Luca Caracciolo

Petrostratigraphic evolution of the Thrace Basin (Bulgaria, Greece, Turkey) within the context of Eocene-Oligocene post-collisional evolution of the Vardar-İzmir-Ankara suture zone

Eocene-Oligocene paleogeographic/paleotectonic reconstructions of the Rhodopian – northern Aegean – western Black Sea region largely ignore the Thrace Basin, a large sedimentary basin up to 9 km thick that has been long interpreted as a forearc basin developed in a context of northward subduction. Recent structural, stratigraphic, petrologic, and sedimentologic data challenge this notion and may instead be interpreted within a context of upper-plate extension during the complex transition between the collisional tectonic regime related to the closure of Vardar-İzmir-Ankara oceanic realm and the extensional regime characterizing the Oligocene-Neogene evolution of the Aegean and peri-Aegean regions. The detritus filling the Thrace Basin was derived from two main sediment source areas: (i) the mostly metamorphic terrains of the Rhodopes to the west and (ii) the Vardar-İzmir-Ankara and Biga (intra-Pontide?) subduction-accretion prisms to the southwest. During most of the Eocene-Oligocene, the entire basin was characterized by a complex physiography, as shown by commercial seismic lines in the subsurface and abrupt lateral facies change at the surface. Such physiography was controlled by a series of basement highs trending from WNW-ESE (in the eastern and northern portions of the basin) to WSW-ENE (in the western and southern portions of the basin) which influenced sediment dispersal and the areal distribution of paleoenvironments.

The Rhodope Zone as a primary sediment source of the southern Thrace basin (NE Greece and NW Turkey): evidence from detrital heavy minerals and implications for central-eastern Mediterranean palaeogeography

Detrital heavy mineral analysis coupled with a regional geological review provide key elements to re-evaluate the distribution of the Rhodope metamorphic zone (SE Europe) in the region and its role in determining the evolution of the Thrace basin. We focus on the Eocene–Oligocene sedimentary successions exposed in the southern Thrace basin margin to determine the dispersal pathways of eroded crustal elements, of both oceanic and continental origins, as well as their different contributions through time. Lithological aspects and tectonic data coupled with geochemistry and geochronology of metamorphic terranes exposed in the area point to a common origin of tectonic units exposed in NW Turkey (Biga Peninsula) with those of NE Greece and SE Bulgaria (Rhodope region). The entire region displays (1) common extensional signatures, consisting of comparable granitoid intrusion ages, and a NE-SW sense of shear (2) matching zircon age populations between the metapelitic and metamafic rocks of the Circum-Rhodope Belt (NE Greece) and those of the Çamlica–Kemer complex and Çetmi mélange exposed in NW Turkey. Detrital heavy mineral abundances from Eocene–Oligocene sandstones of the southern Thrace basin demonstrate the influence of two main sediment sources mostly of ultramafic/ophiolitic and low- to medium-grade metamorphic lithologies, plus a third, volcanic source limited to the late Eocene–Oligocene. Detrital Cr-spinel chemistry is used to understand the origin of the ultramafic material and to discriminate the numerous ultramafic sources exposed in the region. Compositional and stratigraphic data indicate a major influence of the metapelitic source in the eastern part (Gallipoli Peninsula) during the initial stages of sedimentation with increasing contributions from metamafic sources through time. On the other hand, the western and more external part of the southern Thrace margin (Gökçeada, Samothraki and Limnos) displays compositional signatures according to a mixed provenance from the metapelitic and metamafic sources of the Circum-Rhodope Belt (Çamlıca–Kemer complex and Çetmi mélange). Tectonic restoration and compositional signatures provide constraints on the Palaeogene palaeogeography of this sector of the central-eastern Mediterranean region.

