Jurassic-Lower Cretaceous Research Articles

Type and evolution of the Middle Jurassic–Early Cretaceous basin at the northern margin of the Lhasa Block: constraints of sedimentary characteristics and provenance tracing based on zircon U-Pb ages

To identify its type and evolution features of the Middle Jurassic–Early Cretaceous basin at the northern margin of the Lhasa Block (NMLB) is of great significance for reconstructing its tectonic-paleogeography and assessing the petroliferous basins in the Bangong-Nujiang suture zone (BNSZ) and its adjacent area. This study conducted the sedimentary characteristic analyses and detrital zircon U-Pb dating of the Middle Jurassic–Lower Cretaceous strata exposed in the northern part of Nagqu County (NPNC), Tibet. The Middle–Upper Jurassic Lagongtang Formation was mainly deposited in a steep slope delta and its middle part is characterized by debris flows moving southeastward. The lower part of the Upper Jurassic–Lower Cretaceous Duoni Formation was characterized by molasses formation, and its middle and upper part were primarily deposited on a tidal flat-mixed shelf. The 384 detrital zircons from the debris-flow deposits of the Lagongtang Formation yielded ages of 2800∼210 Ma, except for one yielding an age of 174 Ma. The detrital zircons from the lower part of the Duoni Formation yielded ages of 2744∼152 Ma. Comprehensive research results show that the basin located at the NMLB is a peripheral foreland basin controlled by the BNSZ and had dual source supply, and around 152 Ma, the basin was accompanied by a stronger overthrust event and experienced the conversion from flysch basin to molasses one. Subsequently, a new foreland basin formed marked by the deposition of the Shamuluo Formation in the BNSZ.

ВЕРХНЕЮРСКО-НИЖНЕМЕЛОВЫЕ ОТЛОЖЕНИЯ ВОСТОЧНОЙ ЧАСТИ OЛОЙСКОЙ ЗОНЫ: СТРАТИГРАФИЯ, ГЕОХИМИЯ, ВОЗРАСТ И ГЕОДИНАМИЧЕСКИЕ ОБСТАНОВКИ ФОРМИРОВАНИЯ

New data on the geology and stratigraphy of the Upper Jurassic-Lower Cretaceous deposits of the eastern part of the Oloy zone (upper reaches of the Oloy, Ilguveem, Aluchin rivers), including the description of sections, lithological-petrographic and paleontological characteristics of volcaniclastic sedimentary deposits, the results of petrological-geochemical study of volcanic rocks and their isotopic dating are presented. Two concordant dates were obtained using the zircon U-Pb method: 147±2 Ma (Elomskaya Formation) and 140±2 Ma (Glukhovskaya Formation). The island-arc nature of the studied formations is proved, the accumulation conditions and geodynamic settings of all stages of the formation of the volcanic-sedimentary complex in various structural-facies zones are characterized.

DEEP KARST AREAS EVIDENCED BY SEISMIC RESEARCH IN MOESIAN PLATFORM

"Around half of the total carbonate rocks of Romanian territory are Upper Jurassic-Lower Cretaceous age. Most of them are able to develop karst phenomena. In the southern-central part of the Moesian Platform Jurassic-Cretaceous deposits are at 2000-3000 m depth. The existence of the hydrocarbon accumulations in the area was just proved (Talpa, Harlesti, Videle fields). In the calcareous deposits, the seismic profiles and the attributes of seismic traces highlighted some specific geological features: The collapse karst areas, formed in Jurassic-Neocomian deposits. The seismic expression of these areas is one of chaotic reflections zone flanked by converging, strong tilted faults. The paleo-valley systems formed by erosion of the Cretaceous relief, filled with different terms of the Lower Sarmatian (a succession of marls and sands). The reflections configuration is specific to the passing from the valley fill lithology to the Cretaceous calcareous formations of the adjacent areas. The reef build-ups in Upper Jurassic-Lower Cretaceous formations, expressed by chaotic reflection mound zones draped for quasi horizontal superimposed strata. The seismic trace attributes and velocity analyses are important tools in reservoir quality definition, giving information regarding porosity and fluid contents. "

Revision of Decapoda (Glypheidea, Axiidea) from the Upper Jurassic-Lower Cretaceous of Argentina

