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Main geological events and relative sea-level oscillations recorded in the Late Jurassic to mid-Cretaceous shallow-water carbonates of the Mljet island, southern Croatia

During the work on the Geological Map of the Republicof Croatia several teams investigated Uppermost Albian - Cenomanian deposits in the area of Istria and the northern Adriatic islands, an area comprising part of the NW section of the large Mesozoic Adriatic Carbonate Platform (AdCP). This work represents a synthesis of the results achieved through several years of study. The investigated Uppermost Albian -Cenomanian carbonate sequences of the AdCP, the Albian deposits are similar -predominantly composed of thin-bedded alternating peritidal and/or lagoonal mud-and grain-supported lithotypes (skeletal- peloid wackestones/packstones, rarely grainstones). The transition from the Albian to the Cenomanian was characterized by formation of diverse environments in different parts of the investigated area.In southern Istria the Uppermost Albian and Lower Cenomanian deposits indicate evolution bioturbated carbonate sand bars and subaqueous dunes composed of rudist and chondrodont debris, and finally back to the shallow environments with rudist biostromes. The coeval succession of northern Istria records three different depositional settings: the western part indicates the continuation of peritidal deposition, in the central part large-scale foreshore-shoreface carbonate sand bodies developed, while the eastern part was characterized by a deeper lagoonal environment with rare tempestites and intercalations of kerogenous limestones. The Albian-Cenomanian transition in other parts of the study area is characterized by a thick sequence of late-diagenetic dolomites (with rare relics of peritidal early-diagenetic dolomite), some crystalline limestones and tectogenic-diagenetic breccia. A similar transition characterizes the larger part of the AdCP, and indicates very shallow depositional environments. In the NE part of the area investigated the aforementioned succession is overlain by peritidal cycles (Ćićarija, northern Cres), while in its SE part deepening tendencies were recorded (S Cres, NW Krk, Lošinj, Unije, Ilovik), resulting in partial platform drowning and deposition of micritic limestones with pithonellid calcispheres and globotruncanids, gradually thickening southwards (from 10 cm ->130 m). Different environments established in the NW part of the AdCP during the latest Albian and Early Cenomanian, were, in the late Middle Cenomanian, gradually replaced by uniform shallow-marine environments over the entire area, mostly characterized by shallowing-upward cycles. The Latest Cenomanian was characterized by the second important change in the palaeogeography of the studied area.A significant part was influenced by drowning -S Istria andĆićarija (NE Istria), and islands: southern Cres, Lošinj, Susak and Ilovik -as a reflection of the regionally important transgressive event near the Cenomanian-Turonian boundary. All the aforementioned areas are therefore characterized by prolonged deposition into the younger Late Cretaceous.In contrast, N Istria and the northern part of the island of Cres were completely emerged in the Late Cenomanian, and their palaeokarstified relief, in many places filled with bauxite deposits, was subsequently overlain by Lower Eocene Foraminiferal limestones.Hence, the insular area that existed in the central part of Istria from the Lower Cretaceous, or even latest Jurassic, Cenomanian.The transition is characterized by continuous shallow-water deposition (including only very rare and thin interbeds of pithonellid limestones), as the youngest Upper Cretaceous deposits. This facies variability described over a relatively small area of the NW part of the ACP clearly indicates palaeogeographical differentiation of the study area during the Latest Albian -Cenomanian.Despite some apparent evidence of eustatic sea-level were very active on this part of the AdCP during the entire Cretaceous.Generally, two events can be separated: (1)A transient Albian-Cenomanian event, resulting in the formation of laterally very different environments. During the late Middle Cenomanian these areas were gradually merged into a large area again characterized by uniform, typical shallow-marine carbonate deposition. (2)A latest Cenomanian event with the opposite tendencies: platform drowning and coeval emergence of some areas. The significant influence of the described synsedimentary tectonics was a consequence of the specific position of the study area near the NW margin of the ACP, and probably represented an introduction to subsequent events, when drifting of the Adria microplate towards the European continent resulted in significant deformation during the Palaeogene and Neogene - the formation of flysch troughs, major compression and the final uplift of the Dinaride mountain chain.

Dolina smrti

Palorbitolina lenticularis populations from NW of the Adriatic Carbonate Platform

