Palaeogene Strata Research Articles

Palaeogene glendonites from Denmark

Pristinely preserved mineral pseudomorphs called glendonites, up to 1.6 m long, from the Palaeogene strata of Denmark allow detailed crystallographic characterisation and add to the understanding of the transformation of the precursor mineral, ikaite (CaCO3·6H2O), to calcite, which constitutes the glendonite. We describe Danish pseudomorphs after ikaite from two localities and formations: the Early Eocene Fur Formation and the Late Oligocene Brejning Formation. This detailed study highlights that key aspects such as morphology and mode of occurrence of these ancient glendonites are identical to those of their parent mineral ikaite, when it grows in marine sediments. Systematic distortion of the angles in glendonite and marine sedimentary ikaite relative to the ideal ikaite symmetry may arise due to the incorporation of organic matter into the crystal structure, and we demonstrate the similarity between modern and ancient ikaite formation zones in the marine sedimentary realm with respect to organic matter.

Biostratigraphy and provenance analysis of the Cretaceous to Palaeogene deposits in southern Tibet: Implications for the India‐Asia collision

AbstractUpper Cretaceous to Eocene marine sedimentary sequences of the Yarlung‐Tsangpo Suture Zone (YTSZ) provide critical constraints on the initial process of the India–Asia continental collision and the closure time of the Neo‐Tethyan Ocean. New sedimentological, petrographic, biochronological and detrital zircon age data of Cretaceous–Palaeogene strata from the southern margin of the YTSZ are reported in this study. Detrital zircons from the Lower Cretaceous Gyabula Formation are dominated by Archean to Cambrian U–Pb ages, indicating a likely source originating from the Indian continent. In contrast, zircon ages from the Palaeogene Jiachala Formation are predominantly younger than 200 Ma, with a major peak of ca. 76–187 Ma, which is consistent with a source from either an intra‐oceanic island arc system or the Asian continent. Sixty species of radiolarian fossils obtained from the Gyabula, Zongzhuo and Jiachala Formations provide a regional correlation with the Cretaceous Tethyan realm and Palaeogene low‐latitude biozonation schemes based on the Unitary Association method. The Palaeogene radiolarian zonation UAZ JP10 identified in the Jiachala Formation, when combined with existing absolute age models derived from the Deep Sea Drilling Project and Ocean Drilling Program, indicates an age of ca. 61.8–61.1 Ma. Integration of the biochronological and detrital zircon age data suggests that major changes in provenance occurred at the Indian continental margin, allowing an important timing constraint on the onset of collision to be placed no later than the Danian at ca, 61.8 Ma. This study highlights the significance of focusing on distinct sedimentary sequences in collisional orogens to reconstruct the timing and processes of continental collision events.

Kinetics of oil generation from brackish-lacustrine source rocks in the southern Bohai Sea, East China

Oil generation (C14+ hydrocarbons) of three Type II kerogen samples isolated from brackish-lacustrine mudstones from Palaeogene strata (Ed3, Es1, Es3) in the southern Bohai Sea was simulated by closed-system gold tube experiments. In addition, a series of complementary analyses (Rock-Eval pyrolysis, total organic carbon, vitrinite reflectance, trace element, X-ray diffraction and flash pyrolysis-gas chromatography–mass spectrometry) were also performed to identify the bulk geochemistry, palaeo-environment and chemical composition of the kerogen. The aim of this study was to achieve a better understanding of the kinetics of oil generation from lacustrine source rocks in the southern Bohai Sea. The results show that the three samples are Type II source rocks deposited in similar palaeo-environments (hot and arid climates, anoxic conditions, and brackish water in shallow to semi-deep lakes) with consequent similarity in the chemical compositions of their kerogens. The organic matter inputs are predominantly composed of lacustrine microalgae, with a relatively small contribution from land plants. The activation energies of oil generation from these samples show a range of 44–52 kcal/mol, with a frequency factor varying from 1.116 × 1014 to 1.274 × 1014 s−1. Due to the similar palaeo-environments and chemical composition, samples in this study exhibit strong consistencies in kinetic parameters. Transformation ratio (TR) evolution curves of oil generation from the three samples, calculated under a linear heating rate (3 K/Ma), exhibit a slight difference, which varies within 4 °C at a given TR. Due to the great similarities of the three kinetic models, an average kinetic model for the Type II brackish-lacustrine source rocks in the southern Bohai Sea was established. This model integrates the characteristics of the three kinetic models and is still dominated by activation energy of 52 kcal/mol. The geological temperature of the oil generation phase for the average model in the southern Bohai Sea is from 92 to 137 °C.

