John E. Warme

The Deep Sea Drilling Project : a decade of progress

At the present the Glomar Challenger has drilled over 500 holes over the world ocean, involving hundreds of scientists from dozens of countries. This volume is intended as a review of some of theimportant results from the most comprehensive, ambitious and successful earth-bound geologic project ever undertaken. The symposium upon which this volume originated was held April 4, 1979 at the SEPM/AAPG Annual Meeting in Houston. No comprehensive synthesis of all aspects of the DSDP has appeared, and the topic coverage in this volume is biased towards the sediments and fossils, and their significance for certain aspects of earth history – paleogeography, bathymetry, climatology, oceanography, ecology, environments – all in keeping with the audience of sedimentary geologists.

Borings As Trace Fossils, and the Processes of Marine Bioerosion

Marine borers are nearly ubiquitous in the modern seabed. Their distinctive excavations provide abundant potential trace fossils, and their general erosional activities (bioerosion) are important factors in marine sedimentation and benthic ecology.

Trace Fossils and Bathymetry of the Upper Cretaceous Point Loma Formation, San Diego, California

There is disclosed a process for producing diacetoxybutane diol by hydrogenating diacetoxybutene in the presence of a hydrogenation catalyst in which the hydrogenation is carried out in two stages within predetermined temperature ranges, the temperature of the second stage is higher than that of first thereby obtaining the product in high selectivity with high conversion, and a process for producing butanediol by hydrolyzing the diacetoxybutane thus obtained in the presence of a solid acid catalyst.

ANATOMY OF AN ANOMALY : THE DEVONIAN CATASTROPHIC ALAMO IMPACT BRECCIA OF SOUTHERN NEVADA

The Alamo Breccia is a carbonate rock breccia of Late Devonian age in southern Nevada. It is an anomalous sedimentary unit because it has the properties of a massive debris-flow and turbidity-current deposit that would be expected to occur in deep water, but is intercalated over much of its area with typical shallow-water carbonate-platform beds. The Breccia was created by the catastrophic detachment and flow, over a nearly horizontal surface, of previously deposited platform carbonates. It crops out in 14 or more mountain ranges that cover an area of ∼10,000 km2, conservatively averages ∼50 m in thickness, and contains a volume of 500+ km3. Along the base it contains trains of individual detached blocks as much as 500 m long and 90 m high. Clasts generally grade upward to gravel-, sand-, or mud-sized particles at the top. The Breccia was generated by forces unleashed during the impact of an extraterrestrial object with Earth. The impact produced shocked quartz grains, unique ejecta spherules, and an irid...

Shocked quartz in the Alamo breccia, southern Nevada: Evidence for a Devonian impact event

A transmission electron microscope (TEM) study of quartz grains strongly implies that the Alamo breccia of southern Nevada resulted indirectly from a Late Devonian hypervelocity impact event. The Alamo breccia is perhaps the most voluminous marine carbonate megabreccia exposed on land. It covers ≈4,000 km2, averages ≈70 m thick, and contains more than 250 km3 of carbonate-platform debris that was deposited by a giant submarine slide. The breccia is a single bed with the characteristics of a chaotic debrite at the base evolving upward to a graded turbidite at the top. The bed is anomalous, compared to other marine megabreccias, because over a large area it is intercalated with cyclic shallow-water carbonate-platform rocks, rather than with deep-water turbidites as expected. Thin sections of peculiar quartz grains, recovered from insoluble residues of the breccia, show one to six sets of imperfect parallel lamellae and other defects suggesting shock tamorphism. When studied by TEM, the grains clearly display planar deformation features (PDFs) and other defects from a high-pressure shock wave. Straight and narrow planar microstructures consist of a high density of dislocations mostly parallel to crystal habit plane {1012}, but {1013}, {1011}, and {1121} orientations were also detected. The PDFs appear identical to those in quartz grains associated with well-known impact structures such as Manicouagan and Manson. We conclude that energy from an impact triggered the epiplatform slide and the consequent sedimentary processes that formed the Alamo breccia.

