Oliver Lehnert

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Geoscientist interested in many research topics and interdisciplinary work mainly dealing with Early Palaeozoic climate and ecosystem reconstructions including stable isotope studies, micropalaeontology, biofacies, microfacies analysis and sedimentology/basin analysis, palaeogeography, bio-, chemo-, and sequence stratigraphy. Other interests focus on impact geology and terrane analysis

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Papers by Oliver Lehnert

Ordovician reef and mound evolution: the Baltoscandian picture

Geological Magazine, Jun 8, 2016

Widespread growth of reefs formed by a framework of biogenic constructors and of frame-lacking ca... more Widespread growth of reefs formed by a framework of biogenic constructors and of frame-lacking carbonate mounds started on Baltica during the Ordovician. Previously, Ordovician reef and mound development on Baltica was considered to be sporadic and local. A review of all known bioherm localities across the Baltic Basin reveals a more consistent pattern. Ordovician bioherms grew in a wide E/W stretching belt across the Baltic Basin and occur in several places in Norway. Substantial reef development began simultaneously across the region during the late Sandbian / early Katian boundary interval and climaxed during the late Katian Pirgu Stage. The current spatiotemporal distribution of bioherms is a result of interdependent factors that involve original drivers of reef development, such as relative sea level, climate during the time of deposition, and effects of post-depositional erosion. Oceanographic conditions were likely more favorable during times of cooler global climates, low sea level and glacial episodes. At the same time, the likelihood that bioherms are preserved from long time erosion is higher when deposited during low sea level in deeper parts of the basin. A main factor controlling the timing of the reef and mound evolution was Baltica's shift toward palaeotropical latitudes during the Late Ordovician. The time equivalence between initial reef growth and the Guttenberg isotope carbon excursion (GICE) suggests that global climatic conditions were important. The long lasting stability, the resilience of individual mounds, and the increasing taxonomic diversity of the reefs/mounds suggest a significance of biological factors for the reef formation.

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The Hirnantian Isotope Carbon Excursion (Hice) in Southern Norway

GSA Annual Meeting in Seattle, Washington, USA - 2017, 2017

Thermal maturity of Cambrian to Devonian rocks of northeastern Ellesmere Island

ABSTRACT

Accretionary Mechanisms and Temporal Sequence of Formation of the Boda Limestone Mud-Mounds (Upper Ordovician), Siljan District, Sweden

Journal of Sedimentary Research, Apr 1, 2016

Late Ordovician mud-mounds in the Boda Limestone, Siljan area, central Sweden, consist mainly of ... more Late Ordovician mud-mounds in the Boda Limestone, Siljan area, central Sweden, consist mainly of massive spiculitic stromatactis limestone similar to other well-known Paleozoic mud-mounds. The mound cores are predominantly formed by spiculite and ostracod-rich mudstone and/or wackestone, and networks of spar-filled syndepositional cavities. The mounds of the Boda Limestone are specific in two ways: (1) large parts of the lower mound cores are formed by a Palaeoporella framestone and/or bafflestone with signs of early recrystallization and cementation; and (2) the stromatactis facies is accompanied by masses of limestone with non-stromatactis cryptocrystalline patches. Cryptocrystalline patches are filled with massive, fibrous low-Mg calcite, have cloudy, transitional margins, contain randomly spaced skeletal grains and dolomitic micro-inclusions, and are interpreted as recrystallized patches of the original host lime mud. Models of formation of Paleozoic mud-mounds generally hypothesize accretionary processes that are based on sponge biomass degradation and associated diagenetic processes. In the Boda Limestone Palaeoporella skeleton disintegration, early recrystallization, and additionally, cementation were essential for the mound formation. The Boda mounds exemplify that formation of Paleozoic mud-mounds reflects a spectrum of different essentially diagenetic accretionary mechanisms. This diversity should be taken into account in future discussions about Paleozoic mud-mound formation. The new name Osmundsberget Formation is given for a Hirnantian succession of brachiopod-rich limestone above the Boda Limestone. The Osmundsberget Formation occurs only in direct geographical vicinity to the mud-mounds. TABLE 1.-List of localities mentioned in text with coordinates and selected references. Outcrop Locality Coordinates (uN, uE) Selected References

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High-resolution carbon isotope stratigraphy of the Lower and Middle Ordovician succession of the Yangtze Platform, China