Deep burial dissolution of Lower Palaeozoic carbonates and the role of compacted released water from Palaeogene strata in the Zhuanghai area, Jiyang Depression, Bohai Bay Basin, NE China

The Zhuanghai area is located in the northern part of the Jiyang Depression, Bohai Bay Basin, which is a superimposed basin. In this basin, there are very thick Cenozoic sediments that unconformably overlie Lower Palaeozoic rocks, which form buried hills (topographic highs). Through core description and microscopic observations, the diagenetic characters, pore types, reservoir quality and the dissolution characteristics of the Lower Palaeozoic strata have been investigated in the study area. Organic and inorganic gas–liquid bi-phase inclusions with bright orange-yellow fluorescence are evidence of the dissolution of the compacted released water enriched in organic matter released from Palaeogene strata into the Lower Palaeozoic strata. The relatively high homogenization temperatures of fluid inclusions can help explain the temperature condition of secondary low-temperature hydrothermal minerals and the effects of dissolution of the compacted released water on the Lower Palaeozoic carbonates and hydrocarbons within the buried hills. The δ13C values of crystalline calcite in the high-angle fractures of Lower Palaeozoic rocks range from −0.08‰ to −3.5‰, well above those of primary carbonates of the Lower Palaeozoic. The very high values of δ13C of crystalline calcite suggest the effects of dissolution of the compacted released water on the Lower Palaeozoic carbonates. The paper analyses the effects of dissolution of the compacted released water and the character of the reservoir space of the Zhuanggu-10 well in the Zhuangxi Buried Hill and suggests that the Ordovician Majiagou Formation underwent significant dissolution because of the introduction of compacted released water and formed various secondary pores acting as a primary reservoir. The compacted released water that corroded the Lower Palaeozoic carbonates comes from the Palaeogene sediments in the adjacent Zhuangxi Sag. It migrated along the boundary fault of the sag to the Zhuangxi Buried Hill, modified the Lower Palaeozoic carbonates and caused the formation of deeply buried dissolution pores. The dissolution mode of the down-dip faulted block seepage as recognized in the Chengbei 305 to 307 wells is proposed to explain the pore distribution patterns of the buried hills in the research area. Copyright © 2015 John Wiley & Sons, Ltd.

Were a couple of kilometres of Palaeocene–Eocene strata ever deposited across most of the Sichuan basin? Reply