New specimens of Late Jurassic and Early Cretaceous decapods from Argentina document new species and new occurrences. Pehuenchia Rusconi, 1948, originally placed within Palinura and subsequently placed within Callianassidae or Mecochiridae, is herein referred to Mecochiridae. The type species, Pehuenchia tellecheai Rusconi, 1948, is herein illustrated photographically for the first time. A second species of Pehuenchia is herein referred to a new genus, resulting in Zapalianassa, new genus, and Zapalianassa magna (Rusconi, 1948), new combination, and additional specimens of the species are illustrated. A new species of the mecochirid genus Huhatanka, Huhatanka australis, in southern Argentina extends the geographic range from the Western Interior Seaway and the geologic range from the late Early Cretaceous to the early Early Cretaceous. A species of Huhatanka described from Iran is herein moved to Meyeria, resulting in Meyeria iranica (Yazdi et al., 2010), new combination. Additional specimens of Protaxius paucisaetosus Andrada et al., 2022, extend the range of the species southward. Late Jurassic and Early Cretaceous decapod occurrences in Argentina are currently known from Glypheidea, Astacidea, and Axiidea.

The use of titania polymorphs as indicators of mesodiagenesis during hydrocarbon charge

Authigenic titania (TiO2) minerals are observed in the Upper Jurassic-Lower Cretaceous pro-deltaic reservoir sandstones of the Scotian Basin. Although diagenetic rutile is rare, relatively large amounts of diagenetic anatase and brookite are present. Anatase is mostly early diagenetic whereas brookite is usually late diagenetic and is abundant in reservoir sandstones above the free-water level. The availability and mobility of Ti during late diagenesis is attributed to the dissolution of Ti-bearing minerals enhanced by Ti complexes formed from hydrocarbon-rich and highly saline fluids. This study suggests that the precipitation of late diagenetic brookite, rather than anatase or rutile, may be due to the incorporation of Fe and V during hydrocarbon charge and the presence of Cl− in circulating fluids. In addition, the chemical composition, timing and distribution of the diagenetic titania polymorphs relative to other diagenetic minerals further constrains the overall paragenetic evolution of the basin, and thus illustrates the relationship between titania minerals, hydrocarbon charge and fluid conditions in the basin.

Broken Beds, but better science; using multiple hypotheses to interpret geological data

AbstractIn this study, we propose a multiple hypotheses approach to improve interpretations of limited remotely sensed datasets, such as sparsely exposed outcrops, subsurface datasets, or planetary objects using semi‐quantitative scoring and ranking of observable features. This method is demonstrated using an outcrop example from the Broken Beds of the Upper Jurassic–Lower Cretaceous Purbeck Limestone Group exposed along Britain's Jurassic Coast. Four published hypotheses regarding their origin are refined, represented in matrix form, scored and ranked based on carefully selected outcrop features. Semi‐quantitative scoring utilises knowledge of likely processes governing the occurrence of a range of features, some of which might be ignored or down‐played to favour a single hypothesis. Furthermore, by integrating expertise from different sub‐disciplines (e.g. basin analysis, sedimentology, diagenesis), we also consider the combined evidence of multiple features. This new method results in an interpretation that favours a multi‐process origin for the Broken Beds due to evaporite dissolution, overpressure release and tectonic folding, with identified uncertainty, all useful to guide further data collection.

The Late Jurassic–Early Cretaceous lacustrine facies and ichnofossils of the Parnaíba Basin, Brazil: A record of bioactivity in response to post-CAMP thermal subsidence in West Gondwana