Estonian Journal of Earth Sciences, 2023

Variation in the relative abundance of the stable carbon isotopes has been widely used to correla... more Variation in the relative abundance of the stable carbon isotopes has been widely used to correlate Ordovician marine successions over the past two decades. To date, only a few of studies of Ordovician carbon chemostratigraphy have been conducted in South China. Most of the previous studies in this field have focused on specific time intervals and/or events in the Middle and Upper Ordovician. The Lower and Middle Ordovician of the Yangtze Platform is typically represented by a sedimentary succession dominated by carbonate rocks, which is ideal for studying the carbon chemostratigraphy. Three sections spanning the Nantsinkuan/Lunshan, Fenhsiang, Hunghuayuan, and Dawan/Zitai formations, corresponding to the Tremadocian-Dapingian in age, have been sampled for high-resolution δ 13 C chemostratigraphy. Our new δ 13 C data reveal five tie-points with the potential for global correlation: (1) a positive δ 13 C excursion in the lower Nantsinkuan Formation within the Tremadocian Rossodus manitouensis Zone; (2) an excursion with two peaks roughly within the late Tremadocian Paltodus 'deltifer' Zone; (3) a positive δ 13 C shift in the lower Hunghuayuan Formation, within the early Floian Serratognathus diversus Zone; (4) a gradual positive δ 13 C shift in the late Floian, ranging from the uppermost S. diversus Zone to the basal Oepikodus evae Zone; (5) a minor negative shift in the lower Dawan/Zitai Formation, within the early Dapingian Baltoniodus triangularis Zone. These excursions are herein used for correlation of the Yangtze Platform strata with successions from South China, North China, the Argentine Precordillera, North America and Baltica. From a palaeogeographical perspective, the Gudongkou, Xiangshuidong and Daling sections represent depositional environments along an inner to outer ramp profile. The δ 13 C data from these sections show successively heavier (higher) δ 13 C values with increasing depositional depth, which can be interpreted as due to remineralization of organic carbon within the carbonate rocks formed in the shallow-water environment.

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Detrital zircon geochronology of Lower Paleozoic sedimentary rocks from COSC-2 borehole

The Caledonian Orogeny in the Scandinavian Caledonides (COSC) project aims to investigate the oro... more The Caledonian Orogeny in the Scandinavian Caledonides (COSC) project aims to investigate the orogenic processes involving Caledonian allochthons together with the underlying sedimentary cover and Proterozoic igneous basement. The basement comprises Transscandinavian Igneous Belt (TIB) rocks with Hallandian and Central Scandinavian Dolerite Group intrusions and is overlain by a regolith (sub-Cambrian peneplain?). A Lower Cambrian(?) sedimentary succession of conglomerate, carbonate and shale covers this immature soil, followed by coarse-grained gravity flows fining upwards and showing a transition into the Alum Shale Formation. The undisturbed middle part of the formation separates the lower sedimentary cover from its overlying turbiditic part and the Lower Ordovician(?) turbidite sequence fining up to the top of the COSC-2 core.First results of detrital zircon geochronology from the Cambrian succession show that the basal section of the autochthonous cover is characterized by mainly late Paleoproterozoic (c. 45% of all grains) – early Mesoproterozoic (c. 52%) detrital grains with age signatures of c. 1.77 Ga, 1.66 Ga and 1.44 Ga and a subordinate 1.25 Ga age peak. The middle part of the succession is dominated by late Paleoproterozoic detritus (c. 62% of all grains) with minor Mesoproterozoic (c. 21%) and Archean (c. 11%) input. The main age signatures are c. 1.80 Ga and 1.90 Ga with subordinate age peaks at c. 2.72 Ga, 2.00 Ga, 1.16 Ga. The upper part of Lower Cambrian(?) succession is characterized by Archean to Cambrian detritus. Archean grains constitute 12% of grains with dominant age signature at c. 2.67 Ga. Paleoproterozoic grains (25%) are grouped in 2.15-1.65 Ga interval with peaks at c. 2.12 Ga, 1.80 Ga, 1.76 Ga and 1.67 Ga. The Mesoproterozoic population (41%) is characterized by major age peaks at c. 1.55 Ga and 1.20 Ga. Neoproterozoic – Cambrian group (17%) contains major populations at c. 0.60 Ga and 0.53 Ga and a significant peak at c. 0.72 Ga. The maximum depositional age calculated via the maximum likelihood age algorithm yielded 530.5±4 Ma for the upper part of the Lower Cambrian succession. Two samples from the Ordovician succession show Mesoproterozoic – Neoproterozoic sources (c. 75% of grains), with more than 38% of grains yielding late Mesoproterozoic – early Neoproterozoic (1.2-0.9 Ga) ages. The dominant population of c. 1.06-1.02 Ga is accompanied by c. 1.50-1.47 Ga, 1.15 Ga and 0.99-0.97 Ga age peaks.The autochthonous Lower to Lower Middle Cambrian passive margin succession in the lower part is dominated by local detritus provided solely from the Eastern Segment of Sveconorwegian Orogen (including the basement investigated by the COSC-2). The provenance shifts up the profile towards TIB-1 and Svecofennian Orogen sources, with the youngest part of the succession characterized by an input of Timanian Orogen detritus, including the uplifted Karelian protocraton. The Ordovician succession is characterized by Meso-Neoproterozoic age populations most likely sourced from the Sveconorwegian Orogen with a minor cratonic contribution. The youngest detritus is early Neoproterozoic, suggesting a passive margin setting with no early Caledonian input present.This work was funded by the National Science Centre (Poland) projects no. 2019/33/B/ST10/01728 and 2018/29/B/ST10/02315.

