Late Cretaceous Early Paleocene Research Articles

Late Cretaceous–Early Paleocene Geodiversity of Fatehgarh Formation of Petroliferous Barmer Basin, Western Rajasthan, India: A Potential Geopark Site

Late Cretaceous–Early Paleocene Geodiversity of Fatehgarh Formation of Petroliferous Barmer Basin, Western Rajasthan, India: A Potential Geopark Site

Sedimentary and Diagenetic Controls across the Cretaceous—Paleogene Transition: New Paleoenvironmental Insights of the External Ionian Zone from the Pelagic Carbonates of the Gardiki Section (Epirus, Western Greece)

Field investigation, biostratigraphic, paleoecological, and sedimentary microfacies analyses, as well as diagenetic processes characterization, were carried out in the Epirus region (Western Ionian Basin) to define the depositional environments and further decipher the diagenetic history of the Late Cretaceous–Early Paleocene carbonate succession in western continental Greece. Planktonic foraminiferal biostratigraphy of the studied carbonates revealed that the investigated part of the Gardiki section covers the Cretaceous–Paleogene (K-Pg) transition, partly reflecting the Senonian limestone and calciturbidites formations of the Ionian zone stratigraphy. Litho-and bio-facies analyses allowed for the recognition of three distinct depositional facies: (a) the latest Maastrichtian pelagic biomicrite mudstone with in situ planktonic foraminifera, radiolarians, and filaments, (b) a pelagic biomicrite packstone with abundant planktonic foraminifera at the K-Pg boundary, and (c) an early Paleocene pelagic biomicrite wackestone with veins, micritized radiolarians, and mixed planktonic fauna in terms of in situ and reworked (aberrant or broken) planktonic foraminifera. The documented sedimentary facies characterize a relatively low to medium energy deep environment, representing the transition from the deep basin to the deep shelf and the toe of the slope crossing the K-Pg boundary. Micropaleontological and paleoecological analyses of the samples demonstrate that primary productivity collapse is a key proximate cause of this extinction event. Additional petrographic analyses showed that the petrophysical behavior and reservoir characteristics of the study deposits are controlled by the depositional environment (marine, meteoric, and burial diagenetic) and further influenced by diagenetic processes such as micritization, compaction, cementation, dissolution, and fracturing.

Biostratigraphy of the Late Cretaceous-Early Paleocene Succession in Selected Wells, Jambur Oil field, Kirkuk, Northern Iraq

The Late Cretaceous-Early Paleocene Shiranish and Aliji formations have been studied in three selected wells in Jambur Oil Field (Ja-50, Ja-53, and Ja-67) in Kirkuk, Northeastern Iraq. This study included lithostratigraphy and biostratigraphy. The Late Campanian-Maastrichtian Shiranish Formation consist mainly of thin marly and chalky limestone beds overlain by thin marl beds, with some beds of marly limestone representing an outer shelf basinal environment, the unconformable contact with the above Middle Paleocene-Early Eocene Aliji Formation contain layers of limestone with marly limestone and chalky limestone which represents an outer shelf basinal environment. Five Biozones in the Shiranish Formation were determined which are: 1.Globotruncanita calcarata Range Zone (part). 2.Globotruncanella havanensis Partial Range Zone. 3.Globotruncana aegyptiaca Interval Zone. 4.Gansserina gansseri Interval Zone (Part). 5.Abathomphalus mayaroensis Range Zone. While in Aliji Formation there were two biozones determined which are: 1.Guembelitria Cretacea Partial-Range Zone. 2.Parvularugoglobigerina eugubina Total-Range Zone.

A new oospecies of Shixingoolithus (Shixingoolithus qianshanensis oosp. nov.) from the Qianshan Basin, Anhui Province, East China

Here we describe two newly discovered dinosaur eggs from the Upper Cretaceous Chishan Formation in the Qianshan Basin, Anhui Province, East China. These dinosaur eggs can be assigned to a new oospecies of Stalicoolithidae, Shixingoolithus qianshanensis, based on the following combined features: the larger size of eggs, the uniform eggshell microstructure in the radial section, the smaller height and the larger density of radial microstructures at the inner surface of the eggshell. Radial sections of S. qianshanensis show closely arranged columnar eggshell units forming relatively uniform and dense microstructure; some secondary eggshell units and numerous sub-circular radial microstructures appear separately in the middle and inner parts of the tangential sections, respectively. The discovery of S. qianshanensis provides new fossil types of Stalicoolithidae and represents the first dinosaur relative record in the Qianshan Basin, which offer accurate paleontological evidence of Late Cretaceous–Early Paleocene stratigraphic classification in the Qianshan Basin, Anhui Province.

