Geological Reinterpretation Research Articles

Geological control of young orogenic mountain morphology: From geomorphological analysis to reinterpretation of geology of the Outer Western Carpathians

The paper presents a new concept of geological control of the Outer Western Carpathians (OWC) morphology. The establishment of the Carpathians' morphology dates back to the stage of evolution of sedimentary basin, when huge blocks of solidified rock massifs were gravitationally displaced into the foreland sedimentary basins, forming finally isolated hills. The altitudinal difference between the Beskidy Mts. and the Carpathian foothills is caused by the structural positions of these two segments of rock massifs within the orogenic megastructure during the compressional stage. Indeed, the tectonic elements that formed during the earliest stage of compression took (and still take) the highest structural and altitudinal position, whereas the elements incorporated into the orogen as the last have taken a lower topographic position, forming a belt of foothills. Therefore, this difference in topography is not related to rock resistance only, as was previously thought. The rotation of the Carpathian blocks during the orogenic thrusting and the formation of strike-slip fault zones parallel to the Carpathian tectonic thrusts formed a flower structure, which has played a significant role in morphology (insular character of). During the stage of secondary tectonic deformation – including the rotation of the Carpathian tectonic segments, strike-slip faulting and the radial extension and large extensional collapse of the Carpathian massifs – the principal features of the Carpathian relief as well as the main river valleys were formed. Gravitational collapse resulted in back-thrusting and the tectonic exhumation of the Carpathian massifs, which helps to explain the problem of seemingly large denudation of the Carpathian overburden of a thickness estimated at several kilometres. Chaotic complexes (synsedimentary and syntectonic mélanges), which frequently occur in the Carpathians, are very important for the Carpathian morphology and river valley development (controlled not only by faults) as well as the formation of isolated hills. Analysis of the Carpathian morphology supported by the Bouguer's gravity anomalies map, and geological data allow us to present a new hypothesis that the Carpathians were formed as a huge regional flower structure, without the participation of subduction, which has formerly been considered to play the crucial role in the formation of the Carpathian orogen.

Inter-aquifer connectivity between Australia’s Great Artesian Basin and the overlying Condamine Alluvium: an assessment and its implications for the basin’s groundwater management

Coal seam gas (CSG), or coal bed methane, developments in sedimentary basins such as the Great Artesian Basin (GAB) in Australia, have the potential to impact on aquifers overlying and underlying the target coal formations. The extent to which this may occur depends upon the degree of hydrogeological connectivity between the coal formations and the surrounding aquifers or aquifer systems, with general implications for groundwater management. In southeast Australia, one such aquifer system, the Condamine Alluvium (CA), overlies the Walloon Coal Measures (WCM), which is a formation of the GAB and also a target for CSG production. To investigate the connectivity between the two systems, multiple lines of investigation were employed involving field investigations, data gathering and analysis (including reinterpretation of geology, multivariate hydrochemistry analysis, regional water-level mapping, drilling and coring across the contact zone, multiple piezometer installations, long-term pumping tests, groundwater-level monitoring and local-scale modelling). The study found a low level of connectivity between the GAB and the overlying CA. A layer of undifferentiated basement clay (referred to as the ‘transition zone’)—a mixture of alluvial clay and weathered basement—provides an effective impediment to flow across the CA and the underlying GAB formations. Results from the study potentially have wider application across the GAB and sedimentary basins where younger alluvial sediments associated with river systems frequently overlie the erosional surface.

First cranial endocasts of early Miocene sirenians (Dugongidae) from the West Indies

ABSTRACTWe report and describe the first sirenian endocranial casts from the West Indies based on three specimens collected from two quarries of the upper Oligocene–lower Miocene Colón Formation, in the province of Matanzas, western Cuba. We assign them to Dugongidae incertae sedis, based on a phylogenetic analysis of fossil and extant sirenians. Thus, these new specimens provide a unique opportunity to describe the endocranial neuroanatomy of this family. The endocasts are suggestive of dugongids with limited vision and olfaction, based on the diminished olfactory and optic nerves. Additionally, we provide a geological reinterpretation of the Colón Formation and its paleoecological setting. Altogether, these data provide further insight into the diversity and evolution of sirenians, especially Caribbean dugongs.