Did intense volcanism trigger the first Late Ordovician icehouse? REPLY

Geology, May 1, 2011

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Investigation of an Ordovician carbonate mound beneath Gotland, Sweden, using 3D seismic and well data

Journal of Applied Geophysics, Mar 1, 2019

The Swedish island of Gotland is located within the Baltic Basin. During the Late Ordovician the ... more The Swedish island of Gotland is located within the Baltic Basin. During the Late Ordovician the region around Gotland was part of a shallow epicratonic basin in the southern subtropics. In these warm-water environments algae flourished, diverse reefs developed close to the coastline and further outboard carbonate mounds developed. These mounds formed rigid high relief structures surrounded by fine-grained siliciclastics and marls and can be detected on seismic images as isolated concave upwards features. The sedimentary succession beneath Gotland was intensely investigated in the 1970s and 1980s for its hydrocarbon potential, and subsequently, oil was commercially produced from reservoirs within Ordovician mounds. In 1981, a 3D seismic survey was conducted by Horizon Exploration Ltd over the Fardume mound on northern Gotland. To date no results from these 3D data have been published in scientific literature. The region of Gotland aims to produce 100 % of its energy from renewable sources and currently the majority of Gotland's energy is provided by wind turbines. Due to the intermittent nature of wind power, one solution to regulate the supply of electricity from wind energy is Compressed Air Energy Storage (CAES).

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Concurrent sedimentary and isotopic indications for global climatic cooling in the Late Silurian

Early Ordovician and Devonian Conodonts from the Western Karakoram and Hindu Kush, Northernmost Pakistan

DOAJ (DOAJ: Directory of Open Access Journals), Jul 1, 1999

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Conodont biostratigraphy and carbon isotope stratigraphy of the Middle Ordovician (Darriwilian) Komstad Limestone, southern Sweden

GFF, Jan 2, 2018

The Komstad Limestone forms a distal part of the widespread 'orthoceratite limestone' of the Balt... more The Komstad Limestone forms a distal part of the widespread 'orthoceratite limestone' of the Baltoscandian continent. In this paper, we present an integrated conodont biostratigraphy and carbon isotope stratigraphy for a major part of this formation and address its significance for evaluating Middle Ordovician correlation and overall stratigraphy. Four conodont zones are distinguished, including the Lenodus antivariabilis Zone, Lenodus variabilis Zone, the Yangtzeplacognathus crassus Zone, and the Eoplacognathus pseudoplanus Zone. Carbon isotopes have previously not been published from the Komstad Limestone. The data herein show that carbonate strata may retain a comprehensive pristine δ 13 C signal despite relatively strong thermal influence during diagenesis (Conodont Color Alteration Index 4-5).

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High-resolution carbon isotope stratigraphy of the Lower and Middle Ordovician succession of the Yangtze Platform, China: implications for global correlation