Otok Mljet gotovo je u potpunosti izgrađen od mezozojskih karbonatnih naslaga istaloženih u vremenskom razdoblju nešto većem od 70 milijuna godina, odnosno od kimeridža do santona. Tijekom tog razdoblja, s izuzetkom perioda od mlađega gornjeg cenomana do starijega gornjeg santona za koji zbog rasjednog kontakta gornjocenomanskih i gornjosantonskih naslaga nema podataka, kontinuirano su taloženi plitkomorski vapnenci karbonatne platforme, koji su povremeno tijekom rane i kasne dijegeneze dolomitizirani. Mezozojske naslage otoka Mljeta litostratigrafski su klasificirane u devet neformalnih jedinica čija je relativna starost utvrđena i dokumentirana mikrofosilnim sadržajem, a okoliši taloženja i geneza detaljno su interpretirani. Po prvi je puta na istraživanom području dokazana prisutnost pojedinih usko provodnih mikrofosilnih oblika. Izdvojeno je ukupno 10 biozona koje su korelirane s odgovarajućim biozonama u širem Perijadranskom području. Istraživano je područje južnoga dijela Jadranske karbonatne platforme tijekom jure i krede bilo daleko od kopna, odnosno radilo se o izoliranoj platformi smještenoj na Adriji, koja je bila vrlo osjetljiva na klimatske i oceanografske promjene, uključujući i kolebanja morske razine. Rezultati istraživanja mljetskih naslaga, uzimajući u obzir i karbonatni razvoj susjednog poluotoka Pelješca te otoka Korčule i Lastova, upućuju na određene događaje (prijelaz iz jure u kredu, aptski događaji, prijelaz iz starije u mlađu kredu) u geodinamskoj evoluciji koji su od značenja ne samo za južni dio Jadranske platforme, već i za šire područje kako Jadranske, tako i susjedne Apulijske platforme. Diverzitet zajednice bentičkih foraminifera ovisio je o relativnim kolebanjima morske razine, pri čemu je bio najveći tijekom transgresivnih razdoblja i uspostavljanja HST-a. Temeljem analiza vertikalne i lateralne distribucije facijesa utvrđena je dinamika okoliša tijekom taloženja i konstruirana krivulja relativnih promjena morske razine na istraživanome području južnoga dijela Jadranske karbonatne platforme.

An assemblage of rudists, benthic foraminifera, and associated microfossils characterizes Upper Cretaceous peritidal carbonates on the island of Cres (northern Adriatic, Croatia), overlying the hemipelagic Cenomanian/Turonian limestones. The strata investigated are characterized by predominantly mud-rich well-bedded limestones with numerous Aeolisaccus and Thaumatoporella. Oligotypic character of the fossil association suggests deposition in shallow areas of the carbonate platform, with low-energy and restricted circulation. Contrary to the older mid-Cretaceous shallow-water limestones rich in rudists and benthic foraminifera, the Upper Cretaceous strata contain a low-diversity association. However, the association implies that following the hemipelagic conditions, which prevailed during sedimentation of the underlying deposits during the latest Cenomanian-Early Turonian within a wider area environment later again became favourable for population of larger foraminifera, and sporadically, rudists. Rudists (Mollusca, Hippuritacea) are the most frequent macrofossils within the strata investigated. Radiolitids (Radiolitidae) have been sporadically found both in autochthonous (in situ bouquets, clusters and small lens-like thickets) or para-autochthonous position (displaced locally in vicinity of their habitats). Besides poorly preserved radiolitids of minor biostratigraphical value, there are rare hippuritids (Hippuritidae), that have been commonly found in bouquets characterized by three to four conjoined specimens. Due to poor preservation of diagnostic shell features, only several forms that confer to four hippuritid species have been determined: Hippurites cf. incisus DOUVILLÉ, Hippurites cf. socialis DOUVILLÉ, Hippurites cf. toucasi D’ ORBIGNY (=Hippurites cf. praetoucasi TOUCAS) and Vaccinites cf. rousseli (DOUVILLÉ). The aforementioned Hippuri tes species have been frequently reported from Turonian to Santonian deposits of the (peri)Adriatic area. However, within the Croatian part of the area the genus Vaccinites has been reported exclusively from Santonian and stratigraphically younger deposits. This range is also incorporated into an important, recently published biochronostratigraphical review. Thus, this is the first report on the genus from Croatia, which in association with the afforementioned hippuritids imply Turonian to Coniacian age of the strata investigated. Furthermore, a few “ primitive” species of the genus have been previously reported from Turonian to Coniacian deposits of the wider area. Therefore, the defined biostratigraphic range of previously mentioned “ primitive” Vaccinites species from western Europe, is confirmed also within Periadriatic domain, and should be added to the chart. Microfossil association does not contain many stratigraphically relevant taxa as well. Moreover, the stratigraphic ranges of the only three “ index” species, which are very common in the Late Cretaceous of Croatia are still disputable. The least debate is on the first appearance of Moncharmontia apenninica DE CASTRO, which is Late Turonian. On the other hand, various authors gave very different data on the stratigraphic range of Scandonea samnitica DE CASTRO: Turonian to Early Campanian. Similar is the case with Pseudocyclammina sphaeroidea GENDROT, that is Turonian to Santonian. However, there is one additional clue to narrow the stratigraphic range of the examined sequence. Namely, the foraminifera (Dicyclina schlumbergeri MUNIER-CHALMAS, Accordiella conica FARINACCI, Keramospherina tergestina (STACHE), Scandonea mediterranea DE CASTRO, and Nummofalotia apula (LUPERTO SINNI)), that on the Adriatic Carbonate Platform appear in the Santonian, were not found in the study area. Therefore, based on the microfossil and macrofossil association, and knowing that underlying hemipelagic deposits are accurately attributed to the Cenomanian-Turonian boundary, the age of the investigated sequence is Turonian to (?)Coniacian.

