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Record of Late Neogene seismites in turbidite deposits of the Tafna Basin (NW Algeria)

Benzina Mostapha, Pisarska-Jamroży Małgorzata, Hebib Hakim

Geological Quarterly

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2023

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Vol. 67, No. 3

art. no. 25

EN

The wide variety of soft-sediment deformation structures (SSDS) developed within deposits of the same age may hinder the interpretation of their origin. Some types of SSDS may appear similar though have different trigger mechanisms, while others may result from a specific mechanism. Furthermore, the development of particular SSDS may be influenced by several synchronous or semi-synchronous factors. This study deals with the recognition of SSDS trigger mechanisms with respect to lithological and deformational features of the deposits concerned. Turbidite deposits of late Neogene age in the Hadjret El Gat area (Tafna Basin) contain different types of SSDS associated with (1) slope processes (e.g., slump folds) and induced overburden pressure, coupled with broken beds and overloading structures, and (2) liquefaction and fluidisation phenomena, leading to the development of load structures, ball-and-pillow structures, water-escape structures and syndepositional faults. These two mechanisms of SSDS formation in the study area are thought to result from seismically-induced triggers. Recognition of a vertically-repeated, sandwich-like arrangement of deformed and undeformed layers along with the SSDS features ("trapped" within beds) suggests that these internally-deformed beds are seismites, the first recognized in the Tafna Basin of NW Algeria. Large earthquakes may trigger seismic waves energetic enough to deform strata and induce the development of SSDS. This hypothesis is supported here by tectonic evidence, given deposition of the Tafna Basin strata in the convergence zone between Africa and Eurasia, active since the late Neogene.

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First attempt to model numerically seismically-induced soft-sediment deformation structures : a comparison with field examples

Bronikowska Małgorzata, Pisarska-Jamroży Małgorzata, Loon van Tom

Geological Quarterly

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2021

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Vol. 65, No. 4

s. 216--225

EN

No numerical model has thus far addressed seismites, even though seismites are frequently used for the conditions which have to be fulfilled for the development of seismites have also been estimated only empirically. The present contribution is a first attempt to model numerically the soft-sediment deformation structures caused by the passage of S-waves through near-surface sedimentary layers. The simulations are based on the so-reconstruction of seismic events in the geological past. This is the more remarkable since the boundary called pressure tube model and the iSALE2D program. We modelled a seismic S-wave with six different vertical velocities, ranging from 1.6 to 2.6 m · s-1, passing through sediments with different densities and porosities in a sedimentary succession from the surface down to a depth of 10 m. The modelled soft-sediment deformation structures (load casts, flame structures, injection structures and sedimentary volcanoes) show similar geometries and sizes as those known from laboratory experiments and field studies. The geometry, size and type of these structures depend on the sediment properties and on the initial pressure used as a trigger mechanism, rather than on S-wave velocity. In contrast, the depth of the seismites appears to depend strongly on the S-wave velocity.

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Sedimentological distinction in glacigenic sediments between load casts induced by periglacial processes from those induced by seismic shocks

Van Loon Antonius Johannes, Pisarska-Jamroży Małgorzata, Woronko Barbara

Geological Quarterly

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2020

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Vol. 64, No. 3

626--640

EN

Loading processes and the resulting load structures induced by processes related to periglacial conditions are compared to those induced by seismic shocks. The load structures themselves are relatively easily recognizable but the responsible trigger mechanism is, though depending on the geological context, commonly difficult to establish. Load structures like load casts, pseudonodules, ball-and-pillow structures and flame structures are commonly ascribed to instable density gradients within sediments and to differential loading, but their formation always requires liquefaction. In glacigenic sediments, deformation structures have most commonly been ascribed to periglacial processes (as a type of cryoturbations), but it becomes ever more clear that glacigenic sediments can, particularly during ice-front fluctuations, be affected by faulting-related earthquakes (due to glacio-isostatic adjustment), and the thus triggered seismic shocks may result in deformations, including - most commonly - load structures. We inventory the evidence that may help to distinguish, on the basis of textural and structural features, load structures with a seismic origin from those that result from periglacial processes, taking into account that truly diagnostic criteria do not exist.