Journal of the Geological Society, Feb 4, 2020

The Lower and Middle Ordovician of the Yangtze Platform, China, is characterized by a sedimentary... more The Lower and Middle Ordovician of the Yangtze Platform, China, is characterized by a sedimentary succession dominated by carbonate rocks. Three sections spanning the Nantsinkuan/Lunshan, Fenhsiang, Hunghuayuan, and Dawan/Zitai formations, corresponding to the Tremadocian–Dapingian in age, have been sampled for high-resolution δ13C chemostratigraphy (542 samples in total). Our new δ13C data reveal five tie-points with the potential for global correlation: (1) a positive δ13C excursion in the lower Nantsinkuan Formation within the Tremadocian Rossodus manitouensis Zone; (2) an excursion with two peaks roughly within the late Tremadocian Paltodus ‘deltifer’ Zone; (3) a positive δ13C shift in the lower Hunghuayuan Formation, within the early Floian Serratognathus diversus Zone; (4) a gradual positive δ13C shift in the late Floian, ranging from the uppermost S. diversus Zone to the basal Oepikodus evae Zone; (5) a minor negative shift in the lower Dawan/Zitai Formation, within the early Dapingian Baltoniodus triangularis Zone. These excursions are herein used for correlation of the Yangtze Platform strata with successions from South China, North China, the Argentine Precordillera, North America and Baltica. From a palaeogeographical perspective the Gudongkou, Xiangshuidong and Daling sections represent depositional environments along an inner to outer ramp profile. δ13C data from these sections show successively heavier (higher) δ13C values with increasing depositional depth. This is interpreted as due to remineralization of organic carbon within the carbonate rocks. Supplementary material: Carbon and oxygen isotope data are available at: https://doi.org/10.6084/m9.figshare.c.4767080

The first continuous δ13C record across the Late Silurian Lau Event on Gotland, Sweden

GFF, Sep 21, 2016

Abstract The positive δ13C excursion associated with the Late Silurian Lau Event is recognized gl... more Abstract The positive δ13C excursion associated with the Late Silurian Lau Event is recognized globally and is the most prominent carbon isotope excursion of the Phanerozoic. We present new δ13C data (195 samples) and the first continuous carbon isotope stratigraphy across the stratigraphic range of this bioevent based on two drill cores from Gotland, the informal type area for the Lau Event. The positive δ13C anomaly reaches a peak value of 9.01‰ in an interval correlated to the Icriodontid conodont Zone in the upper Eke Formation, an interval with generally impoverished fauna and strongly dominated by one single conodont species, Panderodus equicostatus, and a mass-occurrence of oncoids. The distinct morphology of this Late Ludfordian Carbon Isotope Excursion, including a well-defined rising limb, a plateau and a falling limb can be used for intercontinental correlation of the strata.

Cambro-Ordovician sponge spicule assemblages in the Ordovician of the Argentine Precordillera and paleoenvironmental ties

Neues Jahrbuch für Geologie und Paläontologie, Jun 9, 1997

STIPTOGNATHUSNEW GENUS (CONODONTA: IBEXIAN, LOWER ORDOVICIAN), AND THE APPARATUS OFSTIPTOGNATHUS BOREALIS(REPETSKI, 1982)

Journal of Paleontology, 2000

ABSTRACT

Integrated conodont biostratigraphy and carbon isotope chemostratigraphy in the Lower–Middle Ordovician of southern Sweden reveals a complete record of the MDICE

Geological Magazine, Feb 22, 2016

One of the few and most complete records of the MDICE (Middle Darriwilian Isotope Carbon Excursio... more One of the few and most complete records of the MDICE (Middle Darriwilian Isotope Carbon Excursion) is herein documented from Baltoscandia. Based on a core section penetrating the condensed Lower–Middle Ordovician succession (~46 m) on the island of Öland, southeastern Sweden, we provide an integrated scheme for carbon isotope chemostratigraphy (313 samples) and conodont biostratigraphy (29 samples) for this period. The carbonate succession in the Tingskullen core records 12 conodont zones and 6 subzones, including theOepikodus evae, Trapezognathus diprion, Baltoniodus triangularis, B. navis, B. norrlandicus, Lenodus antivariabilis, L. variabilis, Yangtzeplacognathus crassus, Eoplacognathus pseudoplanus(Microzarkodina hagetianaandMicrozarkodina ozarkodellasubzones),E. suecicus, Pygodus serra(E. foliaceus, E. reclinatus, E. robustusandE. lindstroemisubzones) andPygodus anserinuszones in ascending order. The δ13Ccarbrecord reveals an apparently complete record of the MDICE, including a rising limb, a well-defined peak and a falling limb. The anomaly covers a thickness ofc. 27 m in the core and spans theEoplacognathus pseudoplanus, E. suecicus, Pygodus serraandP. anserinusconodont zones. Combined with the new, detailed conodont biostratigraphy, the MDICE in the Tingskullen core can be used for detailed correlation with successions from Baltica, North America, the Argentine Precordillera, South China and North China.