Paleotectonics of a complex Miocene half graben formed above a detachment fault: The Diligencia basin, Orocopia Mountains, Southern California

The Diligencia basin in the Orocopia Mountains of southeastern California has been one of the primary areas used to test the hypothesis of more than 300 km of dextral slip along the combined San Andreas/San Gabriel fault system. The Orocopia Mountains have also been the focus of research on deposition, deformation, metamorphism, uplift and exposure of the Orocopia Schist, which resulted from fl at-slab subduction during the latest Cretaceous/Paleogene Laramide orogeny. The uppermost Oligocene/Lower Miocene Diligencia Formation consists of more than 1500 m of nonmarine strata, including basalt fl ows and intrusions dated at 24-21 Ma. The base of the Diligencia Formation sits nonconformably on Proterozoic augen gneiss and related units along the southern basin boundary, where low-gradient alluvial fans extended into playa-lacustrine environments to the northeast. The northern basal conglomerate of the Diligencia Formation, which was derived from granitic rocks in the Hayfield Mountains to the north, sits unconformably on the Eocene Maniobra Formation. The northern basal conglomerate is overlain by more than 300 m of mostly red sandstone, conglomerate, mudrock and tuff. The basal conglomerate thins and fines westward; paleocurrent measurements suggest deposition on alluvial fans derived from the northeast, an interpretation consistent with a NW-SE-trending normal fault (present orientation) as the controlling structure of the half graben formed during early Diligencia deposition. This fault is hereby named the Diligencia fault, and is interpreted as a SW-dipping normal fault, antithetic to the Orocopia Mountains detachment and related faults. Deposition of the upper Diligencia Formation was infl uenced by a NE-dipping normal fault, synthetic with, and closer to, the exposed detachment faults. The Diligencia Formation is nonconformable on Mesozoic granitoids in the northwest part of the basin. Palinspastic restoration of the Orocopia Mountain area includes the following phases, each of which corresponds with microplate-capture events along the southern California continental margin: (1) Reversal of 240 km of dextral slip on the San Andreas fault (including the Punchbowl and other fault strands) in order to align the San Francisquito-Fenner-Orocopia Mountains detachment-fault system at 6 Ma. (2) Reversal of N-S shortening and 90° of clockwise rotation of the Diligencia basin and Orocopia Mountains, and 40 km of dextral slip on the San Gabriel fault between 12 and 6 Ma. (3) Reversal of 40° of clockwise rotation of the San Gabriel block (including Soledad basin and Sierra Pelona) and 30 km of dextral slip on the Canton fault between 18 and 12 Ma. These palinspastic restorations result in a coherent set of SW-NE-trending normal faults, basins (including Diligenica basin) and antiformal structures consistent with NW-SE-directed crustal extension from 24 to 18 Ma, likely resulting from the unstable configuration of the Mendocino triple junction.

Comment on Maravelis et al. “Accretionary prism–forearc interactions as reflected in the sedimentary fill of southern Thrace Basin (Lemnos Island, NE Greece)”

