3.1. SCIENTIFIC THEMES: INTRODUCTION:
The International Workshop for a Climatic, Biotic,
and Tectonic, Pole-to-Pole Coring Transect of Triassic-Jurassic Pangea
focused on a series of key generic questions for which a Triassic-Jurassic
venue provides a uniquely useful venue principally, but not uniquely addressed
by coring. Each of these questions developed into a theme on which further
debate towards the selection of specific coring targets focused. These
questions and their associated themes are listed below. Each link takes
you to the sections where these themes are developed in more detail.
1. How is Milankovitch climatic forcing expressed over latitude in continental settings and what insight does that yield for calibrating the chaotic behavior of the planets and constructing robust insolation curves for arbitrary times in Earth History?
Theme 1 - Climate, astronomical forcing, and chaos: The climate, astronomical forcing, and chaos theme involves the development of a global high resolution (~20 ky) spatio-temporal matrix to examine how astronomical forcing plays out over latitude in continental and marine environments. Although efforts are underway to finally obtain comparable climatic records from the Quaternary and rest of the Neogene by others, it is essential to obtain comparably detailed records from more ancient times to understand the long term behavior of the climate system, its forcings, and its age-independent aspects. In addition, the climatic transect for Triassic-Jurassic Pangea can be obtained for longer time periods and at more modest expense than for virtually any other geologic period, including the Neogene.
Integral to this goal of understanding astronomical forcing
over latitude, is the exciting realization that it provides a matrix for
exploring the long-term behavior of the planets. The million year-scale
cycles of eccentricity expressed as modulations of climatic precession
already documented from Triassic-Jurassic tropical regions (Olsen and Kent,
1999a), has allowed calibration of part of the chaotic behavior of the
planets outlined by Laskar (1990) (Figure 2). However, a fuller understanding
and tests of these observations require equally detailed records from other
latitudes, especially where obliquity is prominent (e. g. high latitudes).
Records in which obliquity is prominent are also needed to refine the Triassic-Jurassic
general precessional "constant", needed to constrain the evolution of the
Earth-Moon system as well as certain as yet poorly constrained geophysical
parameters of the Earth. The development of this high-resolution spatio-temporal
matrix will result in general methodologies for producing insolation curves
for time periods far distant from the 20 my limit imposed by the chaotic
behavior of the planets.
2. What is the relationship between giant continental flood basalts, seaward-dipping reflectors, the initiation of seafloor spreading, rift basin development, extensional pulses, and mass extinctions?
Theme 2 - Pangean break-up: The Pangean break-up theme focuses on the evolution of the rift system itself and the initiation of oceanic crust production and drift. The high-resolution time scale now available for the Late Triassic and Early Jurassic allows a quantitative understanding of continental extension and ultimate rupture, both at the basin and trans-continental scales. Recent efforts by Contreras et al. (1997) indicate that it is possible to derive the large scale behavior of rift-basins (e.g. The Newark basin) from first-order fault growth models. However, understanding of the linkages between basins and the time- and geography- dependent aspects of continental rifting will require additional high resolution records from different rifts within the same and different rift systems.
Especially notable is the realization that the CAMP igneous
event (Figure 3) was of gigantic proportions but of very short duration
(Marzoli et al., 1999; Olsen, 1999b). It is plausible that the CAMP Large
Igneous Province (LIP) was related to the development of the extensive
suite of seaward-dipping reflectors (SDRs) bordering the south-central
Atlantic (Oh et al, 1995; Talwani et al. 1995). Because this may very well
be the largest continental LIP known and it appears temporally associated
with the Triassic-Jurassic mass-extinction, it is critical to understand
the links between these entities, and this requires deep sampling of the
seaward-dipping reflectors themselves and the related rifts. Obviously,
the relation between the CAMP, the seaward-dipping reflectors, and rifting
is integral to the understanding of the fundamental processes of plate-motion,
and the deep Earth.
3. What is the structure and tempo of mass extinctions in continental environments over geography?
Theme 3 - Biotic change in a Hot-House world: The biotic change in a Hot-House world theme deals with biological patterns at three scales: global biogeographic patterns characteristic of the Hot-House world; Triassic-Jurassic evolution; and the Triassic-Jurassic mass extinction. According to Zeigler et al. (1993) Hot-House Pangea may have been characterized by a unique phytogeography with extraordinarily limited equatorial humid zones. High resolution climate and phytographic data is needed over a wide swath of geography to allow tests of the efficacy of global climate models under appropriately constrained boundary conditions, at appropriate temporal and spatial scales.
Mammals, lizards, turtles, frogs, salamanders, dinosaurs and pterosaurs evolved during the Triassic. All but pterosaurs survived both the Triassic-Jurassic and Cretaceous-Tertiary mass extinctions (dinosaurs in the form of birds). Understanding the chronology, tempo, and mode of their evolution, as well as that of their contemporaries, is of obvious intrinsic interest, and sheds light on the origin of major groups. Critically needed are high-resolution records to provide chronologies for the diverse biotic assemblages that have been discovered to date, as well new material from particular critical episodes of biotic change such as the Triassic-Jurassic boundary.
There is now growing evidence that the Triassic-Jurassic
mass extinction was of very large magnitude and very abrupt. The cause
is as yet unknown as is the temporal scale outside the Newark basin. However,
very recent work by McElwaine et al. (1999) on sections from Greenland
and Sweden shows that the extinction appears to have been associated with
an abrupt CO2 increase. Such an increase of CO2 could have resulted from
massive outgassing associated with the CAMP flood basalts or even an asteroid
impact. In any case, the temporal and geographic framework for the boundary
and its relationship to the CAMP event require the high-resolution sampling
that a pole-to-pole coring transect would uniquely provide.
4. How can we develop integrated, high-resolution marine and continental time scales for the deep past?
Theme 4 - Integrated,
high-resolution time scales for the Early Mesozoic:
A fundamental problem integral to all studies that rely on information
from the deep past is the development of high-resolution integrated time
scales. The precision and accuracy of geological time scales predetermines
the nature of the kinds of questions that can be meaningfully addressed.
A major outcome of the NSF-funded Newark Basin Coring Project was the development
of an astronomically tuned time scale for most of the Late Triassic and
earliest Jurassic. However, applicability of this time scale globally,
especially in marine environments is severely hampered by a lack of high-resolution
records from other, particularly marine areas. It is also highly desirable
to extend the time scale further into the Jurassic and further back into
at least the Middle Triassic, so that would be overlap with time scales
developing elsewhere, as well as additional radiometric constraints. In
addition, the Newark Basin time scale is not without controversy and tests
of its precision are needed.
These four themes are developed in greater depth in the