Otter Point Research Articles

Protomelas krampus, a new paedophagous cichlid from Lake Malawi (Teleostei, Cichlidae)

A new paedophagous species of Protomelas, P. krampus sp. nov., is described from Lake Malawi. It has been found in Lukoma Bay in Tanzania, near Mara Point in Mozambique, and at Otter Point, Chizumulu, the Likoma Islands and Mazinzi Reef in Malawi. This species is placed in the genus Protomelas based on its melanin pattern, which comprises a continuous midlateral stripe. A morphometric study was done to compare this species with its congeners and similar species of Hemitaeniochromis and Caprichromis. It differs from most congeners by having only one inner tooth row. Furthermore, P. krampus sp. nov. differs from P. insignis, P. spilopterus, H. brachyrhynchus, H. urotaenia, Caprichromis liemi and C. orthognathus by its shorter premaxillary pedicel, shorter prepectoral distances and dentition. It also differs largely in its melanin pattern from the paedophagous species C. liemi, C. orthognathus, Diplotaxodon greenwoodi and Naevochromis chrysogaster, as well as H. brachyrhynchus and H. urotaenia. Protomelas krampus sp. nov. has been observed to ram mouth-brooding cichlids from above to feed on their eggs or larvae.

Conflicts in natural and cultural resource management: Archaeological site disturbances by seals and sea lions on California's Northern Channel Islands

California's Channel Islands currently have around 150,000 breeding seals and sea lions (pinnipeds). Driven to near extinction by 20th-century exploitation, many pinniped populations have recovered dramatically under federal and state management and continue to expand in number and distribution. Some of these pinniped populations are damaging or destroying coastal archaeological sites as they establish new breeding and haul-out areas—places occupied between periods of foraging activity—on upland landforms. We use archaeological excavations from a prehistoric village on San Miguel Island to illustrate the adverse effects pinnipeds can have on archaeological sites. Estimates based on excavations at Otter Point suggest that in one year nearly 10,000 kg of shellfish remains, 840,000 animal bones, and 1700 formal artifacts were lost to erosion caused by the activities of seals and sea lions. Our study documents potential conflicts between natural and cultural resource management suggesting the need for collaborative efforts between archaeologists and biologists to balance the conservation of both resources.

Prehistoric habitat stability and post-settlement habitat change in a Chesapeake Bay freshwater tidal wetland, USA

Analyses of fossil seeds and pollen grains preserved in seven sediment cores and borings were combined with historical land-use records to reconstruct an 1800-yr history of Otter Point Creek (OPC), a freshwater tidal deltaic wetland in the upper Chesapeake Bay. The objectives of the study were to document the role of natural and anthropogenic disturbance on habitat development at different sites within the wetland. Fossil seeds revealed a 1500-yr period (AD 230 to 1700) of subtidal habitat stability characterized by the aquatic macrophytes Zannichellia palustris, Najas gracillima, N guadalupensis, Elodea canadensis and Vallisneria americana. Natural disturbance had little or no impact on the estuarine habitat during this time. By the early 1700s, forest clearance for agriculture and lumber during European settlement led to higher erosion rates in the watershed. This led to rapid sediment efflux and broad habitat changes along a hydrologic gradient within the estuary. The aquatic macrophytes disappeared when estuarine sedimentation rates increased from a pre-1700 mean of 0.05 cm/yr to 0.60 cm/yr after 1730-1750. As the estuary continued to fill behind a prograding delta from AD 1750 to 1950, sub-tidal species were replaced sequentially by increasingly less flood-tolerant dominants of low marsh (Zizania aquatica), middle marsh (Typha angustifolia or Leersia oryzoides), high marsh (Acorus calamus), shrub marsh (Typha latifolia and Salix nigra) and riparian forest (Acer negundo, Fraxinus pennsylvanica and Betula nigra). Habitat change progressed in pulses followed by periods of habitat stasis. The most rapid and extensive period of change occurred between 1840 and 1880, synchronous with the period of highest sedimentation rates, mid-century storms and intensive land use in the watershed. The rate and pattern of community change differed among sites where position relative to the watershed, local disturbance, and channel shifts at or adjacent to the site influenced different community pathways. A conceptual model is proposed to describe the spatial and temporal development of eastern US freshwater tidal wetland habitats, reflecting the importance of the impact of colonial deforestation.

