Jurassic-Lower Cretaceous Research Articles

Middle Jurassic-Lower Cretaceous tectonic-eustatic cyclites of the Southern East European Craton

A methodical approach to assessment of the role played by vertical tectonic movements in the of tectonic-eustatic cyclicity and the facial appearance of the Middle Jurassic-Lower Cretaceous deposits on the eastern part of the East European Craton has been suggested. Resulting from comparison between the global and regional eustatic curves, the modeling of probable versions of the lithological composition for sediments during eustatic oscillations, and the comparison of modeling results with the chronostratigraphic scheme, the global eustatic component and regional “tectonic noise” have been identified. It has been found that the vertical tectonic movements formed the boundaries of the most distinguished cyclites on the eastern part of the East European Craton. The spatial-temporal uniformity in the material composition of cyclites, related to the long periods of stable high-stand sea level, caused their mineralogenic specialization for a broad range of non-ore mineral resources.

Provenance of the Middle Jurassic-Lower Cretaceous (Berriasian-Valanginian) deposits of the Lower Amur region

The petrographic and chemical study of the Middle Jurassic-Lower Cretaceous rocks of the Lower Amur region revealed the important role of granitoids in their provenance. Intermediate, mafic, and ultramafic (?) intrusive rocks, as well as sedimentary, volcanic, and metamorphic complexes were less common. The orientation of the cross bedding and casts of whirlpool pits in the Tithonian-Valanginian turbidites indicates that the provenance was located in the west and southwest. It was mainly made up of the continental granite-metamorphic blocks of the Jiamusi-Khanka-Bureya Massif. At the same time, a significant part of the provenance was occupied by the fragments of the Late Paleozoic-Early Mesozoic active continental margin.

Middle and Upper Jurassic hydrocarbon potential of the Zagross Fold Belt, North Iraq

Structured organic matters of the Palynomorphs of mainly dinoflagellate cysts are used in this study for dating the limestone, black shale, and marl of the Middle Jurassic (Bajocian–Bathonian) Sargelu Formation, Upper Jurassic (Upper Callovian – Lower Oxfordian) Naokelekan Formation, Upper Jurassic (Kimeridgian and Oxfordian) Gotnia and Barsarine Formations, and Upper Jurassic – Lower Cretaceous (Tithonian-Beriassian) Chia Gara source rock Formations while spore species of Cyathidites australis and Glechenidites senonicus are used for maturation assessments of this succession. Materials' used for this palynological study are 320 core and cutting samples of twelve oil wells and three outcrops in North Iraq.Terpane and sterane biomarker distributions, as well as stable isotope values, were determined for oils potential source rock extracts of Jurassic-Lower Cretaceous strata to determine valid oil-to-source rock correlations in North Iraq. Two subfamily carbonate oil types-one of Middle Jurassic age (Sargelu) carbonate rock and the other of mixed Upper Jurassic/Cretaceous age (Chia Gara) with Sargelu sources as well as a different oil family related to Triassic marls, were identified based on multivariate statistical analysis (HCA & PCA). Middle Jurassic subfamily A oils from Demir Dagh oil field correlate well with rich, marginally mature, Sargelu source rocks in well Mk-2 near the city of Baiji. In contrast, subfamily B oils have a greater proportion of C28/C29 steranes, indicating they were generated from Upper Jurassic/Lower Cretaceous carbonates such as those at Gillabat oil field north of Mansuriyah Lake. Oils from Gillabat field thus indicate a lower degree of correlation with the Sargelu source rocks than do oils from Demir Dagh field.Palynofacies assessments are performed for this studied succession by ternary kerogen plots of the phytoclast, amorphous organic matters, and palynomorphs. From the diagram of these plots and maturation analysis, it could be assessed that the formations of Chia Gara and Sargelu are both deposited in distal suboxic to anoxic basin and can be correlated with kerogens classified microscopically as Type A and Type B and chemically as Type II. The organic matter, comprised principally of brazinophyte algae, dinoflagellate cysts, spores, pollen, foraminifera test linings, and phytoclasts in all these formations and hence affected with upwelling current. These deposit contain up to 18 wt% total organic matters that are capable to generate hydrocarbons within mature stage of thermal alteration index (TAI) range in Stalplin's scale (Staplin, 1969) of 2.7–3.0 for the Chia Gara Formation and 2.9–3.1 for the Sargelu Formation. Case study examples of these oil prone strata are; one 7-m (23-ft) thick section of the Sargelu Formation averages 44.2 mg HC/g S2 and 439 °C Tmax (Rock-Eval pyrolysis analyses) and 16 wt% TOC especially in well Mk-2 whereas, one 8-m (26-ft) thick section of the Chia Gara and 1-m (3-ft) section of Naokelekan Formations average 44.5 mg HC/g S2 and 440 °C Tmax and 14 wt% TOC especially in well Aj-8. One-dimension, petroleum system models of key wells using IES PetroMod Software can confirm their oil generation capability.These hydrocarbon type accumulation sites are illustrated in structural cross sections and maps in North Iraq.

