INTRODUCTION in the Ukrainian Precarpathians the Oxfordian – Val
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ОСАдОВІ УТВОРЕННЯ УКРАЇНИ: ОСОБЛИВОСТІ РЕЧОВИННОГО СКЛАдУ, МОдЕЛІ ОСАдКОНАКОПИЧЕННЯ ТА ЛІТОГЕНЕЗУ / SEdImentary formations of Ukraine: peculiarities of composition, sedImentation mOdels and lithogenesis УДК 551.762.3:56.074.6:551.8(477.8) N.M. zhabina SEdimentarY MOdEl OF ThE UPPEr JUrASSIC – LowEr Cretaceous carbonate COMPlEx IN ThE UKrAINIAN PrecarpathIANS жабіна Н.М. СедиМеНТАцІйНА МОдель кАрБОНАТНОГО кОМПлекСУ верхНьОї Юри – НижНьОї крейди в УкрАїНСькОМУ ПередкАрПАТТІ In the Ukrainian Precarpathians the Oxfordian – Valanginian deposits compose a common carbonate complex. Seven types of sections are determined in its composition: fore-reef, reef, back-reef, transitional, lagoon, shallow-water, outlying. The conditions of their sedimen- tation are characterized. The main stages of these deposits sedimentation related with eustatic fluctuations are determined: Oxfordian, Oxfordian – Kimmeridgian boundary, Early Kimmeridgian, Late Kimmeridgian – Early Tithonian, Late Tithonian – Early Berriassian, Early and Late Berriassian boundary, Late Berriassian – Valanginian. The sedimentary model of these deposits has been carried out. keywords: sedimentary model, types of sections, facies, Upper Jurassic, Lower Cretaceous, Ukrainian Precarpathians. В Українському Передкарпатті відклади оксфорду – валанжину складають єдиний карбонатний комплекс. В його складі виді- лено сім типів розрізу: передрифовий, рифовий, зарифовий, перехідний, лагунний, периферійний. Охарактеризовані умови їх формування. Визначено головні стадії седиментації цих відкладів, що пов’язані з евстатичними змінами: оксфорд, межа ок- сфорду і кімериджу, ранній кімеридж, пізній кімеридж – ранній титон, пізній титон – ранній беріас, межа раннього і пізнього беріасу, пізній беріас – валанжин. Створена седиментаційна модель цих відкладів. Ключові слова: седиментаційна модель, типи розрізів, фації, верхня юра, нижня крейда, Українське Передкарпаття. INTRODUCTION world ocean eustatic fluctuations. Changes of the In the Ukrainian Precarpathians the Oxfordian – Val- sedimentation conditions in accordance with the eu- anginian carbonate complex of the genetically relat- static fluctuations caused forming the different types ed rocks extends as submeridional stripe to above of sections and complicated structure of the whole 100 km width along the Stryi depression area. This complex in the vertical and lateral directions. This complex is represented by the deposits of carbon- sedimentary model is shown in the picture (fig. 1). ate shelf from more deep-water in the west till the shallow-water in the east. There are the Oxfordian MATERIALS AND METHODS – Lower Berriassian reefogenic facies and Upper In the Ukrainian Precarpathians the Upper Jurassic – Berriassian – Valanginian open shelf deposits. In Lower Cretaceous carbonate complex outcrops in the accordance with the stratigraphic scheme (Zhabi- river Dnister basin and was opened by wells in the Car- na, Anikeyeva, 2007), these facies are represented pathian Foredeep and adjacent part of the East-Euro- by suites: fore-reef ones – Boniv (Oxfordian), Mo- pean platform. we have conducted a complex study of ranci (Kimmeridgian), Karolina (Tithonian – Lower materials of 240 wells and natural sections of these Valanginian); reef facies – Rudki suite (Oxfordian) deposits having used lithology-sedimentological, bio- and Opary (Kimmeridgian lower subsuite and Titho- and sequens-stratigraphical analysis and having ta- nian – Lower Berriasian upper subsuite), back-reef ken into an account the results of petrographic, pale- facies – Gorodok suite (Oxfordian), Pidluby (Lower ontological and geophysical studies fulfilled by other Kimmeridgian), Nyzhniv (Upper Kimmeridgian – experts (Dulub at al., 1986, 2003, and other). Lower Tithonian), Bukivna (Upper Tithonian – Lower Berriasian), evaporite lagoon facies – Rava-Russka DISCUSSION AND RESULTS suite (Lower Kimmeridgian), shallow-sea deposits The Upper Jurassic – Lower Cretaceous deposits in Stavchany suite (Upper Berriassian – Valanginian). the region studied were formed in the North Tethys This complex is considerably eroded, it lies on the paleobasin. The main factor of this carbonate com- Paleozoic fundament and in the north - west of plex forming was reef-building processes taken place depression on the Middle Jurassic deposits, over- during Late Jurassic and Early Berriasian. There are lapped by the Aptian–Albian, Upper Cretaceous or determined seven types of sections formed in the dif- Miocene deposits. ferent zones of the paleobasin (fig. 2). They are cha- The sedimentation of these deposits took place racterized by the specific lithological and paleontologi- in northern periphery of Tethys by the influence of the cal composition as a result of different sedimentation © N.M. Zhabina, 2014 76 ЗБІРНИК НАУКОВИХ ПРАЦЬ ІНСТИТУТУ ГЕОЛОГІЧНИХ НАУК НАН УКРАЇНИ, ТОМ 7, 2014, 76-82 SEdImentary mOdEL OF THE UppER JURASSIC – Lower Cretaceous carbonate COmpLEx... Fig 1. Sedimentary model of the Upper Jurassic – Lower Cretaceous carbonate complex in the Ukrainian Precarpathians. 