Late Pliocene and Early Pleistocene Variability of the REE and Nd Isotope Composition of Caribbean Bottom Water: A Record of Changes in Sea Level and Terrestrial Inputs During the Final Stages of Central American Seaway Closure

Tonnoidean gastropods have planktotrophic larval lives of up to a year and are widely dispersed in ocean currents; the larvae maintain genetic exchange between adult populations. They therefore are expected to respond rapidly to new geographic barriers by either extinction or speciation. Fossil tonnoideans on the opposite coast of the Americas from their present-day range demonstrate that larval transport still was possible through Central America at the time of deposition of the fossils. Early Miocene occurrences of Cypraecassis tenuis (now eastern Pacific) in the Caribbean probably indicate that constriction of the Central American seaway had commenced by Middle Miocene time. Pliocene larval transport through the seaway is demonstrated by Bursa rugosa (now eastern Pacific) in Caribbean Miocene-latest Pliocene/Early Pleistocene rocks; Crossata ventricosa (eastern Pacific) in late Pliocene rocks of Atlantic Panama; Distorsio clathrata (western Atlantic) in middle Pliocene rocks of Ecuador; Cymatium wiegmanni (eastern Pacific) in middle Pliocene rocks of Atlantic Costa Rica; Sconsia sublaevigata (western Atlantic) in Pliocene rocks of Darien, Pacific Panama; and Distorsio constricta (eastern Pacific) in latest Pliocene-Early Pleistocene rocks of Atlantic Costa Rica. Continued Early or middle Pleistocene connections are demonstrated by Cymatium cingulatum (now Atlantic) in the Armuelles Formation of Pacific Panama. Tonnoideans indicate that the Central American seaway began to be constricted after early Miocene time, and some larval transport through the seaway was possible throughout Pliocene time. Intermittent marine connections were maintained at least during late Pliocene to early Pleistocene interglacial periods of high sea-level, and alternated with a land bridge during glacial periods of low sea-level.

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Neodymium Isotope Geochemistry of a Subterranean Estuary

Frontiers in Water ◽

10.3389/frwa.2021.778344 ◽

2021 ◽

Vol 3 ◽

Author(s):

Darren A. Chevis ◽

T. Jade Mohajerin ◽

Ningfang Yang ◽

Jaye E. Cable ◽

E. Troy Rasbury ◽

...

Keyword(s):

Sea Level ◽

Isotope Composition ◽

Indian River Lagoon ◽

Nd Isotope ◽

Subterranean Estuary ◽

Upper Floridan Aquifer ◽

Indian River ◽

Surficial Aquifer ◽

Nd Isotope Composition ◽

Seepage Face

Rare earth elements (REE) and Nd isotope compositions of surface and groundwaters from the Indian River Lagoon in Florida were measured to investigate the influence of submarine groundwater discharge (SGD) on these parameters in coastal waters. The Nd flux of the terrestrial component of SGD is around 0.7±0.03 μmol Nd/day per m of shoreline across the nearshore seepage face of the subterranean estuary. This translates to a terrestrial SGD Nd flux of 4±0.2 mmol/day for the entire 5,880 m long shoreline of the studied portion of the lagoon. The Nd flux from bioirrigation across the nearshore seepage face is 1±0.05 μmol Nd/day per m of shoreline, or 6±0.3 mmol/day for the entire shoreline. The combination of these two SGD fluxes is the same as the local, effective river water flux of Nd to the lagoon of 12.7±5.3 mmol/day. Using a similar approach, the marine-sourced SGD flux of Nd is 31.4±1.6 μmol Nd/day per m of shoreline, or 184±9.2 mmol/day for the investigated portion of the lagoon, which is 45 times higher than the terrestrial SGD Nd flux. Terrestrial-sourced SGD has an εNd(0) value of −5±0.42, which is similar to carbonate rocks (i.e., Ocala Limestone) from the Upper Floridan Aquifer (−5.6), but more radiogenic than the recirculated marine SGD, for which εNd(0) is −7±0.24. Marine SGD has a Nd isotope composition that is identical to the εNd(0) of Fe(III) oxide/oxyhydroxide coated sands of the surficial aquifer (−7.15±0.24 and −6.98±0.36). These secondary Fe(III) oxides/oxyhydroxides formed during subaerial weathering when sea level was substantially lower during the last glacial maximum. Subsequent flooding of these surficial sands by rising sea level followed by reductive dissolution of the Fe(III) oxide/oxyhydroxide coatings can explain the Nd isotope composition of the marine SGD component. Surficial waters of the Indian River Lagoon have an εNd(0) of −6.47±0.32, and are a mixture of terrestrial and marine SGD components, as well as the local rivers (−8.63 and −8.14). Nonetheless, the chief Nd source is marine SGD that has reacted with Fe(III) oxide/oxyhydroxide coatings on the surficial aquifer sands of the subterranean estuary.

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Nd isotope composition of conodonts: An accurate proxy of sea-level fluctuations

Gondwana Research ◽

10.1016/j.gr.2015.02.022 ◽

2016 ◽

Vol 34 ◽

pp. 284-295 ◽

Cited By ~ 19

Author(s):

J. Dopieralska ◽

Z. Belka ◽

A. Walczak

Keyword(s):

Sea Level ◽

Isotope Composition ◽

Nd Isotope ◽

Sea Level Fluctuations ◽

Nd Isotope Composition

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Nd isotope composition of the Ediacaran and earliest Cambrian phosphorite nodules and Fe sulphide from the East European Platform

Geological Magazine ◽

10.1017/s0016756820000497 ◽

2020 ◽

Vol 157 (12) ◽

pp. 2081-2088

Author(s):

Sergey B Felitsyn ◽

Eugeny S. Bogomolov

Keyword(s):

East European Platform ◽

Isotope Composition ◽

Water Reservoir ◽

Secular Change ◽

Early Cambrian ◽

Iron Sulphide ◽

Nd Isotope ◽

East European ◽

Moscow Syneclise ◽

Nd Isotope Composition

AbstractAn enhanced concentration of phosphorus has been found at the stratigraphic level of the disappearance of Ediacaran taxa in two areas, the Cis-Dniester region and the Moscow syneclise, on the East European Platform (EEP). The isotope composition of neodymium was determined in Fe sulphide and phosphorite in the same beds. Measured εNd(t) values in diagenetic phosphate nodules are similar to those in iron sulphide from the same layer. During the Ediacaran − Early Cambrian, accumulation of radiogenic Nd in the epeiric basins on the EEP increased progressively from −17.9 and −19.4 in pyrite from the sequence bottom to −7.9 and −8.5 in the Early Cambrian pyrite of the central part of the EEP. The Ediacaran phosphate nodules show εNd(t) ranging from −12.9 to −15.0, while that in the Early Cambrian nodules is typically c. −9.0. These data indicate the secular change in Nd isotope composition of the water reservoir on the EEP from Ediacaran to Cambrian.

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