The Fossil Record of Ray-Finned Fishes (Actinopterygii) in Greece

The nowadays hyper-diverse clade of Actinopterygii (ray-finned bony fishes) is characterized by a long evolutionary history and an extremely rich global fossil record. This work builds upon 170 years of research on the fossil record of this clade in Greece. The taxonomy and spatiotemporal distribution of the ray-finned fish record of Greece are critically revisited and placed in an updated systematic and stratigraphic framework, while some new fossil data and interpretations are also provided. Greece hosts diverse ray-finned fish assemblages, which range in age from Lower Jurassic to Quaternary. Most known assemblages are of Miocene–Pliocene age and of marine affinities. A minimum of 32 families, followed by at least 34 genera and 22 species, have been recognized in Greece. From originally two named genera and seven species, only two fossil species, established on Greek material, are accepted as valid. Additional taxonomic diversity is anticipated, pending detailed investigations. From a taxonomic perspective, previous knowledge lies on preliminary or authoritative assessments of fossils, with many decades-old treatments needing revision. Little is known about Mesozoic–early Cenozoic occurrences or freshwater assemblages. Given the proven potential of the Greek fossil record, this chapter stresses the need for additional exploration and the establishment of permanent, curated collections of fossil fishes in Greek institutions. Directions for future research are discussed.

Aspects of the Tectono-magmatic Evolution of Late Mesozoic Silicic Magmatic Systems in Hong Kong

<p>Hong Kong represents a microcosm of the magmatic and tectonic processes that are related to formation of the Southeast China Magmatic Belt (SCMB, ~1,300 km long by 400 km wide). The SCMB is dominated by extensive Mesozoic (Yanshanian Orogeny) igneous rocks, which form part of an extensive, long-lived circum-Pacific igneous province. In Hong Kong, large silicic ignimbrites, produced from several calderas identified through geological mapping, together with their sub-volcanic plutons record a ~26-Myr period of magmatic activities from ~164 to 138 Ma. This work studies these volcanic-plutonic assemblages with the associated Lantau and High Island caldera complexes, with an emphasis on the ~143-138 Ma period from the latter complex. This study uses multiple techniques, including field studies, zircon geochronology and trace element analyses, and zircon and apatite low-temperature thermochronology, to gain new insights into the Mesozoic tectono-magmatic history in this region. Field studies demonstrate that the High Island caldera complex (with its main collapse at 140.9±0.4 Ma in association with the High Island Tuff) is structurally more complex than previously suggested and represents a long-lived, large (320 km²) feature. The volcanic strata exposed in the eastern part of the caldera are inferred to have been tilted during syneruptive, asymmetric collapse of the caldera floor, whereas those in other parts have been affected by block faulting but not overall tilting. Two ignimbrites (e.g. Long Harbour: 141.4±1.0 Ma) exposed within the caldera outline are now interpreted to have accumulated in local volcano-tectonic basins, confined by faults that were later exploited by dyke intrusions. Field observations offer important constraints on the ages of volcanic and plutonic units, which have been tested by zircon U-Pb dating in this study. The field evidence also negates a previous interpretation that there was an overall tilting of the High Island caldera complex. U-Pb dating and trace element analyses using secondary-ion mass spectrometry (SIMS) techniques have been carried out on zircons separated from 21 samples, chosen from both volcanic and plutonic samples within the Lantau and High Island Caldera complexes. The SIMS age datasets reveal two groups: (1) seven samples with unimodal age spectra; and (2) fourteen samples yielding multiple age components. Five samples in group 1 yield mean ages indistinguishable from their previously published ID-TIMS ages, demonstrating that the SIMS techniques have generated results fully in agreement with the ID-TIMS methods, although with overall less precision. Of the two other samples, one is slightly younger than the published ID-TIMS age, and the other has no previous age determination. Thirteen samples in group 2 are interpreted to have crystallisation/eruption ages that are younger (although often within 2.s.d. uncertainties) than their corresponding ID-TIMS values. The remaining sample from this group has no previous age determination. The overall age patterns from both groups suggest that, instead of separate phases of activity at ~143 and 141-140 Ma as previously inferred, magmatic and volcanic activities were continuous (within age analytical uncertainties) over a ~5 Myr period. Direct linkages between several plutonic and volcanic units in this period of activity (e.g. High Island Tuff and the Kowloon Granite) are no longer supported by the age data, and magmatic activity represented by exposed plutons continued until 137.8±0.8 Ma, as with the Mount Butler Granite. Under CL imagery, a wide variety of zircon textures is evident, indicative of complex processes that operated in the magmatic systems. Zircon trace element data coupled with textural characteristics enable identification of some common petrogenetic processes. Overall, the intra-grain (cores-rims, sector-zoned zircons) and intra-sample variations in trace element abundance and elemental ratios are more significant than the differences between individual samples. Zircon chemistries in samples from both the volcanic and plutonic records indicate that there are two groups of volcanic-plutonic products through the history of the High Island Caldera magmatic system. Two evolutionary models are proposed here to explain these two groups. In the first model, the magmatic system comprises a single domain that fluctuated in temperature through varying inputs of hotter melts (and was randomly tapped). In the second model the intrusive and extrusive products represent interplay of two magmatic domains in the crust, with contrasting characteristics. Zircon and apatite fission track analyses have been carried out on several of the rocks dated by U-Pb methods (either SIMS or TIMS), together with a selection of other Mesozoic igneous rocks and post-magmatic Cretaceous and Eocene sediments to cover the geographic area of Hong Kong. The fission-track dataset and associated thermal modelling show that the igneous rocks and Cretaceous sediments (but not the Eocene sediments) together experienced post-emplacement or post-depositional heating to >250 ºC, subsequently cooling through 120-60 ºC after ~80 Ma. The heating reflects the combined effects of an enhanced geothermal gradient and burial. The enhanced geothermal gradient is interpreted to represent continuing Yanshanian magmatic activity at depth, without any documented surface eruption products, until ~100-80 Ma. The data also indicate a long-term, slow cooling (~1 ºC/Myr) since the early Cenozoic, linked to ~2-3 km of erosion-driven exhumation. The thermo-tectonic history of Hong Kong reflects the mid-Cretaceous transition of southeast China from an active to a passive margin bordered by marginal basins that formed in the early Cenozoic. The inferred cessation of magmatism at depth below Hong Kong at ~100-80 Ma is broadly coincident with the cessation of plutonic activity in many other circum-Pacific magmatic provinces related to reorganisation of Pacific Plate motion.</p>