Palynoflora from an Upper Cretaceous freshwater paleolake in central India: paleoecological implications

An Upper Cretaceous paleolake near Jamsavli in the Mandla Lobe of central India has provided a unique opportunity to understand paleoecological conditions during Deccan volcanism. The sedimentary deposits of this paleolake are dominated by freshwater aquatic and semiaquatic flora, such as algae (Pediastrum, Lecaniella), dinocysts (Pierceites deccanensis), diatoms (Aulacoseira), aquatic ferns of Salviniaceae (Azolla), Marsileaceae (Crybelosporites), and pollen grains of Sparganiaceae/Typhaceae (Sparganiaceaepollenites). Such paleolakes, representing a few hundred years of lake history with only aquatic and semiaquatic biota, have rarely been documented from the Deccan volcanic province.An overview of aquatic and semiaquatic flora from the infratrappean and intertrappean beds associated with the Deccan volcanic province across the Cretaceous-Paleogene shows that the floral communities include algal remains of Botryococcaceae, Chlorophyceae, Chlorellaceae, Cyanophyceae, Hydrodictyaceae, Oedogoniaceae, Ulotrichaceae, Zygnemataceae, dinocysts, and diatoms. Bryophytes are scarce, whereas aquatic ferns of Salviniaceae (Azolla) and Marsileaceae (Marsilea and Regnellidium) are the dominating groups in the intertrappean deposits. Aquatic and semiaquatic angiosperms show less taxonomic diversity and are represented by only five families, namely Nymphaeaceae, Typhaceae, Liliaceae, Acanthaceae, and Pontederiaceae. The ubiquitous presence of macrophytes and microfloral fossil remains of Zygnemataceae (Ovoidites), Salviniaceae (Azolla), Marsileaceae (Crybelosporites and Gabonisporis), and palms, along with paleosol, indicate frost-free, warm, humid tropical to subtropical climates with intermittent dry and wet semi-arid conditions across the Late Cretaceous–early Paleocene.

Mesozoic-Cenozoic exhumation history and its implications for the uranium mineralization in the southern Junggar Basin, North China

The phases of tectonic activity and exhumation of the southern margin of the Junggar Basin during the Cretaceous through Cenozoic shows significant relationships with the timing of uranium mineralization episodes. To clarify the succession of metallogenetic stages that were controlled by different phases of uplift and exhumation, apatite fission track (AFT) thermochronology was performed on the Jurassic through Cenozoic sediments from the Manas section in the southern Junggar Basin. The mean ages of the AFT suites range from 63 Ma to 133 Ma, and are younger than the host sediment for the Mesozoic samples and older than the host for the Cenozoic samples. The mean track lengths (MTLs) are between 10 and 11 μm. These results indicate that most of the apatite grain assemblages in these samples experienced complicated annealing histories. AFT ages were combined with thermal history modeling to unravel the timing of the multi-phase regional uplift and exhumation history and to reveal the tectonic constraints on the uranium mineralization. The populations of AFT single-grain ages display four peaks, which are interpreted as regional uplift and cooling episodes: mid-Early Jurassic (189–180 Ma), late Jurassic–early Cretaceous (157–116 Ma), late Cretaceous–early Paleocene (88–59 Ma) and late Eocene–early Oligocene (37–28 Ma). Thermal history modeling indicates two episodes of rapid cooling of the basin sediment deposits during the late Cretaceous–Paleocene (80–50 Ma) and the Pliocene (5 Ma)–Present. A synthesis of the temporal relationship between AFT age peaks, of the modeled time–temperature paths, of a compilation of age data and regional geologic events from the Tianshan mountain belt, suggests a close relationship between tectonic evolution and uranium mineralization. Uranium metallogenesis episodes occurred in conjunction with tectonic uplift and exhumation episodes along the southern margin of the Junggar Basin during the late Cretaceous–early Paleogene and during the latest Miocene-Present. The earlier episode was the primary mineralization stage, and the later episode was a partial transformation stage superimposed on the earlier one.

