Transect across the External Pamir thrust belt and Main Pamir Thrust along the Altyn Darya valley, Kyrgyzstan

2021 ◽  
Author(s):  
Jonas Kley ◽  
Thomas Voigt ◽  
Edward R. Sobel ◽  
Johannes Rembe ◽  
Chen Jie
Keyword(s):  
Cross Section ◽  
Lower Cretaceous ◽  
Upper Cretaceous ◽  
Hanging Wall ◽  
Lower Jurassic ◽  
Late Triassic ◽  
Thrust Belt ◽  
The South ◽  
Late Neogene ◽  
Basal Detachment

<p>The ca. 35 km long, N-S-trending Altyn Darya valley in Kyrgyzstan exposes a nearly complete cross-section of the External Pamir thrust belt (EP), extending from the active Pamir Frontal Thrust in the north to the Main Pamir Thrust (MPT) and some distance into its hanging-wall. The EP comprises a northward imbricated stack of Carboniferous to Late Neogene rocks. From north to south, young clastics of the Alai Valley foreland basin are overthrust by an intensely folded and thrust-repeated frontal stack of Upper Cretaceous to Paleogene limestone, shale and evaporite. Lower Cretaceous red sandstones first emerge above north- and south-verging thrusts forming a triangle zone whose core comprises spectacular isoclinal folds in Upper Cretaceous strata. Towards the south, another thrust imbricate of Lower Cretaceous is overthrust by Late Triassic-Jurassic sandstones and mafic volcanics which are themselves overthrust by an internally deformed, Carboniferous to Triassic succession of, from bottom to top, greywacke and shale, limestone, volcanoclastic conglomerates, variegated sandstone-shale and pink conglomerates. The Carboniferous units in the south are truncated by the MPT which emplaces a succession of greenschist, marble and chert overlain by a km-thick sequence of metamorphosed and deformed, pillow-bearing lavas of Carboniferous age. Structural geometries and fault preference indicate that the basal detachment of the EP deepens southward very gently, stepping down from a detachment in Upper Cretaceous shale to another one near the base of the Lower Cretaceous and eventually a third one in Triassic shale. Cross-section balancing suggests minimum shortening of 75 km for units in the MPT´s footwall. The displacement on the MPT is poorly constrained due to eroded hanging-wall cutoffs, but must exceed 15 km. The basal detachment cuts into basement no earlier than 100 km from the present thrust front, too far south to link up with the top of the Pamir slab.</p><p>The stratigraphic succession exposed in Altyn Darya can be readily correlated with less deformed and less metamorphosed transects in westernmost China (Qimgan and Kawuke), some 250 km to the east. A marble-greenschist sequence similar to that carried on the MPT in Altyn Darya has been identified there as a tectonic nappe of the Karakul-Mazar unit, emplaced from the south already in an Upper Triassic to Lower Jurassic (Late Cimmerian) event. If the correlation is correct, then the MPT had a Mesozoic precursor structure extending over much of the E-W striking segment of the Northern Pamir.</p>

A mountain of folds: triangle zone in the fold-and-thrust belt of the External Pamir, Kyrgyzstan

2020 ◽  
Author(s):  
Thomas Voigt ◽  
Jonas Kley ◽  
Christoph Wehner
Keyword(s):  
Lower Cretaceous ◽  
Upper Cretaceous ◽  
Hanging Wall ◽  
Thrust Belt ◽  
The North ◽  
Triangle Zone ◽  
Classical Models ◽  
Thrust Sheets ◽  
Thickness Variations ◽  
High Level

