Date of Award

1997

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geology and Geophysics

First Advisor

Joseph E. Hazel

Abstract

Foraminifera and ostracods from eight measured sections and three wells located in Romania (Apuseni Mountains, central Carpathian and foreland units) were analyzed. Major Jurassic microfaunal evolutionary events are recorded and biozonations of regional value, based on assemblage zones, are established for the Toarcian of the Apuseni Mountains and the Oxfordian-Kimmeridgian of the Scythian Platform. Microfauna has been calibrated to ammonite zones in the Bratca and Munteana sections, and the Caraorman West F11/7 well. Criteria such as (1) presence/absence of large benthic foraminifera with complex internal structure, (2) paleobiogeographic affinities of smaller foraminifera and ostracods, and (3) distribution of important lithofacies indicate a north Tethyan location for the central Carpathian and foreland units during the Sinemurian-Oxfordian interval. A similar location is assigned during the Lias to the Apuseni Mountains, with evidence for a somewhat more southern position with respect to the central Carpathian units. Paleobiogeographic evidence for a southern drift of the Tisia plate begins to appear during the Oxfordian, supporting the hypothesis that the main Tethyan suture is located between the Apuseni Mountains and the Eastern and Southern Carpathians. Microfaunal evidence also indicates that if during the Triassic the Tisia plate was located on the southern margin of the Paleo-Tethys, this ocean must have closed by Early Jurassic. Depositional environments ranging from inner to outer neritic are identified based on sedimentologic data and microfaunal parameters (diversity, heterogeneity, abundance, percentage of foraminifera fragmentation, rate of faunal change). A sequence stratigraphic framework is established for most sections; inferred relative sea-level variation curves are generally similar to eustatic curves proposed by other authors. Important dysaerobic intervals were identified in the early Toarcian of the Apuseni Mountains and the late Bathonian of the Scythian Platform. Major sea-level rises are recognized during the late Sinemurian, early Toarcian, late Bajocian, late Bathonian, and middle Oxfordian. Models for the paleobathymetric distribution of main microfaunal species are established for the Toarcian and Oxfordian-Kimmeridgian using quantitative analysis to identify biofacies and interpreting the latter according to the identified environments.

ISBN

9780591591699

Pages

212

DOI

10.31390/gradschool_disstheses.6530

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