モンゴル南東部，ゴビ砂漠における湖成堆積物中のジュラ系-下部白亜系カイエビの古生物学的研究

モンゴル南東部，ゴビ砂漠における湖成堆積物中のジュラ系-下部白亜系カイエビの古生物学的研究

Geochemistry, origin and correlation of crude oils in Lower Cretaceous sedimentary sequences of the southern Mesopotamian Basin, southern Iraq

Thirty one crude oil samples from Lower Cretaceous reservoirs in southern Iraq were analyzed using bulk property and molecular methods to determine their maturity and biomarker characteristics, as well as to obtain information on their respective source rocks. All the oils are unaltered, non-biodegraded, have high sulfur content and API gravity is in the range for light to heavy oil (19–40° API). They are characterized by low Pr/Ph values, even/odd predominance and front-end biased n-alkane distributions. Based on these parameters the oils were generated and expelled from a marine carbonate source rock bearing Type II-S kerogen. Compositional similarities of hopane and sterane biomarkers with those from potential source rocks allowed identification of the Upper Jurassic–Lower Cretaceous Sulaiy and Yamama carbonate succession as the effective source beds. A similar composition of normal and isoprenoid hydrocarbons among the oils suggests an origin from a common source rock. However, biomarker maturity ratios indicate a wide range of maturity. This appears to result from the type of burial history of the source rock, characterized by a slow passage through the liquid window interval during an extended period of geologic time.

An Upper Jurassic-Lower Cretaceous carbonate platform from the Vâlcan Mountains (Southern Carpathians, Romania): paleoenvironmental interpretation

An Upper Jurassic-Lower Cretaceous carbonate platform from the Vâlcan Mountains (Southern Carpathians, Romania): paleoenvironmental interpretationThe results of a biostratigraphic and sedimentological study of the Upper Jurassic-Lower Cretaceous limestones cropping out in the southern sector of the Vâlcan Mountains in Romania are presented, including the definition of microfacies types, fossil assemblages and environmental interpretation. Six microfacies types (MFT 1-MFT 6) have been identified, each of them pointing to a specific depositional environment. The deposits are characteristic of a shallow carbonate platform. They contain normal marine or restricted marine facies deposited in low or high energy environments from the inner, middle and outer platform. The age attribution of these deposits (Late Jurassic to Berriasian-Valanginian-?Hauterivian, and Barremian) is based on foraminiferal and calcareous algae associations. The micropaleontological assemblage is exceptionally rich in the Vâlcan Mountains and brings new arguments for dating the Upper Jurassic-Lower Cretaceous limestones in this area.

The Indus–Yarlung Zangbo ophiolites from Nanga Parbat to Namche Barwa syntaxes, southern Tibet: First synthesis of petrology, geochemistry, and geochronology with incidences on geodynamic reconstructions of Neo-Tethys