Graded Bedding in the Recent Sediments of Mugu Lagoon, California

Graded bedding is common in intertidal sediments of Mugu Lagoon, California. This bedding is different from other graded sequences which have been described in that the coarsest size-grade at the top of the bed is the same size as the coarsest size-grade at the base; this size simply becomes less common upwards. The grading is accomplished by burrowing organisms which mix basal sand of the lagoon with tidal flat and salt marsh mud naturally deposited over it. Dense marsh growth inhibits burrowers, causing mixing to diminish and finally to cease as the marsh becomes well-established. The graded sequence then is complete. Biologic energy can give a completely different character to sediments initially deposited by physical processes. In a unit of time, at least 10 to 100 times more sediment is placed on the surface by burrowing animals than is added by tidal currents and other transportational agents in most sedimentary environments of Mugu Lagoon. A rapid sedimentation rate is indicated by a radiocarbon date of about 100 years B. P. on Pecten shells found 75 cm beneath a graded sedimentary sequence. This date also gives an estimate of the time that it took to develop the graded bed, and the rapidity with which the marsh has expanded over open lagoon sediments.

Impact-generated carbonate accretionary lapilli in the Late Devonian Alamo Breccia

Carbonate accretionary lapilli occur in the Late Devonian Alamo Breccia of south-central Nevada. They provide evidence for the extraterrestrial impact origin of the breccia, and help unravel the complicated events that formed it. The accretionary lapilli (Alamo lapilli) are concentrated in lapilli beds, and portions of the latter occur as reworked clasts that are isolated within the upper half of the thick breccia. The Alamo lapilli resemble volcanic accretionary lapilli reported from both silicate and carbonatite volcanoes. They are variable in size and detail, but generally exhibit a nucleus interpreted to be altered target rock, an enveloping mantle of siltand sandsized particles, and a very fine grained peripheral crust. Spherule composition is entirely carbonate, except for sparse shocked quartz grains incorporated into the mantle and diagenetic iron oxides. Rare preservation of undeformed bed segments shows the stratigraphy of the accretionary lapilli; they were deposited in poorly sizesorted layers with varying proportions of matrix. Their preserved form is spherical, deformed, or broken, implying varying degrees of damage before or during deposition, before bed hardening, and during catastrophic reworking and dewatering of the Alamo Breccia. We propose that the carbonate accretionary lapilli were preserved when target carbonate formations were pulverized by impact pressure and calcinated by impact heat, creating quicklime. The lapilli evolved by adhesion of particles within the impact cloud; they were partially cemented in flight by hydration, and then precipitated as one or more beds over early ejectite, debris flows, and/or nearly contemporaneous tsunamites. The cementation process continued in the lapilli beds so that portions of them survived reworking and initial breccia settling and dewatering. Coherent, isolated fragments of lapilli beds and deformed bed masses are preserved as much as 25 m beneath the top of the breccia, indicating the thickness of rock reworked during the Alamo Event. Warme, J.E., Morgan, M., and Kuehner, H.-C., 2002, Impact-generated carbonate accretionary lapilli in the Late Devonian Alamo Breccia, in Koeberl, C., and MacLeod, K.G., eds., Catastrophic Events and Mass Extinctions: Impacts and Beyond: Boulder, Colorado, Geological Society of America Special Paper 356, p. 489–504. J.E. Warme, M. Morgan, and H.-C. Kuehner 490 Figure 1. Alamo carbonate accretionary lapilli exposed on weathered surface of lapilli bed showing sizes, proportions of nuclei, mantles, and crust, and grainy matrix in this sample. Lapilli are circular, flattened, and in various stages of breakage. INTRODUCTION Carbonate spheroidal particles (Fig. 1), interpreted as impact-generated carbonate accretionary lapilli, represent an important constituent of the Late Devonian Alamo impact breccia in Nevada. For brevity, and to distinguish them from other kinds of accretionary spherules and spherical impact products, we call them Alamo lapilli. Shocked quartz grains are dispersed in the Alamo Breccia, and are incorporated into the Alamo lapilli. The beautifully preserved lapilli and shocked quartz are the best observable physical evidence for the impact origin of the breccia, although they compose much less than 1% of the deposit. Probably within only minutes to a day, a series of impactrelated events (Alamo Event of Warme and Sandberg, 1995, 1996; Morrow et al., 1998) eroded and resedimented a thick interval of carbonate platform rock of the Guilmette Formation, which became the thick Alamo carbonate megabreccia. The Alamo lapilli occur in isolated clasts scattered within the Alamo Breccia, and provide a key to understanding the character and the timing of events that led to the Alamo Breccia formation. Alamo lapilli are interpreted to have accreted in a vapor-rich impact plume by adhesion of carbonate particles and other contemporaneous processes. Their structure resembles some kinds of armored accretionary volcanic lapilli, having a central nucleus interpreted as carbonate target rock, an enveloping mantle of sandand silt-sized carbonate fragments, and an outer crust of very fine siltand clay-sized carbonate particles. Alamo lapilli imply that the impact target was dominated by carbonate rock and was wet. Evidence suggests that they precipitated as one or more widespread beds. The beds were then dismembered, by tsunami erosion and/or other energetic impact processes, and redeposited as isolated clasts in the massive breccia. Preserved lapilli survived these events by rapid cementation processes that began in flight and continued in the precipitated bed(s). This early cementation caused segments of the beds to be durable enough to withstand subsequent catastrophic transportation and deposition. Other examples of ancient carbonate lapilli may have formed and been preserved by impact processes. Carbonate strata anywhere may contain unrecognized intervals of impact lapilli and lapillistone.

