The Kamień Pomorski IG-1 borehole (Pomerania, NW Poland) yields a profile through the Triassic–Jurassic (T–J) transition in continental deposits. An integrated study of the sedimentology, sequence stratigraphy, palynology, biostratigraphy and geochemistry of these deposits has been carried out on the boundary interval, which represents a time of major environmental change. Two lithological units within the transitional section are distinguished: the Lower–Middle Rhaetian Wielichowo Beds of alluvial plain facies, which shows evidence of a semi-arid climate, and the Upper Rhaetian to Lower Hettangian Zagaje Formation, lying above a marked erosional sequence boundary, composed of mudstone-claystone and sandstone deposited in a fluvial-lacustrine environment. Carbon isotope values obtained from palynomaceral separates, and thus reflecting isotopic changes in atmospheric CO2, show significant fluctuations through the Rhaetian; the most conspicuous negative δ13Corg excursion is correlated with the Rhaetian ‘initial’ excursion and shows two sub-peaks, pointing to short-term carbon-cycle disturbances of lesser magnitude. Above the ‘initial’ negative excursion, there is a positive excursion followed again by more negative values, representing subordinate fluctuation within a positive excursion and is correlated with the T–J boundary. Seventy-two miospore taxa have been determined from the studied T–J transitional section. Two major palynological assemblages have been distinguished: the lower one, typically Rhaetian, named the Cingulizonates rhaeticus–Limbosporites lundblandii association, which corresponds to the Rhaetipollis–Ricciisporites (= Rhaetipollis–Limbosporites) Zone; and the upper one, typically Hettangian, named the Conbaculatisporites mesozoicus– Dictyophyllidites mortoni–Cerebropollenites thiergartii association (with the age-diagnostic pollen C. thiergartii), which corresponds to the Pinuspollenites–Trachysporites (= Trachysporites–Heliosporites) Zone. The T–J palynofloral turnover occurred in a humid period and is more conspicuous then palynofloral changes observed in Greenland, the Tethyan domain or other parts of NE Europe. The osmium isotope system is studied herein for the first time from T–J continental deposits and shows marked disturbances similar to those measured in marine deposits and attributed to volcanic fallout. Carbon and osmium isotope correlation and coeval increase in polycyclic aromatic hydrocarbon (PAH) content and darkening of miospores confirm that eruptions of the Central Atlantic Magmatic Province (CAMP) contributed to the perturbances in climate and crisis in the terrestrial biosphere. A series of periodical atmospheric loading by CO2, CH4 or alternatively by SO2, sulphate aerosols and toxic compounds is inferred to have caused a series of rapid climatic reversals, directly influencing the ecosystem and causing the Triassic floral crisis. A floral turnover period commenced at the ‘initial’ δ13C excursion, with the onset of CAMP volcanism. Obtained values of initial 187Os/186Os between 2.905 and 4.873 and very low iridium content (about 5 ppt) lend no support to a role for an extraterrestrial impact at the T–J boundary event. The position of the ‘initial’ negative carbon isotope excursion about 12 m below the T–J boundary, position of sequence boundaries (emergence surfaces) and other isotope excursions allow reliable correlation with marine profiles, including St Audrie's Bay (UK), Csövár (Hungary) and the GSSP profile at Kuhjoch (Austria).

We present the first contribution of tracing the source area of ophiolitic detritus in the Alpine molasse deposits by Raman spectroscopy. The lower Oligocene molasse deposits preserved in the Barrême basin, in the SW foreland of the western Alpine arc, are known for the sudden arrival of the first ‘exotic’ detritus coming from the internal Alpine zones. Among them, the pebbles of serpentinized peridotites have so far not been studied. We show that they only consist of antigorite serpentinite, implying that they originate from erosion of high temperature blueschists. In contrast, the upper Oligocene/lower Miocene molasse shows mixed clasts of serpentine including antigorite and lizardite without any evidence of chrysotile. This suggests that they were derived from a less metamorphosed unit such as the low temperature blueschist unit. Taking into account the sediment transport direction in the basin and the varied metamorphic characteristics of the other ocean-derived detritus, we constrain the lithologic nature of the source zones and the location of the relief zones, identified as the internal Alps, SE of the Pelvoux external crystalline massif. Available structural data and in situ thermochronological data allow the reconstruction of the Oligocene to early Miocene collisional geometry of the Palaeogene subduction wedge. This phase corresponds to two major phases of uplift evolving from a single relief zone located above the Ivrea body during early Oligocene times and persisting up to early Miocene times; then during late Oligocene/early Miocene times a second relief zone developed above the Briançonnais zone. At that time, the internal western Alps acquired its double vergency.

