Abstract

The main objective of this research was to understand the sedimentology and depositional environment of the diatomaceous Miocene/Pliocene Pisco Formation in the Ica Valley, Perú. Four stratigraphic sections were studied, sampled and correlated. Field data were integrated with XRD, diatom taxonomy and taphonomy, and thin section analyses to define six facies.

Facies A is composed of diatomaceous siltstone with scour and fill structures formed on a shallow shelf. Facies B was deposited on the transitional zone between the shallow shelf and nearshore where tuffaceous-diatomaceous siltstone and sandstone accumulated. In facies B, lenticular laminations, and flaser, wavy and lenticular bedding record tidal action. Facies C is composed of tuffaceous sandstone formed in the nearshore zone largely in the shoreface. Tuffaceous-diatomaceous lenticular beds of siltstone, channels, erosive surfaces, and hummocky cross stratification are evidence that storms were a major control on nearshore sedimentation. Facies D is composed of medium to very coarse sandstones containing a variety of fossil invertebrates that were deposited in a nearshore environment around a pre-Tertiary island. Facies E is composed of conglomerate and sandstone emplaced in the shallow shelf and transitional zone by currents associated with storms. Facies F is composed of thin, coarse sandstone eroded from the local nearshore environment around islands and emplaced on the shelf during storms.

Diatoms proliferated in the basin due to the incoming nutrients from both an offshore upwelling zone and volcanic activity. The occurrence of a few freshwater diatom species suggests the water was brackish or that salinity fluctuated through time, probably because of fresh water input. As diatoms reached the basin bottom, they became fragmented by the action of waves and tides.

Facies analysis indicates that the location of the depositional environments shifted through time toward the shore because of the advance of the sea onto the continent. As a consequence, an overall transgressive sequence formed with smaller regressive intervals.

LLU Discipline

Geology

Department

Geology

School

Graduate School

First Advisor

Leonard Brand

Second Advisor

Paul Buchheim

Third Advisor

Robert Cushman

Fourth Advisor

Kevin Nick

Degree Name

Master of Science (MS)

Degree Level

M.S.

Year Degree Awarded

2002

Date (Title Page)

3-2002

Language

English

Library of Congress/MESH Subject Headings

Geology, Stratigraphic -- Pliocene; Geology, Stratigraphic -- Miocene; Paleontology -- Miocene; Sediments (Geology) -- Peru; Sediments (Geology) -- Ica River Valley (Peru)

Subject - Local

Pisco Formation (Peru); Pisco River Valley (Peru)

Type

Thesis

Page Count

xi; 107

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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