Foraminiferal biostratigraphy and palaeoenvironments at the Jurassic/Cretaceous and Early/Late Cretaceous boundaries in the Adriatic region: the Mljet island, southern Croatia

Kanjon Bryce

Agglutinated foraminifera at the Lower/Upper Cretaceous boundary of Southern Croatia

Dolina spomenika - zemlja Navajo Indijanaca

America deserta (II.): Okamenjena šuma

America deserta: Grand Canyon

Sequoia - šumsko remek-djelo

U aptskim, albskim i cenomanskim vapnenačkim naslagama Cresa i Lošinja u bogatoj zajednici foraminifera, poglavito orbitolinida, na temelju determiniranih vrsta izdvojena su tri tipa biostratigrafskih jedinica: rasponska zona, zajednišna zona i množinska zona. Četiri izdvojene biozone značajno variraju u debljini i geografskom pružanju. Stratigrafski one obuhvaćaju raspon od donjega apta do srednjega cenomana.

Američki nacionalni park Yosemite.

Study of the stratigraphic distribution of the main benthic foraminifera on the islands of Cres and Lošinj (northern Adriatic) has allowed the identification of different orbitolinid zones, from the Lower Aptian (Palorbitolina lenticularis Taxon.range Zone) to the Middle Cenomanian (Orbitolina (Conicorbitolina) conica Abundance Zone).

U ovomu magistarskom radu predstavljen je dio rezultata biostratigrafskih istraživanja na otoku Cresu, i to u sklopu projekta Geološka karta Republike Hrvatske 1:50.000, zadatak Cres-Lošinj. Unutar aptskih, albskih i cenomanskih plitkomorskih vapnenaca utvrđena je iznimno bogata zajednica foraminifera s obiljem raznolikih formi orbitolinida. Zbog lateralnih i vertikalnih varijacija facijesa i debljina njihova je stratigrafska distribucija istražena na 8 prostorno udaljenih lokaliteta na otocima Cresu i Lošinju. Biostratigrafija, isključivo utemeljena na orbitolinidnim taksonima i njihovom kronostratigrafskom položaju, po prvi je puta uspostavljena za donjokredne naslage otoka Cresa. Izdvojene su 4 biozone: rasponska zona Palorbitolina lenticularis u donjemu aptu, zajednišna zona Orbitolina (Mesorbitolina) texana u donjemu albu, rasponska zona "Valdanchella" dercourti u bazalnom gornjemu albu i množinska zona Orbitolina (Conicorbitolina) conica u donjem i srednjem cenomanu. Biozone su uspoređene s odgovarajućim naslagama okolnih područja, pri čemu je naglasak stavljen na krški dio Dinarida te na širi prostor Sredozemlja. Utvrđeno je 5 rodova orbitolinida s ukupno 12 vrsta čije su morfološke značajke i arhitektura kućica detaljno opisani.

During the work on the Geological map of the Republic of Croatia (1:50.000 scale) it has been determined that Aptian and Albian shallow-water limestones on the Island of Cres (Northern Adriatic) contain a rather rich foraminiferal association, especially concerning the abundance and diversity of orbitolinid forms. Their stratigraphic distribution has been studied on three different localities due to the lateral and vertical facies and thickness variability in the study area. Biostratigraphy, exclusively based on the orbitolinid taxa and their chronostratigraphic position, is for the first time proposed for the Lower Cretaceous deposits on the Island of Cres. Three biozones have been established: Palorbitolina lenticularis Taxon-range Zone in the Lower Aptian, Orbitolina (M.) texana Assemblage Zone in the Uppermost Aptian to Lower Albian and "Valdanchella" dercourti Taxon-range Zone in the basal Upper Albian.

Spontaneous potential and resistivity log curves combined with dipmeter patterns have been used to identify environment of Gamma series deposition on northern part of Žutica oil/gas field. In this study, three principal shapes of spontaneous potential curve have been determined, i.e. cylinder, bell, and funnel, representing uniform deposition, fining upward sequence, and coarsening upward sequence, respectively. Various curve serrations are interpreted as consequence of interrupted sedimentation. Gamma series was subdivided into seven deposits (g6, g5, g4, g3, g2, gx, and g1) which denote either channel sedimentation characteristics or/and out of channel sedimentation characteristics. Deposits are irregularly distributed on the exploration area, and were deposited as individual depositional environments (bell, funnel, and simple spike SP-curves), and as joint depositional environments (cylindric SP-curves). Five characteristic sedimentation units have been established: deposits g1 to g6 as individual sedimentary units, deposits g2 to g6 as joint sedimentary units, deposits g5 and g6 as joint sedimentary units, deposits g4 and g5 as joint sedimentary units, and deposit g5. Three channelised sedimentary units transect the studied area, and predominant sedimentation occurred within them. They are major oil reservoirs in the area. Diplog patterns also reflect changes in depositional energy, but they show no sign of tectonic activity. Environment of Gamma series deposition is interpreted as shallow, brackish, delta plain with well developed distributary channels extending southeastwards. However, since there are many limitations of standard log measurements, a particular curve shapes may not necessarily denote specific units deposited in a unique environment.