Strontium isotope composition of sedimentary rocks and its application to chemostratigraphy and palaeoenvironmental reconstructions

Strontium isotope composition of seawater is homogenous in all oceans and marginal seas but has  varied  through  time  with  changing  strontium  fluxes.  Strontium  isotope  ratio  of  ancient  seawater  may  be  reconstructed  from  well-preserved  authigenic  minerals  and  used  for  dating  marine  sediments.  Because of a change in the strontium isotope ratio between sea- and freshwaters it can also be employed for the determination of palaeosalinities or the reconstruction of diagenetic processes of marine limestones.  A  review  of  methodology  and  practical  hints  concerning  the  utilization  of  strontium  isotopes  in  geological  studies  of  both  marine  and  brackish  sediments  are  presented  in  the  current  article

Clumped isotope record of salinity variations in the Subboreal Province at the Middle–Late Jurassic transition

Results of clumped isotope, oxygen isotope and elemental (Mg/Ca, Sr/Ca) analyses of exceptionally well-preserved belemnite rostra and ammonite shells from the uppermost Callovian–Upper Kimmeridgian (Lamberti–Mutabilis zones) of the Russian Platform are presented. Despite a significant decrease in belemnite δ18O values across the Upper Oxfordian–Lower Kimmeridgian, the clumped isotope data show a constant seawater temperature (ca. 16 °C) in the studied interval. The decrease in belemnite δ18O values and lower δ18O values measured from ammonite shells are interpreted as a result of the salinity decline of the Middle Russian Sea of ca. 12‰, and salinity stratification of the water column, respectively. The postulated secular palaeoenvironmental changes are linked to the inflow of subtropical, saline waters from the Tethys Ocean during a sea-level highstand at the Middle–Late Jurassic transition, and progressive isolation and freshening of the Middle Russian Sea during the Late Oxfordian–Kimmeridgian. The obtained clumped isotope data demonstrate relative stability of the Late Jurassic climate and a paramount effect of local palaeoceanographic conditions on carbonate δ18O record of shallow epeiric seas belonging to the Subboreal Province. Variations in Mg/Ca and Sr/Ca ratios of cylindroteuthid belemnite rostra, which are regarded by some authors as temperature proxies, are, in turn, interpreted to be primarily dependent on global changes in seawater chemistry. The paleoenvironmental variations deduced from clumped and oxygen isotope records of the Russian Platform correspond well with changes in local cephalopod and microfossil faunas, which show increasing provincialism during the Late Oxfordian and the Early Kimmeridgian. Based on the review of literature data it is suggested that the observed salinity decrease and restriction of Subboreal basins during the Late Jurassic played a major role in the formation of periodic bottom water anoxia and sedimentation of organic rich facies

Ammonite stratigraphy and organic matter of the Pałuki Fm.n(Upper Kimmeridgian–Lower Tithonian) from the central-eastern part of the Łódź Synclinorium (Central Poland)

The ammonite biostratigraphy as well as the organic matter content, its type and maturity of the Pałuki Formation, belonging to the fine, siliciclastic Kimmeridge Clay type facies, were investigated in five deep boreholes from the central-eastern part of the Łódź Synclinorium in Central Poland. The studied deposits are assigned to the Eudoxus and Autissiodorensis zones of the Upper Kimmeridgian as well as the Klimovi, Sokolovi, Pseudoscythica and Puschi (=Tenuicostata) zones of the Lower Tithonian (“Lower Volgian”). The Pałuki Formation shows in its lower and middle parts average TOC concentrations of ca. 2.5 wt.% and prominent, restricted increases in organic matter content, which are found in the mid-Eudoxus Zone, the lowermost part of the Autisiodorensis Zone, and at the Sokolovi–Pseudoscythica zone boundary. These stratigraphical intervals correlate well with rich in organic matter levels present in the Kimmeridge Clay Formation of NW Europe. The periodic expansions of Submediterranean and Subboreal-Boreal ammonites corresponded mostly to the transgressive phases, often correlated with a higher content of organic matter. The development of special morphologies of ammonites, such as the small-sized, nectopelagic forms of Nannocardioceras in the Late Kimmeridgian, has also been related to the deposition of shales rich in organic matter during the transgression maxima. The organic matter present in the Pałuki Formation mostly consists of Type II kerogen and is immature or early mature with respect to hydrocarbon generation, which is in agreement with previously published data. Evaluation of the new and published geochemical, lithological and structural data from the Pałuki Formation in the central-eastern part of the Łódź Synclinorium shows that these deposits could not have been a considerable source of crude oil or gas

