Mapping along the eastern coast of Baja California adjacent to the Canal de Las Ballenas (lat. 29°30′ to 29°40′) reveals over 4,000 m of complexly folded and faulted, metamorphosed sedimentary and volcanic strata, locally intruded by tonalite and gabbro of Cretaceous age. Protoliths include lime mudstone, coarse-grained bioclastic packstone, bedded black chert and shale, thin-bedded flysch-type sandstone-shale, thick boulder and cobble conglomerates, minor quartz arenite, and pillowed alkaline basalt. The depositional environment was anoxic slope to basin. The entire sequence is here named the Canal de Las Ballenas Group. Conodont fragments and favositid corals indicate a Devonian age, suggesting correlation with rocks in the Sierra Las Pinta to the northwest, and to southern Sonora to the east. The recognition of these rocks adds an important link to our understanding of the southwestern edge of North America in mid-Paleozoic time. The area has been pervasively deformed, first by tight, isoclinal folding and shearing, which produced large recumbent folds with axes dipping gently to the northeast and verging east-southeast; and second by large synforms with steep, east-trending axes.

Abstract Middle to Late Triassic turbidite sequences are exposed in the states of Zacatecas and San Luís Potosí in central Mexico. These strata, assigned mostly to the Zacatecas Formation, accumulated in continental slope, toe-of-slope, and basin-plain environments along the passive continental margin of western Pangea. Strata of the Zacatecas Formation are age equivalent to rocks of the Antimonio Formation and Barranca Group in Sonora, the La Boca Formation in Tamaulipas and Nuevo León, and unnamed strata in Baja California. Based on their age, the Zacatecas turbidites correlate with a drop in sea level during the Permian-Triassic assembly of Pangea. The Triassic paleogeographic setting of Mexico is complex and poorly understood, because only dispersed Triassic outcrops exist across Mexico. However, the biogeographic affinities of the faunas from the Zacatecas Formation in central Mexico with those from equivalent strata in Baja California and Sonora suggest that these three regions were connected through the eastern Pacific, and that the Atlantic Ocean did not exist during the Ladinian-Carnian. The Zacatecas sequences underwent three periods of compressive deformation: one during their obduction onto the continental margin at some time during the latest Triassic-earliest Jurassic (?); a second during the Middle to Late Jurassic (Oxfordian) (?), apparently related to transpression; and a third during the Late Cretaceous to Tertiary Laramide orogeny.

Abstract Bryomol carbonates, composed of bryozoans and molluscs, are found in non-tropical shelf and upper slope settings where they are sensitive indicators of oceanographic conditions. Few modern bryomol carbonate settings have been investigated to date, despite their importance in the Phanerozoic rock record. Furthermore, no detailed facies mapping and long-term oceanographic observations have been undertaken in modern bryomol settings, even though this is important for accurately interpreting facies, climate and oceanography from fossil bryomol carbonates. A bryomol carbonate factory on the western margin of the northern Gulf of California, Mexico was selected for an integrated high-resolution in situ oceanographic monitoring, acoustic seafloor mapping, sediment and bryozoan growth morphology study. Molluscan- (28%), bryozoan- (25%) and barnacle- (14%) dominated carbonate production takes place under normal saline warm-temperate eutrophic conditions, with average near sea surface temperatures of 20°C. Even though temperatures are unusually warm for the formation of bryomol carbonates, they develop as a result of prevailing eutrophic conditions (average chlorophyll- a contents of 2.2 mg chl- a m -3 ). Eutrophic conditions provide ample food to heterotrophic calcifiers and largely exclude faster-growing phototrophic organisms by drastically restricting the depth of the euphotic zone and, therefore, water clarity. Thus, the presence of high amounts of nutrients can generate cool-water-type carbonate assemblages at temperatures where a warm-water association would be expected.