<p>Triangle zones are thrust sheets or stacks of thrust sheets underlain by foreland-directed thrusts and overlain by a kinematically linked “passive” roof thrust - a backthrust - directed towards the hinterland. They are not uncommon in thin-skinned fold-and-thrust belts. Most triangle zones are known from seismic data and drilling. We describe a km-scale example exposed on a flank of the Altyn Dara valley near the thrust front of the Pamir mountains in Kyrgyzstan. The External Pamir is a high-level thrust belt built from non-metamorphic strata of Permian to Neogene age. It is bounded on its internal, southern side by the Main Pamir thrust with metamorphic rocks in its hanging-wall and in the north by the Pamir Frontal thrust which juxtaposes it with undeformed foreland strata of the Alai valley.</p><p>The triangle zone has formed where the basal detachment of the External Pamir ramps up from Lower Cretaceous redbeds into a succession of Upper Cretaceous marine pelites with a few intercalated limestone horizons. The strongly deformed Upper Cretaceous strata are contained between a north-directed thrust and a south-directed backthrust, both of which carry Lower Cretaceous rocks in their hanging-walls. In stark contrast to classical models, the core of the triangle zone is occupied by a bundle of essentially unfaulted, isoclinal upright folds. The subvertical axial planes diverge slightly upwards and changing elevations of the synclinal troughs suggest an anticlinorium. This structure is exposed over a vertical distance of 1 km in the steep flank of Pik Sverdlova. The folds involve four shaly packages and three limestone horizons. The initial total thickness of this succession was about 500 m. A strong slaty cleavage is developed in the shales, but the limestones do not show marked thickness variations between the long, straight fold limbs and the tight but rounded hinges. Assuming negligible penetrative strain in the limestones, unfolding the sinuous bed length suggests 10 km of horizontal shortening accommodated by folding.</p><p>Its overall geometry suggests that the triangle zone originated as a wide zone of detachment folding above a thrust fault propagating at the base of the weak Upper Cretaceous shales. The strong contraction may indicate some kind of buttress towards the foreland such as a syndepositional fault against which the Cenomanian-Turonian succession thinned or terminated, or the backthrust itself if it initiated early on. At any rate, the highly shortened bundle of folds was at some point bypassed along a deeper detachment in Lower Cretaceous strata into which the backthrust merges.</p><p>The internal structure of the Pik Sverdlova triangle zone would be difficult to image by conventional seismic techniques. Vertical drilling would also be unlikely to fully reveal the folded architecture. We speculate that in many triangle zones folding may be a more important mechanism than incorporated in the prevailing thrust-stacking models.</p><p> </p>

scholarly journals Mesozoic micropalaeontology of exploration well Elf 55/30–1 from the Fasnet Basin, offshore southwest Ireland

1986 ◽  
Vol 5 (1) ◽  
pp. 19-29 ◽  
Author(s):  
Nigel R. Ainsworth ◽  
Nicola F. Horton
Keyword(s):  
Lower Cretaceous ◽  
Lower Jurassic ◽  
Late Triassic ◽  
Ecological Distribution ◽  
Exploration Well

Abstract. The geology, biostratigraphy and palaeoecology of exploration well Elf 55/30–1 in the Fastnet Basin are summarised. The biostratigraphical and ecological distribution of the foraminifera and Ostracoda from the late Triassic, the Lower Jurassic and the Lower Cretaceous are reviewed with reference to microfaunas elsewhere in Europe. Selected microfossil taxa are illustrated.

Using bedrock thermochronometer systems to constrain fold-thrust belt geometry and kinematics, insight from the eastern Himalayas, Arunachal Pradesh, India.

2021 ◽  
Author(s):  
Nadine McQuarrie ◽  
Mary Braza
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Hanging Wall ◽  
Vertical Component ◽  
Eastern Himalaya ◽  
Thrust Belt ◽  
Arunachal Pradesh ◽  
Eastern Himalayas ◽  
Cross Section Geometry ◽  
Geometry And Kinematics