The purpose of this first synthesis is to summarize findings on the Yarlung Zangbo Suture Zone (YZSZ) ophiolites and discuss still remaining problems. The YZSZ studied for almost 30years and is the youngest of the sutures recognized on Tibet Plateau. It is now acknowledged that the YZSZ is a complex assemblage of sedimentary, metamorphic and igneous rocks created during and shortly after the collision between India and Eurasia. The ages of the various lithologies span a time interval from the Jurassic to the Middle Miocene, with some Permian and Devonian exotic blocks from mélange zone. The YZSZ is characterized by ophiolitic complexes and ophiolitic mélange. The ophiolites are of two types: non dismembered and dismembered sections. The non disturbed sections, although tectonically reworked, are observed along the segment from Dazhuqu to Jiding in Xigaze area and Spontang ophiolite. The dismembered sequences are found in various locations such as Nidar, Kiogar, Jungbwa, Saga, Sangsang, Xigugabu, and Luobusa. The incomplete stratigraphic log could be connected to intraoceanic or orogenetic origins. The ophiolites are distributed into two groups of ages: the Luobusa, Zedang and Kiogar sequences being Jurassic-Lower Cretaceous whereas all other sequences are of Lower Cretaceous age. Compilation of geochronological data suggest that some ophiolite sequences might have evolved for over more than 70My from their initial genesis to obduction which occurred around 70–90My ago. Ophiolites differ in terms of petrological and geochemical aspects however, they were all generated in suprasubduction zone and more specifically in arc (few fore-arc) and back-arc settings. Synthesis of more than 700 geochemical analyses show variable mixing of components from N-MORB-type to IAT-CAB and to OIB end-members. The Jurassic ophiolites show the maximum of arc component while the Lower Cretaceous ones show little to strong mixing. In addition, most ophiolites were created in short lived (30My) basins and generated close to the Eurasiatic continental margin. We propose that Ladakh–Tibet ophiolites were generated in a suprasubduction context similar to Mariana arc, interarc and back-arc or Tonga–Lau system. The variable arc signature of these ophiolites is directly related to their initial position within the suprasubduction system.

Prophaenognatha, a New Aclopinae Genus from the Yixian Formation, China and Its Phylogenetic Position Based on Morphological Characters (Coleoptera: Scarabaeidae)

Prophaenognatha robusta gen. et sp. nov. (Scarabaeoidea: Scarabaeidae: Aclopinae), the best-preserved aclopine fossil so far, is described and illustrated from the Upper Jurassic-Lower Cretaceous Yixian Formation of the Jehol Biota, western Liaoning Province, NE China. The key to extinct and extant genera of Aclopinae is given and the monophyly of extant and fossil Aclopinae lineages is supported by five character states. The new taxon provides evidence about the evolution of Scarabaeoidea with its phylogenetic position inferred based on 68 morphological characters.

Prophaenognatha, a New Aclopinae Genus from the Yixian Formation, China and Its Phylogenetic Position Based on Morphological Characters (Coleoptera: Scarabaeidae)

Abstract:Prophaenognatha robusta gen. et sp. nov. (Scarabaeoidea: Scarabaeidae: Aclopinae), the best‐preserved aclopine fossil so far, is described and illustrated from the Upper Jurassic‐Lower Cretaceous Yixian Formation of the Jehol Biota, western Liaoning Province, NE China. The key to extinct and extant genera of Aclopinae is given and the monophyly of extant and fossil Aclopinae lineages is supported by five character states. The new taxon provides evidence about the evolution of Scarabaeoidea with its phylogenetic position inferred based on 68 morphological characters.

New data on the Upper Jurassic-Lower Cretaceous limestones from Bihor Mountains: case study of Gârda Seacă-Hodobana region, Romania

This study refers to some problems regarding the lithological succession, facies and carbonate microfacies, and to biostratigraphic markers of the Upper Jurassic-Lower Cretaceous carbonates from Bihor Mountains. Three types of facies (external marginal facies, subtidal and peritidal facies) were separated for the Upper Jurassic, and two (coastal-peritidal and open shelf facies) for the Lower Cretaceous carbonates. The micropaleontological assemblages identified contain species that allow the separation of the two formations of different age: Labyrinthina mirabilis, Kurnubia palastiniensis, Neokilianina rahonensis, Clypeina sulcata (Kimmeridgian-Lower Tithonian) and Parakoskinolina? jourdanensis, Montseciella arabica, Palorbitolina lenticularis, Falsolikanella danilovae (Barremian – Lower Aptian). Field observations and data obtained from studies on thin sections and polished slabs indicate that a large part of the Triassic (Ladinian-Lower Carnian) and Lower Cretaceous limestones from Gârda Seacă-Hodobana region, delimited on the geological maps 1:50 000 scale, sheets 56b (Poiana Horea) and 56d (Avram Iancu) (Bleahu et al., 1980; Dimitrescu et al., 1977), belong in fact to the Upper Jurassic carbonate succession.