The lateral and vertical distribution of sedimentary facies and ichnofacies in lacustrine systems records sensitive climatic variations and rates of subsidence. The Upper Jurassic–Lower Cretaceous lacustrine system of the Pastos Bons Formation in the Parnaíba Basin, northeastern Brazil, is an excellent opportunity to evaluate the depositional history of the post-CAMP thermal subsidence. This subsidence event succeeded the voluminous emplacement of mafic magma linked to the Central Atlantic magmatic province (CAMP), ∼201 Ma, forming a large subsiding area in West Gondwana. In this sense, this paper developed outcrop-based facies and ichnofacies analysis, allowing the interpretation of two depositional phases and four facies associations (FAs): 1) The lower depositional phase comprises lacustrine deposits showing an aggradational stacking pattern. FA1 - central lake records fibrous gypsum interbedded with fossiliferous shale beds, forming shallowing-upward cycles. 2) The upper depositional phase reveals a fluvio-lacustrine succession, forming a progradational stacking pattern. Central lake (FA1) comprises laminated mudstone and sandstone beds hosting a suite representative of Mermia ichnofacies, forming coarsening-upward cycles. Lakeshore (FA2) comprising mudstone beds, limestone lenses, and sandstone beds hosting a suite representative of Scoyenia ichnofacies, forming shallowing-upward cycles; and conglomerate lenses overlaid by sandstone beds hosting a suite representative of Skolithos ichnofacies, forming fining-upward cycles. A braided fluvial system (FA3) comprises conglomerate and sandstone beds, forming fining-upward cycles. Delta front (FA4) comprises mudstone lenses and sandstone beds hosting a suite representative of Skolithos ichnofacies, organized in coarsening-upward cycles. The fluvial discharge and wave activity oxygenated the water lake in the progradational phase, creating chemical and biological conditions that allowed the establishment of the epifaunal and infaunal benthic communities, represented by the well-preserved ichnological record. The decrease of the post-CAMP thermal subsidence rates (accommodation potential) related with the increase of the wet periods to the top of the succession (sedimentary supply) indicate a depositional evolution from underfilled to overfilled lake basin, during Upper Jurassic–Lower Cretaceous, in West Gondwana.

Jurassic-Lower Cretaceous petroleum system of Faghur Basin, North Western Desert, Egypt

Different parts of the Lower Cretaceous Alam El Bueib (AEB) and the Jurassic Khatatba source and reservoir rock units in the Faghur basin, like in other basins in the north Western Desert, act as hydrocarbon sources and reservoirs. In the present study, well-log data from five wells in Phiops field and geochemical data from the Neith S-2X well from the neighbor Neith field together with reflection 2D seismic data of thirty (30) lines have been utilized to evaluate the Jurassic-Lower Cretaceous petroleum system in the Faghur basin and to give evidence for future hydrocarbon exploration and development in the study area. Source rock evaluation shows that several units from both Alam El Bueib and the Jurassic Khatatba shale source rocks represent good source rocks. Total organic carbon (TOC) values of the studied units of Alam El Bueib shale source rocks range from 0.27 to 6.39 wt.% that reflect fair to very good source rock, while Toc value for the Alam El Bueib-6 shale source rock is 2.52 wt.% that indicates a very good source rock. These units are characterized by type (III) kerogen, reflecting their ability to produce gas with minor oil. On the other hand, the characterization of the Khatatba shale source rocks indicates a very good to fair organic richness and a type (III) kerogen with an input of type (II) as well, which appears their ability to generate gas with minor oil. Most of Alam El Bueib and Khatatba shale source rocks are found to be in the mature stage. Petrophysical evaluation indicates four definite reservoir units from the Alam El Bueib reservoirs (Alam El Bueib-3D, Alam El Bueib-3E, Alam El Bueib-3G, Alam El Bueib-6) and the Khatatba reservoir. Values for the net reservoir, hydrocarbon saturation, and water saturation indicate that these units represent very promising reservoirs in the studied Phiops field in Faghur basin. Local intra-formational shale intervals most probably seal these reservoirs in the AEB and carbonate interval of the Masajid Formation in the Khatatba Formation. Moreover, analysis and interpretation of the 2D seismic lines showed that both structural and stratigraphic traps dominate. Integration of geochemical, petrophysical, and seismic results, in light of available geological information, indicates a complete Mesozoic petroleum system in the Faghur basin.

Hydrocarbon potentiality of the Jurassic-Lower Cretaceous sequence in Abu Sennan area, Abu Gharadig Basin, Egypt

Hydrocarbon potentiality of the Jurassic-Lower Cretaceous sequence in Abu Sennan area, Abu Gharadig Basin, Egypt

Insights on the late Cretaceous-Eocene event in the Tunisian eastern foreland using subsurface data

Tunisia is characterized by a specific structural location in the northern African margin, related to the geodynamic evolution of the Mediterranean basin. In fact, the Tunisian geological history strongly depends on the relative kinematics of the African-Eurasiatic plates, response to the successive opening of the Tethys and the Mesogea oceans which occurred, respectively, during the late Triassic-Jurassic and the Cretaceous periods. These extensional phases were followed, in the late Cretaceous by a compressive event subject to many controversies among many authors. In order to elucidate this event, a study based on both analysis and interpretation of seismic profiles was achieved in the eastern Tunisian foreland (Sahel and pelagian blocks). It indicates that the late Cretaceous-Eocene compressive event is characterized by NNE-SSW shortening axis and seems to be diachronous. This diachronism results from the resumption of local halokinetic structures throughout the late Cretaceous-Paleogene. The latter were active since the Jurassic-lower Cretaceous then reactivated later through the Senonian extension.