A Rapid Marine Regression in the Southwestern Tarim Basin in the Latest Cretaceous: Comparison of Two Different Evaporitic Sequences in the Yarkand Basin, Xinjiang Province, China

AbstractTwo different evaporitic sequences occurred in the latest Cretaceous–Early Paleocene in Yarkand Basin, southwestern Tarim Basin, Xinjiang Province, China: one is characterized by poor gypsum and some small, lenticular‐shaped halite layers in the Tuyiluoke Formation of the latest Cretaceous, the other is characterized by very thick gypsum and halite layers in the Aertashen Formation of the early Paleocene. In the early developmental stage of the Tuyiluoke Formation, the Yarkand ancient saline lake was a long, strip‐shaped depression, NW–SE oriented, along the West Kunlun piedmont, with its eastern boundary to the line along bores Ys1‐T1‐Ks101, the concentrated center located in the area of borehole S1. In the later developmental stage, the depositional scope was shifted inch by inch to the NW of this saline lake, forming a triangular depositional area, with apices at boreholes Wx1, Ak2 and S1, the concentrated center of the saline lake gradually migrating from borehole S1 region to the northwestern area of the lake, developing four small, evaporated‐concentrated sub‐depressions, depositing lenticular‐shaped halite. In the early Paleocene, the ancient saline lake was stretched from the West Kunlun piedmont in the west, to the Markit slope in the east, from the South Tianshan piedmont in the north, to the Hotan area in the south, accompanied by giant thicknesses of halite and large‐scale gypsum layers, mainly interbedded with limestone in the Aertashen Formation. The evaporites in the latest Cretaceous‐early Paleocene were controlled by the marine transgression‐regression geological background in the Yarkand Basin. Generally, integrated evaporitic depositional sequences, such as clasolite‐gypsum‐halite‐potash, usually occur in the presence of persistent seawater through evaporation, but this is not the case in the Tuyiluoke Formation. In contrast, very thick gypsum layers are common in the early Paleocene. Typically, adequate mineral sources for evaporites are found within seawater, such as in large basins undergoing long‐term marine transgression‐regression cycles, where adequate seawater remains, even though the basin was going through a marine regression stage. In the latest Cretaceous, thin gypsum layers indicate a lack of mineral sources. In contrast, the early Paleocene has far larger evaporites, both in width and thickness. This suggests a short‐term marine regression stage must have occurred during the spatiotemporal evolution of the evaporites in the latest Cretaceous–Early Paleocene in the basin, meaning that a rapid marine regressive episode has been identified at the end of the Cretaceous.

Calcareous dinoflagellate cyst distribution across the K/Pg boundary at DSDP site 577, Shatsky Rise, western North Pacific Ocean

An analysis of calcareous dinoflagellate cysts has been carried out on sixteen samples from across the K/Pg boundary interval from Deep Sea Drilling Project Site 577 situated on Shatsky Rise in the western North Pacific. This is the first time that a detailed study of this microfossil group has been undertaken from deep sea sediments of Late Cretaceous–early Paleocene age in the North Pacific realm. Eight species of calcareous dinoflagellate cysts were found to comprise low diversity assemblages of which half are representative of extant taxa. The most pronounced bioevent is that of Cervisiella operculata reaching its highest proportions at the K/Pg boundary transition underscoring the utility and cosmopolitan distribution of the species with its acme as a marker for the earliest Danian. We also identify an indirect sea surface paleotemperature signal as represented by variance in wall thickness in two distinct morphotypes of Thoracosphaera heimii (morphotypes A and B). The cyst concentrations and relative abundances of these taxa are interpreted to reflect the late Maastrichtian warming event and subsequent late Maastrichtian cooling phase prior to the interval of gradual warming in the early Danian marked by the opportunistic capitalization of Cervisiella operculata during a time of ocean recovery following the terminal Cretaceous.

