Antun Husinec

Cenomanian carbonate facies and rudists along shallow intraplatform basin margin-the island of Cres (Adriatic Sea, Croatia)

SummaryThe island of Cres is located in the northern part of the Adriatic Sea. The island is built up of predominantly Cretaceous carbonates deposited in north-western part of extensive and long-lasting Adriatic Carbonate Platform. Owing to the influence of synsedimentary tectonics supported by eustatic changes during the latest Albian/Early Cenomanian, different sedimentary environments were established: from shallow intraplatform basin and related slope, across basin margin to protected shallow-platform. During the Early to Middle Cenomanian rudist communities (ichthyosarcolitid/caprinid/radiolitid)flourished along a relatively high-energy intraplatform basin margin. Fair amounts of coarse-grained bioclasts, derived almost exclusively from broken rudist shells, were deposited over a marginal depocenter. Contemporaneously, pithonellid wackestone-packstones containing microbioclasts and planktonic foraminifera were deposited basinward while marginal bioclastic sediments and limestone blocks of the basin margin origin were sporadically deposited within the basin. The opening of the Cres intraplatform basin was aborted and the basin was finally filled up during the Late Cenomanian. Since the Cres intraplatform basin was established at the beginning of the Cenomanian it probably represented the initiation phase in the north-western extension of the later Adriatic Trough development.

Sequence development influenced by intermittent cooling events in the Cretaceous Aptian greenhouse, Adriatic platform, Croatia

Depositional sequences capped by peritidal carbonates and breccias on the Aptian Adriatic carbonate platform, Croatia, were studied to evaluate evidence for glacioeustasy within an age framework constrained by carbon-isotope chemostratigraphy. Sequence Ad1 (17–60-m [56–197-ft] thick; uppermost Barremian–lower Aptian) is dominated by shallow subtidal parasequences. Sequence Ad2 (7–13-m [23–43-ft] thick; lower Aptian–lowermost upper Aptian) contains oceanic anoxic event (OAE) 1a, associated with lagoonal laminated carbonates. Sequence Ad3 (3–8-m [10–26-ft] thick) probably is lower upper Aptian and likely is separated by a major hiatus from sequence Ad4 (8–20-m [26–66-ft] thick; uppermost Aptian), which spans OAE1b. Both Ad2 and Ad3 are dominated by peritidal parasequences updip in the lower transgressive systems tract and upper highstand systems tract and by subtidal parasequences elsewhere, whereas sequence Ad4 is dominated by shallow subtidal parasequences. Low accommodation rates (4.0–6.0 cm [1.6–2.4 in.] in the earliest Aptian, decreasing to approximately 1.0 cm/k.y. [0.3 in./k.y.] later) promoted widespread breccia development during relative sea level falls, aided by tectonic warping. The sequence-capping breccias, eccentricity-dominated cyclicity, restriction of peritidal facies to late highstands, and coeval off-shelf oxygen-isotope records all suggest that sea level falls occurred during times of cooling and had a significant glacioeustatic component. These intermittent cooler periods and continental ice buildup punctuated the Aptian greenhouse climate.

Transgressive oversized radial ooid facies in the Late Jurassic Adriatic Platform interior: Low-energy precipitates from highly supersaturated hypersaline waters

Dark-gray oolitic units characterized by oversized ooids with primary radial calcite fabrics occur in the interior of the Late Jurassic Late Tithonian, Adriatic Platform, a large Mesozoic, Tethyan isolated platform in Croatia. They differ from open-marine, platform-margin ooid grainstones in their dark color, cerebroid outlines, broken and recoated grains, abundant inclusions, highly restricted biota, and lack of cross-stratifiThey have been interpreted as being of vadose origin (“vadoids”) at tops of upward-shallowing parasequences. However, detailed sections show that most oolitic units occur at bases of precessional parasequences, overlying erosional surfaces on fenestral carbonates. The oolitic units are similar to quiet-water ooids that form today in low-energy settings. They developed in an arid climate during initial transgression of supratidal fl ats, along lowenergy shores seaward of tidal fl ats, and along the margins of restricted lagoons and intertidal ponds. Superimposed fenestral fabrics, meniscus micrite cements, and grain breakage occurred as they aggraded to high-tide level and were subjected to wetting and drying, thermal expansion and contraction, and wind transport. They migrated landward with transgression, forming extensive sheets, and were overlain by subtidal lagoonal facies that shallow up into fenestral carbonates. These distinctive facies may have been overlooked in the geological record, or their geological distribution requires juxtaposition of calcite seas, high-calcite supersaturation states, arid climate, and presence of fl at-topped carbonate platforms in a greenhouse world.