Mid-Cretaceous drainage reorganization and exorheic to endorheic transition in Southeast Tibet

To understand the early topographic growth of the Tibetan Plateau and the causes and effects of climate change in this region, it is important to reconstruct the drainage evolution across Southeast Tibet. Based on age constraints provided by detrital zircons in the fluvial sandstones in the Khorat Plateau Basin, we identified a major Early Cretaceous drainage disruption and reorganization event. The ages and Hf isotope compositions of the detrital zircons in the Upper Jurassic-Lower Cretaceous Phu Kradung to Phu Phan formations (166–122 Ma) suggest the existence of an exorheic continental-scale paleo-Mekong River with headwaters in the Songpan-Garze and Qiangtang terranes. This paleo-river flowed southwards across the Khorat Plateau to what is presently the offshore Phuquoc Basin, which was then part of the Neo-Tethys Ocean. In contrast, the U-Pb-Hf compositions of the detrital zircons in the Lower Cretaceous Khok Kruat Formation (122–113 Ma) indicate that a prominent detrital supply from the Sibumasu magmatic rocks was transported by the paleo-Salween River. This major change reflects the occurrence of ancestral transcontinental river disruption at around 122 Ma, which was driven by the final collision between the Lhasa and Qiangtang and Woyla Arc and Sibumasu terranes. The tectonic uplift and ensuing arid climate corresponded to the reorganization of the ancestral Mekong drainage system during the Mid-Cretaceous (113–94 Ma).

Subsurface geology and geochemical evaluation of the Middle Jurassic-Lower Cretaceous organic-rich intervals, West Kalabsha area, Western Desert, Egypt

The West Kalabsha (WKAL) area is a western extreme exploratory area of the Faghur Basin in the Western Desert of Egypt. The study of four wells (WKAL; A-1 X, K-1 X, P-1X, and C-1 X), interpreted with twenty seismic lines, shows that the area is dissected by a series of normal faults with an irregular, E–W strike direction. The general trend of the throw is toward the south–southeast. The most prospective area for hydrocarbon (HC) migration is toward the north (upthrown side) of an E-W striking normal fault north of the WKAl-K-1 X and A-1 X wells. The WKAL-P-1 X and WKAL-K-1 X wells in the Faghur Basin were selected for both geochemical evaluation of possible source rock intervals and burial history modelling within the basin. Integration of the wire-line logs with geochemical analysis identified six organic matter-rich intervals (OMRIs) within the Middle Jurassic-Lower Cretaceous sequence. Four intervals are in the Alam El-Bueib-3C (AEB-3C) member with a cumulative vertical thickness of 530ft. The other OMRIs are 110ft in thickness recorded within the AEB-6 (10ft) and Upper Safa (100ft) members. The studied organic matter (OM) reveals type III, IIIC, and IV kerogens (mainly gas-prone) with a terrestrial origin. They have reached a maturity level consistent with the late oil window. The expulsion threshold depth detected in the WKAL-P-1 X well is 12000ft in the AEB-3C member, whereas the active source depth limit (ASDL) is 15000ft in the Safa Member. The present study suggests a paleo-geothermal gradient range between 1.13oF/100ft and 1.39oF/100ft with an estimated regional erosion of 5500 to 7000ft of strata mainly between the Paleozoic-Jurassic and Cretaceous-Tertiary boundaries. The present-day geothermal gradient based on bottom-hole temperatures shows a geothermal gradient of 1.4oF/100ft (WKAL-P-1 X), that increases to the north to 1.65oF/100ft (WKAL-K-1 X). Burial history modelling reveals that sedimentary strata entered the mature oil zone in the Early Cretaceous (110–115Ma) at depths of 7500–8000ft in the deepest part of WKAL-P-1 X and WKAL-K-1 X wells (Paleozoic strata). Maturation continued to present, resulting in Jurassic and Lower Cretaceous strata currently falling into the late oil window.

