Andrea Mindszenty

Lithospheric bulges recorded by regional unconformities. The case of mesozoic-tertiary apulia

Abstract Cyclic shallow-water carbonate sequences in the Cretaceous of Southern Italy are punctuated by regional unconformities associated with bauxites and palaeokarst features. Direct and indirect evidence strongly suggests that, despite their apparent plate interior position, tectonics rather than eustasy was responsible for subaerial exposure, long enough to form bauxites. In-plane stress-related lithospheric arching caused by orogenic deformation along the distant active margins of Apulia is invoked to explain the vertical stacking of a series of regional unconformities (one of them marked by bauxites) on land and under the sea. The case history of Apulian bauxites associated with a Turonian arching allows a first estimate of the duration of a stress-related ‘distant’ perturbation of a subsiding passive continental margin.

Birth and early evolution of a Jurassic escarpment: Monte Kumeta Western Sicily

SummaryThe accurate reconstruction of the facies architecture in the Jurassic succession of Monte Kumeta, coupled with a detailed biostratigraphy, allow to define dynamics and genetic factors controlling the conversion of a Bahamian-type carbonate platform to a pelagic escarpment.A change from tidalites to oolites i.e. from the restricted, interior lagoon to a more open-marine sandy depositional environment, records the establishment of a basin south of the Monte Kumeta sector in late Hettangian-Sinemurian times.The oolitic limestones are overlain by earliest Carixian bioclastic grainstones and packstones with micritized grains and by wackestones with radiolarians and sponge spicules, organized in thin sand prisms. The decrease of carbonate productivity indicated by these sediments records the dissection of the platform and the subsequent isolation of a submarine topographic high in the Monte Kumeta sector.Though based only on indirect evidence, it is suggested that a tectonically controlled scarp must have existed between the Monte Kumeta “high” and the basin. Progressive northward retreat of this scarp resulted in the conversion of a shallow platform sector into a gradually steepening slope, along which the distribution of sediments was controlled by repeated tectonic and gravity-induced modifications of the topography of the substrate. Vertical and lateral changes and geometrical relationships of the recognized lithofacies suggest that they were deposited on a stepped surface brought about mainly by, repeatedly reactivated basin ward dipping normal faults.This scenario is clearly reflected by the relationship of platform strata and the overlying encrinites of Carixian/Domerian age. The encrinite bodies show again a prismatic geometry, becoming thicker towards the south and filling the first generation of neptunian dykes.The top of the encrinites is marked by a peculiar jagged dissolution surface with dm-scale pinnacles capped by a thick ferromanganese crust. The formation of this peculiar surface could have been controlled by complex changes in water chemistry probably related to the Early Toarcian anoxic event. The crust itself is dissected by faults of decimetres to metres of throw, sometimes organized into small-scale positive flower structures. In the hollows/depressions of this highly articulated substrate pelagic sediments of Bajocian to Oxfordian age were deposited. They display a clearly onlapping relationship to the encrinites and to the carbonate platform beds. Their thickness rarely exceeds 4 to 5 meters and they are present also as neptunian dykes filling a dense network of fissures.During Late Callovian and Oxfordian times synsedimentary tectonics has intensified resulting in an increase of the inclination of the slope. This led to more and more abundant, gravitationally controlled deformations (slumping and sliding) of semi-lithified and unlithified sediments along the Monte Kumeta escarpment.

Fe–Mn-encrusted “Kamenitza” and associated features in the Jurassic of Monte Kumeta (Sicily): subaerial and/or submarine dissolution?

Abstract An unusually jagged dissolution surface, capped by a thick Fe–Mn crust is well exposed in small quarry-cuts of the Jurassic of Monte Kumeta. It was formed on a crinoidal limestone substrate of Pliensbachian age, and is covered by Upper Bajocian Ammonitico Rosso-type sediments, all cross-cut by several generations of neptunian dykes. This peculiar surface is more or less coeval with hardgrounds, Fe–Mn-capped dissolution surfaces and associated neptunian dykes described from other localities of the Western Tethys and currently subject to fierce debates as to their purely submarine (or perhaps partly subaerial) origin. The major goal of this paper is to add new arguments to this debate by revealing the finest details of field relationships at a site particularly adapted to the study of this phenomenon. Field observations are supported by petrography and, to a lesser extent, by geochemistry. Results are as follows: (i) vertical dissolution grooves, pointing to dissolution by gravitationally controlled waters, were detected on the sides of several micro-topographic highs; (ii) extensive intergranular dissolution (predating the formation of the Fe–Mn crust) was proved in the substrate both on the micro- and meso-scale; (iii) intense (micro)bio-erosion and local phosphate enrichment were detected immediately underneath the crust; (iv) a Toarcian fauna was identified from the hollows of the irregular surface; (v) synsedimentary faults and fractures clearly predating the major Fe–Mn-encrusted surface were observed, and (vi) a meso-scale synsedimentary growth structure, post dating the Fe–Mn crust, which controlled the Liassic depositional environment of Monte Kumeta is documented. Our conclusion is that the studied surface records at least three separate events of dissolution and precipitation/sedimentation each having either erased or overprinted the effects of the previous one and therefore not permitting the exact reconstruction of all the details of the complex story. To form the irregular surface, in addition to a transient phase of subaerial exposure, a complex history of bio-erosion and submarine dissolution by fluids of widely different chemical composition is proposed. To permit the mixing of sea-water with fault-controlled waters of higher temperature and with groundwaters introduced by deep circulation, a scenario of down-faulted blocks and an adjoining, distant subaerially exposed region is invoked. Such a region provided the hydraulic drive for the postulated circulation. The ultimate cause for the unusual phenomena under scrutiny was the combined effect of tectonics (the local manifestation of Early Liassic rifting in the Western Tethys) and the well-known Pliensbachian–Toarcian sea level-rise.