1 – 3 – Carpathian overthrusts; 4 – regional faults (kr – Krakowets, Gr – Gorodok, SV – Sudova Vyshnya, kl – Kalush, nd – Nad- virna, ks – Kosiv); 5 – drilling areas; 6 – wells, 7 – eastern boundary of Upper Jurassic sediments; 8 – 14 – types of section: 8 – fore-reef, 9 – reef, 10 – back-reef, 11 –transitional, 12 – lagoon, 13 – shallow-water, 14 – outlying. The Krakowets Fault is the western boundary of Upper Jurassic sediments. conditions and their changes in time. Fore-reef, reef tonic biota witness about that. Appearance of the and transitional types of section were opened by drill- planctonic foraminifers and tintinnids in Early Ox- ing only in the north - west of the Carpathian Fore- fordian were related to rising sea-level. At the Ox- deep. In the south-east they are overlapped by the fordian – Kimmeridgian boundary, at the end of Carpathians overtrusts. Early Tithonian and Late Tithonian, during Early I type of section (fore-reef) was opened by drill- Valanginian tintinnids associations were poor in ing in Karolina, Niklovichi, Volosha, Oselia, Grushiv, abundance and diversity because of the regressive Orchovichi, Rosiv, Morantci and other areas. These events. New genera of tintinnids appeared at Late deposits were formed in fore-reef zone in the west Kimmeridgian, Late Tithonian, during Berriassian of the reef belt. This section is composed of the correlating with the sea-level rise. Numerous ves- suites: Boniv (to 280 m thick), Morantci (to 300 m), tiges of siliceous sponges in the Lower Oxfordian Karolina (to 500 m). It is represented by the lime- microfacies and bentic foraminifers dominating in stones (micritic, oncoidal, bioclastic, and brec- associations with plantonic microfauna in higher ciated) interbedded with mudstones, siltstones, beds were related to sedimentation in the upper gravellites and breccias. These rocks often contain zone of open shelf on 50-100 m depth (maximum materials of the destruction of reef. Layers of the in Early Oxfordian). Extention of the fore-reef sec- silicified limestones were formed in transgressive tion to the east for 12 km in Oxfordian and for 5 km stages, the sandstones and shallow-water lime- during Kimmeridgian and Tithonian was a result of stones reflect the regressive events. This section the largest amplitude of sea-rise at Late Jurassic lies on the Middle Jurassic Javorov suite and over- beginning and result of the global regressive back- laped by the Miocene deposits. Thickness of fore- ground after that (Zhabina, Anikeyeva, 2003). reef section is to 1130 m, decreasing in some lots. II type of section (reef) was opened by drilling Sedimentation of these deposits took place in in Kochanivka, North Medenichi, Grushiv, Podiltci pelagic environments. Numerous vestiges of planc- and other areas. In the central part the section is COLLECTION OF SCIENTIFIC WORKS OF THE IGS NAS OF UKRAINE, VOL. 7, 2014, 76-82 77 78 ЗБІРНИК НАУКОВИХ ПРАЦЬ ІНСТИТУТУ ПРАЦЬ ЗБІРНИК НАУКОВИХ 76-82 ТОМ7,2014, НАУК ГЕОЛОГІЧНИХ НАНУКРАЇНИ, Fig. 2. Distribution of the Upper Jurassic – Lower Cretaceous types of section in the Ukrainian Precarpathians. 1 – 7 – types of section: 1 – fore-reef, 2 – reef, 3 – back-reef, 4 – transitional, 5 – lagoon, 6 – shallow-water, 7 – outlying. Suites: bn – Boniv (Oxfordian), mr – Moranci (Kimmeridgian); kri – Lower subsuite of Karolina suite (Tithonian – Lower Berriasian); krii – Upper subsuite of Karolina suite (Upper Ber- riassian – Lower Valanginian); rd – Rudki suite (Oxfordian); opi – Lower subsuite of Opary suite (Kimmeridgian); opii – Upper subsuite of Opary suite (Tithonian – Lower Berriasian); gr – Gorodok suite (Oxfordian), pd – Pidluby (Lower Kimmeridgian); nz – Nyzhniv (Upper Kimmeridgian – Lower Tithonian), bk – Bukivna (Upper Tithonian – Lower Berriasian), rri – Lower subsuite of Rava-Russka suite (Lower Kimmeridgian), rrii – Upper subsuite of Rava-Russka suite (Lower Kimmeridgian); st – Stavchany suite (Upper Berriassian – Valanginian). N. m . zHA b ina SEdImentary mOdEL OF THE UppER JURASSIC – Lower Cretaceous carbonate COmpLEx... composed of the Oxfordian bioherms (Rudki suite) Pidluby, Nemyriv, Rudky, North Medenichi and other and Kimmeridgian – Early Berriasian barrier reef areas. This section is determined at the place of (Opary suite). Oxfordian and Kimmeridgian reef de- substitute of the Oxfordian reef and back-reef fa- posits are replaced by the fore-reef Boniv and Mo- cies and the Lower Kimmeridgian back-reef and rantci suites in the western