Deng et al. (2015b) propose that a couple of kilometres of Palaeocene– Eocene strata were deposited across most of the Sichuan basin and later eroded, mainly based on their low-T thermochronological data. They further propose that such a geological process would influence the datum plane of our isostatic model and the Cenozoic elevation history of the Sichuan, Tarim and Qaidam basins. Indeed, we selected the modern state of Suining as the datum plane for all our isostatic calculations (Yu et al., 2015). It is a static datum plane rather than a dynamic datum plane; this approach is conventional (Zhang et al., 2010). Therefore, how Suining evolved during the Cenozoic does not influence the isostatic model and the palaeoelevation estimation of the Qaidam basin. We stress the lack of Cenozoic deposits and the lack of visible Cenozoic uplift in the Sichuan basin (Yu et al., 2015), but we do not rule out the possibility of erosion. The Sichuan basin may have experienced a certain amount of erosion during the Cenozoic. According to the isostatic model, the erosion of crust (including basement and stratigraphy) leads to elevation loss (Fig. 1). Endorheic basins accumulate sediments and increase in elevation, while exorheic basins, under certain conditions, discharge sediments by erosion and thereby decrease elevation. However, compared with the visible deposit thickness, the magnitude of erosion is more difficult to estimate. We do not adopt the low-T thermochronological data provided by Deng et al. (2009, 2013, 2015a,b), because their data and conclusion are contradictory and questionable for the central Sichuan basin. Deng et al. (2015b) suggest that ~1000–2000 m of Palaeogene strata were deposited across the Sichuan basin, and then eroded during the late Cenozoic. However, if such thick Palaeocene–Eocene strata had been deposited, a dramatic drop between 65 and 34 Ma should be seen on the t(time)–T(Temperature) paths of AFT (apatite fission track) thermalhistory modelling (Fig. 2). Regretfully, no such drop is seen in their articles (Deng et al., 2009, 2013, 2015b), and, on the contrary, the area records uplift since the late Cretaceous (Deng et al., 2015b). Furthermore, the Sichuan basin that we refer to is the central part, to the west of the Huaying Mountain and to the east of the Longquan Mountain. Most of the AFT thermal-history modelling results presented by Deng et al. (2009, 2013, 2015b) are distributed at the margins of the Sichuan basin (e.g. the Huaying Mountain, the Longmen Mountain’s piedmont). It is common sense that the exhumation rate of the surrounding mountains or basin-mountain transition zones is much faster than that of the central basin. Therefore, low-T thermochronological results from the basin margin cannot reveal the geological history of the central Sichuan basin. Only four AFT thermal-history modelling results (SLG01, SN01, M24-1, M242) in the central Sichuan basin are presented by Deng et al. (2009, 2013, 2015b). However, the single grain age of SLG01 does not pass the chisquared test (P (v) < 5%), so it is unsuitable for AFT thermal history modelling (Ketcham et al., 2000). P (v) of sample SN01 is only 8.6%. The cooling magnitude of the drilling sample M24-1 is limited since the late Cenozoic, and the region of good fit is broad (Deng et al., 2013). The modern temperature setting of the drilling sample M24-2 on the t–T

Geologic and Geochemical Conditions of Shale Oil of Paleogene in NanPu Sag of Bohai Bay Basin

The exploration practice in NanPu Sag suggests that shale oil&amp;gas as an unconventional natural gas resource,is a kind of current alternative energy resource. According to measured data of geochemistry,mineral,logging and drilling on the Palaeogene strata in NanPu Sag,the shale in palaeogene characterised by large thickness,high abundance of organic matter, favorable types and wide range of thermal maturity, shows that it has the material basis for the formation of shale oil. In addition,the shale of palaeogene in NanPu Sag generally developed fractures,which has fine reservoir property. The shale in this area has high content of brittle minerals which are useful to later fracturing reformation. It is thought after comprehensive analysis that shale oil&amp;gas of paleogene in NanPu Sag has a bright prospect in exploration and development.

Onset of fault reactivation in the Eastern Cordillera of Colombia and proximal Llanos Basin; response to Caribbean–South American convergence in early Palaeogene time

Abstract The inversion of Mesozoic extensional structures in the Northern Andes has controlled the location of syn-orogenic successions and the dispersal of detritus since latest Maastrichtian time. Our results are supported by detailed geological mapping, integrated provenance (petrography, heavy minerals, geochronology) analysis and chronostratigraphical correlation (palynological and geochronology data) of 13 areas with Palaeogene strata across the central segment of the Eastern Cordillera. Spatial and temporal variation of sedimentation rates and provenance data indicate that mechanisms driving the location of marginal and intraplate uplifts and tectonic subsidence vary among syn-orogenic depocentres. In the late Maastrichtian–mid-Palaeocene time, crustal tilting of the Central Cordillera favoured reverse reactivation of the western border of the former extensional Cretaceous basin. The hanging wall of the reactivated fault separated two depocentres: a western depocentre (in the Magdalena Valley) and an eastern depocentre (presently along the axial zone of the Eastern Cordillera, Llanos foothills and Llanos Basin). In late Palaeocene–early Eocene time, as eastern subduction of the Caribbean Plate and intraplate magmatics advanced eastwards, reactivation of older structures migrated eastwards up to the Llanos Basin and disrupted the eastern depocentre. In early Eocene time, these three depocentres were separated by two low-amplitude uplifts that exposed dominantly Cretaceous sedimentary cover. Syn-orogenic detrital sediments supplied from the eastwards-tilted Central Cordillera reached areas of the axial domain of the Eastern Cordillera, whereas unstable metamorphic and sedimentary fragments recorded in the easternmost depocentre were supplied by basement-cored uplifts with Cretaceous and Palaeozoic sedimentary cover reported in the southern Llanos Basin. This tectonic configuration of low-amplitude uplifts separating intraplate syn-orogenic depocentres and intraplate magmatic activity in Palaeocene time was primary controlled by subduction of the Caribbean Plate. Supplementary material: Appendix 1 presents detailed descriptions of analytical methods used in this manuscript. Appendixes 2 to 4 include raw data of sandstone petrography, heavy minerals and U–Pb detrital zircon geochronology, respectively. All this material is available at http://www.geolsoc.org.uk/18597 .