A 6,000 Year Old Red Abalone Midden from Otter Point, San Miguel Island, California

For decades, researchers have been interested in archaeological sites on California's Channel Islands that contain large concentrations of red abalone ( Haliotis rufescens) shells. Known as red abalone middens and dated to between about 7500 and 3500 years ago, these sites have been used to understand broad subsistence patterns, provide chrono-stratigraphic control, and investigate past environmental changes in the region. Most detailed studies have focused on red abalone middens from Santa Cruz Island, with comparatively limited data from other islands. Analysis of a red abalone midden sample excavated from a large dune site on San Miguel Island illustrates the diversity of the red abalone site type and associated human behaviors. Rapid changes in the primary midden constituents, from California mussels ( Mytilus californianus) and sea mammals to red abalones, demonstrate the complexities of differentiating between the effects of environmental change, human food choices, and ecological changes associated with human impacts on local environments.

Impact of historic land‐use change on sediment delivery to a Chesapeake Bay subestuarine delta

AbstractHistoric land use in the Chesapeake Bay drainage basin induced large fluxes of fluvial sediment to subestuarine tributaries. Stratigraphic and palaeoecologic analyses of deltaic deposits may be used to infer changes on the landscape, but are not sufficient to quantify past sediment supply. When viewed as an inverse boundary‐value problem, reconstruction of the sediment supply function may be achieved by combining deltaic sedimentation chronologies with an equation governing delta progradation. We propose that the diffusion equation is appropriate for simulating delta progradation and obtaining the sediment supply function provided a suitable diffusion constant (D) can be determined. Three new methods for estimating D are presented for the case of estuarine deltas. When the inverse boundary‐value technique was applied to Otter Point Creek, a tidal freshwater delta at the head of Bush River in upper Chesapeake Bay, D values ranged from 3763 to 6199 m2 a−1. Delta growth simulations showed a 1740–1760 initial pulse, a 1760–1780 erosive/redistributive interval, a 1780–1920 growth period, and a 1920‐present erosive/redistributive era. Coupling of simulated delta elevations with an empirical plant habitat predictive equation allowed for comparison of predicted versus actual relative habitat areas. Also, the model yielded reconstructed watershed erosion rates and stream suspended sediment concentrations that could be useful for development of water quality regulations. Copyright © 2001 John Wiley & Sons, Ltd.

Sandstone Petrology and Tectonostratigraphic Terranes of the Northwest California and Southwest Oregon Coast Ranges

Projection of Mesozoic terrane boundaries of Blake et al. (1985b) from Oregon into California permits the subdivision of the late Mesozoic Franciscan Complex into units correlative to the Eastern and Central Franciscan (CE) belts. Eastern belt rocks may be further divided into those correlative to the Pickett Peak terrane, and an eastern (EYB) and western (WYB) facies of the Yolla Bolly terrane. At Crescent City, the contact between these Yolla Bolly subterranes is depositional. All other terrane boundaries are faults. In southwest Oregon, the Upper Jurassic Otter Point Complex (OP) is faulted against the Yolla Bolly terrane. Detrital modes determined by the Gazzi-Dickinson point-count method for largely unfoliated Otter Point and Franciscan sandstones are as follows: % QtFL = 15-30-55 (OP), 36-36-28 (EYB), 31-37-32 (WYB), and 34-30-36 (CE); % QmFLt = 5-30-65 (OP), 22-36-42 (EYB), 20-37-43 (WYB), and 19-30-51 (CE); % QpLvLsm = 14-81-5 (OP), 30-60-10 (EYB), 26-66-8 (WYB), and 28-64-8 (CE); and % QmP = 13-87 (OP), 38-62 (EYB), 35-65 (WYB), and 41-59 (CE). No significant compositional, diagenetic or metamorphic differences exist among Franciscan sandstones counted. All are albitized and contain pumpellyite. Otter Point sandstones differ significantly in composition and alteration, and contain an average 3% detrital clinopyroxene. Although Franciscan sandstones were likely derived from the partially dissected Sierran-Klamath magmatic arc, Otter Point sandstones were derived from a less dissected arc which may have been allocthonous with respect to surrounding Franciscan rocks.