Sequence stratigraphy of the Andaman Basin, northern Indian Ocean

Andaman Basin, a poly history basin in the northeastern Indian Ocean, preserves the sedimentary record from Late Cretaceous to Recent with several stratigraphic breaks. Studies from outcropping sedimentary succession, integrated with subsurface data from drilled wells in the offshore, have enables to work out a sequence stratigraphic framework of the sedimentary succession in the basin.The succession comprises of three first-order sequences viz., Late Cretaceous – Eocene, Oligocene and Neogene. These have been related to basin forming tectonic events related to accretionary prism formation and subduction in Paleogene, Oligocene uplift and renewed subduction in Neogene, respectively. Excellent bio-stratigraphic control and field evidence have enabled identification of unconformities of various magnitudes, which in turn has enabled mapping second-order sequence. The 3 second-order sequences within first-order Late Cretaceous–Eocene sequence are: Late Cretaceous-Early Paleocene, Late Paleocene-Middle Eocene and Late Eocene sequence. The Oligocene first-order sequence related to the major uplift and emergence of the main Andaman Island chain, contributed >2000m of flysch sediments. Three second-order sequences within the first-order Neogene sequence are Early Miocene - early Middle Miocene, Middle Miocene - Middle Pliocene and Late Pliocene - Pleistocene sequences separated by unconformities of various magnitude. Each sequence is discussed with respect to its extent, nature of sequence boundaries, sedimentary fill and sequence stratigraphic surfaces to understand the sequence stratigraphic architecture of the basin.

Multi-stage India-Asia collision: Paleomagnetic constraints from Hazara-Kashmir syntaxis in the western Himalaya

The India-Asia collision is the most spectacular, recent, and still active tectonic event of the Earth’s history, leading to the uplift of the Himalayan-Tibetan orogen, which has been explained through several hypothetical models. Still, controversy remains, such as how and when it occurred. Here we report a paleomagnetic study of Cretaceous-Tertiary marine sediments from the Tethyan Himalaya (TH) in the Hazara area, north Pakistan, which aims to constrain timing for the onset of the India-Asia collision and to confirm the validity of already proposed models, particularly in western Himalaya’s perspective. Our results suggest that the TH was located at a paleolatitude of 8.5°S ± 3.8° and 13.1°N ± 3.8° during the interval of ca. 84−79 Ma and 59−56 Ma, respectively. A comparison between paleopoles obtained from the current study and coeval ones of the India Plate indicates that the TH rifted from Greater India before the Late Cretaceous, generating the Tethys Himalaya Basin (THB). Our findings support a model for a multi-stage collision involving at least two major subduction systems. A collision of the TH with the Trans-Tethyan subduction system (TTSS) began first in Late Cretaceous-Early Paleocene times (ca. 65 Ma), followed by a later collision with Asia at 55−52 Ma. The onset of the collision between the TH (plus TTSS) and Asia could not have occurred earlier than 59−56 Ma in the western Himalaya. Subsequently, the India craton collided with the TH, resulting in the diachronous closure of the THB between ca. 50 and ca. 40 Ma from west to east. These findings are consistent with geological and geochemical evidence and have a broad implication for plate reconfigurations, global climate, and biodiversity of collisional processes.

Exhumation history and preservation of the Changjiang uranium ore field, South China, revealed by (U-Th)/He and fission track thermochronology

The Changjiang uranium ore field (CUOF) is one of the most important and representative granite-type uranium ore fields in South China. Previous work on the CUOF has primarily concerned uranium ore genesis, focusing on aspects such as timing of metallogenesis and uranium mineralization mechanisms. However, the exhumation history and preservation of the ore deposits in the CUOF are poorly constrained. This study reports multi-system low-temperature thermochronology data that constrain the thermal history of the CUOF in the south-central Zhuguangshan complex, providing important insights into its tectonic evolution and the degree of ore preservation. Zircon (U-Th)/He (ZHe) ages of the mineralized and non-mineralized samples from fault-bounded Triassic-Jurassic granitic basement blocks range from 123 to 24 Ma and negatively correlate to effective uranium (eU) content (335–6611 ppm). Apatite fission track (AFT) ages of granite samples vary from 63 to 58 Ma with relatively short to moderate track lengths, and apatite (U-Th-Sm)/He (AHe) ages range from 39 to 24 Ma. Inverse thermal history models from individual and grouped samples produce similar time–temperature reconstructions exhibiting a Cretaceous-Cenozoic three-stage thermal history involving an initial Late Cretaceous-Early Paleocene exhumation phase (~80–60 Ma) and subsequent Middle Paleocene to Middle-Late Eocene burial phase (~60–40 Ma), interpreted to be primarily controlled by temporal, spatial and velocity variabilities in Pacific Plate subduction dynamics. A final Late Eocene-Quaternary stage (~40–0 Ma) of exhumation was likely caused by the uplift associated with India-Asia collision and the eastward extrusion of the Tibetan Plateau. The ~ 1.5–3.6 km of post-mineralization regional exhumation estimated from thermal history reconstructions, combined with existing uranium mineralization data (timing, temperature and pressure conditions) consistent with an ore-forming depth of ~ 3.2–5.6 km, suggest that the bulk of CUOF uranium ore bodies may still be preserved at depth.