The tectonic history and time of closure of the Palaeo-Asian ocean of the Altaids are issues of lively current debate. To address these issues, this paper presents detailed geological, petrological and geochemical data of the Liuyuan complex (LC) in the Beishan region in NW China, located in the southernmost Altaids, in order to constrain its age, origin and tectonic setting. The LC mainly comprises massive basalts, pillow basalts, basaltic breccias, gabbros and ultramafic rocks together with cherts and tuffs. Most prominent are gabbros and large volumes of basaltic lavas. These mafic rocks have high TiO2 contents, flat rare earth element (REE) patterns and show high-field-strength elements (HFSEs) similar to those of mid-ocean ridge basalts (MORB). The mafic rocks exhibit positive εNd(t) (6.6–9.0) values, representing magmas derived from the mantle. But these basic rocks are also enriched in Th relative to REEs, and are systematically depleted in Nb–Ta–(Ti) relative to REEs. There is also a large range in initial 87Sr/86Sr (0.7037–0.7093). All these variables indicate that mantle-derived magma was contaminated by fluids and/or melts from a subducting lithospheric slab, and formed in a supra-subduction zone (SSZ) setting. A gabbro intruded in the complex was dated by LA-ICP-MS on 20 zircons that yielded a 206Pb–238U weighted average age of 286 ± 2 Ma. Considering the fact that all these basalts are imbricated against Permian tuffaceous sediments and limestone, we propose that the LC formed as an ophiolite in a fore-arc in Carboniferous–Permian time. This indicates that the Palaeo-Asian ocean still existed at 286 ± 2 Ma in early Permian time, and thus the time of closure of the Palaeo-Asian ocean was in or after the late Permian.

The composition of the soluble organic matter of the Oxfordian–Kimmeridgian Flodigarry Shale Member (Isle of Skye, Scotland) is presented for the first time. A continuous succession of silty clays and nodular limestone beds is exposed on a rocky shore to the north of Staffin Bay. This succession is proposed as a potential stratotype of the boundary between the Oxfordian and Kimmeridgian stages. This paper points out the exceptional preservation and very low thermal degradation of the organic matter. Indeed, the molecular composition is characterized by the abundance of unsaturated biomarkers (hopenes and diasterenes) as well as undamaged bioterpenoids (ferruginol and sugiol). The abundance of long-chain n-alkanes characterized by an odd-over-even predominance reveals a dominant continental contribution. This is also attested to by the relatively high amounts of plant biomarkers (e.g. ferruginol, sugiol, cadalene and retene), which suggest a palaeovegetation largely composed of pinophytes, especially Cupressaceae, Taxodiaceae and Cheirolepidiaceae, on the nearest emerged lands. The water column of the depositional environment was oxic in its upper part and rather dysoxic in its lower part. The composition of the organic matter does not significantly change along the Flodigarry Shale Member. In other words, no evolutionary events or drastic change in palaeoenvironments can be deduced from the molecular content of these sedimentary rocks, and it does not allow us to support a precise location for the Oxfordian/Kimmeridgian boundary in the succession.

A megafossil plant assemblage containing three zosterophyll plants (Gen. nov. A, aff. Huia sp. and a unnamed spike) is described from the Lower Devonian Xitun Formation (Lochkovian) of Qujing, Yunnan Province, China, providing new data on the diversity of plant types during the Lochkovian, a time poorly represented by fossil vascular plants. Gen. nov. A has a character combination of naked axes, a diagnostic branching pattern (i.e. K-type branching as well as small lateral branches scattered along the axes) and lateral stalked sporangia. Aff. Huia sp. has ovate and stalked sporangia which are arranged in loose spirals and are reflexed adaxially. Combining the plants previously reported from the Xitun Formation (i.e. Xitunia spinitheca, Zosterophyllum shengfengense and Z. minorstachyum), the Xitun flora is dominated by zosterophylls and exhibits varied vegetative and fertile morphologies. Unlike the coeval plant assemblages in many localities of Laurussia and western Gondwana, which are mainly composed of plants with isotomous branching and terminal sporangia, the Lochkovian flora of South China is dominated by zosterophylls, documenting the existence of a distinct Northwest Gondwanan phytogeographic unit in the Lochkovian and a strong effect of phytogeographical isolation.