Aspects of the Tectono-magmatic Evolution of Late Mesozoic Silicic Magmatic Systems in Hong Kong

<p>Hong Kong represents a microcosm of the magmatic and tectonic processes that are related to formation of the Southeast China Magmatic Belt (SCMB, ~1,300 km long by 400 km wide). The SCMB is dominated by extensive Mesozoic (Yanshanian Orogeny) igneous rocks, which form part of an extensive, long-lived circum-Pacific igneous province. In Hong Kong, large silicic ignimbrites, produced from several calderas identified through geological mapping, together with their sub-volcanic plutons record a ~26-Myr period of magmatic activities from ~164 to 138 Ma. This work studies these volcanic-plutonic assemblages with the associated Lantau and High Island caldera complexes, with an emphasis on the ~143-138 Ma period from the latter complex. This study uses multiple techniques, including field studies, zircon geochronology and trace element analyses, and zircon and apatite low-temperature thermochronology, to gain new insights into the Mesozoic tectono-magmatic history in this region. Field studies demonstrate that the High Island caldera complex (with its main collapse at 140.9±0.4 Ma in association with the High Island Tuff) is structurally more complex than previously suggested and represents a long-lived, large (320 km²) feature. The volcanic strata exposed in the eastern part of the caldera are inferred to have been tilted during syneruptive, asymmetric collapse of the caldera floor, whereas those in other parts have been affected by block faulting but not overall tilting. Two ignimbrites (e.g. Long Harbour: 141.4±1.0 Ma) exposed within the caldera outline are now interpreted to have accumulated in local volcano-tectonic basins, confined by faults that were later exploited by dyke intrusions. Field observations offer important constraints on the ages of volcanic and plutonic units, which have been tested by zircon U-Pb dating in this study. The field evidence also negates a previous interpretation that there was an overall tilting of the High Island caldera complex. U-Pb dating and trace element analyses using secondary-ion mass spectrometry (SIMS) techniques have been carried out on zircons separated from 21 samples, chosen from both volcanic and plutonic samples within the Lantau and High Island Caldera complexes. The SIMS age datasets reveal two groups: (1) seven samples with unimodal age spectra; and (2) fourteen samples yielding multiple age components. Five samples in group 1 yield mean ages indistinguishable from their previously published ID-TIMS ages, demonstrating that the SIMS techniques have generated results fully in agreement with the ID-TIMS methods, although with overall less precision. Of the two other samples, one is slightly younger than the published ID-TIMS age, and the other has no previous age determination. Thirteen samples in group 2 are interpreted to have crystallisation/eruption ages that are younger (although often within 2.s.d. uncertainties) than their corresponding ID-TIMS values. The remaining sample from this group has no previous age determination. The overall age patterns from both groups suggest that, instead of separate phases of activity at ~143 and 141-140 Ma as previously inferred, magmatic and volcanic activities were continuous (within age analytical uncertainties) over a ~5 Myr period. Direct linkages between several plutonic and volcanic units in this period of activity (e.g. High Island Tuff and the Kowloon Granite) are no longer supported by the age data, and magmatic activity represented by exposed plutons continued until 137.8±0.8 Ma, as with the Mount Butler Granite. Under CL imagery, a wide variety of zircon textures is evident, indicative of complex processes that operated in the magmatic systems. Zircon trace element data coupled with textural characteristics enable identification of some common petrogenetic processes. Overall, the intra-grain (cores-rims, sector-zoned zircons) and intra-sample variations in trace element abundance and elemental ratios are more significant than the differences between individual samples. Zircon chemistries in samples from both the volcanic and plutonic records indicate that there are two groups of volcanic-plutonic products through the history of the High Island Caldera magmatic system. Two evolutionary models are proposed here to explain these two groups. In the first model, the