Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Earth Systems Science

First Advisor's Name

Florentin Maurrasse

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Laurel Collins

Second Advisor's Committee Title

Committee Member

Third Advisor's Name

Rosemary Hickey-Vargas

Third Advisor's Committee Title

Committee Member

Fourth Advisor's Name

Francisco Fernandez Lima

Fourth Advisor's Committee Title

Committee Member

Keywords

Aptian, OAE1a, dysoxic conditions, marine redox conditions, organic-matter preservation, terrestrial fluxes, biomarkers, organic-matter, terrigenous contribution

Date of Defense

11-9-2022

Abstract

The Early Aptian Period (~120Ma) is characterized by a perturbation in the carbon cycle associated with strong greenhouse conditions that caused a global episode of marine anoxia and widespread organic matter (OM)-rich deposits, known as oceanic anoxic event 1a (OAE1a). I investigated the factors that favored the accumulation of OM prior to and during OAE1a from three lower Cretaceous sites: the Organyà Town Section (OTS), Spanish Pyrenees; the Cuchía Section, Northern Spain, and the La Frontera section, Southern Spain. I used a multi-proxy methodology that includes total organic carbon (TOC), total inorganic carbon (TIC), stable isotopes of organic carbon (δ13Corg), trace element analyses, clay and bulk mineralogy, and biomarkers.

In the OTS chemostratigraphic correlation using δ13Corg indicates a Lower Aptian age within carbon isotope segment C2. Biomarkers indicate predominantly marine OM, and five intervals include high TOC with elevated major and redox sensitive trace elements (RSTEs). The results indicate that increased intermittent overland flow prior to OAE1a delivered bio-essential nutrients to the basin which promoted increased primary productivity, and the excess OM induced low oxygen conditions, favoring OM preservation.

The Cuchía section spans segments C2 to C6, coeval with OAE1a. The distribution and abundance of land-derived minerals and OM indicate sustained detrital input and nutrients with paludal influence, which heightened primary productivity throughout OAE1a. However, a moderate correlation between TOC and RSTEs suggests that full anoxia was not reached. Instead, the high sedimentation rate and the type of OM mainly controlled their preservation.

The La Frontera section also spans OAE1a, and biomarkers reveal that OM is thermally immature, mostly marine-derived. Some OM from aquatic macrophytes occurs in intervals with elevated major element concentrations. Elemental results for La Frontera indicate that increases in continental erosion caused episodes of oxygen deficiency prior to OAE1a and more severe anoxia during OAE1a, which favored cable bacteria activity that led to carbonate dissolution during the event. This new finding will help in the interpretation of other carbonate-poor deposits with analogous conditions.

The three different sites highlight how global forcing factors can be modulated by local or regional factors during hyperthermic climates leading to ocean anoxia.

Identifier

FIDC010885

ORCID

https://orcid.org/0000-0001-8896-3802

Comments

Chapter 2 of the dissertation has been published in The Depositional Record.

Previously Published In

Herdocia, C. & Maurrasse, FJ-M.R. (2022) Chemostratigraphic characteristics of trace elements, biomarkers and clay mineralogy indicating environmental conditions within Aptian sediments of the Organyà Basin, North-east Spain, prior to the onset of OAE 1a. The Depositional Record, 8, 931– 957. https://doi.org/10.1002/dep2.186

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