We show that spacing statistics can be obtained for all fracture densities by the same equation. Using the simple ‘shear lag’ theory, it is demonstrated that the results adequately fit experimental measurements. Theoretically, it is shown that two parameters are sufficient to characterize all spacing distributions. It is found that no real spacing saturation exists. Rather, a very low increase in joint densities occurs for a very high incremental stress increase. Moreover the transition to this kind of saturation is gradual and not abrupt. In this way the high density distributions with very small inter-joint distances, which pose a problem for saturation models, are directly explained. Correlation with creep experiments is also established. Comparison of our method with Weibull statistics is performed.

The turtle fauna of the Middle Jurassic Xiashaximiao Formation in the Sichuan Basin and the type series of Chengyuchelys baenoides Young & Chow, 1953 are revised. By the absence of a mesoplastron and other shell characters, both the holotype and paratype of Chengyuchelys baenoides belong to the family Xinjiangchelyidae and come probably from the Upper Jurassic Shangshaximiao Formation. The Middle Jurassic turtle assemblage of the Sichuan Basin is composed of two entities: the Bashuchelyidae fam. nov. (Bashuchelys gen. nov., Chuannanchelys gen. nov.) and Protoxinjiangchelys gen. nov. on the one hand, and Sichuanchelys on the other hand, with the former as the dominant group. Bashuchelyids and xinjiangchelyids are closely related to one another, while Sichuanchelys is more primitive and has no shared apomorphic features with bashuchelyids. The whole assemblage appears to be endemic to the Sichuan Basin at genus level and distinct from the Late Jurassic turtle fauna of the same basin in its relict nature and absence of the Polycryptodira.

Charts are presented showing the correlation of graptolite biozonations for the Lower Ordovician to Lower Devonian, i.e. for the entire stratigraphical range of the planktonic graptoloid graptolites. Regions chosen are those for which the most detailed biostratigraphical studies have been undertaken. For Baltica, average graptolite zone (chron) duration appears to vary from c. 300000 years (Ludlow Epoch) to 2.4 Ma (Lochkovian Epoch).

The Poshtuk metapelitic rocks in northwestern Iran underwent two main phases of regional and contact metamorphism. Microstructures, textural features and field relations indicate that these rocks underwent a polymetamorphic history. The dominant metamorphic assemblage of the metapelites is garnet, staurolite, chloritoid, chlorite, muscovite and quartz, which grew mainly syntectonically during the later contact metamorphic event. Peak metamorphic conditions of this event took place at 580 °C and ~3–4 kbar, indicating that this event occurred under high-temperature and low-pressure conditions (HT/LP metamorphism), which reflects the high heat flow in this part of the crust. This event is mainly controlled by advective heat input through magmatic intrusions into all levels of the crust. These extensive Eocene metamorphic and magmatic activities can be associated with the early Alpine Orogeny, which resulted in this area from the convergence between the Arabian and Eurasian plates, and the Cenozoic closure of the Tethys oceanic tract(s).