Miaolingian (Cambrian) trilobite biostratigraphy and carbon isotope chemostratigraphy in the Tingskullen drill core, Öland, Sweden

Estonian Journal of Earth Sciences, 2021

The Cambrian succession of the Tingskullen drill core from northern Öland comprises Cambrian Seri... more The Cambrian succession of the Tingskullen drill core from northern Öland comprises Cambrian Series 2 and Miaolingian (Wuliuan Stage) siliciclastic strata. The major portion of the succession is represented by the Miaolingian Borgholm Formation, which, in ascending order, is subdivided into the Mossberga, Bårstad and Äleklinta members. The Äleklinta Member is barren of body fossils, whereas the Mossberga and Bårstad members are moderately to highly fossiliferous and biostratigraphically reasonably well constrained. Trilobites and agnostoids from the Bårstad Member are indicative of the Acadoparadoxides pinus Zone. The Mossberga Member has not yielded any zonal guide fossils but is tentatively assigned to the Eccaparadoxides insularis Zone. A δ 13 C org curve throughout the Borgholm Formation shows a general positive trend upsection without any distinctive excursion, suggesting that the Wuliuan Acadoparadoxides (Baltoparadoxides) oelandicus Superzone (the 'Oelandicus beds') of Öland is younger than the negative Redlichiid-Olenellid Extinction Carbon isotope Excursion (ROECE), which is known from near the top of Stage 4 and close to the traditional 'Lower-Middle Cambrian boundary' in several parts of the world.

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Age, facies, and geometry of the Sandbian/Katian (Upper Ordovician) pelmatozoan-bryozoan-receptaculitid reefs of the Vasalemma Formation, northern Estonia

Facies, Jul 31, 2014

The Vasalemma Formation (early Katian, Late Ordovician) of northern Estonia consists of a success... more The Vasalemma Formation (early Katian, Late Ordovician) of northern Estonia consists of a succession of biodetrital grainstones up to 15 m thick with numerous intercalated reef bodies, which reach diameters of more than 50 m. Four dominant facies types are distinguished within the reef core limestones: (1) a bryozoan framestone-bindstone, (2) an echinoderm bindstone, (3) a receptaculitidbryozoan-microbial framestone, and (4) a tabulate bafflestone. A linking theme between the different reef-core limestones is the presence of clotted microbial bindstone, which in some places contains spicules. Except for the tabulate bafflestone, all facies types occur in the youngest and oldest intervals of reef growth. Generally, a tendency can be observed with a dominance of echinoderm framestone low in the formation and at the base of individual reefs, towards a more receptaculitid dominated facies at the top of the formation. The reefs developed in a narrow, ca. 20-km-long and max. 5-km-wide band on a shallow NE-SW-directed platform in the central part of the North Estonian Confacies Belt. Reef growth can be constrained toward the latest Keila age, representing the rising limb and the peak interval of the Guttenberg Isotopic Carbon Excursion (GICE). Reef termination falls within a second-order sea-level lowstand, the Frognerkilen Lowstand Event, which led to partial subaerial exposure of the reefs. The dead reefs subsequently and rapidly drowned during the Nakkholm Drowning Event at the Oandu/Rakvere Stage. This timing is nearly equivalent to a phase of enhanced reef development elsewhere in Baltica and probably is related to locally increased nutrient availability during the GICE interval.

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Stiptognathus new genus (Conodonta: Ibexian, Lower Ordovician), and the apparatus of Stiptognathus borealis (Repetski, 1982)

Journal of Paleontology, 2000

Collections from upper Ibexian (Tulean Stage) rocks of western United States, from the Canning Ba... more Collections from upper Ibexian (Tulean Stage) rocks of western United States, from the Canning Basin in western Australia, and from the Argentine Precordillera contain a seximembrate apparatus of multidenticulate conodonts whose elements have been included by authors in species ofPrioniodusPander, 1986, andReutterodusSerpagli, 1974. The individual elements as well as the complete apparatus are not consistent with assignment of the species to either of these genera or to any other extant genus. A new generic name,StiptognathusEthington, Lehnert, and Repetski, is proposed withReutterodus borealisRepetski, 1982, as type species. The apparatus consists of Pa, Pb, Sa-c, and M elements; the genus represents either the Prioniodontidae or the Periodontidae.

Sedimentology of middle ordovician carbonates in the Argentine precordillera: evidence of regional relative sea-level changes

Geologische Rundschau (1910. Print), Jul 1, 1993

The Las Aguaditas Formation in the Argentine Precordillera of San Juan is the only Ordovician car... more The Las Aguaditas Formation in the Argentine Precordillera of San Juan is the only Ordovician carbonate sequence deposited on a slope. Spiculites, mudstones and calcisiltites represent the autochthonous sediments, characterized by a fine lamination, rare fossils and their dark colour. The pelagic fauna consists of rare radiolarians/calcispheres, trinucleid trilobites, graptolites and conodonts. The latter are typical of an open marine

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