical hallmarks of a subaerial mudflat deposit, its attributes in detail reveal that sedimentation and deformation took place in an entirely submerged setting. This is relevant for the deposits of other ancient epeiric seas as well as continental shelves, and it should invite reconsideration of comparable successions.

Mineral prospectivity analysis for BIF iron deposits: A case study in the Anshan-Benxi area, Liaoning province, North-East China

Banded iron formation (BIF) deposits are the most important source of iron in China, and they are dominantly distributed in the North China Craton (NCC). The Anshan-Benxi area is situated in the northeastern part of the NCC and is considered to be the most fertile and productive iron metallogenic province in China. The recent successive discoveries of large BIF deposits in this area, especially the world-class Dataigou BIF deposit, indicates that there is great potential for iron resources in this area. The BIF deposits are well defined by magnetic and gravity anomalies and thereby extensive petrophysical and geophysical studies are critical for BIF prospective mapping. A data-driven weights-of-Evidence (WofE) analysis was used for BIF prospectivity modeling. The results indicated that prospective areas are generally confined to the Precambrian greenstone belt basin and high-prospectivity zones (Class A) are mainly distributed in the middle and northeastern parts of the study area. Moderate-prospectivity zones (Class B) are mainly distributed in southwestern and northeastern parts of the study area. Finally, we employed selective human intervention to redefine priority targets to be more reliable. The results suggest the method is successful as 82 target areas were narrowed to Class A 20 and 11 Class B targets. The total of Class A and Class B targets was just over one-third of the total number of targets, offering a much smaller but effective selection of targets for consideration by mineral explorers.

Geological Characteristics and Working Suggestions of Shuiquan Ben- tonite Mine in Chaoyang County

The shuiquan bentonite mining area in chaoyang county, liaoning province is located in the northern margin of the north China block - yanshan middle neoproterozoic rifting belt - western liaoning Mesozoic upper superimposed basin belt - chaoyang Mesozoic superimposed basin-ling system nejinling si-yangshan volcanic rock basin. The bentonite ore bodies occur in the rhytitic breccia tuff of the lanqi formation and are stratified deposits. Based on the study of the known ore bodies, this paper summarizes the prospecting marks, summarizes the prospecting direction, and lays a foundation for the next exploration.

Petroleum geological characteristics of two basin belts in southern continental margin in South China Sea

Based on the seismic, drilling, cores and outcrops data, the formation of basins, source rocks and hydrocarbon accumulations in the southern South China Sea (SSCS) were systematically analyzed to reveal the petroleum geological features of continental margin basins and summarize the distribution rule of oil and gas in the SSCS. The results show that the South China Sea (SCS) has experienced three tectonic stages, namely, the formation and development of proto-SCS, the subduction of proto-SCS and development of neo-SCS, the rapid subsidence and shrinking of SCS. The tectonic evolution of proto-SCS and neo-SCS controlled the regional tectonic pattern of continental margin in the SSCS, forming southern and northern basin belts, and also dominated the formation of basins, source rocks and hydrocarbon accumulation characteristics. The source rocks were mainly Miocene coal source rocks in the southern basin belt, with different thermal evolution degree, and the near-shore source rock was chiefly oil-generating while the off-shore source rock was mainly gas-generating. Compressive folding structural belts and reefs were the favorable belts. Within the northern basin belt, the source rocks were gas-prone and dominated by the Eocene to Oligocene, with high thermal evolution degree. Reefs and faulted blocks were the major accumulation areas. Our study demonstrates that the continental marginal basins of SSCS still have great exploration potential and is an important strategic area of oil and gas exploration and development. The southern basin belt focuses on oil and gas exploration and the northern basin belt focuses on gas exploration.