The shale-dominated hemipelagic succession exposed in the southwestern part of the Prague Synform preserves the most complete Ludfordian graptolite record so far encountered from peri-Gondwanan Europe. Four graptolite biozones – the Neocucullograptus inexpectatus, Nc. kozlowskii, Pseudomonoclimacis latilobus–Slovinograptus balticus and Pristiograptus fragmentalis biozones – are recognized in the middle and late Ludfordian, between the Bohemograptus tenuis Biozone and the base of the Pridoli Series. Conodont occurrences are restricted to scattered limestone beds, but enable tentative integration of the graptolite and conodont biozonal schemes. Particular attention was paid to faunal and sedimentary changes and the carbon isotope record across the middle Ludfordian Kozlowskii extinction Event. The Kozlowskii Event caused the almost simultaneous extinction of graptolites with ventrally curved rhabdosomes. The genera Bohemograptus, Polonograptus and Neocucullograptus, along with Pseudomonoclimacis dalejensis, disappeared from the fossil record. The offshore conodont fauna recorded in the section was not strongly affected and similarly the pelagic orthocerids and nektonic Ceratiocaris passed unaffected through the extinction interval. The abundant and widespread pelagic myodocopid ostracod Entomis, however, became extinct. The late Ludfordian graptolite recovery gave origin to a novel fauna of Pridoli type from taxa that emerged or just reappeared above the Kozlowskii crisis. In Všeradice and elsewhere in the Prague Synform, the recovery, manifested by the appearance of Pseudomonoclimacis latilobus and Slovinograptus balticus, closely postdates the end of the isotope excursion but pre-dates the first appearance of the conodont index ‘Ozarkodina’ snajdri. Here the graptolite recovery was delayed relative to the recovery of the benthic fauna. A canalized intraformational limestone conglomerate corresponds with a gap in the sedimentary record above the Kozlowskii extinction and just below the graptolite recovery. The benthic faunas from the conglomerate matrix and pebbles permit correlation with the shallower part of the basin indicating a distinct fall in sea-level. The present data demonstrate the coincidence of the graptolite crisis with benthic faunal change and eustatic fall in sea-level manifested by facies change and the carbon isotope excursion. Polonograptus chlupaci sp. nov., from the Nc. kozlowskii Biozone, is described and several other graptolite taxa are redescribed.

Throughout the high Arctic, from northern Canada (Pearya) to eastern Greenland, Svalbard, Franz Josef Land, Novaya Zemlya, Taimyr and Severnaya Zemlya and, at lower Arctic latitudes, in the Urals and the Scandinavian Caledonides, there is evidence of the Grenville–Sveconorwegian Orogen. The latest orogenic phase (c. 950 Ma) is well exposed in the Arctic, but only minor Mesoproterozoic fragments of this orogen occur on land. However, detrital zircons in Neoproterozoic and Palaeozoic successions provide unambiguous Mesoproterozoic to earliest Neoproterozoic (c. 950 Ma) signatures. This evidence strongly suggests that the Grenville–Sveconorwegian Orogen continues northwards from type areas in southeastern Canada and southwestern Scandinavia, via the North Atlantic margins to the high Arctic continental shelves. The widespread distribution of late Mesoproterozoic detrital zircons far to the north of the Grenville–Sveconorwegian type areas is usually explained in terms of long-distance transport (thousands of kilometres) of either sediments by river systems from source to sink, or of slices of lithosphere (terranes) moved on major transcurrent faults. Both of these interpretations involve much greater complexity than the hypothesis favoured here, the former involving recycling of the zircons from the strata of initial deposition into those of their final residence and the latter requiring a diversity of microcontinents. Neither explains either the fragmentary evidence for the presence of Grenville–Sveconorwegian terranes in the high Arctic, or the composition of the basement of the continental shelves. The presence of the Grenville–Sveconorwegian Orogen in the Arctic, mainly within the hinterland and margins of the Caledonides and Timanides, has profound implications not only for the reconstructions of the Rodinia supercontinent in early Neoproterozoic time, but also the origin of these Neoproterozoic and Palaeozoic mountain belts.

New palaeomagnetic and petrographic data are presented from Cambrian rocks of SW Svalbard to test, for the first time, Palaeozoic reconstructions of the major terranes of Svalbard. In the course of thermal demagnetization three ChRM (characteristic remanent magnetization) components were identified, which were labelled HORNL, HORNM and HORNH, respectively, on the basis of their different unblocking temperatures. The HORNM magnetization is related to the Late Ordovician–Silurian formation of the synmetamorphic S1 foliation. The HORNM palaeopole (Φ = −18.5°, Λ = 359°, Dp/Dm = 5.8°/11.4°, Plat = 6°N) matches exactly the Silurian sectors of the Baltica–Laurentia apparent polar wander paths after the closure of Iapetus (455–415 Ma). The 450 Ma 40Ar–39Ar age determination from mica ages obtained from the broad zone of mylonites along the Billefjorden Fault Zone which separates the Central and Eastern terranes, also suggests that the two terranes were eventually amalgamated by 450 Ma. The HORNMVGP also lies very near the palaeopole derived from the Middle Proterozoic rocks of the Eastern Terrane (Ny Friesland), metamorphosed during Caledonian time, suggesting its close proximity to the study area (Central Terrane). The present study has shown that at least two of the major terranes of Svalbard, as defined by previous authors, occupied similar geographical locations by Silurian time, and the previously proposed large-scale Late Devonian left lateral displacements are not supported.