<div> <p>One of the first order questions regarding a cross-section representation through a fold-thrust belt (FTB) is usually “how unique is this geometrical interpretation of the subsurface?”  The proposed geometry influences perceptions of inherited structures, decollement horizons, and both rheological and kinematic behavior.  Balanced cross sections were developed as a tool to produce more accurate and thus more predictive geological cross sections.  While balanced cross sections provide models of subsurface geometry that can reproduce the mapped surface geology, they are non-unique, opening the possibility that different geometries and kinematics may be able to satisfy the same set of observations. The most non-unique aspects of cross sections are: (1) the geometry of structures that is not seen at the surface, and (2) the sequence of thrust faulting.  We posit that integrating sequentially restored cross sections with thermokinematic models that calculate the resulting subsurface thermal field and predicted cooling ages of rocks at the surface provides a valuable means to assess the viability of proposed geometry and kinematics.  Mineral cooling ages in compressional settings are the outcome of surface uplift and the resulting focused erosion.  As such they are most sensitive to the vertical component of the kinematic field imparted by ramps and surface breaking faults in sequential reconstructions of FTB.  Because balanced cross sections require that the lengths and locations of hanging-wall and footwall ramps match, they provide a template of the ways in which the location and magnitude of ramps in the basal décollement have evolved with time.  Arunachal Pradesh in the eastern Himalayas is an ideal place to look at the sensitivity of cooling ages to different cross section geometries and kinematic models. Recent studies from this portion of the Himalayan FTB include both a suite of different cross section geometries and a robust bedrock thermochronology dataset. The multiple published cross-sections differ in the details of geometry, implied amounts of shortening, kinematic history, and thus exhumation pathways. Published cooling ages data show older ages (6-10 Ma AFT, 12-14 Ma ZFT) in the frontal portions of the FTB and significantly younger ages (2-5 Ma AFT, 6-8 Ma ZFT) in the hinterland. These ages are best reproduced with kinematic sequence that involves early forward propagation of the FTB from 14-10 Ma.  The early propagation combined with young hinterland cooling ages require several periods of out-of-sequence faulting. Out-of-sequence faults are concentrated in two windows of time (10-8 Ma and 7-5 Ma) that show systematic northward reactivation of faults.  Quantitative integration of cross section geometry, kinematics and cooling ages require notably more complicated kinematic and exhumation pathways than are typically assumed with a simple in-sequence model of cross section deformation.  While also non-unique, the updated cross section geometry and kinematics highlight components of geometry, deformation and exhumation that must be included in any valid cross section model for this portion of the eastern Himalaya.</p> </div>

scholarly journals A Cretaceous dinoflagellate cyst zonation for NE Greenland

2019 ◽  
Vol 157 (10) ◽  
pp. 1658-1692 ◽  
Author(s):  
H. Nøhr-Hansen ◽  
S. Piasecki ◽  
P. Alsen
Keyword(s):  
North Sea ◽  
Lower Cretaceous ◽  
Upper Cretaceous ◽  
Barents Sea ◽  
The South ◽  
Norwegian Sea ◽  
Dinoflagellate Cyst ◽  
The North ◽  
Northern North Sea ◽  
First Time

AbstractA palynostratigraphic zonation is for the first time established for the entire Cretaceous succession in NE Greenland from Traill Ø in the south to Store Koldewey in the north (72–76.5° N). The zonation is based on samples from three cores and more than 100 outcrop sections. The zonation is calibrated to an updated ammonite zonation from the area and to palynozonations from the northern North Sea, Norwegian Sea and Barents Sea areas. The palynozonation is primarily based on dinoflagellate cyst and accessory pollen. The Cretaceous succession is divided into 15 palynozones: seven Lower Cretaceous zones and eight Upper Cretaceous zones. The two lowermost zones are new. The following five (Lower Cretaceous) zones have already been described. Two of the Upper Cretaceous zones are new. The zones have been subdivided into 20 subzones, 11 of which have been described previously and one of which has been revised/redefined. Nine subzones (Upper Cretaceous) are new. More than 100 stratigraphical events representing more than 70 stratigraphic levels have been recognized and presented in an event-stratigraphic scheme.

scholarly journals Supplemental material: The Confusion Range, west-central Utah: Fold-thrust deformation and a western Utah thrust belt in the Sevier hinterland

2014 ◽  
Author(s):  
David C. Greene
Keyword(s):  
Cross Section ◽  
Thrust Belt ◽  
The South ◽  
South Central ◽  
West Central

Geosphere, February 2014, v. 10, p. 148-169, doi:10.1130/GES00972.1, Plate 4 - Cross section of the south central Confusion Range, C–C′.

The Auk Field, Block 30/16, UK North Sea

1991 ◽  
Vol 14 (1) ◽  
pp. 227-236 ◽  
Author(s):  
Nigel H. Trewin ◽  
Mark G. Bramwell
Keyword(s):  
North Sea ◽  
Lower Cretaceous ◽  
Upper Cretaceous ◽  
The South ◽  
Well Control ◽  
Western Margin ◽  
The North ◽  
Fault Block ◽  
Definition Of ◽  
Central North Sea