Furthermore, it was a surprise to recognise that Maravelis et al. (2015) did not even mention the Reply of Caracciolo et al. (2013) to their discussion (Maravelis and Zelilidis 2013a, b, cited in Maravelis et al. 2015) where key problems about the provenance of the Thrace Basin sediments were debated. How should this issue be evaluated objectively, when Maravelis et al. (2015) use the evidences provided by Caracciolo et al. (2013) to support part of the provenance aspects included in their 2015 paper without referring to the original sources? Here we like to point out that Caracciolo et al. (2013) highlighted that Maravelis and Zelilidis (2010) have never recognised the occurrence of (1) glaucophane schists, nor of (2) picotite, a term used in d’Atri et al. (2012) for detrital Cr-spinel. Moreover, Maravelis and Zelilidis (2010) mentioned only a minor influx of volcanic material, but volcanic detritus is widely documented by other authors (Caracciolo et al. 2011, 2012; d’Atri et al. 2012; Cavazza et al. 2014). These data are mingled in the Maravelis et al. (2015) “Provenance” section, where the authors, for instance, falsely cite Caracciolo et al. (2011) as evidence for the scarcity of volcanic material. Conversely, the latter authors have demonstrated the dominance of volcanic lithic fragments, as shown in an Lm–Lv–Ls ternary diagram included in the respective paper (Fig. 6c in Caracciolo et al. 2011). The incorrect use of all these informations and the insufficient credit given to the results from other authors lead to a manipulation of the conclusions provided by Caracciolo et al. (2011, 2013), d’Atri et al. (2012) and Cavazza et al. (2014). Another point of discussion is related to both the analytical techniques and the “provenance” diagrams used by Maravelis et al. (2015). In particular, we refer to the use of hand-held XRF to determine the chemical data used for their interpretation. It is well known that measurement accuracy of hand-held XRF has limitations and needs a This contribution is intended to shed light on the content of the paper by Maravelis et al. (2015) about the evolution of the island of Limnos, a small portion of the Cenozoic Thrace Basin (Turkey, Greece and Bulgaria). Although we appreciate their approach to use sediment provenance for paleotectonic reconstructions, we have concerns how this subject has been dealt with and how it is presented to the scientific community. Most of our criticism is about the attempt of Maravelis et al. to provide a review of the evolution of the Thrace Basin using (1) an inadequate dataset, (2) an inadequate area (Limnos is <5 % of the Thrace Basin) and (3) the interpretation provided by different authors in previous papers without properly citing the source of the information. In their introduction section, Maravelis et al. (2015) summarise the results from previous provenance studies done in the whole Thrace Basin (extending through Greece, Bulgaria and Turkey). Interestingly, they do not mention the work by Meinhold and BouDagher-Fadel (2010) and Caracciolo et al. (2012) for the Eocene–Oligocene successions exposed on the island of Samothraki (NE Greece) and in Southern Bulgaria, respectively.

Fluvial-aeolian sedimentary facies, Sossusvlei, Namib Desert

ABSTRACT Aeolian sedimentary processes and corresponding facies shape the Earth’s surface and control the evolution of dune fields. The Namib Sand Sea with its Sossusvlei playa-lake is a perfect example to investigate the spatial distribution of fluvially influenced aeolian deposits. Remote sensing in combination with ground observations allowed for mapping of the facies distribution pattern of associated fluvial and aeolian sediments. Laboratory spectral signature measurements were used to further improve the separation between six groups of facies: modern aeolian sand, deflation surface, mud pool/mud drapes, heavy mineral lag, reworked fluvial–aeolian sediments, and fossil dune remnant. The best results were achieved through a supervised classification algorithm trained by field observations, a combination of Principal Component Analysis, band ratios, texture and geomorphologic indices. Consequently, a map outlining the facies distribution pattern of the Sossusvlei area at a scale of 1:10,000 was created. We propose this as a possible workflow to efficiently map and monitor desert environments and to investigate the interplay of aeolian and fluvial sediments.

A New Provenance Tool for the Exploration of Unconventional Plays - The Provenance and Mineralogy of Silt

Provenance analysis has traditionally focused on sandstones, which are much easier to analyse than conglomerates - which must be analysed in the field with limited tools - and mudrocks - which cannot be dealt with easily with classical optical methods. However, it is important to recognise that the silt fraction transported in suspension actually represents the majority of the sediment in large river systems and the predominant grain-size in major deltas and submarine fans, as well as in most of ancient sedimentary basins and reservoirs. Quantitative provenance analysis of silt represents a step forward in provenance studies as it provides the access to an unexplored world where detrital minerals can be easily identified and their history reconstructed. The technique can be applied to both siltstone and shale making it attractive for the hydrocarbon industry, particularly in the area of research of Unconventional Plays. This contribution is therefore intended to prove the validity and efficacy of the method and its possible application to both QPA studies and to hydrocarbon exploration. The latter is located in the onshore Mandawa basin in southern Tanzania. where hydrocarbon exploration is particularly important for the presence of huge deep-water gas fields.