Submarine Canyon Erosion: Contribution of Marine Rock Burrowers

Rocks of the rim and upper walls of Scripps Submarine Canyon are intensely burrowed by marine invertebrates. Important excavators are bivalves, polychaetes, and sipunculoids whose activities culminate in a network of passageways and eventual disintegration of the rocks. In many localities erosion by animals is more important than erosion by physical and chemical processes.

Jurassic Sedimentation in the High Atlas Mountains of Morocco during Early Rifting of Africa and North America

The High Atlas Trough was formed during the early rifting of Africa and North America. Sedimentologic evidence indicates that subsidence of the trough was not accompanied by intense crustal deformation. The trough was a site of active sedimentation from Lower (Liassic) to Middle (Dogger) Jurassic time, and it contains a sequence of predominantly carbonate sedimentary rocks that do not indicate extensive syntectonic activity. The numerous tectonic features (that is, faulting and folding) associated with the Jurassic sedimentary rocks of this area today probably developed at a later, post-Jurassic date.

Geology of Great Abaco Submarine Canyon (Blake Plateau): Observations from the research submersible “Alvin”

Abstract Nine dives in the research submersible “Alvin” were made into Great Abaco Submarine Canyon to depths ranging from 1850 to 3666 m. Our observations indicate that the walls of this canyon are distinctly terraced, consisting of nearly vertical to overhanging rock cliffs and intervening, less steep sediment-covered slopes. The wall rock consists mostly of massive, shallow-water limestones and dolostones of Cretaceous age, coated on exposed surfaces with manganese oxides. These rocks are heavily jointed/fractured and thus very blocky to angular in appearance, with sponges and other sessile organisms commonly attached. Talus slopes and sedimentary breccia deposits containing angular boulders are present at the base of these steep escarpments. Short-term bottom current measurements in the axis of the eastern part of the canyon indicate that currents are relatively weak, reaching velocities of only 10 cm/sec. This relatively placid setting is further corroborated by the abundance of turtle grass ( Thalassia ) found along the canyon axis. However, abundant subdued, symmetrical ripple marks and large scour depressions at the base of boulders, indicate that high-energy events sporadically impact the canyon axis. Contemporary erosional activity along the axis of the western (headward) part of the canyon appears to be more significant, as evidenced by asymmetrical ripple marks, sand waves and bioerosion. Great Abaco Canyon has evolved with time via a variety of processes, including: (1) faulting: (2) subsidence; (3) defacement; and (4) erosional down-cutting. The location, orientation and initiation of this canyon appear to be structurally controlled by the Great Abaco Fracture Zone during pre-Santonian time. Regional subsidence during the Mesozoic allowed the walls of Great Abaco Canyon to build vertically by accretion of shallow-water limestones, whereas joint-controlled defacement has widened the canyon while maintaining steep walls. Erosional down-cutting in the canyon axis by carbonate sediment gravity flows also appears to have been important episodically, particularly during the Miocene and Pleistocene.