magmatic system comprises a single domain that fluctuated in temperature through varying inputs of hotter melts (and was randomly tapped). In the second model the intrusive and extrusive products represent interplay of two magmatic domains in the crust, with contrasting characteristics. Zircon and apatite fission track analyses have been carried out on several of the rocks dated by U-Pb methods (either SIMS or TIMS), together with a selection of other Mesozoic igneous rocks and post-magmatic Cretaceous and Eocene sediments to cover the geographic area of Hong Kong. The fission-track dataset and associated thermal modelling show that the igneous rocks and Cretaceous sediments (but not the Eocene sediments) together experienced post-emplacement or post-depositional heating to >250 ºC, subsequently cooling through 120-60 ºC after ~80 Ma. The heating reflects the combined effects of an enhanced geothermal gradient and burial. The enhanced geothermal gradient is interpreted to represent continuing Yanshanian magmatic activity at depth, without any documented surface eruption products, until ~100-80 Ma. The data also indicate a long-term, slow cooling (~1 ºC/Myr) since the early Cenozoic, linked to ~2-3 km of erosion-driven exhumation. The thermo-tectonic history of Hong Kong reflects the mid-Cretaceous transition of southeast China from an active to a passive margin bordered by marginal basins that formed in the early Cenozoic. The inferred cessation of magmatism at depth below Hong Kong at ~100-80 Ma is broadly coincident with the cessation of plutonic activity in many other circum-Pacific magmatic provinces related to reorganisation of Pacific Plate motion.</p>

Geology of the Tinui district

<p>The Tinui District is assumed to be typical of the more deformed part of the New Zealand Mobile Belt. It contains an unusually complete stratigraphic record, rocks representing most stages from Upper Jurassic to Recent being present. Although the rocks are strongly deformed, the complex diapiric structures that occur in the northeast of the mobile belt are absent. The stratigraphy is described in terms of formations which are then used to infer the paleogeography for eight periods of time. An attempt is made to treat the structure according to its development with time. The main conclusion is that there was a change in the strike of the fold axes and in the sense of movement of the faults. Strong folds, striking approximately northeast, are Paleocene in age and weak folds, striking approximately north, are post-Miocene. There are two fault trends, one NNE and the other ENE. The ENE striking faults were dominant in the Early Cenozoic and the NNE striking faults were dominant in the Late Cenozoic. The sense of movement on the NNE faults changed from sinistral to dextral. The change in the direction of the axes and in the sense of movement on the faults can be expressed as a change in the direction of maximum horizontal shortening, which is inferred to have changed with time. It is also found that the rates of tilting, and probably faulting, have not been constant with time, but occurred as bursts (disturbances) in the Paleocene, Early Miocene Late Pliocene, and Late Quaternary. The Mesozoic part of the geological history of the Tinui District is scrappy and far less complete than the Cenozoic part. In order to place the Tinui District in a broader setting, the central part of the New Zealand landmass in the Cenozoic, called the New Zealand Mobile Belt, is discussed in some detail. The mobile belt consists of fault blocks which form a geanticline along the New Zealand landmass and a geosynclinal trough between the east coast and the Hikurangi Trench. It is shown that a clear distinction has to be made between tilting and uplift. A main feature of the New Zealand Mobile Belt is the dextral faulting, on major NNE striking faults, in the Late Cenozoic. A major reversal in the direction of maximum horizontal shortening was found in the Tinui District to have taken place at the beginning of the Miocene or in the Oligocene. The reversal indicates that the dextral faulting of the New Zealand Mobile Belt may have started at that time, and that earlier strike-slip movement had been sinistral. This conclusion contradicts existing reconstructions of the New Zealand landmass with time, and a more complex reconstruction is required to satisfy the tectonics of the Tinui District.</p>