On taxonomy and distribution of fossil Cerophytidae (Coleoptera: Elateriformia) with description of a new Mesozoic species of Necromera Martynov 1926

In this paper the data on fossils of the family Cerophytidae are reviewed. New synonymy on generic names Necromera Martynov 1926 (proposed in composition of the family Oedemeridae); Idiomerus Dolin in Dolin et al. 1980, n. syn. (proposed in composition of Elateridae) and Leptocnemus Hong & Wang 1990, n. syn. (proposed without any family attribution) is established. New materials on this family from Mesozoic deposits of Asia are cited. As a result, it was established that this spreads in deposits of both Upper Jurassic and Lower Cretaceous. Mercata festira Lin 1986 described from Lower Jurassic as member of Silphidae and Abrotus reconditus Dolin in Dolin et al. 1980 described from Upper Jurassic as a member of Elateridae are transferred to Cerophytidae. Diagnoses of the genus Necromera and family Cerophytidae in compression fossils are elaborated. Necromera admiranda n. sp. is described from the Upper Jurassic-Lower Cretaceous in Liaoning, China. The historical development of the family from the Lower Jurassic is discussed.

Composition and depositional environments of the Upper Jurassic-Lower Cretaceous Mar’yanovo formation (Southeastern West Siberian Sea Basin)

The study of the composition and depositional environments of sediments from the Mar’yanovo Formation (Upper Jurassic-Lower Cretaceous Bazhenov and Georgiev horizons) recovered by boreholes Vostok-1 and Vostok-3 in the southeastern part of the West Siberian Sea Basin revealed the following fact: in the latter hole located closer to the basin boundaries as compared with the former one, they are characterized by lower organic carbon and pyrite contents, indicating reduced salinity of the basin and higher oxidation degree of sediments. The same trend is derived from comparison of rocks from the Mar’yanovo Formation in both holes with the over- and underlying strata. In Borehole Vostok-4, the closet one to the former shoreline of the basin, the Mar’yanovo Formation is indistinguishable. Intense chemical weathering of rocks in provenances during their deposition noted by Kontorovich et al. (1971) is considered a most important factor responsible for its composition and formation conditions. Elevated influx of dissolved weathering products into the sea basin intensified its biogenic activity and stimulated the accumulation of high organic matter concentrations. This inference is valid for all Upper Jurassic-Lower Cretaceous organic carbon-rich sediments that are synchronous to the Mar’yanovo Formation and developed over a spacious area of the West Siberian basin.

New Fossil Elaterids (Coleoptera: Polyphaga: Elateridae) from the Jehol Biota in China

Abstract Three new genera and six new species of fossil elaterids of the tribe Desmatini Dolin, 1975 from second Bed of the Upper Jurassic-Lower Cretaceous Yixian Formation in Huangbanjigou, Liaoning Province, China are described: Paradesmatus dilatatus sp. nov., Desmatinus cognatus gen. et sp. nov., Apoclion clavatus gen. et sp. nov., A. dolini gen. et sp. nov., A. antennatus gen. et sp. nov. and Anoixis complanus, gen. et sp. nov. This tribe demonstrates some characters similar to those in Throscidae and Eucnemidae, elucidating the evolutionary process of the Elateroidea. New materials make clear the distinctness of the genera related to DesmatusDolin, 1975 (tribe Desmatini) from all other Elateridae. Tetraraphes ebersiniIablokoff-Khnzorian, 1961 could be regarded somewhat nearby the subfamily Protagrypninae; however, this species seems to be similar to some Cenozoic groups rather than any of Mesozoic groups.