Seismic-stratigraphic architecture of the Oligocene-Pliocene Camaná Formation, southern Peruvian forearc (Province of Arequipa)

The Camaná-Mollendo Basin is an active-margin depression ~NW-SE elongated, which is located in the forearc of southern Perú and extends from the Coastal Cordillera to the Perú-Chile Trench. This basin consists of a grabens and half-graben complex, filled with deltaic and fluvial sedimentary rocks of the Oligocene-Pliocene Camaná Formation (~500 m thick). An integration of compiled onshore stratigraphic logs, reinterpreted 2D seismic offshore information, sediment provenance data, and previous zircon U-Pb geochronology on volcanic reworked ash supports a refined tectono-chronostratigraphic framework for the whole Camaná-Mollendo Basin fill. To complete this integration we needed firstly to elaborate a geological reinterpretation of seismic offshore data and highlight their most prominent features (i.e., erosive surfaces). This step allowed establishing a first correlation between onshore and offshore deposits of Camaná Formation by means of their sequence boundaries, giving as result a consistent division for Camaná Formation: (i) “CamA Unit” (coarse-grained deltas) and (ii) “CamB Unit” (fluvial deposits). CamA Unit is further subdivided into three subunits based on minor erosive surfaces (i.e., A1: Oligocene, A2: Early Miocene, and A3: Middle Miocene). CamA reflects prograding geometry (subunits A1 and A2) as well as onlapping geometry (subunit A3). CamB Unit (Late Miocene to Pliocene) consists of high-energy hyperpycnal flows composed of fluvial conglomerates in onshore, which very possibly changes to progradational deltaic in offshore. Each one of these units and subunits extends offshore and preserves similarities in depositional geometry and sequence boundaries with Camaná Formation onshore. Subunits A1 and A2 observed in offshore are grouped in this paper as “A1+A2” (Oligocene to Middle Miocene) because they show similar progradational geometry and it is difficult to differentiate them from each other. A regressive systems tract (RST) represents these subunits. These deposits reach up to ~2.5 km thick, and they are intensely affected by normal faulting associated to pinch-out depositional geometry. Strata of subunit A3 (Middle Miocene) reflect a transgressive systems tract (TST), and blanket the entire basin with fine-grained sediments. These deposits are up to ~1 km thick, being less affected by synsedimentary tectonic and show minor effects of synsedimentary tectonics. Finally, deposition of CamB Unit (Late Miocene to Pliocene) occurred during a new regressive systems tract (TST), which turned to progradational geometry similar to deltaic deposits in offshore, and according to seismic lines they are much less affected by synsedimentary faulting. Stratigraphic boundaries between “A1+A2” and A3, and between A3 and CamB observed in onshore outcrops are used here as tools to differentiate, correlate and predict the main depositional geometries in offshore. High-frequency seismic reflectors represent such boundaries and support divisions and subdivisions within Camaná Formation. These boundaries are also used to define depocentres of Camaná Formation along the entire Camaná-Mollendo Basin, where the thickests are located in the proximity of the large river mouths (e.g., Planchada, Camaná, and Punta de Bombón). Strata of subunits “A1+A2” are considered as potential reservoir for hydrocarbon due to their high rate of sediment accumulation. Deposits of A3 are transgressive and they are considered as potential potential seal rock. Structurally, Camaná-Mollendo Basin is composed of graben and half-graben components ~NW-SE-oriented, typical of a trantensional tectonic regime.

Integrated stratigraphy of the Campanian–Maastrichtian boundary succession of the Middle Vistula River section, central Poland; Part II

Integrated stratigraphy of the Campanian–Maastrichtian boundary succession of the Middle Vistula River section, central Poland; Part II

Structure and petroleum plays of the St. Lawrence Platform and Appalachians in southern Quebec: insights from interpretation of MRNQ seismic reflection data

Abstract This study presents the results of the reprocessing and geological reinterpretation of a trio of regional seismic reflection lines acquired by the Ministere des Ressources naturelles du Quebec in 1978. The three profiles (M-2001, M-2002 and M-2003), which represent 280 km of data, cross the Chambly-Fortierville syncline and provide images of the St. Lawrence Platform and the Appalachian foreland thrust belt of southern Quebec. Profile M-2001, the longest profile, extends across the full width of the southern Quebec Appalachians. Post-stack seismic data processing has improved the quality of the original seismic sections by enhancing coherent reflection events and attenuating reflection noise. Time migration further improved the seismic data. The seismic interpretations provide new information on subsurface geology, including the recognition of complex structural patterns in platform and foreland units, the presence of a triangle zone at the structural front, and the geometry of thrust slices of platform units and Appalachian thrust nappes. The M-2001 line also provides images of the internal Humber Zone, including back-thrust faults on the flanks of Notre Dame Mountains Anticlinorium and mega thrust wedges, possibly involving Grenvillian basement, within the core of the anticlinorium. In southern Quebec, six conventional petroleum plays, plus shale gas potential, are recognized in the St. Lawrence Platform and Appalachian Foreland. From these, the Saint-Flavien field (161 million m3 of past natural gas production) and other potential targets are imaged by the three seismic profiles studied. The reprocessing and reinterpretation of these seismic reflection profiles provide new insights into the structure, geological evolution and petroleum potential of the St. Lawrence Platform and the Appalachian foreland thrust belt of southern Quebec.

