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Title: Type 1 and Type 2 unconformity development in response to differential subsidence rates and eustatic sea level fluctuations, Pletmos basin, offshore South Africa

Abstract

The Pletmos basin, offshore South Africa, has had variable subsidence rates from mid-Valanginian to mid-Campanian times. During this period, third-, fourth-, and fifth-order sea level fluctuations occurred. The interplay of eustasy and differential subsidence rates caused 67 unconformities. Seventeen are major type 1 unconformities, 44 are minor type 1 unconformities, and 3 are type 2 unconformities. A further three exhibit type 2 characteristics and grade laterally into equivalent type 1 unconformities. Slow subsidence rates permitted fourth- and fifth-order eustatic variations to move sea level below the shelf edge and to erode minor type 1 unconformities. Periodically, when higher order cycles coincided with the trough of a third-order cycle, major type 1 unconformities occurred. Later periods of rapid subsidence precluded fourth- and fifth-order cycles being recorded in the stratigraphic section, and only third-order cycles were interpreted. When the rate of third-order eustatic falls were of the same order of magnitude as subsidence rates, relative sea level did not shift beyond the shelf edge, resulting in type 2 erosion. Deep-seated growth faulting established differential subsidence rates in the central Pletmos basin. In areas of slow subsidence the effects of eustatic variations were amplified relative to areas of rapid subsidence. This resulted inmore » enhanced erosion associated with the former where major and minor type 1 unconformities coalesce and type 2 unconformities grade laterally into equivalent type 1 unconformities.« less

Authors:
 [1]
  1. Soekor Ltd., Parow (South Africa)
Publication Date:
OSTI Identifier:
5569960
Report Number(s):
CONF-890404-
Journal ID: ISSN 0149-1423; CODEN: AABUD
Resource Type:
Conference
Journal Name:
AAPG Bulletin (American Association of Petroleum Geologists); (USA)
Additional Journal Information:
Journal Volume: 73:3; Conference: AAPG annual convention with DPA/EMD Divisions and SEPM, San Antonio, TX (USA), 23-26 Apr 1989; Journal ID: ISSN 0149-1423
Country of Publication:
United States
Language:
English
Subject:
02 PETROLEUM; SEDIMENTARY BASINS; GEOLOGIC STRUCTURES; SOUTH AFRICA; STRATIGRAPHY; AFRICA; GEOLOGY; 020200* - Petroleum- Reserves, Geology, & Exploration

Citation Formats

Jollands, A. Type 1 and Type 2 unconformity development in response to differential subsidence rates and eustatic sea level fluctuations, Pletmos basin, offshore South Africa. United States: N. p., 1989. Web.
Jollands, A. Type 1 and Type 2 unconformity development in response to differential subsidence rates and eustatic sea level fluctuations, Pletmos basin, offshore South Africa. United States.
Jollands, A. 1989. "Type 1 and Type 2 unconformity development in response to differential subsidence rates and eustatic sea level fluctuations, Pletmos basin, offshore South Africa". United States.
@article{osti_5569960,
title = {Type 1 and Type 2 unconformity development in response to differential subsidence rates and eustatic sea level fluctuations, Pletmos basin, offshore South Africa},
author = {Jollands, A},
abstractNote = {The Pletmos basin, offshore South Africa, has had variable subsidence rates from mid-Valanginian to mid-Campanian times. During this period, third-, fourth-, and fifth-order sea level fluctuations occurred. The interplay of eustasy and differential subsidence rates caused 67 unconformities. Seventeen are major type 1 unconformities, 44 are minor type 1 unconformities, and 3 are type 2 unconformities. A further three exhibit type 2 characteristics and grade laterally into equivalent type 1 unconformities. Slow subsidence rates permitted fourth- and fifth-order eustatic variations to move sea level below the shelf edge and to erode minor type 1 unconformities. Periodically, when higher order cycles coincided with the trough of a third-order cycle, major type 1 unconformities occurred. Later periods of rapid subsidence precluded fourth- and fifth-order cycles being recorded in the stratigraphic section, and only third-order cycles were interpreted. When the rate of third-order eustatic falls were of the same order of magnitude as subsidence rates, relative sea level did not shift beyond the shelf edge, resulting in type 2 erosion. Deep-seated growth faulting established differential subsidence rates in the central Pletmos basin. In areas of slow subsidence the effects of eustatic variations were amplified relative to areas of rapid subsidence. This resulted in enhanced erosion associated with the former where major and minor type 1 unconformities coalesce and type 2 unconformities grade laterally into equivalent type 1 unconformities.},
doi = {},
url = {https://www.osti.gov/biblio/5569960}, journal = {AAPG Bulletin (American Association of Petroleum Geologists); (USA)},
issn = {0149-1423},
number = ,
volume = 73:3,
place = {United States},
year = {Wed Mar 01 00:00:00 EST 1989},
month = {Wed Mar 01 00:00:00 EST 1989}
}

Conference:
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