Earthquake-induced soft-sediment deformation structures in Upper Jurassic open-marine microbialites (Neuquén Basin, Argentina)

Penecontemporaneous decimetre-scale soft-sediment deformation structures are reported from the basal part of the Upper Jurassic–Lower Cretaceous Vaca Muerta Formation, in the Malargüe–Las Leñas area of the back-arc Neuquén Basin (Mendoza Province, Central Andes). The deformed interval (Amarillas bed) is only 0.3 to 0.9 m thick but occurs in a wide area, larger than 1500 km 2. Its age, determined by ammonite biostratigraphy, is Early Tithonian. The soft-sediment deformation structures were generated in finely laminated, partially consolidated, organic-rich, carbonate microbialites that were deposited in open-marine, poorly oxygenated settings, apparently devoid of any significant slope. Those structures include boudins of different sizes and complexity, a variety of folds, normal (listric) dm-scale faults, sub-horizontal detachment surfaces and other features, which are part of several larger-scale, complex slump structures. Deformation was dominantly plastic but near to the ductile–brittle field transition. On the basis of the observed soft-deformation structures, their geographic distribution, their lateral homogeneity, and the geodynamic framework of the basin in which it was generated, the Amarillas bed can be tentatively attributed to a large, intermediate-depth earthquake that occurred within the plate that subducted beneath the Andean continental margin and the Neuquén back-arc basin.

EVIDENCIAS DE ACTIVIDAD EOLICA EN LA FORMACION QUEBRADA MONARDES OURASICO-CRETACICO INFERIOR) EN LA PRECORDILLERA DE COPIAPO, CHILE

RESUMEN:The Quebrada Monardes Formation (Upper Jurassic?-Lower Cretaceous) exposed in the Precordillera of Copiapo, presents sedimentary structures which could be interpreted as formed by eolian processes. Ventifacts included in conglomerates of this formation exposed in Quebrada Codocedo, are the best proof of this. Slumped foresets are structures best explained as formed under subaerial conditions. Structures resembling runzelmarken (?) may also be indicative of wind activity. These data are consistent with the sabkha environmental conditions inferred for the deposition of part of the Quebrada Monardes Formation. Keywords: Eolian activity, Ventifacts, Upper Jurassic-Lower Cretaceous, Atacama desert, Chile. Palabras claves: Actividad eolica, Ventifactos, Jurasico Superior-Cretacico Inferior, Desierto de Atacama, Chile.

Late Jurassic lungfishes (Dipnoi) from Uruguay, with comments on the systematics of Gondwanan ceratodontiforms

ABSTRACT We describe herein the only known fossil dipnoans from Uruguay, recovered from continental deposits of Kimmeridgian–?early Cretaceous age (Batoví Member of the Tacuarembó Formation). The material includes several tooth plates referred herein to “Ceratodus” tiguidiensisTabaste, 1963 (the current generic assignment being either Arganodus or Asiatoceratodus), and one to Ceratodus africanusHaug, 1905. “C.” tiguidiensis was so far only recorded in the Upper Jurassic–Lower Cretaceous of Saharan Africa and the ‘middle’ Cretaceous of Brazil (and perhaps the Lower Triassic of Australia), and C. africanus in the Lower to Upper Cretaceous of Saharan Africa and the ‘middle’ Cretaceous of Brazil. Hence, these are the oldest and southernmost South American records of both taxa, and the oldest and southernmost record of C. africanus in the world. These findings reveal an unrecognized dipnoan diversity in South America prior to ‘middle’ Cretaceous times. In the Late Jurassic–Early Cretaceous of western Gondwana only the ceratodontiform genera Ceratodus, Arganodus/Asiatoceratodus, and Retodus were present, Neoceratodus being absent. The Tacuarembó Formation paleoichthyofauna comprises a low-diversity freshwater assemblage including, besides dipnoans, putative semionotids (the most abundant fossils) and hybodontid sharks.

Revision and New Taxa of Fossil Prophalangopsidae (Orthoptera: Ensifera)