The results of apatite fission-track analyses of the Western Pontides of NW Turkey point to three discrete episodes of Cenozoic exhumation correlatable with major supraregional tectonic events. (1) Paleocene–early Eocene exhumation reflected the closure of the İzmir–Ankara ocean. (2) Late Eocene–earliest Oligocene exhumation was the result of renewed tectonic activity along the İzmir–Ankara suture. (3) Late Oligocene–early Miocene exhumation recorded the onset of northern Aegean extension. Samples collected north and south of the tectonic contact between the two terranes forming the Western Pontides (i.e. İstanbul and Sakarya terranes) record the same cooling events, suggesting that such terranes were amalgamated in pre-Cenozoic times.

The duration of polarity Chron C31r is estimated with a cyclostratigraphic approach. Two sites are investigated: ODP Site 762 (Indian Ocean) and the Contessa Highway section (Gubbio, Italy). Cyclostratigraphic analysis is performed on greyscale variations (Site 762) and magnetic susceptibility variations (Contessa section). Both sites reveal an astronomical control of the sedimentation, highlighted by the identification of all the orbital periodicities. Cyclostratigraphic signals are tuned on 405 ka eccentricity cycles extracted from the La04 astronomical solution. In both sites, cycle counting gives an estimate of the duration of polarity Chron C31r of about 2.09 ± 0.03 Ma.

Study of the lower Silurian black shale succession of the Prague Synform has enabled detailed insight into graptolite faunal dynamics and diversity trends from the mid-Aeronian diversity maximum through to the late Aeronian crisis. Graptolite diversity decreased from 33 taxa in the Lituigraptus convolutus Biozone to 17 taxa in the upper part of the Stimulograptus sedgwickii Biozone and newly erected Lituigraptus rastrum Biozone. The graptolite assemblages of the latter biozones exhibit low species richness along with high dominance. Many graptolite species that became extinct in the early part of the sedgwickii Zone were promptly replaced by new forms. In the later part of the sedgwickii Zone, however, replacement of extinct species by new forms considerably decelerated. The increased rate of graptolite extinction recorded in the convolutus–sedgwickii biozone boundary beds coincided with subtle changes in black shale lithologies and a positive shift in δ13Corg (of 2.2 ‰) compared to baseline values. Sea-level drawdown can be inferred from siltstones and/or temporary nondeposition in the middle sedgwickii Zone. This level also sees total organic carbon (TOC) fluctuations and a strong positive δ13Corg excursion with a peak shift of at least 7 ‰. The sedgwickii Event exhibits substantial reorganization of the graptolite fauna, its taxonomic impoverishment and concomitant increase in species dominance rather than a sudden collapse of the pre-extinction assemblage. Associated changes in lithology, TOC and the pronounced δ13Corg excursion suggest a relatively extended and probably multi-phase period of stressed conditions that affected the pelagic realm inhabited by graptolites in the course of the late Aeronian interval.

The lava domes in the northwestern (Cuma), northern (Punta Marmolite) and central (Accademia) parts of the Phlegrean Fields are the subject of this study. The Cuma and Punta Marmolite trachyphonolitic lava domes are among the oldest Phlegrean products cropping out. The Cuma rocks have an agpaitic groundmass, with early alkali feldspar, Fe-rich clinopyroxene, Fe-edenite and sodalite and late rosenbuschite, fluorite, baddeleyite, pyrochlore, britholite, monazite, aegirine (often Zr-rich) and exceptionally Fe–Mn-rich olivine. The bulk-rock compositions at Cuma have some of the highest concentrations of Zn, Mn, Zr, Nb, Th, U and lanthanides among the Phlegrean Fields rocks, and some of the lowest MgO, P2O5, Sr, Eu and Ba. The Punta Marmolite dome is chemically less evolved, and lacks characteristic agpaitic minerals, but features alkali feldspar, sodalite, nepheline and relatively Na-poor, Fe-rich hedenbergite, with rare Ca-rich plagioclase xenocryst cores. The Accademia dome, belonging to the recent activity, is latitic to trachytic in composition, has highly forsteritic olivine (with chromiferous spinel inclusions), calcic plagioclase and Mg-rich diopside (± phlogopite) xenocrysts in an evolved host rock (with phenocrysts and microlites of alkali feldspar, Fe-rich clinopyroxene, Fe-rich amphibole, magnetite, Fe-rich olivine and accessory baddeleyite, zirconolite and fluorite). There is clear evidence of open-system magma crystallization in the form of interaction between a crystallizing, primitive shoshonitic basalt in a reservoir already filled by rather evolved trachytic magma. The magmatic evolution towards the evolved compositions is dominated by crystallization of more and more Na-rich alkali feldspar in a Cl-, F-rich and relatively H2O-poor environment. Input of mafic magma is evident in many trachytic eruptions of the Phlegrean Fields and even in the products of the Campanian Ignimbrite, but eruptions having mineral assemblages rich in xenocryst phases as well as eruptions virtually free of mafic magma input are also frequently observed throughout the history. This suggests a variable pattern of open- and closed-system crystallization, which may or may not be linked to explosive activity, and that can be caused by intermittent supply of basaltic magma from depth.

