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Interactive comment on Clim. Past Discuss., https://doi.org/10.5194/cp-2019-3, 2019.

Despite the abundance of Paleozoic epeiric sea carbonates and vast research on various aspects of their stratigraphy, sequence stratigraphic, chemostratigraphic and diagenetic studies of mixed carbonate-evaporite cratonic successions are relatively scarce. The Williston Basin of North America is a large interior cratonic basin underlying the great plains of North Dakota, South Dakota, Montana, Saskatchewan, and Manitoba. The Williston Basin province contains ten petroleum systems, with 13 conventional and six unconventional assessment units spanning the Upper Cambrian through Tertiary. During the Late Ordovician, oceanic communication with the Williston Basin was periodically limited, which during sea-level lows and under a tropical semi-arid climate resulted in the development of basin-central evaporitic units as parts of shallowing and brining-upward, anhydrite-bound sequences of the Red River Formation, the 2nd major conventional reservoir in the basin. Sequences record a change from semi-arid transgressive (TST) and early highstand (HST) to arid late highstand (HST) and lowstand systems tracts (LST). The small number of parasequences (3-15 per sequence) and their durations are suggestive of eccentricity and obliquity forcing, which is compatible with transitional eustasy during the Late Ordovician global cooling and further suggests the existence of moderate ice sheets and the onset of icehouse conditions in Late Ordovician. In the absence of ocean floor sediments, the epeiric sea carbonates are the major recorders of the Paleozoic global carbon cycle. However, the restricted circulation coupled with local (regional) environmental influences can result in geographic variations in C-isotope record, and possibly excursions that are unrelated to the pelagic surface ocean. Deep burial commonly results in multiple replacement episodes of metastable, early formed dolomite crystals by later, more stable phases. This also may reset the stable isotope signature of dolomite at progressively higher temperatures. Although deeply buried (up to 4.9 km), the Upper Ordovician dolomites of the Williston Basin, for the most part, exhibit no multiple events of post-depositional recrystallization, and both dolomite and limestone have similar carbon-isotope values, suggesting that carbon was rock buffered, and could be representing the original marine C-isotope record. This further suggests that the Upper Ordovician mixed carbonate-evaporite Red River Fm. of the Williston Basin provides a superb example of a large, periodically isolated evaporitic basin in which the carbon isotope signal has been greatly influenced primarily by local (regional) environmental conditions, and stabilized by later burial diagenesis, but without greatly resetting the original reflux dolomite petrography.

Karta prikazuje geološku građu, odnosno raspon iprostorni raspored, stratigrafske i tektonske odnose te temeljnu paleontologiju i petrologiju 11 litostratigrafskih jedinica geološke starosti od gornje jure do donje i dijela gornje krede te kvartar, cijelog otoka Mljeta. List je izrađen prema pisanom geološkom standardu (Upute za izradu Osnovne geološke karte Republike Hrvatske mjerila 1:50 000) u okviru projekta od strateškog nacionalnog interesa.

Ovaj list prikazuje geološku građu, odnosno prostorni raspored, stratigrafske i tektonske odnose te temeljnu paleontologiju i petrologiju 20 litostratigrafskih jedinica različite geološke starosti (kreda, paleogen i kvartar) otoka Hvara. List je izrađen prema pisanom geološkom standardu (Upute za izradu Osnovne geološke karte Republike Hrvatske mjerila 1:50 000) u okviru projekta od strateškog nacionalnog interesa.

Ovaj list prikazuje geološku građu, odnosno prostorni raspored, stratigrafske i tektonske odnose te temeljnu paleontologiju i petrologiju 22 litostratigrafske jedinice različite geološke starosti (kreda, paleogen, i kvartar) otoka Cresa i Lošinja. List je izrađen prema pisanom geološkom standardu (Upute za izradu Osnovne geološke karte Republike Hrvatske mjerila 1:50 000), u okviru projekta od strateškog nacionalnog interesa.

Ovaj list prikazuje geološku građu, odnosno prostorni raspored, stratigrafske i tektonske odnose te temeljnu paleontologiju i petrologiju 19 litostratigrafskih jedinica različite geološke starosti (kreda, paleogen, i kvartar) južnog dijela otoka Cresa i otok Lošinj. List je izrađen prema pisanom geološkom standardu (Upute za izradu Osnovne geološke karte Republike Hrvatske mjerila 1:50 000), u okviru projekta od strateškog nacionalnog interesa.

Ovaj list prikazuje geološku građu, odnosno prostorni raspored, stratigrafske i tektonske odnose te temeljnu paleontologiju i petrologiju 11 litostratigrafskih jedinica različite geološke starosti (kreda, paleogen i kvartar) zapadnog dijela otoka Hvara. List je izrađen prema pisanom geološkom standardu (Upute za izradu Osnovne geološke karte Republike Hrvatske mjerila 1:50 000) u okviru projekta od strateškog nacionalnog interesa.