Taxonomy is investigated and revised for some prophalangopsid insects, yielded by the Middle Jurassic Jiulongshan and Upper Jurassic-Lower Cretaceous Yixian formations in China. Flexaboilus retinervius Li, Ren & Meng, 2007 and Furcaboilus excelsus Li, Ren & Meng, 2007 are considered as synonyms of Allaboilus gigantus Ren & Meng, 2006. Protaboilus lini Ren & Meng, 2006 is considered a synonym of Aboilus stratosus Li, Ren & Wang, 2007. Hebeihagla Hong, 1982b, Habrohagla Ren, Lu, Guo & Ji, 1995, Grammohagla Meng & Ren, 2006, Trachohagla Meng, Ren & Li, 2006 are considered as synonyms of Parahagla Sharov, 1968; Athehagla Meng & Ren, 2006 is considered a synonym of Ashanga Zherichin 1985. Genera Allaboilus, Circulaboilus Li, Ren & Wang, 2007 and Ashangopsis Lin, Huang & Nel, 2008 are revised. In addition, one new genus Scalpellaboilus gen. nov. and four new species: Scalpellaboilus angustus sp. nov., Circulaboilus priscus sp. nov., Allaboilus robustus sp. nov. and A. hani sp. nov. are described. Some wing venation variability in Prophalangopsidae is briefly discussed.

Paleogeographic evidence on the Jurassic tectonic history of the Pontides: new paleomagnetic data from the Sakarya continent and Eastern Pontides

The Jurassic paleogeographic position of the Pontides is not well studied because of insufficient paleomagnetic data. For this reason, a paleomagnetic study was carried out in order to constrain the paleolatitudinal drift of the Turkish blocks during the Jurassic period. A total of 32 sites were sampled from volcanic and volcanoclastic rocks of the Lower/Middle Jurassic Kelkit formation (Eastern Pontides), Mudurnu formation (Sakarya continent) and Upper Jurassic–Lower Cretaceous Ferhatkaya formation exposed around Amasya region (Eastern Pontides). Rock magnetic experiments demonstrate that the main ferromagnetic mineral is pseudo-single-domain titanomagnetite in these rocks. Paleomagnetic analysis revealed two main components of the natural remanent magnetization during stepwise thermal and alternating field demagnetization. The first component is a low-coercivity (unblocking temperature) component with a direction sometimes similar to that of the earth’s present field or a viscous component. The second component, which is interpreted as the characteristic remanent magnetization (ChRM) direction, has low to high coercivity properties between 20 and 100 mT or unblocking temperatures between 300 and 580°C. A positive fold test at the 95% level of confidence proved that the ChRM of the sites is primary. Paleomagnetic directions calculated for the Kelkit formation in the Eastern Pontides have a mean direction of D = 334.8°, I = 49.7°, α95 = 7.1° after tilt-correction. A mean direction of D = 332.2°, I = 48.5°, α95 = 14.6° was obtained from the volcanoclastic rocks of the Mudurnu formation, and D = 324.3°, I = 43.3°, α95 = 9.5° was calculated for the Upper Jurassic–Lower Cretaceous limestones/Ferhatkaya formation of the Amasya region. The Jurassic rocks in the Eastern Pontides and Mudurnu region are considered to represent products of the rifted Neo-Tethys ocean, while the Upper Jurassic–Lower Cretaceous sediments in Amasya are related to basin-filling materials. The data suggest that the Kelkit formation was formed at 30.5°N paleolatitude and the equivalent Mudurnu formation at 29.5°N paleolatitude. The paleolatitude of the Eastern Pontides indicates that this rifting block was separated from Eurasia by a marginal basin instead of being a part of Eurasia. The lower paleolatitude of the Amasya region at 24.8°N in the Upper Jurassic to Lower Cretaceous clearly indicates southward drift of the Turkish blocks during the Jurassic to Lower Cretaceous period together with the motion of Eurasia.

Cretaceous petroleum system of the Khasib and Tannuma oil reservoir, East Baghdad oil field, Iraq