Recruitment of juvenile mbuna (Pisces: Cichlidae) to experimental rock shelters in Lake Malawi, Africa

Mbuna are species of small cichlids that inhabit the rocky shoreline of Lake Malawi. They are mouthbrooders and do not guard their young. Recruitment to the community first occurs when the female deposits free-swimming young, approximately 11 mm standard length, among the rocks. Juvenile mbuna recruit to any refuge in the rock habitat and in this study, small rock shelters were monitored daily to follow the recruitment and subsequent persistence of young. Initial mortality rate was high; less than 10% of the fish survived more than 3 weeks after deposition by the female. At the two locations studied, recruitment was greater at West Thumbi Island (11 fish per day) than at Otter Point (8 fish per day). However, fewer recruits persisted as residents at Thumbi Island because mbuna young at Thumbi were capable of excluding subsequent recruits to their shelter. Similar priority effects were not observed at Otter Point. Mbuna lack pelagic stages in the life-cycle and the species composition of local adult assemblages is an important determinant of the number and type of subsequent recruits. Priority effects may help maintain stochastic influences on recruitment success and reduce the importance of deterministic processes that are directly linked to community structure.

Stratigraphy and sedimentology of Upper Cretaceous rocks in coastal southwest Oregon: Evidence for wrench-fault tectonics in a postulated accretionary terrane

Southwest Oregon is a region of complex juxtaposition of tectonostratigraphic terranes. In southwest Oregon, three Upper Cretaceous (Campanian-?Maastrichtian) formations occur in fault and depositional contact with the Upper Jurassic Otter Point complex, an oceanic assemblage. These four units occur only west of high-angle, north-northwest-trending faults, and they make up a terrane (Gold Beach terrane) unlike any terrane east of these faults. The patterns of sedimentation and the stratigraphic relationships of the three Upper Cretaceous formations indicate that they were deposited in a tectonically active setting influenced by vertical tectonics. Source areas for clasts in the Cretaceous conglomerates cannot be found in the adjacent Klamath Mountains or other nearby terranes. We postulate that they were deposited in a borderland-type basin with a sediment source at least as far south as southern California. They were translated north during latest Cretaceous to early Paleogene time and were then accreted to the Oregon margin.

Metamorphic History of a High-Grade Blueschist Exotic Block from the Franciscan Complex, California

A high-grade blueschist tectonic block from the Franciscan Complex of the northeast Diablo Range shows evidence of three episodes of retrograde blueschist facies metamorphism ± deformation developed under progressively declining P-T conditions. The first retrograde metamorphism involved formation of an outer rind of actinolite + chlorite + rutile ± phengite, and the growth of coarse-grained chlorite + pumpellyite within the block. During the second event the rind and outer edge of the blueschist were folded, sheared and fractured, and primary glaucophane within the blueschist was replaced by albite, medium-grained chlorite, and glaucophane-crossite. The third retrograde metamorphism was marked by the pseudomorphic replacement of rind actinolite by aragonite and quartz. Aragonite also crystallized extensively within th block, accompanied by lawsonite, chlorite, jadeitic pyroxene, and crossite; this last mineral assemblage is identical to that of the surrounding Franciscan metasedimentary rocks. Features characteristic of the first and second retrograde metamorphic events are readily observed in other high-grade tectonic blocks of the Franciscan Complex and the correlative Otter Point Formation of Oregon. In contrast, evidence of a third retrograde metamorphism, matching that of presently associated Franciscan and Otter Point rocks, has been found in some but not all blocks examined so far. The high P/T conditions of prograde metamorphism and the available metamorphic age determinations suggest that the tectonic blocks originally formed in a pre-Franciscan subduction zone setting. Fragments of blueschist and eclogite from this metamorphic terrain were tectonically incorporated in a serpentinite diapir, and they developed alteration rinds through interaction with the enclosing ultramafic rock. The available data suggest that the examined exotic block and at least some others were transferred to the Franciscan as detritus from a body of serpentinite that reached the earth's surface. Such blocks were then resubducted and metamorphosed along with their presently associated sedimentary sequences.