Geology of the Tinui district

<p>The Tinui District is assumed to be typical of the more deformed part of the New Zealand Mobile Belt. It contains an unusually complete stratigraphic record, rocks representing most stages from Upper Jurassic to Recent being present. Although the rocks are strongly deformed, the complex diapiric structures that occur in the northeast of the mobile belt are absent. The stratigraphy is described in terms of formations which are then used to infer the paleogeography for eight periods of time. An attempt is made to treat the structure according to its development with time. The main conclusion is that there was a change in the strike of the fold axes and in the sense of movement of the faults. Strong folds, striking approximately northeast, are Paleocene in age and weak folds, striking approximately north, are post-Miocene. There are two fault trends, one NNE and the other ENE. The ENE striking faults were dominant in the Early Cenozoic and the NNE striking faults were dominant in the Late Cenozoic. The sense of movement on the NNE faults changed from sinistral to dextral. The change in the direction of the axes and in the sense of movement on the faults can be expressed as a change in the direction of maximum horizontal shortening, which is inferred to have changed with time. It is also found that the rates of tilting, and probably faulting, have not been constant with time, but occurred as bursts (disturbances) in the Paleocene, Early Miocene Late Pliocene, and Late Quaternary. The Mesozoic part of the geological history of the Tinui District is scrappy and far less complete than the Cenozoic part. In order to place the Tinui District in a broader setting, the central part of the New Zealand landmass in the Cenozoic, called the New Zealand Mobile Belt, is discussed in some detail. The mobile belt consists of fault blocks which form a geanticline along the New Zealand landmass and a geosynclinal trough between the east coast and the Hikurangi Trench. It is shown that a clear distinction has to be made between tilting and uplift. A main feature of the New Zealand Mobile Belt is the dextral faulting, on major NNE striking faults, in the Late Cenozoic. A major reversal in the direction of maximum horizontal shortening was found in the Tinui District to have taken place at the beginning of the Miocene or in the Oligocene. The reversal indicates that the dextral faulting of the New Zealand Mobile Belt may have started at that time, and that earlier strike-slip movement had been sinistral. This conclusion contradicts existing reconstructions of the New Zealand landmass with time, and a more complex reconstruction is required to satisfy the tectonics of the Tinui District.</p>

Evidence for variable precipitation and discharge from Upper Cretaceous–Paleogene fluvial deposits of the Raton Basin, Colorado–New Mexico, U.S.A.

ABSTRACT The Raton Basin of Colorado–New Mexico, USA, is the southeasternmost basin of the Laramide intraforeland province of North America. It hosts a thick succession (4.5 km or 15,000 ft) of Upper Cretaceous to Paleogene marine and continental strata that were deposited in response to the final regression of the Western Interior Seaway and the onset of Laramide intraforeland deformation. The Upper Cretaceous–Paleogene Raton and Poison Canyon formations were previously described as meandering river and braided river deposits that represented distal and proximal members of rivers that drained the basin-bounding Sangre de Cristo–Culebra uplift. We present new observations of fluvial-channel architecture that show that both formations contain the deposits of sinuous fluvial channels. However, fluvial channels of the Raton Formation formed in ever-wet environments and were affected by steady discharge, whereas channels of the overlying Poison Canyon Formation formed in drier environments and were affected by variable discharge. The apparent transition in fluvial discharge characteristics was coeval with the progradation of fluvial fans across the Raton Basin during the Paleocene, emanating from the ancestral Sangre de Cristo–Culebra uplift. The construction of fluvial fans, coupled with the sedimentary features observed within, highlights the dual control of Laramide deformation and early Cenozoic climatic patterns on the sedimentary evolution of the Raton Basin.