Biostratigraphy of Turonian to (?)Coniacian Platform Carbonates: A Case Study from the Island of Cres (Northern Adriatic, Croatia)

The shallow marine carbonate deposits on the island of Cres, overlying deeper-water Cenomanian–Turonian limestones, are characterized by an assemblage of rudists, benthic foraminifera, and associated microfossils. The paucispecific character of the fossil association suggests deposition in shallow areas of a carbonate platform, with low current-energies and restricted circulation. Similar assemblages indicating similar palaeoenvironments, are common in the Upper Cretaceous deposits of the Adriatic Carbonate Platform and adjacent areas. The assemblage of rudists (hippuritids) and microfossils indicate the Turonian to (?)Coniacian age of the investigated carbonate succession. The biostratigraphic importance of the so-called “primitive” hippuritids within the micropalaeontologically poorly defined biostratigraphy of deposits of this age, is accentuated.

FISCHERPLOTS: An Excel spreadsheet for computing Fischer plots of accommodation change in cyclic carbonate successions in both the time and depth domains

Fischer plots are plots of accommodation (derived by calculating cumulative departure from mean cycle thickness) versus cycle number or stratigraphic distance (proxies for time), for cyclic carbonate platforms. Although many workers have derived programs to do this, there are currently no published, easily accessible programs that utilize Excel. In this paper, we present an Excel-based spreadsheet program for Fischer plots, illustrate how the data are input, and how the resulting plots may be interpreted. The plots can be used to derive periods of increased accommodation, shown on the plots as a rising limb (which commonly matches times of more open marine, subtidal parasequence development). Times of decreased accommodation, shown on the plots as a falling limb, generally are coincident with thin, shallow, peritidal parasequences.

Importance of Dimorphosiphon (Chlorophyta, Bryopsidales) for Facies and Paleobiogeographic Studies of the Upper Ordovician Richmondian Red River Formation, Williston Basin

ABSTRACT Early Paleozoic calcareous algae are potentially useful for stratigraphic correlation but remain underutilized, likely due to presence of graptolites, conodonts, brachiopods, and other fossils that are commonly used in high-resolution biostratigraphy. This study focuses on the siphonous green algae within a 2-to-24-m-thick B interval of the Red River Formation, North Dakota, where the abundance of green algae suggests an important paleoenvironmental control; the algae also had a major role in carbonate production during that narrow stratigraphic interval. The bryopsidalean genus Dimorphosiphon Høeg is abundant in algal wacke-packstone facies interpreted as shallow subtidal deposits. One hundred and twenty-two individual Dimorphosiphon thalli were identified and studied in detail in randomly oriented thin sections; measurements indicate that Williston Basin specimens belong to the species D. talbotorum Boyd, previously reported exclusively from the Bighorn Mountains, Wyoming. Dimorphosiphon is found in Upper Ordovician low-latitude, warm-water shelf carbonates of Kazakhstania, Baltica, and Laurentia; commonly, it is a major component of sediment. Several species of Dimorphosiphon appeared simultaneously in different and remote parts of the Paleotethys and Iapetus Oceans, suggesting a geologically instantaneous dispersal of the genus. Dimorphosiphon talbotorum, the focus of this study, has only been reported from western North America where it occurs within strata corresponding to the upper Katian Aphelognathus divergens Subzone of the Aphelognathus ordovicicus conodont Zone. Given its abundance, ease of identification, and short stratigraphic range, D. talbotorum potentially is very useful for regional correlation, facies, and paleobiogeographic studies of Upper Ordovician Richmondian shallow-marine strata of western North America.

Siphodinarella costata n. gen., n. sp., a new benthic foraminifer from the Coniacian of the Adriatic Carbonate Platform (Slovenia, Croatia)

A new benthic foraminifer is described as Siphodinarellacostata n. gen., n. sp. from Coniacian shallow-water platform-interior carbonates of Slovenia and Croatia. The new foraminifer is found in skeletal wackestone in association with small benthic foraminifera, thaumatoporellaceans, and calcimicrobes (Decastronema, Girvanella-type tubes). The existence of an internal siphon in Siphodinarella n. gen. is interpreted as an entosolenian tube and discussed in terms of its generic and suprageneric importance.

Clypeina lagustensis n.sp., a new calcareous alga from the Lower Tithonian of the Lastovo Island (Croatia)

Clypeina lagustensis n.sp. has been found in the Lower Tithonian deposits of the Lastovo Island (Dalmatia, Croatia). It is visually similar, obviously related and in some sections appearing almost identical, to Clypeina jurassica FAVRE, from which it differs by visible swellings and thinning of the central cavity, more pronounced distance between neighbouring whorls of fertile branches, and shape and structure of the interverticillate thallus parts, characterized by having well developed, hairy, sterile branches. These, after emerging from the exit pore, divide into several bundles which form a common turf with a calcareous envelope in the proximal part. Normal 0 21 false false false HR X-NONE X-NONE