AbstractThe Auk field is located in Block 30/16 at the western margin of the Central Graben. Oil is contained in a combination stratigraphic and structural trap which is sealed by Cretaceous chalk and Tertiary claystones. An oil column of up to 400 ft is contained within Rotliegend sandstones, Zechstein dolomites, Lower Cretaceous breccia and Upper Cretaceous chalk. Production has taken place since 1975 with 80% coming from the Zechstein, in which the best reservoir lithology is a vuggy fractured dolomite where porosity is entirely secondary due to the dolomitization process and leaching of evaporites. Both Rotliegend dune slipface sandstones, and the Lower Cretaceous breccia comprising porous Zechstein clasts in a sandy matrix, also contribute to production. Poor seismic definition of the reservoir results in reliance on well control for detailed reservoir definition. The field has an estimated ultimate recovery of 93 MMBBL with 13 MMBBL remaining at the end of 1988.The Auk field is situated in Block 30/16 of the Central North Sea about 270 km ESE from Aberdeen in 240-270 ft of water (Fig. 1). The field covers an area of about 65 km2 and is a combination of tilted horst blocks and stratigraphic traps, located at the western margin of the South West Central Graben. The Auk horst is about 20 km long and 6-8 km wide, with a NNW-SSE trend. It is bounded on the west by a series of faults with throws of up to 1000 ft, and the eastern boundary fault has a throw of 5000 ft in the north reducing to zero in the south (Fig. 2). The horst is a westward tilted fault block in the north which grades into a faulted anticline in the south. The Auk accumulation is largely contained within Zechstein dolomites and is ultimately sealed by Cretaceous chalk which overlies the base Cretaceous erosion surface. An E-W cross-section of the field is illustrated by Fig. 3. Auk was the first of the alphabetical sequence of North Sea sea-bird names used for Shell/ Esso fields.

Calcareous nanoplankton of Cretaceous sediments of Bahchisaray area of the South-Western Crimea

2019 ◽  
pp. 57-69
Author(s):  
M. A. Ustinova ◽  
R. R. Gabdullin
Keyword(s):  
Lower Cretaceous ◽  
Upper Cretaceous ◽  
Calcareous Nannoplankton ◽  
The South ◽  
Calcareous Nanoplankton ◽  
Cretaceous Deposits

The calcic nannoplankton of the Cretaceous deposits of the Bakhchsarai region of the South-Western Crimea was studied. In the Lower Cretaceous, it is extracted from the Rezan and Biasala Formations, in the Upper Cretaceous — from the Belogorsk, Prokhladnoye and Kudrino Formations. The age of the enclosing sediments by calcareous nannoplankton has been specified. In the Rezan Formation, the nannoplankton zone is not singled out; in the Biasala Formation, apparently, part of the NC5 zone is present. In the Belogorsk Formation, the UC3 zone, subzone b, is allocated (partially), in the Kudrino Formation — the UC20 zone, and the UC20b subzone. Upper and lower boundaries of the zones are not traced.

scholarly journals Using Chaos and Ant Track Attributes to Recognize The Faulting Systems and Subtle Faults of a Jurassic - Cretaceous Sedimentary Packages in Merjan_West Kifl Oil Fields - Central Iraq

2019 ◽  
pp. 1350-1361
Author(s):  
Mohammed Sadi Fadhil ◽  
Ali M. Al-Rahim
Keyword(s):  
Gravitational Collapse ◽  
Seismic Data ◽  
Lower Cretaceous ◽  
Upper Cretaceous ◽  
Three Dimensional ◽  
Lower Jurassic ◽  
Passive Margin ◽  
Oil Fields ◽  
Normal Faults ◽  
Seismic Sections

Study of three dimensional seismic data of Merjan area-central Iraq has shown that the Jurassic – Cretaceous succession is affected by faulting system. Seven major normal faults were identified and mapped. Synthetic traces have been calculated by using sonic and density log data of the well Me-1.Two exploration wells were drilled in the area Me-1 and Wkf-1 wells, the distance between them is 15.82 km. Discussion about the effect of this system on the sedimentary package has been presented. The tight faults that couldn’t be distinguished it on seismic sections were determined using seismic attributes. They have different strike and limited in their vertical and horizontal extension. They are system facilitates the movement or migration of the fluid across the stratigraphic column in the study area. Faulting framework can be divided into two groups: the first affects the Jurassic and lower Cretaceous rocks and the second effect the upper Cretaceous and lower Tertiary rocks. The first group is associated with the post rift thermal sag, passive margin progradation and gravitational collapse (lower Jurassic – upper Cretaceous (Turonian) 022 – 93 Ma); approximately Sargelue – NahrUmr depositional time. The second group is few and is associated with the rifting creating the Euphrates graben (Late Turonian – Maastrichtian 90 – 70 Ma) approximately Tanuma shale / Sadi – Shiranish) depositional time.

