Sedimentary history of Upper Silurian biostromes of Podolia (Ukraine) based on stromatoporoid morphometry

Self Cite

ABSTRACT:Łuczyński, P., Skompski, S. and Kozłowski, W. 2016. Recent studies on the Silurian of the western part of Ukraine. Acta Geologica Polonica, 66 (3), 281-297. Warszawa.The paper summarises the effects of recent studies carried out by a team from the Department of Historical and Regional Geology of the Faculty of Geology, University of Warsaw on the upper Silurian of Podolia (western part of Ukraine).The sedimentary history of the Silurian succession of Podolia is characterised by its cyclic pattern, with shallowing-upward cyclothems. In the traditional interpretation, the occurrence of stromatoporoid beds within each cyclothem marks the deepest (or most open-marine) sedimentary environment within the cycle. According to the results of recent studies, their occurrence is connected rather with a relatively shallow-water environment and with high energy phenomena. A substantial reinterpretation of the main sedimentary processes governing the deposition and facies distribution on the shelf is presented. Particularly, there are recognised and described high-energy sedimentary events repeatedly punctuating the generally calm sedimentation that prevailed in the lagoonal settings, some of which are interpreted as tsunami induced.Further perspectives for studies on the Silurian successions of Podolia are also discussed. The main problem is the precise correlation of particular sections that are scattered over vast distances and developed in similar facies associations.

Section: Tsunami Interpretation Of Stromato-poroid Beds and Flat-pebbmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 82%

Recent studies on the Silurian of the western part of Ukraine

Łuczyński

Skompski²,

Kozłowski³

2016

Self Cite

“…In previous papers (Skompski et al 2008;Łuczyński et al 2009; Łuczyński 2011), we have described lenticular stromatoporoid beds from the Upper Silurian of Podolia and attributed their origin to onshore redeposition of stromatoporoid material, tentatively suggesting their tsunami origin. Recent field studies have revealed that several sections exposed along the Zbruch River abound in stromatoporoid horizons that can be traced over distances of several kilometres.…”

Section: High-energy Event Bedsmentioning

confidence: 82%

“…Predtechensky et al 1983). However, recent studies (Skompski et al 2008;Łuczyński et al 2009) of the Ludlow and Pridoli strata cropping out in the vicinities of Skala Podil'ska and Kam'janec' Podil'skyj have revealed that the stromatoporoid beds are in fact developed as lenticular parabiostromes (sensu Kershaw 1994) composed of overturned and often fragmented massive skeletons, which is typical of most SilurianDevonian stromatoporoid "reef" deposits. The biogenic material has been transported landward from their offshore habitats by high-energy sedimentary events punctuating the shallow-water shelf (Skompski et al 2008) and deposited in shallow lagoonal or even near-shore settings.…”

Section: Sedimentary and Stratigraphical Settingmentioning

confidence: 99%

Stromatoporoid Beds and Flat-Pebble Conglomerates Interpreted as Tsunami Deposits in the Upper Silurian of Podolia, Ukraine

Łuczyński¹,

Skompski²,

Kozłowski³

2014

Self Cite

ABSTRACT:Łuczyński, P., Skompski, S. and Kozłowski, W. 2014. Stromatoporoid beds and flat-pebble conglomerates interpreted as tsunami deposits in the Upper Silurian of Podolia, Ukraine. Acta Geologica Polonica, 64 (3), 261-280. Warszawa.Tsunami deposits are currently a subject of intensive studies. Tsunamis must have occurred in the geological past in the same frequency as nowadays, yet their identified depositional record is surprisingly scarce. Here we describe a hitherto unrecognized example of probable palaeotsunamites.The Upper Silurian (Pridoli) carbonate succession of Podolia (southwestern Ukraine) contains variously developed event beds forming intercalations within peritidal deposits (shallow water limestones, nodular marls and dolomites). The event beds are represented by stromatoporoid and fine-grained bioclastic limestones, in some places accompanied by flat-pebble conglomerates. The interval with event beds can be traced along the Zbruch River in separate outcrops over a distance of more than 20 km along a transect oblique to the palaeoshoreline. The stromatoporoid beds have erosional bottom surfaces and are composed of overturned and often fragmented massive skeletons. The material has been transported landward from their offshore habitats and deposited in lagoonal settings. The flat-pebble conglomerates are composed of sub-angular micritic clasts that are lithologically identical to the sediments forming the underlying beds.Large-scale landward transport of the biogenic material has to be attributed to phenomena with very high energy levels, such as tropical hurricanes or tsunamis. This paper presents a tsunamigenic interpretation. Morphometric features of redeposited stromatoporoids point to a calm original growth environment at depths well below storm wave base. Tsunami waves are the most probable factor that could cause their redeposition from such a setting. The vastness of the area covered by parabiostromal stromatoporoid beds resembles the distribution of modern tsunami deposits in offshore settings. The stromatoporoid beds with unsorted stromatoporoids of various dimensions evenly distributed throughout the thickness of the beds and with clast-supported textures most probably represent deposition by traction. In some sections, the stromatoporoids are restricted to the lowermost parts of the beds, which pass upwards into bioclastic limestones. In this case, the finer material was deposited from suspension. The coexistence of stromatoporoid beds and flat-pebble conglomerates also allows presenting a tsunami interpretation of the latter. The propagating tsunami waves, led to erosion of partly lithified thin-layered mudstones, their fragmentation into flat clasts and redeposition as flat-pebble conglomerates.

“…Our earlier studies (Skompski et al 2008;Łuczyński et al 2009, 2014 have revealed that part of these beds, particularly those in the higher part of the Silurian succession, are in fact represented by sediments composed of material redeposited shoreward and derived from open marine regions. One can assume that some of the stromatoporoid biostromes on Gotland are of a similar origin (compare, Kershaw 1990).…”

Section: Introductionmentioning

confidence: 97%

Regressive-transgressive cyclothem with facies record of the re-flooding window in the Late Silurian carbonate succession (Podolia, Ukraine)

Łuczyński¹,

Kozłowski²,

Skompski³

2015

Self Cite

ABSTRACT:Łuczyński, P., Kozłowski, W. and Skompski, S. 2015. Regressive-transgressive cyclothem with facies record of the re-flooding window in the Late Silurian carbonate succession (Podolia, Ukraine). Acta Geologica Polonica, 65 (3), 297-318. Warszawa.The term "re-flooding window" was recently proposed as a time-interval connected with the transgressive stage of present day peri-reefal development. In the analysis presented here, a fossil record of a re-flooding window has been recognized. Nine Late Silurian carbonate sections exposed on the banks of the Dnister River in Podolia (Ukraine) have been correlated base on bed-by-bed microfacies analysis and spectral gamma ray (SGR) measurements. Correlated were sections representing settings ranging from the inner part of a shallow-water carbonate platform to its slope, through an organic buildup. The reconstructed depositional scenario has been divided into six development stages, with the first three representing a regressive interval and the latter three a transgressive interval of the basin's history. The re-flooding window has been identified at the beginning of a transgressive part of the succession. Surprisingly, it is characterized by an extremely fast growth of a shallow, tide-dominated platform and by deposition of calciturbiditic layers in a more basinal area. The interpreted succession is a small-scale model illustrating the reaction of carbonate depositional sub-environments to sea level changes and determining the facies position of the stromatoporoid buildups within the facies pattern on a Silurian shelf. The use of SGR analyses in shallow water, partly high-energy, carbonate facies, both for correlation purposes and for identifying depositional systems, is a relatively new method, and thus can serve as a reference for other studies of similar facies assortment.