Late Eocene detrital laterites in central Oregon: Mass balance geochemistry, depositional setting, and landscape evolution

Detrital laterites interbedded with clayey, Ultisol-like paleosols in the late Eocene strata of central Oregon record periods of soil erosion, colluvial concentration of iron-cemented soil nodules, and deposition of these weathered products in hillslope settings. Two sets of lateritic paleosols are extensively exposed in the Painted Hills area of Oregon and span the transition from Eocene Clarno Formation andesitic volcanism to the initiation of late Eocene–Miocene pyroclastic volcanism of the John Day Formation. These late Eocene lateritic paleosols developed along the margins of several different lava flows where they formed local accumulations of iron-rich strata, which are now exposed in deep-red and ocher-colored badlands along the exhumed flow margins. Stratigraphically, the lateritic paleosols are above upper Clarno Formation rhyodacite flows, below the thick tuffaceous Oligocene–early Miocene part of the John Day Formation, and sandwich the welded tuff of member A that defines the base of the John Day Formation. In each of several cases from different lava flows studied, a similar sequence of detrital laterites and clayey paleosols rest on weathered lava flow breccia. The basal paleosol of these sequences consists of a thick (5–10 m), very strongly weathered saprolite zone developed in lava flow breccia and an overlying clayey B horizon. This paleosol is overlain by 8–12 m of alternating clayey, kaolinite-rich paleosols (Ultisol-like paleosols) and weakly developed paleosols with iron-rich, claystone breccia fragments (detrital laterites). The iron-cemented claystone fragments are up to 35% Fe 2 O 3 , very base poor, and weather-resistant, and they contain abundant cross-cutting clay skins and clay-filled pedotubules indicative of polycyclic weathering. The lower of the two sets of detrital laterites is associated with a thick rhyodacite flow in the upper Clarno Formation and has an up-section increase in the degree of weathering and concentration of resistate constituents, as determined by mass-balance geochemical analysis. The time span represented by this well-developed weathering trend is estimated to be between 2 and 4 m.y. based on estimates of the time of formation of interbedded paleosols. This long-lasting weathering trend is probably the result of a lack of soil rejuvenation resulting from the late Eocene hiatus between Clarno and John Day volcanism. A developmental model for the formation of the detrital laterites and Ultisol-like paleosols involves alternating episodes of soil formation and soil erosion in which iron-rich soil nodules are concentrated as a colluvial lag deposit on the toe slope of hills. Subsequent colluvial pulses of iron-cemented gravel were increasingly weathered and rich in resistate constituents because of longer residence time in up-slope soils. During periods of landscape stability, slow vertical accretion of soils by small additions of volcanic ash and dust produced the strongly developed, but nonlateritic, Ultisol-like paleosols. The episodes of soil erosion probably correspond to periods of climatic change during the late Eocene climatic deterioration. The John Day Formation detrital laterites and clayey paleosols are very similar to the Clarno formation laterites except for the presence throughout the section of 1%–3% pyrogenic feldspar crystals. No up-section increase in weathering is observed in the John Day detrital laterites, perhaps because of rejuvenation of soils by volcanic ash. The similar textures and chemistries of the two groups of detrital laterites, despite the onset of John Day pyroclastic volcanism, indicate that climate remained subtropical and humid up to the Oligocene-Eocene boundary.

Diagenetic Salinity Cycles and Sea Level Along a Major Unconformity, Monte Composauro, Italy