The geological history of the Isle of Wight: an overview of the ‘diamond in Britain's geological crown’

The geology of the Isle of Wight has attracted both the amateur and professional geologist alike for well over two centuries. It presents a cornucopia of things geological and offers a window into the fascinating story of the geological history and landscape development of southern England, as well as an important teaching resource for all levels of study from primary education through to academic research. This paper provides a geological framework and a summary of the history of research as context for the papers in this issue can be placed. Inevitably, it can only offer a précis of the huge amount of information available, but it is hoped will also give added impetus to further investigation of the literature or, indeed, new research. The island offers a field workshop for topics such as lithostratigraphy, sequence stratigraphy, tectonics and climate change; studies that are becoming ever more international in their influence. There are 15 Sites of Special Scientific Interest designated because of their geological importance and a number of these are internationally significant. After a brief discussion on the concealed geology, this paper concentrates on an outline of the near-surface geology on the coast and inland, and introduces a different view on the structure of the Cretaceous and Palaeogene strata. The enigmatic Quaternary deposits are discussed particularly with reference to the development of the Solent River, human occupation and climate change.

Reworked and indigenous palynomorphs from the Norwich Crag Formation (Pleistocene) of eastern Suffolk: implications for provenance, palaeogeography and climate

Analysis of samples of clays from the Pleistocene Norwich Crag Formation near Southwold in eastern Suffolk, England has revealed the presence of relatively abundant reworked palynomorphs derived from Carboniferous, Jurassic, Cretaceous and Palaeogene strata. A further sample of similar age from a borehole at Sudbourne, near Ipswich, contains additional evidence for the reworking of Silurian sediments. The presence of the derived palynomorphs is consistent with input from rivers flowing eastwards into the western margin of the Crag depositional basin during the Baventian. The input in the Southwold area was via the forerunner of the Byfham River, a river which flowed from the English Midlands to the East Anglian coast prior to the onset of the Anglian glaciation. The proto-Thames is argued as the transporting medium for the Silurian palynomorphs in the Sudbourne sample.

Petroleum geology of the Carpathian Foredeep and overthrust zones in the Czech Republic

The area is situated at the contact of two regional megastructures -the Bohemian Massif and the Western Carpathians. The eastern slope of the Bohemian Massif dips under the Carpathian Foredeep and thick Flysch nappes and is covered by Variscan and Neoidic autochthonous Palaeozoic, Mesozoic and Palaeogene sediments. In the southeast, the Vienna basin's Neogene fill overlies the units of the Magura Flysch and a part of the Zdanice unit. The area can be divided into three parts. The south is characterized by a thick Jurassic sedimentary complex that overlies the crystalline basement. The basal elastics of this Jurassic complex are very prospective and in the central part of the area the oil field Uhrice II is situated in these strata. In this central part two deep depressions - the Vranovice and Nesvacilka grabens - are the most important buried geomorphological elements. Both are filled with Palaeogene strata. The north of the area is characterized by uplifted crystalline basement with thin autochthonous sediments, mostly with Miocene strata of the foredeep and with the flysh nappes. Thick Palaeogene and Upper Jurassic pelites are supposed to be the main source rocks. The cap rocks are pelitic sequences of variable thicknesses including Jurassic marls, Palaeogene and Miocene claystones and basal claystones of flysch units. Traps are delimited by faults, lithology changes and unconformities.