Calcareous nannofossil biostratigraphy of the Late Cretaceous‒early Paleocene interval in the Zagros basin (southeastern Tethys), Iran

Calcareous nannofossil biostratigraphy reveals a continuous depositional record through the Upper Cretaceous‒Paleocene succession in the Zagros Basin; southwest Iran (southeastern part of the Neo-Tethys), especially through the Cretaceous‒Paleogene and the Danian‒Selandian boundaries. The upper part of the Gurpi Formation and the lower part of the Pabdeh Formation were investigated. Calcareous nannofossil assemblages from these formations are characterized by abundant, diverse and moderate- to well-preserved forms with Tethyan affinities. This study concentrates on two sections (the Gurpi and Kabir-Kuh sections) in the west and southwest of Iran in the Zagros Basin, which span biozones CC25c/UC20bTP to NP6/NTp10B in the Kabir-Kuh and CC25b/UC20aTP to NP5/NTp9 in the Gurpi section. Late Maastrichtian nannofossil abundance and diversity in the studied intervals is high with a sharp decrease slightly above the K/Pg boundary. The K/Pg boundary interval is marked by the FO of Biantholithus sparsus, an acme of the dinoflagellate cyst Thoracosphaera operculata, a notable decrease in Cretaceous calcareous nannofossil abundance and diversity, and the appearance of new Paleocene taxa. An increased abundance of Thoracosphaera is recorded similar to that in the El Kef (Global Stratotype Section and Point, GSSP, for the K/Pg boundary), Ellés (auxiliary section), Egypt, Atlantic Ocean and sections elsewhere in the world. Reworked Cretaceous calcareous nannofossils are recorded from the base of the Danian along with the new Paleocene species. The Danian‒Selandian boundary is marked by the appearance of Lithoptychius ulii, Lithoptychius pileatus and Lithoptychius janii at the base of NTp8C; this level is also marked by the second radiation of Fasciculithus. Azam Mahanipour [a_mahanipour@uk.ac.ir], Department of Geology, Faculty of Science, Shahid Bahonar University of Kerman, Kerman, Iran; Mohammad Parandavar [parandavar.m@gmail.com], Paleontological Research Department, Exploration Directorate of Oil and Gas, NIOC, Tehran; Mohamed Youssef [myousefgeology@gmail.com], Department of Geology, Faculty of Science, South Valley University, 83523 Qena, Egypt.

Upper Cretaceous–lower Paleocene subsurface sequence, Farafra Oasis, Western Desert, Egypt: stratigraphical and paleoenvironmental inferences

This work presents details litho-, bio-, and sequence stratigraphy and paleoenvironmental studies on the Upper Cretaceous–lower Paleocene subsurface rocks of Sahl Baraka at Farafra Oasis, Western Desert, Egypt. Lithostratigraphically, two rock units were recognized: the Wadi Hennis (at the base) and the Khoman (at the top) formations. Ten planktonic foraminiferal zones were identified from the Khoman Formation covering the Campanian–Danian chronostratigraphic interval. Using the R-mode hierarchical cluster analyses, four benthonic foraminiferal biofacies (A, B, C, and D) were recognized. The data indicates that the sediments of the Khoman Formation were deposited in marine environments ranging from deep marine (outer neritic–upper bathyal setting) for the lower and middle parts to shallow marine one (middle–outer neritic setting) for the upper part. The Sahl Baraka area was located in a sedimentary basin subjected to three tectonic events during the Late Cretaceous–early Paleocene time which were related to the Syrian Arc Orogeny. These tectonic events interrupted the eustatic sea-level curve. The integrated data led to define three depositional sequences (sequence-1 to sequence-3) separated by three sequence boundaries (SB1–SB3) throughout the Late Cretaceous–early Paleocene time.