Abstract In shallow-water carbonates, position of the water table and the chemistry of early diagenetic fluids are controlled in large part by sea-level and climate fluctuations. These fluctuations may result in cyclic progression from marine diagenesis or sedimentation, to mixing zone, meteoric, mixing zone, and then marine diagenesis or sedimentation. Herein we term such a cyclic progression as a diagenetic salinity cycle. This diagenetic study along a single unconformity in Cretaceous limestones of Monte Camposauro, southern Apennines, Italy, demonstrates the presence of four diagenetic salinity cycles and their link to relative changes in sea level. Data consist of field observations, transmitted light and cathodoluminescence microscopy, fluid inclusions, and carbon and oxygen isotopes. They show that twenty-one unconformity-related diagenetic features predated deposition of marine limestones above the unconformity. Fossiliferous internal sediments and stable-isotope data from radiaxial fibrous calcite and recrystallized aragonite are used to indicate marine diagenesis. Fluid-inclusion and stable-isotope data are used to indicate precipitation of calcite cement in all mixing ratios of the mixing-zone environment and in the freshwater phreatic zone. Paleocave morphology indicates vadose and water-table dissolution, and bauxite sediments support extensive vadose diagenesis. In each diagenetic salinity cycle, there is evidence for relative fall or rise of sea level, indicated by transitions from marine sedimentation to mixing zone and freshwater phreatic diagenesis, marine phreatic to freshwater vadose diagenesis, vadose diagenesis to marine phreatic diagenesis, and freshwater phreatic diagenesis to normal marine sedimentation. During the time interval of the development of the unconformity (beginning some time in the Aptian and ending in the early middle Cenomanian) at least seven third-order eustatic fluctuations have been hypothesized during an overall second-order eustatic rise. At a given elevation, the third-order eustatic fluctuations would not be able to produce four diagenetic salinity cycles without tectonic uplift of 3.5 to 8 mm/ky. Our study illustrates that the formation and the timing of diagenetic salinity cycles are highly sensitive to paleoelevation. Diagenetic salinity cycles, preserved along unconformities, can be used to interpret relative changes of sea level and to predict the presence of depositional sequences in downdip positions. Conversely, downdip depositional sequences, tectonic history, and sea-level history can be used to predict some aspects of diagenetic alteration updip.

Stable isotope geochemistry of calcrete nodules and septarian concretions in a Quaternary ‘red clay’ paleovertisol from Hungary

Calcrete nodules and concretions in unusually large amounts are embedded in the Quaternary clay-rich (Vertisol-type) ‘red clay’ soil-sedimentary complex at the pediment of the Mátra Mountains (Hungary). Stable isotope signatures were studied in nodules and septarian concretions, uncommon due to their several millimeter sized calcite crystals filling voids and fractures, to reveal their origin. The isotope composition of calcrete covers a wide range: δ18O=−5.9 to−10.4 ‰ and δ13C=−8.9 to−12.3 ‰ (vs. V-PDB). Isotope compositions support pedogenic (sensu stricto) and/or shallow groundwater origin for the calcrete nodules and concretions, the role of ‘evolved’ (isotopically modified) groundwaters in the formation of secondary carbonate was possibly subordinate. Late-stage, large, Mn-rich euhedral calcite crystals in concretions have the lowest δ13C values, which are interpreted as a result of larger contribution of isotopically light organic carbon due to decomposition of organic matter under reducing conditions. Precipitation of late calcite crystals in concretions occurred in early diagenetic environment after shallow burial of the ‘red clay’ paleovertisol. †Revised version of a paper presented at the VIII Isotope Workshop of the European Society for Isotope Research (ESIR), June 25 to 30, 2005, Leipzig-Halle, Germany

Reconstructing Quaternary pedogenesis in a paleosol sequence in Hungary

Abstract In addition to field observations, mineralogical, chemical, and micromorphological analyses, and scanning electron microscope studies were conducted to reconstruct soil forming processes in a paleosol profile sequence located in an open-cast lignite mine in North Central Hungary (Visonta, pediment of the Matra Mountains). Based on these investigations, several different, sometimes contradictory processes were identified: bioturbation on various scales, shrinking–swelling, leaching, CaCO 3 and Fe-oxide precipitation, erosion, sedimentation, weathering, clay mineral transformation, clay illuviation, organic matter accumulations, reduction and oxidation, and frost action. Joint occurrence of these phenomena indicates environmental changes during the formation of the studied sequence. Many of these processes overlap and might have occurred several times. The presence of erosional surfaces makes it more difficult to establish the exact age of this complex formation. All observations suggest that sedimentation and soil formation on the Matra pediment were not continuous during the Quaternary.

CONCLUSIONS FROM A NEGATIVE TRACER TEST IN THE URBAN THERMAL KARST AREA, BUDAPEST, HUNGARY

To prove the hydraulic connection between the urban Rózsadomb recharge area (Buda Thermal Karst System, Budapest, Hungary) – through its hydrothermal inactive caves – and the springs at the foothills has been an important question since the 1980s. These cold and lukewarm springs have been utilized as thermal baths since Roman times, and in modern times, occasionally, chemical and bacterial contaminants of human origin have been detected in them. It is hence of considerable importance to know whether these contaminants originated from the Rózsadomb recharge area or from close to the discharge points. According to the results of a previous test in a cave passage high upon the hill, it was tempting to suppose direct connection between the Rózsadomb area and the Boltív Spring in the foothills. The expected breakthrough-time predicted from this previous study was between 10 hours and 42 days. The tracer test documented in this present work showed that no breakthrough occurred. It is proposed therefore that the risk of the Boltív Spring being contaminated by infiltration in the Rózsadomb recharge area is low as compared with the possible contamination from sources near the discharge area. We suggest that in this case the negative tracer test clearly helped to prove and to understand better the role of “natural attenuation” in the Rózsadomb area. The efficient dilution observed in the tracer test facilitated the prediction of a hitherto unknown, large, phreatic cave-system as well.