THE PETROLEUM GEOLOGY OF THE OUTER DAMPIER SUB-BASIN

1978 ◽  
Vol 18 (1) ◽  
pp. 13
Author(s):  
A. Crostella ◽  
M. A. Chaney
Keyword(s):  
Middle Jurassic ◽  
Upper Cretaceous ◽  
Lower Jurassic ◽  
Upper Triassic ◽  
Petroleum Geology ◽  
Late Triassic ◽  
Well Data ◽  
Western Australian ◽  
Outer Area ◽  
Outer Section

The Dampier Sub-basin represents the northern part of a depositional downwarp along the Western Australian coast within the greater Carnarvon Basin. The sub-basin can be separated into an inner and outer section by the depositional Lewis Trough, which drilling and seismic results indicate to have been active since at least earliest Jurassic times.The Dampier Sub-basin originated as an intracratonic depocentre at the end of the Carboniferous and has developed progressively into a marginal basin at the present day. The oldest sediments penetrated to date in the outer area are fluviatile Upper Triassic clastics. Well data have shown that sedimentation continued without a break from the Late Triassic until the late Middle Jurassic, with gradually increasing marine influences. This phase of deposition was terminated by uplift in the Early Callovian, resulting in the emergence of various parts of the basin. These areas were transgressed at different stages, but by the late Early Cretaceous a marine environment was firmly established over the whole region.Eleven hydrocarbon accumulations have been discovered to date in the Outer Dampier Sub-basin where the primary hydrocarbon generating section is believed to consist of pre- Upper Cretaceous shales, particularly in the Lewis Trough. The feature of major relevance to the petroleum geology is the Rankin Platform where the main discoveries occur in Triassic to Lower Jurassic reservoirs. Trapping is provided primarily by the drape and differential compaction of Cretaceous shales over the pre-tectonic horsts, but the water level in individual fields appears to depend on a combination of both drape and fault trapping. In the Angel Field, on the Madeleine Trend, hydrocarbons occur in Tithonian sands within a fold structure sealed by conformable Cretaceous shales.

THE BARROW ISLAND OILFIELD

1967 ◽  
Vol 7 (1) ◽  
pp. 130
Author(s):  
J. C. Parry
Keyword(s):  
Production Rate ◽  
Lower Cretaceous ◽  
Upper Cretaceous ◽  
Seismic Refraction ◽  
Upper Jurassic ◽  
Northwest Coast ◽  
The South ◽  
Primary Methods ◽  
Reservoir Characteristics

Barrow Island lies 35 miles off the northwest coast of Australia, 800 miles north of Perth, and has an area of 90 square miles. Miocene Trealla Limestone crops out over most of the island. Eocene Giralia Calcarenite is found in some valleys of the crestal region and Quaternary sand covers the island fringes.The Barron No. 1 well was located at the highest point in the sub-surface, as indicated by seismic refraction work, and in the crestal area of a gently dipping surface anticline. It was mapped as having at least 80 feet of vertical closure with an area of 24,000 acres. This well was completed as a new field discovery in August, 1964, with an initial production rate of 985 BOPD from sand in the Jurassic. In February, 1965, Barrow No. 4 was completed as a shallower pool discovery with an initial production rate of 125 BOPD from a Lower Cretaceous sand. By December, 1966, 33 wells had been drilled for a total footage of 155,409 feet.Barrow No. 1 is the deepest well at 9875 feet although it is considered that the sedimentary section may exceed 20,000 feet. The known sequence begins with Upper Jurassic siltstones. These pass upwards into a predominantly sandstone sequence containing minor shale and siltstone, and are followed by the dark-coloured marine shales and siltstones and minor sandstone of Lower Cretaceous age. In the Upper Cretaceous and Tertiary, fossiliferous, micro-crystalline Limestones and calcareous siltstones were deposited.The field contains two petroliferous intervals. The deeper interval is within the Upper Jurassic and contains a number of small irregular pools with good reservoir characteristics, these, however, are not commercial in themselves. The shallower interval contains the widespread "Windalia Sand" which has an average pay thickness of 44 feet and generally poor reservoir characteristics. Drilling is now developing the "Windalia Sand" pool which covers 24,700 acres and contains reserves currently estimated at 114 million barrels recoverable by primary methods. Structure at this pay horizon is a broad north plunging nose truncated at the south by a down-to-the- south fault. One hundred and forty-four development wells will he drilled in 1967.

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