Gas chromatography, palynomorph constituents, and maturation are analyzed for oil samples of the Campanian Khasib and Tannuma Formations in the wells of East Baghdad oil field for biomarker studies, while palynomorph constituents and their maturation, Rock Eval pyrolysis, total organic carbon (TOC) analysis are carried on for the Upper Jurassic and the Cretaceous Formations of core samples from the same wells for dating and evaluation of the source rocks. The gas chromatography of these oils have shown biomarkers of abundant ranges of n-alkanes of less than C22(C17–C21) with C19 and C18 peaks to suggest mainly liquid oil constituents of paraffinic hydrocarbons from marine algal source of restricted palaeoenvironments in the reservoir as well as low nonaromatic \( {\hbox{C}}_{15}^{+} \) peaks to indicate their slight degradation and water washing. Oil biomarkers of \( \Pr ./{\hbox{Ph}}{.} = {0}{.85,}{{\hbox{C}}_{31}}/{{\hbox{C}}_{30}} < 1.0 \), location is in the triangle of C27–C29 sterane, C28/C29 of 0.6 sterane, oleanane of 0.01, and CPI = 1.0, could indicate anoxic marine environment with carbonate deposition of Upper Jurassic–Early Cretaceous source. The recorded palynomorph constituents in this oil and associated water are four miospore, seven dinoflagellates, and one Tasmanite species that could confirm affinity to the Upper most Jurassic–Lower Cretaceous Chia Gara and Ratawi Formations. The recorded palynomorphs from the reservoir oil (Khasib and Tannuma Formations) are of light brown color of \( {\hbox{TAI}} = 2.8 - 3.0 \) and comparable to the mature palynomorphs that belong to Chia Gara and Lower part of Ratawi Formations. Chia Gara Formation had generated and expelled high quantity of oil hydrocarbons according their TOC weight percent of 0.5–8.5 with \({S_2} = 2.5 - 18.5\,{\hbox{mg}}\,{\hbox{Hc/g}}\;{\hbox{rock}} \), high hydrogen index of the range 150–450 mg Hc/g Rock, good petroleum potential of 4.5–23.5 mg Hc/g rock, mature (\( {\hbox{TAI}} = 2.8 - 3.0 \) and \( {\hbox{T}}\max = 428 - 443{\hbox{C}} \)), kerogen type II, and palynofacies parameters of up to 100 amorphous organic matters with algae deposited in dysoxic–anoxic to suboxic–anoxic basin, while the palynomorphs of the rocks of Khasib Formation are of amber yellow color of TAI = 2.0 with low TOC and hence not generated hydrocarbons. But, this last formation could be considered as oil reservoir only according their high porosity (15–23%) and permeability (20–45 mD) carbonate rocks with structural anticline closure trending NW-SE. That oil have generated and expelled during two phases; the first is during Early Palaeogene that accumulated in traps of the Cretaceous structural deformation, while the second is during Late Neogene’s.

Stratigraphy and Mesozoic–Cenozoic tectonic history of northern Sierra Los Ajos and adjacent areas, Sonora, Mexico

Abstract Geologic mapping in the northern Sierra Los Ajos reveals new stratigraphic and structural data relevant to deciphering the Mesozoic–Cenozoic tectonic evolution of the range. The northern Sierra Los Ajos is cored by Proterozoic, Cambrian, Devonian, Mississippian, and Pennsylvanian strata, equivalent respectively to the Pinal Schist, Bolsa Quartzite and Abrigo Limestone, Martin Formation, Escabrosa Limestone, and Horquilla Limestone. The Proterozoic–Paleozoic sequence is mantled by Upper Cretaceous rocks partly equivalent to the Fort Crittenden and Salero Formations in Arizona, and the Cabullona Group in Sonora, Mexico. Absence of the Upper Jurassic–Lower Cretaceous Bisbee Group below the Upper Cretaceous rocks and above the Proterozoic–Paleozoic rocks indicates that the Sierra Los Ajos was part of the Cananea high, a topographic highland during the Late Jurassic and Early Cretaceous. Deposition of Upper Cretaceous rocks directly on Paleozoic and Proterozoic rocks indicates that the Sierra Los Ajos area had subsided as part of the Laramide Cabullona basin during Late Cretaceous time. Basal beds of the Upper Cretaceous sequence are clast-supported conglomerate composed locally of basement (Paleozoic) clasts. The conglomerate represents erosion of Paleozoic basement in the Sierra Los Ajos area coincident with development of the Cabullona basin. The present-day Sierra Los Ajos reaches elevations of greater than 2600 m, and was uplifted during Tertiary basin-and-range extension. Upper Cretaceous rocks are exposed at higher elevations in the northern Sierra Los Ajos and represent an uplifted part of the inverted Cabullona basin. Tertiary uplift of the Sierra Los Ajos was largely accommodated by vertical movement along the north-to-northwest-striking Sierra Los Ajos fault zone flanking the west side of the range. This fault zone structurally controls the configuration of the headwaters of the San Pedro River basin, an important bi-national water resource in the US-Mexico border region.