Middle Jurassic fossils document an early stage in salamander evolution

Salamanders are an important group of living amphibians and model organisms for understanding locomotion, development, regeneration, feeding, and toxicity in tetrapods. However, their origin and early radiation remain poorly understood, with early fossil stem-salamanders so far represented by larval or incompletely known taxa. This poor record also limits understanding of the origin of Lissamphibia (i.e., frogs, salamanders, and caecilians). We report fossils from the Middle Jurassic of Scotland representing almost the entire skeleton of the enigmatic stem-salamander Marmorerpeton. We use computed tomography to visualize high-resolution three-dimensional anatomy, describing morphologies that were poorly characterized in early salamanders, including the braincase, scapulocoracoid, and lower jaw. We use these data in the context of a phylogenetic analysis intended to resolve the relationships of early and stem-salamanders, including representation of important outgroups alongside data from high-resolution imaging of extant species. Marmorerpeton is united with Karaurus, Kokartus, and others from the Middle Jurassic-Lower Cretaceous of Asia, providing evidence for an early radiation of robustly built neotenous stem-salamanders. These taxa display morphological specializations similar to the extant cryptobranchid "giant" salamanders. Our analysis also demonstrates stem-group affinities for a larger sample of Jurassic species than previously recognized, highlighting an unappreciated diversity of stem-salamanders and cautioning against the use of single species (e.g., Karaurus) as exemplars for stem-salamander anatomy. These phylogenetic findings, combined with knowledge of the near-complete skeletal anatomy of Mamorerpeton, advance our understanding of evolutionary changes on the salamander stem-lineage and provide important data on early salamanders and the origins of Batrachia and Lissamphibia.

Geochemistry and organic petrology of organic-rich shales of the Upper Jurassic – Lower Cretaceous Bazhenov Horizon in the Frolov Region, West Siberian Basin: Implications for the reconstruction of the organic matter origin and paleoredox conditions

The objective of this study is the reconstruction of paleodepositional conditions that have prevailed in the Bazhenov Sea during the sedimentation of the organic matter-rich black shales of the Upper Jurassic-Lower Cretaceous Bazhenov Horizon from the western West Siberian Basin, with the aim to gain insights into the primary forces and mechanisms favouring enhanced organic matter preservation and accumulation. Elemental analysis, rock pyrolysis and petrographic observations were carried out on a total of 298 core samples from a 60.6 m thick well section, covering black shales of the Tutleim Formation and parts of the under- and overlying Abalak and Frolov Formations from the south-western West Siberian Basin (Frolov region). The results reveal systematic depth variation of sedimentary and diagenetic conditions, e.g. detrital influx and paleoredox conditions.The sediments were deposited in a marine environment with a significant contribution of authigenic minerals and subordinate detrital influence. The organic matter composition suggests an aquatic and bacterial origin with minor input of land plant-derived material. The enrichment of redox-sensitive inorganic and organic compounds results from reducing and periodically sulfidic conditions in the bottom and uppermost pore water columns during deposition. Sections that show evidence of anoxia or euxinic conditions simultaneously represent the lowest terrigenous influence, suggesting that anoxia is closely linked to sea-level fluctuations in the course of eustatic transgression-regression cycles. A distinctive correlation pattern of organic matter quantities and redox proxies suggests that organic matter accumulation and preservation are mainly controlled by paleoredox conditions and, therefore, regression-transgression cycles. The most prolific source rock sections are defined as the central Tutleim units, T4 and T5, marking the transition from marine transgression to regression at the Upper Jurassic-Lower Cretaceous boundary.

ICHNOLOGY OF MUDDY SHALLOW-WATER CONTOURITES FROM THE UPPER JURASSIC–LOWER CRETACEOUS VACA MUERTA FORMATION, ARGENTINA: IMPLICATIONS FOR TRACE-FOSSIL MODELS