Subsurface structure and tectonic style of the NE Outer Carpathians (Poland) on the basis of integrated 2D interpretation of geological and geophysical images

Subsurface structure and tectonic style of the NE Outer Carpathians (Poland) on the basis of integrated 2D interpretation of geological and geophysical imagesIntegration of the information from surface and subsurface geological exploration (maps and well sections) and results of geological reinterpretation of more than ten archival seismic sections and several dozen magnetotelluric soundings (MT; published and archival) implies a new structural picture of the Carpathian tectogene, interpreted to depths exceeding 10 km. The tectonics of nappes and their basement is illustrated by four regional cross-sections (derived from geological and petroleum-exploration traverses) and examples of detailed interpretation of zones with complicated structure, as well as results of testing the initial structural models with application of the balanced cross-section method and gravimetric modelling. In the tectonics, a complicated system of overthrusts and detachments of sedimentary covers (from their heterogeneous basement) represents a predominant feature. It induced, within particular nappes and tectonically altered structural-facies units, specific systems of narrow folds with diversified geometries. Broad folds of the intermediate structural stage, which are gently sloping in the hinterland of the nappes, were interpreted on the basis of geophysics as paraautochthonous elements. They cover deep-seated faults with large throws, which obliquely or subvertically dip to the SW and were distinguished in the basement on the grounds of extreme contrasts at the resistivity boundaries. Zones of dramatically low resistivities, which separate blocks of the uplifted basement, were interpreted as tectonic sutures with geometry rebuilt in the stage of the Neogene lithosphere subduction. Therefore, the structural layout of the sedimentary cover is characterized by more gently dipping nappe overthrusts of the sequential type and secondary, out-of-sequence thrust slices, most frequently imbricate ones. The flysch covers resting over the tectonic sutures, particularly in margins of inherited structural depressions, are characterized by more diversified tectonic style in comparison with peripheral, gently-sloping covers thrust over the flexural platform slope, and with steep slices and imbricate thrusts having consequent NE vergence. A specific type of dislocation is represented by flat inversional detachments (seismically documented) which are accompanied by disharmonic folding of "thin-skinned" structural elements. In the eastern part of the foreland of the Dukla overthrust, they form a developed system of backthrusts on the slope of a triangular structure superposed on a "shallower" tectonic suture of the basement; the system replaces sets of fault-propagation folds developed in the eastern part of this zone.

Lessons from a case study of a geophysical interpretation in Western Victoria

This paper compares the predictions and results of the Victorian Initiative for Minerals and Petroleum drilling programme, mostly over the Horsham 1:250 000 map sheet area of western Victoria. Sixteen holes were drilled beneath thin cover of the Cainozoic Murray Basin at targets identified in Moore's (1996) geological interpretation of the airborne magnetic and ground based gravity data. This integrated interpretation divided the region into the Stawell and Glenelg Zones. The Stawell Zone metaturbidites and metabasalts form the eastern edge of the Lachlan Fold Belt. The Glenelg Zone included weakly metamorphosed andesites of the Dimboola Subzone, greenschist to amphibolite facies metaturbidites and metavolcanics of the Miga Subzone and amphibolite grade rocks of the Ozenkadnook Subzone. All were deformed in the 500 Ma Delamerian Orogeny.Drilling depths were estimated both from magnetic modelling and previous drilling in the region. Drilling targeted basement depths between 30 m and 250 m. Where magnetic modelling was the main depth control, basement depths were within 20% of predicted depths, slightly more reliable than those estimated from nearby drilling.Of the sixteen holes, nine intersected the predicted lithologies and another three intersected lithologies that substantially agreed with the predictions. While four drill holes intersected quite different lithologies to those predicted, no major geological reinterpretation was needed. The drilling intersected both Cambrian continental island arc volcanic rocks and Upper Proterozoic metasedimentary basement, strengthening the temporal and tectonic correlations between western Victoria and western Tasmania.The study showed that a careful interpretation can give a reliable indication of the basement, even in areas of total cover. Integrating geological and geophysical data and using standard geological logic and techniques, like drawing sections to test plan interpretations, are powerful aids. Drilling complemented the interpretation by providing samples that could be used to test the interpretive hypothesis.

Expansion of the Old Oil Field of Bunjani on the Basis of Geological Reinterpretation

Due to the non-defined contouring of the Bunjani field and the positive exploration well Jo-2 at the southwest of the field outside the concession, a need for the geological reinterpretation of the area was discovered in order to solve the petroleum-geological relationships in the arcea, and determine field expansion and reservoir contouring in a more qualitative way. The recent geological reinterpretation was performed on the basis of a review of all available data from the existing wells, the results of field development to the present , the interprttation of new seismic profiles and the knowledge of the petroleum-geological relationships in the part of the basin previously acquired. The reinterpretation proved to be justified and it resulted in the determination of new well locations and their drilling in 1993 and 1994. In this way, the field expanded towards the southwest and the north. With the new reservoir geometry, better quality data of the reservoir characteristics, analyses obtained from the new wells, together with the reinterpretation of electric log analyses obtained from old wells, the reserves of oil have been increased by 31.4%.