REGIONAL AND GLOBAL CLIMATIC IMPLICATIONS OF 
HIGH-RESOLUTION ASTRONOMICALLY CALIBRATED 
PALEOMAGNETIC POLARITY TIME SCALE FOR THE LATE 
TRIASSIC AND EARLY JURASSIC 

	OLSEN, P. E. ,  and KENT, D. V., Lamont-Doherty Earth 	
		Observatory of  Columbia University, Palisades, NY 
		10964 

Triassic-Jurassic lacustrine and paralic strata preserved in numerous 
rift basins and rift-related basins from Svalbard to the Gulf of Mexico 
display a hitherto baffling array of humid to arid facies.  These 
seemingly conflicting associations of facies have prompted several ad 
hoc explanations evoking non-zonal climatic processes such as 
monsoons, the effects of orography, and global climate change.  
Cyclostratigraphic and paleomagnetic analysis of 6700 m of core from 
the Newark basin collected by the Newark Basin Coring Project 
(NBCP) provided a high-resolution astronomically calibrated 
magnetic polarity time scale for the Late Triassic and Early Jurassic.  
About 30 million years and 59 polarity intervals are recorded in this 
sequence.  Paleomagnetic results show that the position of the 
paleoequator was in present-day Virginia during the Carnian of the 
Late Triassic and that Pangea drifted about 9 north from the Carnian 
to the Early Jurassic. 
	With this time scale and pole position data in hand, the overall 
pattern of climate sensitive facies in the Triassic and Early Jurassic is 
greatly simplified.  There was a seeming symmetrical arrangement of 
facies around the paleoequator during Carnian time.  Coals and deep-
water lacustrine deposits were produced at the paleoequator (Deep 
River, Dan River, Richmond, and Taylorsville basins) while strikingly 
cyclical lacustrine and playa deposits and bioturbated red beds were 
produced 10 to the north and south.  Contemporaneous deposits near 
30 N paleolatitude in Greenland and the Haltenbaken area of offshore 
Norway consist of eolian sand dunes and evaporite beds, while further 
north in Svalbard, deltaic coals and black mudstone again dominate.  
This pattern conforms to a simple zonal one, with a narrow equatorial 
humid zone, with an arid belts centered on 30, in turn passing 
northward into temperate climates.
	To first order, as Pangea drifted northward, the vertical 
sequence of climate sensitive facies in individual basins change as 
they pass from one climate zone to another.  Thus, in the Newark 
Supergroup of North America (North Carolina to Nova Scotia) and in 
Morocco the transition from Carnian through Norian is characterized 
by apparent drying with shallow water cyclical lacustrine strata 
predominating in the southern basins (Norian of Newark Gettysburg, 
Culpeper, Taylorsville, and Dan River basins).  Conversely, in 
England, Sweden, Haltenbaken area and Greenland, the Late Triassic 
gets progressively wetter with coals being produced by the Rhaetian 
in Greenland.
	In the Newark Supergroup and Morocco, there is one major, 
but short lived, departure from this pattern.  In the latest Rhaetian and 
earliest Jurassic, more humid cyclical deposits appear simultaneously 
with the extrusion of flood basalts. Because this apparent reversal in 
the paleoclimatic trend is not accompanied by a  drift of Pangea to the 
south, it probably reflects a true climate change.  This is the kind of 
climate change that would be anticipated by the spread of the ocean 
closer to the region, as did occur in the Early Jurassic flooding of 
western Europe. 
	On a global scale, most of the apparent large climate changes 
seen in early Mesozoic basins can be explained by the northward drift 
of Pangea.  Thus the drying seen in the classic Colorado Plateau 
sequence of the Chinle and Glen Canyon groups in the Western US is 
parallel to that seen in eastern North America.  Similarly, the drying 
seen in the Late Triassic and Early Jurassic sequences of the Karoo 
basin and Argentinean and Brazilian basins can be explained by their 
drift from the south temperate regions into the southern arid belt. 
	Thus, in contrast to previous analyses of Triassic paleoclimate, 
the overall patterns of Late Triassic- Early Jurassic climate fit into a 
simple more or less stationary zonal climate pattern, albeit with a very 
narrow equatorial humid zone.  These observations emphasize the 
need for careful paleogeographic reconstructions constrained by long 
sequences of data in direct superposition, before ad hoc, non-zonal 
explanations of climate are brought to bear on scattered paleoclimatic 
data. Such control is especially important geological data are to be 
used in a credible way to validate global climate models designed to 
predict future climate.


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