ABSTRACT Contourites are increasingly being recognized in ancient fine-grained depositional environments. However, detailed ichnologic analyses focusing on shallow-water examples of these deposits are scarce. The Upper Jurassic–Lower Cretaceous Vaca Muerta Formation from Argentina constitutes an important unconventional reservoir that displays dm- to m-thick, laminated, rippled and bioturbated, crinoidal mudstone and fine to coarse mudstone deposited by wind- and thermohaline-driven contour currents. Four ichnofabrics were recognized in three facies associations. The Palaeophycus heberti ichnofabric is dominant in facies association 1, forming highly bioturbated intervals. The Palaeophycus heberti, Nereites isp., and Phycosiphon incertum ichnofabrics are present in facies association 2, displaying highly, moderately and sparsely bioturbated intervals, respectively. This association is locally characterized by m-thick successions comprising an upward decrease and then increase in bioturbation index, which may have a similar origin to bigradational sequences. The Equilibrichnia-Fugichnia ichnofabric mostly occurs in facies association 3 and less commonly in 2, forming distinctive bioturbated intervals within sparsely bioturbated successions. Benthic activity was controlled by food distribution, oxygenation, hydrodynamic energy, and water turbidity. Food was delivered to the surface or in suspension by currents, promoting deposit- or suspension-feeding strategies in the infauna, respectively. Oxygen levels increased during contour current activity yet remained relatively low (upper dysoxic). Hydrodynamic energy controlled bioturbation intensity, resulting in lower degrees of bioturbation during higher energy events. Suspension-feeding strategies suggest that water turbidity was relatively low during current transport. The herein example increases our understanding of environmental controls of shallow-water contour currents, supporting the fact that high bioturbation levels are typical of contourite deposits and providing an example of muddy contourites showing high preservation of sedimentary structures due to oxygen deficiency in bottom waters.

Organic-rich, fine-grained contourites in an epicontinental basin: The Upper Jurassic-Lower Cretaceous Vaca Muerta Formation, Argentina

Over the last few years, recognition and characterization of sedimentary processes in fine-grained successions is receiving considerable attention in part due to the increased importance of unconventional reservoirs. Recent sedimentologic analyses of these successions have revealed abundant traction transport structures that suggest bottom current activity of different origins. The present study constitutes a detailed sedimentologic analysis of the Upper Jurassic-Lower Cretaceous Vaca Muerta Formation (Neuquén Basin, Argentina), which comprises organic-rich, fine-grained subaqueous clinoform deposits. Locally, intervals showing traction structures such as parallel lamination, ripple cross-lamination and cross-bedding, and displaying high bioturbation, occur. These intervals can be differentiated into three facies associations, namely crinoidal mixed to calcareous mudstone, mixed to calcareous mudstone, and calcareous to mixed mudstone interbedded with calcareous mudstone. These facies associations were deposited by contour currents showing semi-permanent activity, low sediment concentration, and generating long-term oxygen supply to the seafloor. Locally, some successions display an increasing to decreasing bioturbation intensity pattern that may have a similar origin to the bi-gradational sequence of contourites. The present sedimentologic analysis supports the idea that contour currents are associated with high bioturbation levels due to increased oxygenation, which controls the degree of preservation of traction structures, and consequently the possibility to delineate these processes in fine-grained successions. These currents occurred in relatively shallow water, probably as part of a weakened estuarine or anti-estuarine, basin-wide circulation system intensified by the enhanced action of dense water cascading during arid and cool climate periods.

Correction to: Microtextural properties of ooids in the middle Jurassic-lower Cretaceous, central taurus carbonate platform, Antalya, Turkey

Correction to: Microtextural properties of ooids in the middle Jurassic-lower Cretaceous, central taurus carbonate platform, Antalya, Turkey

Jurassic-recent stratigraphy, structure, and hydrocarbon potential of the Mesozoic-Cenozoic rifted-passive margin of the Tarfaya-Dakhla basin of southern Morocco