Regional subsurface mapping and 3D flexural modeling of the obliquely converging Putumayo foreland basin, southern Colombia

The Putumayo foreland basin (PFB) is an underexplored hydrocarbon-bearing basin located in southernmost Colombia. The PFB forms a 250 km long segment of the 7000 km long corridor of Late Cretaceous-Cenozoic foreland basins produced by eastward thrusting of the Andean mountain chain over Precambrian rocks of the South American craton. We have used approximately 4000 km of 2D seismic data tied to 28 exploratory wells to describe the basin-wide structure and stratigraphy. Based on seismic interpretation and comparison with published works from the southward continuation of the PFB into Peru and Ecuador, three main across strike, structural zones include (1) the 20 km wide, western structural zone closest to the Andean mountain front characterized by inversion of older, Jurassic half-grabens during the Late Miocene, (2) the 45 km wide, central structural zone characterized by moderately inverted Jurassic half-grabens, and (3) the 120 km wide, eastern structural zone (ESZ) characterized by the 40 km wide, north–south-trending Caquetá arch. The five mainly clastic tectonosequences of the PFB include (1) Lower Cretaceous pre-foreland basin deposits, (2) upper Cretaceous-Paleocene foreland basin deposits, (3) Eocene foreland basin deposits related to the early uplift of the eastern Cordillera, (4) Oligocene-Miocene underfilled, foreland basin deposits, and (5) Plio-Pleistocene overfilled, foreland basin deposits. We used 3D flexural modeling to identify the elastic thickness ([Formula: see text]) of the lithosphere below the PFB, and to model the location of the sedimentary-related and tectonically related forebulges of Cretaceous to Oligocene age. Flexural analysis finds two pulses of rapid, foreland-related subsidence first during the Late Cretaceous-early Paleocene and later during the Oligocene-Miocene. Despite the present-day oblique thrusting of the mountain front, flexure of the PFB basement has produced a tectonic forebulge now located in ESZ and controls a basement high that forms the eastern updip limit for most hydrocarbons found in the PFB.

BIOSTRATIGRAPHY OF THE LATE CRETACEOUS/EARLY PALEOCENE SUCCESSIONS AT K.H 5\6 AND K.H 5\8 CORE INTERVAL, WESTERN DESERT OF IRAQ

The core interval at the K.H5\6 and K.H5\8 wells in the west of Rutba province reveals a significant succession across the Late Cretaceous-Early Paleocene transition. The sampled interval encompasses a series of carbonates belong to Digma Formation of Latest Cretaceous age, which underlies the Akashat Formation of Danian age. Fifty-five species belong to thirty-five genera were recognized. Based on the distribution of these species, eight biozones were distinguished, three biozones are recorded from the K.H 5\6 studied section and two biozones are documented from the K.H 5\8 studied section which refers to Late Maastrichtian age of Digma Formation. Five biozones are recorded from Akashat Formation in the K.H 5\6 studied section and only one biozone is documented from the K.H 5\8 studied section which refers to Danian age. The depositional environment of the studied successions proposed it accumulated in the outer ramp environments.

Southward-Directed Subduction of the Farallon–Aluk Spreading Ridge and Its Impact on Subduction Mechanics and Andean Arc Magmatism: Insights From Geochemical and Seismic Tomographic Data

Since the initial proposal of the past existence of a southward-directed mid-ocean ridge-subduction interaction in the Andes during Late Cretaceous-Paleogene times, several studies have been devoted to uncover the tectonomagmatic evidence of this process. The collision of a spreading ridge against a subduction margin provoke important tectonomagmatic changes; including between them variations in arc-related magmatic activity and in the plate-margin stress regime. However, the cryptic nature of the geological record often hampers assessing the influence and along-strike evolution of this process. In this study, we integrate new isotopic data with previous field and geochemical data on Andean arc-related magmatism, together with seismic tomography to track the main tectonic changes that affected the Andes between 35° and 42oS from Latest Cretaceous to early Miocene times. In particular, we carry out a new tomotectonic analysis combining the regional bedrock record of the Late Cretaceous-early Miocene arc with upper-lower mantle seismic tomography. This analysis allowed us to unravel the main geodynamic changes that affected the Andean active-margin when the Farallon-Aluk spreading ridge was subducting. Besides, new isotopic analyses reveal the variable nature of the mantle source that fed the Late Cretaceous-early Miocene arc. Hence, the integration of geological, geochemical and geophysical data, together with new isotopic data studying the geochemical composition of the main Andean arc-related magmatic units in three main periods: 1) Latest Cretaceous-early Paleocene; 2) Early Paleocene-late Eocene; 3) Late Eocene-early Miocene, allow us to understand with an unprecedented detail the geochemical and spatio-temporal evolution of the passage of this spreading ridge along the Andean margin

