Uncorrected Proof
GEOLOGIC NOTE
1 Structure and kinematics of
2 an outcrop-scale fold-cored
3 triangle zone
4 David Colin Tanner, Christian Brandes, and
5 Bernd Leiss
6 ABSTRACT
7 Triangle zones are widespread structural elements that link
8 fold and thrust belts with their foreland basins. We present a
9 structural analysis of an outcrop-scale (~6 m [20 ft] wide) tri-
10 angle zone that is exposed in the siliciclastic Carboniferous strata
11 of the Harz Mountains in northern Germany. The geometry
12 of the triangle zone is critically compared with larger outcrop
13 and seismic-scale structures. The external form of the triangle
14 zone is the same as that proposed for larger examples, with two
15 bounding detachments that dip in opposing directions. How-
16 ever, the interior of the triangle zone is characterized by tight
17 to isoclinal folds. We demonstrate how the triangle zone prob-
18 ably evolved from a fault-bend fold, which accreted further folds
19 behind it. This is an alternative fold-based interpretation for
20 a structure that is commonly modeled as a duplex stack. We
21 present the resulting consequences for seismic interpretation
22 and hydrocarbon reservoir evaluation.
23 INTRODUCTION
24 Triangle zones are common structural elements that occur all
25 over the world, especially at the transition between fold and
26 thrust belts and foreland basins. The expression “triangle zone”
27 has been used for various different types of structures with a
28 triangular shape in cross section (e.g., McClay, 1992). In most
29 cases, it is used to describe an antiformal feature on the leading
30 edge of a fold and thrust belt, which is internally characterized by
AUTHORS
David Colin Tanner Leibniz Institute
for Applied Geophysics, Stilleweg 2,
D-30655 Hannover, Germany;
DavidColin.Tanner@liag-hannover.de
David Tanner received a B.Sc. degree in Geology
from Liverpool University, United Kingdom;
an M.Sc. degree from Imperial College, London,
United Kingdom; and a doctorate from Giessen
University, Germany. His interests lie in structural
geology. He specializes in three-dimensional
kinematic modeling of complexly deformed
terrains.
Christian Brandes Institute of Geology,
Leibniz University Hannover, Callinstr. 30,
30167 Hannover, Germany;
brandes@geowi.uni-hannover.de
Christian Brandes is a research scientist and
lecturer at the Institute of Geology at Hannover
University, Germany. He received a diploma
in Geology in 2002 and a doctorate in 2006 from
Hannover University. His research focuses on
basin dynamics with an emphasis on numerical
basin modeling and structural geology.
Bernd Leiss Geoscience Centre, Georg
August University Göttingen, Goldschmidtstr. 3,
37077 Göttingen, Germany; bleiss1@gwdg.de
Bernd Leiss specializes in quantitative analysis
of microfabrics to understand deformation
mechanisms, kinematics, and anisotropies of
physical properties at microscale to regional
scale. He received a diploma in Geology and
a doctorate from Göttingen University, Ger-
many, where he is now employed as research
scientist and lecturer in Structural Geology and
Geodynamics.
ACKNOWLEDGEMENTS
We greatly appreciate being introduced to the
field area by Axel Vollbrecht and Klaus Weber, as
well as stimulating discussions with them.
The AAPG Editor thanks the following reviewers
for their work on this article: Alfred Lacazette,
Stephen J. Naruk, and an anonymous reviewer.
Copyright ©2010. The American Association of Petroleum Geologists. All rights reserved.
Manuscript received November 23, 2009; provisional acceptance February 16, 2010; revised manuscript
received April 12, 2010; final acceptance June 30, 2010.
DOI:10.1306/06301009188
AAPG Bulletin, v. 94, no. XX (XXXX 2010), pp. 1 – 11 1