Advances and Challenges in Palaeoenvironmental Studies Based on Oxygen Isotope Composition of Skeletal Carbonates and Phosphates

Oxygen isotopes are widely used in palaeoenvironmental and palaeoclimatic studies as they record variations in the precipitation temperature of biogenic carbonates and phosphates. Problems associated with the preservation state of fossils, selection of the proper temperature equation, vital effects occurring during biomineralization, habitat effects of organisms as well as salinity, bathymetry and water circulation changes limit, however, the applicability of oxygen isotopes to reconstruction of ancient environmental settings. The progress of oxygen isotope studies, temperature calculations and ambiguities of the isotope record are discussed in this paper. The same applies to the methods of retrieving reliable temperature signals and the record of water chemistry changes based on well-preserved calcareous and phosphatic fossils. Sometimes neglected importance of sedimentological and faunistic data associated with sea-level changes and salinity variations is emphasised as an important tool for refinement of the temperature trends of epeiric sedimentary basins. In addition, published case datasets and new laboratory techniques, including micro-area and clumped isotope analyses, are presented to demonstrate examples and prospective ways of extension of the scope of palaeoenvironmental research. The provided information may be used in discussion and a critical review of published oxygen isotope data and their palaeoenvironmental interpretations

Strontium isotope composition of sedimentary rocks and its application to chemostratigraphy and palaeoenvironmental reconstructions

Strontium isotope composition of seawater is homogenous in all oceans and marginal seas but has  varied  through  time  with  changing  strontium  fluxes.  Strontium  isotope  ratio  of  ancient  seawater  may  be  reconstructed  from  well-preserved  authigenic  minerals  and  used  for  dating  marine  sediments.  Because of a change in the strontium isotope ratio between sea- and freshwaters it can also be employed for the determination of palaeosalinities or the reconstruction of diagenetic processes of marine limestones.  A  review  of  methodology  and  practical  hints  concerning  the  utilization  of  strontium  isotopes  in  geological  studies  of  both  marine  and  brackish  sediments  are  presented  in  the  current  article

Strontium isotope composition of sedimentary rocks and its application to chemostratigraphy and palaeoenvironmental reconstructions

Strontium isotope composition of seawater is homogenous in all oceans and marginal seas but has  varied  through  time  with  changing  strontium  fluxes.  Strontium  isotope  ratio  of  ancient  seawater  may  be  reconstructed  from  well-preserved  authigenic  minerals  and  used  for  dating  marine  sediments.  Because of a change in the strontium isotope ratio between sea- and freshwaters it can also be employed for the determination of palaeosalinities or the reconstruction of diagenetic processes of marine limestones.  A  review  of  methodology  and  practical  hints  concerning  the  utilization  of  strontium  isotopes  in  geological  studies  of  both  marine  and  brackish  sediments  are  presented  in  the  current  article

Isotope composition of fossil chaetognath spines and conodonts from Poland, Spitsbergen and Sweden

This dataset contains oxygen isotope data from fossil chaetognath spines (Phakelodus) and conodonts (Cordylodus, Palmatolepis, Neospathodus) measured using an ion microprobe. Samples labelled with "Dur" refer to the calcium phosphate reference "Durango 3"

Chemical and isotope composition of fossil chaetognath spines and conodonts from Poland, Spitsbergen and Sweden, and chemical composition of modern chaetognath spines

This dataset contains chemical data from fossil chaetognath spines (Phakelodus) and conodonts (Cordylodus, Palmatolepis, Neospathodus) measured using an electron microprobe

Detection limits for microprobe measurements of fossil chaetognath spines and conodonts from Poland, Spitsbergen and Sweden

This dataset contains detection limits for chemical data from fossil chaetognath spines (Phakelodus) and conodonts (Cordylodus, Palmatolepis, Neospathodus) measured using an electron microprobe