Cretaceous magmatic evolution in the Deylaman igneous complex, Alborz zone, Iran: change from extensional to compressional regime

The Deylaman igneous complex, as a part of the Late Cretaceous rock unit that lies behind the Paleogene Alborz magmatic arc, in the northern Alborz zone, is composed of basaltic sheet lavas alternating with the pelagic calcareous sediments, basaltic pillow lavas, felsic lavas and gabbroic-monzodioritic intrusions. The pelagic calcareous deposits contain microfossils representing the Santonian–Maastrichtian ages. Furthermore, petrographic textures such as the hyalomicrolitic texture and swallow-tail plagioclase crystals in the pillow lavas, and also segregation vesicles in the basaltic sheet lavas, imply high external (hydrostatic) pressures as the magma was extruded in a deep-water environment. The rock samples show both compositional bimodality and characteristic trends in the variation diagrams. Also, some geochemical characteristics imply that the basaltic lavas originated from the partial melting of an undepleted deep mantle source containing spinel lherzolite: the enrichment patterns of LREE/HREE ratios of the samples [(La/Yb)n = 3.93–4.16 for basaltic lavas and 10.92 for felsic lavas] lying between those characteristic of OIBs [(La/Yb)n = 12.92] and EMORBs [(La/Yb)n = 1.91]; similarities between the patterns of multi-element spider-diagrams; LILE bulges in the basaltic samples compared with those of OIBs. Moreover, the samples show influence from two geotectonic environments: supra-subduction zone (SSZ) settings and plume-type within-plate magmas. Therefore, because of the deep submarine environment inferred for the effusive volcanic eruptions in Santonian–Maastrichtian time, it seems that the Deylaman igneous complex evolved through two stages: first, a tensional regime in a supra-subduction zone (farther from the Mesozoic magmatic arc) and formation of an embryonic rift-related oceanic basin in the Late Jurassic–Early Cretaceous; secondly, a compressive regime in the Late Cretaceous–Early Paleocene and inland migration of the magmatic arc. Consequently, the Cretaceous magmatism can be interpreted as a prelude to the Eocene magmatic flare-up in the magmatic arcs of Iran.

Palynoflora from intertrappean localities in southeastern part of Deccan volcanic province: taxonomic composition, age and paleogeographic implications

Understanding the flora preserved in the Late Cretaceous–Early Paleocene Deccan volcanic associated sediments is significant as it gives insight into the floral composition during Deccan volcanic activity. This time interval is also associated with extinction and evolution of many angiosperm families on the Indian subcontinent. The record of palynomorph bearing intertrappean beds of Shankar Lodhi in Chandrapur district and Shimbala in Yavatmal district of Maharashtra from southeastern part of Deccan volcanic province provides information on biodiversity, age and depositional environment of the Deccan province. These intertrappean beds are characterized by presence of Maastrichtian age marker taxa such as Azolla cretacea, Jiangsupollis and Echitricolpites. Aquatic palynoassemblage such as, Azolla cretacea, Crybelosporites intertrappea, Gabonisporis vigourouxii and Sparganiaceaepollenites are dominant in Shankar Lodhi intertrappean beds. Presence of taxa Crybelosporites, Incrotonipollis and Periporopollenites in the intertrappean beds of the study area and their global geological history suggest their Gondwanan origin.

Neoproterozoic crystalline exotic clasts in the Polish Outer Carpathian flysch: remnants of the Proto-Carpathian continent?