A continuous, ∼350 m thick succession of cyclic, predominantly muddy upper Callovian-lower Kimmeridgian shallow-marine carbonates was logged in southern Croatia to define the sequence stratigraphy. The basal, late Callovian part contains three sequences (AdCal-x to AdCal-z) dominated by parasequences consisting of intraclast-skeletal-peloid packstone-grainstone capped by fenestral-laminated carbonates. The bulk of the Oxfordian (eight sequences: AdOx-1 to AdOx-8) and lower Kimmeridgian (AdKimm-1) is represented by low energy and muddy lithofacies. The parasequences consist of basal skeletal-microbial lump wackemudstone capped by barren lime mudstone. Lack of tidal flat facies caps to parasequences indicates incomplete shallowing to intertidal depths, and suggests that some parasequences are amalgamated. Given the duration of Oxfordian (∼8 m.y.), these likely represent third-order cycles with an average duration of ∼1 m.y. (suggestive of long-term obliquity forcing). The total number of Oxfordian parasequences (57, ∼100 k.y. duration) is suggestive of short-term eccentricity forcing. Samples for δ13C analysis were collected every meter from bulk carbonate matrix. The carbon-isotope values vary from −2.3 to +4.0‰ PDB, and show two significant isotope excursions in the Oxfordian The isotopic signature shows relatively constant values (0.8–1.8 ‰PDB) for the late Callovian, followed by a negative excursion to 0‰ at the beginning of Oxfordian, and a stepwise increase to 2.7‰. The subsequent negative excursion (-2.3‰) is followed by a stepwise increase to 3.8‰ in the middle of Oxfordian, slight decrease with values remaining between 1.5‰ and 3.3‰, and finally by a stepwise increase with a positive excursion to 4.1‰ in the late Oxfordian. Stepwise positive shifts in carbon-isotope values in the middle and late Oxfordian are both associated with shallowing upward parts of sequences AdOx-3 and AdOx-6, respectively. The remainder of the curve shows generally decreasing C-isotope values into the lower Kimmerdgian. The studied succession supports overall late Callovian cooling (marked by tidal flats) followed by mid-Oxfordian maximum flooding (widespread subtidal facies), with parasequence development suggestive of short-term eccentricity forcing and superimposed long-term obliquity forcing. It is interesting that the dominantly subtidal Oxfordian of the Adriatic platform corresponds to time of intrabasin source rock formation in the Middle East.

Carbonate Facies, Carbon Isotopes, Greenhouse, Aptian, Adritc Platform

Upper Callovian to Oxfordian Muddy Supersequence of Southern Adriatic Platform, Croatia

Sequence Stratigraphy and Oxygen-Carbon Isotope Signal from Albian Platform-Interior Carbonates, Southern Croatia

Early Paleozoic calcareous algae are potentially useful for stratigraphic correlation but remain under- utilized, 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-meters-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 intverval. The bryopsidalean genus Dimorphosiphon Høeg is abundant in algal wacke-packstone facies interpreted as, shallow subtidal deposits facies. One hundred and twenty-two individual Dimorphosiphon thalli were identified and studied in detail in randomly oriented thin sections ; these 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 component. 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 lLate 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.

Facies- and wireline log-based high-resolution subsurface sequence stratigraphy of the Late Ordovician Richmondian Red River "B" Interval, Williston Basin, North Dakota

Ovaj list prikazuje geološku građu, odnosno prostorni raspored, stratigrafske i tektonske odnose te temeljnu paleontologiju i petrologiju 21 litostratigrafske jedinice različite geološke starosti (trijas, kreda, paleogen, neogen i kvartar) na području šireg viškog arhipelaga. Ovo je prvi list OGK RH koji je izrađen prema pisanom geološkom standardu (Upute za izradu Osnovne geološke karte Republike Hrvatske mjerila 1:50 000), u okviru projekta od strateškog nacionalnog interesa, koji pokriva jednu geološko-geografsku cjelinu.

Sequence development influenced by intermittent cooling events in Aptian greenhouse, Adriatic Platform, Croatia

This study focuses on a 343-m-thick section of Upper Jurassic (Upper Calovian-Lower Kimmeridgean ; the bulk of the section is Oxfordian) shallow-marine limestone and lesser dolostone from Jasenice near Dubrovnik, Croatia. The section was logged bed-by-bed noting color, sedimentary structures, grain size, shape, sorting, constituents, and diagenetic overprints. The lower units in the section are characterized by small packages of cyclic subtidal to intertidal facies consisting of dolomite layers (some weakly laminated), peloidal skeletal wacke-packstone, packstone and grainstone, and capped by lime mudstone or burrowed laminite. Caps have fenestrae and rare scalloped contacts, indicative of subaerial exposure. The exposure contains some thrust faulting and associated breccia. Upsection, the facies become muddier and microbial lumps and burrows are more common. The transition into the Oxfordian is distinguished by thick packages of brown-colored lime mudstone, which alternates with coarse, thick to massive dolostone. The lime mudstones contain microbial lumps, shell fragments, and abundant nubeculariid foraminifera. Thin beds of lime wacke-mudstone and intermittent skeletal wackestone break up these larger beds. Both the lime mudstone and wacke-mudstone become barren for a span of almost 30 meters up-section. The presence of these thick mudstones suggests that the platform deposition slightly lagged accommodation due to sea level rise coupled with subsidence. The accommodation rate began to decrease or production rate began to increase in the later Oxfordian units indicated by an increase in microbial lumps, benthic foraminifera, and fragments of calcareous algae. The section extends into the basal Kimmeridgian, which is regionally identified by the appearance and abundance of calcareous alga Clypiena jurassica.

Magnetic susceptibility profiles as a tool for correlation: a case study from Upper Ordovician Red River Fm., North Dakota and Bighorn Dolomite, Wyoming