A geological transect between the Klamath Mountains and the Pacific Ocean (Southwestern Oregon): A model for paleosubductions

A geological cross-section between Vulcan Peak (Klamath Mountains) and Gold Beach (Pacific Ocean) shows several tectonic sheets thrust to the west. From the coast to the east, in tectonic superposition: 1. (1) The metamorphosed Franciscan Complex includes the Tithonian-Neocomian Otter Point and Dothan Formations, and, above them, a mélange unit and the Colebrooke Schist. 2. (2) Over them all lie the Red Flat, Game Lake and Snow Camp peridotite units, which are cut by granodioritic dykes of the Nevadan Orogeny and covered by Tithonian-Neocomian sediments (Myrtle Group). We have considered these granite-bearing ultramafic units as klippen thrust westward from the Klamath Mountains. Several stages of deformation are superimposed: 1. (1) Disconformable upon the Otter Point Formation are the unmetamorphosed detrital Cape Sebastian and Hunters Cove Formations. Their Late Cretaceous age gives here an upper limit to the Franciscan metamorphism and tectonics. 2. (2) The first reworked fragments of Colebrooke Schist or ultramafic units are not found in the Campanian Cape Sebastian basal conglomerates (which are affected by some thrusting), but in the Middle Eocene Lookingglass Formation. Thus, major thrusting happened during Late Cretaceous and Early Tertiary times. A geodynamic model is given: in southwestern Oregon, the Franciscan was probably deposited during Late Jurassic and earliest Cretaceous (Tithonian and Neocomian) times in a marginal basin, between an island arc to the west (Otter Point Formation in part) and the North American continent (Klamath Mountains) to the east. This Franciscan marginal basin was probably closed during the Early Cretaceous (i.e. Franciscan subduction). The present day structures (thrust plates, folds) are probably due mainly to the later collision between the continental margin and the arc and, to a much lesser degree, to early subduction, the marginal basin being consumed by subduction first, and then by collision.

Clay Mineralogy in Relation to Landscape Instability in the Coast Range of Oregon

AbstractField and laboratory data reported in this study indicate that the kind of mass movement and the mineralogy of the materials involved vary with the parent material. The clay fraction of debris avalanches is dominated primarily by nonexpanding layer silicates that have large particle sizes and small water‐holding capacities. Dehydrated halloysite, chloritic intergrade, and mica were the common minerals in those areas underlain by sandstones and siltstones of the Tyee Formation as well as the massive basalt flowrock of the Siletz River Volcanic Series. The clay fraction of soils derived from Tertiary sandstones of the Galice and Lookingglass Formations is dominated by chloritic intergrade, chlorite, mica, and kaolinite. Serpentine, chlorite, and mica were the soil clays associated with debris avalances on serpentinite of the Otter Point Formation. Expandable layer silicates, or those with high charge or water‐holding capacity, were not major constituents of debris avalanches although smectite and vermiculite commonly occurred in a thin layer of soil above the underlying bedrock.The clay fraction of samples from sites undergoing failure by creep and slump consisted primarily of smectite. Smectite, chloritic intergrade, dehydrated and hydrated halloysite, and mica were the minerals commonly associated with soil creep and slump on slopes underlain by siltstones of the Tyee Formation. Montmorillonite was the major constituent of a large rotational slump at the contact between the Nye Mudstone and the sandstones of the Astoria Formation. Smectite, chlorite, and serpentine were identified in sites underlain by serpentinite of the Otter Point Formation.The mineralogy of soils involved in earthflow consisted predominantly of hydrated and dehydrated halloysite, amorphous material, and chloritic intergrade. No difference in mineralogy could be detected between sites underlain by siltstones of the Tyee and Nestucca Formations and tuffaceous siltstones and tuff of the Siletz River Volcanic Series. Surface samples were more poorly crystallized than samples taken at lower horizons. Electron micrographs reveal an abundance of amorphous gels and “coatings” on the surface of mineral grains. The abundance of “pores” may account for the fluid behavior of these materials during failure.

Provenance of Eocene graywackes of the Flournoy Formation near Agness, Oregon — A geochemjcal approach

Systematic variations in major elements, U and Th contents, and Sr isotope ratios in graywackes of the Flournoy Formation near Agness, Oregon, are interpreted to indicate a multilithologic provenance. At the time of deposition, Rb-Sr systems in the graywackes defined a pseudo-isochron corresponding to an age of 110 m.y. Calculated 87 Sr/ 86 Sr ratios range from 0.7050 to 0.7074, and compositional variations relate to these values in simple mixing patterns. Rb, U, Th, and K 2 O show a positive correlation with increasing ( 87 Sr/ 86 Sr) O and decreasing MgO, CaO, and Sr. Average values of Rb/Sr and 87 Sr/ 86 Sr (at 50 m.y. ago) for Mesozoic graywackes—Otter Point, Dothan, Galice, and Colebrooke Formations–are coincident with the mixing line defined by the Rb-Sr systems of the Flournoy graywackes, suggesting that some combination of the Mesozoic graywackes comprised part of the felsic component of the source terrane. A mafic source is also required by chemical, isotopic, and mineralogic features of the Flournoy graywackes. This was probably equivalent to basalts in the Paleocene and Eocene Roseburg Formation beneath the Flournoy.