We describe the structure, stratigraphy, and hydrocarbon potential of the 1000-km-long Tarfaya-Dakhla Basin (TDB) along the Atlantic rifted-passive margin of Morocco. Our dataset consists of a 4885-line km grid of depth-converted industry seismic data tied to three DSDP wells in the deepwater area and exploratory wells on the slope and shelf. Based on mapping of this seismic grid, the tectonostratigraphic events that have affected this margin include: 1) a Late Triassic-Early Jurassic rift phase that separated the Moroccan margin from its conjugate margin in eastern Canada began during the Late Triassic-Early Jurassic; 2) early passive margin sedimentation consists of Middle Jurassic-Early Cretaceous passive margin phase consisting of a massive, 14-km-thick, reefal-carbonate platform formed above the rifted margin during the Early Jurassic and was subsequently buried by the 6-km-thick, Early Cretaceous (Berriasian) Boujdour deltaic complex. During this period continued high rates of clastic sedimentation resulted in margin steepening and gravitational collapse during the Valanginian and formed a 480-km-long and 68-km-wide passive margin fold belt characterized by a zone of updip normal faults of 480 km in length and 30 km in width and a zone of downdip folds and thrusts of 117 km in length and 15 km in width. Geochemical data from DSDP 397 and 369 wells and two pseudo-wells were used to evaluate source rock potential and hydrocarbon prospectivity of the Jurassic to Recent section. Basin modeling reveals that the Jurassic source rocks known from DSDP drilling are presently overmature in the study area with hydrocarbon generation beginning in the Upper Jurassic-Lower Cretaceous. The Lower Cretaceous source rocks are immature except for localized areas, and the Upper Cretaceous is immature across the study area.

Detrital zircon provenance of the Cretaceous–Neogene East Coast Basin reveals changing tectonic conditions and drainage reorganization along the Pacific margin of Zealandia

Abstract The Upper Cretaceous–Pliocene strata of New Zealand record ~100 m.y. of Zealandia's evolution, including development of the Hikurangi convergent margin and Alpine transform plate boundary. A comprehensive, new detrital zircon U-Pb data set (8315 analyses from 61 samples) was generated along a ~700 km transect of the East Coast Basin of New Zealand. Age distributions were analyzed and interpreted in terms of published data available for Cambrian–Cretaceous igneous and metasedimentary source terranes using a Monte Carlo mixture modeling approach. Results indicate a widespread Early Cretaceous transition in sediment source from the Gondwana interior to the Median Batholith magmatic arc prior to Late Cretaceous rifting from Antarctica. Submergence of Zealandia during a Late Cretaceous–Paleogene drift phase led to major drainage reorganization and the influx of Eastern Province sediment to the East Coast Basin. A long-lived sediment conduit that transported extraregional Western Province detritus to the south-central East Coast Basin may have developed along a structural precursor to the Alpine Fault. Marked Neogene increase of Upper Jurassic–Lower Cretaceous Torlesse Composite Terrane sediment to the central East Coast Basin resulted from exhumation of the Axial Ranges, convergence along the Hikurangi subduction margin, and concurrent development of the Alpine Fault. Concurrent influx of contemporaneous Neogene zircon in the northern East Coast Basin indicated the onset of subduction-related volcanism of the Northland–Coromandel Volcanic Arc. Middle Miocene–Pliocene exhumation and dextral translation of the Nelson region along the Alpine Fault resulted in the eastward routing of Western Province sediment to the central East Coast Basin. Finally, topography developed across the plate boundary and ultimately partitioned continental drainage of Zealandia, such that sediment from the Murihiku, Caples, and Rakaia Terranes in the Otago region was routed to the southern extent of the East Coast Basin. These results illuminate the evolution of the Zealandia continental drainage divide in response to the initiation of the Pacific-Australian plate boundary and demonstrate the power of mixture modeling and large data sets for deciphering sediment routing in dynamic tectonic environments.

A shallow-water cyrtocrinid crinoid (Articulata) from the upper Albian of the Western Pyrenees, North Spain

The cyrtocrinid crinoid Proholopus holopiformis (Remeš, 1902) is described from the upper Albian succession that may be included in the Albeniz unit to the east of Iruñea-Pamplona (Navarre, Western Pyrenees, Spain). Although based on partially disarticulated material, this taxon preserve calyx, stem, attachment structure, and brachial plates from the arms. Proholopus holopiformis was previously described from the Upper Jurassic-Lower Cretaceous of the Czech Republic and Lower Cretaceous of France and Crimea, thus the occurrence from Spain represents the youngest of the species. This allows a better characterization of the family Proholopodidae that was originally described based on calyx morphology only and expands its distribution to the upper Albian. Proholopus holopiformis inhabited the fore-reef areas of coral-sponge bioconstructions. Based on coral types, crinoids are thought to have dwelled near the euphotic-oligophotic zones transition and, thus, thrive in shallow depths. Most specimens have bite marks compatible with cidaroid predation. This represents one of the youngest occurrences of cyrtocrinids inhabiting shallow marine environments before their migration to the deep sea due to the ongoing Mesozoic Marine Revolution.