4

Miocene quartz sands redeposited on subaqueous and alluvial fans during the Saalian: Interpretation of the depositional scenario at Ujście, western Poland

Mleczak Mateusz, Pisarska-Jamroży Małgorzata

Geologos

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2019

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Vol. 25, No. 2

125--137

EN

The 14-m-thick sandy succession at Ujście in western Poland formed during the Odranian stadial of the Saalian glaciation, is exceptional in being very well sorted, almost mono-fractional (fine-grained sands) and mono-mineral (mainly quartz grains) and in lacking Scandinavian erratics. The lower sequence (5 metres in thickness) consists of three stacked packages of clinoforms (inclined cross-stratified sands) and is interpreted as having been deposited on a subaqueous fan in a shallow lake during two phases of rising water levels. The upper sand (9 metres in thickness) with (sub) horizontal stratification was redeposited on a subaerial alluvial fan. Distinctive distributary channels that occur in the uppermost part of the subaqueous fan and in the lowermost portion of the alluvial fan may indicate a change in sedimentation style from subaqueous to subaerial. Moreover, the subaerial position of the fan supports the presence of ice-wedge casts that developed under periglacial conditions in the upper part of alluvial fan. The results of granulometric analysis, rounding and frosting of grains and mineral analysis indicate that the sands are derived from Gorzów Formation of Early Miocene age. The only feasible explanation is that the 14-m-thick unit must have been redeposited during the Saalian glaciation.

5

Is the Charlottenthal fan (marginal zone of the Pomeranian phase, NE Germany) an end moraine?

Pisarska-Jamroży Małgorzata, Börner Andreas

Geologos

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2011

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Vol. 17, No. 1

17--28

EN

The maximum ice-sheet extent of a glaciation or glacial phase is in most cases indicated by the position of end moraines. In some cases, however, the maximum extent of the ice sheet is indicated by a fan which represents the transitional zone between the end moraine and the proximal outwash plain (sandur). Such a fan from the Pomeranian phase near Charlottenthal in NE Germany has been investigated for its lithofacies, and the depositional mechanisms of the two sedimentary environments (end moraine and outwash plain) are reconstructed. The Charlottenthal profile is not characteristic in a sedimentological sense of a typical marginal end moraine or a sandur. The deposits represent subaerial debris flows, sheet floods and channelized currents, which are typically processes for transitional fan. Gravel samples from the till complex show typical Weichselian till compositions. These till compositions indicate a general transport direction from North to South, which is consistent with the known movement of the ice sheet during the Pomeranian phase of the Weichselian.

6

Adjustment coefficients for planimetric analysis of the granulometry of coarse-grained sediments

Pisarska-Jamroży Małgorzata, Kossowski Tomasz, Jamroży Jerzy

Geologos

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2011

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Vol. 17, No. 4

221--226

EN

The relationship between results from granulometric analyses of by sieving and by planimetry was investigated by numerical simulation of cubes filled with boulders, cobbles and pebbles. Cross-sections through the sediment were simulated and compared with photos of an actual outcrop wall. Volumes estimated on the basis of planimetric analysis using the cross-sections were compared with sieve analyses, thus allowing to determine adjustment coefficients. The coefficients for pebbles and cobbles have a small standard error, but are larger for boulders, which might be a consequence of too small areas formed by the cross-sections.

7

Sedimentation style of a Pleistocene kame terrace from the Western Sudety Mountains, S Poland

Pisarska-Jamroży Małgorzata, Machowiak Katarzyna, Krzyszkowski Dariusz

Geologos

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2010

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Vol. 16, No. 2

101--110

EN

The depositional conditions of kame terraces in a mountain valley were analysed sedimentologically and petrologically through a series of kame terraces in the Rudawy Janowickie mountains. The kame terraces comprise five lithofacies associations. Lithofacies association GRt, Sp originates from deposition in the high-energy, deep gravel-bed channel of a braided river. Lithofacies association GC represents a washed out glacial till. Probably a thin layer of till was washed out by sandy braided rivers (Sp). The fourth association (Fh, Fm) indicates a shallow and quite small glaciomarginal lake. The last association (GRt, GRp) indicates the return of deposition in a sandy-bed braided channel. The petrography of the Janowice Wiekie pit and measurements of cross-stratified beds indicate a palaeocurrent direction from N to S. The Janowice Wielkie sedimentary succession accumulated most probably during the Saalian (Odranian, Saale I, Drenthe) as the first phase of ice-sheet melting, because the kame terrace under study is the highest one, 25-27 m above the Bóbr river level. The deposits under study are dominated by local components. The proglacial streams flowed along the margin of the ice sheet and deposited the kame terrace. The majority of the sedimentary succession was deposited in a confined braided-river system in quite deep channels.