Distribution and Age of High-Grade Blueschists, Associated Eclogites, and Amphibolites from Oregon and California

Isolated blocks of high-grade blueschist and amphibolite facies metamorphic rocks occur within the Jurassic and Cretaceous eugeosynclinal deposits of the Coast Ranges of southwestern Oregon and California. The blocks range in size from individual rock masses commonly 5 to 1,000 ft in diameter to a few larger masses as much as 7 mi long and 2 mi wide. The high-grade blocks are predominantly basaltic in composition and include glaucophane schists, eclogites, and gneissic rocks of the amphibolite facies. Field relationships indicate that the blocks are closely associated with serpentine, that high-grade blueschist and amphibolite blocks, lower grade blueschists, volcanic rocks, and cherts occupy disturbed zones that may be related to thrusting, and that there is no exposed in situ provenance for the high-grade blueschists, eclogites, and amphibolites. Potassium-argon mineral ages of white mica and actinolite from the blueschists and of hornblende from the amphibolites indicate that these minerals crystallized approximately 150 m.y. ago, but the ages measured on glaucophane from the blueschist blocks are commonly younger. These data suggest that the high-grade blue-schist and amphibolite blocks represent fragments of a cryptic metamorphic terrane of pre-Tithonian age that have been tectonically mixed with younger rocks of the Franciscan Formation in California and Otter Point Formation in Oregon. The younger ages for glaucophane probably reflect metamorphic episodes in which lower grade in situ blueschist facies mineral assemblages were developed in the blocks after their emplacement within the Franciscan Formation. This pre-Tithonian cryptic metamorphic terrane probably developed as a result of interaction between oceanic and continental plates. The occurrence of tectonic blocks of this terrane within melange zones in Oregon and California may be related to later plate interaction.

Late Mesozoic Stratigraphy and Tectonic History, Port Orford-Gold Beach Area, Southwestern Oregon Coast

During Nevadan orogenesis (ca. 145 m.y. ago), the Galice(?) Formation was regionally metamorphosed (greenschist facies) to phyllites and schists of the Colebrooke Formation, the Pearse Peak Diorite was emplaced, and the Port Orford-Gold Beach area, Oregon, underwent intense compressional deformation. The ancestral Klamath Mountains and Sierra Nevada became important source areas for sediments. Eugeosynclinal conditions in coastal Oregon, however, persisted into latest Jurassic (Tithonian) time. The uppermost Jurassic Otter Point Formation (new name) includes volcanic rocks, radiolarian cherts, and many graded beds--lithologic types that are unknown in the correlative Riddle Formation. Thus, the distribution of latest Jurassic facies in southwestern Oregon was comparable with that of the coastal Franciscan and the inland Knoxville Formations of northern California. Late Mesozoic eugeosynclinal conditions in southwestern Oregon were terminated by Diablan orogenesis at the end of the Jurassic (ca. 135 m.y. ago). Northwest-striking wrench faults and related folds were superimposed on the northeast-striking, Nevadan structural grain. Dioritic, gabbroic, and ultramafic bodies, including the Vondergreen Hill Peridotite (new name), were emplaced. Tectonic lands probably rose by differential movements related to wrench faulting. Coarse gravels of the Humbug Mountain Conglomerate (new name) and, later, progressively finer sediments of the Rocky Point Formation (new name) were shed into a transgressing and deepening Early Cretaceous (Valanginian) sea. Younger Cretaceous and Tertiary evolution of the Port Orford-Gold Beach area, although poorly documented, involved extensive fragmentation and folding of the Lower Cretaceous about north- to northeast-striking axes. Several post-Diablan orogenies affected this area, including widespread major diastrophism that began in middle and late Miocene time along the Pacific coast. The most recent phases of structural development were uplift of Pleistocene terrace deposits and faulting. Middle Miocene(?) deposits near Port Orford perhaps represent the southern limit of the Miocene within the coastal, westward-facing Tertiary embayment centered about Newport, Oregon. The Miocene has favorable reservoir characteristics and should be a prime target for offshore exploration.