Crystalline exotic boulders within the sedimentary sequences of the Outer Carpathians likely represent Proto-Carpathian basement, which was exposed and eroded during the Mesozoic and Cenozoic evolution of the Western Carpathian basin. The majority of the boulders were derived from the Silesian Ridge, which separated the Magura Basin and the Silesian Domains, and which became a source region during Late Cretaceous–Early Paleocene tectonism. Felsic crystalline clasts within the Silesian Nappe yield U–Pb zircon magmatic protolith ages of 603.7 ± 3.8 Ma and 617.5 ± 5.2 Ma while felsic crystalline clasts within the Subsilesian Nappe yield an age of 565.9 ± 3.1 Ma and thus represent different magmatic cycles. The U–Pb zircon data also imply that the Silesian Ridge was a fragment of the eastern part of the Brunovistulia microcontinent. The presence of inherited zircon cores, dated at 1.3 and 1.7 Ga, suggests a Baltican source for the clasts, as opposed to Gondwana. We infer that Late Neoproterozoic felsic magmatism within the Proto-Carpathian continent represents a long-living magmatic arc, which formed during prolonged Timmanian/Baikalian rather than Pan-African/Cadomian orogenesis. Mafic exotic blocks, found within the Magura Nappe, yield U–Pb zircon ages of 613.3 ± 2.6 Ma and 614.6 ± 2.5 Ma and likely represent a fragment of an obducted ophiolitic sequence. The protolith of these mafic boulders could represent Paleoasian Ocean floor located to the east of Cadomia, obducted during later orogenic processes and incorporated into the accretionary prism. All analysed exotic clasts show no evidence for younger (Variscan) reworking, which is characteristic of both western Brunovistulia and the Central Western Carpathians and the Cadomian elements of Western Europe. The Silesian and Subsilesian basins thus had a likely source area in the eastern part of Brunovistulia, while the source of the Magura Basin was the Fore-Magura Ridge, whose basement potentially represents an accretionary prism on the margin of the East European Craton.

Burial and exhumation history controls on shale compaction and thermal maturity along the Norwegian North Sea basin margin areas

Abstract The North Sea area has been subjected to significant erosion and subsequent deposition of sediments in the basin margin and deeper basin areas, respectively, during the late Neogene. A large amount of Cretaceous-early Quaternary sediments have been removed below the angular unconformity along the west and southwest coast of Norway and deposited in the huge North Sea Fan at the mouth of the Norwegian Channel. At the same time, a considerable thickness of early Quaternary-Paleocene sediments was also eroded towards the east in the central North Sea and subsequently deposited in the deeper basin areas to the west. This study seeks to estimate exhumation from compaction and thermal maturity based techniques by using sonic velocities of shales/carbonates and vitrinite reflectance data in a large number of boreholes in the central, eastern and northern North Sea. The results indicate no or minor exhumation in the Central Graben and flanking high areas, whereas more than ∼1 km sediments are eroded in the basin margin areas towards the Norwegian coast. More than ∼500 m sediments are eroded in the Egersund Basin and Stord Basin areas. A similarity of exhumation estimates from the Early Cretaceous-Early Miocene shales and Late Cretaceous-Early Paleocene carbonates indicates maximum burial sometime after the Early Miocene in most of the central and northern North Sea areas. However, the maximum burial throughout the North Sea Basin may be diachronous. Seismostratigraphic analysis indicates maximum burial sometime during the Oligocene in the Sorgenfrei-Tornquist Zone area in the eastern North Sea. Maximum burial in the Norwegian-Danish Basin varies from Miocene-Pliocene in eastern parts to early Pleistocene in western parts, whereas sediments are currently at their maximum burial in the Central Graben and southern Viking Graben areas. Restoration of surface elevations to their original position before the onset of erosion indicated large subaerially exposed areas in the Norwegian-Danish Basin and along the southwest coast of Norway. This is also supported by predominantly coastal and/or deltaic environments in the Norwegian-Danish Basin area during the late Neogene. These subaerially exposed areas may be linked to the regional tilting and erosion of the basin margin areas to the east and progressive basinward migration of deposition centres to the west since the Oligocene. The exhumation had significant effects on the petroleum system in the basin margin areas by cooling down the source rock. However, the deeper burial of sediments may also have changed the rheological properties of sediments from more ductile to brittle due to compaction and diagenetic processes which makes them more failure prone during exhumation leading to hydrocarbon leakage or seal failure in case of CO2 injection.