Numerous calc-alkaline granitoid intrusions in the eastern Kunlun Orogen provide a valuable opportunity to constrain the evolution of the orogen. The age and genesis of these intrusions, however, remain poorly understood. The granitoid intrusions near the Balong region, eastern Kunlun Orogen, consist of granodiorite, diorite and syenogranite. The granodiorite contains crystallized segregations, abundant mafic microgranular enclaves (MMEs) and small quartz diorite stocks. In situ zircon U–Pb dating reveals that the granodiorites and quartz diorites were emplaced between 263 and 241 Ma, whereas the syenogranite was produced at c. 231 Ma. The granodiorite and quartz diorite have a calc-alkaline affinity and are metaluminous and Na-rich, with slightly enriched Sr–Nd isotope compositions. The granodiorite is characterized by fractionated REE patterns, whereas the quartz diorite displays a relatively flat REE pattern. The MMEs are consistent with the granodiorite in terms of incompatible elements and Sr–Nd isotope composition. Compared to the granodiorite and diorite, the syenogranite has higher SiO2, K, Rb, Th and Sr contents and a lower Rb/Sr ratio. The results presented here, when combined with regional geological data, indicate that the granodiorite and quartz diorite were derived from dehydration melting of mafic lower crustal rocks during the N-directed subduction of the Anyemaqen ocean lithosphere in Late Permian–Middle Triassic times, whereas the syenogranite was produced at a higher crustal level in a syn-collisional setting compared to the granodiorite.

Knowing when the Tibetan Plateau reached its present elevation is important for understanding the uplift history of Tibet. Recently, Rowley & Currie (2006) suggested that central Tibet exceeded 4000 m from 35 Ma to the Pliocene using the oxygen-isotope composition of calcareous minerals in Lunpola basin sediments. However, they adopted a poor age assignment for the Dingqing Formation in the Lunpola basin based on previous microfossil studies. In this study, we present SIMS U–Pb zircon dates from a bentonite layer intercalated within the middle to lower Dingqing Formation. Twenty-six measurements yield a highly reliable U–Pb age of 23.5 ± 0.2 Ma (2σ, MSWD = 1.1), suggesting that the deposition age of the Dingqing Formation is late Oligocene to early Miocene, much older than the Miocene–Pliocene age used by Rowley & Currie (2006). This age robustly constrains the age of Cenozoic sedimentary strata in central Tibet, and hence provides an important basis for estimating the palaeoelevation in the high Tibet during the geological past.

The Zhuhai Formation of the Huizhou Oilfield has been interpreted as being deposited in a tide-dominated estuarine setting. This paper uses stratigraphic principles, cores and logging data to analyse the facies changes of tidal sedimentation in response to the base level cycle. We conclude that the mud flat progradational allocycle is the result of a long-term base level fall, while the fining-upwards autocycle is in response to a short-term base level fall. Region-wide mud layers of supratidal zones and scour surfaces of subtidal zones are stratigraphic surfaces of tidal sedimentation. By integrating high-resolution stratigraphic correlations with seismic attributes extracted from the stratal slicing of 3-D data volumes, we use an attribute map of RMS (root mean square) amplitude to image the distribution and evolution of tidal deposits in the study area. Intertidal zones and the upper parts of the tidal cycle are favourable areas for prospecting and oil reserves and thus provide a basis for petroleum exploration and development.